1. Dvt 1102 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
Figure 4.1

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
Figure 4.3a

9. Simple Cuboidal Epithelium
Figure 4.3b

10. Simple Columnar Epithelium
Figure 4.3c

11. Pseudostratified Ciliated Columnar Epithelium
Figure 4.3d

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
Figure 4.3e

17. Transitional Epithelium
Figure 4.3h

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
Integral proteins of adjacent
cells fuse together
Completely encircle the cell
and form an adhesion belt.
Form an impermeable
junction.
Common near apical region

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
Linker proteins extend from plaque like teeth of a zipper.
Intermediate filaments extend across width of cell.
Common in superficial layers of skin; skin
peels after a sunburn
Reduces chance of tearing, twisting, stretching
Figure 3.5b

24. Membrane Junctions: Gap Junction
Connexon proteins are trans-
membrane proteins.
Present in electrically excitable
tissues (heart, smooth muscle)

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
Figure 4.5

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 Ground substance 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
Figure 4.12b

36. Adipose Tissue
Figure 4.12c

37. Reticular Connective Tissue
Figure 4.12d

38. Dense Irregular Connective Tissue
Figure 4.12e

39. Dense Regular Connective Tissue
Figure 4.12f

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
Figure 4.12g

43. Elastic Cartilage
Figure 4.12h

44. Fibrocartilage
Figure 4.12i

45. Bone Tissue
Figure 4.12j

46. Blood Tissue
Figure 4.12k

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
Figure 4.14a

49. Cardiac Muscle Tissue
Figure 4.14b

50. Smooth Muscle Tissue
Figure 4.14c

51. Nervous Tissue
Figure 4.15

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