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Epithelial Tissues Vinyas (2).pptxnajsjjs
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- 2. Epithelial Tissues Epithelial tissueconsists of cells arranged in continuous sheets, in either single or multiple layers. Closely packed and held tightly together, it covers and lines the body with a free surface. It has three major functions: • Selective barrier that regulates the movement of materials in and out of the body. • Secretory surfaces that release products onto the free surface. • Protective surfaces against the environment.
- 3. General Features ofEpithelial Cells The surfaces of epithelial cells differ in structure and have specialized functions: • Apical (free) surface: Faces the body surface, body cavity, lumen, or duct. • Lateral surfaces: Faces adjacent cells. • Basal surface: Opposite of the apical layer and adheres to extracellular materials.
- 4. Basement Membrane • Thebasement membrane is a thin double extracellular layer that serves as the point of attachment and support for overlying epithelial tissue. • Basal lamina: Closer to and secreted by the epithelial cells; contains laminin, collagen, glycoproteins, and proteoglycans. • Reticular lamina: Closer to the underlying connective tissue; contains collagen secreted by connective tissue cells.
- 5. Epithelial Cells • Ownnerve supply: Epithelial tissue has its own nerve supply. • Avascular: Lacks its own blood supply; blood vessels in the connective tissue bring in nutrients and eliminate waste. • High rate of cell division: Allows for renewal and repair. • Numerous roles: Includes protection and filtration. • Covering and lining epithelium: Outer covering of the skin and some internal organs. • Glandular epithelium: Secreting portion of glands (thyroid, adrenal, and sweat glands).
- 6. Covering and LiningEpithelium Normally classified according to: • Arrangement of cells into layers. • Shapes of cells.
- 7. Arrangement of Cellsin Layers •Simple epithelium: Single layer of cells that function in diffusion, osmosis, filtration, secretion, or absorption. •Pseudostratified epithelium: Appears to have multiple layers because cell nuclei are at different levels; not all cells reach the apical surface. •Stratified epithelium: Two or more layers of cells that protect underlying tissues in areas of wear and tear.
- 8. Different Types ofCovering and Lining Epithelium • Cells vary in shape depending on their function: • Squamous: Thin cells, arranged like floor tiles; allows for rapid passage of substances. • Cuboidal: As tall as they are wide, shaped like cubes or hexagons; may have microvilli; function in secretion or absorption. • Columnar: Much taller than they are wide, like columns; may have cilia or microvilli; specialized function for secretion and absorption. • Transitional: Cells change shape, transition from flat to cuboidal; organs such as the urinary bladder stretch to a larger size and collapse to a smaller size.
- 9. Simple Epithelium •Simple squamousepithelium: Single layer of cells that resembles a tiled floor on the surface; nucleus is centrally located and appears flattened oval or sphere; found at sites for filtration or diffusion. •Endothelium: Lines the heart, blood vessels, and lymphatic vessels. •Mesothelium: Epithelial layer of serous membranes such as the pericardium, pleura, or peritoneum.
- 10. Simple Cuboidal Epithelium •Cuboidal shaped cells with round and centrally located nuclei. Found in the thyroid gland and kidneys, functions in secretion and absorption.
- 11. Simple Columnar Epithelium •Nonciliated simple columnar epithelium: Contains columnar cells with microvilli at their apical surface and goblet cells; secreted mucus serves as a lubricant for the lining of digestive, respiratory, reproductive, and urinary tracts; prevents the destruction of the stomach lining by acidic gastric juices. • Ciliated simple columnar epithelium: Columnar epithelial cells with cilia at the apical surface; in the respiratory tract, goblet cells are interspersed among ciliated columnar epithelia; secreted mucus on the surface traps inhaled foreign particles; beating cilia move particles to the throat for removal by coughing, swallowing, or sneezing; cilia also move oocytes to the uterine tubes.
- 12. Pseudostratified Columnar Epithelium •Appears to have several layers due to nuclei at various depths. • All cells are attached to the basement membrane in a single layer, but some do not extend to the apical surface. • Ciliated cells secrete mucus and bear cilia; nonciliated cells lack cilia and goblet cells.
- 13. Stratified Epithelium • Twoor more layers of cells. The specific kind of stratified epithelium depends on the shape of cells in the apical layer: • Stratified squamous epithelium: Several layers of cells that are flat in the apical layer; new cells are pushed up toward the apical layer; as cells move further from the blood supply, they dehydrate, harden, and die. • Keratinized form: Contains the fibrous protein keratin; found in superficial layers of the skin. • Nonkeratinized form: Does not contain keratin; found in the mouth and esophagus.
- 14. •Stratified cuboidal epithelium:Fairly rare; apical layers are cuboidal; functions in protection. •Stratified columnar epithelium: Very uncommon; columnar cells in the apical layer only; basal layers have shortened, irregular-shaped cells; functions in protection and secretion. •Transitional epithelium: Found only in the urinary system; variable appearance; in a relaxed state, cells appear cuboidal; upon stretching, cells become flattened and appear squamous; ideal for hollow structures subjected to expansion.
- 15. Glandular Epithelium • Endocrineglands: Secretions, called hormones, diffuse directly into the bloodstream; function in maintaining homeostasis. • Exocrine glands: Secrete products into ducts that empty onto the surfaces of epithelium; secretions include mucus, sweat, oil, earwax, saliva, and digestive enzymes.
- 16. Structural Classification ofExocrine Glands • Multicellular glands are categorized according to two criteria: • Ducts: Branched or unbranched. • Shape of the secretory portion of the gland: • Simple gland: Duct does not branch. • Compound gland: Duct branches. • Tubular glands: Have tubular secretory parts. • Acinar glands: Have rounded secretory parts. • Tubuloacinar glands: Have both tubular and rounded secretory parts.
- 17. Connective Tissue • Mostabundant and widely distributed tissues in the body; has numerous functions, including binding tissues together, supporting and strengthening tissue, protecting and insulating internal organs, compartmentalizing and transporting, and serving as energy reserves and immune responses.
- 18. Characteristics of ConnectiveTissue • Three characteristics of connective tissue: • Extracellular matrix • Fibers • Cells of various types
- 19. Extracellular Matrix ofConnective Tissue • The extracellular matrix is the material located between the cells. • It consists of protein fibers and ground substance. • Connective tissue is highly vascular and supplied with nerves. • Exceptions are cartilage and tendons, which have little or no blood supply and no nerves.
- 20. Connective Tissue Cells •Fibroblasts:Secrete fibers and components of ground substance. •Adipocytes (fat cells): Store triglycerides (fat). •Mast cells: Produce histamine. •White blood cells: Involved in immune response (e.g., neutrophils and eosinophils). •Macrophages: Engulf bacteria and cellular debris by phagocytosis. •Plasma cells: Secrete antibodies.
- 21. Connective Tissue ExtracellularMatrix • Ground substance: Located between cells and fibers; can be fluid, semifluid, gelatinous, or calcified; functions to support and bind cells, store water, and allow exchange between blood and cells. • Fibers: Include collagen fibers, elastic fibers, and reticular fibers.
- 22. Classification of ConnectiveTissues •Embryonic connective tissue: Includes mesenchyme and mucous connective tissue. •Mature connective tissue: •Loose connective tissue: Areolar, adipose, and reticular. •Dense connective tissue: Dense regular, dense irregular, and elastic. •Cartilage: Hyaline, fibrocartilage, and elastic cartilage. •Bone tissue •Liquid connective tissue: Blood and lymph.
- 24. Embryonic Connective Tissue •Mesenchyme:Gives rise to all other connective tissues. •Mucous (Wharton’s Jelly): Found in the umbilical cord of the fetus.
- 25. Loose Connective Tissue •- Areolar Tissue: Most widely distributed, contains multiple cell types and fibers. - Adipose Tissue: Contains adipocytes, provides insulation and energy reserves (white and brown types). - Reticular Tissue: Contains fine reticular fibers, forms stroma of liver, spleen, lymph nodes.
- 26. Dense Connective Tissue •- Dense Regular Tissue: Collagen fibers arranged in parallel for strength, found in tendons and ligaments. - Dense Irregular Tissue: Collagen fibers arranged irregularly, withstands pulling forces in multiple directions, found in dermis and heart. - Elastic Tissue: Contains elastic fibers, can recoil after stretching, found in lung tissue and arteries.
- 27. Cartilage • - HyalineCartilage: Most abundant, provides flexibility, support, reduces friction, surrounded by perichondrium. • - Fibrocartilage: Strongest type, found in intervertebral discs, lacks perichondrium. • - Elastic Cartilage: Contains chondrocytes in a network of elastic fibers, provides strength and elasticity.
- 28. Bone Tissue • Composedof bone tissue, periosteum, and endosteum. - Compact Bone: Contains osteons (Haversian system). - Spongy Bone: Lacks osteons, has trabeculae (columns).
- 29. Liquid Connective Tissue •- Blood Tissue: Connective tissue with liquid matrix called blood plasma. - Lymph: Liquid connective tissue.
- 30. Epithelial Membranes • -Mucous Membranes: Line cavities opening to the exterior, protect against pathogens, contain lamina propria. - Serous Membranes: Line closed body cavities, secrete lubricating serous fluid, consist of mesothelium and areolar tissue. - Synovial Membranes: Line joints, contain connective tissue without epithelium.
- 31. Muscular Tissue • -Skeletal Muscle: Attached to bones, striated, voluntary movement. - Cardiac Muscle: Found in the heart, striated, involuntary movement, contains intercalated discs. - Smooth Muscle: Found in walls of hollow organs, non-striated, involuntary movement.
- 32. Nervous Tissue • -Composed of neurons and neuroglia. - Excitable Cells: Neurons and muscle fibers can respond to stimuli by generating electrical signals (action potentials), leading to neurotransmitter release or muscle contraction.
- 33. Tissue Repair &Aging • - Tissue repair involves fibroblasts, collagen fiber production, and formation of granulation tissue. - Tissues heal faster in young adults, fetal surgery typically leaves no scars. - Aging affects tissue repair and structure due to changes in glucose, collagen, and elastic fibers.