Histology

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Histology

  1. 1. Anatomy and Physiology, Seventh Edition Rod R. Seeley Idaho State University Trent D. Stephens Idaho State University Philip Tate Phoenix College Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. *See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes. Chapter 04 Lecture Outline *
  2. 2. Tissues and Histology <ul><li>Tissue classification based on structure of cells, composition of noncellular extracellular matrix, and cell function </li></ul><ul><li>Major types of adult tissues </li></ul><ul><ul><li>Epithelial </li></ul></ul><ul><ul><li>Connective </li></ul></ul><ul><ul><li>Muscle </li></ul></ul><ul><ul><li>Nervous </li></ul></ul><ul><li>Histology : Microscopic Study of Tissues </li></ul><ul><ul><li>Biopsy : removal of tissues for diagnostic purposes </li></ul></ul><ul><ul><li>Autopsy : examination of organs of a dead body to determine cause of death </li></ul></ul>
  3. 3. Embryonic Tissue <ul><li>Germ layers </li></ul><ul><ul><li>Endoderm </li></ul></ul><ul><ul><ul><li>Inner layer </li></ul></ul></ul><ul><ul><ul><li>Forms lining of digestive tract and derivatives </li></ul></ul></ul><ul><ul><li>Mesoderm </li></ul></ul><ul><ul><ul><li>Middle layer </li></ul></ul></ul><ul><ul><ul><li>Forms tissues as such muscle, bone, blood vessels </li></ul></ul></ul><ul><ul><li>Ectoderm </li></ul></ul><ul><ul><ul><li>Outer layer </li></ul></ul></ul><ul><ul><ul><li>Forms skin and neuroectoderm </li></ul></ul></ul>
  4. 4. Epithelium Characteristics <ul><li>Covers body surfaces, lines hollow organs, and forms glands </li></ul><ul><ul><li>Outside surface of the body </li></ul></ul><ul><ul><li>Lining of digestive, respiratory and urogenital systems </li></ul></ul><ul><ul><li>Heart and blood vessels </li></ul></ul><ul><li>Cellularity - Consists almost entirely of cells held together by tight junctions </li></ul><ul><li>Polarity - Has apical , basal , and lateral surfaces </li></ul><ul><li>Basal region bound to a basement membrane </li></ul><ul><li>Avascular - lack blood vessels </li></ul><ul><li>Regenerative -Replaces cells lost at exposed surface by cell division </li></ul>
  5. 5. Functions of Epithelia <ul><li>Provide Physical rotection </li></ul><ul><ul><li>Protect exposed & internal surfaces from abrasion, dehydration, destruction by chem/biol. agents </li></ul></ul><ul><li>Control Permeability </li></ul><ul><ul><li>Any substance entering or leaving body must cross an epithelium </li></ul></ul><ul><ul><li>Some epi. are impermeable; others very permeable </li></ul></ul><ul><li>Produce Specialized Secretions </li></ul><ul><ul><li>These cells are called gland cells </li></ul></ul>
  6. 6. Basement Membrane <ul><li>Extracellular: formed by secretions of both epithelium lying above it and connective tissue lying beneath. Acellular “glue” </li></ul><ul><ul><li>Attachment to C.T. </li></ul></ul><ul><ul><li>Guides cell migration during tissue repair </li></ul></ul><ul><ul><li>Not every epithelium has a basement membrane associated with it </li></ul></ul>
  7. 7. Membrane Junctions <ul><ul><li>1. Tight junction – impermeable junction that encircles the cell </li></ul></ul><ul><ul><li>2. Desmosome – anchoring junction scattered along the sides of cells </li></ul></ul><ul><li>3.Gap junction – a junction that allows chemical substances to pass between cells </li></ul><ul><li>Some cells (RBC’s, sperm, phagocytes) are “footloose” </li></ul><ul><li>To be effective as a barrier, epithelia must form a com- </li></ul><ul><li>plete cover or lining </li></ul><ul><li>Held together by special membrane junctions called: </li></ul>
  8. 8. Membrane Junctions: Tight Junction <ul><li>Integral proteins of adjacent </li></ul><ul><li>cells fuse together. </li></ul><ul><li>Completely encircle the cell </li></ul><ul><li>and form an adhesion belt. </li></ul><ul><li>Form an impermeable </li></ul><ul><li>junction. </li></ul><ul><li>Common near apical region </li></ul>
  9. 9. Membrane Junctions: Desmosome Figure 3.5b Linker proteins extend from plaque like teeth of a zipper. Intermediate filaments extend across width of cell. <ul><li>Common in superficial layers of skin; skin </li></ul><ul><li>peels after a sunburn </li></ul><ul><li>Reduces chance of tearing, twisting, stretching </li></ul>
  10. 10. Membrane Junctions: Gap Junction Figure 3.5c <ul><li>Connexon proteins are trans- </li></ul><ul><li>membrane proteins. </li></ul><ul><li>Present in electrically excitable </li></ul><ul><li>tissues (heart, smooth muscle) </li></ul>
  11. 11. Classification of Epithelium <ul><li>Number of layers of cells </li></ul><ul><ul><li>Simple - one layer of cells. Each extends from basement membrane to the free surface </li></ul></ul><ul><ul><li>Stratified - more than one layer. </li></ul></ul><ul><ul><li>Pseudostratified - tissue appears to be stratified, but all cells contact basement membrane so it is in fact simple </li></ul></ul><ul><li>Shape of cells </li></ul><ul><ul><li>Squamous - flat, scale-like </li></ul></ul><ul><ul><li>Cuboidal - about equal in height and width </li></ul></ul><ul><ul><li>Columnar - taller than wide </li></ul></ul>
  12. 12. Functional Characteristics How does shape affect function? <ul><li>Simple: allows diffusion of gases, filtration of blood, secretion, absorption </li></ul><ul><li>Stratified: protection, particularly against abrasion (epidermis of skin) </li></ul><ul><li>Squamous: allow diffusion or act as filters </li></ul><ul><li>Cuboidal and columnar: secretion and/or absorption. </li></ul>
  13. 13. Simple Squamous Epithelium <ul><li>Structure: single layer of extremely flat cells </li></ul><ul><li>Functions: diffusion, filtration, lining. </li></ul><ul><li>Location: simple squamous- lining of the heart (endocardium), blood and lymphatic vessels (endothelium), alveoli of the lungs, lining of serous membranes (mesothelium). </li></ul>
  14. 14. Simple Cuboidal Epithelium <ul><li>Structure: single layer of cube-shaped cells with large, central nuclei </li></ul><ul><li>Some types have microvilli (kidney tubules) or cilia (terminal bronchioles of the lungs) </li></ul><ul><li>Functions: </li></ul><ul><ul><li>Secretion and absorption in the kidney </li></ul></ul><ul><ul><li>Secretion in glands and choroid plexus (produce CSF in CNS) </li></ul></ul><ul><ul><li>Movement of mucus out of the terminal bronchioles by ciliated cells. </li></ul></ul><ul><li>Locations: Kidney tubules, glands and their ducts, choroid plexus of the brain, and surface of the ovaries. </li></ul>
  15. 15. Simple Columnar Epithelium <ul><li>Structure: single layer of tall, narrow cells. Some have cilia (bronchioles, </li></ul><ul><li>auditory tubes, uterine tubes, and uterus) or microvilli (intestine). </li></ul><ul><li>Functions: </li></ul><ul><ul><li>Movement of particles out of the bronchioles by ciliated cells </li></ul></ul><ul><ul><li>Aids in the movement of oocytes through the uterine tubes by ciliated cells </li></ul></ul><ul><ul><li>Secretion of gastric and intestine juices </li></ul></ul><ul><ul><li>Absorption by cells of the intestine. </li></ul></ul><ul><li>Location. Glands and some ducts, bronchioles of lungs, uterus, uterine tubes, stomach, small and large intestines. </li></ul>
  16. 16. Pseudostratified Columnar Epithelium <ul><li>Structure: Single layer of cells with different heights; all cells reach basement membrane; some do not reach the free surface. Appears stratified because nuclei are at various levels. Almost always ciliated and associated with goblet (mucus-producing) cells. </li></ul><ul><li>Functions: </li></ul><ul><ul><li>Synthesize and secrete mucus onto the free surface </li></ul></ul><ul><ul><li>Move mucus (or fluid) that contains foreign particles over the free surface and from passages </li></ul></ul><ul><li>Locations: </li></ul><ul><ul><li>Ciliated type in lining of nasal cavity, trachea, and bronchi of lungs. </li></ul></ul><ul><ul><li>Nonciliated type in male’s sperm-carrying ducts </li></ul></ul>
  17. 18. Stratified Squamous Epithelium <ul><li>Structure: multiple layers of cells that are cuboidal in the basal layer and progressively flatten toward the surface. In moist, surface cells retain a nucleus and cytoplasm. In keratinized, surface cells are dead. </li></ul><ul><li>Locations: </li></ul><ul><ul><li>Keratinized (Dry)- skin (epidermis) </li></ul></ul><ul><ul><ul><li>Surface cells are very flat and dead; appear as scales </li></ul></ul></ul><ul><ul><li>Non-keratinized (Moist)- mouth, throat, larynx, esophagus, anus, vagina, inferior urethra, and cornea </li></ul></ul><ul><ul><ul><li>Surface cells retain a nucleus and cytoplasm; not as flattened as in dry type </li></ul></ul></ul><ul><li>Functions: protection against abrasion, caustic chemicals, water loss, and infection. </li></ul>
  18. 19. Transitional Epithelium <ul><li>Structure: stratified; basal cells are cuboidal, surface cells are dome shaped </li></ul><ul><li>Functions: stretches to permit the distension of the urinary bladder </li></ul><ul><li>Location: lining of urinary bladder, ureters, and superior urethra. </li></ul>
  19. 20. Epithelium: Glandular <ul><li>A gland is one or more cells that makes and secretes an aqueous fluid </li></ul><ul><li>Two types of glands formed by infolding of epithelium: </li></ul><ul><ul><li>Endocrine : no contact with exterior of body; ductless ; produce hormones (pituitary, thyroid, adrenals, pancreas) </li></ul></ul><ul><ul><li>Exocrine : open to exterior of body via ducts (sweat, oil) </li></ul></ul><ul><li>Exocrine glands classified either by structure or by the method of secretion </li></ul><ul><li>Classified by structure </li></ul><ul><ul><li>Unicellular: goblet cells </li></ul></ul><ul><ul><li>Multicellular: sweat, oil, pituitary, adrenal </li></ul></ul>
  20. 21. Multicellular Exocrine Glands <ul><li>Classified on the basis of types of ducts or mode of secretion </li></ul><ul><li>Types of ducts </li></ul><ul><ul><li>Simple: ducts with few branches </li></ul></ul><ul><ul><li>Compound: ducts with many branches </li></ul></ul><ul><ul><ul><li>If ducts end in tubules or sac-like structures: acini . Pancreas </li></ul></ul></ul><ul><ul><ul><li>If ducts end in simple sacs: alveoli . Lungs </li></ul></ul></ul>
  21. 22. Classified by Method of Secretion Types <ul><li>Merocrine </li></ul><ul><ul><li>No loss of cytoplasm. Secretion leaves by exocytosis. </li></ul></ul><ul><ul><li>Sweat glands, pancreas, and salivary glands </li></ul></ul><ul><li>Apocrine </li></ul><ul><ul><li>Fragments of the gland go into the secretion. Apex of cell pinches off. </li></ul></ul><ul><ul><li>Mammary glands. </li></ul></ul><ul><li>Holocrine </li></ul><ul><ul><li>Whole cell becomes part of secretion. Secretion accumulates in cell, cell ruptures and dies. </li></ul></ul><ul><ul><li>Sebaceous glands (Oil glands of skin) </li></ul></ul>
  22. 23. Connective Tissue <ul><li>Abundant; found in every organ </li></ul><ul><li>Consists of cells and fibers separated by extracellular matrix </li></ul><ul><li>Many diverse types </li></ul><ul><li>Performs variety of important functions </li></ul>
  23. 24. Connective Tissue: Embryonic Origin Figure 4.5
  24. 25. Characteristics of Connective Tissue <ul><li>Connective tissues have: </li></ul><ul><ul><li>Mesenchyme as their common tissue of origin (mesenchyme derived from mesoderm) </li></ul></ul><ul><ul><li>Varying degrees of vascularity </li></ul></ul><ul><ul><li>Nonliving extracellular matrix, consisting of ground substance and fibers </li></ul></ul><ul><ul><li>Cells are not as abundant nor as tightly packed together as in epithelium </li></ul></ul>
  25. 26. Functions of Connective Tissue <ul><li>Enclose organs as a capsule and separate organs into layers. Areolar </li></ul><ul><li>Connect tissues to one another. Tendons and ligaments. </li></ul><ul><li>Support and movement. Bones. </li></ul><ul><li>Storage. Fat. </li></ul><ul><li>Insulation. Fat. </li></ul><ul><li>Transport. Blood. </li></ul><ul><li>Protection. Bone, cells of the immune system. </li></ul>
  26. 27. Structural Elements of Connective Tissue <ul><li>Ground substance – unstructured material that fills the space between cells </li></ul><ul><li>Fibers – collagen, elastic, or reticular </li></ul><ul><li>Cells – fibroblasts, chondroblasts, osteoblasts, hematopoietic stem cells, and others </li></ul>
  27. 28. Ground Substance <ul><li>Interstitial (tissue) fluid within which are one or more of the molecules listed below: </li></ul><ul><ul><li>Hyaluronic acid: polysaccharide. Good lubricant. Vitreous humor of eye. </li></ul></ul><ul><ul><li>Proteoglycans: protein and polysaccharide complex. Protein part attaches to hyaluronic acid. Trap large amounts of water. </li></ul></ul><ul><ul><li>Adhesive molecules: hold proteoglycan aggregates together. Chondronectin in cartilage, osteonectin in bone, fibronectin in fibrous connective tissue. </li></ul></ul><ul><li>Functions as a molecular sieve through which nutrients diffuse between blood capillaries and cells </li></ul>
  28. 29. Ground Substance: Proteoglycan Structure Figure 4.6b
  29. 30. Composition of Extracellular Matrix: Fibers <ul><li>Protein fibers </li></ul><ul><ul><li>Collagen fibers . Composed of the protein collagen. Strong, flexible, inelastic; great tensile strength (i.e. resist stretch). Perfect for tendons, ligaments </li></ul></ul><ul><ul><li>Elastic fibers . Contain molecules of protein elastin that resemble coiled springs. Returns to its original shape after distension or compression. Perfect for lungs, large blood vessels </li></ul></ul><ul><ul><li>Reticular fibers . Formed from fine collagenous fibers; form branching networks ( stroma). Fill spaces between tissues and organs. </li></ul></ul>
  30. 31. Connective Tissue Cells <ul><li>Fibroblasts - secrete the proteins needed for fiber synthesis and components of the extracellular matrix </li></ul><ul><li>Adipose or fat cells ( adipocytes ). Common in some tissues (dermis of skin); rare in some (cartilage) </li></ul><ul><li>Mast cells . Common beneath membranes; along small blood vessels. Can release heparin, histamine, and proteolytic enzymes in response to injury. </li></ul><ul><li>Leukocytes (WBC’s) . Respond to injury or infection </li></ul><ul><li>Plasma cells - type of WBC that secretes antibodies </li></ul><ul><li>Macrophages . Phagocytic or provide protection </li></ul><ul><li>Chondroblasts - form cartilage </li></ul><ul><li>Osteoblasts - form bone </li></ul><ul><li>Hematopoietic stem cells - form blood cells </li></ul><ul><li>Undifferentiated mesenchyme (stem cells). Have potential to differentiate into adult cell types. </li></ul>
  31. 32. Embryonic Connective Tissue <ul><li>Mesenchyme : source of all adult connective tissue. </li></ul><ul><ul><li>Forms primarily from mesoderm </li></ul></ul><ul><ul><li>Delicate collagen fibers embedded in semifluid matrix </li></ul></ul><ul><li>Mucus : found only in the umbilical cord. Wharton’s jelly. </li></ul>
  32. 33. Loose (Areolar) Connective Tissue <ul><li>Loose packing material of most organs and tissues </li></ul><ul><li>Location: Attaches skin to underlying tissues. Superficial fascia = subcutaneous layer = hypodermis; surrounding b.v.’s, nerves </li></ul><ul><li>Contains collagen, reticular, elastic fibers and many types of cells (fibroblasts, adipose, mast, leukocytes, mcacrophages </li></ul>
  33. 34. Connective Tissue : Adipose <ul><li>Predominant cells are adipocytes </li></ul><ul><li>Yellow ( white ). Most abundant type, has a wide distribution. White at birth and yellows with age. </li></ul><ul><ul><li>Cells has scant ring of cytoplasm surrounding single large lipid droplet. Nuclei flattened </li></ul></ul><ul><ul><li>Under skin, around kidneys and eyeballs, within abdomen, in breasts </li></ul></ul><ul><li>Brown . Found only in specific areas of body: axillae, neck and near kidneys </li></ul><ul><ul><li>Cells are polygonal in shape, have a considerable volume of cytoplasm and contain multiple lipid droplets of varying size. </li></ul></ul>
  34. 35. Connective Tissue Proper: Reticular C.T. Figure 4.8d
  35. 36. Dense Regular Connective Tissue <ul><li>Has abundant parallel collagen fibers that resist stretching </li></ul><ul><li>Major cell type is fibroblast (interspersed amongst fibers) </li></ul><ul><ul><li>Tendons : Connect muscles to bones </li></ul></ul><ul><ul><li>Ligaments : Connect bones to bones. Collagen often less compact, usually flattened, form sheets or bands </li></ul></ul><ul><ul><li>Aponeuroes: flattened sheet of tendon in abdominal wall </li></ul></ul>
  36. 37. Dense Irregular Connective Tissue <ul><li>Irregularly arranged collagen fibers with some elastic fibers </li></ul><ul><li>Major cell type is the fibroblast </li></ul><ul><li>Withstands tension in many directions </li></ul><ul><li>Forms innermost layer of the dermis of the skin, scars, capsules of kidney, spleen, testis </li></ul>
  37. 38. Elastic Connective Tissue <ul><li>Bundles and sheets of collagenous and elastic fibers oriented in multiple directions </li></ul><ul><li>In walls of elastic arteries (aorta), lungs, vocal ligaments </li></ul><ul><li>Strong, yet elastic </li></ul>
  38. 39. Connective Tissue: Cartilage <ul><li>Composed of chondrocytes located in matrix-surrounded spaces called lacunae . </li></ul><ul><li>Type of cartilage determined by components of the matrix. </li></ul><ul><li>Firm consistency. </li></ul><ul><li>Ground substance: Proteoglycans and hyaluronic acid complexed together trap large amounts of water. Tissue can spring back after being compressed. </li></ul><ul><li>Avascular and no nerve supply. Heals slowly. </li></ul><ul><li>Perichondrium . Dense irregular connective tissue that surrounds cartilage. Fibroblasts of perichondrium can differentiate into chondroblasts (cartilage-forming cells) </li></ul><ul><li>Types of cartilage </li></ul><ul><ul><li>Hyaline </li></ul></ul><ul><ul><li>Fibrocartilage </li></ul></ul><ul><ul><li>Elastic </li></ul></ul>
  39. 40. Hyaline Cartilage <ul><li>Structure: large amount of collagen fibers evenly distributed in matrix. Smooth surface in articulations </li></ul><ul><li>Locations: </li></ul><ul><ul><li>Found in areas for strong support and some flexibility: rib cage (costal cartilage), ext. nose, trachea, and bronchi, most joints ( articular cartilage ) </li></ul></ul><ul><ul><li>In embryo forms most of skeleton </li></ul></ul><ul><ul><li>Involved in growth that increases bone length ( epiphyseal plate) </li></ul></ul>
  40. 41. Elastic Cartilage <ul><li>Structure: elastic and collagen fibers embedded in proteoglycans. Rigid but elastic properties </li></ul><ul><li>Locations: external ears and epiglottis </li></ul>
  41. 42. Fibrocartilage <ul><li>Structure: thick collagen fibers distributed in proteoglycan matrix; slightly compressible and very tough </li></ul><ul><li>Locations: found in areas of body where a great deal of pressure is applied to joints </li></ul><ul><ul><li>Menisci of knee joint, pubic symphysis, intervertebral discs </li></ul></ul>
  42. 43. Connective Tissue: Bone <ul><li>Hard connective tissue composed of living cells ( osteocytes ) and mineralized matrix </li></ul><ul><li>Matrix: gives strength and rigidity; allows bone to support and protect other tissues and organs </li></ul><ul><ul><li>Organic components: collagen fibers </li></ul></ul><ul><ul><li>Inorganic components: calcium salts ( hydroxyapatites) </li></ul></ul><ul><li>Osteocytes located in lacunae </li></ul><ul><li>Types </li></ul><ul><ul><li>Cancellous or spongy bone </li></ul></ul><ul><ul><li>Compact bone </li></ul></ul><ul><li>Stores calcium, minerals, and fat </li></ul><ul><li>Marrow inside bones is the site of hematopoiesis </li></ul>
  43. 44. Bone, cont. <ul><li>Cancellous or spongy bone: trabeculae of bone with spaces between. Looks like a sponge. Found inside bones. </li></ul><ul><li>Compact bone: arranged in concentric circle layers around a central canal which contains a blood vessel. Found on periphery of long bones. </li></ul>
  44. 45. Blood <ul><li>A fluid connective tissue consisting of plasma and formed elements: </li></ul><ul><ul><li>Matrix: plasma; Liquid and lacks fibers. </li></ul></ul><ul><ul><li>Formed elements: red cells, white cells, and platelets </li></ul></ul><ul><li>Functions in the transport of respiratory gases, nutrients, and wastes </li></ul>
  45. 46. Muscle Tissue <ul><li>Characteristics </li></ul><ul><ul><li>Cells are referred to as fibers ; some types are multinucleated </li></ul></ul><ul><ul><li>Contracts or shortens with force when stimulated </li></ul></ul><ul><ul><li>Moves entire body and pumps blood </li></ul></ul><ul><li>Types </li></ul><ul><ul><li>Skeletal: attached to bones </li></ul></ul><ul><ul><li>Cardiac : muscle of the heart. </li></ul></ul><ul><ul><li>Smooth : muscle associated with tubular structures and with the skin. Nonstriated and involuntary. </li></ul></ul>
  46. 47. Skeletal Muscle <ul><li>Most attached to skeleton. </li></ul><ul><li>Striated and voluntary. </li></ul>
  47. 48. Cardiac Muscle <ul><li>Striated, branching fibers </li></ul><ul><li>Involuntary. </li></ul>
  48. 49. Smooth Muscle <ul><li>Found in tubular structures and the skin. </li></ul><ul><li>Nonstriated and involuntary. </li></ul>
  49. 50. Nervous Tissue: Neurons <ul><li>Neurons or nerve cells have the ability to produce action potentials </li></ul><ul><ul><li>Parts: </li></ul></ul><ul><ul><ul><li>Cell body : contains nucleus </li></ul></ul></ul><ul><ul><ul><li>Axon : cell process that conducts impulses away from cell body; usually only one </li></ul></ul></ul><ul><ul><ul><li>Dendrite : cell process that receive impulses from other neurons; many per neuron </li></ul></ul></ul><ul><ul><li>Types: </li></ul></ul><ul><ul><ul><li>Multipolar , bipolar , and unipolar </li></ul></ul></ul><ul><li>Found in brain, spinal cord, and peripheral nerves </li></ul>
  50. 51. Neurons
  51. 52. Epithelial Membranes <ul><li>Cutaneous - skin </li></ul><ul><li>Mucous </li></ul><ul><ul><li>Line cavities that open to the outside of body </li></ul></ul><ul><ul><li>Secrete mucus </li></ul></ul><ul><ul><li>Contains epithelium with goblet cells, basement membrane, lamina propria (sometimes with smooth muscle) </li></ul></ul><ul><ul><li>Found in respiratory, digestive, urinary and reproductive systems. </li></ul></ul><ul><li>Serous . simple squamous epithelium called mesothelium; basement membrane, thin layer of loose C.T. </li></ul><ul><ul><li>Line cavities not open to exterior </li></ul></ul><ul><ul><ul><li>Pericardial, pleural, peritoneal </li></ul></ul></ul><ul><li>Synovial </li></ul><ul><ul><li>Line freely movable joints </li></ul></ul><ul><ul><li>Produce fluid rich in hyaluronic acid </li></ul></ul>
  52. 53. Tissues and Aging <ul><li>Cells divide more slowly </li></ul><ul><li>Collagen fibers become more irregular in structure, though they may increase in number </li></ul><ul><ul><li>Tendons and ligaments become less flexible and more fragile </li></ul></ul><ul><li>Elastic fibers fragment, bind to calcium ions, and become less elastic </li></ul><ul><ul><li>Arterial walls and elastic ligaments become less elastic </li></ul></ul><ul><li>Changes in collagen and elastin result in </li></ul><ul><ul><li>Atherosclerosis and reduced blood supply to tissues </li></ul></ul><ul><ul><li>Wrinkling of the skin </li></ul></ul><ul><ul><li>Increased tendency for bones to break </li></ul></ul><ul><li>Rate of blood cell synthesis declines in the elderly </li></ul><ul><li>Injuries don’t heal as readily </li></ul>

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