Epithelial Tissue Class Notes

Epithelial tissue ● ● ● ● ● ‘Lining tissue’ Found on all internal and external body surfaces ○ Derived from the endoderm (inside of tubes) and ectoderm (external surface) No visible ECM Selectively permeable to act as a barrier between the internal and the external environment Epidermis has no nerves and is avascular so the connective tissue underneath has the nerves and vessels to nourish the epithelium to keep it alive and detects pressure and pain on the epithelium Major functions: ● ● ● ● ● ● ● Protection Immune defences Secretion Transport Sensation Vitamin D synthesis Thermoregulation (vasodilation and vasoconstriction) Classifying epithelial tissue → ‘number of layers - cell shape’ ● Number of layers ○ Simple = one layer ○ Stratified = two or more layers ● Cell shape ○ Squamous = flattened ○ Cuboidal = cube/square ○ Columnar = rectangular Simple epithelia Simple squamous ○ ○ ○ Nucleus looks like a pancake Allows for diffusion Found in blood vessels and air sacs of the lungs Simple cuboidal ○ ○ ○ ○ Large central nucleus (look for this in cuboidal) Allows for diffusion Found in respiratory passages, ducts of glands, endocrine glands, blood vessels Arranged in circles/donuts Simple columnar ○ ○ ○ ○ Pseudostratified Nucleus is towards the basal (bottom) end Associated with microvilli and cilia Microvilli ■ Wavy extension of the apical section of the cell to increase SA ■ Found in areas of absorption e.g. small intestine Cilia ■ Hair like structures glued to the top of the cell ■ Creates turbulence and propulsion e.g. hollow organs such as the uterine tube ○ ○ ○ ○ Looks stratified but is only one cell layer thick Typically has cilia on the apical surface The nuclei are at different heights (focus on the apical and basal sides to identify if its a single cell) Found in upper respiratory passages and nasal cavity for protection e.g. where mucus traps particles and pathogens and propels them so that they can be excreted Stratified epithelia Stratified squamous (non keratinised) ○ ○ ○ ○ ○ Nucleated All of the cells are still alive There is the rapid regrowth of cells, constant turnover Each cell is distinct looking Found in areas that are exposed to mechanical abrasion but need to be moist ■ Mouth ■ Throat ■ Vagina Squamous (keratinised) ○ ○ ○ ○ ○ Dead apical cells that are tough because they are filled with keratin ■ Keratin are the waste products of dead epithelial cells that have hardened Forms the epidermis (outer layer of the skin) Tough and resistant to friction Dry areas that are prone to high levels of mechanical stress e.g. palms of the hands Stratified cuboidal/columnar epithelium (rare) Stratified cuboidal lines glands (particularly sweat glands, exocrine glands) ○ Stratified columnar lines glands (urethra and in large ducts of some glands) Connective tissue ● Connects one tissue type to another (makes an organ) ● Derived from the mesoderm ● ECM is present and it distinguishes between epithelium and connective (which are located close to one another) ● Components of the ECM: ○ Ground substance = a fluid (mainly water) but can be mineralised or solid ○ Fibroblast = secretes fibres (collagen, elastic, reticular), which are the proteins that make up the ECM ○ Collagen = strength ○ Elastic = able to stretch and recoil (elastin stains purple) ○ Reticular = anchor and provide support to the functional cells, blood vessels, nerves ● There are two types of connective tissue: ○ Connective tissue proper ■ Tendon = muscles to bones ■ Ligaments = bone to bone ■ Fat = skin to muscles ○ Specialised connective tissue ■ Cartilage ■ Bone ■ Blood