A&P Notes: Test #2
Histology-> the study of tissues
Tissue-groups of similar cells with common embryological origin, which function together in a specialized way. 4 types:
1. Epithelial Tissues (or epithelium)-specialized either for covering/lining body surfaces and cavities, or it is the secretory of a gland. General features:
a.) Composed of closely packed cells with little or no extracellular matrix. The cells are tightly bound into continuous sheets or either single or multi-layered cells.
b.) It is innervated (has a nerve supply) but is avascular (no blood vessels). Epithelium is dependent on diffusion from blood vessels found in underlying connective tissue for its nourishment and waste removal.
c.) Epithelium has an exposed surface and a basal surface, which is attached to an underlying, non-living, adhesive basement membrane:
-Basal Lamina-“Glycoprotein” glue secreted by epithelial cells.
-Reticular Lamina-collagen fibers secreted by connective tissue.
d.) Epithelial cells are highly regenerative. Unlike most specialized cells, epithelial cells are capable of mitosis and continually divide to replace those damaged or lost.
Epithelium is classified by:
a.) Shape-squamous (flat), cuboidal, or columnar
b.) Layers-simple-1 cell think…adapted for absorption/filtration and not subjected to wear and tear
c.) Stratified-layered…generally protective and found exposed to hostile environments.
2.) Simple Epithelial:
-Simple Squamous-very thin and permeable, highly adapted to allow diffusion and filtration. Found in:
-Lung>gas exchange
-Kidneys>filtration membrane
Endothelium>lines heart, blood vessels, and lymph vessels
-Simple Cuboidal-adapted mainly for secretion and some absorption (Found in glands and kidneys).
-Simple Columnar-usually consists of 2 types of cells (1 absorptive, 1 secretive).
-Absorptive cells have microvilli which are folds serving to increase absorptive surface area
-Goblet cells are secretory (mucus) found amongst the other cells.
-In the respiratory tracts, uterus and some glands are columnar cells with cilia.
3.) Stratified epithelium-function=protection-layered
-Stratified Squamous-lines mouth, throat, anus, vagina, and covers body
4.) Glandular Epithelium-
-Gland> 1 too many epithelial cells which produce and secrete some product. 2 types:
-Exocrine-secretes into a duct (tube) which opens onto a surface (ex. Sweat, oil, saliva, digestive, goblets)
-Endocrine-no ducts (tubes), they secrete into extracellular fluids, their fluids, their secretions are hormones and diffuse into blood stream.
-Glands can be described as unicellular (in humans…goblet cell only) or multicellular
-Merocrine-secrete their products by exocytosis (which does not harm the cells), (ex. Sweat, or salivary glands)
-Apocrine-a part of the cell “pinches off with the enclosed secretory product, cell then repairs itself, mammary glands. (ex. Milk)
-Holocrine-product keeps accumulating until cell dies and ruptures…so the cells is part of the secretion. (ex. Oil glands).
II.) Connective Tissues:
-Functions: a.) Binding and support. b.) Protects and insulates. c.) Separates tissues. d.) Transports (blood).
-Characteristics:
a.) Have an extensive extracellular matrix which is non-living with widely separated cells scattered throughout the matrix. b.) Are highly vascular and enervated (except for cartilage). c.) Do not occur on free surfaces. d.) The non-living matrix contains fibers, the matrix is maintain by the scattered cells and it is the matrix which determines the tissues qualities
-Fibers: a.) Collagen Fibers-the strongest and most abundant… consists of bundles of the protein (collagen). These fibers are flexible but do not stretch. b.) Elastic fibers-thinner, branching fibers made of elastin (protein) it does stretch and recoil. c.) Reticular fibers-thin, branching collagen fibers from a net-like mesh. (threads).
-Cells: a.) “blast”-refers to immature cells actively secreting extracellular matrix. (Creating or fixing