Epithelia and Glands Flashcards
5 types of contact points between plasma mmbranes of tissue cells - connections
- tight junctions
- adherens junctions
-desmosomes
-hemidesmosomes - gap junctions
tight junctions
web like strands of transmembrane proteins, which encircle the membranes.
seals off passegways between adjacen cells and imparis passage of substances between the cells or leakage into blood or surrounding tissue
adherens junctions
forms a dense layer of protins called a plaque. located inside the plasma membrane attached to bothmembrane proteins and microfilaments of the cytoskeleton. transmembrane glycoproteins called cadherins insert into the plaque and join cells.
- resists seperation of cells during contractions
desmosomes
- plaque and cadherins that extend into the intercelullar space
- plaque attahced to intermediate filaments that contain keratin
-preveent seperation under tension and cardiac muscles during contrcaction
hemidesmosomes
-resemble half a desmosome
- do not link adjacnet cells but anchor to basement membrane
-transmembrane glycoprotein integrin, attahces to intermediate filaments and protein laminin in basement membrane
gap junctions
connect cells via tiny fluid filled tunnels called connexons
- very narrow intercellualr gap between adjacent membranes
- allowsfor ion, nutrient, waste, to travel from cell to cell
- for communication of cells within a tissue
3 types of surfaces of epithelia
- apical : face body cavitity, lumen, duct
- lateral surface facing adjacent cells
- basal surface: opposite of apical,
2 layers making up the basement membrane
basal lamina: top layer in contact with cells, secreted by epithelial cells, laminin, collagen, glycoproteins
reticular lamina: closer to underlying connective tissue, collagen secreted by connective tissue
do epithelia have blood vessels?
no they are avascular, blood vessels in underlying connective tissue provide nutrients and eliminate waste
outer covering of skin and some internal organs is called
covering and lining epithelium
the secreting portion of glands is called what type of epithelium
glandular epithelium
3 types of layers of epithelia- arrangemenft of cells in layers
simple- 1 layer, diffusion, osmosis, filtration, secretion and absorption
pseudostratified- appear as more than 1 due nuclei at different levels, but 1 layer
stratified- 2 or more layers, protect underlying tissue in areas of wear and tear
4 shapes of epithelia
squamous- thin, arranged like floor tiles, rapid passage of substances
cuboidal: cubes or hexagons, may have microvilli, secretion and absorption
columnar: may ahev cilia or microvilli, secretion and absorption
transitional: transition from flat to cuboidal, to stretch and collapse
types of simple epithelia
simple squamous
simple cuboidal
simple columar (ciliated and non ciliated)
pseudostratified columnar
simple squamous
flattened oval or sphere, cetral nucleus, filtration and diffusion, found in lung, renal capsules
make up the covering anfd lining epithelia:
endothelium: lines heart, blood vessels, lymphvessels
mesothelium: pericardium, pleura or peritoneum
simple cuboidal
central nuclei
thyroid gland, kidney tubules
secretion and absorption
non ciliated simple columnar
oval nuclei near the base
microvilli at apical surface and goblet cells
mucus used as lubricant in digestve, rspiratory, reproductive and urinary tracts. prevents destruction of lining by acid
ciliated simple columnar
cilia on apical surface
may have goblet cells
moves mucus by ciliary action
bronchioles, uterus and falopian tubes, ducts of testes
pseudostratified columnar
not all reach apical surface
can have ciliated, non ciliated and golet cells
types of stratified epithelia
stratified squamous
stratified cuboidal
stratified columnar
transitional
stratified squamous
- new cells pushed towards they surface
- as they lose blood supply they dehydrate, harden and die
- found in mouth and oesophegus, vaginal canal: non keratinized
found in skin- keratinized
stratified cuboidal and stratified columnar
rare and for protection
columnar for secretions as well
transitional
relaxed state- cuboidal, upon stretching they flatten and become squamous
for hollow structure subject to expansion
exocrine vs endocrine
exocrine have ducts and secrete onto body surface directly, endocrine are ductless and release hormones into circulation
3 types of glands
endocrine- acts on distant cells
autocrine- cells of smae secreting gland
paracrine: do not reach circulation but act locally on cells of same tissue
exocrine glands have 3 types of release mechanisms
merocrine - release by exocytosis, fusion of vesicles to apical surface
apocrine- release of contents by pinching off part of the cell therefore surrounded y cytoplasm and membrane. mammary glands, ciliary lands of eyelid
holocrine- products accumulate in maturing cell, cell undergoes apoptosis and discharges products and cell debris into lumen, sebacous glands of skin
classification of multicellular glands,
they form tubular invaginations made up of 2 parts:
Secretory Portion shape
- TUBULAR: straight, branched or coiled
- ACINAR/ALVEOLAR: rounded: single or branched
- TUBULOALVEOLAR : tubular and rounded.
Duct branching:
branched—compound
non branched—simple
exocrine glands that empty into internal surfaces also release what?
mucous or serous secretion
mucous vs serous secretions
mucus: thick and viscous, salivary glands, glycosylated proteins, mucinogenic granules lost in tissue prep leading to cytoplsasm on mucous cells appearing empty on staining
serous: watery, non glycosylated proetins, cells have cytoplasm that stains intensly with eosin
integumentary system
skin and its accessory structures
skin: epidermis, dermis and hypodermis
cells of the epidermis
keratinized stratified squamous epithelium with keratinocytes,
melanocytes (melanin producing cells absorb UV light),
langerhans cells (dendritic cells with Birbeck granules, antigen presenting cells)
merkel cells (contact tactile disc of sensory neurons,, for sensation of touch- mechanotransduction)
layers of the epidermis
Stratum basale - deepest layer of cuboidal/columnar cells, melanocytes, langerhans
Stratum Spinosum: layer above basal layer, keratinocytes take a flatter appearance,
Stratum Granulosum: middles layer of keratinocytes undergoing apoptosis, keratohyalin granules, lamellar granules
Stratum Lucidum: only in very thick skin like palms and soles, pale staining, dying keratinocytes contain a lot of keratin but have not been completely replaced by it
Stratum Corneum: consistenly shed off and replaced, dead flat squame keratinocytes and densly packed intermediate filaments and keratohyalin
the dermis composition and layers
typical connective tissue
2 regions: superfiical papillary dermis and deeper reticular dermis
papillary dermis
loose areolar connective tissue with collagen and elastin
dermal papillae - finger like projections- have capillaries
freenerve endings
reticular dermis
dense irregular coarse collagen fibres and thick elastic fibres interspersed with fibroblasts, blood vessels and nerves,,
sweat and sebacous glands
