5-1 Endocrine and Exocrine Glands Secrete substances –composed of epithelial tissue Exocrine glands connect to surface with a duct (epithelial tube) Endocrine glands secrete (hormones) directly into bloodstream Mixed organs do both –liver, gonads, pancreas Unicellular glands – endo or exocrine –goblet or intrinsic cells of stomach wall

5-2 Exocrine Gland Structure Stroma = capsule and septa divide gland into lobes and lobules Parenchyma = cells that secrete Acinus = cluster of cells surrounding the duct draining those cells

5-3 Types of Exocrine Glands Simple glands - unbranched duct Compound glands - branched duct Shape of gland –acinar - secretory cells form dilated sac –tubuloacinar - both tube and sacs

Classification according to the shape of secretory parts: tubes in tubular glands, acini in acinar glands or alveoli in alveolar glands Combinations exist. tubulo- acinar gland, Cords are epithelial cells arranged into sheets separated by vascular sinusoids. In section, the predominant pattern appears linear (hence, "cord"), even though the lines may twist and branch.sinusoids An acinus (from Latin, grape) is a small ball of secretory epithelial cells containing a tiny central lumen. A typical acinar cell is shaped like a pyramid.

Shapes of Exocrine Glands

5-6 Types of Secretions Serous glands –produce thin, watery secretions sweat, milk, tears and digestive juices Mucous glands –produce mucin that absorbs water to form a sticky secretion called mucus Mixed glands contain both cell types Cytogenic glands release whole cells –sperm and egg cells

5-7 Holocrine Gland Secretory cells disintegrate to deliver their accumulated product –oil-producing glands of the scalp

5-8 Merocrine and Apocrine Secretion Merocrine glands release their product by exocytosis –tears, gastric glands, pancreas, etc. Apocrine glands are merocrine glands with confusing appearance (apical cytoplasm not lost) –mammary and armpit sweat glands

Glandular secretions Merocrine – vesicles synthesized by ribosomes are secreted in small portions. Most exocrine glands are of this type in the body. –(Ex. salivary, gastric and pancreatic glands). Apocrine – accumulate their secretion at the surface and then pinch off from the rest of the cell. - (Ex. Sweat glands in armpit and groin). Holocrine – whole cell is released as a secretion and is then replaced by mitosis. – (Ex. Sebaceous glands of skin).

Exocrine secretions

Special Characteristics of Epithelia

Lateral Surface Features Factors holding epithelial cells together –Adhesion proteins link plasma membranes of adjacent cells –Contours of adjacent cell membranes –Special cell junctions Tight Junctions Adherens Junctions Desmosomes

Lateral Surface Features – Cell Junctions Tight junctions (zona occludens) – close off intercellular space –Found at apical region of most epithelial types –Some proteins in plasma membrane of adjacent cells are fused –Prevent molecules from passing between cells of epithelial tissue

Tight Junction

Lateral Surface Features – Cell Junctions Adherens junctions (zonula adherens) – anchoring junction –Transmembrane linker proteins attach to actin microfilaments of the cytoskeleton and bind adjacent cells –Along with tight junctions, form the tight junctional complex around apical lateral borders of epithelial tissues

Lateral Surface Features – Cell Junctions Desmosomes – two disc-like plaques connected across intercellular space –Plaques of adjoining cells are joined by proteins called cadherins –Proteins interdigitate into extracellular space –Intermediate filaments insert into plaques from cytoplasmic side

Desmosome

Lateral Surface Features – Cell Junctions Gap junctions – passageway between two adjacent cells –Let small molecules move directly between neighboring cells –Cells are connected by hollow cylinders of protein

Gap Junction

Basal Feature: The Basal Lamina Noncellular supporting sheet between the epithelium and the connective tissue deep to it Consists of proteins secreted by the epithelial cells Functions: –Acts as a selective filter, determining which molecules from capillaries enter the epithelium –Acts as scaffolding along which regenerating epithelial cells can migrate Basal lamina and reticular layers of the underlying connective tissue deep to it form the basement membrane