Epithelial tissue Flashcards
what are the 4 types of tissue?
- epithelial
- connective
- muscle
- nervous
what are tight and adherent junctions?
At the apical end, tight junctions (zonulae occludens) and adherent junctions (zonulae adherens) are typically close together and each forms a continuous ribbon around the cell. Multiple ridges of the tight junction prevent passive flow of material between the cells but are not very strong; the adhering junctions immediately below them serve to stabilize and strengthen the circular occluding bands and help hold the cells together.
describe desmosomes and gap junctions
Both desmosomes and gap junctions are spot-like, not circular, structures between two cells. Bound to intermediate filaments inside the cells, desmosomes form very strong attachment points that supplement the zonulae adherens and play a major role to maintain the integrity of an epithelium. Gap junctions, each a patch of many connexons in the adjacent cell membranes, have little strength but serve as intercellular channels for flow of molecules.
what is the role of hemidesmososmes
bind epithelial cells to the underlying basal lamina.
what is the function fo microvilli?
Absorptive cells lining the small intestine demonstrate the highly uniform microvilli of a striated or brush border particularly well, with various actin-binding proteins important for F-actin assembly, capping, cross-linking, and movement. Like microfilaments in other regions of the cytoskeleton, those of microvilli are highly dynamic, with tread-milling and various myosin-based interactions. Myosin motors import various -microvilli components along the actin filaments
function of stereocilia
which increase the surface area available for absorption. Stereocilia are much longer than microvilli and often have distal branching
where can well developed cillia be seen?
- Epithelial cells lining the respiratory tract have many very well-developed cilia.
descirbe simple squamous epithelia
Simple epithelia are typically specialized as lining of vessels and -cavities, where they regulate passage of substances into the underlying tissue. The thin cells often exhibit transcytosis.
Ex. lining the thin renal loops of Henle, covering the outer wall of the intestine, and lining the inner surface of the cornea
describe simple cuboidal epithelium
thickness allows cytoplasm to be rich in mitochondria and other organelles for a high level of active transport across the epithelium and other functions.
Ex. from a renal collecting tubule, a large thyroid follicle, and the thick mesothelium covering an ovary
describe simple columnar epithelium
- always taller than they are wide, with apical cilia or microvilli, and are often specialized for absorption
Stratified squamous epithelia serve what function?
protective functions: protection against easy invasion of underlying tissue by microorganisms and protection against water loss. These functions are particularly important in the epidermis
what are keratinized vs nonkeratinized cells?
keratinized, filled with keratin and other substances, eventually lose their nuclei and organelles, and form superficial layers flattened squames that impede water loss. Keratinized cells are sloughed off and replaced by new cells from more basal layers
Nonkeratinized, epithelia occur in many organs, such as the esophageal lining or outer covering of the cornea. Here cells accumulate much less keratin and retain their nuclei but still provide protection against microorganisms
where do stratified cuboidal or columnar epithelial appear?
Stratified cuboidal or columnar epithelia are fairly rare but occur in excretory ducts of certain glands, such as sweat glands where the double layer of cells allows additional functions.
describe transitional epithelium
Cells of this epithelium are also able to adjust their relationships with one another and undergo a transition in their appearance as the urinary bladder fills and the wall is distended.
ex. urothelium, stratified and lines the urinary tract
describe pseudostratified epithelium
appear to be in several layers, but their basal ends all rest on the basement membrane.
