Epithelial Tissue (Part 1) PDF - Histology - Helwan University

HISTOLOGY BMS (I) Module Epithelial Tissue (Part 1) Prepared by Dr. Haitham Sewilam Lecturer of Histology Faculty of Medicine - Helwan University - Egypt  THE BODY TISSUES How body tissues are formed? ❖ One sperm fertilizes an ovum → single undiffere...

HISTOLOGY BMS (I) Module Epithelial Tissue (Part 1) Prepared by Dr. Haitham Sewilam Lecturer of Histology Faculty of Medicine - Helwan University - Egypt  THE BODY TISSUES How body tissues are formed? ❖ One sperm fertilizes an ovum → single undifferentiated cell termed zygote. ❖ Zygote undergoes successive mitotic divisions → morula → blastocyst having an inner cell mass (blastomere) and outer trophoblast.  ❖ The undifferentiated blastomere undergoes proliferation and differentiation to give rise to the differentiated cells of: ✓Ectoderm (skin & nervous tissue). ✓Mesoderm (muscle, connective tissue, bone, cartilage & blood). ✓Endoderm (respiratory & gastrointestinal systems). ✓Genito-urinary ridge (genital & urinary systems). ❖ The human body is composed of four basic tissues; each of them has its own structure and function. These tissues are: 1) Epithelial tissue: covers the body and lines its cavities from inside. 2) Connective tissue: connects, mainly, other tissues together. 3) Muscular tissue: responsible for movement. 4) Nervous tissue: responsible for transmission of nervous impulse.  Epithelium General characters: ❖It is formed of closely aggregated cells with little intercellular substance. ❖The epithelial cells rest on and are tightly adherent to a thin basement membrane which separates them from the underlying C.T. (lamina propria) ❖No blood vessels enter between the cells but nerves ramify between them. ❖Epithelium is subjected to continuous degeneration and regeneration. ❖It is derived from all the three germ layers.  Basement membrane It is the border which lies between the epithelial cells and underlying C.T. Nutrients must diffuse across the basement membrane. It provides structural support and allow repair & regeneration of epithelial cells Nerve fibers normally penetrate this structure but small blood capillaries normally never enter epithelia. Structure by E/M: Formed of two layers: a- basal lamina. b- reticular lamina. a- Basal lamina: (20- 100 nm thickness) formed of: i- Laminin: large glycoprotein molecules. ii-Type IV collagen: associated with the laminin layer. * All these components are synthesized by the epithelial cells and secreted from its basal sides b- Reticular lamina: formed of type III collagen (reticular fibers), synthesized by underlying connective tissue cells. Classification of Epithelium: Epithelium is classified according to its function into: I) Covering Epithelium: covers the body from outside and lines its cavities from inside. II) Glandular epithelium: specialized in production of secretions. III) Neuroepithelium: specialized in perception of sensory stimuli. I) Covering Epithelium: ❖ It can be classified according to the number of cell layers into: A- Simple Formed of one layer of cells lying on the basement membrane. B- Stratified Formed of many layers of cells, the first lie on the basement membrane. A- Simple Epithelium: It has four types: (1) Simple squamous epithelium: ❖ Formed of one layer of flat cells with flat bulging nuclei. ❖ Is found in the lining of the: ✓ Blood vessels (endothelium). ✓ The mesothelium of serous membranes as pleura , pericardium and peritoneum (2) Simple cubical epithelium: ❖ Formed of a single layer of cubical shaped cells with central rounded nuclei. ❖ It is found in the lining of the: ✓ Renal tubules. ✓Thyroid follicles (3) Simple columnar epithelium: ❖ Formed of a single layer of tall cells with basal oval nuclei. ❖ This type can be further sub-classified into: A- Non-modified simple columnar epithelium: * The columnar cells aren’t modified e.g. lining of large ducts of exocrine glands. B- Modified simple columnar epithelium: * The columnar cells acquire some modifications to perform additional functions. * It has three types (secretory, absorptive and ciliated). i. Simple columnar secretory epithelium: ✓ Specialized in production of mucous secretion. ✓ The cytoplasm is vacuolated. ✓ Example → lining of the stomach. ii. Simple columnar absorptive epithelium: ✓ Specialized in absorption of molecules as the apical surface of the columnar cells is provided with microvilli (brush border) to increase its surface area. ✓ Example → lining of the intestine iii. Simple columnar ciliated epithelium: ✓ Cilia project from the free surface of the cells. ✓ Example → lining of the fallopian tube and uterus. (4) Pseudostratified columnar epithelium: ❖ Formed of a single layer of cells which were crowded during development. ❖ As a result of crowding, some cells became short and squeezed between the bases of the tall ones. ❖ The nuclei appeared to be arranged in more than one level, so there is a false appearance for this epithelium to be stratified. ❖ This type of epithelium can be sub-classified into: a-Pseudostratified columnar non-ciliated epithelium: * The surface of the tall columnar cells is not provided with cilia e.g.: ✓ Lining of large ducts of exocrine glands. b-Pseudostratified columnar ciliated epithelium: The surface of the tall cells is provided with cilia e.g.: ✓ Lining of the nasal sinuses, trachea and bronchi. N.B: Some of the columnar cells in this type may be modified into mucous secreting cells (goblet cells) → pseudostratified columnar ciliated epithelium with goblet cells.