Epithelial Tissue PDF 2024-2025

Faculty of Veterinary Medicine Course name: Histology A EPITHELIAL TISSUE Dr/ Amel Marzouk Professor of Histology 2024-2025  EPITHELIAL TISSUE Learning Objectives:  List the basic types of tissues in the body.  Enumerate the g...

Faculty of Veterinary Medicine Course name: Histology A EPITHELIAL TISSUE Dr/ Amel Marzouk Professor of Histology 2024-2025  EPITHELIAL TISSUE Learning Objectives:  List the basic types of tissues in the body.  Enumerate the general characters of epithelial tissue.  Mention the specializations of lateral cell surfaces (intercellular junctions). Mention the specializations of apical cell surfaces.  Identify the structure & functions of basement membrane.  List the main types of epithelial tissue.  Enumerate the types of covering & lining epithelium & glandular epithelium.  1. Epithelial tissue Basic Types 2. Connective tissue of Tissues 3. Muscular tissue 4. Nervous tissue  EPITHELIAL TISSUE General Characters of Epithelial Tissue: 1. Epithelial tissue is formed of closely aggregated cells that adhere strongly to one another by intercellular junctions, and small amount of extracellular matrix (ECM). 2. The basal surface of epithelia adheres strongly to basement membrane which attaches the epithelial tissue to the underlying connective tissue. 3. Epithelial tissue is avascular (=no blood vessels enter the epithelia). 4. Nerve fibers normally enter the epithelia.  Specializations of Lateral Cell Surface (Intercellular Junctions) a- Tight Junctions (= occluding junctions): form a seal between cells. b- Anchoring Junctions: are sites of strong adhesion between cells. They include: 1. Zonula adherens. 2. Desmosomes. c- Gap Junctions (= communicating junctions): are channels for communication between cells. Intercellular Junctions  Specializations of Apical Cell Surface 1- Microvilli: increase apical surface area of the cell for absorption. 2- Cilia: are motile apical structures to move substances along the epithelial surface.  Basement Membrane - With L.M: It is a thin layer of extracellular matrix (ECM) that lies between the epithelium and the underlying connective tissue. Basement Membrane (Continued) - With E.M: It is formed of two parts: 1. Basal lamina. 2. Reticular lamina. - Function: 1- Diffusion of nutrients for epithelial cells. 2- Support for the epithelial cells. Let’s Think A. What is the thin layer of extracellular matrix between the epithelium and the underlying connective tissue (label I):………… B. Enumerate its parts (labels a & b): a-…………………………..… b-…………………..……….….. C. Enumerate its functions: 1-…………….…. 2-……..………… Types of Epithelial Tissue a- Covering &lining epithelium are sheets of cells covering all surfaces &lining all cavities in the body. b- Glandular epithelium are clusters of cells specialized for secretion, forming glands. c- Neuroepithelium (or sensory epithelium) are specialized sensory cells as in taste buds. d- Myoepithelium are specialized contractile cells.  Covering & Lining Epithelium Simple Epithelium Stratified Epithelium Formed of one layer of cells Formed of more than one 1- simple squamous ep. layer of cells 2- simple cuboidal ep. 1- stratified squamous ep. 3- simple columnar ep. 2- stratified columnar ep. 4- pseudostratified columnar ep. 3- transitional ep.  I- Simple Epithelium 1. Simple squamous epithelium Structure: Formed of one layer of flat cells with flat nuclei. Site: lining blood vessels. 2. Simple Cuboidal epithelium Structure: Formed of one layer of cubical cells with rounded nuclei. Site: lining renal tubules. 3. Simple Columnar epithelium Structure: Formed of one layer of tall cells with oval nuclei. Site: lining the gall bladder. 4. Pseudostratified Columnar epithelium Structure: Formed of one layer of tall & short cells with their nuclei at different levels. Site: lining the trachea. II- Stratified Epithelium 1- Stratified Squamous Epithelium (St. Sq. Ep.) Structure: Formed of several layers of cells, the superficial cells are St sq non-keratinized epithelium squamous. Site: It has two types: 1. St. sq. non keratinized ep. lines the esophagus. 2 St. sq. keratinized ep. covers the skin. St sq keratinized epithelium 2. Transitional epithelium Structure: Formed of several layers of cells, the superficial cells are large dome-like cells. Site: It lines the urinary bladder.  Glandular Epithelium Classification of Glandular Epithelium: a. According to presence or absence of ducts: 1. Exocrine glands: have ducts that carry their secretion to the surface of the epithelium, e.g. salivary glands. 2. Endocrine glands: are ductless glands (=have no ducts). They secrete hormones directly into blood, e.g. pituitary gland.  Types of Exocrine glands Exocrine glands are classified according to: I- Nature of secretion: 1. Serous glands: secrete watery secretion rich in enzymes e.g. parotid salivary gland & pancreatic acini. 2. Mucous glands: secrete viscid mucous secretion e.g. esophageal glands. 3. Sero-mucous glands: secrete serous & mucous secretion e.g. sublingual and submandibular salivary glands.  Types of Exocrine glands According to Nature of secretion Serous gland Mucous gland Sero-mucous gland  Types of Exocrine glands (Continued) Exocrine glands are classified according to: II. Mechanism of secretion: 1. Merocrine glands: -Secretion by exocytosis. -No part of the cell is lost during secretion. -e.g. salivary glands. 2. Apocrine glands: -Secretion by extrusion of portions of the cell apex. -Apical part of the cell is lost during secretion. -e.g. mammary glands. 3. Holocrine glands: -Secretion by disintegration of the secretory cell. -All the cell is lost during secretion. -e.g. sebaceous glands. What is the type of Gland in A, B & C  Enumerate: 1. General characters of epithelial tissue. 2. Types of intercellular junctions. 3. Apical cell specializations. 4. Parts of basement membrane. 5. Functions of basement membrane. 6. Types of simple epithelium. 7. Types of stratified epithelium. 8. Types of exocrine glands according to nature of secretion. 9. Types of exocrine glands according to mechanism of secretion.  Complete: 1. The basement membrane is formed …..………&…………… 2. The urinary bladder is lined by …………….……epithelium. 3. The trachea is lined by …………………...….……epithelium. 4. ……………. is an apical cell specialization that increases apical surface area of the cell. 5. ……………. is an example of holocrine glands. 6. ……………. is an example of mucous glands. 7. ……………. is an example of serous glands. 8. Stratified squamous keratinized epithelium covers the ……..  Choose the correct answer: 1- Which of the following is a general character of epithelial tissue? A. Contains blood vessels. B. Has abundant extracellular matrix. C. Has NO nerve fibers. D. Formed of closely aggregated cells. 2- Submandibular salivary glands are: A. Serous glands. B. Mucous glands. C. Sero-mucous glands. D. Endocrine glands. 3- Salivary glands are: A. Endocrine glands. B. Apocrine glands. C. Holocrine glands. D. Merocrine glands. 4- Which of the following types of epithelia lines blood vessels? A. Simple squamous. B. Simple cuboidal. C. Simple columnar. D. Pseudostratified columnar. 5- Which of the following junctions form a seal between cells? A. Tight junction. B. Desmosome. C. Gap junction. D. Zonula adherens. 6- Which of the followings are motile apical cell structures? A. Microvilli. B. Cilia. C. Tight junction. D. Basement membrane.  Lecture References - Junqueira's Basic Histology: Text and Atlas 17th Edition. Thank you