Epithelium vocab Flashcards
Functions of epithelia
- protect underlying tissues
- provide selective barrier between a lumen and underlying tissue
- synthesize substances like hormones, saliva for secretion
- transport substances by endo- and exocytosis
Characteristics of epithelia
- composed of continuous sheets of cells
- have specialized cell junctions
- are polarized
- are avascular
squamous
long, flat, much wider than tall
cuboidal
roughly even width and height
columnar
taller than wide
simple
one layer of cells only
stratified
have more than one layer of cells- one contacting basement membrane, one on free surface, maybe some layers in between
pseudostratified
appear stratified but are not; all cells contact basement membrane but not all reach apical surface; nuclei found at two levels
goblet cells
unicellular exocrine glands that secrete mucus onto a free surface; found in simple or pseudostratified epithelia
endothelium
simple squamous epithelium that lines the heart and all blood and lymphatic vessels
mesothelium
simple squamous epithelium that lines pleural and peritoneal cavities
metaplasia
chronic irritation in epithelia is prolonged so normal epithelia replaced by stratified squamous epithelia- very resistant to stress; reversible change
functions of basement membrane
- separate and bind epithelium and connective tissues
- form a selective sieve-like barrier to regulate which molecules and cells cross interface between tissues
- establish polarity of epithelium
- guide repair
Lamina rara
clear layer that lies directly adjacent to basal surface of epithelia
lamina densa
darkly stained layer that lies immediately beneath lamina rara; together they form the basal lamina
lamina reticularis
secreted by cells in the adjacent connective tissue; third component of basement membrane
Alport syndrome
inherited disorder of Type IV collagen that affects kidney, eye, cochlea of ear; most common in males; gene mutation prevents proper production of type IV collagen network
lateral interdigitations
sites where the membranes of adjacent cells do not form a straight line to from the base to the apex- fit together like puzzle pieces
occluding junctions
seal cells together and form a barrier to regulate what crosses the epithelium; prevent passage of molecules via paracellular pathway
anchoring/ adhering junctions
hold epithelia together by attaching cells and their cytoskeletons to each other or to the extracellular matrix; incl adhesion belts and spot desmosomes
communicating/ gap junctions
allow cells to communicate with each other by chemical or electrical signals
tight junctions
only in epithelia; closest to apex; form barrier between epithelium’s free surface and connective tissue ex to prevent microbes from entering bloodstream; maintain the apical and lateral cell membranes by preventing diffusion of integral membrane proteins from one surface to the other
apical modifications
microvilli, sterocilia, cilia on an epithelial cell
basal lamina
lamina rara+ lamina densa
basement membrane
basal lamina+ lamina reticularis
paracellular pathway
the space between two epithelial cells through which solutes can pass
Steps in epithelial repair
a. Epithelial cells are depolarized
b. Cells become repolarized along lateral axis
c. Epithelial cells divide by mitosis
d. When cells from opposite sides of the wound meet, they make a new basement membrane, reestablish polarity, and restore the epithelium
adhesion belts
just below tight junction; hold epithelial cells in a continuous sheet by forming a complete ring around the apex of the cell
cadherins
transmembrane proteins in adhesion belts that connect to actin cytoskeleton; external portion of proteins have 5 domains interact in a calcium-dependent manner to bind with identidal proteins on adjacent cells cell. adhesion is disrupted if calcium concentration is low
terminal web
network of cytoskeletal proteins that extends across apical cytoplasm and provides an attachment point for the basal bodies of cilia and for the actin filaments in microvilli and stereocilia
spot desmosomes
type of anchoring junction; composed of dense protein plaques; keratin filaments extend away from plaques to link different spot desmosomes and to absorb and dissipate mechanical stress
gap junctions
communicating junctions formed between cytoplasm of two cells by a connexon of six intermembrane protein connexins; allow small molecules to pass through; can open and close
microvilli
extensions of cell membrane on apical surface; contain actin filaments
stereocilia
long like cilia; contain actin filaments like microvilli; function to increase surface area
cilia
extensions of apical membrane specialized for movement; contain microtubules
hemidesmosomes
anchoring junctions that anchor basal surfaces of epithelial cells to basal lamina with plaque of integrin proteins
basal infoldings
increase surface area on basal surface for ion transport; active transport so surrounded by many mitochondria
merocrine
exocrine glands that release product by exocytosis; can be constitutive or regulated
apocrine
exocrine glands that accumulate secretory products in apex then a portion of the apex pinches off and is released (ex mammary glands)
holocrine
exocrine glands that secrete the entire cell along with its content (sebaceous glands only)
