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Histology

Histology. Other topics. Extracellular Junctions. Purpose: to allow cells to function as a unit (the definition of a tissue). They are connections along the lateral and basal sides of cells of a tissue. These connections allow cells to chemically “talk” to one another.

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Histology

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  1. Histology Other topics

  2. Extracellular Junctions • Purpose: to allow cells to function as a unit (the definition of a tissue). • They are connections along the lateral and basal sides of cells of a tissue. These connections allow cells to chemically “talk” to one another.

  3. Extracellular Junction Types • Tight Junctions: zipper-like connection between neighboring cells due to the membrane being bound together with the plasma membrane proteins. Impermeable. EX: Urine stays in kidney tubules because their cells are bound by tight junc. • Gap Junctions: protein channels join together between neighboring cells. Helps in strength of tissue as well as allowing communication between the cells. EX: intercalated disks in cardiac muscle. • Adhesion Junctions: (desmosomes and hemidesmosomes) plasma membranes don’t touch. Bound together with filaments attached in the cytoplasm.

  4. Fig. 4.15a

  5. Fig. 4.15b

  6. Fig. 4.15c

  7. Glands (Epithelium) • Endocrine Glands: Ductless and associated with the production and release of hormones for the endocrine system. • Exocrine Glands: Have a duct. • Types: Apocrine: (Mammary) discharge fragments of the epithelial cells with the secretion. Merocrine: (Sweat) release of contents without loss of cellular material. Holocrine: (Sebaceous/Oil) shed entire cells because the release of the substance kills the cell.

  8. Fig. 4.16 Tubular, Alveolar, and Acini

  9. Membranes • Mucous: line tubes and organs that open to the outside. Composed of epithelium over connective tissue. Goblet cells secrete mucous. • Serous: • Synovial: line freely movable joint cavities and are composed of connective tissue. • Meninges: • Cutaneous: skin

  10. Tissue Development • In gastrulation (13-14 days after fertilization) three layers form in the ball of cells. • Endoderm-forms into the inner gut • Ectoderm-forms the skin and the nervous system • Mesoderm-forms into bones, muscles, and blood vessels.

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