Chapter 2 Epithelium PDF

EPITHELIUM DR/ Ghada Mohamed 2024- 2025  Chapter 2 Epithelium ❖ General characters of epithelial tissue: 1. Develop from ectoderm, mesoderm or endoderm. 2....

EPITHELIUM DR/ Ghada Mohamed 2024- 2025  Chapter 2 Epithelium ❖ General characters of epithelial tissue: 1. Develop from ectoderm, mesoderm or endoderm. 2. Epithelial cells rest on basement membrane which may be clear or non-clear. 3. Consist of numerous crowded cells with minimal intercellular spaces between cells. 4. No blood vessels can enter between epithelial cells, so epithelial tissue is avascular tissue 5. nerves can pass between cells. 6. It receives nutrition by diffusion from underlying C.T. 7. It can regenerate in a short time (Highly regeneration power). ❖ Types of Epithelium a) Cells may form continuous sheet which cover surfaces or lines cavities →called surface epithelium. b) Cells may give secretion →called glandular epithelium c) Cells may receive sensation →called neuroepithelium d) Cells have contractile function →myoepithelium Surface epithelium ❖ Its classified according to numbers of layers into: - Simple →formed of one layer - Stratified→formed of more than one layer a- Simple epithelium Definition→ It formed of one layer of cells resting on basement membrane. It divides according to shape of cells into 1. Simple squamous epithelium 2. Simple cubical epithelium 3. Simple columnar epithelium 4. Pseudo-stratified columnar epithelium. Types 1-Simple squamous 2-Simple cubical 3-Simple columnar 4- Simple columnar ciliated Formed One layer One layer One layer One layer of Flat cell Cube shaped Tall cells Tall cells Flat N Round N Basal oval N Basal oval N Cilia Character Form XXXXXX - Smooth - Thin layer Functions - Important for Important for Important for - Movement a- Easy movement a- Secretion a- Secretion b- Exchange of b- Reabsorption b- Absorption gases and fluids 1 Sites 1. Pleura, pericardium, 1) Thyroid follicles 1- Stomach 1- Female genital peritoneum→called 2) Acini & small ducts (secretion). system mesothelium of all exocrine 2- Intestine 2- Lower Respiratory 2. Blood vessels and glands. e.g.: salivary (absorption & Tract heart →called glands secretion). endothelium 3) Convoluted tubules In intestine → have 3. Lung alveoli of kidney. microvilli & goblet 4. Bowman’s capsule cells of kidney (filtration of body ) 5- Pseudo-stratified columnar Epi: It is a simple epithelium as all the cells rest on the B.M. It is formed of a) crowded cells some cells are tall with central nuclei & others are short with basal nuclei. b) Nuclei are present at more than one level o This gives the epithelium a false appearance of being stratified. Types Pseudo- St. Col non- Pseudo- St. Col with motile cilia Pseudo- St. Col with non-motile ciliated epithelium & goblet cells: cilia (stereocilia): Sites Vas deferens Upper respiratory tract Epididymis. Male urethra (Nose, trachea & bronchi). b- Stratified epithelium Definition→ It formed of more than one layer of cells It divides according to shape of cells of top layer into Types 1-St. squamous Epi 2-Transitional (uroepithelium) No 5-30 Relaxed (Empty) → 6-8 Full → 3- 4 + cells flatter 2 BM Clear+ wavy Non clear + non wavy Basal layer Columnar + basal oval N Cuboidal cell Intermediate Polyhedral + central round N Polyhedral + central round N layer Crowded + small spaces Non crowded + wide spaces+ mucous Joined together by Desmosomes No desmosomes Top layer Flat cell + flat N Dome shaped cells + may be binucleated + mucous on the surface Sites Keratinized St. squamous → skin + Ureter + urinary bladder ear Non- Keratinized St. Squamous→ oral cavity + cornea+ esophagus Functions Protection 4- Stratified columnar Epi. 5- Stratified cubical Epi. Cells Similar St. squamous but - Rare Tupe - Less number of layers. - Formed of Two layers of cube shaped - Top layer columnar cells. cells Sites a) Stratified columnar ciliated epithelium: Sweat gland Foetal oesophagus b) Stratified columnar non ciliated epithelium: Recto-anal junction. Large ducts of glands. Male urethra (penile part). 3