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Tissues and Histology Tissues - collections of similar cells with same embryonic origin performing a similar function.

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1 Tissues and Histology Tissues - collections of similar cells with same embryonic origin performing a similar function

2

3 Tissues and Histology Tissues - collections of similar cells with same embryonic origin performing a function 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

4 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

5 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

6 Special Characteristics of Epithelia
Figure 4.1

7 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

8 Classifications of Epithelia

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10 Simple Squamous Epithelium
Figure 4.3a

11 Simple Cuboidal Epithelium
Figure 4.3b

12 Simple Columnar Epithelium
Figure 4.3c

13 Pseudostratified Ciliated Columnar Epithelium
Figure 4.3d

14 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

15 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

16 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

17 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

18 Stratified Squamous Epithelium
Figure 4.3e

19 Transitional Epithelium
Figure 4.3h

20 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

21 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

22 Lateral Surface Features
Tight junctions Desmosomes Gap junctions

23 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

24 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

25 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

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

27 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

28 Epithelial cells Basal lamina Collagen fibers

29 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

30 Connective Tissue

31 Connective Tissue Most diverse and abundant tissue Main classes
Connective tissue proper Cartilage Bone tissue Blood Characteristics Vascular Nonliving extracellular matrix, consisting of ground substance and fibers Cells are not abundant as in epithelium

32 Connective Tissue: Embryonic Origin
Figure 4.5

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34 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 and Insulation - Fat Transport - Blood Protection - Bone, cells of the immune system

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

36 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 enzymes in response to injury. Leukocytes (WBC’s). Respond to injury or infection Macrophages - Phagocytic; provide protection Chondroblasts - form cartilage Osteoblasts - form bone Hematopoietic stem cells - form blood cells

37 Extracellular Matrix - ECM
ECM has 3 major components 1. Protein fibers Ground substance Fluid Protein fibers Collagen fibers. Made of protein collagen. Strong, flexible, inelastic; great tensile strength (i.e. resist stretch). Perfect for tendons, ligaments Elastic fibers. Made of protein elastin that resemble coiled springs. Found in lungs, large blood vessels Reticular fibers. Made from fine collagenous fibers; fill spaces between tissues and organs.

38 Ground Substance Interstitial 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. Proteoglycans: protein and polysaccharide complex. Able to trap large amounts of water. Adhesive molecules: hold proteoglycan aggregates together. Functions as a molecular sieve through which nutrients diffuse between blood capillaries and cells

39 Areolar Connective Tissue
Figure 4.12b

40 Adipose Tissue Figure 4.12c

41 Reticular Connective Tissue
Figure 4.12d

42 Dense Irregular Connective Tissue
Figure 4.12e

43 Dense Regular Connective Tissue
Figure 4.12f

44 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. Types of cartilage Hyaline Fibrocartilage Elastic

45 Hyaline Cartilage Figure 4.12g

46 Elastic Cartilage Figure 4.12h

47 Fibrocartilage Figure 4.12i

48 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

49

50 Bone Tissue Figure 4.12j

51 Blood Tissue Figure 4.12k

52 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.

53 Skeletal Muscle Tissue
Figure 4.14a

54 Cardiac Muscle Tissue Figure 4.14b

55 Smooth Muscle Tissue Figure 4.14c

56 Nervous Tissue Figure 4.15

57 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

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