Epithelial Tissue PDF

# Epithelia Tissue ## An Epithelium is a cohesive sheet of cells that: 1. **Covers the external surfaces and lines the internal surfaces of the body.** - **Barrier** - Protection (by withstanding wear and tear, from hydration and dehydration) - Selective absorption: (Control t...

# Epithelia Tissue ## An Epithelium is a cohesive sheet of cells that: 1. **Covers the external surfaces and lines the internal surfaces of the body.** - **Barrier** - Protection (by withstanding wear and tear, from hydration and dehydration) - Selective absorption: (Control the movement of substances between the outside environment and the internal compartments, or between compartments in the body.) - Transport (Ions, O2 and CO2) - Secretion (secretory cells) 2. **Forms endocrine and exocrine secretory glands.** - A diagram of an epithelial gland with a duct and secretory portion is included. ## Abdomen - Abdominal Wall and Intestines 1. **Skin** - Epidermis - **Epithelium** (stratified) - Dermis - Connective Tissue 2. **Superf. Fascia:** Hypodermis - Fatty Connective Tissue 3. **Deep Fascia:** Epimysium - Connective Tissue - A cross section illustration of the Abdomen showing the abdominal wall and intestines. Arrows point to: - 1. Skin - 2. Superf. Fascia - 3. Deep Fascia - 4. Intestinal Mucosa 4. **Intestinal Mucosa** - **Epithelium** (Simple) - Connective Tissue ## Epithelial Cells: 1. **Form avascular sheets that differ in number of cell layers, shape of the cells and structural specializations of the free (apical) cell surface, depending on the tissue function(s).** 2. **Are capable of renewal and regeneration.** - Non-specialized epithelium - all cells - Specialized epithelium - stem cells 3. **Are structurally and functionally polarized: Have apical, lateral and basal domains.** 4. **Are held together by several basolateral specializations, known as the intercellular junctions, and bind to the underlying connective tissue via the basement membrane (LM) or basal lamina (EM).** - A diagram shows a close-up of epithelial cells with an apical, lateral, and basal section: - Apical specialization - Junctional complex - Epithelial cells - Basement membrane - Connective tissue ## Classification of Epithelium **A diagram shows various epithelial cells and how they are classified (Simple and Stratified):** **Simple** - Squamous - Cuboidal - Columnar **Stratified** - Squamous - Transitional - Pseudostratified columnar (respiratory) ## Simple Squamous Epithelium - Composed of very thin flat irregular shaped cells that form a continuous surface. - Also called pavement epithelium. - Found in: - Lining of blood & lymph vessels - Alveoli of lungs - Parietal layer of Bowman’s - A diagram shows a close-up of a simple squamous epithelium, labeled with: BM (basement membrane) and E (epithelium) ## Simple Squamous Epithelium - Endothelium and mesothelium (non-specialized: renewal via mitosis) - A diagram shows a close-up of an endothelium and a mesothelium. - A diagram shows a cross-section of a simple squamous epithelium ## Simple Cuboidal Epithelium - Cells appear cube or box like. - Nucleus is rounded & placed in the center of the cell. - Cells rest on the basement membrane - Present in: - Follicles of thyroid gland - Distal convoluted tubules of kidney - **FUNCTION** - Absorption - A diagram shows a close-up of simple cuboidal epithelium. ## Simple Cuboidal Epithelium - Kidney tubules (“non-specialized:" renewal via mitosis) - A diagram shows a close-up of kidney tubules, labeled with: - Simple Cuboidal Epithelium - Simple cuboidal epithelium - Basal lamina - Lumen ## Simple Columnar Non-Ciliated Epithelium - Composed of tall columnar cells - Rests on basement membrane - Nucleus in elongated & lies in the basal half of the cell - Apical surface of cells may have microvilli which give appearance of brush border - **Found in:** - **Lining of GIT** - **FUNCTIONS:** - Absorption - Excretion - A diagram shows a close-up of simple columnar non-ciliated epithelium. ## Simple Columnar Epithelium - Gut mucosa (*"specialized:"* renewal via stem cells) - Striated Border - Goblet cells - A diagram shows a close-up of simple columnar epithelium, labeled with: - Lumen - Simple Columnar Epithelium - Striated Border - Goblet cells - Basal lamina - Goblet cell - Lumen - Brush Border ## Simple Columnar Ciliated Epithelium - **CILIA** present on the surface of simple columnar epithelium - Present in: - Small intrapulmonary bronchi - Simple columnar non-ciliated cells may be present between ciliated cells. - Example: - Uterine tube - Efferent ductules of testis - A diagram shows a close-up of Simple Columnar Ciliated Epithelium. ## Pseudostratified Epithelium - **NON-CILIATED** - **Variant** of simple columnar epithelium - Tall & short cells are present - All cells rest on the basement membrane - Nuclei disposed at different levels - Present in; - Parts of male urethra - A diagram shows a close-up of Pseudostratified Epithelium. ## Pseudostratified Epithelium - **CILIATED** - This epithelium may be ciliate with goblet cells. - Example: - Trachea - Larger bronchi - A diagram shows a close-up of Pseudostratified Epithelium, labeled with: - Mucus - Cilia - Terminal bars - Epithelial cell - Goblet cells - Basal cell - Basement membrane - Lamina propria ## Stratified Squamous Epithelium - **Non-keratinized** - Nucleated superficial squamous cells - Basal cell - Basal lamina - **Keratinized** - Highly keratinized cells of the superficial layer lack nuclei. - Basal cell - Basal lamina - A diagram shows a close-up of Stratified Squamous epithelium, labeled with non-keratinized and keratinized sections. ## Stratified Squamous Epithelium - **Non-Keratinized** - Lines esophagus, oral cavity, vagina.... - **Keratinized** - Lines thick and thin skin - A diagram shows a close-up of Stratified Squamous epithelium, labeled with non-keratinized and keratinized sections. ## Stratified Epithelia - **Stratified Squamous Non-Keratinize Epithelium** - Multi-layered - Basal layer low columnar or high cuboidal - This layer divides - Subsequent layers polygonal - Surface layers flattened - Underlying connective tissue raised into ridges - Examples - Oesophagus - Anal canal - Cervix - Vagina - A Diagram shows a close-up of Stratified Squamous Non-Keratinize Epithelium. ## Stratified Squamous Keratinized Epithelium - Features same as non-keratinized epithelium except - Surface layer composed of non-nucleated cells - They acquire protein keratin - Example - Skin - A Diagram shows a close-up of Stratified Squamous Keratinized Epithelium. ## Transitional Epithelium - **IN RELAXED STATE** - Is 4-5 cell layer thick - Basal layer is cuboidal - Intermediate layer is polyhedral - Surface layer is cuboidal with binucleate cells - **IN STRETCHED STATE** - Is 2-3 cell thick - Surface layer is squamous - Example - Urinary tract - A Diagram shows a close-up of Transitional Epithelium. ## Transitional Epithelium - (urothelium) - Lines the urinary tract, ureter, bladder and urethra - A Diagram shows a close-up of Transitional Epithelium with cells on the surface in dome (umbrella) shapes. ## Stratified Cuboidal - Consists of two layers of cuboidal cells - Cells of superficial layer are smaller - Examples: - Ducts of salivary glands - Ducts of sweat - A Diagram shows a close-up of Stratified Cuboidal.