Anatomy and Physiology Tissue Level of Organization

1. Anatomy and PhysiologyTissue Level of Organization Dr. John M. Bartlett, D.C.

2. Introduction • Differentiation-each cell develops characteristic structural features and limited number of functions • 200 different types of cells in human body, but trillions of cells total • Cells combine to form tissues • Histology – study of tissue

3. Examination of Tissue definition • A group of cells of similar embryonic origin sometimes with some intercellular substances – all dedicated to a common function. • Of the four tissue types – 3 types of tissue cells are not attached to one another – thus they have room to have some substances in between the cells (intercellular substances) – these tissues are connective, muscle, and nerve • Epithelial tissue cells are attached to one another – thus no room between the cells

4. Tissue types (4) • Epithelial – covers exposed surfaces, lines internal passageways, forms glands • Connective – fills internal spaces, provide structural support for other tissues, transport, and storage • Muscle – contractile • Nervous (neural) – carries information as electrical impulses

5. Nervous tissue: Internal communication • Brain, spinal cord, and nerves Muscle tissue: Contracts to cause movement • Muscles attached to bones (skeletal) • Muscles of heart (cardiac) • Muscles of walls of hollow organs (smooth) Epithelial tissue: Forms boundaries between different environments, protects, secretes, absorbs, filters • Skin surface (epidermis) • Lining of GI tract organs and other hollow organs Connective tissue: Supports, protects, binds other tissues together • Bones • Tendons • Fat and other soft padding tissue Figure 4.1

6. Epithelial tissue • Epithelia and glands • Epithelium – layer of cells that forms a barrier with specific properties • Cover every exposed bodypart and line all passageways such as respiratory and digestive system. • Also line chest cavity, abdominal cavity, fluid-filled chambers in brain, eye, and inner ear.

7. Characteristics of epithelia • Cellularity –cells closely bound together by one or more types of cell junctions (covered later). • Polarity – always has an exposed surface…apical surface. Also has attached basal surface where the epithelium is attached to underlying tissues • Organelles and other cytoplasmic components are distributed unevenly between apical and basal surfaces.

8. Characteristics of epithelia • Attachment – basal surface attached to thin basement membrane. • Avascularity – epithelia do not contain blood vessels. Obtain nutrients by diffusion and absorption across apical or basal surface. • Regeneration – cells on apical surface continually replaced through division of stem cells within the epithelium.

9. Functions of epithelial tissue • Protection – from abrasion, dehydration, destruction by physical or chemical agents. • Control permeability – any substance entering your body has to cross an epithelium (digestion). Some epithelia rather impermeable and others very permeable even to large proteins. Epithelia contain necessary “machinery” for selective absorption and secretion. Can be altered in response to stimuli (hormones). Can be altered in response to physical stress (calluses on hands/feet)

10. Functions of epithelial tissue • Provide sensation – many epithelia innervated by many nerve endings. Touch, tickle, pain, heat, cold, mechanoreception, smell, taste, sight, hearing, equilibrium. • Produce specialized secretions – called gland cells. Classified according to discharge location: • Exocrine – discharge onto surface of skin or other epithelial surface. EX> digestive enzymes, perspiration • Endocrine – released into surrounding interstitial fluid and blood. Hormones.

11. Maintaining integrity of epithelia • Three factors: • 1. intercellular connections • 2. attachment to basement membrane • 3. epithelial maintenance and repair

12. Intercellular connections • Cells in an epithelium are firmly attached to each other and the epithelium as a unit is attached to extracellular fibers of the basement membrane. • Large areas of opposing cell membranes are connected by transmembranr proteins called cell adhesion molecules (CAMs). • Membranesof adjacent cells can also be bonded by intercellular cement, which is a thin layer of proteoglycans. • Contain polysaccharide derivatives called glycosaminoglycans like hyaluronic acid.

13. Cell Junctions • Three major types • 1. tight junctions • 2. desmosomes • 3. gap junctions

14. Tight Junction • Partial fusion of lipid portions of 2 cell membranes. • This blocks passage of water and solutes between the cells. • Found near apical surface of cells that line digestive tract to prevent enzymes, acids, and wastes from damaging underlying tissue. • For example in something known as the “Blood – Brain barrier”

15. Microvilli Plasma membranes of adjacent cells Intercellular space Basement membrane Interlocking junctional proteins Intercellular space (a) Tight junctions:Impermeable junctions prevent water soluble molecules from passing through the intercellular space (between the cells). Figure 3.5a

16. Desmosome • CAMS and proteoglycans linking opposing cell membranes. • stronger anchoring junction than the adherens (tight) junction. • Uses Keratin and Stronger Cadherin • Resist stretching and twisting • Most abundant between cells of superficial layers of the skin. • This is why dead skin cells shed in sheets rather than individual cells. • Also interconnect cardiac muscle cells

17. Microvilli Plasma membranes of adjacent cells Intercellular space Basement membrane Intercellular space Stronger filaments Plaque Stronger cadherin Intermediate filament (keratin) Linker glycoproteins (cadherin) (b) Desmosomes: Anchoring junctions bind adjacent cells together and help form an internal tension-reducing network of fibers. Figure 3.5b

18. Gap Junction • Two cells held together by interlocking membranr of proteins called connexons. • These are channel proteins so result is a narrow passageway that lets small molecules and ions pass from cell to cell. • Common among epithelial cells where they help coordinate beating of cilia. • Most abundant in cardiac muscle and smooth muscle to coordinate muscle contraction.

19. Gap junctions: Communicating junctions that allow water soluble substances (ions and small molecules) to pass from one cell to the next cell. Basement membrane Intercellular space Six transmembrane integral proteins move (fluid mosaic) into position on each of the two adjoining cells to form a circle of proteins called a connexon. The two connexons fuse to form a pore between the two cells. Channel between cells (connexon) Figure 3.5c

20. Gap Junctions

21. Basement Membrane • Inner surface of epithelium connected to two-part basement membrane. • Layer closest to epithelia is called basal lamina. • Secreted by adjacent layer of epithelial cells and provides a barrier that restricts the movement of proteins and other large molecules from the underlying connective tissue. • Deeper portion is called reticular lamina. • Gives basement membrane strength.

25. Maintenance and Repair of Epithelium • Epithelial cells exposed to rather harsh environments and must constantly be renewed and repaired. • Continual division of stem cells maintains integrity of the tissue. • Stem cells also called germinative cells. • Located in deepest layer near basement membrane

26. Classification of Epithelia (Step One) Shape • What is the type of epithelia according to the shape of the epithelial cell? • Squamous – flat cells • Cuboidal – cube shaped • Columnar – column shaped taller than wide • Transitional – can assume all the above shapes according to stretch

27. Squamous Cuboidal Columnar Classification based on cell shape. Figure 4.2b

28. Classification of Epithelia (Step Two) Stacking • Is it one layer of epithelial cells or is it more than one layer (is one layer stacked on top of another layer)? • If it is one cell layer it is termed a “simple epithelium” • If it is more than one cell layer (stacked) then termed a “stratified epithelium” • If it appears that the cells are stacked (stratified) but they really are not – it is termed “pseudostratified” • Pseudo – a prefix meaning false

29. Apical surface One cell layer Basal surface Simple Apical surface Basal surface Stacked layers Stratified Classification based on number of cell layers. Figure 4.2a

30. Apical surface Stratified Basal surface When stratified – the epithelia is named in accordance with the shape of the cells in the top (apical) layer. In this case the bottom layer of cells are cuboidal – the top squamous – thus this is termed a stratified squamous. Figure 4.2a

31. TYPES OF EPITHELIA

32. Squamous epithelium • Cells thin, flat, and slightly irregular in shape. • Nucleus is in thickest portion of the cell. • From surface, look like fried eggs laid side to side. • Simple Squamous: • Most delicate • Found in protected regions where absorption takes place or a slick, slippery surface reduces friction. • Alveoli of lungs, lining of ventral body cavities, and lining of heart and blood vessels.

33. Simple Squamous Epithelium (a) Simple squamous epithelium Description: Single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm; the simplest of the epithelia. Air sacs of lung tissue Function: Allows passage of materials by diffusion and filtration in sites where protection is not important; secretes lubricating substances in serosae. Nuclei of squamous epithelial cells Location: Kidney glomeruli; air sacs of lungs; lining of heart, blood vessels, and lymphatic vessels; lining of ventral body cavity (serosae). Photomicrograph: Simple squamous epithelium forming part of the alveolar (air sac) walls (125x). Figure 4.3a

34. Epithelia: Simple Squamous • Special names by location- • Endothelium – lines blood vessels, lymphatic vessels and the inside of the heart • Mesothelium – simple squamous epithelium lining serous membranes – pleura, pericardium and peritoneum

35. Stratified Squamous Epithelium • Located where mechanical stresses are severe. • Cells form a series of layers, like a stack of plywood sheets. • Found at surface of skin, lining of mouth, esophagus, and anus. • Skin: apical layers of these cells filled with keratin to make them tough and water resistant. Keratinized. • Nonkeratinized provides resistance to abrasion but will dry out easily (esophagus, pharynx, anus, vagina)

36. Stratified Squamous (e) Stratified squamous epithelium Description: Thick membrane composed of several cell layers; basal cells are cuboidal or columnar and metabolically active; surface cells are flattened (squamous); in the keratinized type, the surface cells are full of keratin and dead; basal cells are active in mitosis and produce the cells of the more superficial layers. Stratified squamous epithelium Function: Protects underlying tissues in areas subjected to abrasion. Nuclei Location: Nonkeratinized type forms the moist linings of the esophagus, mouth, and vagina; keratinized variety forms the epidermis of the skin, a dry membrane. Basement membrane Connective tissue Photomicrograph: Stratified squamous epithelium lining the esophagus (285x). Figure 4.3e

37. Cuboidal Epithelium • Appear square in typical sections seen under microscope. • Distance between nuclei roughly equal to height of the epithelium. • Three types: • Simple • Stratified • Transitional

38. Simple Cuboidal • Limited protection. • Found where secretion and absorption takes place. • Kidney tubules, pancreas, salivary glands, thyroid gland.

39. Simple Cuboidal (b) Simple cuboidal epithelium Description: Single layer of cubelike cells with large, spherical central nuclei. Simple cuboidal epithelial cells Function: Secretion and absorption. Basement membrane Location: Kidney tubules; ducts and secretory portions of small glands; ovary surface. Connective tissue Photomicrograph: Simple cuboidal epithelium in kidney tubules (430x). Figure 4.3b

40. Stratified Cuboidal • Relatively rare • Located in ducts of sweat glands and in larger ducts of mammary glands.

41. Epithelia: Stratified Cuboidal • Quite rare in body • They protect areas such as ducts of sweat glands, mammary glands and the male urethra.

42. Transitional epithelium • Unique. • Can undergo considerable stretching • Called transitional because appearance changes as the stretching occurs. • Found in bladder.

43. (f) Transitional epithelium Description: Resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells dome shaped or squamouslike, depending on degree of organ stretch. Transitional epithelium Function: Stretches readily and permits distension of urinary organ by contained urine. Location: Lines the ureters, urinary bladder, and part of the urethra. Basement membrane Connective tissue Photomicrograph: Transitional epithelium lining the urinary bladder, relaxed state (360X); note the bulbous, or rounded, appearance of the cells at the surface; these cells flatten and become elongated when the bladder is filled with urine. Figure 4.3f

47. Columnar Epithelium • Taller and more slender than cuboidal cells • Nuclei crowded into narrow band close to basement membrane • Three types • Simple • Pseudostratified • Stratified

48. Simple Columnar Epithelium • Found where absorption and secretion occur • Digestive tract

49. Simple Columnar (c) Simple columnar epithelium Description: Single layer of tall cells with round to oval nuclei; some cells bear cilia; layer may contain mucus- secreting unicellular glands (goblet cells). Simple columnar epithelial cell Function: Absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action. Location: Nonciliated type lines most of the digestive tract (stomach to anal canal), gallbladder, and excretory ducts of some glands; ciliated variety lines small bronchi, uterine tubes, and some regions of the uterus. Basement membrane Photomicrograph: Simple columnar epithelium of the stomach mucosa (860X). Figure 4.3c