Stratified Epithelia

Stratified epithelia range from 2 to 20 or more layers of cells, with some cells resting directly on others and only the deepest layer resting on the basement membrane. Three of the stratified epithelia are named for the shapes of their surface cells: stratified squamous, stratified cuboidal, and stratified columnar epithelia. The deeper cells, however, may be of a different shape than the surface cells. The fourth type, transitional epithelium, was named when it was thought to represent a transitional stage between stratified squamous and stratified columnar epithelium. This is now known to be untrue, but the name has persisted.

Before You Go On

Answer the following questions to test your understanding of the preceding section:

5. Distinguish between simple and stratified epithelia, and explain why pseudostratified columnar epithelium belongs in the former category.

6. Explain how to distinguish a stratified squamous epithelium from a transitional epithelium.

7. What function do keratinized and nonkeratinized stratified squamous epithelia have in common? What is the structural difference between these two? How is this structural difference related to a functional difference between them?

8. How do the epithelia of the esophagus and stomach differ? How does this relate to their respective functions?

7 squam = scale

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Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

Table 5.2 Simple Epithelia

Simple Squamous Epithelium

Simple Squamous Epithelium

Simple Squamous Epithelial Saladin

Microscopic appearance: Single layer of thin cells, shaped like fried eggs with bulge where nucleus is located; nucleus flattened in the plane of the cell, like an egg yolk; cytoplasm may be so thin it is hard to see in tissue sections; in surface view, cells have angular contours and nuclei appear round Representative locations: Air sacs (alveoli) of lungs; glomerular capsules of kidneys; some kidney tubules; inner lining (endothelium) of heart and blood vessels; serous membranes of stomach, intestines, and some other viscera; surface mesothelium of pleurae, pericardium, peritoneum, and mesenteries Functions: Allows rapid diffusion or transport of substances through membrane; secretes lubricating serous fluid

Simple Cuboidal Epithelium

-Cuboidal epithelial cells

-Cuboidal epithelial cells

Simple Cuboidal Epithelium Sperm

Figure 5.5 Kidney Tubules.

Figure 5.5 Kidney Tubules.

Microscopic appearance: Single layer of square or round cells; in glands, cells often pyramidal and arranged like segments of an orange around a central space; spherical, centrally placed nuclei; often with a brush border of microvilli in some kidney tubules; ciliated in bronchioles of lung Representative locations: Liver, thyroid, mammary, salivary, and other glands; most kidney tubules; bronchioles Functions: Absorption and secretion; production of protective mucous coat; movement of respiratory mucus

Saladin: Anatomy & Physiology: The Unity of Form and Function, Third Edition

5. Histology

Text

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Simple Columnar Epithelium

Brush border -(microvilli)

r Columnar cells

Simple Columnar Epithelium

Brush border -(microvilli)

r Columnar cells

Simple Scaly Epithelium

Figure 5.6 Internal Surface (Mucosa) of the Small Intestine.

Figure 5.6 Internal Surface (Mucosa) of the Small Intestine.

Microscopic appearance: Single layer of tall, narrow cells; oval or sausage-shaped nuclei, vertically oriented, usually in basal half of cell; apical portion of cell often shows secretory vesicles visible with TEM; often shows a brush border of microvilli; ciliated in some organs; may possess goblet cells Representative locations: Inner lining of stomach, intestines, gallbladder, uterus, and uterine tubes; some kidney tubules Functions: Absorption and secretion; movement of egg and embryo in uterine tube; secretion of mucus

Pseudostratified Columnar Epithelium

Goblet cell-

Cilia

Goblet cell-

Cilia

Mucosa The Trachea

Figure 5.7 Mucosa of the Trachea.

Figure 5.7 Mucosa of the Trachea.

Microscopic appearance: Looks multilayered; some cells do not reach free surface but all cells reach basement membrane; nuclei at several levels in deeper half of epithelium; often with goblet cells; often ciliated Representative locations: Respiratory tract from nasal cavity to bronchi; portions of male reproductive tract Functions: Secretes and propels mucus

Saladin: Anatomy & I 5. Histology I Text I I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

Table 5.3 Stratified Epithelia

Stratified Squamous Epithelium—Keratinized

Dead squamous cells Living epithelial cells Connective tissue

Dead squamous cells Living epithelial cells Connective tissue

Sole Stratified Squamous Epithelium
Figure 5.8 Skin from the Sole of the Foot.

Microscopic appearance: Multiple cell layers with cells becoming increasingly flat and scaly toward surface; surface covered with a layer of compact dead cells without nuclei; basal cells may be cuboidal to columnar Representative locations: Epidermis; palms and soles are especially heavily keratinized Functions: Resists abrasion; retards water loss through skin; resists penetration by pathogenic organisms

Stratified Squamous Epithelium—Nonkeratinized

-Squamous epithelial cells

-Squamous epithelial cells

Sole Stratified Squamous Epithelium
Figure 5.9 Mucosa of the Vagina.

Microscopic appearance: Same as keratinized epithelium but without the surface layer of dead cells Representative locations: Tongue, oral mucosa, esophagus, anal canal, vagina Functions: Resists abrasion and penetration by pathogenic organisms

Saladin: Anatomy & Physiology: The Unity of Form and Function, Third Edition

5. Histology

Text

© The McGraw-Hill Companies, 2003

Stratified Cuboidal Epithelium i- Stratified cuboidal cells i- Stratified cuboidal cells

Microscopic Anatomy Sperm

Figure 5.10 Wall of a Follicle in the Ovary.

Figure 5.10 Wall of a Follicle in the Ovary.

Microscopic appearance: Two or more layers of cells; surface cells square or round

Representative locations: Sweat gland ducts; egg-producing vesicles (follicles) of ovaries; sperm-producing ducts (seminiferous tubules) of testis Functions: Contributes to sweat secretion; secretes ovarian hormones; produces sperm

Transitional Epithelium

Connective tissue—.

-Blood vessels

Connective tissue—.

-Blood vessels

Epithelial And Connective Tissue

Figure 5.11 Allantoic Duct of Umbilical Cord.

Figure 5.11 Allantoic Duct of Umbilical Cord.

Microscopic appearance: Somewhat resembles stratified squamous epithelium, but surface cells are rounded, not flattened, and often bulge above surface; typically five or six cells thick when relaxed and two or three cells thick when stretched; cells may be flatter and thinner when epithelium is stretched (as in a distended bladder); some cells have two nuclei Representative locations: Urinary tract—part of kidney, ureter, bladder, part of urethra; allantoic duct in umbilical cord Functions: Stretches to allow filling of urinary tract

Saladin: Anatomy & I 5. Histology I Text I I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

166 Part One Organization of the Body

166 Part One Organization of the Body

Allantoic Duct Ureter

Figure 5.12 Exfoliation of Squamous Cells from the Mucosal Surface of the Vagina. From R. G. Kessel and R. H. Kardon, Tissues and Organs: A Text-Atlas of Scanning Electron Microscopy (W. H. Freeman, 1979). Aside from the gums and vagina, name another epithelium in the body that would look like this to the scanning electron microscope.

Figure 5.12 Exfoliation of Squamous Cells from the Mucosal Surface of the Vagina. From R. G. Kessel and R. H. Kardon, Tissues and Organs: A Text-Atlas of Scanning Electron Microscopy (W. H. Freeman, 1979). Aside from the gums and vagina, name another epithelium in the body that would look like this to the scanning electron microscope.

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  • sisko niinist
    What Is Simple Squamous Epithelium?
    6 years ago

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