Transcript Histology

Histology
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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.
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.
Fig. 4.15a
Fig. 4.15b
Fig. 4.15c
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 and some sweat)
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.
Fig. 4.16
Tubular, Alveolar, and Acini
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
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.