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What are the main differences between lab-grown tissues and natural tissues from living animals?

What are the main differences between lab-grown tissues and natural tissues from living animals?


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What are the main differences between lab-grown tissues and natural tissues from living animals?

Using a biologist's classic "structure (anatomy) and function (physiology)" idea, I thought about the followings:

Structure:

  • It might be difficult to recreate the composition of different tissues / cells in living things precisely with artificial methods. This may lead to bad results when the tissue is used for tests of medicines and cosmetics.

Function:

  • Cells might not function and produce as expected (or is harder to make them function) in artificial compositions, as cells need strictly regulated environments to function correctly.

Also, I think using artificial tissues for drug tests helps researchers to avoid ethical issues which may arise if they use living animals instead. I think the cost is generally higher to make artificial tissues than to gather test animals; however I am not sure if this applies to every case - maybe some tissues are relatively cheap to grow in labs.

What are some other differences? The answer can be about the advantages and the disadvantages of making / using lab-grown tissues and using living animals as well.


Immortalized cell lines are often cancerous, which has large effects on their gene expression profiles. They also adapt to cell culture conditions after several hundred passages in culture. I've cultured both HepG2 cells and primary mouse hepatocytes. The HepG2 are a hepatocellular carcinoma line and grow fine in culture, while the primary hepatocytes don't really grow in culture and only live for a few days after you extract them from a mouse. We were doing gene transfer assays with both sets of cells. The quickly dividing HepG2 cells were easy to transform using PEI, and while primary hepatocytes could be transformed with PEI, they worked better with calcium phosphate, probably because it was less toxic. I noticed that HepG2 cells were smaller than primary hepatocytes, and the primaries were far more fragile, we could run HepG2 through a peristaltic pump with no problems, but had to handle all the primary cells by hand.

As far as cost goes, tissue culture is almost always cheaper. You can make a bottle of media for a few dollars worth of material and use it for several passages. The cost of running an incubator and biosafety cabinet are also minimal. So unless you're doing something unusual, cell culture is affordable. However, it's an incomplete model at best. Trying to create whole tissues in the lab counts as unusual.

Doing work with animals is far more accurate than cell culture, but much more expensive. Our mice are cheap, but still cost about a dollar each, and about 20 cents a day for housing. A typical biodistribution experiment will use 3 mice per time point and 8 - 10 time points, so 24 to 30 mice assuming no mistakes during dosing. On top of that, doing animal work has a lot more bureaucracy involved, with animal use protocols and approvals and inspections.

The question about whether to use animal models vs cell culture comes down to what you're trying to accomplish. If you're studying gene regulation or protein interactions, cell culture usually works better because it's more amenable to gene transfer and allows you to use techniques like fluorescent fusion proteins and bioconjugation. If you're studying drug metabolism and toxicity you should use whole animals because the interactions between metabolites and specific tissues are hard to reproduce in cell culture. In some far off future we may be able to totally replace animal models with cell culture or even computer models, but we're not even close.


Plant tissues

Learners need to be able to examine and identify some plant tissues using microscopes, bio viewers, photomicrographs and posters. Learners need to be able to draw the cells that make up the various plant tissues, showing the specialised structures.

TEACHER RESOURCES:

Plants are typically made up of roots, stems and leaves. Plant tissues can be broadly categorised into dividing, meristematic tissue or non-dividing, permanent tissue. Permanent tissue is made up of simple and complex tissues.

There are over ( ext<200𧄀>) types of plant species in the world. Green plants provide the Earth's oxygen, and also directly or indirectly provide food for all animals because of their ability to photosynthesise. Plants also provide the source of most of our drugs and medicines. The scientific study of plants is known as botany.

Learn more about plant tissues:

Figure 4.2 provides an overview of the types of plant tissues being studied in this chapter.

Figure 4.2: The diagram above depicts how several cells adapted for the same function work in conjunction to form tissues.

It is important that for each tissue type you understand:

  • where it is located
  • what its key structural features are and how these relate to function
  • how each tissue type looks under the microscope
  • how to draw biological diagrams of each structure

Meristematic tissue (ESG66)

Meristematic tissue is undifferentiated tissue. Meristematic tissue contains actively dividing cells that result in formation of other tissue types (e.g. vascular, dermal or ground tissue). Apical meristematic tissue is found in buds and growing tips of plants. It generally makes plants grow taller or longer. Lateral meristematic tissue make the plant grow thicker. Lateral meristems occur in woody trees and plants. Examples of lateral meristematic tissue include the vascular cambium that results in the rings you see in trees, and cork cambium or 'bark' found on the outside of trees.

Figure 4.3: Meristematic cells in the growing root-tip of the onion, from a longitudinal section.

Figure 4.4: Micrograph of meristematic tissue

The following table highlights how the structure of the meristematic tissue is suited to its function.

Structural adaptationFunction
Cells are small, spherical or polygonal in shape.This allows for close packing of a large number of cells.
Vacuoles are very small or completely absent.Vacuoles provide rigidity to cells thus preventing rapid division.
Large amount of cytoplasm and a large nucleus.The lack of organelles is a feature of an undifferentiated cell. Large amount of nuclear material contains the DNA necessary for division and differentiation.

Table 4.1: Structural adaption and function of meristematic tissue

Meristematic tissue is found in root tips as this is where roots are growing and where dividing cells are produced. Figure 4.5 shows a micrograph image of a root tip.

Figure 4.5: Image shows meristematic tissue in a root tip as observed under an electron microscope.

Permanent tissues (ESG67)

The meristematic tissues give rise to cells that perform a specific function. Once cells develop to perform this particular function, they lose their ability to divide. The process of developing a particular structure suited to a specific function is known as cellular differentiation. We will examine two types of permanent tissue:

Simple permanent tissues

Complex permanent tissues

  • xylem vessels (made up of tracheids and vessels)
  • phloem vessels (made up of sieve tubes and companion cells)

Epidermis tissue (ESG68)

The epidermis is a single layer of cells that covers plants' leaves, flowers, roots and stems. It is the outermost cell layer of the plant body and plays a protective role in the plant. The function of key structural features are listed in table:epidermaltissue.

StructureFunction
Layer of cells covering surface of entire plant.Acts as a barrier to fungi and other microorganisms and pathogens.
Layer is thin and transparent.Allow for light to pass through, thereby allowing for photosynthesis in the tissues below.
Epidermal tissues have abundant trichomes which are tiny hairs projecting from surface of epidermis. Trichomes are abundant in some plant leaves.Leaf trichomes trap water in the area above the stomata and prevent water loss.
Root hairs are elongations of epidermal cells in the root.Root hairs maximise the surface area over which absorption of water from the soil can occur.
Epidermal tissues in leaves are covered with a waxy cuticle.The waxy outer layer on the epidermis prevents water loss from leaves.
Epidermal tissues contain guard cells containing chloroplasts.Guard cells control the opening and closing of the pores known as stomata thus controlling water loss in plants.
Some plant epidermal cells can secrete poisonous or bad-tasting substances.The bitter taste of the substances deter browsing and grazing by animals.

Figure 4.6: Scanning electron microscope image of Nicotiana alata (tobacco plant) upper leaf surface, showing trichomes (also known as `hairs') and a few stomata.

The chemicals in trichomes make plants less easily digested by hungry animals and can also slow down the growth of fungus on the plant. As such they act as a form of protection for the plant against predation.

Guard cells and Stomata (ESG69)

A stoma is a pore found in the leaf and stem epidermis that allows for gaseous exchange. The stoma is bordered on either side by a pair of specialised cells known as guard cells. Guard cells are bean shaped specialised epidermal cells, found mainly on the lower surface of leaves, which are responsible for regulating the size of the stoma opening. Together, the stoma and the guard cells are referred to as stomata.

The stomata in the epidermis allow oxygen, carbon dioxide and water vapour to enter and leave the leaf. The guard cells also contain chloroplasts for photosynthesis. Opening and closing of the guard cells is determined by the turgor pressure of the two guard cells. The turgor pressure is controlled by movements of large quantities of ions and sugar into the guard cells. When guard cells take up these solutes, the water potential decreases causing water to flow into the guard cells via osmosis. This leads to an increase in the swelling of the guard cells and the stomatal pores open.

Figure 4.7: Stomata in a tomato leaf as seen under a scanning electron microscope.

Figure 4.8: The above is a microscopic image of an Arabidopsis thaliana (commonly known as `Thale cress' or `mouse ear') stoma showing two guard cells exhibiting green fluorescence, with chloroplasts staining red.


Tissue Preparation

The most common mode of routine tissue preparation involves fixation with buffered formaldehyde, embedding in paraffin, sectioning into slices about 5 micrometers in thickness, and staining with hematoxylin and eosin.

Modern cell biology uses many tools to reveal cell structures and functions that are not apparent on routine H&E slides. Many of these involve sophisticated reagents based on the specificity of enzymes, immunological antibodies, or gene sequences to label and localize specific proteins or other molecules. Some textbooks present additional detail.

FIXATION

Fresh tissue samples must be preserved for future examination. This process is called fixation, and the resulting specimen is described as fixed.

Boiling an egg and pickling a cucumber represent examples of fixation, in which heat or chemistry stabilizes the organic materials.

A variety of chemicals can be used for fixing histological specimens. Routine fixation often uses a solution of formaldelhyde (formalin) to react with proteins and other organic molecules to stabilize cell structures. This solution is buffered and osmotically balanced to minimize shrinkage, swelling, and other collateral damage.

Ideally, fixation should be accomplished extremely quickly to minimize post-mortem changes in cell structure. Since fixation rate is limited by diffusion, ideal tissue preservation requires that fixative be delivered as closely as possible to each cell. Rapid delivery of fixative can be accomplished either by perfusion or by immersion.

Perfusion involves the delivery of fixative through the circulatory system of living tissue, by direct injection into a major artery. Such a procedure is commonly used with experimental animals but is obviously impractical for obtaining clinical specimens from patients.

Successful fixation by immersion requires very small samples. However, surgical removal of very small tissue samples often entails incidental mechanical damage, especially with punch biopsies.

These constraints on ideal fixation mean that tissue quality may vary across a specimen, with possible distortion near edges (especially with needle or punch biopsies) and with variation in fixation quality (and attendant staining character) in deeper areas (into which fixative diffuses more slowly).

An alternative to chemical fixation is freezing, followed by direct sectioning of the frozen specimen.

Frozen sections are seldom as "pretty" as well-fixed specimens, but they do have certain advantages. Because frozen sections do not require hours for the normal schedule of fixation and embedding, they can provide immediate diagnostic information to a surgeon in the operating room. Frozen sections can also permit analysis of small diffusable molecules or of enzyme activity whose presence would be lost during chemical fixation.

EMBEDDING and SECTIONING

After fixation, tissue specimens are routinely embedded in a solid material which will support very thin sectioning.

To embed a tissue sample, tissue water is replaced first by solvents (such as alcohol and xylene) and then with a liquid such as melted wax (paraffin) or epoxy solution which can be subsequently solidified by cooling or polymerization.

Sectioning is the production of very thin slices from a tissue sample. The tool used for sectioning is called a microtome (tom = to cut, as in appendectomy). A microtome may be as simple as razor blade, or it may be a complex machine costing several tens of thousands of dollars (for producing the ultrathin sections needed for electron microscopy).

Sections for routine light microscopy are typically 5-10µm (micrometers, microns) in thickness. Exceptionally thin sections may less than 2µm thick. For electron microscopy, sections are typically 50-100 nanometers (millimicrons) in thickness.

Sectioning necessarily reduces the specimen to a two-dimensional representation. Reconstructing the three-dimensional structure of the original sample requires either the "stacking" of multiple images from serial sections, or else judicious use of imagination (3-D visualization). A very small amount of three-dimensional information may be directly visualized under the microscope, by focussing up and down through the thickness of the specimen.

For a further account of 3-D visualization, see here.

Sectioning can certain introduce artifacts.

Among the commonest artifacts, and most distracting for a beginner, are wrinkles. To appreciate why wrinkles form, imagine trying to lay a sheet of wet tissue paper (representing the slice from the sample) flat onto a table (representing the microscope slide). Even with great care, wrinkles sometimes appear. Sometimes wrinkles are "forced" when the tissue section stretches unevenly around structures of differing consistencies.

Another sectioning-related artifact is the disappearance of small structures which fall out of their proper place on the specimen, and the occasional reappearance of such structures at other inappropriate locations. This happens most often when the process of slicing separates a part which is attached only outside the plane of section, such as a hair shaft within a hair follicle. Except in the case of perfect lengthwise slices, the hair shaft will be cut into an oval slice that is not attached to the sides of the hair follicle and may therefore come out (leaving the follicle apparently empty) and then alight somewhere else (as an odd oval structure anywhere on the slide).

Yet other common artifacts are scratches and "chatter". Scratches are caused by flaws or dirt on the cutting edge, and appear as straight slashes or ragged tears across the specimen. "Chatter" is the visible record of knife vibration. The the process of slicing sometimes induces vibrations in the knife edge, which then cause variations in thickness (ripples) in the section. These appear as narrow parallel bands, usually evenly spaced, across a tissue specimen. They are often most evident in areas of smooth texture, such as the colloid in thyroid follicles.

STAINING

Most cells are essentially transparent, with little or no intrinsic pigment. Even red blood cells, packed with hemoglobin, appear nearly colorless when unstained, unless packed into thick masses. Stains are used to confer contrast, to make tissue components visibly conspicuous. Certain special stains, which bind selectively to particular components, may also be used to identify those structures. But the essential function for staining is simply to make structures easier to see.

NOTE that all stain color is artifactual and does not represent the natural color of the tissue. The same structures may have very different colors with different stains. For example, collagen is pink with H&E but blue or green with trichrome. You should generally use specific aspects of actual structure (location, size, shape, texture) to identify cells and tissues, rather than color. Color can offer additional information if used wisely, but is unreliable by itself.

Routine histology uses the stain combination of hematoxylin and eosin, commonly referred to as H&E.

  • Note that, basophilic cell structures are NOT necessarily acidic they only happen to stain with basic stains. Likewise for acidophilic structures, which are NOT necessarily basic. Many tissue staining properties are determined by the complex chemistry of proteins and other macromolecules after interactions with fixatives and other processing agents, and defy simple analysis.
  • Also note that absolute color intensity on H&E-stained slides can be quite variable, with the same cell structure appearing red on one slide, pink on another, and possibly even blue on yet another. Relative stain intensity on the same slide is a more reliable indicator of acidophilic/basophilic quality than is absolute color, but this can also vary, especially between edges and center of a section.

Some cell structures do not stain well with aqueous dyes and so routinely appear clear. This is especially so for those which are hydrophobic, containing fat. Included in this category are adipocytes, myelin around axons, and cell membranes of the Golgi apparatus.

Trichrome uses three dyes (hence the name), including one that is specific for the extracellular protein collagen. Depending on the particular stain combination, a trichrome stain may color collagen fibers sky-blue or bright green. The principle use for trichrome is to differentiate collagen from other eosinophilic structures, such as muscle fibers.

Trichrome stains can be especially useful for highlighting an accumulation of scar tissue, as in glomerulosclerosis of the kidney (see WebPath) or cirrhosis of the liver.

Other stains. Be aware that many other stain techniques exist, for special cases. Some of these are classical procedures can yield beautiful results but depend on mysterious art and alchemy for success. Other, more-modern techniques have been rationally designed to exploit recent developments in molecular biology.

In the "classic" category are a number of stains based on metal salts.

A silver-based stain that demonstrates reticular fibers and basement membranes is especially useful for diagnosing certain pathologies of kidney glomeruli.

A variety of silver stains have been very powerful for research into the central nervous tissue. Their only common feature is that silver grains form a dark precipitate on selected structures, with empirical variables determining which structures are visualized.

Some cells have traditional names based on their demonstration with certain stains, such as the "argentaffin cells" (cells with an affinity for silver) and "chromaffin cells" (cells with an affinity for chromium) of the gastrointestinal tract.

In the "modern" category are stains based on the application of particular molecules that can be selectively stained using radioactive labels, enzyme reactions or specific antigen binding. The techniques of autoradiography, enzyme histochemistry and immunocytochemistry often require sections of frozen rather than fixed tissue.


Observing parenchyma cells.

To observe the structure of fresh parenchyma cells.

Materials

petri dishes or watch glasses

microscopes, microscope slides and cover slips

Instructions

  1. Use the dissecting needle to lift off a small piece of the soft banana tissue.
  2. Put the sample onto a petri dish or watch glass and mash it slightly using the dissecting needle (and a pencil if you want).
  3. Lift a small sample of the tissue onto a microscope slide on which you already have placed a drop of iodine solution. Put the cover slip on.
  4. Observe the cells under low power and find a section where the cells are lying separate, not all over each other.
  5. Enlarge this section and focus carefully to see if you can find nuclei in some of the cells (they will be bigger than the purple plastids and transparent).
  6. Draw 2 or 3 cells and label.

Questions

  1. Describe the shape of the cells and their wall thickness.
  2. What are the plastids called which appear purple and what is their function?

Activity: Practical investigation to observe the structure of fresh parenchyma cells

Learners to use microscope and slide preparation skills.

NOTES TO TEACHERS

The cells will be large and have very thin walls. Many cells have leucoplasts storing starch.

Encourage learners to use the diaphragm on the microscope to prevent their cells being over-exposed to light – this can make the cells difficult to see.

  1. Describe the shape of the cells and their wall thickness.
  2. What are the plastids called which appear purple and what is their function?

Cells are rounded or oval and have very thin walls.

The plastids are leukoplasts and they store starch.

Collenchyma tissue (ESG6C)

Collenchyma is a simple, permanent tissue typically found in the shoots and leaves of plants. Collenchyma cells are thin-walled but the corners of the cell wall are thickened with cellulose. This tissue gives strength, particularly in growing shoots and leaves due to the thickened corners. The cells are tightly packed and have fewer inter-cellular spaces.

Figure 4.11: Collenchyma cells are thin walled with thickened corners.

Figure 4.12: Light microscope image of collenchyma cells.

Collenchyma
StructureFunction
Cells are spherical, oval or polygonal in shape with no intercellular spaces.This allows for close packing to provide structural support.
Corners of cell wall are thickened, with cellulose and pectin deposits.Provides mechanical strength.
Cells are thin-walled on most sides.Provides flexibility, allowing plant to bend in the wind.

Collenchyma tissues make up the strong strands observed in stalks of celery.

The growth of collenchyma tissue is affected by mechanical stress on a plant. For instance if the plant is constantly shaken by the wind the walls of collenchyma may be ( ext<40>)–( ext<100>\%) thicker than those that are not shaken.

Learn more about permanent simple tissues.

Sclerenchyma tissue (ESG6D)

Sclerenchyma is a simple, permanent tissue. It is the supporting tissue in plants, making the plants hard and stiff. Two types of sclerenchyma cells exist: fibres and sclereids.

Sclerenchyma fibres are long and narrow and have thick lignified cell walls. They provide mechanical strength to the plant and allow for the conduction of water.

Sclereids are specialised sclerenchyma cells with thickened, highly lignified walls with pits running through the walls. They support the soft tissues of pears and guavas and are found in the shells of some nuts.

Figure 4.13: Sclerenchyma tissue provides support in plants.

Figure 4.14: Cross-section of sclerenchyma fibres.

Sclerenchyma tissues are important components in fabrics such as flax, jute and hemp. Fibres are important components of ropes and mattresses because of their ability to withstand high loads. Fibres found in jute are useful in processing textiles, given that their principal cell wall component is cellulose. Other important sources of fibres are grasses, sisal and agaves. Sclereid tissues are the important components of fruits such as cherries, plums or pears.

A useful way to remember the difference between collenchyma and sclerenchyma is to remember the 3 Cs pertaining to collenchyma: thickened at corners, contain cellulose, and named collenchyma.


Artificial cartilage under tension as strong as natural material

Biomedical engineers at the University of California, Davis, have created a lab-grown tissue similar to natural cartilage by giving it a bit of a stretch. The tissue, grown under tension but without a supporting scaffold, shows similar mechanical and biochemical properties to natural cartilage. The results are published June 12 in the journal Nature Materials.

Articular cartilage provides a smooth surface for our joints to move, but it can be damaged by trauma, disease or overuse. Once damaged, it does not regrow and is difficult to replace. Artificial cartilage that could be implanted into damaged joints would have great potential to help people regain mobility.

Natural cartilage is formed by cells called chondrocytes that stick together and produce a matrix of proteins and other molecules that solidifies into cartilage. Bioengineers have tried to create cartilage, and other materials, in the lab by growing cells on artificial scaffolds. More recently, they have turned to "scaffold-free" systems that better represent natural conditions.

The UC Davis team, led by Professor Kyriacos Athanasiou, Department of Biomedical Engineering, grew human chondrocytes in a scaffold-free system, allowing the cells to self-assemble and stick together inside a specially designed device. Once the cells had assembled, they were put under tension -- mildly stretched -- over several days. They showed similar results using bovine cells as well.

"As they were stretched, they became stiffer," said Jerry Hu, a research engineer and co-author on the study. "We think of cartilage as being strong in compression, but putting it under tension has dramatic effects."

The new material had a similar composition and mechanical properties to natural cartilage, they found. It contains a mix of glycoproteins and collagen, with crosslinks between collagen strands giving strength to the material.

Experiments with mice show that the lab-grown material can survive in a physiological environment. The next step, Hu said, is to put the lab-grown cartilage into a load-bearing joint, to see if it remains durable under stress.

"In this comprehensive study, we showed that we can finally engineer tissue that has the tensile and compressive characteristics of native tissue," Athanasiou said. "The artificial cartilage that we engineer is fully biological with a structure akin to real cartilage. Most importantly, we believe that we have solved the complex problem of making tissues in the laboratory that are strong and stiff enough to take the extremely high loads encountered in joints such as the knee and hip."


Prokaryotes

Prokaryotes are organisms made up of cells that lack a cell nucleus or any membrane-encased organelles. This means the genetic material DNA in prokaryotes is not bound within a nucleus. In addition, the DNA is less structured in prokaryotes than in eukaryotes: in prokaryotes, DNA is a single loop while in Eukaryotes DNA is organized into chromosomes. Most prokaryotes are made up of just a single cell (unicellular) but there are a few that are made of collections of cells (multicellular).

Scientists have divided the prokaryotes into two groups, the Bacteria, and the Archaea. Some bacteria, including E Coli, Salmonella, and Listeria, are found in foods and can cause disease   others are actually helpful to human digestion and other functions.   Archaea were discovered to be a unique life form which is capable of living indefinitely in extreme environments such as hydrothermal vents or arctic ice.

A typical prokaryotic cell might contain the following parts:

    : the membrane surrounding and protecting the cell : all of the material inside a cell except the nucleus
  • Flagella and pili: protein-based filaments found on the outside of some prokaryotic cells
  • Nucleoid: a nucleus-like region of the cell where genetic material is kept
  • Plasmid: a small molecule of DNA that can reproduce independently

Early Observations

The invention of the microscope allowed the first view of cells. English physicist and microscopist Robert Hooke (1635�) first described cells in 1665. He made thin slices of cork and likened the boxy partitions he observed to the cells (small rooms) in a monastery. The open spaces Hooke observed were empty, but he and others suggested these spaces might be used for fluid transport in living plants. He did not propose, and gave no indication that he believed, that these structures represented the basic unit of living organisms.

Marcello Malpighi (1628�), and Hooke's colleague, Nehemiah Grew (1641�), made detailed studies of plant cells and established the presence of cellular structures throughout the plant body. Grew likened the cellular spaces to the gas bubbles in rising bread and suggested they may have formed through a similar process. The presence of cells in animal tissue was demonstrated later than in plants because the thin sections needed for viewing under the microscope are more difficult to prepare for animal tissues. The prevalent view of Hooke's contemporaries was that animals were composed of several types of fibers, the various properties of which accounted for the differences among tissues.

At the time, virtually all biologists were convinced that organisms were composed of some type of fundamental unit, and it was these Ȫtomistic" preconceptions that drove them to look for such units. While improvements in microscopy made their observations better, it was the underlying belief that there was some fundamental substructure that made the microscope the instrument of choice in the study of life.

In 1676 the Dutch microscopist Antony van Leeuwenhoek (1632�) published his observations of single-cell organisms, or "little animalcules" as he called them. It is likely that Leeuwenhoek was the first person to observe a red blood cell and a sperm cell. Leeuwenhoek made numerous and detailed observations on his microorganisms, but more than one hundred years passed before a connection was made between the obviously cellular structure of these creatures and the existence of cells in animals or plants.


Cartilage

Cartilage is a type of supporting connective tissue. Cartilage is a dense connective tissue, consisting of the chondrocyte cells. Cartilage connective tissue includes hyaline cartilage, fibrocartilage and elastic cartilage. The fibers in the cartilage connective tissue include collagen and elastic fibers. Cartilage connective tissue has limited ground substance and can range from semisolid to a flexible matrix.

Bone is another type of supporting connective tissue. Bone, also referred to as osseous tissue, can either be compact (dense) or spongy (cancellous), and contains the osteoblasts or osteocytes cells. Bone connective tissue is made up of collagen fibers and has rigid, calcified ground substance.


The truth about lab-grown meat

An open field where plump, well-fed livestock waddle their way through the grass under the eye of honest, local farmers — that’s how people like to envision where their meat comes from.

The reality, however, is that most of the beef consumed in the U.S. comes by way of an industrialized system that confines cows to small pens in vast feedlots, where they are fattened with hormone-laced grains before being shipped away for slaughter in what are essentially meat factories.

The industrial system makes meat products more affordable, but not particularly humane — and that’s beside the environmental costs and health concerns about meat-centric diets. Agriculture contributes to about 14 percent of global greenhouse gas emissions, destroys natural habitats and pollutes water worldwide.

Yet people are reluctant to give up their steaks and chickens. According to the U.S. Department of Agriculture, beef and poultry consumption hit record highs in 2018, with the average American eating over 200 pounds of meat. But soon, meat lovers will have a new option for satisfying their cravings — one that involves neither open fields nor industrial slaughterhouses: laboratory-produced meat.

Until recently, the idea of lab-grown meat was constrained to a distant, futuristic realm, but by the end of 2018, the U.S. Department of Agriculture and the Food and Drug Administration announced a joint agreement to oversee the production of cell-cultured meat. And if manufacturers succeed in driving down current sky-high production costs, you may soon see lab-grown meat not just in fancy restaurants, but on grocery store shelves, too.

Advocates tout lab-grown meat (they prefer to call it “clean meat,” for marketing reasons) as a much more sustainable alternative to the current industrial system. Still, consumers remain skeptical. In a 2017 study published in Public Library of Science, nearly two-thirds of people surveyed were willing to try clean meat, but only one in three was willing to eat it regularly as a replacement for conventional meat. Some were skeptical of the taste and appeal of lab-grown meat while others cited safety or health concerns.

The survey also found many people had little or no understanding of what clean meat actually is. To clear up some of those misconceptions, here are some basics about lab-grown meat.

How is clean meat made?

The idea of growing cells outside of a living body has been around since the 19th century and used in everything from tissue preservation and vaccine production to chemical safety testing and much more. But it wasn’t until 2013 that the first lab-grown burger was unveiled to the world by Mark Post, a vascular physiology professor at Maastricht University in the Netherlands.

Start-ups have since raced to perfect the technology. Companies including JUST, Memphis Meat, and Mosa Meat each use a slightly different technique but the basic concept is the same: begin with a stem cell from a live animal.

“All meat starts with cells,” explains Parendi Birdie, a research associate and member of the cell development team at JUST. “And for these cells to grow, they require nurture in order to naturally grow as they would in a cow, chicken or pig.”

Developers feed the extracted cell salts, sugars and amino acids so it can grow and multiply via hundreds of cell divisions. The cells created can be of different lineages — muscle cells, fat cells or tissues — allowing producers to create different types of meat such as steak or chopped burger.

So is it really meat?

Well, sort of. Clean meat is made from stem cells extracted from real, live animals. There are all sorts of ways to extract them, including a conventional surgical biopsy. They can even be extracted from the feather of a bird, according to Isaac Emery, a senior environmental scientist at The Good Food Institute, a non-profit organization that helps companies develop clean meat products.

However, not everyone agrees that the product should be labeled as meat. Food safety expert Catherine Hutt, a former assistant administrator for the U.S. Department of Agriculture’s Food Safety and Inspection Service, advocates a cautious approach with clear labelling. “It’s about transparency for the consumer,” she says, “in order to make sure that the consumer knows [whether] they’re choosing this cell-based meat-like product, or an actual meat product.”

But Birdie argues that all that matters is the taste, and that, in her experience, clean meat tastes just like the real thing. At tastings with potential investors and consumers, she says, “when they actually eat it, it tastes exactly like meat.”

Is it better for the environment?

That’s a definite yes. A 2011 study found that clean meat produces 78 to 96 percent lower greenhouse gas emissions, uses 99 percent less land and between 82 and 92 percent less water. Research at the Good Food Institute has concluded that a cell culture the size of one chicken egg can produce a million times more meat than a chicken barn stacked with 20,000 chickens, according to Emery. Energy costs, too, are much lower — and no animal parts are wasted, he adds.

“We won’t be growing the bones and the skin and the intestines that take up resources,” Emery says. “We’ll be vastly more efficient in the land we use.”

How much will it cost?

Experts say cost is the main obstacle standing between consumers and clean meat products.

In 2013, the first clean burger cost $325,000. While the price has decreased dramatically since then, current estimates range from $363 to $2,400 per pound, making it much more expensive than regular meat. (A pound of conventionally produced lean ground beef costs less than $6. Organically raised beef typically costs about a dollar more.)

JUST’s Birdie says the company is pushing hard to drive down production costs. “How do we make these products in order to compete with the price of a Big Mac?” she asks.

The biggest expense, she says, is protein used to feed the cells as they grow. In an effort to improve cost efficiency, JUST has developed a robotic platform capable of screening thousands of proteins to find the best at spurring growth, she says.

How soon can I try some?

Depending on where you live and your willingness to pay a very expensive restaurant tab, you may be able to try some clean meat in 2019. While JUST promises a product in the coming months, it’s a ‘limited-edition release,’ and likely available only at select restaurants.

Through his work with various producers, Emery says he expects that clean meat will be in the supermarket within two to five years, and could be as inexpensive as conventional meat in a decade.

Former USDA official Hutt, however, is less optimistic. She argues that the process behind food regulation takes a long time, and expects the debate behind labeling clean meat to drag on.

“The federal regulatory system moves slowly, deliberately,” she says. “It’s a process that takes time… the federal government is doing what it needs to do to protect the consumer.”

Emery is confident that once clean meat is available in stores, consumers will be blind to the difference. “People are driven by the same factors when we buy food, and that’s price, taste and convenience,” he says. “Once clean meat is being produced, and it’s in the restaurants and grocery stores we usually go to, there will be a lot less concern about what it’s called and where it came from.”


Difference Between Collagen and Hyaluronic Acid

Definition

Collagen: Collagen is the main protein in human connective tissue.

Hyaluronic acid: Hyaluronic acid is a linear insoluble polymer – mucopolysaccharide.

Origin of the name

Collagen: The name of collagen originates from the Greek word “kola”, which means glue, and the suffix “-gen”, which denotes for production.

Hyaluronic acid: The name is derived from the Greek word “hyalos”, meaning glass.

Occurrence in nature

Collagen: In nature, collagen is found mainly in mammals, exclusively in animals.

Hyaluronic acid: Hyaluronic acid is synthesized by all living organisms except algae.

Occurrence in the human body

Collagen: Collagen represents 30% of the human protein. Its concentration varies in different parts of the human body and is 23% in the cranial bones, 50% in the cartilage, up to 75% in the skin, etc.

Hyaluronic acid: A 70 kg person has approximately 15 g of hyaluronic acid in the body. More than 50% of it is contained in the skin.

Chemical structure

Collagen: Collagen is made up of long spiral peptide chains. Each chain contains between 19 and 105 amino acids.

Hyaluronic acid: Hyaluronic acid is a long, linear, insoluble biopolymer, made up of recurrent disaccharide units of D-glucuronic acid and N-acetyl-glucosamine, linked by glycosidic bonds.

Molecular mass

Collagen: 300 000– 400 000 Da

Hyaluronic acid: 5 000 to 20 000 000 Da

Synthesis in the human body

Collagen: Collagen is constantly produced in the body, after the age of 30 this process progressively weakens over the years.

Hyaluronic acid: In the human body, hyaluronic acid is synthesized by proteins located in the plasma membrane of fibroblast cells.

Function

Collagen: The collagen is responsible for the tightness, firmness, proper humidity, elasticity, and constant renewal of skin cells. It is a major component of the cartilage and joints, teeth and bones, vital for muscle function and blood vessels structure.

Hyaluronic acid: The hyaluronic acid is responsible for the smoothness of the skin and is associated with skin repair. It is the main building block of the vitreous of the human eye, an important structural component of articular cartilage, and a major part of the synovial fluid.

Collagen: The use of collagen includes bone grafts, tissue regeneration, burn surgery, cosmetic surgery, wound care, reconstructive surgical uses, slowing down the aging of the skin, strengthening nails and hair, etc.

Hyaluronic acid: Hyaluronic acid of different concentration and under different trade names is used in ophthalmic surgery, neurosurgery, orthopedics and traumatology, skin care, etc.


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