Chapter 4 Tissues and Histology

1. Chapter 4Tissues and Histology Tissues - collections of similar cells and the substances surrounding them Tissue classification based on structure of cells, composition of noncellular extracellular matrix, and cell function Major types of adult tissues Epithelial Connective Muscle Nervous Histology: Microscopic Study of Tissues Biopsy: removal of tissues for diagnostic purposes Autopsy: examination of organs of a dead body to determine cause of death

2. Embryonic Tissue 3 major germ layers that form the embryonic disc (source of stem cells) Endoderm Inner layer Forms lining of digestive tract and derivatives Mesoderm Middle layer Forms tissues as such muscle, bone, blood vessels Ectoderm Outer layer Forms skin and neuroectoderm

3. I. Epithelial Tissue Cellularity - Consists almost entirely of cells Covers body surfaces, lines hollow organs, and forms glands Outside surface of the body Lining of digestive, respiratory and urogenital systems Heart and blood vessels Linings of many body cavities Polarity - Has apical, basal, and lateral surfaces Rests on a basement membrane Specialized cell contacts bind adjacent cells together Avascular - no blood vessels Regenerative -Replaces lost cells by cell division

4. Functions of Epithelia Protecting underlying structures; e.g., epithelium lining the mouth Acting as barriers; e.g., skin Permitting the passage of substances; e.g., cells lining air sacs in lungs and nephrons in kidney Secreting substances; e.g., pancreatic cells Absorbing substances; e.g., lining of stomach and small intestine

5. Special Characteristics of Epithelia

6. Classification of Epithelium Number of layers of cells Simple- one layer of cells. Each extends from basement membrane to the free surface Stratified- more than one layer. Pseudostratified- tissue appears to be stratified, but all cells contact basement membrane so it is in fact simple Shape of cells Squamous- flat, scale-like Cuboidal- about equal in height and width Columnar- taller than wide

7. Classifications of Epithelia

8. Simple Squamous Epithelium

9. Simple Cuboidal Epithelium

10. Simple Columnar Epithelium

11. Pseudostratified Ciliated Columnar Epithelium

12. 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

13. 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

14. 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

15. 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

16. Stratified Squamous Epithelium

17. Transitional Epithelium

18. Epithelium: Glandular A gland is one or more cells that makes and secretes an aqueous fluid Two types of glands formed by infolding of epithelium: Endocrine: no contact with exterior of body; ductless; produce hormones (pituitary, thyroid, adrenals, pancreas) Exocrine: open to exterior of body via ducts (sweat, oil) Exocrine glands classified either by structure or by the method of secretion Classified by structure Unicellular: goblet cells Multicellular: sweat, oil, pituitary, adrenal

19. Multicellular Exocrine Glands Classified on the basis of types of ducts or mode of secretion Types of ducts Simple: ducts with few branches Compound: ducts with many branches If ducts end in tubules or sac-like structures: acini. Pancreas If ducts end in simple sacs: alveoli. Lungs

20. Lateral Surface Features Tight junctions Desmosomes Gap junctions

21. Membrane Junctions: Tight Junction

22. 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

23. Membrane Junctions: Desmosome

24. Membrane Junctions: Gap Junction

25. Basal Feature: The Basal Lamina ? Noncellular 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

26. Epithelial Surface Features Apical surface features Microvilli – finger-like extensions of plasma membrane Abundant in epithelia of small intestine and kidney Maximize surface area across which small molecules enter or leave Cilia – whip-like, highly motile extensions of apical surface membranes Movement of cilia – in coordinated waves

27. Connective Tissue Most diverse and abundant tissue Main classes Connective tissue proper Cartilage Bone tissue Blood Characteristics Mesenchyme as their common tissue of origin (mesenchyme derived from mesoderm) Varying degrees of vascularity Nonliving extracellular matrix, consisting of ground substance and fibers Cells are not as abundant nor as tightly packed together as in epithelium

28. Connective Tissue: Embryonic Origin

29. Functions of Connective Tissue Enclose organs as a capsule and separate organs into layers. Areolar Connect tissues to one another. Tendons and ligaments. Support and movement. Bones. Storage. Fat. Insulation. Fat. Transport. Blood. Protection. Bone, cells of the immune system.

30. Structural Elements of Connective Tissue Ground substance – unstructured material that fills the space between cells Fibers – collagen, elastic, or reticular Cells – fibroblasts, chondroblasts, osteoblasts, hematopoietic stem cells, and others

31. Connective Tissue Cells Fibroblasts - secrete the proteins needed for fiber synthesis and components of the extracellular matrix Adipose or fat cells (adipocytes). Common in some tissues (dermis of skin); rare in some (cartilage) Mast cells. Common beneath membranes; along small blood vessels. Can release heparin, histamine, and proteolytic enzymes in response to injury. Leukocytes (WBC’s). Respond to injury or infection Macrophages. Derived from monocytes (a WBC). Phagocytic; provide protection Chondroblasts - form cartilage Osteoblasts - form bone Hematopoietic stem cells - form blood cells Undifferentiated mesenchyme (stem cells). Have potential to differentiate into adult cell types.

32. Extracellular Matrix - ECM ECM has 3 major components 1. Protein fibers 2. Ground substance 3. Fluid Protein fibers Collagen fibers. Composed of the protein collagen. Strong, flexible, inelastic; great tensile strength (i.e. resist stretch). Perfect for tendons, ligaments Elastic fibers. Contain molecules of protein elastin that resemble coiled springs. Returns to its original shape after stretching or compression. Perfect for lungs, large blood vessels Reticular fibers. Formed from fine collagenous fibers; form branching networks (stroma). Fill spaces between tissues and organs.

33. Ground Substance Interstitial (tissue) fluid within which are one or more of the molecules listed below: Hyaluronic acid: a polysaccharide. Very slippery; serves as a good lubricant for joints. Common in most connective tissues. Proteoglycans: protein and polysaccharide complex. Polysaccharides called glyocosaminoglycans (chondroitin sulfate, keratin sulfate). Protein part attaches to hyaluronic acid. Able to trap large amounts of water. Adhesive molecules: hold proteoglycan aggregates together. Chondronectin in cartilage, osteonectin in bone, fibronectin in fibrous connective tissue. Functions as a molecular sieve through which nutrients diffuse between blood capillaries and cells

34. Embryonic Connective Tissue Mesenchyme: source of all adult connective tissue. Derived from mesoderm Delicate collagen fibers embedded in semifluid matrix Mucus: found only in the umbilical cord. Wharton’s jelly.

35. Areolar Connective Tissue

36. Adipose Tissue

37. Reticular Connective Tissue

38. Dense Irregular Connective Tissue

39. Dense Regular Connective Tissue

40. Elastic Connective Tissue Bundles and sheets of collagenous and elastic fibers oriented in multiple directions In walls of elastic arteries (aorta), lungs, vocal ligaments Strong, yet elastic; allows for recoil of tissue after being stretched

41. Connective Tissue: Cartilage Composed of chondrocytes (cells) located in matrix-surrounded spaces called lacunae. Type of cartilage determined by components of the matrix. Firm consistency. Ground substance: Proteoglycans and hyaluronic acid complexed together trap large amounts of water (microscopic sponges). Allows tissue to spring back after being compressed. Avascular and no nerve supply. Heals slowly. Perichondrium. Dense irregular connective tissue that surrounds cartilage. Fibroblasts of perichondrium can differentiate into chondroblasts (cartilage-forming cells) Types of cartilage Hyaline Fibrocartilage Elastic

42. Hyaline Cartilage

43. Elastic Cartilage

44. Fibrocartilage

45. Bone Tissue

46. Blood Tissue

47. Muscle Tissue Characteristics Cells are referred to as fibers Contracts or shortens with force when stimulated Moves entire body and pumps blood Types Skeletal:attached to bones Cardiac: muscle of the heart. Smooth: muscle associated with tubular structures and with the skin. Nonstriated and involuntary.

48. Skeletal Muscle Tissue

49. Cardiac Muscle Tissue

50. Smooth Muscle Tissue

51. Nervous Tissue

52. Tissues and Aging Cells divide more slowly Collagen fibers become more irregular in structure, though they may increase in number Tendons and ligaments become less flexible and more fragile Elastic fibers fragment, bind to calcium ions, and become less elastic Arterial walls and elastic ligaments become less elastic Changes in collagen and elastin result in Atherosclerosis and reduced blood supply to tissues Wrinkling of the skin Increased tendency for bones to break Rate of blood cell synthesis declines in the elderly Injuries don’t heal as readily