PRELIM: EPITHELIAL TISSUE Flashcards
is a tissue in which cells are bound
tightly together structurally and functionally to form a sheetlike or tubular structure with little extracellular material between the cells.
EPITHELIUM
facing the sheet’s free surface
APICAL SIDE
facing a basement membrane and
underlying connective tissue
BASAL SIDE
pinocytosis of material at the
apical side
TRANSCYTOSIS
at the basolateral side
EXOCYTOSIS
a thin extracellular layer of specialized proteins, usually having two parts: a basal lamina and a more fibrous reticular lamina
BASEMENT MEMBRANE
2 parts of Basement membrane:
BASAL LAMINA
RETICULAR LAMINA
is a thin meshwork of type IV collagen and laminin produced by the epithelial cells
BASAL LAMINA
contains type III collagen and anchoring of VIII collagen, all secreted by cells of the immediately adjacent connective tissue
RETICULAR LAMINA
FUNCTIONS OF BASEMEMENT MEMBRANE:
attach epithelia to connective tissue
regulate (filter) substances passing from connective tissue into epithelia
provide a guide or scaffold during tissue regeneration after injury
compartmentalize epithelial cells from other tissues
INTERCELLULAR JUNCTIONS
3 MAJOR TYPES
TIGHT OR OCCLUDING JUNCTIONS
ADHERENT OR ANCHORING JUNCTIONS
GAP OR COMMUNICATING JUNCTIONS
TIGHT OR OCCLUDING JUNCTIONS
Claudin and occludin surround the apical ends of the cells and prevent paracellular passage of substances (between the cells.)
ADHERENT OR ANCHORING JUNCTIONS
- formed by interacting proteins of the cadherin family
- points of strong attachment holding together cells of the epithelium
encircle epithelial cells just below their tight junctions or scattered
Zonula adherens
desmos (binding) soma (body) disc shaped structures
Desmosomes
composed of transmembrane integrins attach cells to proteins of the basal lamina
Hemidesmosomes
- Mediate intercellular communication rather than adhesion or occlusion between cells
- Connexins form hexameric complexes called connexons
GAP OR COMMUNICATING JUNCTIONS
APICAL STRUCTURES OF EPITHELIAL CELLS
- Brush or striated border
- increase epithelial cells’ apical surface area for absorption
MICROVILLI
APICAL STRUCTURES OF EPITHELIAL CELLS
- Important components of inner ear
sensory cells - for absorption in tissues of male
reproductive tract
STEREOCILIA
- larger projecting structures with a
well-organized core of microtubules - primary cilium: not motile but enriched with receptors and signal transduction complexes for detection of light, odors, motion, and flow of liquid past the cells
CILIA
assembly of microtubules; axon: axis, nema: thread
AXONEME
TYPES OF EPITHELIA
2 main groups:
Covering – lining epithelia
Secretory – glandular epithelia
Cells of covering epithelia are organized into one or more layers that cover the surface or line the cavities of an organ
COVERING OR LINING EPITHELIA
one cell layer
SIMPLE EPITHELIA
two or more layers
STRATIFIED EPITHELIA
two or more layers
STRATIFIED EPITHELIA
TYPE OF SIMPLE EPITHELIA
thin cells
Squamous
TYPE OF SIMPLE EPITHELIA
cell width and thickness roughly similar
Cuboidal
TYPE OF SIMPLE EPITHELIA
cells taller than they are wide
Columnar
MORPHOLOGICAL TYPES OF EPITHELIA
elongated nuclei
COLUMNAR CELLS
MORPHOLOGICAL TYPES OF EPITHELIA
flattened nuclei
SQUAMOUS CELLS
MORPHOLOGICAL TYPES OF EPITHELIA
spherical nuclei
CUBOIDAL OR PYRAMIDAL
Classified according to the cell shape of the superficial outer layer(s)
STRATIFIED EPITHELIA
packed with keratin filaments
KERATINIZED
with relatively sparse keratin
NONKERATINIZED
found mainly in the epidermis skin, where it helps prevent dehydration from the tissue
STRATFIED SQUAMOUS KERATINIZED EPITHELIUM
accumulate keratin
KERATINIZATION
lines moist internal cavities (ex. Mouth, esophagus, and vagina) where water is not a problem
STRATIFIED SQUAMOUS NONKERATINIZED EPITHELIUM
occurs in the excretory ducts of salivary and sweat glands
STRATIFIED CUBOIDAL EPITHELIUM
is seen in the conjunctiva lining the eyelids, where it is both protective and mucus secreting
STRATIFIED COLUMNAR EPITHELIUM
lines much of the urinary tract, extending from the kidneys to the proximal part of the urethra.
TRANSITIONAL EPITHELIUM or UROTHELIUM
– superficial layer of large, dome-like cells
- These cells protects underlying tissues from the hypertonic and potentially cytotoxic effects of urine
UMBRELLA CELLS
tall, irregular cells all are attached to the basement membrane but their nuclei are at different levels and not all cells extend to the free surface, giving a stratified appearance
Ex. Lining the upper respiratory tract where the cells are also heavily ciliated
PSEUDOSTRATIFIED COLUMNAR EPITHELIUM
