Chapter 4: The Tissue Level of Organization
I. Tissues of the Body: An Introduction, p. 107
There are 4 basic types of tissues:
covers surfaces exposed to the environment (skin, airways, digestive tracts,
fills internal spaces, supports other tissues, transports materials and stores
is specialized for contraction (skeletal muscle, heart muscle, walls of hollow
carries electrical signals from one part of the body to another.
II. Epithelial Tissue, p. 107
Epithelial tissue includes:
: layers of cells that cover internal or external surfaces.
: structures that produce fluid secretions.
Epithelia line digestive, respiratory, urinary and reproductive tracts. Also fluid or gas-filled internal
cavities and passageways such as the chest cavity, inner surfaces of blood vessels and chambers of heart.
Epithelia have 5 important characteristics:
: cells are tightly bound together by cell junctions.
: the structural and functional differences between the exposed (apical
) and attached
) surfaces of the tissue.
: the base of the epithelia is bound to a basal lamina
or basement membrane.
: epithelia are avascular
(lacking blood vessels)
: a high rate of cell replacement by stem cells in the epithelium.
Functions of Epithelial Tissue
, p. 107
There are 4 basic functions of epithelial tissues:
Provide Physical Protection
from abrasion, dehydration, biological and chemical agents.
to proteins, hormones, ions or nutrients.
such as touch or pressure.
are specialized for the sensations of smell, taste, sight, equilibrium, and hearing.
Produce Specialized Secretions
for physical protection or chemical messengers.
- gland cells
are scattered among other epithelial cells.
- in glandular epithelium
, most cells produce secretions.
Specializations of Epithelial Tissue
, p. 108
Individual epithelial cells may be specialized for:
Movement of fluid over the epithelial surface (protection or lubrication).
Movement of fluid through the epithelium (permeability).
Production of secretions (protection or chemical messengers).
Polarity of Epithelial Cells
The apical surfaces of cells lining internal passageways (such as digestive and urinary tracts) have
on their surfaces which increase surface area to aid in absorption, secretion and transport.
Longer epithelial extensions called cilia
(ciliated epithelium) move fluids across the surface of the
epithelium. Cilia in the respiratory tract move mucus, containing particles such as smoke, out of the
Maintaining the Integrity of Epithelia