Epithelium Flashcards
Primary tissues
Group of similar cells that w/ extra cellular products are specialized to perform a common function
Types of primary tissues
Epithelium, CT, muscle, nervous tissue
Epithelia
. Closely associated cells w/ little ECM
. Cover and line almost all body and organ surfaces
. Avascular
What is epithelia derived from?
All primary germ layers (ectoderm, endoderm, and mesoderm
Basic epithelial functions
. Protection . Absorption . Secretion . excretion . Gas exchange . Gliding between inner body surfaces
Epithelial regions/domains
. Apical
. Basal
. Lateral
Epithelial apical domain
. Faces external environment or lumen of tubular structure
. Can exhibit structural surface modifications (cilia, microvilli, stereocilia) important for protection and absorption/movement of substances
Epithelial basal domain
Assoc. w/ basal lamina that separates epithelium from CT
Lateral domain in epithelia
In contact w/ neighboring cells
Microvilli
. Finger-like protections that inc. surface area (1um)
. Closely packed ones can be seen in LM as striated/brush border
. Single microvilli only seen in EM
What cells are microvilli found?
Cells involved in fluid transport and absorption (# microvilli correlates w/ cell absorptive capacity)
Microvilli structure
. Has cross-linked actin filament core from tip of microvillus into apical cytoplasm
. Anchored in terminal web
Terminal web structure
. Network of actin filaments added by spectrin, myosin, tropomyosin
Spectrin function in terminal web
Connects terminal web to apical cell membrane
Myosin and tropomyosin role in terminal web
Contractile proteins that affect size of apical cell surface
Stereocilia
. Long, branching finger-like projections in male reproductive system
. Supported by actin filaments and are immotile
Cilia
. Motile cell surface projections originating from basal bodies
. 5-10 um long
Structure of cilia
. Axoneme has 2 central microtubules surrounded by 9 microtubule doubles (9+2)
. Basal bodies formed by 9 triplets of microtubules w/o central microtubules (9+0)
. Axonemal doublets are continuous w/ 2 of 3 microtubules of basal body
Are 9+2 cilia motile?
YES
Cilia functions
. On cels used to transport substances over epithelial cell surface
. Protection of epithelial surface in respiratory tract
. Transport of fertilized egg from oviduct to uterus
What is axoneme a component of?
Sperm tail/flagellum
Genetic defects in axonemal proteins (kertagener’s Syndrome) cause what problems?
. Resp. Tract problems bc cilia can’t clear mucus
. Males are sterile bc sperm is immotile
Primary cilia
. 9+0 pattern
. immotile single primary cilium on every cell
Primary cilia function
Cellular antenna in sensing extra cellular environment
What diseases are linked to primary cilia damage?
Cancer, obesity, and polycystic kidney disease
Lateral domain specialization in epithelium
. Close contact between epithelial cells maintained by CAMs and junctions
. Terminal bar
Basal domain specializations in epithelial cells
. Basal lamina produced by epithelial cells
. Hemidesmosomes
. Basal infoldings in cells w/ active transport of ions (striations in LM)
Basal lamina
. Sheet of ECM that anchors epithelia to CT
. Visible in EM only as lamina densa
Major components of basal lamina
Type IV collagen and laminin and proteoglycans
External lamina
Basal lamina around other cell types besides epithelia hat come in contact w/ CT and completely surrounds cell (muscle, fat cells)
Basement membrane
. Basal lamina and lamina reticularis (underlying CT)
. Visible under LM
Disruption in external lamina in skeletal muscles causes ___
Muscular dystrophies
What pathological conditions change basal lamina thickness?
Diabetes and glomerulonephritis
Size and shape types of epithelia
. Simple or stratified in number of layers
. Squamous, cuboidal, or columnar in shape
Simple squamous epithelia
. Sheet of flat cells
. Mosaic appearance
. Prominent nucleus and attenuated cytoplasm
. Lines structures or spaces
Mesothelium
Simple squamous epithelium that lines body cavities
Endothelium
Simple squamous epithelium that lines blood vessels
Simple cuboidal epithelium
. Single layer cuboidal cells
. Square w/ round nucleus/ polygonal on surface view
. Secretory
. Lines ducts leading from secretory units
. Forms secretory units pyramid or square in shape
Simple columnar epithelium
. Single layer columnar cells
. Rectangle w/ basally located nucleus/ polygonal in surface view
. Absorptive or secretory
Stratified squamous epithelium
. Basal cells cuboidal (along basal lamina, area of mitotic activity)
. Middle layers for cellular differentiation
. Surface cells squamous (less active)
. Lining or protective, metabolically less active
. Can be keratinized or nonkeratinizing
Stratified cuboidal
. 2+ layers of cuboidal cells
. Found in large ducts of exocrine glands
Stratified columnar epithelium
. Layers of cells w/ top layer columnar shape
. Found in largest ducts of exocrine glands and in parts of male urethra
Pseudostratified columnar
. All cells contact basal lamina but are diff. Heights to looks layered
. Cell shape varies w/ nuclei at diff. Levels
. Lining type, frequently ciliated
. Found in resp. System
Transitional (uroepithelium) epithelium
. Found lining dispensable organs (bladder)
. Relaxed state: many layers, surface cells bulge into lumen
. Distended state: fewer layers, surface cells squamous
Endocrine glands
. Have no ducts, cells secrete products into blood/lymph indirectly
. Hormones diffuse via interstitium
. Single cells/groups of cells organized into sheets, cords, lumps, or follicles
Exocrine glands
. Secrete products onto body surfaces via duct system
. Form sheet of cells secreting into common lumen (stomach)
. Have secretory units that secrete into duct system
Types of exocrine glands and describe them
. Unicellular: 1-cell glands (goblet cells )
. Multicellular: secretory portion (alveolar v. Tubular), duct system (simple v compound), nature (mucous v. Serous), mode (merocrine, apocrine, Holocrine)
Types of duct system
Simple: unbranched
. Compound: branched
Shapes of secretory units
. Sac-like (acinar, alveolar, saccular)
. Tube-shapes (tubular)
. Mix (tubuloalveolar or tubuloacinar)
Merocrine secretion
Secretory product released by. Exocytosis (most common)
Apocrine secretion
Secretory products released in apical area of cell along with portion of cytoplasm and plasma membrane
Holocrine exocrine secretion
Whole cell is secretory product
Products secreted by merocrine glands
. Mucins produced by mucous cells (glycosylated, form mucus after hydrated, pale cytoplasm)
. Serous cells produce nonglycosylated proteins (have strongly staining cytoplasm and round nucleus)
Secretory unit types
. Mucous (mucous glands)
. Serous (serous glands)
. Mixed: mucous secretory units capped by serous cells (serous demilune)
Metaplasia
Transformation of 1 type of epithelium to another
Carcinoma
Malignant tumor of epithelial origin
Adenocarcinoma
Malignant tumor derived from glandular epithelium
Papilloma
Benign tumor (wart) projecting from surrounding surface from overgrowth of epithelial tissue on papillae of vascularized CT
Basal infoldings
Indents in basal side of epithelium
. Mitochondria found there
. Found in cells that transport ions a lot
Umbrella cells
Cells that are puffing out in transitional epithelium
Acinar shape
Look like grapes, balls of secretory cells
