The Skeletal System PDF

The Skeletal System Ryan R. Williams, M.D., Ph.D. Biology 122 California State University Dominguez Hills  Overview of the Skeletal System The skeletal system is made of: Skeletal bones Cartilage...

The Skeletal System Ryan R. Williams, M.D., Ph.D. Biology 122 California State University Dominguez Hills  Overview of the Skeletal System The skeletal system is made of: Skeletal bones Cartilage Ligaments Connective tissue to stabilize the skeleton Bones are dynamic organs, which consist of several tissue types © 2015 Pearson Education, Inc.  Functions of the Skeletal System Support Protection Assistance in movement Mineral storage and release Blood cell production Triglyceride storage © 2015 Pearson Education, Inc.  Functions of the Skeletal System Support Provides the framework for the attachment of other organs Storage of minerals Calcium ions: 98 percent of the body’s calcium ions are in the bones Phosphate ions Blood cell production Bone marrow produces erythrocytes, leukocytes, and platelets © 2015 Pearson Education, Inc.  Introduction Leverage Muscles pull on the bones to produce movement Protection Ribs protect heart and lungs Skull protects the brain Vertebrae protect the spinal cord Pelvic bones protect the reproductive organs © 2015 Pearson Education, Inc.  Anatomy of a Bone Diaphysis Epiphyses Metaphysis Articular surface cartilage Periosteum Medullary cavity Endosteum © 2015 Pearson Education, Inc.  Anatomy of a Bone Epiphysis (ends of the long bones) The spongy bone consists of red marrow (blood progenitor cells) Diaphysis (shaft of the long bones) The medullary cavity consists of yellow marrow (fat cells) Metaphysis Narrow growth zone between the epiphysis and the diaphysis © 2015 Pearson Education, Inc.  Spongy bone Epiphysis Articular Metaphysis surface of head of femur Compact bone Articular surface=joint surface Diaphysis (shaft) Articulate ~ interact with Medullary cavity Metaphysis Epiphysis Posterior view Sectional view a The femur, or thigh bone © 2015 Pearson Education, Inc.  Anatomy of a Bone Bones (Osseous Tissue) Supporting connective tissue (inside) Specialized cells Solid matrix Outer lining Called the periosteum Inner lining Called the endosteum Lines the medullary cavity © 2015 Pearson Education, Inc.  Articular cartilage Spongy bone (contains red bone marrow) Red bone marrow Epiphyseal line Compact bone Endosteum (lines medullary cavity) Nutrient artery Medullary cavity (contains yellow bone marrow in adults) Periosteum Humerus Articular cartilage (a) Partially sectioned humerus (arm bone) © 2015 Pearson Education, Inc.  Anatomy of a Bone The Histological Organization of Mature Bone The matrix of bone Calcium phosphate converts to hydroxyapatite crystals Makes up 2/3 of the bone mass Hydroxyapatite crystals resist compression © 2015 Pearson Education, Inc.  Anatomy of a Bone The Histological Organization of Mature Bone Collagen fibers Make up 1/3 of the bone matrix Contribute to the tensile strength of bones, making them less brittle Collagen and hydroxyapatite make bone tissue extremely strong Bone cells (i.e. osteocytes) Contribute only 2 percent of the bone mass © 2015 Pearson Education, Inc.  Anatomy of a Bone The Cells of Mature Bone Osteocytes Mature bone cells Maintain the protein and mineral content of the matrix Sit in depressions called lacunae Matrix layer associated with osteocytes is lamellae Small channels extending from the osteocytes to the bone capillaries are called canaliculi © 2015 Pearson Education, Inc.  Anatomy of a Bone The Cells of Mature Bone Osteoblasts Immature bone cells Found on the inner and outer surfaces of bones Produce osteoid, which is involved in making the matrix Osteoblasts are involved in making new bone. This is a process called osteogenesis “-blast” = immature cell © 2015 Pearson Education, Inc.  Anatomy of a Bone The Cells of Mature Bone Osteoprogenitor cells These are bone stem cells Found on the innermost layer of the periosteum and the inner lining of the endosteum Differentiate to form new osteoblasts Heavily involved in the repair of bones after a break © 2015 Pearson Education, Inc.  Anatomy of a Bone The Cells of Mature Bone Osteoclasts Multinucleated cells Secrete acids, which dissolve the bones thereby causing the release of stored calcium ions and phosphate ions into the blood This process is called osteolysis Derived from bone marrow (similar lineage to macrophages) “-Clasts”>>> Chew bone “-Blasts”>>> Build bone © 2015 Pearson Education, Inc.  Canaliculi Osteocyte Matrix Endosteum Osteoprogenitor cell Medullary cavity Osteocyte: Mature bone cell Osteoprogenitor cell: Stem that maintains the bone matrix Cells that produce osteoblasts Osteoblast Osteoid Matrix Osteoclast Matrix Medullary cavity Osteoblast: Immature bone Osteoclast: cell that secretes organic a Multinucleate cell The cells of bone. components of matrix that secretes acids and enzymes to dissolve bone matrix © 2015 Pearson Education, Inc.  Anatomy of a Bone Two Types of Osseous Tissue Compact bone (dense bone) Compact bones are dense and solid Forms the walls of bone Spongy bone (aka trabecular or cancellous bone) Open network of plates Surrounds the medullary cavity The medullary cavity and the spaces in-between spongy bone contains bone marrow © 2015 Pearson Education, Inc.  Spongy bone Blood vessels Compact bone Medullary cavity Endosteum Periosteum Compact Spongy Medullary bone bone cavity a Gross anatomy of © 2015 Pearson Education, Inc. the humerus.  Anatomy of a Bone Compact Bone Consists of osteons Basic functional unit of bone Consists of: Central canal Canaliculi Osteocytes Lacunae Lamellae (layers) © 2015 Pearson Education, Inc.  Canaliculi Concentric lamellae (layers) Central canals Osteon Lacunae Osteons LM × 220 c A thin section through compact bone; in this procedure the intact matrix and central canals appear white, and the lacunae and canaliculi are shown in black. © 2015 Pearson Education, Inc.  Anatomy of a Bone Functional Differences between Compact and Spongy Bone Compact bone Conducts stress from one end of the long bone to the other end of the long bone Generates tremendous strength from end to end Weak strength when stress is applied to the side Osteon arrangement is parallel to the bone axis Generates tremendous strength from end to end © 2015 Pearson Education, Inc.  Concentric lamellae Collagen fiber orientation Central canal Endosteum c The organization of collagen fibers within concentric lamellae of the Osteon. © 2015 Pearson Education, Inc.  Capillary Small vein Circumferential lamellae Concentric Osteons lamellae Periosteum Interstitial lamellae Trabeculae of Artery Vein spongy bone Perforating Central canal canal b Diagrammatic view of the histological organization of compact and spongy bone. © 2015 Pearson Education, Inc.  Canaliculi Central canal (haversian canal) Lacunae LM 100x Lamellae LM 400x (d) Sectional view of several osteons (haversian systems) of femur (thigh bone) and details of one osteon © 2015 Pearson Education, Inc.  Anatomy of a Bone Spongy Bone Spongy bone Arranged in parallel struts Forms branching plates called trabeculae Trabeculae form an open network Creates the lightweight nature of bones © 2015 Pearson Education, Inc. Compact bone Medullary Spongy Cavity bone Osteocyte External Interstitial Periosteum circumferential Concentric Canaliculi lamellae lamellae lamellae Lacunae See Figure 6.4b, c Blood for details vessels Medullary cavity Trabeculae Osteon Inner circumferential Periosteal vein lamellae Periosteal artery Periosteum: Outer fibrous layer Inner osteogenic layer Central canal Spongy Bone Interosteonic canal Compact Perforating Bone (Sharpey’s) fibers (a) Osteons (haversian systems) in compact bone and trabeculae in spongy bone © 2015 Pearson Education, Inc.  Lacunae Lamellae Space for red Canaliculi Osteocyte bone marrow Osteoclast Osteoblasts aligned Trabeculae along trabeculae of new bone (b) Enlarged aspect of spongy (c) Details of a section of a trabecula bone trabeculae © 2015 Pearson Education, Inc.  Cartilage Cartilage—not as strong as bone, but is more flexible Matrix contains collagen and elastic fibers Chondrocytes—cartilage cells; lie within lacunae Has no nerves or blood vessels; relies on neighboring tissues for nutrient and waste exchange This makes it slow to heal There are three types of cartilage: Hyaline cartilage: ends of long bones, nose, ends of ribs, larynx, and trachea Fibrocartilage: disks between vertebrae and in the knee Elastic cartilage: ear flaps and epiglottis © 2015 Pearson Education, Inc.  Fibrous Connective Tissue Made of rows of fibroblasts separated by bundles of collagenous fibers Makes up ligaments and tendons Ligaments connect bone to bone Tendons connect muscle to bone at a joint (also called an articulation) © 2015 Pearson Education, Inc.  Bone Development and Growth Osteogenesis Bone formation Calcification The deposition of calcium ions (into the bone tissue) Before six weeks of development, the skeleton is hyaline cartilage When chondrocytes are replaced by bone cells its called endochondral ossification Occurs in long bones Intramembranous ossification The formation of bone directly from mesenchyme (stem cells from mesoderm) Occurs flat bones (Ex skull bones) © 2015 Pearson Education, Inc.  Perichondrium Proximal epiphysis Cartilage (Hyaline cartilage) Diaphysis Distal epiphysis 1 Development of cartilage: mesenchymal cells (connective tissue progenitor cells from somties) develop into chondroblasts, which form the cartilage. (a) Sequence of events © 2015 Pearson Education, Inc.  Perichondrium Calcified extracellular matrix 2 Growth of cartilage: growth occurs by cell division of chondrocytes derived from chondroblasts. © 2015 Pearson Education, Inc.  Periosteum Primary ossification Nutrient center artery Spongy bone 3 Development of primary ossification center: in this region of the diaphysis, bone tissue has replaced most of the cartilage. © 2015 Pearson Education, Inc.  Calcified extracellular matrix Periosteum Medullary cavity Nutrient artery and vein 4 Development of the medullary (marrow) cavity: bone breakdown by osteoclasts forms the medullary cavity. © 2015 Pearson Education, Inc.  Secondary ossification Epiphyseal center artery and vein 5 Development of secondary ossification centers: these occur in the epiphyses of the bone. © 2015 Pearson Education, Inc.  Articular cartilage Spongy bone Epiphyseal Plate 6 Formation of articular cartilage and epiphyseal plate: both structures consist of hyaline cartilage. © 2015 Pearson Education, Inc.  Calcified Uncalcified (b) Twelve-week-old fetus. The red areas represent bones that are forming (calcified). Clear areas represent cartilage (uncalcified). © 2015 Pearson Education, Inc.  Bone Development and Growth Epiphyseal Plate An area of cartilage in the metaphysis During bone growth, this cartilage is converted to bone near the diaphysis The width of this zone gets narrower as we age Eventually the area is devoid of cartilage and only bone remains, then referred to as the epiphyseal line © 2015 Pearson Education, Inc.  a X-ray of the hand of a young b X-ray of the hand of an child. The arrows indicate adult. The arrows indicate the locations of the the locations of epiphyseal epiphyseal cartilages of the lines in the metaphysis. metaphysis. © 2015 Pearson Education, Inc.  (a) Radiograph showing the epiphyseal plate of the femur of a 3-year-old Femur Epiphyseal Plate Tibia © 2015 Pearson Education, Inc.  Articular cartilage Spongy bone (contains red bone marrow) Red bone marrow Epiphyseal line Compact bone Endosteum (lines medullary cavity) Nutrient artery Medullary cavity (contains yellow bone marrow in adults) Periosteum Humerus Articular cartilage (a) Partially sectioned humerus (arm bone) © 2015 Pearson Education, Inc.  Bone Development and Growth Vitamin D—formed in the skin when exposed to sunlight. Is converted to a hormone that is necessary for absorption of calcium from the digestive system Low vitamin D levels in children causes rickets Bone deformities, including bowed long bones © 2015 Pearson Education, Inc.  Bone Development and Growth Factors Regulating Bone Growth Hormones Parathyroid gland releases parathyroid hormone Stimulates osteoclasts Increases calcium levels Maintains calcium homeostasis Increases calcium ion absorption from the small intestine to the blood Reduces the rate of calcium ion loss from the kidneys © 2015 Pearson Education, Inc.  Bone Development and Growth Factors Regulating Bone Growth Hormones Thyroid gland releases calcitonin Inhibits osteoclasts Decreases or “Tones down” calcium levels Maintains calcium homeostasis Increases rate of calcium ion loss in the urine Removes calcium ions from blood and adds it to bone © 2015 Pearson Education, Inc.  Bone Development and Growth Factors Regulating Bone Growth Hormones Pituitary gland releases growth hormone (somatotropin) Stimulates bone growth Maintains normal activity of the epiphyseal cartilage Dwarfism—too little GH in childhood Gigantism—excess GH in childhood Acromegaly—excess GH in adults Excessive growth of bones in the hands and face © 2015 Pearson Education, Inc.  Bone Development and Growth Factors Regulating Bone Growth Hormones Estrogen and testosterone stimulate osteoblast activity Osteoblast activity produces bone faster than epiphyseal cartilage expansion Ultimately the epiphyseal cartilage narrows and bone growth ceases (about age 25) Paget disease—new bone is generated at a faster-than-normal rate Produces softer and weaker bones Can cause bone pain, deformities, and fractures © 2015 Pearson Education, Inc.  Bone Maintenance, Remodeling, and Repair Remodeling of Bone Inactivity of bones can cause degeneration After a few weeks, unstressed bones can lose about a third of their mass Stress (weight) stimulates osteoblasts © 2015 Pearson Education, Inc.  Bone Maintenance, Remodeling, and Repair Aging and the Skeletal System When we’re young, osteoblast activity balances with osteoclast activity When we get older, osteoblast activity declines Osteoclast activity maintains its previous level of activity When osteoclast activity is faster than osteoblast activity, bones become porous © 2015 Pearson Education, Inc.  Bone Maintenance, Remodeling, and Repair Aging and the Skeletal System There are two principal effects of aging on bone tissue Loss of bone mass results from the loss of calcium and other minerals from bone extracellular matrix (demineralization) Brittleness occurs as the production of collagen slows (which give bone tissue its tensile strength) slows As women age, estrogen levels drop Osteoblasts are no longer stimulated and osteoclasts are overactive Bones become porous This is osteoporosis © 2015 Pearson Education, Inc.  SEM 30x SEM 30x (A) Normal bone (B) Osteoporotic bone © 2015 Pearson Education, Inc.  Articulations Articulations (joints) Where bones come together Classified as fibrous, cartilaginous, or synovial Most fibrous joints are immovable That is, sutures between the cranial bones Cartilaginous joints are connected by hyaline cartilage, (that is, costal cartilages) or fibrocartilage (that is, intervertebral disks) Slightly movable Synovial joints are freely movable © 2015 Pearson Education, Inc. Articulations Ligaments support and strengthen joints Joint capsule—formed by ligaments Surrounds the joint Synovial membrane—lines the joint capsule Secretes synovial fluid for lubrication Bursae (singular, bursa)—fluid-filled sacs that ease friction Menisci (singular, meniscus)—C-shaped fibrocartilage; give stability and absorb shock Types of synovial joints: Ball-and-socket joints—allow movement in all planes, even rotational movement That is, the hips and shoulders Hinge joints—permit movement in only one direction That is, the elbow and knee  bursae articular joint cavity filled with cartilage synovial fluid meniscus meniscus ligament ligament head of humerus scapula Generalized synovial joint ulna humerus Ball-and- socket joint A gymnast depends on flexible Hinge joints. joint © 2015 Pearson Education, Inc.