Tissues and Membranes - Study Notes

Tissue Membranes

  • Thin layers of cells covering body surfaces, organs, internal passageways, and joint cavities.

  • 22 types: connective tissue membranes and epithelial membranes.

  • Mucous membranes: Line digestive, respiratory, urinary, and reproductive tracts; coated with mucus.

  • Serous membranes: Line body cavities closed to the exterior (peritoneal, pleural, pericardial).

  • Cutaneous membrane: Skin, covers body surface.

  • Synovial membranes: Line joint cavities, produce synovial fluid.

Embryonic Origin of Tissues

  • Zygote forms after fertilization; first embryonic cells are totipotent.

  • Germ layers (33 in number) differentiate:

    • Ectoderm: Gives rise to epidermis, nervous system, glands on skin, some bones (e.g., Skin cells, Neurons).

    • Mesoderm: Gives rise to connective tissues (bone, cartilage, blood), muscle, endothelium, kidneys, serous membranes (e.g., Muscle types, Red blood cells).

    • Endoderm: Gives rise to lining of airways/digestive system, and glands (e.g., Lung cells, Thyroid cells, Pancreatic cells).

Four Types of Tissues

  • Group of cells with common embryonic origin and shared morphological features, supporting function.

  • 44 broad categories:

    • Epithelial tissue: Covers surfaces, lines cavities, forms glands.

    • Connective tissue: Binds, protects, supports body parts.

    • Muscle tissue: Excitable, contracts for movement (skeletal, smooth, cardiac).

    • Nervous tissue: Excitable, propagates electrochemical signals.

Connective Tissue Membranes

  • Formed solely from connective tissue; encapsulate organs and line movable joints.

  • Synovial membranes: Line freely movable joint cavities. Fibroblasts release hyaluronan, forming synovial fluid for lubrication.

Epithelial Membranes

  • Composed of epithelium attached to connective tissue.

  • Mucous membranes (mucosae): Line passageways open to external environment (e.g., digestive tract). Mucus covers epithelium; underlying connective tissue is lamina propria.

  • Serous membranes: Mesothelium supported by connective tissue. Line coelomic cavities (closed to outside) and cover organs. Secrete serous fluid for lubrication.

    • Located in thoracic cavity (pleurae, pericardium) and abdominal cavity (peritoneum).

  • Cutaneous membrane (skin): Stratified squamous epithelium with dead, keratinized cells for protection.