Tissues

1. 4 Tissues

2. Tissues • Tissue • A group of closely associated cells that perform related functions and are similar in structure • Epithelial tissue—covering (Ch 4 and 5) • Connective tissue—support (Ch 4, 5, 6, and 9) • Muscle tissue—movement (Ch 10 and 11) • Nervous tissue—control (Ch 12–16 and 25)

3. Epithelial Tissue Epithelial Tissue Functions of epithelia Protection Diffusion Absorption, secretion, and ion transport Filtration Forms slippery surfaces • Covers a body surface or lines a body cavity • Forms parts of most glands

4. Special Characteristics of Epithelia • Support by connective tissue • Avascular butinnervated • Epithelia receive nutrients from underlying connective tissue • Regeneration • Lost cells are quickly replaced by cell division

5. Special Characteristics of Epithelia Narrow extracellular space Cilia Microvilli Apical region of an epithelial cell Cell junctions Tight junction Epithelium Adhesive belt Desmosome Gap junction Basal region Basal lamina Basement membrane Reticular fibers Nerve ending Connective tissue Capillary Figure 4.1

6. Classifications of Epithelia First name Last name describes shape of cells Squamous—cells are wider than tall (plate-like) Cuboidal—cells are as wide as tall, like cubes Columnar—cells are taller than they are wide, like columns • indicates number of cell layers • Simple—one layer of cells • Stratified—more than one layer of cells

7. Classifications of Epithelia Apical surface Squamous Basal surface Simple Apical surface Cuboidal Basal surface Stratified (a) Classification based on number of cell layers Columnar (b) Classification based on cell shape Figure 4.2

8. Simple Squamous Epithelium • Description—single layer; flat cells with disc-shaped nuclei • Function • Passage of materials by passive diffusion and filtration • Secretes lubricating substances in serosae • Location • Renal corpuscles • Alveoli of lungs • Lining of heart, blood, and lymphatic vessels • Lining of ventral body cavity (serosae)

9. Simple Squamous Epithelium (a) Simple squamous epithelium Description: Single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm; the simplest of the epithelia. Air sacs of lung tissue Function: Allows passage of materials by diffusion and filtration in sites where protection is not important; secretes lubricating substances in serosae. Nuclei of squamous epithelial cells Location: Kidney glomeruli; air sacs of lungs; lining of heart, blood vessels, and lymphatic vessels; lining of ventral body cavity (serosae). Photomicrograph: Simple squamous epithelium forming part of the alveolar (air sac) walls (200). Figure 4.3a

10. Simple Cuboidal Epithelium • Description • Single layer of cubelike cells with large, spherical central nuclei • Function • Secretion and absorption • Location • Kidney tubules, secretory portions of small glands, ovary surface

11. Simple Cuboidal Epithelium (b) Simple cuboidal epithelium Description: Single layer of cubelike cells with large, spherical central nuclei. Simple cuboidal epithelial cells Function: Secretion and absorption. Basement membrane Location: Kidney tubules; ducts and secretory portions of small glands; ovary surface. Connective tissue Photomicrograph: Simple cuboidal epithelium in kidney tubules (430). Figure 4.3b

12. Simple Columnar Epithelium • Description—single layer of column-shaped (rectangular) cells with oval nuclei • Function • Absorption • Secretion of: • Mucus • Enzymes • other substances • Ciliated type propels mucus or reproductive cells by ciliary action

13. Simple Columnar Epithelium • Location • Nonciliated form lines: • digestive tract • gallbladder • ducts of some glands • Ciliated form • Lines small bronchi, uterine tubes, and uterus

14. Simple Columnar Epithelium (c) Simple columnar epithelium Description: Single layer of tall cells with round to oval nuclei; some cells bear cilia; layer may contain mucus- secreting unicellular glands (goblet cells). Simple columnar epithelial cell Function: Absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action. Location: Nonciliated type lines most of the digestive tract (stomach to anal canal), gallbladder, and excretory ducts of some glands; ciliated variety lines small bronchi, uterine tubes, and some regions of the uterus. Basement membrane Photomicrograph: Simple columnar epithelium of the stomach mucosa (1150). Figure 4.3c

15. Pseudostratified Columnar Epithelium • Description • All cells originate at basement membrane • Only tall cells reach the apical surface • May contain goblet cells and bear cilia • Nuclei lie at varying heights within cells • Gives false impression of stratification

16. Pseudostratified Columnar Epithelium • Function—secretion of mucus; propulsion of mucus by cilia • Locations • Nonciliated type • Ducts of male reproductive tubes • Ducts of large glands • Ciliated variety • Lines trachea and most of upper respiratory tract

17. Pseudostratified Ciliated Columnar Epithelium (d) Pseudostratified columnar epithelium Cilia Description: Single layer of cells of differing heights, some not reaching the free surface; nuclei seen at different levels; may contain mucus-secreting goblet cells and bear cilia. Mucus of goblet cell Pseudo- stratified epithelial layer Function: Secretion, particularly of mucus; propulsion of mucus by ciliary action. Location: Nonciliated type in male’s sperm-carrying ducts and ducts of large glands; ciliated variety lines the trachea, most of the upper respiratory tract. Basement membrane Photomicrograph: Pseudostratified ciliated columnar epithelium lining the human trachea (780). Trachea Figure 4.3d

18. Stratified Epithelia • Properties • Contain two or more layers of cells • Regenerate from below (basal layer) • Major role is protection • Named according to shape of cells at apical layer

19. Stratified Squamous Epithelium • Description • Many layers of cells are squamous in shape • Deeper layers of cells appear cuboidal or columnar • Thickest epithelial tissue • Adapted for protection from abrasion

20. Stratified Squamous Epithelium • Two types—keratinized and non-keratinized • Keratinized • Location—epidermis • Contains the protective protein keratin • Waterproof • Surface cells are dead and full of keratin • Non-keratinized • Forms moist lining of body openings

21. Stratified Squamous Epithelium • Function—Protects underlying tissues in areas subject to abrasion • Location • Keratinized—forms epidermis • Nonkeratinized—forms lining of mucous membranes • Esophagus • Mouth • Anus • Vagina • Urethra

22. Stratified Squamous Epithelium (e) Stratified squamous epithelium Description: Thick membrane composed of several cell layers; basal cells are cuboidal or columnar and metabolically active; surface cells are flattened (squamous); in the keratinized type, the surface cells are full of keratin and dead; basal cells are active in mitosis and produce the cells of the more superficial layers. Stratified squamous epithelium Nuclei Function: Protects underlying tissues in areas subjected to abrasion. Basement membrane Location: Nonkeratinized type forms the moist linings of the esophagus, mouth, and vagina; keratinized variety forms the epidermis of the skin, a dry membrane. Connective tissue Photomicrograph: Stratified squamous epithelium lining the esophagus (430). Figure 4.3e

23. Stratified Cuboidal Epithelium • Description—generally two layers of cube-shaped cells • Function—protection • Location • Forms ducts of: • Mammary glands • Salivary glands • Largest sweat glands

24. Stratified Cuboidal Epithelium (f) Stratified cuboidal epithelium Description: Generally two layers of cubelike cells. Basement membrane Cuboidal epithelial cells Function: Protection Location: Largest ducts of sweat glands, mammary glands, and salivary glands. Duct lumen Photomicrograph: Stratified cuboidal epithelium forming a salivary gland duct (285). Figure 4.3f

25. Stratified Columnar Epithelium • Description—several layers; basal cells usually cuboidal; superficial cells elongated • Function—protection and secretion • Location • Rare tissue type • Found in male urethra and large ducts of some glands

26. Stratified Columnar Epithelium (g) Stratified columnar epithelium Description: Several cell layers; basal cells usually cuboidal; superficial cells elongated and columnar. Basement membrane Function: Protection; secretion. Stratified columnar epithelium Location: Rare in the body; small amounts in male urethra and in large ducts of some glands. Underlying connective tissue Photomicrograph: Stratified columnar epithelium lining of the male urethra (315). Urethra Figure 4.3g