SKELETAL SYSTEM

1. SKELETAL SYSTEM

2. SKELETAL SYSTEM Form strong & flexible body framework Bone 206 bones in human skeleton Cartilage All three types Ligaments

3. SKELETAL CARTILAGE Cartilage tissue High water content Confers resilience Avascular, no nerves Surrounded by dense irregular connective tissue “Perichondrium” Vascular, supplies nutrients Prevents outward expansion of cartilage during compression All three types of cartilage represented Hyaline cartilage Elastic cartilage Fibrocartilage

4. SKELETAL CARTILAGE Hyaline cartilage Most abundant skeletal cartilage Chondrocytes, fine collagen fibers Subtypes Articular cartilages Cover ends of most bones at movable joints Costal cartilages Connect ribs to sternum Respiratory cartilages Form skeleton of larynx Reinforce other respiratory organs Nasal cartilages Support the external nose

5. SKELETAL CARTILAGE Elastic cartilage Similar to hyaline cartilage Contain more stretchy elastic fibers Withstand repeated bending Locations External ear Epiglottis

6. SKELETAL CARTILAGE Fibrocartilage Highly compressible Great tensile strength Intermediate between hyaline and elastic cartilages Parallel rows of chondrocytes alternating with thick collagen fibers Occur in areas subjected to heavy pressure and stretch e.g., knee, between vertebrae

7. CARTILAGE GROWTH Appositional growth Cartilage-forming cells in perichondrium secrete new matrix against external face of existing cartilage tissue “Growth from the outside” Interstitial growth Lacunae-bound chondrocytes divide and secrete new matrix “Growth from the inside” Cartilage growth typically ends during adolescence

8. BONES 206 named bones of human skeleton Divided into two groups Axial skeleton Forms long axis of body Includes bones of skull, vertebral column, and rib cage Appendicular skeleton Consists of bones of limbs and girdles attaching these bones to the axial skeleton Arms, legs, hip bones, shoulder bones

9. BONE SHAPES Long bones Short bones Flat bones Irregular bones

10. BONE SHAPES Long bones e.g., femur, humerus, tibia, fibula, radius, ulna Longer than wide Rigid levers + muscle ? movement Short bones e.g., carpals, tarsals Similar in length and width Glide across each other

11. BONE SHAPES Flat bones e.g., scapula, ribs, sternum, os coxae, most cranial bones Enclose and protect soft organs Provide broad surfaces for muscle attachment Irregular bones e.g., vertebrae, some skull bones (sphenoid, ethmoid) Elaborate shapes

12. BONE FUNCTIONS Support Protection e.g., ribs, skull Movement Muscles use bones as levers to move Mineral storage Most importantly Ca & P Hematopoiesis Formation of most of the circulating blood cells

13. BONE STRUCTURE Bones are organs containing various types of tissue Osseous tissue dominates bones Bones also contain Nervous tissue in nerves Cartilage tissue in articular cartilages Fibrous connective tissue lining cavities Muscle and epithelial tissue in blood vessels

14. BONE STRUCTURE Gross Anatomy: Bone Markings Bone surfaces display various features “Bone markings” Depressions, projections, & openings Sites of muscle, ligament, and tendon attachment Joint surfaces Conduits for muscles or nerves

15. BONE STRUCTURE Gross Anatomy: Bone Textures Dense outer layer “Compact bone” Appears smooth to naked eye Honeycomb-like inner layer “Spongy bone” Small needle-like or flat pieces (“trabeculae”) Spaces between trabeculae filled with bone marrow Red or yellow bone marrow

16. BONE STRUCTURE Gross Anatomy: Long Bone Structure Diaphysis Shaft forming long axis of bone Relatively thick collar of compact bone Central medullary cavity “Marrow cavity” Yellow bone marrow cavity Contains fat in adults

17. BONE STRUCTURE Gross Anatomy: Long Bone Structure Epiphyses Bone ends Generally more expanded than diaphysis Compact bone forms exterior Spongy bone forms interior Joint surface covered with thin layer of articular (hyaline) cartilage Absorbs stress, cushions during movement

18. BONE STRUCTURE Gross Anatomy: Long Bone Structure Epiphyseal line a.k.a., “metaphysis” Found between diaphysis and each epiphysis of adult long bone Remnant of epiphyseal plate Hyaline cartilage disk that grows during childhood to lengthen bone

19. BONE STRUCTURE Gross Anatomy: Long Bone Structure Membranes Most of external surface of entire bone is covered by a double-layered membrane “Periosteum” Absent on joint surfaces

20. BONE STRUCTURE Gross Anatomy: Long Bone Structure Membranes: Periosteum Outer fibrous layer is dense irregular connective tissue Inner osteogenic layer consists mainly of osteoblasts and osteoclasts Osteoblasts are bone-forming cells Osteoclasts are bone-destroying cells

21. BONE STRUCTURE Gross Anatomy: Long Bone Structure Membranes: Periosteum Numerous nerve fibers, lymphatic vessels, & blood vessels Enter diaphysis via a nutrient foramen Secured to underlying bone by perforating fibers a.k.a., “Sharpey’s fibers” Tufts of collagen fibers

22. BONE STRUCTURE Gross Anatomy: Long Bone Structure Membranes: Endosteum Internal bone surfaces covered with delicate membrane “Endosteum” Contains both osteoblasts and osteoclasts

23. BONE STRUCTURE Gross Anatomy: Structure of Short, Irregular, & Flat Bones Outside: thin plates of periosteum-covered compact bone Inside: endosteum-covered spongy bone Not cylindrical No diaphysis, epiphyses Contain marrow between trabeculae No marrow cavity

24. BONE STRUCTURE Gross Anatomy: Location of Hematopoietic Tissue in Bones “Red marrow” typically found within trabecular cavities of spongy bone within long bones Medullary cavity of diaphysis also filled with red marrow in newborn Medullary cavity contains fat in adult long bones Fat extends into epiphyses Only head of femur and humerus possess red marrow Most blood cell production occurs elsewhere Flat bones (e.g., sternum) & irregular bones (e.g., hip bone) Yellow marrow in medullary cavity can revert to red marrow in the severely anemic

25. BONE STRUCTURE Microscopic Anatomy: Compact Bone Compact bone appears dense and solid Actually contains numerous passageways Conduits for nerves, blood & lymphatic vessels

26. BONE STRUCTURE Microscopic Anatomy: Compact Bone Structural unit of compact bone is the osteon a.k.a., Haversian system Elongated cylinder parallel to long axis of bone Tiny, weight-bearing pillars

27. BONE STRUCTURE Microscopic Anatomy: Compact Bone Osteon Group of concentric hollow tubes “Lamellae” (Compact bone is sometimes called “lamellar bone)

28. BONE STRUCTURE Microscopic Anatomy: Compact Bone Not all lamellae are part of an osteon Interstitial lamellae are incomplete lamellae between osteons Circumferential lamellae extend around circumference of diaphysis Just deep to the periosteum and just superficial to the endosteum

29. BONE STRUCTURE Microscopic Anatomy: Compact Bone Osteon Collagen fibers Parallel within each lamella Perpendicular in adjacent lamella Arrangement withstands twisting force ( torsion) Crystals of bone salts align with collagen fibers

30. BONE STRUCTURE Microscopic Anatomy: Compact Bone Osteon Central canal runs through osteon core a.k.a., Haversian canal Lined with endosteum Contains nerve fibers and small blood vessels

31. BONE STRUCTURE Microscopic Anatomy: Compact Bone Osteon Perforating canals lie at right angles to long axis of bone a.k.a., Volkman’s canals Lined with endosteum Connect to blood and nerve supply of periosteum (Also connects to that of medullary cavity)

32. BONE STRUCTURE Microscopic Anatomy: Compact Bone Osteon Osteocytes occupy lacunae between lamellae Mature bone cells Lacunae connected by canaliculi Hair-like canals Also connect to central canal

33. BONE STRUCTURE Microscopic Anatomy: Compact Bone Formation Osteoblasts surround blood vessels Maintain contact through gap junctions Osteoblasts secrete bone matrix Mature cells become trapped as matrix hardens Canaliculi form around processes Osteocytes are all connected through these canaliculi Nutrients shared, wastes jointly removed

34. BONE STRUCTURE Microscopic Anatomy: Spongy Bone Appears poorly organized Trabeculae contain irregularly arranged lamellae and osteocytes No osteons Trabeculae align along lines of stress Help bone resist stress (similar to flying buttresses of a Gothic cathedral) Nutrients: capillaries of endosteum ? canaliculi ? osteocytes

35. BONE COMPOSITION Organic Components Cells Osteoblasts, -clasts, & -cytes Osteoid Organic ~1/3 portion of matrix Ground substance Proteoglycans & glycoproteins Collagen fibers Contribute to structure, flexibility, and tensile strength

36. BONE COMPOSITION Inorganic Components ~65% of bone mass Hydroxyapatites a.k.a., Mineral salts Mainly calcium phosphate Form tiny, tightly-packed crystals surrounding collagen fibers Impart hardness Ability to resist compression

37. BONE DEVELOPMENT Ossification / osteogenesis Process of bone formation Formation of the bony skeleton in the embryo Bone growth until early adulthood Bone remodeling throughout life

38. SKELETON FORMATION Prior to week 8 Embryonic skeleton is comprised of hyaline cartilage and fibrous membranes Week 8 and beyond Bone tissue begins to develop Majority of fibrous or cartilaginous structures eventually replaced with bone Fibrous membrane ? (membrane) bone Intramembranous ossification Hyaline cartilage ? (cartilage) bone Endochondral ossification

39. OSSIFICATION Intramembranous Ossification Formation of clavicles and cranial bones

40. OSSIFICATION Endochondral Ossification Formation of almost all bones

41. POSTNATAL GROWTH Long bones lengthen by interstitial growth of epiphyseal plates “Growth from the inside” All bones grow in thickness by appositional growth “Growth from the outside” Most bones stop growing during adolescence Some bones continue very slow growth e.g. some bones of nose and lower jaw

42. LONG BONE GROWTH Cartilage of epiphyseal plate Inactive on side facing epiphysis Active on side facing diaphysis Rapid mitosis forms tall columns of chondrocytes Cells at “top” push epiphysis away from diaphysis Long bone lengthens Then… “Bottom” chondrocytes hypertrophy Lacunae erode & enlarge Surrounding cartilage matrix calcifies Chondrocytes die and deteriorate

43. LONG BONE GROWTH Long spicules of calcified cartilage (This is different than bone) Invaded by marrow elements from medullary cavity Spicules partially eroded by osteoclasts Spicules covered with bone matrix Spongy bone formed Spicule tips ultimately digested by osteoclasts Medullary cavity grows longer

44. LONG BONE GROWTH Epiphyseal plate maintains a constant thickness Rate of cartilage growth = rate of replacement Longitudinal growth is accompanied by remodeling of epiphyseal ends Involves new bone formation Involves bone reabsorption (More on this later) End of adolescence Epiphyseal plate chondrocytes divide less often Plates become thinner Entire replacement ? epiphyseal line “Epiphyseal plate closure” at ~18 (?) – 21 (?)

45. LONG BONE GROWTH Growth in Width Growing bones widen as they lengthen Appositional growth “Growth from the outside” Two processes Osteoblasts beneath periosteum secrete bone matrix onto external bone surface Osteoclasts on endosteal surface remove bone

46. BONE GROWTH Hormonal Regulation Growth of epiphyseal plate stimulated by growth hormone Released by pituitary Activity modulated by thyroid hormone Regulated by testosterone and estrogens Growth spurt in adolescence Masculinization / feminization of skeleton Later induce epiphyseal plate closure

47. BONE REMODELING Bone tissue is active and dynamic ~5-7% of bone mass recycled weekly Spongy bone replacement every ~3-4 years Compact bone replacement every ~10 years Bone deposition and absorption Occur at surfaces Periosteum and endosteum Coordinated by packets of cells Osteoblasts and osteoclasts

48. BONE DEPOSITION Occurs when bone is injured Occurs when added bone strength is required

49. BONE RESORPTION Accomplished by osteoclasts Giant multinucleate cells Arise from hematopoietic stem cells Same cells give rise to macrophages Dig grooves into bone surface “Resorption bays” Release of HCl and lysosomal enzymes Solubilizes calcium salts Phagocytosis of demineralized matrix

50. REMODELING CONTROL Hormonal negative feedback mechanism Maintains blood Ca2+ homeostasis Calcium is important in many processes Nerve impulses Muscle contraction Blood coagulation Secretion Cell division Etc.

51. REMODELING CONTROL Hormonal negative feedback mechanism Regulated by two hormones Parathyroid hormone (PTH) Produced in parathyroid Low [Ca2+] ? release Osteoclasts stimulated Calcitonin Produced in thyroid High [Ca2+] ? release Inhibits resorption Stimulated salt deposition

52. REMODELING CONTROL Response to mechanical & gravitational forces Bone is remodeled in response to demands placed upon it Hormonal mechanisms act to regulate blood Ca2+ levels Bone deposition occurs where stress occurs Hormonal regulation determines if bone remodeling will occur, mechanical stress determines where it will occur e.g., Stronger compact bone on outside e.g., Bony projections at sites of muscle attachment

53. BONE REPAIR Bones are susceptible to fractures Fractures classified by Position of bone ends after fracture Displaced vs. nondisplaced (alignment altered) Completeness of break Complete vs. incomplete Orientation of break relative to long axis of bone Linear (parallel) vs. transverse (perpendicular) Whether bone ends penetrate skin Open (ends penetrate skin) vs. closed

54. BONE REPAIR Treated by reduction Realignment of bone ends Closed reduction Coaxed into place by hand Open reduction Bone ends surgically secured together Immobilization follows reduction Facilitates healing

55. BONE REPAIR Bone repair involves multiple steps Hematoma formation Fibrocartilaginous callus formation Bony callus formation Bone remodeling

56. BONE REPAIR Hematoma formation Blood vessels are torn and hemorrhage Bone, periosteum, surrounding tissue Hematoma formed at fracture site Mass of clotted blood Some cell death, swelling, pain, inflammation

57. BONE REPAIR Fibrocartilaginous callus formation Formation of soft granulation tissue (“soft callus”) Capillaries grow into hematoma Phagocytic cells enter Clean up debris Fibroblasts, osteoblasts enter Produce collagen fibers Span break, connect broken bone ends Some differentiate into chondroblasts Secrete cartilage matrix Osteoblasts enter Form spongy bone

58. BONE REPAIR Bony callus formation New bone trabeculae appear in fibrocartilaginous callus within ~ 1 week Gradual conversion to bony (hard) callus Spongy bone

59. BONE REPAIR Bone remodeling Bony callus is remodeled Begins during bony callus formation Continues for several months Excess material removed Compact bone laid down

60. BONE IMBALANCES Osteoporosis Bone resorption outpaces bone deposition Bones become fragile Spine, neck of femur especially susceptible Occurs most often in aged Especially postmenopausal women Estrogen and testosterone reduce osteoclast activity Treatment Calcium, vitamin D supplements Hormone (estrogen) replacement therapy Slows loss, does not reverse loss

61. JOINTS

62. WHAT ARE JOINTS? a.k.a., “Articulations” Sites where two or more bones meet Functions Hold skeleton together Confer mobility

63. JOINT CLASSIFICATION Functional classification Synarthroses Immovable joints Amphiarthroses Slightly movable joints Diarthroses Freely movable joints Structural classification Fibrous joints Generally immovable Cartilaginous joints Some immovable Some slightly movable Synovial joints Generally freely movable

64. FIBROUS JOINTS Bones joined by fibrous tissue No joint cavity present Most immovable, some slightly movable Amount of movement dependent on length of connective tissue fibers connecting bones Three types Sutures Syndesmoses Gomphoses

65. FIBROUS JOINTS Sutures Occur only between bones of the skull Wavy articulating bone edges interlock Junction filled with very short connective tissue fibers Continuous with periosteum Functions Hold bones tightly together Allow bone growth during youth Ossified later in life “Synostoses”

66. FIBROUS JOINTS Syndesmoses Bones connected by a ligament Cord or band of fibrous tissue Variable length, but longer than fibers in sutures Amount of movement depends on length of fibers e.g., short tibia-to-fibula ligament ? slight movement e.g., longer radius-to-ulna connection ? allows rotation

67. FIBROUS JOINTS Gomphoses Peg-in-socket fibrous joint Articulation of tooth into alveolar socket Fibrous connection is short peridontal ligament

68. CARTILAGINOUS JOINTS Articulating bones joined by cartilage Lack a joint cavity Two types Synchondroses Symphyses

69. CARTILAGINOUS JOINTS Synchondroses Bar or plate of hyaline cartilage unites bones Generally immovable joints e.g., Epiphyseal plate joining diaphysis to epiphysis (a temporary joint) e.g., Joint between sternum and ribs

70. CARTILAGINOUS JOINTS Symphyses Amphiarthrotic joints Limited movement Articular surfaces of bones covered with articular (hyaline) cartilage Cartilage fused to shock-absorbing pad of fibrocartilage e.g., Intervertebral joints, pubic symphysis

71. SYNOVIAL JOINTS Articulating bones separated by a fluid-filled joint cavity Permits freedom of movement Features Articular cartilage Joint cavity (synovial cavity) Articular capsule Synovial fluid Reinforcing ligaments

72. SYNOVIAL JOINTS Articular Cartilage Hyaline cartilage covers opposing bone surfaces Thin (1 mm thick or less) Spongy, cushioning Joint Cavity (Synovial Cavity) Potential space containing small amount of fluid

73. SYNOVIAL JOINTS Articular Capsule Two-layered capsule enclosing joint cavity External layer is fibrous capsule Dense irregular connective tissue Continuous with periostea Strengthens joint Inner layer is a synovial membrane Loose connective tissue Covers all internal joint surfaces not hyaline cartilage

74. SYNOVIAL JOINTS Synovial Fluid Occupies all free space within capsule Also present within cartilages Viscous fluid Large amount of hyaluronic acid Reduces friction between cartilages Reinforcing Ligaments Numerous band-like ligaments Mainly thickened parts of fibrous capsule Reinforce and strengthen joint

75. SYNOVIAL JOINTS Some synovial joints have additional features Fatty pads between fibrous capsule and synovial membrane or bone Provide cushioning e.g., hip and knee joints Fibrocartilage disks separating articular surfaces “Articular disks” / “menisci” Improve fit between articulating bone ends Stabilize joint Reduce wear and tear e.g., knee, jaw

76. SYNOVIAL JOINTS Bursae and Tendon Sheaths Closely associated with synovial joints Bags of lubricant Reduce friction Bursae Flattened fibrous sacs Lined with synovial membrane Filled with synovial fluid Tendon sheath Elongated bursa wrapping around a tendon

77. SYNOVIAL JOINTS Factors Influencing Stability Shapes of articular surfaces Determine possible movements Generally minor role in joint stability Ball and deep socket of hip does provide stability Number and positioning of ligaments More ligaments = stronger joint Insufficient alone Muscle tone Muscle tendons crossing joint usually most important stabilizing factor Muscle tone keeps tendons taut Especially important in shoulder, knee, arch of feet

78. SYNOVIAL JOINTS Movements Allowed by Synovial Joints Skeletal muscles attached to bone or other features at two or more points Muscle’s origin attached to less movable bone Muscle’s insertion attached to movable bone Movement occurs when muscles contract across joints Insertion moves toward origin Different joints allow different types of movement

79. SYNOVIAL JOINTS Gliding Movements One flat or nearly flat bone surface glides or slips over another without appreciable angulation or rotation

80. SYNOVIAL JOINTS Angular Movements Increase or decrease angle between two bones May occur in any body plane Include Flexion Extension Hyperextension Abduction Adduction Circumduction

81. SYNOVIAL JOINTS Angular Movements: Flexion Bending movement decreasing angle of joint Brings articulating bones closer together Bending usually along sagittal plane

82. SYNOVIAL JOINTS Angular Movements: Extension & Hyperextension Reverse of flexion occurring at same joints Bending movement increasing angle of joint Brings articulating bones further apart

83. SYNOVIAL JOINTS Angular Movements: Dorsiflexion & Plantar Flexion Up-and-down movements of the foot at the ankle joint

84. SYNOVIAL JOINTS Angular Movements: Abduction Movement of a limb along frontal plane & away from midline or median plane of body

85. SYNOVIAL JOINTS Angular Movements: Adduction Opposite of abduction Movement of a limb along frontal plane & toward midline or median plane of body

86. SYNOVIAL JOINTS Angular Movements: Circumduction Moving a limb to describe a cone in space Flexion, abduction, extension, & adduction performed in succession Quickest way to exercise the many muscles moving hip and shoulder ball-in-socket joints

87. SYNOVIAL JOINTS Rotation The turning of a bone around its long axis Only movement allowed between first two cervical vertebrae Common at the hip

88. SYNOVIAL JOINTS Special Movements: Supination & Pronation Movement of radius around ulna Supination = “turning backward” Pronation = “turning forward”

89. SYNOVIAL JOINTS Special Movements: Inversion & Eversion Special movement of the feet Inversion: sole turns medially Eversion: sole turns laterally

90. SYNOVIAL JOINTS Special Movements: Protraction & Retraction Nonangular movement in a transverse plane Protraction: anterior movement Retraction: posterior movement

91. SYNOVIAL JOINTS Special Movements: Elevation & Depression Elevation: lifting a body part superiorly Depression: moving a body part inferiorly

92. SYNOVIAL JOINTS Special Movements: Opposition Movement allowed by the saddle joint between the thumb’s metacarpal and the carpals Opposable thumbs are nice things to have

93. SYNOVIAL JOINTS Types of synovial joints Plane joints Hinge joints Pivot joints Condyloid joints Saddle joints Ball-and-socket joints

94. SYNOVIAL JOINTS

95. SYNOVIAL JOINTS

96. JOINT INJURIES Sprains Ligaments reinforcing a joint stretched or torn esp., ankle, knee, lumbar region of spine Partially torn ligaments will repair themselves Slow to heal sue to poor vascularization Completely torn ligaments require surgery Surgical repair difficult Replacement with grafts or substitutes common

97. JOINT INJURIES Cartilage Injuries Typical injuries Tearing of knee menisci Overuse damage to articular cartilages Cartilage is avascular Insufficient nutrients for repair Generally remains torn Arthroscopic removal of damaged cartilage

98. JOINT INJURIES Dislocations Bones are forced out of alignment Generally accompanied by sprains, inflammation, and joint immobilization Commonly result from falls or sports injuries esp., shoulders, fingers, thumb Dislocation must be reduced Manipulation by hand restores proper alignment

99. JOINT CONDITIONS Bursitis Inflammation of the bursa Usually caused by a blow or friction Can be caused by repeated prolonged joint stress Rest, ice, anti-inflammatory drug treatment Tendonitis Inflammation of tendon sheaths Typically caused by overuse Similar symptoms and treatment to bursitis

100. JOINT CONDITIONS Arthritis Over 100 different types of inflammatory and degenerative diseases that damage joints Pain, stiffness, swelling of the joint Most widespread crippling disease in the U.S. 1/7 of population suffers Acute Generally result from bacterial infection Chronic Osteoarthritis, rheumatoid arthritis, gouty arthritis

101. JOINT CONDITIONS Osteoarthritis Most common chronic arthritis “Wear-and-tear arthritis” 85% of all Americans develop Most prevalent in aged More women than men Cartilage destroyed ? bone exposed ? exposed bone tissue thickens ? joint movement restricted

102. JOINT CONDITIONS Rheumatoid Arthritis Autoimmune disease Body’s immune system attacks body’s own tissues Usually arises between 40 and 50 Affects >1% of American population Affects more women than men (3:1) Inflammation in synovial membranes Excessive inflammatory response causes tissue damage

103. JOINT CONDITIONS Gouty Arthritis (“Gout”) Uric acid produced as waste product of nucleic acid metabolism Uric acid level in blood can rise Deposition as needle-like crystals in soft tissue of joints Inflammatory response ? pain, joint damage Who gets it? More common in males than females Naturally higher levels of uric acid Genetic factors contribute Treatment Colchicine, anti-inflammatory drugs, etc.