Epithelial Tissue PDF

INTRODUCTION TO BODY STRUCTURE 22 I-Epithelial Tissue This tissue is called epithelial tissue because it can cover surfaces or line cavities all over the body. o General characters of epithelial tissue: 1- It may develop from ectoderm,...

INTRODUCTION TO BODY STRUCTURE 22 I-Epithelial Tissue This tissue is called epithelial tissue because it can cover surfaces or line cavities all over the body. o General characters of epithelial tissue: 1- It may develop from ectoderm, mesoderm or endoderm. 2- The epithelial cells rest on a basement membrane (B.M.) which may be clear or not clear. 3- No blood vessels can enter in between epithelial cells, but nerves can, so epithelial tissue is avascular tissue. 4- Epithelial tissue receives nutrition by diffusion from the underlying connective tissue. 5- Epithelial tissue consists of numerous crowded cells with minimal intercellular substance between the cells that form continuous sheets, which cover surfaces or line cavities &is called surface epithelium. 6- Epithelial tissue may be modified to give secretion & is called glandular epithelium. 7- Epithelial tissue may modify to receive sensation & is called neuroepithelium & may acquire a contractile function & is called myoepithelium. 8- Epithelium can regenerate in a short time i.e. there is a continuous process of regeneration. o Epithelial tissue is classified into: I- Surface epithelium. II- Glandular epithelium. III- Neuro-epithelium IV- Myo-epithelium. I- Surface epithelium Surface epithelium is classified according to its number of layers into: a) Simple epithelium. b) Stratified epithelium. INTRODUCTION TO BODY STRUCTURE 23 a- Simple Epithelium Definition: It is formed of one layer of cells resting on basement membrane. It is divided according to shape of cells into: 1- Simple squamous epithelium 2- Simple cubical epithelium 3- Simple columnar epithelium 4- Simple columnar ciliated epithelium 5- Pseudo-stratified columnar epithelium POC 4-Simple 1-Simple squamous 2-Simple cubical 3-Simple columnar epithelium columnar ciliated Shape Flat Cube-like -Tall cells Tall cells of cells Flat nucleus Central carry rounded -Basal oval cilia nucleus nucleus -Basal oval nucleus Functi Smooth surface Secretion Secretion Movement ons (easy movement) Reabsorpti Absorption of Thin surface on (microvilli particles (gas &fluid e.g. intestine) or fluids exchange) over the surface Sites Mesothelium[pleu Thyroid -Stomach -Lung ra, pericardium follicle -Intestine bronchiole &peritoneum] Small -Goblet cells s Endothelium[hear ducts of [secrete t &blood vessels] salivary g. mucous -Uterus Lung alveoli Renal which Bowman's convoluted accumulates -Fallopian capsule of kidney tubules in its apex] tubes Hanaa.AK. INTRODUCTION TO BODY STRUCTURE 24 5-Pseudostratified Columnar Epithelium: It is actually a simple epithelium as all the cells rest on the B.M. It is formed of crowded cells. Nuclei are present at more than one level; this gives the epithelium a false appearance of being stratified. POC a-Pseudostratified b-Pseudostratified c-Pseudostratified columnar non-ciliated columnar ciliated columnar ciliated with motile cilia with non-motile &goblet cells cilia Sites 1- male genital system Respiratory epithelium Epididymis Nose (vas deferens). Larynx 2- Membranous part of Trachea male urethra Bronchi Hanaa.AK. Pseudostratified columnar epith. b- Stratified Epithelium: Definition: Epithelium is formed of more than one layer, the basal layer resting on the B.M. It is classified according to shape of the top layer into:- 1- Stratified squamous epithelium. 2- Transitional epithelium [stratified cuboidal]. 3- Stratified columnar epithelium. 4- Stratified cubical epithelium. INTRODUCTION TO BODY STRUCTURE 25 Function: The main function of stratified epithelium is protection. 2- Transitional 1- Stratified Squamous Epithelium Epithelium Number of 5-30 6-8 [empty bladder] 3-4 [full layers bladder] Basement Clear & wavy Non-clear, non-wavy membrane Basal cell Columnar with basal oval nuclei High cuboidal cells with rounded layer Intermediate Crowded polygonal cells with polyhedral with rounded layers central rounded nuclei nuclei Minimal intercellular substance. wide intercellular spaces Cells are held together with containing mucous like desmosomes. substance which helps gliding They gradually decrease in size of the cells over each other. NO desmosomes Cells become flat in full bladder Top layer Flat cells with flat nuclei. Cells are dome shape with upper convex, lower concave surface & have rounded nuclei, Some cells are binucleated. The top layer is covered with mucous to protect against the action of urine. Types Non-Keratinized Keratinized One type: In full bladder the cells of the top change in number of layers is due layer gradually to gliding of cells help of mucus die& change present between the cells so the into keratin number of layers decrease & the scales. surface area increase. Sites Line any wet Skin & dry Urinary bladder, ureters, some surface opening opening over it parts of urethra, renal calyces and over the skin 1-Epidermis of renal pelvis 1-Oral cavity skin. 2-Oesophagus 2- External ear. 3- Cornea. 3- Nasal orifices. Functions Protection Protection &accommodation (distensibility) INTRODUCTION TO BODY STRUCTURE 26 3- Stratified Columnar Epithelium: Like stratified squamous epithelium , but the number of layers is fewer & the top layer is formed of columnar cells which may be ciliated or not ciliated: - a- Stratified columnar ciliated epithelium:(Fig15) Sites: Fetal esophagus (a rare type). Fig:15- Stratified columnar ciliated epithelium b- Stratified columnar non ciliated epithelium:(Fig 16) Sites: 1- Recto-anal junction. 2- Large ducts of glands. 3- Male urethra (penile part). Fig16: Stratified columnar non ciliated epithelium: 4- Stratified Cubical Epithelium: (Fig17) It is a rare type of epithelium which is formed of few layers of cells, may be only two layers of cubical cells as in ducts of sweat glands Fig17 INTRODUCTION TO BODY STRUCTURE 27 Definition: It is a type of epithelium which modifies to act as a gland & give secretion. Classification of glandular epithelium according to: 1-Presence or absence of duct: a) Exocrine gland (salivary glands): The exocrine gland is formed of secretory portion & duct system b) Endocrine gland, ductless gland,(thyroid gland): NO duct system. Their secretion is called hormones. Secretion is carried by blood. c) Mixed gland (pancreas): The gland is formed of two parts exocrine part & endocrine part 2-Number of cells forming the gland: a) Unicellular gland, formed of one cell (goblet cell) b) Multicellular glands formed of many cells (all glands) 3-Type of secretion: a) Watery secretion (Sweat gland) b) Serous secretion: The secretion is watery but contains enzymes e.g. parotid gland & pancreas. c) Mucous secretion: e.g. Salivary gland & goblet cells. d) Muco-serous secretion e.g. sublingual & submandibular gland. e) Fatty secretion e.g. sebaceous gland. f) Waxy secretion e.g. glands of external ear. h) Cellular secretion e.g. ovary (ova) &testis (sperms). 4-Mode (mechanism) of secretion: a) Merocrine secretion: The most common mechanism Secretion come out by exocytosis No changes in the cell e.g. pancreas. b) Apocrine secretion: The secretion is released surrounded by a part of cytoplasm & the cell membrane usually the apex of the cell INTRODUCTION TO BODY STRUCTURE 28 e.g. mammary gland & some sweat glands. c) Holocrine secretion: The secretion accumulates within the cell. The swollen cell ruptures & secretions come out with the cell components e.g. sebaceous glands. 5-Branching of the duct: a) Simple gland: The gland has a single non branching duct. b) Simple branched gland: The gland has a single non branching duct & a branched secretory portion. c) Compound gland: The gland has a branching duct system. 6-Shape of secretory part: a) Tubular: Secretory part is in the form of a long tube b) Alveolar (acinar):- Secretory part is rounded or ball shape. c) Tubuloalveolar:- Secretory part is flask shape. N.B. Since all exocrine glands consist of a secretory part & a duct system so they are classified into: i) Tubular : - Simple tubular glands e.g. intestinal glands. - Simple branched tubular glands e.g. fundic glands of stomach - Simple coiled tubular e.g. sweat glands. - Compound tubular glands e.g. kidney, liver ii) Alveolar: - Simple alveolar glands e.g. sebaceous glands. - Simple branched alveolar glands e.g. sebaceous glands. - Compound alveolar glands e.g. mammary gland iii) Tubulo-alveolar: - Simple tubulo-alveolar gland, not present in man. - Simple branched tubulo-alveolar glands e.g. lingual, labial glands (minor salivary glands). - Compound tubulo-alveolar glands e.g. major salivary glands (parotid) & pancreas. INTRODUCTION TO BODY STRUCTURE 29 III-NEURO-EPITHELIUM Definition: It is a specialized type of epithelium. It acts as a receptor. It consists of three types of cells Hair cells which receive sensation. Supporting cells for support Basal cells act as stem cells for regeneration. 1-Taste buds (Fig 17) in the tongue for taste sensation. 2-Organ of Corti in the ear for hearing. Fig17 Tast buds IV-MYO-EPITHELIUM Definition: It is a special type of epithelium, which has a contractile function The myo-epithelial cells are present around the base of secretory cells Between the cells & the basement membrane When they contract, they squeeze the secretory cells Help them to evacuate their secretion inducts of glands e.g. around salivary glands, mammary gland & sweat glands. INTRODUCTION TO BODY STRUCTURE 30 Cell polarity [Specializations] Cell modifications I. Apical Modifications 1- Microvilli :(Fig 18) - Finger like projections from the cell Membrane. - L.M: apical brush border. - EM: have a core of actin filaments which maintain its shape & help shortening & elongation of microvilli. - Site & function: Increase the apical surface area for absorption e.g., in small intestine Fig.18 2- Stereocilia: (solid= non- motile): (Fig:19) - Not true cilia but long microvilli. - L.M: hairlike processes from the free surface of some cells. - E.M: Have a core of actin filaments. - Function & Site: help absorption e.g. epididymis. Fig19: showing stereocilia of epididymis 3- Cilia: - L.M: hairlike processes which arise from the free surface of some cells. - E.M: have a core of 20 microtubules arranged as 9 peripheral doublets & 2 central singlets covered with cell membrane. - Function & sites: Their rhythmic beating propels fluids or particles in one direction e.g. trachea, bronchi & Fallopian tube. INTRODUCTION TO BODY STRUCTURE 31 4- Flagella: (Fig:20) The flagellum is an extra-long cilium that forms the tail of sperm & helps its movements. Fig:20 Flagella II. Lateral specializations= Cell junctions 1] Tight junction: a- Zonnula Occludens: (Fig 21) The 2 adjacent cell Membranes fuse completely at certain points to prevent passage of any substance between cells. It surrounds the apex of the cell like a belt. Fig:21 b- Fascia Occludens: It is patchy fusion of the 2 cell membranes (not like a belt) e.g. between endothelial cells. 2] Adherens junction= zonula adherens: - The 2 adjacent cell membranes are separated by a wide space (20nm) filled with adhesive cell coat material with condensed actin filaments at the cytoplasmic side. It surrounds the cell like a belt Function: It fixes adjacent cells & prevents their separation. INTRODUCTION TO BODY STRUCTURE 32 3] Macula Adherens= Desmosome Fig:22 - The 2 adjacent cell membranes are separated by a very wide space (30 nm) filled with adhesive substance. The cytoplasmic side is thickened forming attachment plates in which tonofilaments are inserted forming hair pin- like loops. It does not encircle the cell but appears as spot. Function: Strongest type fixes epithelial cells e.g. in skin. Fig:22 Desmosomes 4] Gap junction: [Communicating J.] = nexus.(Fig:23) - The 2 adjacent cell membranes are separated by a very narrow gap (2nm) but connected by narrow channels. - Function: allows passage of ions or impulses from one cell to the other e.g. cardiac &smooth muscles. N.B. If more than one junction is present between adjacent cells e.g. cells of small intestine it is called junctional complex. Fig:23 Gap junction INTRODUCTION TO BODY STRUCTURE 33 III. Basal specializations 1] Hemidesmosome 1/2 a desmosome at the basal part of basal cells. It fixes epithelium to basement membrane & connective tissue 2] Basement membrane: The membrane that connects epithelium to connective tissue. L.M: Red line (by PAS) or brown (by AG). It is either clear (thick) as in skin OR non- clear (thin) as in transitional epithelium. E.M: 2 components 1-Basal lamina formed mainly by the cell coat of epithelium (glycoprotein) &collagen fibers (IV) 2-Reticular lamina : consists of reticular fibers (type III collagen) & glycoprotein. - Functions: 1- Supports epithelium. 2- Fixes epithelium to connective tissue. 3- Controls passage of ions & nutrients e.g. kidney & lung. 3] Basal Infoldings: (Fig:24) The basal cell membrane shows invaginations Dividing the base of the cell into compartments Contain mitochondria to give energy for active transport of ions e.g. in kidney tubules. Fig:24 Basal infoldings