Tissues

1. Tissues • Cells work together in functionally related groups called tissues • Tissue – a group of closely associated cells that perform related functions and are similar in structure

2. Four Basic Tissue Types and Basic Functions • Epithelial tissue – covering • Connective tissue – support • Muscle tissue – movement • Nervous tissue – control

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

4. Special Characteristics of Epithelia • Cellularity • Specialized contacts • Polarity • Support by connective tissue • Avascular but innervated • Regeneration

5. Special Characteristics of Epithelia Figure 4.1

6. Classifications of Epithelia Figure 4.2

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

8. Simple Squamous Epithelium • Description – single layer of flat cells with disc-shaped nuclei • Special types • Endothelium (inner covering) – slick lining of hollow organs • Mesothelium (middle covering) • Lines peritoneal, pleural, and pericardial cavities • Covers visceral organs of those cavities

9. Simple Squamous Epithelium • 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)

10. Simple Squamous Epithelium Figure 4.3a

11. Simple Cuboidal Epithelium • Description – single layer of cube-like cells with large, spherical central nuclei • Function – secretion and absorption • Location – kidney tubules, secretory portions of small glands, ovary surface

12. Simple Cuboidal Epithelium Figure 4.3b

13. Simple Columnar Epithelium • Description – single layer of column-shaped (rectangular) cells with oval nuclei • Some bear cilia at their apical surface • May contain goblet cells • Function • Absorption; secretion of mucus, enzymes, and other substances • Ciliated type propels mucus or reproductive cells by ciliary action

14. Simple Columnar Epithelium • Location • Non-ciliated form • Lines digestive tract, gallbladder, ducts of some glands • Ciliated form • Lines small bronchi, uterine tubes, and uterus

15. Simple Columnar Epithelium Figure 4.3c

16. 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

17. Pseudostratified Columnar Epithelium • Function – secretion of mucus; propulsion of mucus by cilia • Locations • Non-ciliated type • Ducts of male reproductive tubes • Ducts of large glands • Ciliated variety • Lines trachea and most of upper respiratory tract

18. Pseudostratified Ciliated Columnar Epithelium Figure 4.3d

19. Stratified Epithelia • Contain two or more layers of cells • Regenerate from below • Major role is protection • Are named according to the shape of cells at apical layer

20. Stratified Squamous Epithelium • Description • Many layers of cells – squamous in shape • Deeper layers of cells appear cuboidal or columnar • Thickest epithelial tissue – adapted for protection

21. Stratified Squamous Epithelium • Specific types • Keratinized – contain the protective protein keratin • Surface cells are dead and full of keratin • Non-keratinized – forms moist lining of body openings

22. Stratified Squamous Epithelium • Function – Protects underlying tissues in areas subject to abrasion • Location • Keratinized – forms epidermis • Non-keratinized – forms lining of esophagus, mouth, and vagina

23. Stratified Squamous Epithelium Figure 4.3e

24. Stratified Cuboidal Epithelium • Description – generally two layers of cube-shaped cells • Function – protection • Location • Forms largest ducts of sweat glands • Forms ducts of mammary glands and salivary glands

25. Stratified Cuboidal Epithelium Figure 4.3f

26. 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

27. Stratified Columnar Epithelium Figure 4.3g

28. Transitional Epithelium • Description • Basal cells usually cuboidal or columnar • Superficial cells dome-shaped or squamous • Function – stretches and permits distension of urinary bladder • Location • Lines ureters, urinary bladder and part of urethra

29. Transitional Epithelium Figure 4.3h

30. Exocrine Glands • Ducts carry products of exocrine glands to epithelial surface • Include the following diverse glands • Mucus-secreting glands • Sweat and oil glands • Salivary glands • Liver and pancreas

31. Unicellular Exocrine Glands (The Goblet Cell) • Goblet cells produce mucin • Mucin + water  mucus • Protects and lubricates many internal body surfaces (small intestine)

32. Goblet Cells Figure 4.5

33. Multicellular Exocrine Glands • Have two basic parts • Epithelium-walled duct • Secretory unit

34. Multicellular Exocrine Glands • Classified by structure of duct • Simple • Compound • Categorized by secretory unit • Tubular • Alveolar • Tubuloalveolar

35. Types of Multicellular Exocrine Glands Figure 4.6

36. Endocrine Glands • Ductless glands • Secrete substances directly into bloodstream • Produce molecules called hormones

37. Lateral Surface Features – Cell Junctions • Factors holding epithelial cells together • Adhesion proteins link plasma membranes of adjacent cells • Contours of adjacent cell membranes • Special cell junctions

38. Tight Junction Figure 4.7a

39. Lateral Surface Features – Cell Junctions • Tight junctions (zona occludens) – close off intercellular space • Found at apical region of most epithelial types • Some proteins in plasma membrane of adjacent cells are fused • Prevent molecules from passing between cells of epithelial tissue

40. Desmosome Figure 4.7b

41. Lateral Surface Features – Cell Junctions • Desmosomes – two disc-like plaques connected across intercellular space • Plaques of adjoining cells are joined by proteins called cadherins • Proteins interdigitate into extracellular space • Intermediate filaments insert into plaques from cytoplasmic side

42. Gap Junction Figure 4.7c

43. Lateral Surface Features – Cell Junctions • Gap junctions – passageway between two adjacent cells • Let small molecules move directly between neighboring cells • Cells are connected by hollow cylinders of protein

44. Basal Feature: The Basal Lamina  Non-cellular supporting sheet between the epithelium and the connective tissue deep to it  Consists of proteins secreted by the epithelial cells  Functions:  Acts as a selective filter, determining which molecules from capillaries enter the epithelium  Acts as scaffolding along which regenerating epithelial cells can migrate  Basal lamina and reticular layers of the underlying connective tissue deep to it form the basement membrane

45. Connective Tissue • Most diverse and abundant tissue • Main classes • Connective tissue proper • Cartilage • Bone tissue • Blood • Cells separated by large amount of extracellular matrix • Common embryonic origin – mesenchyme

46. Classes of Connective Tissue Figure 4.9

47. Major Functions of Connective Tissue • Support and binding of other tissues • Holding body fluids • Defending body against infection • Storing nutrients as fat

48. Connective Tissue Proper • Two main subclasses • Loose connective tissue • Dense connective tissue

49. Areolar Connective Tissue – A Model Connective Tissue • Areolar connective tissue • Underlies epithelial tissue • Surrounds small nerves and blood vessels • Has structures and functions shared by other connective tissues • Borders all other tissues in the body • Fibers provide support • Three types of protein fibers in extracellular matrix • Collagen fibers • Reticular fibers • Elastic fibers • Fibroblasts produce these fibers

50. Areolar Connective Tissue • Description • Gel-like matrix with all three fiber types • Cells – fibroblasts, macrophages, mast cells, white blood cells • Function • Wraps and cushions organs • Holds and conveys tissue fluid • Important role in inflammation