Histology Objectives Once you have completed this unit, you should be able to 1

Question

Histology Objectives Once you have completed this unit, you should be able to 1 Identify epithelial tissues by number of layers, cell shape, and specializations. 2 Identify and describe a variety of connective tissues. 3 Identify and describe muscle and nervous tissues 4 Relate tissue structure to tissue function and describe how organs are formed from two or more tissue types. 5 Give examples of organs where each tissue type is found. PRE-LAB EXERCISES Complete the following exercises prior to coming to lab, using your textbook and lab atla PRE-LAB EXERCISE 5-1 Key Terms Define the key terms with which you should be familiar before coming to lab. Definition Term Extracellular Matrix Ground substance hat for st Twisted rope ? "b collage. strtchy, elastic fbers mad Thin rehiculin Ceo lagen 1I1) Collagen fiber Elastic fiber eticular fiber pithelial Tissue An ar ranges imple epithelial tiseSs (abio tifiod enithelial tissue

Explanation / Answer

Ground substance is an amorphous gel-like substance in the extracellular space that contains all components of the extracellular matrix except for fibrous materials such as collagen and elastin.

Ground substance is active in the development, movement, and proliferation of tissues, as well as their metabolism. Additionally, cells use it for support, water storage, binding, and a medium for intercellular exchange (especially between blood cells and other types of cells). Ground substance provides lubrication for collagen fibers.

The components of the ground substance vary depending on the tissue. Ground substance is primarily composed of water, glycosaminoglycans (GAGs) most notably hyaluronan, proteoglycans which GAGs are bound to, and glycoproteins. Components of the ground substance are secreted by fibroblasts. Usually it is not visible on slides, because it is lost during staining in the preparation process.

Collagen has great tensile strength, and is the main component of fascia, cartilage, ligaments, tendons, bone and skin. Along with elastin and soft keratin, it is responsible for skin strength and elasticity, and its degradation leads to wrinkles that accompany aging.

Collagen is a type of protein fiber found abundantly throughout our body. It provides strength and cushioning to many different areas of the body, including the skin. More specifically, collagen is found in our various types of connective tissue such as cartilage, tendons, bones, and ligaments. Collagen is a protein made up of amino-acids, which are in turn built of carbon, oxygen and hydrogen. Collagen contains specific amino acids – Glycine, Proline, Hydroxyproline and Arginine. Collagen makes up approximately 30% of the proteins within the body.

Elastic fibers (or yellow fibers) are bundles of proteins (elastin) found in extracellular matrix of connective tissue and produced by fibroblasts and smooth muscle cells in arteries. These fibers can stretch up to 1.5 times their length, and snap back to their original length when relaxed.

Reticular fibers, reticular fibres or reticulin is a type of fiber in connective tissue composed of type III collagen secreted by reticular cells. Reticular fiberscrosslink to form a fine meshwork (reticulin).

The fibers form a soft skeleton (stroma) to support the lymphoid organs (lymph node stromal cells, red bone marrow, and spleen). Adipose tissue is held together by reticular fibers.

Reticular connective tissue is named for the reticular fibers which are the main structural part of the tissue. The cells that make the reticular fibers are fibroblasts called reticular cells. Reticular connective tissue forms a scaffolding for other cells in several organs, such as lymph nodes and bone marrow.

Simple epithelium consists of a single layer of cells. They are typically where absorption, secretion and filtration occur. The thinness of the epithelial barrier facilitates these processes.

Simple epithelial tissues are generally classified by the shape of their cells. The four major classes of simple epithelium are: 1) simple squamous; 2) simple cuboidal; 3) simple columnar; and 4) pseudostratified.

Stratified epithelium differs from simple epithelium by being multilayered. It is therefore found where body linings have to withstand mechanical or chemical insults.

Stratified epithelia are more durable and protection is one their major functions. Since stratified epithelium consists of two or more layers, the basal cells divide and push towards the apex, and in the process flatten the apical cells.

Stratified epithelia can be columnar, cuboidal, or squamous type. However, it can also have the following specializations:

Keratinized Epithelia

In keratinized epithelia, the most apical layers (exterior) of cells are dead and lose their nucleus and cytoplasm. They contain a tough, resistant protein called keratin. This specialization makes the epithelium waterproof, and it is abundant in mammalian skin. The lining of the esophagus is an example of a non-keratinized or moist stratified epithelium.

Transitional Epithelia

Transitional epithelia are found in tissues that stretch and it can appear to be stratified cuboidal when the tissue is not stretched, or stratified squamous when the organ is distended and the tissue stretches. It is sometimes called the urothelium since it is almost exclusively found in the bladder, ureters, and urethra.

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