Histology Lecture 6 (Epithelium) PDF

EPITHELIUM By Dr. Dalia Abd El-Razik Noya Assistant Prof. of Histology Faculty of Medicine Menoufia University ILOS Identify the general histological characters of epithelial tissue. Classify the epithelial tissue. Identify simple &stratified epithelium and correlate...

EPITHELIUM By Dr. Dalia Abd El-Razik Noya Assistant Prof. of Histology Faculty of Medicine Menoufia University ILOS Identify the general histological characters of epithelial tissue. Classify the epithelial tissue. Identify simple &stratified epithelium and correlate each type to its function. Describe the glandular epithelium histology and it’s classifications. Differentiate neuro-epithelium and myo-epithelium from surface epithelium.  The basic tissues of the body The basic tissues of the body are: 1. Epithelial tissue. 2. Connective tissue. 3. Muscular tissue. 4. Nervous tissue.  1- General characters of epithelial tissue 1. It may be ectodermal , mesodermal or endodermal in origin 2. Crowded cells with minimum intercellular substance 3. Cells are resting on a basement membrane (B.M.). 4. No blood or lymph vessels can penetrate epithelial tissue (avascular tissue).It receives nutrition by diffusion from underlying connective tissue (C.T.) 5.It is highly innervated. 6.It has a high power of regeneration.  Classification of epithelial tissue I. Surface epithelium: formed of continuous sheets of epithelial cells which cover surfaces or line cavities. It is classified according to number of layers into: Simple (one layer) & Stratified(more than one layer). II.Glandular epithelium: formed of epithelial cells modified to give secretion III.Neuro-epithelium: formed of epithelial cells modified to receive stimuli IV.Myo-epithelium: formed of epithelial cells modified to be contractile  Functions of epithelial tissue 1.Protection 2.Secretion 3.Absorption 4.Excretion 5.Reproduction 6.Sensation 7.Contraction  I-Surface epithelium It is named according to: 1.Number of layers:  Simple epithelium : one layer  Stratified epithelium : several layers 2.Shape of cells on the top layer:  Squamous  Cubical  Columnar 3.Surface specializations:  Keratinized or not (with stratified squamous)  Ciliated or not (with columnar)  Simple squamous epithelium Type of epithelium Shape Sites Function 1. Simple Squamous Formed of one layer of Forms thin sheets & Forms thin & flat cells with flat nuclei looks like scales of fish smooth surface epithelium resting on basement from top view : facilitating : membrane a) Lining heart & blood a) Flow of fluids and lymphatic vessels & Easy (Endothelium) movement b) Lining serous due to membranes secretion of (Mesothelium) lubricating material c) Lining alveoli of b) Gas exchange lungs(Pneumocytes I) d) Lining Bowman’s c) Filtration & capsule of kidney diffusion  2.Simple cubical epithelium 2. Simple Cubical Formed of one layer a) Thyroid follicles. a) Secretion epithelium: of cube-like cells with central rounded nuclei resting on basement membrane  3.Simple columnar epithelium 3. Simple Columnar Formed of one layer o Stomach Secretion and epithelium: of tall cells with o Small & large absorption basal oval nuclei intestines resting on basement membrane  4. Simple columnar ciliated epithelium 4. Simple Columnar Formed of one layer  Uterus & Beating by ciliated epithelium: of tall cells provided Fallopian cilia fluid or with cilia & have tubes particles in basal oval nuclei.  Bronchioles one Resting on basement direction. membrane. 5. Pseudo-stratified columnar epithelium  5. Pseudo-stratified columnar epithelium 5. Pseudo-stratified Formed of :  Membranous protection columnar non ciliated Crowded cells, all are urethra epithelium: resting on the BM, so it is  Large ducts of simple epithelium. salivary glands Some cells are tall with central nuclei reaching the surface & other cells are short with basal nuclei and not reaching the surface Nuclei of cells appear at more than one level giving false impression of stratification (Pseudo = false)  6. Pseudo-stratified columnar ciliated with non-motile cilia (stereocilia) 6. Pseudo-stratified The stereocilia Male genital Protection columnar ciliated with are found to be system: non-motile cilia long microvilli  Vas (stereocilia): deferens  Epididymis  7.Pseudo-stratified columnar ciliated with goblet cells 7.Pseudo-stratified The cilia are true Respiratory Protection & columnar ciliated with &motile system: secretion goblet cells: Goblet cells are  Trachea Beating by cilia fluid mucous secreting cells  Bronchi or particles in one direction  Stratified epithelium It is formed of more than one layer of cells, the basal layer resting on B.M. The function of stratified epithelium is protection. It is divided according to shape & structure of cells in the top layer into:  1.Stratified squamous epithelium Type of epithelium Shape Sites 1. Stratified squamous  Formed of 5-30 layers of o Cornea epithelium: cells resting on clear & wavy o Esophagus B.M. divided into 2 subtypes  Basal cell layer is columnar a) Non keratinized Stratified with basal oval nuclei Squamous epithelium  Intermediate layers are polygonal crowded cells with minimal intercellular substance.  Top layer is formed of flat cells with flat nuclei.  This type of epithelium may be keratinized or not.  Stratified squamous epithelium b) keratinized Stratified The top layer is  Epidermis of skin Squamous epithelium covered with keratin scales.  2.Stratified cubical epithelium 2.Stratified cubical Formed of 2-3 Ducts of sweat epithelium: layers of glands cubical cells  3.Stratified columnar epithelium divided into 2 subtypes Similar to stratified  Penile urethra squamous epithelium, 1- Stratified columnar non but with few layers& ciliated epithelium the top layer is formed of columnar cells, which may be ciliated 2- Stratified columnar ciliated or not.  Fetal esophagus epithelium  4- Transitional epithelium It is a highly specialized type of stratified cuboidal epithelium. Lines the urinary bladder and ureter. Empty bladder:  4-8 layers of cells resting on non clear - non wavy B.M  Basal cells are cuboidal  Intermediate layers are polygonal with wide intercellular spaces containing mucous like substance , allowing gliding of cells  Superficial cells are large, rounded with convex free border & may be bi-nucleated  Transitional epithelium Full bladder Becomes 2-3 layers only due to gliding of cells over each other Cells in Superficial& intermediate become flattened.  II. Glandular epithelium Glandular epithelium can be classified according to: 1. Presence or absence of ducts. 2. Number of cells forming the gland 3. Nature (type) of secretion. 4. Mode (mechanism) of secretion.  1. Presence or absence of the duct Exocrine glands Endocrine glands Mixed glands Structure Formed of 2 components: Formed of 2 portions: Formed of 2 parts: a. Groups of secretory cells a. Secretory units exocrine part with pour their secretion into forming the secretion duct system b. Blood capillaries b. duct system to carry To reach blood stream & go &endocrine part the secretion from to target tissues which is ductless secretory units No duct system outside the gland Example Salivary glands Thyroid gland Pancreas Sweat glands Suprarenal glands liver  2. The number of cells forming the gland Unicellular gland Multicellular gland Formed of one cell Formed of several cells Goblet cell : All glands e.g. Salivary  Unicellular mucous secreting cells glands- Thyroid gland  Scattered in the epithelial lining of the digestive & respiratory systems  Flask shaped with slender base containing the nucleus and organelles &expanded apical part full of mucous granules  Mucous dissolves during H&E preparation & the apex of cell appears empty.  The mucous stained with PAS.  3.NATURE OF SECRETION Nature (type of secretion) Example Watery secretion Sweat gland Serous secretion Parotid gland Mucous secretion Sublingual salivary gland & Mucoserous secretion Submandibular salivary gland Fatty secretion Sebaceous gland Waxy secretion Glands of external ear Cellular secretion Ovary & testis  3.NATURE OF SECRETION Serous acinus Mucous acinus Diameter small large Lumen narrow wide Secretion Watery secretion containing enzymes Viscid Mucous secretion Lining Cells  Dark basophilic pyramidal cells  Pale basophilic cuboidal cells  with indistinct cell boundaries  with distinct cell boundaries  Granular cytoplasm  vacuolated cytoplasm  single rounded nearly central nucleus  Single flattened basal nucleus Myoepithelial cells few Numerous (Basket cells) (to squeeze viscid secretion)  4.Mode of secretion Merocrine Apocrine Holocrine The cells are not The apical parts of cells Whole cells are destroyed during the are destroyed duing destroyed during secretion secretion process of secretion Salivary glands Mammary glands Sebaceous glands  III. Neuro-epithelium  It is a specialized type of epithelial tissue, formed of cells modified to receive stimuli  It consists of 3 types of cells: hair cells for perception of stimuli, provided at its base with nerve endings, tall columnar cells for support & short basal cells.  Neuroe-pithelium site type Sensation 1-Tongue Taste buds Taste 2-Nose Olfactory epithelium Smell  IV: Myo-epithelium  It is a specialized type of epithelial tissue, formed of cells modified to be contractile ( contain abundant actin filaments in the cytoplasm).  They are present around secretory cells, between the base of cells & the basement membrane  Function: help secretory cells to squeeze & evacuate the secretion & called basket cells.  Sites: salivary & mammary glands THANK YOU