This chapter should help the student to:

• Name the four basic tissue types.
  
• Explain the characteristics that distinguish epithelial tissues from other basic tissue types.
  
• List the epithelial tissue types and give examples of sites where each may be found.
  
• Describe the functional capabilities of each epithelial tissue type and relate them to tissue structure.
  
• Describe the special functions of epithelial cell types and sites where each may be found.
  
• Recognize epithelia in micrographs and predict their function from their structure and location.
  
• List the criteria used to classify glands.
  
• List the classes of glands in humans and give examples of sites where each may be found.
  
• Recognize glands in micrographs or diagrams and identify gland types.

1. List the principal functions of epithelial tissues (II.A).

2. From which embryonic germ layer(s) are epithelial tissues derived? Give examples of epithelia derived from each (II.H; Table 4–1).

3. List the characteristics of epithelial tissues that distinguish them from other basic tissue types. Consider cell polarity (IV); specializations of the apical (IV.A), lateral (IV.B), and basal (IV.C) surfaces; nutrition (II.F); and mitotic rate (II.E).

4. Describe the basal lamina in terms of location, composition, and staining (IV.C.1.a).

5. Which structures and molecules help attach epithelial cells to their basal laminae (IV.C.1.a and 2) and to each other (IV.B.1-3)?

6. Compare basal laminae and basement membranes (IV.C.1.a).

7. Name four types of junctions found between epithelial cells (IV.B. 1-4).

8. Which junction(s) named in the answer to question 7 is (are) associated with:

1. 
   

   A disklike structure (IV.B.3 and 4)?

   
   
2. 
   

   A bandlike structure (IV.B.1 and 2)?

   
   
3. 
   

   Plasma membrane fusion (IV.B.1)?

   
   
4. 
   

   A sealing effect (IV.B.1)?

   
   
5. 
   

   Cytokeratins (IV.B.2 and 3)?

   
   
6. 
   

   Attachment plaques (IV.B.2 and 3)?

   
   
7. 
   

   Connexons (IV.B.4)?

   
   
8. 
   

   Integrins (IV.C.1.b and 2)?

   
   
9. 
   

   Cadherins (IV.B.2 and 3)?

   
   
10. 
    

    Microfilaments (IV.B.2 and C.1.b)?

    
    
11. 
    

    Intermediate filaments (IV.B.3)?

    
    
12. 
    

    Alpha-actinin (IV.B.2)?

9. Which junction is more important in cell-to-cell communication than cell–cell adhesion (IV.B.4)?

10. Compare microvilli, stereocilia, motile cilia, and flagella (IV.A.1–4) in terms of:

1. 
   

   Width and length

   
   
2. 
   

   The presence of a plasma membrane covering

   
   
3. 
   

   The presence of microtubules or microfilaments

   
   
4. 
   

   Motility

   
   
5. 
   

   The presence of axonemes and basal bodies

   
   
6. 
   

   Function and location in the body

11. List the types of simple and stratified epithelia and give examples of their locations (III.B.1–8).

12. Compare endocrine and exocrine glands in terms of their embryonic origins and how their products are transported (V.A; Table 4–3).

13. What structural criteria are used to classify exocrine glands (Table 4–5)?

14. Compare merocrine, holocrine, and apocrine secretion in terms of the part of the cell released, and give an example of each type of gland (Table 4–4).

15. Describe the structural modifications and staining properties of epithelial cell types specialized for the following function and give examples of each type:

1. 
   

   Transport of ions and water (VI.A.1)

   
   
2. 
   

   Synthesis and secretion of proteins (VI.C.1)

   
   
3. 
   

   Synthesis and secretion of mucus (VI.C.3)

   
   
4. 
   

   Synthesis and secretion of steroids (VI.C.5)

16. Compare paracrine (VI.C.2) and endocrine (V.A) cells in terms of the distances their products travel to reach their targets. Give examples of each type of cell.

17. Describe DNES (APUD) cells in terms of what the acronyms stand for, embryonic origin, structure, secretory product, and distribution (VI.C.2).

18. Give examples of DNES (APUD) cells, and name the substance each produces (VI.C.2).

19. Compare serous and mucous cells in terms of appearance and secretory product (VI.C.3 and 4).

I. The Four Basic Tissue Types

A tissue is a complex assemblage of cells and cell products that have a common function. The body’s tissues are grouped according to their cells and cell products into four basic types: epithelial, connective, muscular, and nervous.

II. General Features of Epithelial Tissues

Epithelial tissues often are structurally minor but functionally important components of an organ. Glands derive from the invagination of lining epithelia into underlying connective tissue. Composed primarily of epithelial cells, glands are considered a type of epithelial tissue.

A. Diversity

Epithelial tissues range from one to many cell layers and form sheets, solid organs, or glands. Their functions include protection, secretion, and absorption.

B. Metaplasia

When exposed to chronic environmental changes, epithelia undergo metaplasia (i.e., change from one type to another).

C. Lining and Covering

Epithelia cover or line all body surfaces and cavities except articular cartilage in joint cavities. Their function is analogous to that of cell membranes: they (1) separate self from nonself, (2) divide the body into functional compartments, and (3) form barriers that monitor, control, and modify substances that traverse them.

D. Basal Lamina

Epithelia rest on an extracellular basal lamina (or basement membrane) that separates them from an underlying connective tissue layer or lamina propria.

E. Renewal

Epithelia are continuously renewed and replaced. Cells closest to the basal lamina undergo continuous mitosis, and their progeny replace the surface cells.

F. Avascularity

Blood vessels in the subjacent connective tissue rarely penetrate the basal lamina to invade epithelia.

G. Cell Packing

Epithelial tissues have little intercellular substance. The cells are densely packed, closely apposed, and joined by specialized junctions.

H. Derivation

Ectoderm, mesoderm, and endoderm all give rise to epithelia (Table 4–1).