Epithelial Tissue Types and Connective Tissue Classes

1. PART 2 Tissues

2. 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 • Proximal urethra

3. Transitional Epithelium Figure 4.3h

4. 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

5. Unicellular Exocrine Glands (The Goblet Cell) • Goblet cells produce mucin • Mucin + water  mucus • Protects and lubricates many internal body surfaces • Goblet cells are a unicellular exocrine gland

6. Goblet Cells Figure 4.5

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

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

9. Types of Multicellular Exocrine Glands Figure 4.6

10. Endocrine Glands • Endocrine glands are ductless glands • Secrete substances directly into bloodstream • Produce molecules called hormones

11. Lateral Surface Features – Cell Junctions • Factors holding epithelial cells together • Adhesion proteins link plasma membranes of adjacent cells • Contours of adjacent cell membranes • (Like puzzle pieces) • Special cell junctions

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

13. Tight Junction Figure 4.7a

14. Lateral Surface Features – Cell Junctions • Adherens junctions (zonula adherens) – anchoring junction • Transmembrane linker proteins attach to actin microfilaments of the cytoskeleton and bind adjacent cells • With tight junctions, form the tight junctional complex around apical lateral borders of epithelial tissues

15. Lateral Surface Features – Cell Junctions • Desmosomes – two disclike plaques connected across intercellular space • Plaques of adjoining cells are joined by proteins called cadherins • Regulate cell shape/structure by cell-cell interactions • Class of calcium-dependent adhesion molecules

16. Lateral Surface Features – Cell Junctions • Proteins interdigitate into extracellular space • Intermediate filaments insert into plaques from cytoplasmic side • Also found in the heart

17. Desmosome Figure 4.7b

18. 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 • Function in intercellular communication

19. Gap Junction Figure 4.7c

20. Basal Feature: The Basal Lamina • Noncellular supporting sheet between the ET and the CT deep to it • Consists of proteins secreted by ET cells

21. Basal Feature: The Basal Lamina • Functions • Acts as a selective filter, determining which molecules from capillaries enter the epithelium • Acts as scaffolding along which regenerating ET cells can migrate • Basal lamina and reticular layers of the underlying CT deep to it form the basement membrane

22. Epithelial Surface Features • Apical surface features • Microvilli – fingerlike extensions of plasma membrane • Abundant in ET of small intestine and kidney • Maximize surface area across which small molecules enter or leave • Act as stiff knobs that resist abrasion

23. Epithelial Surface Features • Apical surface features • Cilia – whiplike, highly motile extensions of apical surface membranes • Contains a core of nine pairs of microtubules encircling one middle pair • Axoneme – a set of microtubules • Each pair of microtubules – arranged in a doublet • Microtubules in cilia – arranged similarly to cytoplasmic organelles called centrioles • Movement of cilia – in coordinated waves

24. A Cilium Figure 4.8

25. Classes of 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 • Extracellular matrix is composed of ground substance

26. Connective Tissue Proper • Has two subclasses • Loose connective tissue • Areolar, adipose, and reticular • Dense connective tissue • Dense irregular, dense regular, and elastic

27. Classes of Connective Tissue Figure 4.9

28. 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 CT • Borders all other tissues in the body • Is a “model” connective tissue – why?

29. Major Functions of Connective Tissue • Structures within areolar CT and function • Support and binding of other tissues • Holding body fluids (interstitial fluid  lymph) • Defending body against infection • Storing nutrients as fat

30. Areolar Connective Tissue • Fibers provide support • Three types of protein fibers in extracellular matrix • Collagen fibers • Reticular fibers • Elastic fibers • Fibroblasts produce these fibers

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

32. Areolar Connective Tissue • Locations • Widely distributed under epithelia • Packages organs • Surrounds capillaries

33. Areolar Connective Tissue Figure 4.12b

34. Areolar Connective Tissue • Tissue fluid (interstitial fluid) • Watery fluid occupying extracellular matrix • Tissue fluid derives from blood • Ground substance • Viscous, spongy part of extracellular matrix • Consists of sugar and protein molecules • Made and secreted by fibroblasts

35. Areolar Connective Tissue • Main battlefield in fight against infection • Defenders gather at infection sites • Macrophages • Plasma cells • Mast cells • White blood cells • Neutrophils, lymphocytes, and eosinophils