Comprehensive Study Notes on Cell Junctions, Glands, Membranes, and Tissue Repair

Tight Junctions

Impermeable or semi-impermeable barriers between adjacent epithelial cells that prevent molecules and fluids from leaking between cells.

Desmosomes

Anchoring junctions that act like mechanical rivets, holding adjacent cells together to withstand physical stress and mechanical tension.

Gap Junctions

Specialized transmembrane channels connecting the cytoplasm of adjacent cells to allow free movement of fluids, ions, and small molecules.

Endocrine Glands

Ductless glands that secrete hormones directly into surrounding interstitial fluid to diffuse into the bloodstream for transport.

Exocrine Glands

Glands that release their products directly onto internal or external epithelial surfaces, often through duct systems.

Goblet Cell

The principal unicellular exocrine gland that synthesizes and secretes protective mucus.

Merocrine Secretion

The most common secretory mode where products are released via exocytosis from membrane-bound vesicles without damaging the host cell.

Holocrine Secretion

A secretory mode where the cell accumulates products until it bursts (undergoes total lysis), destroying the cell and releasing all cellular contents.

Apocrine Secretion

A secretory mode where accumulated products in the apical region are released by pinching off the apical membrane, after which the cell repairs itself.

Cutaneous Membrane

The skin; a dry membrane composed of a keratinized stratified squamous epithelium anchored to dense irregular connective tissue.

Mucous Membrane (Mucosa)

A wet membrane lining internal body passages open to the external environment, rich in mucus-secreting cells.

Serous Membrane (Serosa)

A wet membrane lining closed internal body cavities, producing watery fluid to minimize friction between organs.

Synovial Membrane

A membrane composed of connective tissue that lines fibrous joint cavities and secretes lubricating synovial fluid.

Hyperplasia

Tissue growth achieved through an increase in the total number of cells via active cell division (mitosis).

Hypertrophy

Tissue growth achieved through an increase in the size of existing individual cells without increasing overall cell count.

Regeneration

The replacement of damaged or dead tissue with the exact same functional cell type, fully restoring original organ structure and function.

Fibrosis

The replacement of damaged functional tissue with non-functional collagenous scar tissue, resulting in permanent loss of original function in that area.

Granulation Tissue

A delicate, highly vascularized collagenous matrix formed during wound healing by active fibroblasts and newly sprouted capillaries.

Atrophy

The reduction in total tissue size or volume due to a decrease in cell size or cell count.

Necrosis

Pathological, unprogrammed cell or tissue death resulting from irreversible external injury, trauma, ischemia, or toxins, causing inflammation.

Apoptosis

Programmed, genetically regulated cell death that cleanly removes aging or damaged cells without triggering inflammation.