tissues.txt

A tissue is a group of similar cells and their intercellular matrix functioning together to perform a specialized activity.

• 1. Epithelial - covers of lines (body surfaces and cavities), forms glands
• 2. Connective - binds and supports
• 3. Muscular - movement
• 4. Nervous - conducts impulses

• 1. Tight junctions
• 2. Desmosomes
• 3. Gap junctions

To prevent leakage of molecules from tissue.

Proteins in 2 adjacent cell membranes interlock (zipper).

Hold adjacent cells together for greater stability.

Dense mats of microfilaments below cell membrane hold membranes together; with intercellular proteoglycans

Communication between cells.

Protein pores in both cell membranes line up to form continuous channel from one cell to another.

• Covering and lining epithelium --> protection and secretion
• 1. skin
• 2. mucus membranes (digestive, respiratory, reproductive tracts)
• 3. endothelium - lines blood vessels
• 4. mesothelium - covers organs, lines cavities

Manufactures and secretes products into ducts and body.

• 1. closely packed cells with little or no intercellular matrix between cells.
• 2. apical surface - free surface exposed to exterior of body or internal surface of a cavity
• 3. basement membrane - (glycoproteins secreted by epithelium and collagen fibers secreted by underlying connective tissue).

Avascular - no blood supply.

Mitotically active.

• 1. by arrangement of layers
• 2. by shape of cell

• 1. simple
• 2. stratified
• 3. pseudostratified

Single layer

Stacked in layers

Appears to be in layers, but all cells are in contact with the basement membrane --> only one layer, not all reach the surface.

• 1. squamous
• 2. cubodial
• 3. columnar
• 4. transitional

Flattened, scale-like with a central nuclei

Good for diffusion, osmosis, filtration. (ie, endothelium and mesothelium)

• 1. shape classified by outermost layer
• 2. keratinized (tough and waterproof skin)
• 3. nonkeratinized (inner surfaces)

Cube or hexagon shape, central nucleus.

Kidney tubules, glands

Rare

Tall rectangular, nucleus towards base

Digestive tract, with mircovilli

upper respiratory tract, with cilia

Rare

Mucus cells - unicellular gland that secretes mucus.

Stratified (only) - can change shape on surface when stretched or relaxed, in bladder and ureter.

• 1. endocrine glands
• 2. exocrine glands

• 1. ductless
• 2. secrete product directly into bloodstream

• Exocrine glands secrete products into ducts or directly onto free surface.
• -- unicellular goblet or mucus cells
• -- multicellular glands

Classified by structure of duct.

• Simple - unbranched duct
• Compound - branched duct

Classifed by secretory portion structure

• tubular
• acinar = alveolar -flask-shape, sac-like

Classified by mode of secretion (formation)

• merocrine - secretes product only from cell
• holocrine - secretory cell dies and discharged it's contents
• apocrine - outer part of secretory cell pinched off with product in it

• 1. support and protection
• 2. binding together of organs
• 3. insulation
• 4. as blood - transportation

• 1. Few widely scattered cells in a large amount of matrix.
• 2. Matrix or intercellular material determines tissue's qualities
• 3. Usually highly vascular

Embryonic connective tissue = mesenchyme - give rise to all other connective tissue

Epithelial tissue is closely packed cells with little or no intercellular matrix. It is avascular, no blood supply.

Connective tissue has few widely scattered cells in a large amount of matrix. Usually highly vascular.

• 1. fibroblasts
• 2. macrophages
• 3. mast cells
• 4. plasma cells
• 5. adipocytes

Fibroblasts produce intercellular matrix (fibers and ground substances)

phagocytes (fixed and wandering)

allergic mediators (histamine and heparine)

To produce antibodies.

Cell surrounds lipid droplets.

• 1. hyaluronic acid
• 2. fibers - protein
• a. collagenous
• b. elastic

• Thick and strong.
• Vitamin C necessary for proper formation.

Very flexible.

Loose = Areolar connective tissue

• 1. below epithelium and between muscles
• 2. contains all connective type cells
• 3. randomly arranged collagenous and elastic fibers in hyaluronic acid

• 1. sparse ground substance (hyaluronic acid) with many closely packed collagenous fibers
• 2. fibroblasts between fibers

Dense regular connective tissue - parallel bundles of fibers, ligaments, and tendons.

Dense irregular connective tissue - interwoven fibers, dermis of skin.

In walls of elastic arteries, elastic ligaments.

Mainly elastic (yellow) fibers with fibroblasts.