Chapter 5: Histology- Cellular Junctions, Glands, and Membranes

Tight junction

• zipper-like, interlocking linkage between two adjacent cells by transmembrane cell-adhesion protein

• Seals off intercellular space, making it difficult for substance to pass between cells

Desmosome

• patch that holds cells together (like a clothing snap)

• Keeps cells from pulling apart—resists mechanical stress

• Hook-like, J-shaped proteins arise from cytoskeleton

Hemidesmosome

• half-desmosome that anchors basal cells of an epithelium to an underlying basement membrane

• Epithelium cannot easily peel away from underlying tissues

Gap (communicating) junction

• formed by ring-like connexons

• Connexon consists of six transmembrane proteins arranged like segments of an orange around water filled pore

• Ions, nutrients, and other small solutes pass between cells

• Located in cardiac and smooth muscle, embryonic tissue, lens and cornea

Adherens junction

• Adherens junctions hold cells together via cadherins. Intracellularly, these proteins are connected to actin filaments that form a belt around the cell—provide stability to tissues

• not as impermeable as tight junctions

glands

• cell or organ that secretes substances for use elsewhere in the body or releases them for elimination from the body

• Usually composed of epithelial tissue in a connective tissue framework and capsule

Secretion

product useful to the body

Excretion

waste product

Exocrine glands

• maintain their contact with surface of epithelium by way of a duct

• Surfaces can be external (e.g., sweat, tear glands) or internal (e.g., pancreas, salivary glands)

Endocrine glands

• have no ducts; secrete hormones directly into blood

• Examples: thyroid, adrenal, and pituitary glands

Hormones

chemical messengers that stimulate cells elsewhere in the body

Unicellular glands

• found in an epithelium that is predominantly non-secretory

• Can be exocrine or endocrine

• Examples: mucus-secreting goblet cells in trachea or endocrine cells of stomach

merocrine secretion

Apocrine secretion

holocrine secretion

membranes

• superficial epithelium sheet + underlying connective layer (called lamina propria)

• cover and protect

what are the four types of membrane?

Serous, Mucous, Cutaneous, Synovial membrane

Mucous Membrane

serous membrane

Cutaneous Membrane

Synovial membrane