Epithelial Flashcards
Simple squamous epithelium
Single layer of flattened plate-like cells
Parallel oval nuclei
Where are simple squamous epithelium found
lines inside of blood vessels (endothelium), outside of lungs (mesothelium) and abdominal organs (peritoneum)- layers are kept moist by a serous exudate that prevents organs sticking together and allows free movement- if layer destroyed, adhesions form
• also found within alveoli
Simple cuboidal epithelium
single layer of cells with similar height and width on a basement membrane
• central spherical nucleus (one per cell)
Where are simple cuboidal epithelium found
line kidney tubules, small ducts eg salivary gland
Simple columnar epithelium
single layer of cells taller than they are wide on a basement membrane
May have cilia or microvilli
Where are simple columnar epithelium found
line the stomach, intestines (enterocytes) and uterus (fallopian tube), respiratory tract
Cilia
microscopic motile projections on luminal surface of cells. Contain contractile proteins (tubulin and dyneine) that allows these to rhymically beat, wafting the material across the epithelium in the same direction- respiratory tract and reproductive tract (fallopian tube to move ovum towards the uterus).Around 300 cilia per epithelial cell
Microvilli
microscopic projections on luminal surface of absorptive cells. Increase surface area for absorption- intestinal brush border and severe as attachment sites of exo-enzymes involved in digestion. A carbohydrate-rich glycocalyx is attached to their surface
Stratified squamous non-keratinising epithelium
multiple layers of cells on a basement membrane
• mature surface layer are plate-like squamous
Kept moist by secretion of glands and a fluid that exudes through the cell layers
Where are Stratified squamous non-keratinising epithelium found
lines the mouth, oropharynx, oesophagus, vocal chords and vagina
Stratified squamous keratinising epithelium
waterproof layer of keratin
• Keratin accumulated in cytoplasm of cells, killing the cells, leaving dead flare plates of keratin before eventually being sloughed off (desquamated)
Cells considerably restrict inward and outward movement of fluids
Where are Stratified squamous keratinising epithelium found
Skin
Thick skin eg palm of hand/ sole of foot
Thin skin eg eyelid
Pseudostratified epithelium
• single layer of cells of variable height, mimicking multiple layers all cells in contact with basement membrane
Where are Pseudostratified epithelium found
• lines the conducting airways (respiratory epithelium) with cilia eg trachea- cells stretch during inspiration
Urothelium
surface layer of umbrella cells
• cells between umbrella cells appear 3-7 cells thick and this layer is pseudostratified
• lines the collecting part of urinary tract- bladder, renal pelvis and ureter
Stretchy
Waterproof due to tight junctions between cells which prevent urine passing between them
Basement membrane
difference between epithelium and underlying connective tissue
• composed of several extra-cellular proteins including collagen IV and fibronectin
• essential for proper functioning and survival of epithelium
• can be seen if stained with PAS due to hexose sugar contains glycoproteins
Tight junctions
band-like fusions between cells that are impervious to most molecules- prevent diffusion between cells- can establish a gradient for absorption or secretion of molecules from or into the gut and act as a barrier as only water and some small molecules can pass through
Desmosomes
plaques that form physical joints between cells and connect the cytoskeletons of adjacent cells - spread forces across several cells eg in epithelia exposed to abrasive forces, skin.
Hemi-desmosomes
found on basement layer binding the epithelial cells to the basement membrane
Gap junctions
electrical junctions that permit the transfer of small molecules and ions via pores eg water soluble ions. Electrically couple adjacent cells- synchronise activity of epithelium as a whole
Adherens
joins an actin bundle in one cell to a similar bundle in another
Glands
Glands are epithelial in origin, developing as ingrowths from the epithelial surface. Exocrine glands remain in contact with the surface from which they are derived by means of ducts. Often the glands secrete fluids, lubricants or digestive enzymes on to the epithelial surface.
Notable examples are the sweat glands of the skin, the salivary glands that produce lubricants and enzymes to digest food and the glands of the respiratory tract that produce a protective layer of mucus.
Skin
The skin has twomain layers, an outer epidermis and a deeper dermis. The epidermis is composed of a stratified squamous keratinizing epithelium
The lower layers of the epidermis are similar to those of a moist stratified epithelium but the upper layers synthesize a unique collection of proteins that interact with the cytoskeleton of the cells to produce keratin, a dense protein which fills the cytoplasm of the cells rendering them tough and waterproof. The cells of this layer considerably restrict both the inward and outward movement of fluids. Once filled with keratin, the cells die and eventaully become detached from the underlying layers and are sloughed off.
At the boundary between the living epithelial cells and the dead pink-staining kerating layers is a layer of cells with blue keratohyaline granules within them (precursors of keratin)- the granular layer (stratum granulosum).
Desmosomes present in ‘prickle cell layer’- a thick layer above the basal layer
Prickle cell layer
Desmosomes present in ‘prickle cell layer’- a thick layer above the basal layer of skin
Holocrine Secretion
Secretion via loss of entire cells from gland
Merocrine secretion
Release of cell products by exocytosis from apical cell surface
Apocrine secretion
Pinching off part of the apex of the cell
Exocrine secretion
Umbrella term for apocrine, melocrine and Holocrine secretion
Endocrine secretion
Release of products from base of cell into bloodstream
Julian is examining a skin biopsy. Upon examining the skin sample under the microscope he has added some stain which highlights the basement membrane. What type of collagen is found in basement membranes?
Type 4
