Epithelium Flashcards
Cytoskeleton
Microfilaments - actin - tie cells together, muscle contraction
Intermediate filaments - keratin - strength
Microtubules
Tight Junction
- transmembrane proteins (claudins and occludins mainly) joining adjacent plasma membranes cytoskeletons
- keeps cell polarity by preventing migration of proteins from apical and basal surfaces
- electrically tight
- lateral surfaces
- stomach, intestines and bladder
Adherens Junction
- more basal located than tight junction
- plaque layer of proteins (catenins), with cadherins (transmembrane glycoprotein) spanning gap
- actin - catenins - cadherins
- adhesion belts in some epithelial cells
Desmosome Junction
- lateral junction
- resist shearing forces
- plaque
- cadherins span gap, link to keratin
- keratin spans from one desmosome to another (structural integrity)
- binds muscle cells
- skin epithelium and cardiac muscle cells of heart
Gap Junction
- direct connection between cells
- 6 connexin molecules form 1 connexon
- 2 hemichannels make 1 gap junction (allows 1kDa molecules through)
- communication network
Hemidesmosome
- basal junction (welds cell to basement membrane by linking keratin)
- laminin in basement membrane binds to integrin (transcellular glycoprotein) which binds to keratin
Junctional complex
-tight junction, adherens junction and desmosome
Basement Membrane
Basal lamina (top layer) - secreted by epithelial cells, contains collagen and laminin
Reticular lamina - produced by fibroblasts in connective tissue, has fibrous proteins (fibronectin, collagen)
-in between epithelia and connective tissue
-epithelia has nerves but is avascular so exchange of nutrients comes from connective tissue
Melanoma warning signs (ABCD)
asymmetry - one half of mole does not match the other
border irregularity - edges ragged, notched or blurred
colour - mix of brown, black, red or blue
diameter - greater than 6nm
Simple squamous epithelium
- delicate
- filtration (kidney), diffusion (lung), secretion, where slippery surface needed
- thin, flat and irregular like jigsaw
- mesothelium - lines pericardial (heart), pleural (lung) , peritoneal cavities (abdomen)
- endothelium - lines inside of heart and blood and lymphatic vessels
- also found in eye
Simple cuboidal epithelium
- secretion and absorption
- cuboidal or hexagonal boxes, distance between adjacent nuclei approx height of the epithelium
- ducts (pancreas, smaller ones of many glands), kidney tubules, thyroid secretory chambers, lens anterior surface
Simple columnar epithelium (ciliated and non-ciliated)
- rectangular, more cytoplasm so more organelles
- elongated nuclei
- secretion, lubrication, absorption
Ciliated - goblet cells, cilia
-bronchioles, ventricles, sinuses, spinal cord central canal, uterine fallopian tubes
Non ciliated - microvilli, goblet cells
-gut mucosa, ducts of many glands, gall bladder
Goblet cells - modified simple columnar cells
Stratified squamous epithelium (keratinised and non-keratinised)
- where there is high mechanical or chemical stress
- protect against microbes
- like pancakes, cells furtherest from nutrition are thinner and less active
Keratinised - keratin makes surface tough and waterproof - skin
Non-keratinised - protection from abrasion and microbes still
-mouth, throat, tongue, oesophagus, anus, vagina
Stratified cuboidal epithelium
- fairly rare, apical layer cells cube shaped
- protection
- ducts of adult sweat glands, part of male urethra, esophageal glands
Stratified columnar epithelium
- fairly rare, protection and secretion
- part of urethra, large excretory ducts of some glands (esophageal), anal mucosal membrane, conjunctiva of eye
