Chapter 6- Bones

What do bones do for you other than make up 18% of your weight? 1. Support- muscles 2. Protection- organs 3. Movement- with muscles 4. Mineral storage- calcium (99% of body's), phosphorus, 45% of bone weight 5. Hemopoiesis- Blood cell production, in the Red bone marrow 6. Fat storage- Yellow bone marrow

Figure 6-1 A Classification of Bones by Shape Sutures Sutural bone Vertebra Carpal bones Parietal bone External table Internal table Diploë (spongy bone) Humerus Patella Sutural Bones Flat Bones Long Bones Sesamoid Bones Irregular Bones Short Bones

Structure of Bone (pg 173) 1. Diaphysis- shaft 2. Epiphyses- ends 3. Metaphyses- b/w 1 & 2, includes the epiphyseal plate (cartilage) - cartilage replaced by bone when done growing = epiphyseal line 4. Articular cartilage- reduces friction 5. Periosteum-covering for protection & nourishment 6. Medullary cavity/ Marrow cavity- yellow marrow 7. Endosteum- lines the marrow cavity

6-3 Bone (Osseous) Tissue Matrix composed of: –Minerals: Hydroxyapatite (Calcium) Function: Hard, brittle and can withstand compression –Protein Fibers: Collagen Function: Tensile strength, tolerates twisting/bending

Bone Cells Maintain matrix, help repair damage bone Secrete new matrix (osteoid), become osteocytes Produce osteoblasts, repair fractures Remove/recycle matrix by dissolving with acids/enzymes (osteolysis) Resorption- breakdown of bone *every 7 years you make a new skeleton

Bone Tissue 1. Compact- 80% of bone, few spaces – Haversian canals (bld vessels), Lamellae (layers), Lacunae(pockets with osteocytes) * All bone tissue has a rich supply of blood

2. Spongy- 20% of bone, found in the epiphyses No osteons Matrix = trabeculae (lattice structures), appears to have holes stores red marrow –Open network of fibers w/ no blood vessels

6-4 Compact Bone and Spongy Bone Periosteum: –Outer membrane covering compact bone –fibrous and cellular layer –Functions: –Isolates bone –Route for blood vessels/nerves –Bone growth/repair

6-4 Compact Bone and Spongy Bone Endosteum –incomplete cellular layer lining the medullary cavity –Contains osteoblasts, osteoprogenitor cells and osteoclasts –Functions: –Covers trabeculae –Lines central canals –bone growth and repair

6-5 Bone Formation and Growth Ossification The process of replacing other tissues with bone Includes calcification: deposition of Ca salts Two Main forms of ossification: Endochondral Ossification and Intramembranous Ossification

Endochondral Ossification Ossifies bones that originated as hyaline cartilage Step 1: Chondrocytes increase in size Matrix begins to calcify Enlarged chondrocytes die

Endochondral Ossification Step 2: BVs grow into perichondrium Cells of perichondrium convert to osteoblasts and produce thin layer of superficial bone

Endochondral Ossification Step 3: BVs penetrate cartilage Fibroblasts migrate and differentiate into osteoblasts Form primary ossification center, cartilage replaced with spongy bone

Endochondral Ossification Step 4: Remodeling occurs Osseous tissue becomes thicker Cartilage near epiphysis replaced by bone Osteoclasts erode spongy bone and form medullary cavity

Step 5: Capillaries and osteoblasts migrate into epiphyses Secondary ossification centers form Endochondral Ossification

Step 6: Epiphyses fill with spongy bone Articular cartilage remains Metaphysis: epiphyseal cartilage separates epiphysis from diaphysis Epiphyseal cartilage lost after puberty complete females 23, males 25 when complete-no epiphyseal disks

Figure 6-11a Bone Growth at an Epiphyseal Cartilage An x-ray of growing epiphyseal cartilages (arrows) Epiphyseal lines in an adult (arrows)

Intramembranous (Dermal) Ossification Bone Formation Video

6-6 Bone Remodeling The adult skeleton: Maintains itself Replaces mineral reserves Recycles and renews bone matrix

6-7 Exercise, Hormones, and Nutrition Exercise –Mineral recycling allows bones to adapt to stress –Heavily stressed bones become thicker and stronger Bone Degeneration –Bone degenerates quickly –Up to one third of bone mass can be lost in a few weeks of inactivity

6-7 Exercise, Hormones, and Nutrition Nutrition –Diet must include calcium and phosphate salts, plus small amounts of magnesium, fluoride, iron, and manganese –Calcitriol Vitamin C required for collagen synthesis and stimulation of osteoblast differentiation Vitamin A stimulates osteoblast activity Vitamins K and B 12 help synthesize bone proteins

6-7 Exercise, Hormones, and Nutrition Hormones –Growth hormone and thyroxine stimulate bone growth –Estrogens and androgens stimulate osteoblasts –Calcitonin and parathyroid hormone regulate calcium levels

Figure 6-16b Factors That Alter the Concentration of Calcium Ions in Body Fluids Bone Response Intestinal Response Kidney Response Thyroid Gland Response Factors That Decrease Blood Calcium Levels These responses are triggered when plasma calcium ion concentrations rise above 11 mg/dL. HIgh Calcium Ion Levels in Plasma (above 11 mg/dL) Parafollicular cells (C cells) in the thryoid gland secrete calcitonin. Osteoclasts inhibited while osteoblasts continue to lock calcium ions in bone matrix Bone Rate of intestinal absorption decreases Kidneys allow calcium loss Calcitonin less calcitriol Calcium stored Calcium absorbed slowly Calcium excreted Increased calcium loss in urine ↓Ca 2+ levels in bloodstream

Figure 6-16a Factors That Alter the Concentration of Calcium Ions in Body Fluids Bone ResponseIntestinal ResponseKidney Response Parathyroid Gland Response Factors That Increase Blood Calcium Levels These responses are triggered when plasma calcium ion concentrations fall below 8.5 mg/dL. Low Calcium Ion Levels in Plasma (below 8.5 mg/dL) Low calcium plasma levels cause the parathyroid glands to secrete parathyroid hormone (PTH). Osteoclasts stimulated to release stored calcium ions from bone Osteoclast Bone Rate of intestinal absorption increases Kidneys retain calcium ions PTH more calcitriol Calcium released Calcium absorbed quickly Calcium conserved Decreased calcium loss in urine ↑Ca 2+ levels in bloodstream

Cracks/breaks in bones Caused by physical stress Repaired in four steps

Figure 6-17 Types of Fractures and Steps in Repair Immediately after the fracture, extensive bleeding occurs. Over a period of several hours, a large blood clot, or fracture hematoma, develops. An internal callus forms as a network of spongy bone unites the inner edges, and an external callus of cartilage and bone stabilizes the outer edges. Periosteum Spongy bone of external callus Fracture hematoma Bone fragments Dead bone REPAIR OF A FRACTURE

Figure 6-17 Types of Fractures and Steps in Repair The cartilage of the external callus has been replaced by bone, and struts of spongy bone now united the broken ends. Fragments of dead bone and the areas of bone closest to the break have been removed and replaced. A swelling initially marks the location of the fracture. Over time, this region will be remodeled, and little evidence of the fracture will remain. External callus External callus Internal callus

Fractures 1. Open/Compound- through the skin 2. Closed/ Simple- not through the skin 3. Comminuted- smaller fragments 4. Greenstick- only children, 1 side broken, 1 side bends 5. Impacted- bone through bone Stress fracture- microscopic, repeated stress can withstand 24,000 lbs/sq in, 4x greater than steel

Transverse- break along shaft Spiral- from twisting Displaced- produces abnormal bone alignment

6-10 Effects of Aging on the Skeletal System Bones become thinner and weaker with age Osteopenia begins between Inadequate ossification/osteoblast activity declines = loss of bone mass Women lose 8% of bone mass/decade, men 3% The epiphyses, vertebrae, jaws most affected Result = fragile limbs, reduction in height, tooth loss

SEM  25 Normal spongy bone Spongy bone in osteoporosis SEM  21 Osteoporosis Severe bone loss Affects normal function/increases possibility of fracture Causes: inadequate intake of calcium and vitamin D lack of weight-bearing exercise lack of certain hormones, particularly estrogen in women (menopausal women are at higher risk) Cigarette smoking eating disorders such as anorexia nervosa or bulimia

Abnormal Development of Bone Pituitary dwarfism =inadequate production of growth hormone resulting in short bones Gigantism= overproduction of HGH Robert Wadlow (Alton) 8ft, 11in Marfan’s syndrome = excess cartilage at epiphyseal plates