Chapter Summary

I. EPITHELIUM

A. Types

1.Simple Squamous—single layer of uniform flat cells.

2.Simple Cuboidal—single layer of uniform cuboidal cells.

3.Simple Columnar—single layer of uniform columnar cells.

4.Pseudostratified Columnar—single layer of cells of varied shapes and heights.

5.Stratified Squamous—several layers of cells whose superficial layers are flattened. These may be nonkeratinized, parakeratinized, or keratinized.

6.Stratified Cuboidal—two or more layers of cells whose superficial layers are cuboidal in shape.

7.Stratified Columnar—two or more layers of cells whose superficial layers are columnar in shape.

8.Transitional—several layers of cells, characterized by large, dome-shaped cells at the free surface, that help maintain the integrity of the epithelium during distention of the various components of the urinary tract.

B. General Characteristics

1. Free Surface Modifications

Cells may possess microvilli (brush border, striated border), short finger-like projections that increase the surface area of the cell; stereocilia (long anastomosing microvilli), which are only found in a few places in the body such as in the epididymis; and cilia, which are long, motile projections of the cell with a 9 + 2 microtubular substructure (axoneme).

2. Lateral Surface Modifications

For the purposes of adhesion, the cell membranes form junctional complexes involving the lateral plasmalemma of contiguous cells. These junctions are known as desmosomes (maculae adherentes), zonulae occludentes, and zonulae adherentes. For the purpose of intercellular communication, the lateral cell membranes form gap junctions (nexus, septate junctions).

3. Basal Surface Modifications

The basal cell membrane that lies on the basal membrane forms hemidesmosomes to assist the cell to adhere to the underlying connective tissue.

4. Basal Membrane

The basement membrane of light microscopy is composed of an epithelially derived basal lamina (which has two parts, lamina densa and lamina lucida) and a lamina reticularis derived from connective tissue, which may be absent.

II. GLANDS

A. Exocrine Glands

Exocrine glands, which deliver secretions into a system of ducts to be conveyed onto an epithelial surface, may be unicellular (goblet cells) or multicellular.

Multicellular glands may be classifi ed according to the branching of their duct system. If the ducts are not branched, the gland is simple; if they are branched, the gland is compound. Moreover, the three-dimensional shape of the secretory units may be tubular, acinar (alveolar), or a combination of the two, namely, tubuloacinar (tubuloalveolar). Additional criteria include

(1) the type of secretory product produced: serous (parotid, pancreas), mucous (palatal glands), and mixed (sublingual, submandibular), possessing serous and mucous acini and serous demilunes, and (2) the mode of secretion: merocrine (only the secretory product is released, as in the parotid gland), apocrine (the secretory product is accompanied by some of the apical cytoplasm, as perhaps in mammary glands), and holocrine (the entire cell becomes the secretory product, as in the sebaceous gland, testes, and ovary). Glands are subdivided by connective tissue septa into lobes and lobules, and the ducts that serve them are interlobar, intralobar, interlobular, and intralobular (striated, intercalated).

Myoepithelial (basket) cells are ectodermally derived myoid cells that share the basal lamina of the glandular parenchyma. These cells possess long processes that surround secretory acini and, by occasional contraction, assist in the delivery of the secretory product into the system of ducts.

B. Endocrine Glands

Endocrine glands are ductless glands that release their secretion into the bloodstream. These glands are described in Chapter 10.

CHAPTER OUTLINE

Graphics

Graphic 3-1 Collagen p. 66

Graphic 3-2 Connective Tissue Cells p. 67

Tables

Table 3-1 Types of Glycosaminoglycans (GAGs) Table 3-2 Mast Cells Factors and Functions

Plates