22. Question - Compare and contrast the structure of epithelia and connective tissues. What is the composition of connective tissue matrix? What is the function of ground substances? Diagram the structure of proteoglycans.
Epithelia and connective tissues both consist of cells and extracellular matrix and there are nerve endings in both but there the similarities end. Epithelial cells are closely attached to each other but except for adipose tissue connective tissue cells are separated from each other by extracellular matrix.
Connective tissue matrix consists of fibers (collagen, elastic and reticular), ground substance and interstitial fluid.
The ground substance consists of proteoglycans and glycoproteins which are very viscous and bind the interstitial fluid preventing flow by convection and thus rapid spread of infectious agents. Organisms that produce hyaluronidase can break down the ground substance allowing convection to occur. This can be explained from the chemical structure of ground substance.
Proteoglycan consists of a core protein and numerous unbranched glycosaminoglycans. Numerous proteoglycans are attached to hyaluronic acid to constitute the ground substance
23. Question - Diagram the molecular events (intra- and extracellular) in the formation of collagen.
The tripeptide is synthesized in RER, moved to Golgi via transfer vesicles, processed and packaged in Golgi. Procollagen in secretion granules is released by exocytosis. Intercellular procollagen peptidase converts procollagen to tropocollagen (also called collagen) which self assembles to form collagen fibrils.
24. Question - Identify the distribution of four types of collagen. Identify two components of elastic fibers.
Collagen Type I the major fibrillar component of most regular and irregular connective tissues.
Collagen Type II hyaline cartilage is the most common location
Collagen Type III reticular fibers consist of this type of collagen. They are found in the reticular lamina of the basement membrane, in lymphoid tissue (except thymus) and in bone marrow.
Collagen Type IV this is a non-fibrillar component of the basal lamina in the basement membrane. Synthesized by epithelial cells, muscle cells and Schwann cells all of which have a basal lamina.
Elastic fibers consist largely of an amorphous component, elastin, and a fine fibrillar component consisting of fibrillin.
25. Question - Describe the components and functional relationships of the fibers and cells in dense regular connective tissue; in irregular connective tissue.
Dense regular connective tissue consists of bundles of type I collagen packed closely together with very elongate fibrocytes wedged in between. There are few other cells and blood vessels are found in loose connective tissue channels surrounding large collagen bundles. This tissue is designed to resist tension in one direction.
Irregular connective tissues vary considerably in the size and packing of the collagen bundles. These bundles are separated from each other by ground substances allowing a variety of cells and blood vessels to be distributed throughout its matrix. In addition to fibrocytes and solitary fat cells any or all of the following cells may reside or be wandering through the matrix depending upon the location. Macrophages (histiocytes), mast cells, plasma cells and leukocytes. Depending upon the size and packing of the collagen bundles these connective tissues may allow freedom of movement between adjacent structures or they may hold structures rigidly in place resisting tearing as in the dermis.
26. Question - Diagram the cytology in relation to the function of macrophages (histiocytes).
Primary lysosomes contain acid hydrolases (activated by low pH). They fuse with the phagosome (heterophagic vacuole) to form the secondary lysosome. This activates vesicular proton ATPase and protons are pumped into the vesicle to promote digestion of the contents. In long lived cells organelles are removed by a similar process when they are sequestered (surrounded by membrane) in autophagic vacuoles.
27. Question - Diagram the cytology in relation to the function of mast cells. Diagram the cytology in relation to the function of plasma cells.
Mast cells have numerous cytoplasmic granules (basophilic in frozen sections but eosinophilic in H&E sections) which contain histamine and heparin that are released in allergies and injuries (regulated secretion). These substances are important in inflammatory reactions.
Plasma cells are oval with an eccentric nucleus and abundant RER. The Golgi region is evident but there are few secretion granules because they secrete immunoglobulins continuously (constitutively).
28. Question - Diagram and label the components of hyaline cartilage. How are elastic and fibrocartilage different?
Hyaline cartilage matrix consists of ground substance and type II collagen. The latter are fibers that are not evident in histological sections. Elastic cartilage has larger lacunae and evident elastic fibers in the matrix Fibrocartilage has fewer and smaller lacunae and the collagen fibers which can be seen are of Type I rather than Type II as in hyaline cartilage. An isogenous group consists of chondrocytes derived from a single precursor cell and have been kept in close proximity because of the stiff matrix surrounding them.
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Last Revised: Tue, Jan 23, 2007