Jeff Kerr; Week 6 MED1011; Anatomy
Four primary tissue types: muscle, epithelium, connective tissue and nervous tissue. Epithelial tissues can be derived from all germ cell layers, are for protection, secretion or absorption, cells can change types (metaplasia), can divide and line body cavities, basal lamina sits on EC matrix to separate them from deeper connective tissues, are renewed and replaced, have no direct blood vessels, close associations joined by junctions. Can be simple or stratified. Can be squamous, cuboidal, columnar or irregular. Mucosa refers to tissue lines with epithelium and deeper connective tissue, when healthy mucosa is pink. Cuboidal found in kidney tubules, squamous in blood vessels, columnar in stomach and gall bladder, stratified in oesophagus, stratified with keratin in thick skin, pseudostratified in trachea. Epithelium can be 'transitional' between squamous or columnar depending on state of relaxaiton such as in the bladder.
Glands can be simple tubular, simple coiled tubular, simple branched tubular, simple branched acinar. Compound glands are many glands feeding into one. Exocrine glands secrete into a duct, endocrine into blood/tissue fluid. Sebaceous glands are tubular, sweat glands are highly coiled.
Connective tissues have proportion of cells in a minority, extracellular material dominates, is protein rich with fibres and macromolecules. Major connective tissue producing cells are fibroblasts (most common in most CT), chondrocytes in cartilage, osteoblasts in bone. ECM is usually made by the cells within it. All components of connective tissue are embedded in a matrix of hydrated proteins. Collagen is most abundant fibres, elastic can be stretched, reticular is a type of collagen for 3D scaffold. ECM is made of glycoproteins (proteins with carbohydrates), proteoglycans (proteins with sugar units), hyaluronic acid (chain of sugars). ECM can be gel like due to hydration, strong due to fibres, rock hard like bone/teeth due to mineralisation, fluid-like due to dissolved proteins.
Collagen is made by fibroblasts, and is tough, flexible and resists stretching. Collagen molecules are triple helices with alpha chains, and is found in tendons (90% collagen), tensile strength is 280-1300kg/cm (muscle is 5kg/cm). Cartilage matrix has large proteoglycan molecules in between the collagen, tough but is deformable due to water content. Loose connective tissues form a packing material for the body such as fat, and semi solid gel/fibres for tissue support. It is flexible, has open network of mostly collagen fibres, suspends nerves and vessels and has many immune defence cells (loose or areolar CT). In irregular CT collagen runs in different directions. In loose CT such as in mesenteries elastin stretches, has cross links between them which keep them together.
Fat cells look empty in staining because the fat is removed to process the tissue. Dense connective tissues have a high fibre content and may be hard due to mineralisation in bone and enamel. There is dense irregular connective tissue (woven patterns of skin that resist tension from any direction) and dense regular (parallel bundles with few fibroblasts, resists force in one direction, tendons, ligaments, covering of bones and some organs). Dense connective tissues are dermis, ligaments and tendons, cartilage, bone. Dense regular is very strong, up to 350kg strain, in basketballers 2000kg has been recorded.
Chondrocytes secrete cartilage matrix, collagen, proteins and have a high water content. Hyaline is in trachea and bronchi, resists compression and keeps airway open, also at the ends of bone inside synovial joints. Bone is made from cells/mineralised collagen fibres/matrix. Bone matrix is mineralised with calcium phosphate.