Porth's Essentials of Pathophysiology, 4e

22

Cell and Tissue Function

U N I T 1

Cell junctions

Simple squamous

Microvilli

Apical surface

Epithelial cells

Simple cuboidal

Basement membrane

N

W

Connective tissue Nerve fiber Blood vessel

Simple columnar

columnar epithelia are found in the ducts of salivary glands and the larger ducts of the mammary glands. In smokers, the normal columnar ciliated epithelial cells of the trachea and bronchi are often replaced with strati- fied squamous epithelial cells that are better able to with- stand the irritating effects of cigarette smoke. Pseudostratified epithelium is a type of epithelium in which all of the cells are in contact with the underly- ing intercellular matrix, but some do not extend to the surface. A pseudostratified ciliated columnar epithelium with goblet cells forms the lining of most of the upper respiratory tract. All of the tall cells reaching the sur- face of this type of epithelium are either ciliated cells or mucus-producing goblet cells. The basal cells that do not reach the surface serve as stem cells for ciliated and goblet cells. Transitional epithelium is a stratified epithelium characterized by cells that can change shape and become thinner when the tissue is stretched. Such tissue can be stretched without pulling the superficial cells apart. Transitional epithelium is well adapted for the lining of organs that are constantly changing their volume, such as the urinary bladder. Glandular Epithelium Glandular epithelial tissue is formed by cells special- ized to produce a fluid secretion. This process is usually accompanied by the intracellular synthesis of macromol- ecules. The chemical nature of these macromolecules is variable. The macromolecules typically are stored in the cells in small membrane-bound vesicles called secretory granules . For example, glandular epithelia can synthe- size, store, and secrete proteins (e.g., insulin), lipids (e.g., adrenocortical hormones, secretions of the sebaceous FIGURE 1-14. Typical arrangement of epithelial cells in relation to underlying tissues and blood supply. Epithelial tissue has no blood supply of its own but relies on the blood vessels in the underlying connective tissue for nutrition (N) and elimination of wastes (W).

Pseudostratified columnar ciliated

Transitional

Stratified squamous

FIGURE 1-15. Representation of the various epithelial tissue types.

glands), and complexes of carbohydrates and proteins (e.g., saliva). Less common are secretions that require minimal synthetic activity, such as those produced by the sweat glands.