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WEEK 4:
Building bodies 1- cells to tissues:
| Question | Answer |
|---|---|
| epithelia are separated from surrounding tissue by | basement membrane |
| different functions/ specialisations of epithelia | Protect underlying tissue from outside world Protects/separates areas within the body Help hold tissues together Thermoregulation Hormone release Absorption |
| simple squamous epithelia | thin layer of flattened cells with a small intracellular volume, responsible for exchanging gases and molecules and is found in the alveoli kidney, glomerulus, blood vessel lining and capillaries |
| simple cuboidal epithelia | cuboid shaped cells responsible for absorption and secretion which have a larger intracellular volume (more contents), secretory glands (sweat, sebaceous) and is found in renal tubules |
| simple columnar epithelia | tall rectangle shaped cells with a large intracellular volume with the potential for energy reserves and high organelle density and is responsible for absorption, motility, and processing |
| pseudo-stratified epithelia | appear stratified with nuclei at different levels but all cells are in contact with the basement membrane and is usually found in respiratory tract |
| stratified squamous epithelia | several layers with the top layer being a layer of flattened cells and acts as area of wear and tear (abrasion resistance) and is found in oesophagus, vagina, skin (almost) |
| transitional epithelia | stretchy and waterproof allowing cell distension and returns to original shape and is found in the bladder and urinary tract |
| examples of stratified columnar epithelium | conjunctiva of eye, male urethra, anus, pharynx |
| 2 layers making up the basement membrane | basal lamina and reticular lamina |
| basement membrane is | sheets of extracellular matrix at interface of functional tissue (epithelium) and support tissue (connective tissue) |
| components of the basement membrane | type IV collage, glycoproteins (laminin secreted by epithelial cells and fibronectin from fibroblasts) and glycosaminoglycans (GAGs) |
| functions of basememnt membrane | Adhesion and provides anchor (for epith.), barrier (permeability), organisation of cells |
| what happens to basement membrane in metastatic carcinoma (malignant melanoma) | cancer cells must breach basement membrane barrier to invade underlying tissue (local invasion to migrate from epidermis into dermis) and enter blood or lymphatic vessels (intravasation) |
| what happens to the basement membrane in epidermolysis bullosa | separation of epidermis from dermis (blistering) where there are mutations in laminin or type VII collage causing skin to separate within basement membranes lamina lucida resulting in fragile blisters which can be severe/ fatal in infants |
| what happens in basement membrane in kidney in chronic hyperglycaemia (leading to CKD and renal failure) | GBM thickening (due to increases synthesis + deposition of EXM proteins eg type IV collagen causing GBM to thicken) and increased permeability (hyperglycaemia disrupts GBMs charge selective properties making it leaky+ allowing large proteins into urine) |
| how to increase secretion in epithelia | increase folds and make more glands |
| difference between secretions in columnar and cuboidal | columnar = secretory portion and cuboidal = ducts |
| shapes of glands | tubular, acinar or mixed which can be simple or compound (branched) |
| simplest form of gland example | goblet cell in GI tract |
| cancers from epithelial cells called | carcinomas |
| cancers in glands are called | adenocarcinoma |
| exocrine cells | secrete products onto epithelial surface directly via duct for LOCAL action eg sweat glands |
| endocrine cells | release secretions directly into blood to act on DIFFERENT tissues eg pituitary gland |
| connective tissue | support tissue originating from embryonic mesoderm and characterised by abundance of matrix (95%) with a few cells (5%) |
| ECM composed of | fibres (collagen and elastin) and ground substance (glycoproteins and glycosaminoglycans) |
| cells in the CT | fibroblasts which secrete ECM for most tissues |
| function of fibroblasts | secrete ECM |
| collagen | structural protein that is long straight and unbranched providing tensile strength and structural support |
| elastic | are branched and wavy containing elastin to provide elasticity |
| reticular | contain same protein subunits as collagen but are thinner and branched |
| type I collagen | in most connective tissues eg bone ligaments tendon and skin |
| type II collagen | less well organised fibres than type I and are found in cartilage |
| type III collagen | thinner fibres than type I and make up reticulin fibres in organs and help organise cells within organs |
| type IV collagen | form branched networks and help organise basement membrane |
| type V collagen | found in small amounts in tissues eg skin bone cornea and placenta and often works alongside type I collagen helping regulate the diameter and organisation of collagen fibrils |
| collagen synthesis | procollagen chains made in RER -> modified via hydroxylation and glycosylation(+ OH) -> 3 modified chains wrap around each other making triple helix (procollagen) -> leaves cell to extracellular space -> cleaved N and C propeptides -> line up + cross link |
| function of collagen | provide tensile strength |
| examples when reduced tensile strength from collagen disorders | tissue laxity and joint hypermobility eg Elhers Danlos syndrome |
| elastin fibres | stretching and elastic recoil where tropoelastin polymerises to elastin and requires fibrillin for assembly Marfans syndrome is when genes coding for fibrillin are deffective leading to rupture of aorta |
| fibrillin function | links to elastin |
| fibronectin function | deposition and orientation of collagen and its links to cells via integrin |
| laminin function | major component of basement membrane |
| GAGs | polysaccharide chains attracting water and are found forming the centre of the intervertebral disc forming a compression resistant core |
| 4 groups of GAGs (CHHK) | chondroitin sulfate heparan sulfate hyaluronan keratan sulfate |
| losse CT function | packing material eg areolar tissue with more ground substance and fewer fibres for flexibility and cushioning |
| dense CT function | tough physical support: dermis, organ capsule, ligaments, tendons - with a high collagen content acting strong and resistant to tension |
| areolar CT function | fatty |
| specialised support CT found in | cartilage and bone |
| functions of CT | metabolic (adipose tissue) immune mechanical and structural role mediate exchange |
| tendon needs | dense regular CT matrix with fibroblasts with a composition of high concentration of collage type I fibres arranged in parallel bundles and minimal ground substance to provide tensile strength along one direction |
| dermis of skin needs | dense irregular connective tissue with fibroblasts with a composition of collagen type I and II fibres arranged in multiple directions and moderate ground substance to provide strength and flexibility in multiple directions |
| cartilage needs | specialised connective tissue (cartilaginous matrix) and chrondroblasts (immature) and chrondrocytes (mature) with a composition of collage type II fibres, abundant GAGs in ground substance to provide support with flexibility and resistance to compression |
| bone needs | mineralised connective tissue, osteoblasts and osteocytes with a composition of collagen type I fibres and ground substance rich in calcium phosphate crystal s(hydroxyapatite) to provide rigid structural support and protection |
| adipose tissue | dominated by adipocytes for storing energy and insulation |
| ECM stains what colour | prominent pink |
Created by:
kablooey
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