Compound Epithelium PDF

Lecture II  Compound(Stratified)Epithelium - It is formed of many layers of epithelial cells (2 or more). The basal layer is the only one that is in contact with the basal lamina. It undergoes mitotic division producing cells in the upper layers. - It is named according to the most superf...

Lecture II  Compound(Stratified)Epithelium - It is formed of many layers of epithelial cells (2 or more). The basal layer is the only one that is in contact with the basal lamina. It undergoes mitotic division producing cells in the upper layers. - It is named according to the most superficial cells : 1- Stratified Squamous Epithelium: (the superficial cells are squamous). 2- Stratified cubical Epithelium: (the superficial cells are cubical). 3- Stratified Columnar Epithelium: (the superficial cells are columnar ).  1. Stratified Squamous Epithelium It is a thick type of stratified epithelium formed of many layers of cells one above the other. The cells rest on a clear wavy basement membrane. The basal layer (Malpighian layer), are columnar cells and well nourished. The other layers germinate from this layer. The intermediate layers (spongy layer)are polygonal cells. The superficial layers of cells, are flat squamous cells nucleated or not. The surface may be covered with keratinized or non-keratinizied layer.. Its main function is protection: It protects the underlying tissues and internal organs against several physical and microbial damages. It is present in: the outermost layer of the skin and the inner lining of the mouth, esophagus and vagina. stratified squamous keratinized stratified squamous non- epithelium keratinized epithelium The surface cells are very flat, The surface cells are living and they are no longer alive. They cells, Keratin is absent from have no nucleus or organelles, these cells. They produce filled with a protein (keratin) mucus to keep the surface which makes our skin waterproof. moist and helps to balance the It is present in : skin, epidermis pH of the surrounding. of the palm of the hand and sole It is present in: lining of the of the foot, external ear, external buccal cavity, pharynx, nose, outer surface of the lip. oesophagus, tongue, gum, cornea and the exposed parts of the conjunctiva, vagina, terminal parts of male and female urethrae , inner surface of the lip.  2. Stratified cubical Epithelium It consists of multiple cellular layers, with the surface layer being made up of cube-shaped cells and the other layers can be other types of cells.. Its function is : protection of ducts areas of glands.. It is present in: sweat glands, mammary glands, salivary glands  3. Stratified columnar Epithelium It is a rare type of epithelial tissue composed of column shaped cells arranged in multiple layers. It is present in : The conjunctiva of the eye , parts of pharynx, anus, uterus, and male urethra and vas deferens. Its functions are: - It protects the conjunctiva of the eyes and other delicate structures in the eyes. -It has secretory functions.  Transitional Epithelium It consists of multiple layers of epithelial cells: - Dome-shaped superficial cells with specialized protective membranes, can contract and expand in order to adapt distension needed, and -Basal cubical to columnar cells attached to the basal lamina.. Its function is: The cells stretch in order to accommodate a volume of the liquid and return to normal state without damage.. It present in: It lines the organs of the urinary system and is known here as urothelium.  Glandular Epithelium The glands are formed of collections of epithelial cells which are modified to produce different types of secretion. They are classified into: a. Endocrine or ductless glands, secreting hormones directly in the blood as: Thyroid, pituitary, adrenal,… b. Exocrine glands: They have ducts to carry their secretions. e.g. salivary glands. c. Mixed glands: which possess the exocrine and endocrine functions as: pancreas, testis and ovary.  Goblet cell: - Unicellular intraepithelial mucin-secreting gland. - It scattered within simple cuboidal, columnar, and pseudostratified epithelia. - Its name corresponds to its shape a narrow base and wide apex.  Cell junctions - They are called also intercellular bridges. - They consist of multiprotein complexes that provide contact or adhesion between neighboring cells or between a cell and the extracellular matrix in animals. - Tight junctions (zonula occludens),adherens junctions, desmosomes, gap junctions and hemidesmosomes.  Tight junctions : They are impermeable seals that encircle cells and bind them together into leak proof sheets. The plasma membranes of adjacent cells fuse together tightly in order to limit the leakage of various substances between the two cells. They perform vital functions : holding cells together and form protective and functional barriers. The major types of proteins are: claudins and occludins.  Adherens junction : They are bundles of protein complexes that occur at cell– cell junctions, binding and adhering cells strongly to one-another. They are usually more basal than tight junctions. The cytoplasmic face is linked to the actin cytoskeleton. They allowing cells within a tissue to respond to forces, biochemical signals and structural changes in their microenvironment.  Desmosomes: They are intercellular junctions that provide strong adhesion between cells. They form links between cells, and provide a connection between intermed iate filaments of the cell cytoskeletons of adjacent cells. They are also known as a macula adherens They are responsible for maintaining the mechanical integrity of tissues.  Gap junction: They are aggregates of intercellular protein channels that permit direct cell–cell transfer of ions and small molecules. They are expressed in all tissues and cells, but most notably in cell types that are involved in direct electrical communication, such as neurons and cardiac muscle.  Hemidesmosomes: They are multi‐protein complexes that provide firm adhesion of basal epithelial cells to the underlying basement membrane. They are similar in form to desmosomes.