Epithelial Tissue PDF

Tissue Introduction & Epithelial Tissue  Cells to Tissues ◼ As human body develops from single to multicellular, cells specialize. ◼ Body is interdependent system, malfunction of one group of cells is catastrophic. ◼ Cells specialize into types of tissues, then intersp...

Tissue Introduction & Epithelial Tissue  Cells to Tissues ◼ As human body develops from single to multicellular, cells specialize. ◼ Body is interdependent system, malfunction of one group of cells is catastrophic. ◼ Cells specialize into types of tissues, then interspersed into organs. Tissues = groups of cells that are similar in structure and function. ◼ Epithelium ◼ Muscle ◼ Coverings ◼ Movement ◼ Linings of surfaces ◼ Connective ◼ Nervous ◼ Support ◼ Control ◼ Bone, ligaments, ◼ Brain, nerves, fat spinal cord  Function of Epithelial Tissue ◼ Protection ◼ Skin protects from sunlight & bacteria & physical damage. ◼ Absorption ◼ Lining of small intestine, absorbing nutrients into blood ◼ Filtration ◼ Lining of Kidney tubules filtering wastes from blood plasma ◼ Secretion ◼ Different glands produce perspiration, oil, digestive enzymes and mucus  Characteristics of Epithelial Tissue ◼ Form continuous sheets (fit like tiles) ◼ Apical Surface ◼ All epithelial cells have a top surface that borders an open space – known as a lumen ◼ Basement Membrane ◼ Underside of all epithelial cells which anchors them to connective tissue ◼ Avascularity (a = without) ◼ Lacks blood vessels ◼ Nourished by connective tissue ◼ Regenerate & repair quickly  Classification of Epithelial Tissue ◼ Cell Shape ◼ Squamous – flattened like fish scales ◼ Cuboidal - cubes ◼ Columnar - columns ◼ Cell Layers ◼ Simple (one layer) ◼ Stratified (many layers) ◼ Named for the type of cell at the apical surface.  Simple Squamous Epithelium ◼ Structure ◼ Single Layer of flattened cells ◼ Function ◼ Absorption, and filtration ◼ Not effective protection – single layer of cells. ◼ Location ◼ Walls of capillaries, air sacs in lungs ◼ Form serous membranes in body cavity  Simple Cuboidal Epithelium ◼ Structure ◼ Single layer of cube shaped cells ◼ Function ◼ Secretion and transportation in glands, filtration in kidneys ◼ Location ◼ Glands and ducts (pancreas & salivary), kidney tubules, covers ovaries  Simple Columnar Epithelium ◼ Structure ◼ Elongated layer of cells with nuclei at same level ◼ Function ◼ Absorption, Protection & Secretion ◼ When open to body cavities – called mucous membranes ◼ Special Features ◼ Microvilli, bumpy extension of apical surface, increase surface area and absorption rate. ◼ Goblet cells, single cell glands, produce protective mucus. ◼ Location ◼ Linings of entire digestive tract  Pseudostratified Epithelium ◼ Structure ◼ Irregularly shaped cells with nuclei at different levels – appear stratified, but aren’t. ◼ All cells reach basement membrane ◼ Function ◼ Absorption and Secretion ◼ Goblet cells produce mucus ◼ Cilia (larger than microvilli) sweep mucus ◼ Location ◼ Respiratory Linings & Reproductive tract  Cilia Basement Membrane Stratified Squamous Epithelium ◼ Structure ◼ Many layers (usually cubodial/columnar at bottom and squamous at top) ◼ Function ◼ Protection ◼ Keratin (protein) is accumulated in older cells near the surface – waterproofs and toughens skin. ◼ Location ◼ Skin (keratinized), mouth & throat  Keratin Stratified Cubodial (layers of cubodial only)  Transitional Epithelium ◼ Structure ◼ Many layers ◼ Very specialized – cells at base are cuboidal or columnar, at surface will vary. ◼ Change between stratified & simple as tissue is stretched out. ◼ Function ◼ Allows stretching (change size) ◼ Location ◼ Urinary bladder, ureters & urethra  Glands ◼ One or more cells that make and secrete a product. ◼ Secretion = protein in aqueous solution: hormones, acids, oils. ◼ Endocrine glands ◼ No duct, release secretion into blood vessels ◼ Often hormones ◼ Thyroid, adrenal and pituitary glands ◼ Exocrine glands ◼ Contain ducts, empty onto epithelial surface ◼ Sweat, Oil glands, Salivary glands, Mammary glands.  Shapes of Exocrine glands ▪Branching ▪ Simple – single, unbranched duct ▪ Compound – branched. ▪Shape: tubular or alveolar ▪ Tubular – shaped like a tube ▪ Alveolar – shaped like flasks or sacs ▪ Tubuloalveolar – has both tubes and sacs in gland  Modes of Secretion ◼ (How the gland’s product is released) ◼ Merocrine ◼ Just released by exocytosis without altering the gland at all. ◼ Ex: Sweat glands and salivary glands ◼ Holocrine ◼ The gland ruptures and releases secretion and dead cells as well. ◼ Sebaceous (oil glands on the face) only example