Tissue and Epithelial Tissues

epithelial tissue

-cover exposed surfaces

-lines internal passageways

-forms glands (exocrine)

muscle tissue

-specialized for contraction

-skeletal muscle, heart muscle, and walls of hollow organs

connective tissue

-fills internal spaces

-supports other tissues

-transports materials

-stores energy

neural tissue

-carries electrical signals from one part of body to another

glands

structures that produce secretions (exocrine) or hormones (endocrine)

exocrine glands

have ducts and produce secretions

mostly composed of tightly packed cells

first characteristic of epithelia

covers body surfaces and forms glands

second characteristic of epithelia

has distinct tissue surfaces

third characteristic of epithelia

cells connect to surrounding cells and ECM

fourth characteristic of epithelia

nonvascular/avascularity

fifth characteristic of epithelia

high regeneration capacity

sixth characteristic of epithelia

1. physical protection

2. control permeability

3. absorbing substances

4. produce specialized secretion

functions of epithelial tissue

cilia

motile extensions that move substances across the surface of the cell. (mucus in the respiratory system)

microvilli

extensions of the cell membrane that increase cell surface area and allow for greater absorption. (lining of the small intestine to absorb nutrients)

Basolateral surfaces

surface that attach one cell to another along the sides and also to the basement membrane

Squamous cell shape fxn

Allows diffusion or acts as filter

Cuboidal and columnar cell shape fxn

Secretion or absorption. May include goblet cells that produce and secrete mucus.

Simple layering fxn

Allows diffusion of gases, filtration of blood, secretion, absorption.

Stratified layering fxn

Protection, particularly against abrasion

Intracellular connection structures

-form permeability layer

-bind cells together

-provide mechanisms for communication

desmosomes

-disk-shaped regions of cell membrane; often found in areas that are subjected to stress

-have adhesive glycoproteins

-intermediate protein filaments extend into cytoplasm of cells

Hemidesmosomes

half of a desmosome; attach epithelial cells to basement membrane.

Tight Junctions

hold cells together, form permeability barrier

adhesion belt

composed of glycoproteins that act as a weak glue to hold cells together; found just below tight junction

Gap Junctions

-protein channels aid intercellular communication

-allows ions and small molecules to pass through

-coordinate function of cardiac and smooth muscle

unicellular glands

-exocrine gland

-single cell

-goblet cells

multicellular glands

-exocrine gland

-further classified by structure of ducts, secretory regions

merocrine secretion

-produced in golgi apparatus

-released by vesicles (exocytosis)

-sweat glands

apocrine secretion

-produced in golgi apparatus

-released by shedding cytoplasm

-mammary glands

holocrine secretion

-released by cell bursting, killing gland cells

-gland cells replaced by stem cells

-sebaceous glands