Unicellular (goblet cells in the large and small intestine and respiratory airways)
(b) Simple glands (single, nonbranched ducts)
Simple tubular (glands in stomach and colon)
Simple coiled tubular (lower portion of stomach and small intestine)
Simple branched tubular (glands in lower portion of stomach)
Simple coiled tubular occurrence is listed here again for context
(c) Compound glands (multiple, branched ducts)
Simple acinar (sebaceous glands of skin)
Simple branched acinar (sebaceous glands of skin)
Compound tubuloacinar
Compound acinar (mammary glands) and (pancreas)
Notes
The figures show various gland types and their duct arrangements (unicellular, simple, compound).
Common examples: goblet cells in mucosa; sebaceous glands in skin; mammary glands; pancreatic glands.
Exocrine Glands and Secretion Types
Secretion in duct
Merocrine (exocytosis): Vesicle releasing contents into duct; Secretory products stored in the cell; Duct of eccrine sweat gland is merocrine in nature.
Apocrine: A portion of the cell containing secretory products is pinched off the cell; Replacement cell forms; Hair follicle is associated with apocrine sweat glands.
Holocrine: Entire cells are shed by the gland and become part of the secretion; Example: sebaceous glands
Duct and gland associations
Duct of eccrine sweat gland (merocrine)
Sebaceous gland (holocrine)
Eccrine sweat gland (merocrine)
Hair follicle (associated with apocrine sweat glands)
Summary of secretion mechanisms
Merocrine: Vesicles empty their contents into the duct through exocytosis; Secretory products stored in the cell prior to release.
Apocrine: Puzzle-like loss of a portion of the cell containing secretory products; the cell regenerates to continue secretion.
Holocrine: Whole cells shed and become part of the secretion; requires continuous cell proliferation to replace shed cells.
Cells of Connective Tissue 2
Osteoblasts form bone, osteocytes maintain it, and osteoclasts break it down.
Other cell types:
Chondroblasts, Chondrocytes
Fibroblasts, fibrocytes
These cells coordinate growth, maintenance, and turnover of connective tissue components (bone and cartilage).
Cells of Connective Tissue 3
Adipose or fat cells (adipocytes)
Mast cells
White blood cells (leukocytes)
Fixed or wandering
Macrophages
Undifferentiated mesenchyme (stem cells)
Extracellular Matrix
Three major components of the extracellular matrix: protein fibers, ground substance, fluid
Protein fibers in matrix: Collagen, Elastic, Reticular
Ground substance: hydrated gel that fills space between cells and fibers
Molecules of the Connective Tissue Matrix
(a) Collagen fibers
Composed of collagen fibrils with polypeptide chains linked together; provide tensile strength
(b) Elastic fibers
Comprised of elastin; allow stretching and recoil; enable tissue elasticity
(c) Proteoglycan aggregates
Proteoglycan monomers bound to hyaluronic acid via link proteins; hydrated with water to form a gel-like ground substance
Related components shown in figures: collagen fibers, elastic fibers, proteoglycan aggregates, hyaluronic acid, link proteins, water
Structure: Cells (e.g., fibroblasts, macrophages, lymphocytes) within a fine network of mostly collagen fibers; often merges with denser connective tissue
Function: Loose packing, support, nourishment for structures with which it is associated
Location: Widely distributed throughout the body; underlying epithelial basement membranes; packing between glands, muscles, and nerves; attaches skin to underlying tissues
Structure: Little extracellular matrix; adipocytes are so full of lipid that cytoplasm is pushed to the periphery
Function: Packing material, thermal insulation, energy storage, protection of organs against injury from bumps or jarred movement
Location: Predominantly in subcutaneous areas, in mesenteries, in renal pelvis, around kidneys, attached to surface of colon, in mammary glands, within loose connective tissue of spaces and crevices
Visuals: LM 100x; adipocytes; adipose tissue in mammary gland
Reticular Tissue
TABLE 4.8 (continued): Reticular Tissue
Structure: Fine network of reticular fibers
Function: Provides a superstructure for lymphatic and hemopoietic tissues
Location: Within lymph nodes, spleen, bone marrow
Visuals: Leukocytes; reticular fibers; LM 280x
Dense Regular Collagenous Connective Tissue
TABLE 4.9
Structure: Matrix composed of collagen fibers running in somewhat the same direction
Function: Withstands great pulling forces exerted in the direction of fiber orientation; high tensile strength and resistance to stretch
Location: Tendons (attach muscle to bone) and ligaments (attach bones to each other)
Visuals: LM 165x; nuclei of fibroblasts; collagen fibers
Dense Regular Elastic Connective Tissue
TABLE 4.9
Structure: Matrix composed of regularly arranged collagen fibers and elastic fibers
Function: Ability to stretch and recoil like a rubber band; strength in the direction of fiber orientation
Location: Vocal folds and elastic ligaments between the vertebrae, along the dorsal aspect of the neck
Visuals: Elastic fibers; nucleus of fibroblast; base of tongue; true vocal cords (vocal folds) and vestibular fold (false vocal cord)
Dense Irregular Collagenous Connective Tissue
TABLE 4.9 (Continued)
Structure: Matrix composed of collagen fibers that run in all directions or in alternating planes
Function: Tensile strength capable of withstanding stretching in all directions
Location: Dermis of the skin; organ capsules and septa; outer covering of body tubes
Visuals: Dense irregular collagenous tissue in dermis; epidermis, skin, dermis
Dense Irregular Elastic Connective Tissue
TABLE 4.9 (Continued)
Structure: Matrix composed of bundles and sheets of collagenous and elastic fibers oriented in multiple directions
Function: Strength with stretching and recoil in several directions