ANA109 week 7
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This 5 page Class Notes was uploaded by Ally Merrill on Friday October 7, 2016. The Class Notes belongs to ANA 109 at University of Kentucky taught by Dr. Platt in Fall 2016. Since its upload, it has received 3 views.
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Date Created: 10/07/16
ANA109 Week 7—Unit 2 material (Bones/Muscles) 10/4/16 How is compact bone organized? What are the major structures associated with compact bone? Osteons form repeating structural unites aligned in same direction with few spaces Central canal with blood and lymph vessels and nerves Concentric lamellae of extracellular matrix Lacunae (with osteocytes) between lamellae Canaliculi connect lacunae and central canal Interstitial lamellae between osteons Circumferential lamella encircle bone Perforating canals penetrate How is spongy bone organized? What are the major structures associated with spongy bone? Trabeculae for irregular lattice of lamellae extracellular matrix oriented in many directions Lacunae with osteocytes Canaliculi connect lacunae Osteoblasts and osteoclasts under periosteum Spaces between trabeculae filled with red bone marrow (OR YELLOW MARROW) NO CENTRAL CANALS Since bone is a living and dynamic organ, how does it receive blood and nerve supple? Highly vascular with blood vessels passing into bones from periosteal artery o Nutrient foramen—leads to perforating canal through periosteum o Nutrient artery/vein—diaphysis (and parts of metaphysis) o Metaphyseal artery/vein o Epiphyseal artery/vein Sensory nerves accompany blood vessels Hoe do bones grow? What is ossification? Ossification = laying down of bone (osteoblast) 1. Initial formation of bones before birth 2. Growth of bones until adult size reached 3. Remodeling and repair of bones What are the two types of ossification? Intramembranous ossification o Bone develops directly within sheet-like layers (multipotent stem cells) CONNECTIVE TISSUE o Flat bones of skull, mandible, and clavicle Endochondral ossification o Most bones in body form within hyaline cartilage template What is intramembranous ossification? 1. Ossification center a. Progenitor cells cluster and differentiate into osteogenic cells, then osteoblasts 2. Calcification a. Osteoblasts secrete extracellular matrix 3. Formation of trabeculae that fuse into lattice, with blood vessels growing into spaces 4. Development of the periosteum a. Progenitor cells at periphery of trabeculae form What is endochondral ossification and how does it differ from intramembranous ossification? 1. Development of cartilage model a. Progenitor cells cluster and develop into chondroblasts b. Hyaline cartilage template with perichondrium forms 2. Growth of the cartilage model a. Chondrocytes HYPERtrpohy in center b. Development of the primary ossification center c. Bone tissue replaces cartilage in diaphysis under periosteum (technically endosteum) 3. Development of the medullary cavity a. Osteoclasts break down middle trabeculae 4. Development of secondary ossification center a. Bone tissue replaces cartilage in epiphysis 5. Formation of articular cartilage and epiphyseal plate a. Hyaline cartilage over epiphysis and in metaphysis remains How does bone grow in length? (interstitial lengthening) Epiphyseal plate involved in growth in length o Throughout childhood and adolescence long bones grow o Growth of cartilage on epiphyseal side and replacement of cartilage on diaphysis side o Epiphyseal line remains when growth has stopped Four zones of epiphyseal plate in metaphysis o Zone of resting cartilage—ANCHOR o Zone of proliferating cartilage—MITOSIS o Zone of hypertrophic cartilage—FATTENING o Zone of calcified cartilage—DEATH and HARDENING—PAVE THE WAY FOR OSTEOCLASTS/BLASTS Appositional growth—bone grows in diameter as osteoblasts in periosteum secrete extracellular matrix to form new lamellae while osteoclasts of endosteum enlarge medullary cavity Growth of cartilage on epiphyseal side & replacement of cartilage on diaphysis side What factors influence bone growth and remodeling? Growth and maintenance of bones depends on adequate nutrition (energy, calcium, vitamins) Hormones o Growth hormone (pituitary = associated structure of the brain) and IGF’s (IGF = insulin-like growth factors = liver) stimulate bone growth—INTERSTITIAL GROWTH o Thyroid hormone and insulin also promote bone growth o Sex steroids (estrogen and testosterone) stimulate bone growth in gender specific patterns o Epiphyseal plate closure results from higher levels of estrogens 10/6/16 Maintenance of bone and regulation of bone calcium levels Why do we care about calcium (Ca++) levels in the body? Ca++ is critical for: o Bone health o Muscle contraction o Blood clotting What are the parathyroid glands? What is the function of parathyroid hormone? Parathyroid hormone is essential for raising blood calcium levels It does this by o Increasing Ca++ absorption in the guts o Increasing Ca++ reabsorption in the kidney o Stimulating osteoclasts What gland releases calcitonin? What does calcitonin do? Calcitonin is a complementary hormone to parathyroid hormone It decreases blood calcium levels by promoting osteoblast activity How does bone act as a reservoir for calcium in blood? To increase Ca++ levels in blood we must deplete calcium reservoirs o Parathyroid hormone secreted by the parathyroid gland increases blood calcium level PTH—stimulates osteoclasts Vitamin D (needed to form calcitriol—a hormone) increases blood calcium levels through enhanced absorption of calcium from food Other vitamins beyond D: o Vitamin C, K, B12 help in the synthesis of collagen o Vitamin A—Can stimulate osteoblasts To enhance our Ca++ reservoir (in the bone) we must deplete the Ca+ + floating around in the blood o Calcitonin from thyroid gland has the potential to decrease blood calcium level Inhibits osteoclast activity Stimulates osteoblasts When does bone remodeling occur? Why does it occur? What is Wolff’s law of bone? Bone remodeling occurs throughout life—10% per year o Repairs microfractures, releases minerals into blood, reshapes bones in response to use and disuse o Wolff’s law of bone: architecture of bone determined by mechanical stresses placed on it and bones adapt to withstand those stresses Remodeling is a collaborative and precise action of osteoblasts and osteoclasts Bony processes grow larger in response to mechanical stress What are the major fracture types? How are fractures repaired? Stress fracture—break caused by abnormal trauma to a bone (falls or athletics) Pathological fracture—break in a bone weakened by some other disease o Bone cancer or osteoporosis o Usually caused by stress that would not break a healthy bone Fractures classified by structural characteristics o Direction of fracture line, break in the skin, and how many pieces (ex: compound) Closed reduction—procedure in which the bone fragments are manipulated into their normal positions without surgery Open reduction—involves surgical exposure of the bone and use of plates, screws, or pins to realign the fragments Cast—normally used to stabilize and immobilize healing bone Clinical Reasoning: Osteoporosis Osteoporosis—the most common bone disease o Severe loss of bone density How many grams of calcium and other bone minerals are packed into a segment of bone Bones lose mass and become brittle due to loss of organic matrix and minerals o Affects spongy bone the most since it is the most metabolically active o Subject to pathological fractures of hip, wrist, and vertebral column o Kyphosis (widow’s hump)—deformity of spine due to vertebral bone loss o Complications of loss of mobility are pneumonia and thrombosis Estrogen maintains density in both sexes; inhibits resorption by osteoclasts o Testes and adrenals produce estrogen in men o In women, rapid bone loss after menopause since ovaries cease to secrete estrogen Osteoporosis is common in young female athletes with low body fat causing them to stop ovulating and ovarian estrogen secretion is low Treatment? o Estrogen replacement therapy (ERT) slows bone resorption, but increase risk of breast cancer, stroke, and heart disease o Best treatment is prevention: exercise and a good bone-building diet between ages 25 and 40 Postmenopausal white women at greatest risk Begin to lose bone mass as early as age 35 o By age 70, average loss is 30% of bone mass o Risk factors: race, age, gender, smoking, diabetes mellitus, diet poor in calcium, protein, vitamins C and D