Lab 12: Endocrine System - Biology

Lab 12: Endocrine System - Biology

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An animal’s endocrine system controls body processes through the production, secretion, and regulation of hormones, which serve as chemical “messengers” functioning in cellular and organ activity and, ultimately, maintaining the body’s homeostasis. The endocrine system plays a role in growth, metabolism, and sexual development. In humans, common endocrine system diseases include thyroid disease and diabetes mellitus. In organisms that undergo metamorphosis, the process is controlled by the endocrine system. The transformation from tadpole to frog, for example, is complex and nuanced to adapt to specific environments and ecological circumstances.

Table 1: Different Classes of Hormones
Hormone ClassComponentsExample(s)
Amine HormoneAmino acids with modified groups (norepinephrine's carboxyl group is replaced with a benzene ring.)
Peptide HormoneShort chains of linked amino acids.
Protein HormoneLong chains of linked amino acids.
Steroid HormoneDerived from the lipid cholesterol

Maintaining homeostasis within the body requires the coordination of many different systems and organs. Communication between neighboring cells, and between cells and tissues in distant parts of the body, occurs through the release of chemicals called hormones. Hormones are released into body fluids (usually blood) that carry these chemicals to their target cells. At the target cells, which are cells that have a receptor for a signal or ligand from a signal cell, the hormones elicit a response. The cells, tissues, and organs that secrete hormones make up the endocrine system. Examples of glands of the endocrine system include the adrenal glands, which produce hormones such as epinephrine and norepinephrine that regulate responses to stress, and the thyroid gland, which produces thyroid hormones that regulate metabolic rates. Although there are many different hormones in the human body, they can be divided into three classes based on their chemical structure: lipid-derived, amino acid-derived, and peptide (peptide and proteins) hormones.

If endocrine glands are not functioning properly the body can be out of homeostasis and a patient may be diagnosed with an endocrine system disease or disorder (Figure 1). In today’s lab, you will be using your knowledge of the endocrine system and various hormones to diagnose patients. The objectives of today’s lab are to identify the main human endocrine glands, diagnose “patients” with endocrine diseases based on their symptoms, and write a case study for another endocrine disease.

Exercise 1:

Endocrine glands function by releasing hormones that move through the blood to targets throughout the body. The structures labeled A-J in Figure 2 are true endocrine glands; however, other tissues and organs, like adipose tissue and your kidneys and heart, can also produce hormones. Identify the endocrine glands in the figure and then match them with the hormone(s) they produce.

_____ Adrenocorticotropic hormone (ACTH) _____ Insulin

_____ Antidiuretic hormone (ADH) _____ Luteinizing hormone (LH)

_____ Aldosterone _____ Melatonin

_____ Cortisol _____ Oxytocin

_____ Epinephrine _____ Progesterone

_____ Estrogen _____ Prolactin

_____ Follicle stimulating hormone (FSH) _____ Testosterone

_____ Glucagon _____ Thyroxine

_____ Growth hormone (GH) _____ Thyroid stimulating hormone (TSH)

Exercise 2:

Endocrine disorders can often be difficult to diagnose because many can present very similar symptoms. Diagnosis often requires a combination of lab work and a patient’s history. On Table 2, you will see several different endocrine disorders with common physical symptoms and lab results. Use this information to answer the questions below.

Table 2: Endocrine Disorders
DisordersSymptomsLab Test Results
AcromegalyEnlarged hands and feet, excessive sweating, fatigue, muscle weakness, pain, limited joint mobilityElevated levels of insulin, like growth factor I
Addison's DiseaseFatigue, increased pigment in the skin, weight loss, muscle weaknessLow sodium, high potassium, high ACTH, low cortisol in the blood
Cushing's SyndromeBackache, anxiety, muscle weakness, extra fat deposits on the back of the neck and upper back (aka "buffalo hump"), females may experience irregular menstrual cycleHigh levels of cortisol in the blood
Diabetes InsipidusFrequent urination, excessive thirstNormal blood glucose level, no glucose in the urine, low ADH level in the blood
HyperparathyroidismExcessive thirst, weak or broken bones, fatigue, nauseaHigh calcium and parathyroid hormone levels in the blood
HyperthyroidismElevated body temp, extreme sweating, nervousness, rapid heart rate, weight loss, irregular menstrual cycle in femalesHigh thyroxine and low TSH in the blood
HypothyroidismFatigue, muscle weakness, depression, weight gain, low body temperature, intolerant of coldLow thyroxine and high TSH in the blood
Polycystic Ovarian Syndrome (PCOS)Acne, unwanted hair growth, weight gain, fatigue, infertility, mood changes, sleep problemsElevated levels of testosterone and LH, low levels of FSH in blood
Type I Diabetes MellitusFrequent urination, excessive thirst, weight lossGlucose in urine, elevated blood glucose, islet cell antibody in the blood
Type 2 Diabetes MellitusFrequent urination, excessive thirstGlucose in urine, elevated blood glucose, no islet cell antibody in the blood


1. What is the most frequent physical symptom of the disorders described above?

2. Why are blood tests used to diagnose endocrine disorders?

3. Why is it so important to consider age and sex when diagnosing an endocrine disorder?

Case Study 1:

A 37-year-old woman goes to her doctor and complains of anxiety, muscle weakness, and depression. Which of the disorders listed on the table above could explain her symptoms? What other symptoms might you look for or what other tests might you run to distinguish between these disorders?

Case Study 2:

A 34-year-old man complains he is tired a lot and he has lost a substantial amount of weight over the past few months. A routine blood test shows low sodium levels, but his blood glucose levels are normal. What test would you order next? Why? What results could help you make a diagnosis?

Case Study 3:

Your patient is a 28-year-old woman who has complained of menstrual irregularities and infertility despite actively trying to get pregnant for 14 months. She also mentioned that she has to wax her face a lot due to hair growth. How would you diagnose this patient? Which lab result may explain the hair growth? What does this patient have to be careful of developing in the future?

Case Study 4:

A seemingly healthy 42-year-old-man comes into the ED with a broken arm. The doctor set the bone with no issue but is concerned that the patient’s bones are unusually weak. The man follows up with an endocrinologist and during that appointment, he reports fatigue and nausea. What disorder could this patient have? How could you confirm the diagnosis?

Table 1 from WikiCommons, Figure 1 from WikiCommons, and additional information from OpenStax Biology. This lab is licensed under a Creative Commons Attribution License License (3.0)

Hands-on Activity Endocrine Excitement!

Units serve as guides to a particular content or subject area. Nested under units are lessons (in purple) and hands-on activities (in blue).

Note that not all lessons and activities will exist under a unit, and instead may exist as "standalone" curriculum.

  • Engineering and the Human Body
    • Spaced Out
    • Move Your Muscles!
      • Walk, Run, Jump!
      • Muscles, Muscles Everywhere
      • Our Amazing Skeleton
        • Fascinating Friction!
        • Digestive System
          • Design Devices to Help Astronauts Eat: Lunch in Outer Space!
          • The Heart of the Matter
            • Blood Cell Basics
            • The Beat Goes On
            • Do You Have the Strength?
            • Nerve Racking
              • 20/20 Vision
              • Sound Line
              • Engineering a Mountain Rescue Litter
              • Unlocking the Endocrine System
                • Endocrine Excitement!
                • Just Passing Through
                  • Kidney Filtering
                  • Out of Breath
                    • Creating Model Working Lungs: Just Breathe
                    • Fighting Back!
                      • Hot or Not

                      TE Newsletter


                      An example hormone in the human body

                      Engineering Connection

                      One important aspect of engineering is communication. Engineers need to be able to explain their ideas and designs so that other people can understand their work. Biomedical engineers work to produce growth hormone and insulin for people who have challenges growing, or have diabetes. Engineers also design the technologies that make communication in space and on earth possible, including cell phones, digital video equipment and satellites.

                      Learning Objectives

                      After this activity, students should be able to:

                      • Explain that hormones help tell our body what to do
                      • Describe how hormones and receptors work together
                      • Relate how engineers are involved in communication

                      Educational Standards

                      Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

                      All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (

                      In the ASN, standards are hierarchically structured: first by source e.g., by state within source by type e.g., science or mathematics within type by subtype, then by grade, etc.

                      NGSS: Next Generation Science Standards - Science

                      Do you agree with this alignment? Thanks for your feedback!

                      International Technology and Engineering Educators Association - Technology
                      • Technological advances have made it possible to create new devices, to repair or replace certain parts of the body, and to provide a means for mobility. (Grades 3 - 5) More Details

                      Do you agree with this alignment? Thanks for your feedback!

                      Do you agree with this alignment? Thanks for your feedback!

                      State Standards
                      Colorado - Science
                      • Analyze and interpret data to generate evidence that human systems are interdependent (Grade 5) More Details

                      Do you agree with this alignment? Thanks for your feedback!

                      Do you agree with this alignment? Thanks for your feedback!

                      Materials List

                      To share with the entire class:

                      More Curriculum Like This

                      Students learn how the endocrine system works and compare it to the mail delivery system. Students discuss the importance of communication in human body systems and relate that to engineering and astronauts.

                      Students learn about the function and components of the human nervous system, which helps them understand the purpose of our brains, spinal cords, nerves and five senses. In addition, how the nervous system is affected during spaceflight is also discussed.


                      Communication is important for everyone! It's a great skill for you, astronauts and engineers alike to have. Why do you think communication is important? Well, communication helps engineers, astronauts and anyone to get ideas across to each other. Astronauts need to be able to communicate with ground control on Earth while they are exploring space. If we could not communicate, then we could not let others know what we are thinking, or when we are sad or happy. Engineers would not be able to let you know what cool new technologies they have designed to help people out. In fact, engineers are the ones who design all the cool new technologies that help us communicate with friends far away, like cell phones, emails and text messaging. In our activity today, we are going to see one way that the body actually communicates with itself ─ through hormones.

                      Hormones help our body know what to do. They are part of our body's communication system ─ called the endocrine system. The endocrine system helps messages travel throughout our body so that our body can do all the different things it needs to do. There are four main parts to this endocrine system, glands, hormones, bloodstream and receptors. Glands make and send hormones through the bloodstream to specific receptor sites. These hormone messages tell our body to do things like make more blood cells, digest food, absorb vitamins or even grow. There has to be one specific receptor site for each hormone message, otherwise your glands might tell your stomach to produce more blood cells or your bones to digest food. That would not work! When a hormone matches up with its specific receptor, then the body knows what it is supposed to do next. It is kind of like receiving a letter in the mail.

                      One of the most fascinating things about hormones is how incredibly specific they are! In fact, hormones act like real puzzle pieces, or like a lock and key. Sometimes, when you are putting together a puzzle, you can force a puzzle piece in next to another piece when it is not really meant to fit there. But, hormones and receptors are not quite like that: they have to match up perfectly, or they will not send a message. Today, we are going to do an activity that will help us learn more about how the hormones and receptor sites fit together like puzzle pieces. You are going to be either a hormone or a receptor. If you are a receptor, you will stand still and wait for your hormone to come and find you. If you are a hormone, you will search around the classroom until you find the receptor that is a perfect match for you. Are you ready? Let's get started!


                      • Create puzzle pieces by cutting shapes out of cardboard and cut them in half, or use pieces from a jigsaw puzzle and label the back (plain) side of them.
                      • Each pair of puzzle pieces should be labeled: with an H on one half for hormone, and with an R for receptor on the other half (see Figure 1). Note: Write an action across both pieces, so that it can only be fully read when they are joined together. Possible actions include: jump up and down, jump on one foot, put your hand on your head, act like a monkey, turn in a circle, clap your hands, etc.

                      Figure 1. Example of a hand-made puzzle piece pair.

                      1. Explain the procedure and discuss the specificity of the hormone-receptor interaction.
                      2. Pass out puzzle pieces, one per student, but tell the students not to look at the label on their piece.
                      3. Have students scatter throughout the entire classroom and then freeze.
                      4. Tell students to look at their pieces: students who are "receptors" must remain frozen in place the "hormone" students may now move throughout the classroom. "Hormone" students must try to match their piece with each receptor piece until they successfully find a match.
                      5. Once all students have found their match, have each pair act out together the action written on their puzzle pieces.
                      6. You can repeat the activity if time permits.


                      Endocrine Gland: A gland in the body which secretes hormones into the bloodstream.

                      Hormone: A chemical secreted by endocrine glands which carries instructions to the body.

                      Receptor: A specific site on a cell designed to recognize and accept a specific hormone.


                      Discussion Topic: Talk with students what it means to have a specific receptor site. Compare it to the child's toy where you fit the shapes into the different holes. Can they think of examples of specificity in their own lives? (One clear example is a lock and key, but encourage them to come up with other ideas.)

                      Activity Embedded Assessment

                      Formation: As a way to actively engage all students and assess their knowledge, have them all participate in the activity of matching hormones to receptor sites. Closely observe students as they interact with each other in this activity and notice if they seem to be grasping the concepts of specificity and hormone-receptor interactions.

                      Telephone Game: Play the game "telephone" with the students. Have all the students stand in a circle. Whisper, "Engineers need good communication to talk about new technologies" in the first student's ear. Have that student turn to the person next to her/him and whisper the message to them. Continues whispering the message around the circle until it is relayed to the last person. The message can only be given once to each student. Have the last student say the message they heard aloud to the whole class. See how much the message has changed.

                      Discuss with the students how communication can be a problem when it goes through many receptor sites. This is why the endocrine system makes hormones that can only relay a message to one receptor site. When engineers design new technologies for communication, they need to understand how signals and messages can get changed if there are too many middle receptor sites as well. Ask the students if they can think of any times in their own lives when a message has been messed up because of bad communication.

                      Review Discussion: Review with the students what they learned. Discuss again how communication is so important for astronauts, engineers and for them. Discuss why it is such a good thing that the hormones in our bodies only match up with specific receptors. (This is good because it ensures that the hormones tell the "right" cells what to do.) Ask students students the following questions:

                      • Of which body system are hormones are part? (Answer: Hormones are part of the endocrine system.)
                      • What are some examples of body functions that are triggered by hormones? (Answer: Hunger, digestion, muscle growth, "fight or flight" reflex, among others.)

                      Safety Issues

                      Remind students to be careful not to bump into each other when moving around the classroom.

                      Troubleshooting Tips

                      If there are an uneven number of students in the class, the teacher may need to participate.

                      Activity Extensions

                      A related activity might be to have the students act out the "mail delivery" system of the endocrine system. One student could be the mail carrier, and several students could be the endocrine glands and write out "hormone" instructions for the "receptor" students to read. Once the mail carrier delivers the mail to the correct students, the "receptor" students could read the "mail" and then tell other "body" students what to act out.

                      Activity Scaling

                      For upper grades, you may design a more complicated system of interactions. For example, have one hormone-receptor pair interact with another pair, or create a chain-reaction of interactions.

                      For lower grades, you may use matching shapes, or matching colors instead of puzzle pieces.

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                      Lab 12: Endocrine System - Biology

                      • Atoms, Molecules, and Chemical Bonds (VIDEO)
                      • Biologically Important Molecules (VIDEO)
                      • Cell Membrane and Transport (VIDEO)
                      • Cell Phone Quiz: Biochemistry (QUIZ)
                      • Drag-and-Drop Cooler Molecules (GAME)
                      • Enzyme Regulation (VIDEO)
                      • Functional Groups Tutorial (VIDEO)
                      • Functional Groups Tutorial 2 (VIDEO)
                      • Functional Groups Tutorial 3 (VIDEO)
                      • GyroQuiz 1: Biochemistry (QUIZ)
                      • Have-a-Java Quiz 8: Cellular Biochemistry (QUIZ)
                      • Membrane and Transport (VIDEO)
                      • Multi-Panel Quiz: Biochemistry (QUIZ)
                      • True-False Quiz: Atoms, Molecules and Chemical Bonds (QUIZ)
                      • True-False Quiz: Biochemistry (QUIZ)
                      • Alcoholic Fermentation Lab (WORKSHEET, HTML)
                      • Chloroplasts and Pigments (WORKSHEET, HTML)
                      • Chloroplast Structure Diagram (WORKSHEET, PDF) [Use with video]
                      • Chromatography Lab (WORKSHEET, PDF)
                      • Electron Transport System Diagram WORKSHEET, PDF) [Use with video]
                      • Electron Transport System (WORKSHEET, HTML)
                      • Fermentation Diagrams (WORKSHEET, PDF) [Use with video]
                      • Glycolysis (WORKSHEET, PDF)
                      • Key Scientists in Photosynthesis Research (WORKSHEET, PDF)
                      • Light Dependent and Light Independent Reactions (WORKSHEET, HTML)
                      • Matrix Reactions (WORKSHEET, HTML)
                      • Membrane Transport Diagrams (WORKSHEET, PDF) [Use with video]
                      • Metabolism of Food Diagram (WORKSHEET, PDF) [Use with video]
                      • Nutrient Analysis Lab (WORKSHEET, PDF)
                      • Photosynthesis Microviewer (WORKSHEET, PDF)
                      • Review for Metabolism (WORKSHEET, PDF)
                      • Review for Photosynthesis Test (WORKSHEET, PDF) [Use with video]
                      • BioFax Quiz 12: Glycolysis (QUIZ)
                      • BioFax Quiz 13: Matrix Reactions (QUIZ)
                      • BioFax Quiz 13b: More Matrix Reactions (QUIZ)
                      • Cell Phone Quiz: Metabolism (QUIZ)
                      • Chloroplast Structure (VIDEO)
                      • Chromatography For Photosynthesis (VIDEO)
                      • Drag-and-Drop Alcoholic Fermentation (GAME)
                      • Drag-and-Drop Glycolysis (GAME)
                      • Drag-and-Drop Kreb's Cycle (GAME)
                      • Electron Transport System (VIDEO)
                      • Factors Affecting Photosynthesis (VIDEO)
                      • Fermentation (VIDEO)
                      • Forensic Flash Quiz 3: Glycolysis (QUIZ)
                      • Glycolysis and Matrix Reactions (VIDEO)
                      • Have-a-Java Quiz 10: Electron Transport System (QUIZ)
                      • Have-a-Java Quiz 3: Photosynthesis (QUIZ)
                      • Jingle Bells Photosynthesis (MUSIC)
                      • Light and Dark Rxns of Photosynthesis (VIDEO)
                      • Metabolism of Food (VIDEO)
                      • MultiPanel Quiz: Photosynthesis (QUIZ)
                      • Photosynthesis Odds + Ends (VIDEO)
                      • Photosynthesis Review For Test (VIDEO)
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                      • Endocrine Histology Lab (WORKSHEET, HTML)
                      • Endocrine System (WORKSHEET, HTML)
                      • Glands and Hormones of The Endocrine System (WORKSHEET, HTML)
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                      • Hypothalamus and Pituitary Gland (WORKSHEET, HTML)
                      • Kidney and Hormones Diagrams (WORKSHEET, PDF)
                      • List of Hormones To Know (WORKSHEET, PDF)
                      • Patient Assessment (WORKSHEET, HTML)
                      • Pharmacology (WORKSHEET, HTML)
                      • Regulation of Sodium and Water Balance (Diagram/Explanation) (WORKSHEET, HTML)
                      • Review for Strand 2A Test: Nervous System (Questions) (WORKSHEET, HTML)
                      • Review for Strand 2A Test: Nervous System (Answers) (WORKSHEET, HTML)
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                      • Signaling in the Nervous System (WORKSHEET, PDF)
                      • Sheep Brain Lab (WORKSHEET, HTML)
                      • Sodium/Potassium Pump (Diagram/Explanation) (WORKSHEET, HTML)
                      • Synpatic Transmission Worksheet (WORKSHEET, PDF)
                      • Alien Encounter (GAME)
                      • BioFax Quiz 16: Hormones (QUIZ)
                      • Cell Phone Quiz: Hormones (QUIZ)
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                      • Drag-and-Drop Hormones (GAME)
                      • Drag-and-Drop Synaptic Transmission (GAME)
                      • Endocrine Glands and Hormones (VIDEO)
                      • FlashPanel Quiz: Brain (QUIZ)
                      • FlashPanel Quiz: Homeostasis (QUIZ)
                      • Have-a-Java Quiz 9: Endocrine System (QUIZ)
                      • Have-a-Java Quiz 11: Kidney (QUIZ)
                      • Have-a-Java Quiz 6: Nervous System (Part 1) (QUIZ)
                      • Have-a-Java Quiz 7: Nervous System (Part 2) (QUIZ)
                      • Inject-A-Quiz: Hormones (QUIZ)
                      • Mixer Quiz: Endocrine System (QUIZ)
                      • MultiPanel Quiz: Hormones (QUIZ)
                      • MultiPanel Quiz: Nervous System (QUIZ)
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                      • QuizBot: Nervous System (QUIZ)
                      • QuizBot: Nervous System 2 (QUIZ)
                      • QuizProbe: Hormones (QUIZ)
                      • QuizProbe: Nervous System (QUIZ)
                      • Synaptic Transmission (VIDEO)
                      • Target Practice Quiz: Kidney (QUIZ)
                      • Chromosomes And Genes In Action: Microviewer (WORKSHEET, HTML)
                      • DNA Extraction From Calf Thymus (WORKSHEET, HTML)
                      • DNA Replication (WORKSHEET, HTML)
                      • Genetic Challenge Worksheet (WORKSHEET, HTML)
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                      • Gene Control in Eukaryotes (WORKSHEET, PDF)
                      • Gene Control in Prokaryotes (WORKSHEET, HTML)
                      • Mutations Assignment (WORKSHEET, PDF)
                      • Review for Strand 3 Test: Genetics (WORKSHEET, HTML)
                      • Review for Strand 3 Test: Genetics (Interactive Web Version)
                      • Unit Outline for Strand 3: Genetics (WORKSHEET, PDF)
                      • 5 Second Quiz: Genetics Basic DNA (QUIZ)
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                      • 5 Second Quiz: Genetics 3 (QUIZ)
                      • 5 Second Quiz: Genetics 4 (QUIZ)
                      • 5 Second Quiz: Genetics 5 (QUIZ)
                      • 5 Second Quiz: Genetics 6 (QUIZ)
                      • 5 Second Quiz: Genetics 7 (QUIZ)
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                      • Sanger Method of DNA Sequencing (VIDEO)
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                      Endocrine System

                      S tudent Performance Objectives - for the lecture
                      1. Explain the difference between an endocrine and an exocrine gland.
                      2. Describe the relationship between a hormone and its target organ.
                      3. Explain how hormones are transported in the blood
                      4. Explain why hormones secreted yesterday or even a few hours ago have little or no effect on metabolic processes going on now.
                      5. List the 6 classes of hormones and give one example of each class.
                      6. Describe the difference in the interaction of the hydrophilic and hydrophobic hormones with their target cells.
                      7. Describe the process of negative feedback and give 2 examples.
                      8. Describe the process of positive feedback and give 2 examples.
                      9. Describe the interactions occurring within each of the following endocrine gland axes: hypothalamic-pituitary-thyroid axis, hypothalamic-pituitary-adrenal axis, and the hypothalamic-pituitary-gonadal axis.
                      10. For each of the following body regions, describe 2 endocrine glands, their hormonal secretions, and the hormone's actions: the head, the neck, the thoracic cavity, and the abdominopelvic cavity.

                      Lesson Outline

                      In General

                      1. Ductless glands produce hormones- While exocrine glands have a duct through which the gland's product reaches its destination (e.g., the parotid salivary gland secretes saliva through Stensen's duct into the mouth the lacrimal gland secretes tears through the lacrimal duct onto the eye's surface), endocrine glands have no ducts - they are ductless glands. They secrete their products, called hormones, into the interstitial fluid surrounding the gland. From there the hormone diffuses into the blood and is carried throughout the body.
                      Hormones and target organs- when the product from an exocrine gland reaches its local destination, it carries out its intended effect: saliva lubricates and begins digestion of food, tears lubricate the eye's surface. When the hormone from an endocrine gland circulates in the blood, it travels far from the endocrine gland that secreted it. It comes into contact with all cells of the body but only influences cells that have receptors for that specific hormone. We say that the hormone only affects its target organ, or target structure. Receptors can be at the cell surface in which case the hormone never enters the target cell. Or, the hormone's receptors can be located inside the cell requiring that the hormone enter the cell through the cell membrane. In either case, the hormone exerts its effects after attaching to chemical receptors designed for the hormone to fit into.

                      Hormonal transport - some hormones ca n travel freely in the blood because they are water soluble (hydrophilic). The steroid hormones, being fat soluble (hydrophobic), must be bound to and carried around by transport proteins (like albumin and globulins which are blood proteins produced by the liver). Free (unbound) hormones are able to enter target organs. Bound hormones must be released from the transport proteins to get into their target organs.
                      Hormonal breakdown - hormones are broken down in target cells, in the liver and in the kidneys. The hormonal breakdown products are excreted from the body in urine and feces. Hormones that are freely dissolved in blood and other body fluids are broken down rapidly - they are said to have a short half-life. Examples are epinephrine and norepinephrine that have half-lives measured in minutes. Hormones that are bound to transport proteins can circulate longer and break down only after they disassociate from their transport proteins and are free in the body fluids. Hormonal breakdown is important in that at any given moment, the hormones circulating within us are mostly freshly made in response to recent environmental conditions. We are adapted hormonally to current conditions. The hormones from yesterday or several hours ago are mostly gone.

                      B. Hormonal Classification - most hormones fall into the following six classes. Some specific hormonal examples are given with a brief idea of the wide-range of activities of these hormones.
                      1. Polypeptides (small proteins: 14 - 199 amino acids)-
                      a. Growth hormone - stimulates growth of epiphyseal plates in the long bones.
                      b. Insulin - lowers the blood sugar after a meal.
                      c. Glucagon - raises the blood sugar if it falls when you are not eating.
                      2. Oligopeptides (very small proteins: 3 - 10 amino acids)
                      a. Anti-diuretic hormone - ADH - helps the body hold on to its water preventing dehydration.
                      b. Oxytocin - helps the uterus to contract during childbirth and causes the breasts to pump out milk.
                      c.Angiotensin II - a vasoconstrictor that raises blood pressure.
                      3. Modified amino acids
                      a. Thyroxine - regulates the basal metabolic rate. Thyroxine consists of two attached amino acids (both are tyrosine) with attached iodine atoms.
                      b. Epinephrine - a "fight or flight" hormone affecting heart and breathing rate.
                      c. Norepinephrine - works much like epinephrine but as a "local" neurotransmitter. Both epinephrine and nor epinephrine are modifications of a single amino acid, tyrosine, and are in a class frequently called monoamines.
                      4. Steroids (derivatives of cholesterol)
                      a. Androgens, like testosterone, that stimulate male sexual characteristics.
                      b. Estrogens, like estradiol, that stimulate female sexual characteristics.
                      c. Aldosterone (an adrenal steroid) regulates blood sodium and potassium levels.
                      5. Glycoproteins (combinations of protein and carbohydrate)
                      a. Follicle stimulating hormone - FSH - stimulates egg and sperm development.
                      b. Luteinizing hormone - LH - causes ovulation.
                      c. Thyroid stimulating hormone - TSH - stimulates the thyroid gland to release its hormone, thyroxine.
                      6. Paracrines - There are other substances that act as hormones, but more locally. These are called paracrines: e.g., neurotransmitters like acetylcholine, histamine (a mediator of inflammation), and the eicosanoids, which are fatty acid derivatives influencing metabolism (e.g., blood pressure, blood clotting, and inflammation). The neurotransmitters are discussed in the nervous system area. Eicosanoids are generally considered as a group in courses in nutrition, and also, often, in the cardiovascular system area with regard to their influence on cardiovascular health and inflammatory processes.

                      C. Hormonal-Cell interactions
                      1. Hydrophilic (water soluble) hormones
                      like epinephrine, norepinephrine, dopamine, glucagon, and ADH, attach to receptors on the cell surface. These water soluble hormones cannot easily penetrate through the cell membrane which is mostly hydrophobic. Attachment of hydrophilic hormones to surface receptors activates second messenger systems on the cytoplasmic side of the cell membrane.
                      There are several different 2nd messenger systems, but they operate in the same general way. The second messenger system eventually produces the hormone's effects. It is an intracellular enzyme amplification system in that 5 or 6 sequential chemical reactions are triggered inside the cell by the initial attachment of a hormone to the surface receptor: the hormone's attachment stimulates thousands of molecules of GTP (a high energy molecule) to break down which causes thousands of cyclic AMP molecules to be produced from ATP each cyclic AMP molecule stimulates production of thousands of enzymes called protein kinases each protein kinase molecule stimulates formation of thousands of other enzymes, and so on. Taken as a whole, an initial stimulus from one molecule of hormone attaching to a receptor, results in thousands, times thousands, times thousands (at least 6 times) of "downstream" molecules being produced that carry out the hormone's work. So hormones are very potent chemicals and only tiny amounts are necessary to create powerful effects on cells and the body as a whole.
                      2. Hydrophobic (fat soluble) hormones
                      like the steroid hormones do not attach to surface receptors. They break off from their blood transport proteins and then pass right through the cell and nuclear membranes attaching to receptors near or on specific regions of DNA (genes).
                      DNA is then stimulated to transcribe messenger RNA resulting in new cytoplasmic protein synthesis that redirects cell metabolism. The thyroid hormones, also lipid soluble, enter the cytoplasm and attach to receptors on mitochondria and ribosomes as well as in the nucleus. The effect of thyroid hormones is to increase mitochondrial oxidations, increase protein synthesis, and to increase production of membrane ionic (sodium and potassium) transporters, all of which result in increases in the body's metabolic rate and overall heat production.

                      D. Feedback, negative and positive - When the body receives a signal (input signal), there is a response - the output signal. We call any activity of the body a parameter. If we are measuring body temperature, then body temperature is the parameter. If we are measuring blood sodium concentration (level), then blood sodium level is the parameter. All body parameters have a normal range of values (e.g., body temperature is 37 1 C). We will utilize this terminology to explain negative and positive feedback in the endocrine system.
                      1. In a negative feedback mechanism, an input signal changes a body parameter from the normal range: it goes either above or below the normal range. This causes the body to respond (output signal) so as to return the parameter back to the normal range. Within the endocrine system, negative feedback mechanisms keep the level of circulating hormones within a "normal" range. The parameter being measured here is the level of a given circulating hormone. If the circulating level of hormone rises above the normal range (this is the input signal), then the negative feedback mechanism slows down further hormonal secretion: the hormonal level falls back to the normal range (output signal). If the circulating level of hormone falls below the normal range (new input signal) , then the negative feedback mechanism increases hormonal secretion: the hormonal level rises up to the normal range (new output signal). Notice that whether the hormone level (parameter) goes above or below the normal range, the negative feedback mechanism brings the level back to the normal range. E.g., when TSH from the pituitary stimulates the thyroid gland to produce thyroxine (increased blood thyroxine is the input signal), thyroxine is said to feed back to the pituitary: further secretion of TSH is slowed down (output signal). As thyroxine does its work and is broken down (decreased blood thyroxine is the new input signal), less thyroxine is available to inhibit the pituitary: the pituitary secretes more TSH (new output signal).
                      In a positive feedback mechanism, an input signal changes a body parameter from the normal range: it goes either above or below the normal range. This causes the body to respond (output signal) so as to intensify the level of the parameter even further outside the normal range. In positive feedback mechanisms t he body responds to an input signal by intensifying the direction of the signal, either above or below the normal range.
                      a. Birth of a baby: contractions of the body of the uterus stretches the cervix or uterine neck which is where the baby emerges from during birth. Stretching the cervix (input signal) results in even more intense contractions of the body of the uterus (output signal). This stretches the cervix even more (new input signal) resulting in even more intense contractions of the uterine body (new output signal), and so on until the baby is squeezed out. Then, with the baby out of the body, the cervix is stretched less (new input signal) and the uterine body contracts less (new output signal). Notice that this positive feedback system results in a baby being born and then the uterus slowing and eventually stopping its contractions.
                      b. Milk production: the more a baby nurses, the more milk the body produces. As the baby grows and becomes more hungry, it nurses longer (even if the breast is depleted of milk), and the result is that within a day or two the breast's milk production increases to meet the new increasing demand. Notice how a growing baby will always be a bit hungry as the breast cannot quite supply all the milk the baby demands, but the demand is met within a short time. For this reason, breast-fed babies, in general, weigh less than bottle-fed babies - that is the way nature intended for it to be. When the baby is weaned from human milk through the introduction of other food, the baby nurses less (new input signal). This results in the breast producing less milk (new output signal). When nursing stops completely, milk production stops completely.
                      c. Cardiac output (volume of blood the heart pumps per minute): at any given moment when you are not exercising, about 60% of your blood is in your veins. When you begin walking, running or engaging in some other exercise, the veins are signaled by the ANS to contract (vasoconstriction) and more blood is squeezed back to the heart (increased venous return) which stretches the heart muscle. The result of the stretching (input signal) is an increased force of contraction of the heart. This results in an increase in cardiac output (output signal). When you stop exercising, the veins receive less ANS signals and undergo vasodilation. So less blood returns to the heart - decreased venous return - (new input signal) - resulting in decreased cardiac output (new output signal). So you see that in both cases the output signal is in the same direction as the input signal.
                      d. Serious bleeding - This cardiac output mechanism in section c, working by itself, can result in shock after serious injury. If you sustain a major injury and are seriously bleeding, with each beat of the heart, less blood returns to the heart (input signal) because some of the blood actually leaves your body. The heart responds to reduced return of blood by pumping out less blood (the output signal). This leads to even less blood returning to the heart (new input signal) and the result is even less blood pumped out of the heart (new output signal). Eventually so little blood leaves the heart that it is not enough to maintain consciousness and the body lapses into a coma.

                      E. Endocrine glands in the head and their secretions

                      1. Pituitary gland
                      a. Location - this pea-sized gland is nestled in the sella turcica of the sphenoid bone and is connected to the hypothalamus by a stalk called the infundibulum. The pituitary consists of 2 parts: the adenohypophysis (anterior pituitary), and the neurohypophysis (posterior pituitary). The infundibulum conducts a portal vein from the hypothalamus to the adenohypophysis which permits hypothalamic influence on the adenohypophysis through hypothalamic hormones (see below) released into the blood. The infundibulum conducts axons from the hypothalamus to the neurohypophysis which permits hormones made in the hypothalamus to travel down the axons (axon flow) to the neurohypophysis to be stored there and secreted when required (see below).
                      b. Function
                      (1) There are 6 adenohypophyseal hormones (hormones from the anterior pituitary):
                      (a) GH (growth hormone, somatotropin) - directly stimulates mitosis and protein synthesis in most body cells, especially bone, cartilage and muscle leading to growth in height in children, and thickening of bone and hypertrophy of skeletal muscles in exercising adults. It also stimulates fat breakdown from adipose tissue. GH also stimulates the liver to release somatomedins that do the same thing as GH only with a longer half-life. The major stimulus for the release of GH into the blood is vigorous exercise. Since baseline levels of the hormone drop with age, to prevent muscle atrophy and fat accumulation with age, one must exercise more. The typical American high carbohydrate fast-food diet suppresses GH secretion. This stimulates fat accumulation and muscular atrophy - the typical flabby-muscled, overweight, middle-aged adult (on a diet, only between meals). Higher protein diets supply amino acids which act as a stimulus for GH secretion (particularly the amino acid arginine).
                      (b) TSH (thyroid stimulating hormone, thyrotropin) - stimulates the thyroid gland to produce thyroid hormones that help to regulate the metabolic rate.
                      (c) ACTH (adrenocorticotropic hormone, corticotropin) - secreted in response to stress , ACTH stimulates the adrenal cortex to secrete a group of hormones called glucocorticoids, of which the major one is cortisol. In general, the glucocorticoids help the body resist and overcome stress.
                      (d) FSH (follicle stimulating hormone) - stimulates egg (follicle) development in ovaries, and stimulates sperm development in testes.
                      (e) LH (luteinizing hormone) - stimulates an egg to ovulate from the ovaries each month during a female's ovulatory-menstrual cycle. Stimulates the secretion of testosterone from the testes.
                      (f) Prolactin - its main effect is in females where it stimulates the breasts to produce milk after a pregnancy.
                      (2) There are 2 neurohypophyseal hormones (hormones from the posterior pituitary):
                      (a) ADH (anti-diuretic hormone) - secreted from the neurohypophysis due to a signal from the hypothalamus. The hypothalamus sends this signal when the body is dehydrated. The action of ADH is to stimulate water retention from fluid flowing in the kidneys. The body is trying to conserve its water content. The result is urine with minimal amounts of water - a concentrated urine often deeply colored and with an odor.
                      (b) Oxytocin - the main roles for oxytocin are in females: it stimulates smooth muscle contractions of the uterus during childbirth and smooth muscle contractions of the mammary glands expelling milk during nursing.
                      2. Hypothalamus
                      a. Location - the hypothalamus, part of the diencephalon, extends from the optic chiasma to the mammillary bodies and forms part of the walls of the 3rd ventricle. It is connected to the pituitary by the infundibulum.
                      b. Function - The hypothalamus sends 7 hormones by blood to the anterior pituitary, and 2 hormones by axonal flow to the posterior pituitary. It is clear that the CNS regulates many of the endocrine secretions, working through the hypothalamus.
                      (1) Hormones to the anterior pituitary - their names indicate their functions except for #7. These hormones reach the anterior pituitary through the hypothalmic-hypophyseal portal system (through the blood).
                      (a) GHRH (Growth hormone releasing hormone)
                      (b) TRH (Thyrotropin releasing hormone)
                      (c) CRH (Corticotropin, adrenocorticotropic hormone)
                      (d) GnRH (Gonadotropin releasing hormone)
                      (e) PRH (Prolactin releasing hormone)
                      (f) PIH (Prolactin inhibiting hormone)
                      (g) Somatostatin - inhibits GH and TSH secretion
                      (2) Hormones to the posterior pituitary. These hormones travel to the posterior pituitary through axon flow and are released from the pituitary upon nerve signal from neurons of the hypothalamus (the same neurons that send the hormones down their axons).
                      (a) ADH - anti-diuretic hormone - helps the body conserve its water (see above).
                      (b) Oxytocin - stimulates smooth muscle contractions in uterus and breasts (see above).
                      3. Pineal gland
                      a. Location - the pineal is easily observed in the sheep's brain by gently depressing the brainstem and cerebellum and observing the region inferior to the occipital lobes: the pineal is seen as a medial, pea-sized bulge just superior to the corpora quadrigemina. In humans, the pineal, once proposed to be the residence of the human soul, is just below the posterior portion of the corpus callosum, on the roof of the third ventricle, and not easily seen.
                      b. Function - The gland produces serotonin during the day and melatonin during the night. It is thought to be related to human biorhythms such as helping to determine the onset of puberty and also helping to regulate human cycles of sleep and wakefulness. It is largest in children and becomes smaller and more fibrous (or even calcified) in adults. Definitive, detailed knowledge of the gland's actions is still lacking.

                      F. Endocrine glands in the neck and their secretions
                      1. Thyroid gland
                      a. Location - this largest of endocrine glands consists of two large lobes connected by an isthmus and is located just above the soft spot in your neck (just anterior to the suprasternal notch). It is wrapped around the anterior and lateral portions of the trachea. b. Function - The thyroid's secretion of hormones is regulated by TSH from the pituitary gland. Since the pituitary secretion of TSH is regulated by TRH from the hypothalamus, physiologists speak of a hypothalamic-pituitary-thyroid axis. Three major hormones are secreted by this gland: T 3 , T 4 , and calcitonin .
                      (1) T ri-iodothyronine (T 3 ) and thyroxine (T 4 ) are mainly regulators of the metabolic rate of other tissues of the body.
                      (a) They enter the cytoplasm and nucleoplasm of target cells and increase the rate of mitochondrial oxidations, protein synthesis, and m-RNA production. These hormones increase the production of adrenal gland and pituitary hormones, raise blood pressure, respiratory rate and body heat production, stimulate bone teeth and nail growth in adults and during fetal development, and promotes fat breakdown for energy.
                      (b) T 3 is the active form of the hormone intracellularly (T 4 is converted to T 3 in the cytoplasm of target cells).
                      (c) T 4 feeds back to the pituitary and inhibits (slows down) TSH secretion. As T 4 is broken down, TSH secretion increases. This is a negative feedback mechanism.
                      (2) Calcitonin - this hormone is most important for helping to regulate blood calcium levels when a woman is pregnant or lactating. During pregnancy and lactation, the reduction of blood calcium as it passes from the maternal blood into the fetus or the milk, results in parathyroid gland activity (see below) that increases blood calcium levels. Whenever calcium levels of the blood rise, calcitonin is then secreted by the thyroid: it activates osteoblasts resulting in an overall reduction of blood calcium levels as some calcium is deposited in the woman's bones as well as entering the milk and the fetus. This hormone is also important in controlling the blood calcium concentration of infants and children whose blood calcium levels are generally higher than those of adults due to the bone growth and remodeling. Calcitonin has been used therapeutically to help individuals with osteoporosis.
                      2. Parathyroid glands
                      a. Location - Although their number and location can vary, most people have 4 yellowish, rice-grain sized parathyroid glands located on the posterior surface of the thyroid gland.
                      b. Function - They secrete the hormone, parathormone, when the blood calcium level drops. Parathormone has the following effects, all of which attempt to raise the blood calcium level back to the normal range (a negative feedback mechanism):
                      (1) Stimulates osteoclast activity which releases calcium into the blood from osseus tissue.
                      (2) Inhibits secretion of calcium into the urine by the kidneys thus maintaining the calcium level of the blood.
                      (3) Stimulates active vitamin D (calcitriol) formation in the kidneys. Calcitriol then increases calcium, phosphate and magnesium absorption from digested food in the intestine.

                      F. Endocrine glands in the thoracic cavity and their secretions
                      1. Thymus gland
                      a. Location - The thymus is easily observed in the mediastinum of a pig or cat as a large cap of tissue covering the anterior surface of the heart (cranial portion of the heart). In humans the thymus is large in infants, gets larger during childhood and covers the superior and anterior portion of the heart. It is much smaller in adults and is located superior to the heart and medial to the upper (superior) lung lobes. It becomes very small and fibrous in old age.
                      b. Function - The thymus is central to the operation of the immune system: T-lymphocytes (T-cells) develop and mature in the thymus different classes of T-cells are responsible for cellular immunity (the other type of immunity is humoral immunity and is carried out by proteins called antibodies). The thymus produces hormones (thymosin, thymulin, thymopoietin) that stimulate other parts of the immune system (e.g., lymph nodes) to function.
                      2. Heart - although not generally considered part of the endocrine system, the heart's upper chambers, the atria, when stretched, produce a hormone, atrial natriuretic peptide (ANP), that results in blood pressure decrease. ANP causes vasodilation (reducing blood pressure) and increased kidney excretion of sodium (which causes increased body water loss by osmosis that reduces blood pressure). ANP can be thought of as opposing the actions of both aldosterone (helps the body retain sodium) and angiotensin II (a vasoconstrictor).

                      G. Endocrine glands in the abdominopelvic cavity and their secretions.
                      1. Pancreas
                      a. Location - Technically the abdominal cavity is enclosed by the peritoneum. Since the pancreas is located behind the parietal portion of the peritoneum, its location is described as retroperitoneal. It is an elongated organ consisting of a head, neck, body and tail. The head is located next to the first part of the small intestine, the duodenum the body passes anterior to the left kidney with the tail located next to the inferior portion of the spleen.
                      b. Function - About 99% of the mass of the pancreas is concerned with exocrine secretion: production of pancreatic enzymes for digestion of food. Pancreatic juice empties into the duodenum through the pancreatic duct. Pancreatic endocrine secretions come from 1 -2 million islets of Langerhans:groupings of cells scattered throughout the pancreas that secrete 3 hormones: insulin, glucagon and somatostatin.
                      (1) Insulin is produced from islet beta cells: it is the only hormone that lowers blood glucose concentrations and is secreted after meals when the blood glucose level rises. Insulin stimulates target cells to produce the receptors that bind and transport glucose into cells, thus lowering the blood glucose levels. Insulin also stimulates adipocytes to absorb and store fat, muscle fibers to absorb and utilize amino acids, and the liver to synthesize both glycogen and triglycerides.
                      (2) Glucagon is produced from islet alpha cells: it raises blood glucose concentrations as would be required when we fast between meals: glucagon stimulates the liver's breakdown of stored glycogen into glucose, a process called glycogenolysis. Glucagon also stimulates the liver to convert amino acids into glucose, a process called gluconeogenesis which also promotes a rise in blood glucose.
                      (3) Somatostatin is produced from the islet delta cells and has the ability to locally inhibit secretion of both insulin and glucagon and to inhibit overall digestive activity whenever blood glucose and amino levels are high.
                      2. Adrenal glands (suprarenal glands). Due to the interaction of the hypothalamus and the pituitary with the adrenal gland, endocrinologists speak of a hypothalmic-pituitary-adrenal axis.
                      a. Location - like the pancreas, the kidneys are also located behind the parietal peritoneum and are called retroperitoneal. The adrenal glands are positioned like caps on the superior surface of each kidney.
                      b. Function - the adrenal gland consists of an outer cortex and an inner medulla.
                      The cortex secretes three classes of hormones (mineralocorticoids, glucocorticoids, and sex hormones) the medulla secretes mainly 2 hormones - epinephrine and norepinephrine..
                      (1) Adrenal cortex - from superficial to deep regions, the adrenal cortex is divided into a zona glomerulosa, zona fasciculata, and a zona reticularis.
                      (a) Zona glomerulosa - secretes mainly mineralocorticoids, the main one being aldosterone. Aldosterone's function is to conserve body salt (sodium chloride) and water, and to excrete potassium.
                      (b) Zona fasciculata - secretes mainly glucocorticoids of which the main ones are cortisol and corticosterone. The glucocorticoids have two main functions: to reduce the body's inflammatory responses, and to promote gluconeogenesis, meaning that proteins and fats are stimulated to break down: the proteins are hydrolyzed into amino acids that are converted to glucose in the liver the fats are converted to fatty acids. These actions give the body fuel - glucose and fatty acids - to combat stress by having energy sources readily available in the blood.
                      (c) Zona reticularis - secretes mainly sex hormones - androgens (sometimes called 17-ketosteroids) and estrogens. The adrenal's output of these sex hormones is not as great as that from the testes and ovaries in youth and middle age. However, at older ages, the adrenals become important sources of sex hormones that maintain energy levels and the sex drive.
                      (2) Adrenal medulla - The cells of the adrenal medulla are actually modified postganglionic neurons of the sympathetic nervous system that secrete epinephrine and norepinephrine in approximately a 75%:25% proportion when stimulated by sympathetic preganglionic neurons of the autonomic nervous system (ANS). The effect of epinephrine and norepinephrine is to prepare the body for "fight or flight" (see ANS section).
                      3. Gonads - ovaries and testes. Due to the interaction of the hypothalamus and the pituitary with the gonads, endocrinologists speak of a hypothalmic-pituitary-gonadal axis.
                      a. Ovaries
                      (1) Location - the ovaries, the female sex glands, are located in the pelvic cavity, being suspended and anchored in place by several ligaments - the ovarian ligament attaching to the uterus, the suspensory ligament attaching to the pelvic wall, and a broad ligament attaching to the uterus and uterine tubes.
                      (2) Function - The function of the ovaries is to ovulate eggs and to produce female sex hormones. The ovaries possess an outer cortex containing the germinal epithelium that produces eggs and female sex hormones. The inner medulla contains blood vessels and nerves.
                      (a) Eggs - Eggs, all of which were produced during the embryonic period, are enclosed in follicles consisting of the egg cell immersed in fluid surrounded by follicle cells arranged as a squamous epithelium. Hormonal signals from the pituitary gland and the ovary itself result in the maturation of a single follicle each month and the discharge of its egg from the surface of the ovary - a process called ovulation. If the egg is fertilized and pregnancy is successful, a baby will be born an average of 266 days (38 weeks) later, a little longer than 9 months. Other details of the maturation and ovulation of eggs are the subject matter of a section dealing with the reproductive system.
                      (b) Female sex hormones - estrogens are female sex hormones and there are three of them - estradiol (the most abundant), estriol, and estrone. They are responsible for female secondary sexual characteristics including maturation of the external genitalia and breasts, patterns of fat deposition under the skin, and patterns of brain development. Progesterone is another female sex hormone that prepares the uterine inner lining (the endometrium) and the breasts for pregnancy by stimulating the secretory capacity of these organs. Estrogens and progesterone are produced during a monthly cycle known as the ovulatory-menstrual cycle. This cycle is influenced by releasing hormones from the hypothalamus. Details of these hormonal interactions are provided elsewhere.
                      b. Testes
                      (1) Location - the testes are suspended outside the body in the scrotal sacs where the temperature is about 3 below the normal body temperature, which is optimal for sperm development.
                      (2) Function - The function of the testes is to form and mature sperm and to produce male sex hormones, mainly testosterone. The testes are divided by connective tissue partitions into about 300 lobules containing the seminiferous tubules whose walls consist of a germinal epithelium where sperm cells are formed. Male sex hormones are produced by interstitial cells of Leydig located between the seminiferous tubules. Testosterone and other androgens are responsible for male secondary sexual characteristics including maturation of the external genitalia, the development of the musculature, and patterns of brain development. Further details about male reproductive function are presented elsewhere.
                      4. Other abdominopelvic organs that have endocrine functions.
                      a. Liver - the liver produces several hormones and hormone precursors:
                      (1) Somatomedins - these are hormones whose synthesis is induced by GH and which stimulate growth throughout the body in a manner like GH itself. The main somatomedin is IGF-1 (insulin-like growth factor).
                      (2) Erythropoietin (EPO) is a hormone produced by both the liver and kidneys that stimulates erythrocyte production in the bone marrow.
                      (3) The liver produces an intermediate (called calcidiol) a precursor in the pathway to the production of active vitamin D.
                      (4) Angiotensinogen is a hormone precursor to the ultimate formation of angiotensin II, an important vasoconstrictor that raises blood pressure.
                      b. Kidneys - the kidneys produce erythropoietin, along with the liver, that stimulates erythrocyte formation, and calcitriol, the active form of vitamin D that stimulates the absorption of calcium, phosphorus and magnesium from the intestine and which inhibits the body's excretion of calcium through the kidneys - both actions making calcium more available for bone formation.
                      c. Organs of digestion - the stomach and small intestine produce many hormones that regulate digestive processes: e.g., the stomach produces gastrin, that stimulates the stomach's acid production, the duodenum produces secretin, that stimulates pancreatic secretion of sodium bicarbonate into the duodenum to neutralize gastric acid arriving mixed with food, and the duodenum also produces cholecystokinin (CCK), that stimulates the secretion of bile and pancreatic enzymes in response to the arrival of food from the stomach.

                      Biomedical Terminology : Define each term:

                      antidiuretic hormone
                      atrial natriuretic peptide
                      endocrine gland
                      exocrine gland
                      interstitial cells of Leydig
                      negative feedback
                      positive feedback
                      seminiferous tubules
                      zona glomerulosa
                      zone fasciculata
                      zona reticularis

                      Endocrine System Problems

                      1. Choose one of the problems described below.
                      2. Prepare your solution as a word document.
                      3. Send it to your professor as an email attachment. You will receive an email response.

                      Problem #1: A nineteen year old college student regularly experiences anxiety, abdominal bloating, craving for sugary foods, and mild depression during the 2 weeks prior to menstruation. She also regularly experiences cramping during the first 2 days of menstruation. Her doctor recommends hormone pills to relieve the pre-menstrual symptoms as well as pain medication for the menstrual cramping. Utilize the Internet to research the pros and cons of hormonal therapy for PMS (pre-menstrual syndrome) and alternatives for such hormonal therapy.
                      Your report should include
                      1. A definition of PMS (sometimes referred to as PMT - pre-menstrual tension) and a description of its effects on the body.
                      2. A proposed physiological explanation of why these symptoms are occurring.
                      3. The benefits and side effects of taking hormones to relieve PMS symptoms.
                      4. The potential long-term side-effects of hormonal therapy.
                      5. A description of nutritional/herbal treatments for PMS and their side effects.
                      6. A decision, based on your research, of which therapy(ies) for PMS might be best to try.

                      Problem #2: A 45 year old female, 5'4" and 220 lbs., experiencing low energy levels, periods of dizziness, and knee pain, decides to see her doctor. Examination reveals hypertension, elevated blood sugar, elevated total cholesterol levels, elevated triglycerides, and elevated blood insulin levels. Her doctor's diagnosis is diabetes mellitus Type II and she is initially placed on "oral insulin" and after a year with marginal sign and symptom relief, she begins injecting insulin. She receives some benefit but indicates she does not feel a sense of well-being. Utilize the Internet to answer the following questions:
                      1. What are the possible causes of type II diabetes mellitus?
                      2. How is diabetes type II different from diabetes type I?
                      3. What are the long-term consequences to health from diabetes mellitus? What is the underlying physiological reason for these consequences?
                      4. What is the medical/physiological reason for giving oral insulin and then injectable insulin to a type II diabetic who already has an abundance of insulin in their blood?
                      5. Are there any dietary (nutritional) measures that might help this situation? Are they practical- can they be accomplished?
                      6. If you were the son or daughter of the individual in this case, what treatment would you suggest to your parent for relief from the symptoms of this condition?

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                      Chapter 12 Endocrine System - PowerPoint PPT Presentation

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                      Major endocrine systems Edit

                      The human endocrine system consists of several systems that operate via feedback loops. Several important feedback systems are mediated via the hypothalamus and pituitary. [2]

                      Glands Edit

                      Endocrine glands are glands of the endocrine system that secrete their products, hormones, directly into interstitial spaces and then absorbed into blood rather than through a duct. The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid gland, parathyroid gland, hypothalamus and adrenal glands. The hypothalamus and pituitary gland are neuroendocrine organs.

                      The hypothalamus and the anterior pituitary are two out of the three endocrine glands that are important in cell signaling. They are both part of the HPA axis which is known to play a role in cell signaling in the nervous system.

                      Hypothalamus: The hypothalamus is a key regulator of the autonomic nervous system. The endocrine system has three sets of endocrine outputs [3] which include the magnocellular system, the parvocellular system, and autonomic intervention. The magnocellular is involved in the expression of oxytocin or vasopressin. The parvocellular is involved in controlling the secretion of hormones from the anterior pituitary.

                      Anterior Pituitary: The main role of the anterior pituitary gland is to produce and secret tropic hormones. [4] Some examples of tropic hormones secreted by the anterior pituitary gland include TSH, ACTH, GH, LH, and FSH.

                      Cells Edit

                      There are many types of cells that make up the endocrine system and these cells typically make up larger tissues and organs that function within and outside of the endocrine system.

                      • The posterior pituitary gland is a section of the pituitary gland. This organ secretes hormones such as antidiuretic hormone (ADH) and oxytocin. ADH functions to help the body to retain water this is important in maintaining a homeostatic balance between blood solutions and water. Oxytocin functions to induce uterine contractions, stimulate lactation, and allows for ejaculation. [5][6]
                        of the thyroid gland produce and secrete T3 and T4 in response to elevated levels of TRH, produced by the hypothalamus, and subsequent elevated levels of TSH, produced by the anterior pituitary gland, which further regulates the metabolic activity and rate of all cells, including cell growth and tissue differentiation.
                      • cells of the parathyroid glands are richly supplied with blood from the inferior and superior thyroid arteries and secrete parathyroid hormone (PTH). PTH acts on bone, the kidneys, and the GI tract to increase calciumreabsorption and phosphate excretion. In addition, PTH stimulates the conversion of Vitamin D to its most active variant, 1,25-dihydroxyvitamin D3, which further stimulates calcium absorption in the GI tract. [1]
                    • Pancreas contain nearly 1 to 2 million islets of Langerhans (a tissue which consists cells that secrete hormones) and acini. Acini secretes digestive enzymes. [7]
                        • The alpha cells of the pancreas secrete hormones to maintain homeostatic blood sugar. Insulin is produced and excreted to lower blood sugar to normal levels. Glucagon, another hormone produced by alpha cells, is secreted in response to low blood sugar levels glucagon stimulates glycogen stores in the liver to release sugar into the bloodstream to raise blood sugar to normal levels. [8]
                        • 60% of the cells present in islet of Langerhans are beta cells. Beta cells secrete insulin. Along with glucagon, insulin helps in maintaining glucose levels in our body. Insulin decreases blood glucose level ( a hypoglycemic hormone) whereas glucagon increases blood glucose level. [7]

                        The fetal endocrine system is one of the first systems to develop during prenatal development.

                        Adrenal glands Edit

                        The fetal adrenal cortex can be identified within four weeks of gestation. The adrenal cortex originates from the thickening of the intermediate mesoderm. At five to six weeks of gestation, the mesonephros differentiates into a tissue known as the gonadal ridge. The gonadal ridge produces the steroidogenic cells for both the gonads and the adrenal cortex. The adrenal medulla is derived from ectodermal cells. Cells that will become adrenal tissue move retroperitoneally to the upper portion of the mesonephros. At seven weeks of gestation, the adrenal cells are joined by sympathetic cells that originate from the neural crest to form the adrenal medulla. At the end of the eighth week, the adrenal glands have been encapsulated and have formed a distinct organ above the developing kidneys. At birth, the adrenal glands weight approximately eight to nine grams (twice that of the adult adrenal glands) and are 0.5% of the total body weight. At 25 weeks, the adult adrenal cortex zone develops and is responsible for the primary synthesis of steroids during the early postnatal weeks.

                        Thyroid gland Edit

                        The thyroid gland develops from two different clusterings of embryonic cells. One part is from the thickening of the pharyngeal floor, which serves as the precursor of the thyroxine (T4) producing follicular cells. The other part is from the caudal extensions of the fourth pharyngobranchial pouches which results in the parafollicular calcitonin-secreting cells. These two structures are apparent by 16 to 17 days of gestation. Around the 24th day of gestation, the foramen cecum, a thin, flask-like diverticulum of the median anlage develops. At approximately 24 to 32 days of gestation the median anlage develops into a bilobed structure. By 50 days of gestation, the medial and lateral anlage have fused together. At 12 weeks of gestation, the fetal thyroid is capable of storing iodine for the production of TRH, TSH, and free thyroid hormone. At 20 weeks, the fetus is able to implement feedback mechanisms for the production of thyroid hormones. During fetal development, T4 is the major thyroid hormone being produced while triiodothyronine (T3) and its inactive derivative, reverse T3, are not detected until the third trimester.

                        Parathyroid glands Edit

                        A lateral and ventral view of an embryo showing the third (inferior) and fourth (superior) parathyroid glands during the 6th week of embryogenesis

                        Once the embryo reaches four weeks of gestation, the parathyroid glands begins to develop. The human embryo forms five sets of endoderm-lined pharyngeal pouches. The third and fourth pouch are responsible for developing into the inferior and superior parathyroid glands, respectively. The third pharyngeal pouch encounters the developing thyroid gland and they migrate down to the lower poles of the thyroid lobes. The fourth pharyngeal pouch later encounters the developing thyroid gland and migrates to the upper poles of the thyroid lobes. At 14 weeks of gestation, the parathyroid glands begin to enlarge from 0.1 mm in diameter to approximately 1 – 2 mm at birth. The developing parathyroid glands are physiologically functional beginning in the second trimester.

                        Studies in mice have shown that interfering with the HOX15 gene can cause parathyroid gland aplasia, which suggests the gene plays an important role in the development of the parathyroid gland. The genes, TBX1, CRKL, GATA3, GCM2, and SOX3 have also been shown to play a crucial role in the formation of the parathyroid gland. Mutations in TBX1 and CRKL genes are correlated with DiGeorge syndrome, while mutations in GATA3 have also resulted in a DiGeorge-like syndrome. Malformations in the GCM2 gene have resulted in hypoparathyroidism. Studies on SOX3 gene mutations have demonstrated that it plays a role in parathyroid development. These mutations also lead to varying degrees of hypopituitarism.

                        Pancreas Edit

                        The human fetal pancreas begins to develop by the fourth week of gestation. Five weeks later, the pancreatic alpha and beta cells have begun to emerge. Reaching eight to ten weeks into development, the pancreas starts producing insulin, glucagon, somatostatin, and pancreatic polypeptide. During the early stages of fetal development, the number of pancreatic alpha cells outnumbers the number of pancreatic beta cells. The alpha cells reach their peak in the middle stage of gestation. From the middle stage until term, the beta cells continue to increase in number until they reach an approximate 1:1 ratio with the alpha cells. The insulin concentration within the fetal pancreas is 3.6 pmol/g at seven to ten weeks, which rises to 30 pmol/g at 16–25 weeks of gestation. Near term, the insulin concentration increases to 93 pmol/g. The endocrine cells have dispersed throughout the body within 10 weeks. At 31 weeks of development, the islets of Langerhans have differentiated.

                        While the fetal pancreas has functional beta cells by 14 to 24 weeks of gestation, the amount of insulin that is released into the bloodstream is relatively low. In a study of pregnant women carrying fetuses in the mid-gestation and near term stages of development, the fetuses did not have an increase in plasma insulin levels in response to injections of high levels of glucose. In contrast to insulin, the fetal plasma glucagon levels are relatively high and continue to increase during development. At the mid-stage of gestation, the glucagon concentration is 6 μg/g, compared to 2 μg/g in adult humans. Just like insulin, fetal glucagon plasma levels do not change in response to an infusion of glucose. However, a study of an infusion of alanine into pregnant women was shown to increase the cord blood and maternal glucagon concentrations, demonstrating a fetal response to amino acid exposure.

                        As such, while the fetal pancreatic alpha and beta islet cells have fully developed and are capable of hormone synthesis during the remaining fetal maturation, the islet cells are relatively immature in their capacity to produce glucagon and insulin. This is thought to be a result of the relatively stable levels of fetal serum glucose concentrations achieved via maternal transfer of glucose through the placenta. On the other hand, the stable fetal serum glucose levels could be attributed to the absence of pancreatic signaling initiated by incretins during feeding. In addition, the fetal pancreatic islets cells are unable to sufficiently produce cAMP and rapidly degrade cAMP by phosphodiesterase necessary to secrete glucagon and insulin.

                        During fetal development, the storage of glycogen is controlled by fetal glucocorticoids and placental lactogen. Fetal insulin is responsible for increasing glucose uptake and lipogenesis during the stages leading up to birth. Fetal cells contain a higher amount of insulin receptors in comparison to adults cells and fetal insulin receptors are not downregulated in cases of hyperinsulinemia. In comparison, fetal haptic glucagon receptors are lowered in comparison to adult cells and the glycemic effect of glucagon is blunted. This temporary physiological change aids the increased rate of fetal development during the final trimester. Poorly managed maternal diabetes mellitus is linked to fetal macrosomia, increased risk of miscarriage, and defects in fetal development. Maternal hyperglycemia is also linked to increased insulin levels and beta cell hyperplasia in the post-term infant. Children of diabetic mothers are at an increased risk for conditions such as: polycythemia, renal vein thrombosis, hypocalcemia, respiratory distress syndrome, jaundice, cardiomyopathy, congenital heart disease, and improper organ development.

                        Gonads Edit

                        The reproductive system begins development at four to five weeks of gestation with germ cell migration. The bipotential gonad results from the collection of the medioventral region of the urogenital ridge. At the five-week point, the developing gonads break away from the adrenal primordium. Gonadal differentiation begins 42 days following conception.

                        Male gonadal development Edit

                        For males, the testes form at six fetal weeks and the sertoli cells begin developing by the eight week of gestation. SRY, the sex-determining locus, serves to differentiate the Sertoli cells. The Sertoli cells are the point of origin for anti-Müllerian hormone. Once synthesized, the anti-Müllerian hormone initiates the ipsilateral regression of the Müllerian tract and inhibits the development of female internal features. At 10 weeks of gestation, the Leydig cells begin to produce androgen hormones. The androgen hormone dihydrotestosterone is responsible for the development of the male external genitalia.

                        The testicles descend during prenatal development in a two-stage process that begins at eight weeks of gestation and continues through the middle of the third trimester. During the transabdominal stage (8 to 15 weeks of gestation), the gubernacular ligament contracts and begins to thicken. The craniosuspensory ligament begins to break down. This stage is regulated by the secretion of insulin-like 3 (INSL3), a relaxin-like factor produced by the testicles, and the INSL3 G-coupled receptor, LGR8. During the transinguinal phase (25 to 35 weeks of gestation), the testicles descend into the scrotum. This stage is regulated by androgens, the genitofemoral nerve, and calcitonin gene-related peptide. During the second and third trimester, testicular development concludes with the diminution of the fetal Leydig cells and the lengthening and coiling of the seminiferous cords.

                        Female gonadal development Edit

                        For females, the ovaries become morphologically visible by the 8th week of gestation. The absence of testosterone results in the diminution of the Wolffian structures. The Müllerian structures remain and develop into the fallopian tubes, uterus, and the upper region of the vagina. The urogenital sinus develops into the urethra and lower region of the vagina, the genital tubercle develops into the clitoris, the urogenital folds develop into the labia minora, and the urogenital swellings develop into the labia majora. At 16 weeks of gestation, the ovaries produce FSH and LH/hCG receptors. At 20 weeks of gestation, the theca cell precursors are present and oogonia mitosis is occurring. At 25 weeks of gestation, the ovary is morphologically defined and folliculogenesis can begin.

                        Studies of gene expression show that a specific complement of genes, such as follistatin and multiple cyclin kinase inhibitors are involved in ovarian development. An assortment of genes and proteins - such as WNT4, RSPO1, FOXL2, and various estrogen receptors - have been shown to prevent the development of testicles or the lineage of male-type cells.

                        Pituitary gland Edit

                        The pituitary gland is formed within the rostral neural plate. The Rathke’s pouch, a cavity of ectodermal cells of the oropharynx, forms between the fourth and fifth week of gestation and upon full development, it gives rise to the anterior pituitary gland. By seven weeks of gestation, the anterior pituitary vascular system begins to develop. During the first 12 weeks of gestation, the anterior pituitary undergoes cellular differentiation. At 20 weeks of gestation, the hypophyseal portal system has developed. The Rathke’s pouch grows towards the third ventricle and fuses with the diverticulum. This eliminates the lumen and the structure becomes Rathke’s cleft. The posterior pituitary lobe is formed from the diverticulum. Portions of the pituitary tissue may remain in the nasopharyngeal midline. In rare cases this results in functioning ectopic hormone-secreting tumors in the nasopharynx.

                        The functional development of the anterior pituitary involves spatiotemporal regulation of transcription factors expressed in pituitary stem cells and dynamic gradients of local soluble factors. The coordination of the dorsal gradient of pituitary morphogenesis is dependent on neuroectodermal signals from the infundibular bone morphogenetic protein 4 (BMP4). This protein is responsible for the development of the initial invagination of the Rathke’s pouch. Other essential proteins necessary for pituitary cell proliferation are Fibroblast growth factor 8 (FGF8), Wnt4, and Wnt5. Ventral developmental patterning and the expression of transcription factors is influenced by the gradients of BMP2 and sonic hedgehog protein (SHH). These factors are essential for coordinating early patterns of cell proliferation.

                        Six weeks into gestation, the corticotroph cells can be identified. By seven weeks of gestation, the anterior pituitary is capable of secreting ACTH. Within eight weeks of gestation, somatotroph cells begin to develop with cytoplasmic expression of human growth hormone. Once a fetus reaches 12 weeks of development, the thyrotrophs begin expression of Beta subunits for TSH, while gonadotrophs being to express beta-subunits for LH and FSH. Male fetuses predominately produced LH-expressing gonadotrophs, while female fetuses produce an equal expression of LH and FSH expressing gonadotrophs. At 24 weeks of gestation, prolactin-expressing lactotrophs begin to emerge.

                        Hormones Edit

                        A hormone is any of a class of signaling molecules produced by cars in glands in multicellular organisms that are transported by the circulatory system to target distant organs to regulate physiology and behaviour. Hormones have diverse chemical structures, mainly of 3 classes: eicosanoids, steroids, and amino acid/protein derivatives (amines, peptides, and proteins). The glands that secrete hormones comprise the endocrine system. The term hormone is sometimes extended to include chemicals produced by cells that affect the same cell (autocrine or intracrine signalling) or nearby cells (paracrine signalling).

                        Hormones affect distant cells by binding to specific receptor proteins in the target cell resulting in a change in cell function. This may lead to cell type-specific responses that include rapid changes to the activity of existing proteins, or slower changes in the expression of target genes. Amino acid–based hormones (amines and peptide or protein hormones) are water-soluble and act on the surface of target cells via signal transduction pathways steroid hormones, being lipid-soluble, move through the plasma membranes of target cells to act within their nuclei.

                        Cell signalling Edit

                        The typical mode of cell signalling in the endocrine system is endocrine signaling, that is, using the circulatory system to reach distant target organs. However, there are also other modes, i.e., paracrine, autocrine, and neuroendocrine signaling. Purely neurocrine signaling between neurons, on the other hand, belongs completely to the nervous system.

                        Autocrine Edit

                        Autocrine signaling is a form of signaling in which a cell secretes a hormone or chemical messenger (called the autocrine agent) that binds to autocrine receptors on the same cell, leading to changes in the cells.

                        Paracrine Edit

                        Some endocrinologists and clinicians include the paracrine system as part of the endocrine system, but there is not consensus. Paracrines are slower acting, targeting cells in the same tissue or organ. An example of this is somatostatin which is released by some pancreatic cells and targets other pancreatic cells. [1]

                        Juxtacrine Edit

                        Juxtacrine signaling is a type of intercellular communication that is transmitted via oligosaccharide, lipid, or protein components of a cell membrane, and may affect either the emitting cell or the immediately adjacent cells. [11]

                        It occurs between adjacent cells that possess broad patches of closely opposed plasma membrane linked by transmembrane channels known as connexons. The gap between the cells can usually be between only 2 and 4 nm. [12]

                        April: “If it’s not a cancer, let’s not call it a cancer”

                        In one of the biggest endocrine stories 0f the year, a type of thyroid tumour is no longer classified as a cancer. As it turns out, certain types of tumours are encapsulated in impenetrable tissue and should not be classified as cancer. The tumour, known as encapsulated follicular variant of papillary thyroid carcinoma (EFVPTC), makes up 10-20% of all thyroid cancers diagnosed in Europe and North America.

                        Previously, people diagnosed with the non-threatening condition would have their entire thyroid removed, undergo treatment with radioactive iodine, and have regular check-ups for the rest of their lives. EFVPTC involves small abnormal lesions in the thyroid gland which look like cancer, but are completely contained by a fibrous capsule and unable to spread.

                        A group of 24 pathologists, two endocrinologists, a thyroid surgeon and a psychiatrist reviewed a hundred cases of patients with EFVPTC, who had the capsules removed but no further treatment. After 10 years, all patients with encapsulated tumours were cancer free.

                        The move means thousands of patients world-wide will be spared the diagnosis of cancer, avoiding excessive treatments and the psychological trauma of cancer diagnosis.

                        The new name for the lesion is NIFTP or “Nift-P” which stands for non-invasive follicular thyroid neoplasm with papillary-like nuclear features”. Pretty Nifty.


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