Body Membranes and Tissue Repair

Overview

This lecture covers body membranes, their types, structures, functions, and how different tissues repair themselves after injury.

Membranes are thin sheets composed of one or more tissue types lining body surfaces or cavities.
Most membranes have an epithelial layer, a connective tissue layer, and sometimes a smooth muscle layer.
Membranes serve roles in anchoring organs, creating barriers, aiding immunity, and secretion.

True membranes do not open to the body's exterior and are found internally.
Serous membranes (serosa) line internal cavities (pericardial, peritoneal, pleural) and have mesothelium (simple squamous epithelium), basement membrane, and connective tissue.
Mesothelial cells produce serous fluid to reduce friction between moving organs and their surrounding membranes.
Serous membranes have a parietal layer (lining body cavity) and a visceral layer (covering organ); serous fluid lies between them.
Synovial membranes line cavities around movable joints (e.g., knee, shoulder), consist only of connective tissue, and contain synoviocytes that secrete lubricating synovial fluid; lack epithelial cells.

Cutaneous membrane is the skin, composed of an outer epidermis (keratinized stratified squamous epithelium) and a deeper dermis (loose and dense irregular connective tissue).
Mucous membranes (mucosa) line body surfaces that open to the exterior; include epithelial layer with goblet cells (mucus-secreting), and underlying lamina propria (connective tissue).

Tissue repair depends on the cells' ability to undergo mitosis (cell division).
Regeneration replaces damaged cells with the same type, restoring function.
Fibrosis replaces dead cells with dense irregular connective (scar) tissue; function is not fully restored.

Epithelial tissue repairs by regeneration.
Most connective tissues regenerate; cartilage heals by fibrosis.
Smooth muscle usually regenerates; skeletal muscle tends to heal by fibrosis (some limited regeneration); cardiac muscle heals by fibrosis only.
Nervous tissue (neurons) repairs by fibrosis; neuroglial cells can regenerate.

Nutrition and adequate blood supply are essential for regeneration even in tissues capable of mitosis.

Membrane — Thin sheet of tissue lining body surfaces or cavities.
Serous membrane (serosa) — Membrane lining internal cavities, secreting serous fluid.
Synovial membrane — Membrane lining joint cavities, secreting synovial fluid.
Cutaneous membrane — The skin.
Mucous membrane (mucosa) — Membrane lining surfaces opening to the exterior, secreting mucus.
Regeneration — Replacement of damaged cells with identical cells.
Fibrosis — Repair via scar tissue (dense irregular connective tissue).
Mesothelium — Simple squamous epithelial layer of serous membranes.
Goblet cell — Unicellular gland secreting mucus.