BIO 238

 Support  Protection  Leverage- for motion  Mineral Homeostasis  Blood cell production  Hemopoiesis in red bone marrow  Triglyceride Storage

 Parts of a long bone:  Diaphysis  Epiphysis  Metaphysis  Articular cartilage  Periosteum  Medullary cavity  Endosteum

FIGURE 6.1A

FIGURE 6.1B

 Matrix=  25% water, 25% collagen fibers, 50% crystallized mineral salts  Osteogenic cells- in periosteum; Osteoblasts- secrete collagen fibers-  Build matrix and become trapped in lacunae  Become osteocytes- maintain bone  Osteoclasts – formed from monocytes  Digest bone matrix for Normal bone turnover

 few spaces, right below periosteum  Units = osteons (Haversian system)  Central canal- blood vessels, nerves, lymphatics  Concentric lamellae- layers of matrix  Lacunae- “lakes” contain osteocytes  Canaliculae- little canals  nutrient flow from canals and between osteocytes

 units containing trabeculae  spaces between trabeculae often contain marrow  Two types-  Red bone marrow- produces blood cells and platelets  Yellow bone marrow- stores fat  No osteons but include lacunae & canaliculae

FIGURE 6.2B

Ossification- formation of bone  1. initially in embryo & fetus  2. Growth  3. remodeling  4. repair of fractures

 Mesenchyme model - replaced with bone  Intramembranous - Bone forms directly in mesenchyme layers (membrane like)  Endochondrial - forms within hyaline cartilage developed from mesenchyme

FIGURE 6.3

 Length- chondrocytes in the epiphyseal plate divide and increase cartilage layer  On diaphyseal side they die and are replaced by bone  Stops during adolescence  Periosteum supports surface growth for thickness

FIGURE 6.5

 The adult skeleton:  maintains itself  replaces mineral reserves  Remodeling:  recycles and renews bone matrix  involves osteocytes, osteoblasts, and osteoclasts

 Mineral recycling allows bones to adapt to stress  Heavily stressed bones become thicker and stronger

 Bone degenerates quickly  Up to 1/3 of bone mass can be lost in a few weeks of inactivity  What you don’t use, you lose  Stresses applied to bones during physical activity are essential to maintain bone strength and mass

 A dietary source of calcium and phosphate salts:  plus small amounts of magnesium, fluoride, iron, and manganese

 Vitamin C is required for collagen synthesis, and stimulates osteoblast differentiation  Vitamin A stimulates osteoblast activity  Vitamins K and B 12 help synthesize bone proteins  Vitamins D helps with calcium and phosphate absorption.

 Growth hormone and thyroid hormones stimulate bone growth  Estrogens and androgens stimulate osteoblasts  Calcitonin and parathyroid hormone regulate calcium and phosphate levels

 Bones store calcium and other minerals  Calcium is the most abundant mineral in the body  Calcium ions are vital to:  membranes  neurons  muscle cells, especially heart cells

 Calcium ions in body fluids:  must be closely regulated  Homeostasis is maintained:  by calcitonin and parathyroid hormone  which control storage, absorption, and excretion

 Bones:  where calcium is stored  Digestive tract:  where calcium is absorbed  Kidneys:  where calcium is excreted

 Produced by parathyroid glands in neck  Increases calcium ion levels by:  stimulating osteoclasts  increasing intestinal absorption of calcium  decreases calcium excretion at kidneys

 Secreted by C cells (parafollicular cells) in thyroid  Decreases calcium ion levels by:  inhibiting osteoclast activity  increasing calcium excretion at kidneys

 Nutrition is also important for bone health  Each night we deposit minerals in our bones  These minerals are stored for use by the rest of the body  If we do not replenish the mineral supply equally or faster than it is used osteoporosis results Copyright 2010, John Wiley & Sons, Inc.

 Calcium and phosphate ions in blood are lost in urine  Ions must be replaced to maintain homeostasis  If not obtained from diet, ions are removed from the skeleton, weakening bones  Exercise and nutrition keep bones strong

 Fractures:  cracks or breaks in bones  caused by physical stress  Fractures are repaired in 4 steps

Copyright 2010, John Wiley & Sons, Inc.

 Pott’s fracture

 Comminuted fractures

 Transverse fractures

 Spiral fractures

 Displaced fractures

 Colles’ fracture

 Greenstick fracture

 Epiphyseal fractures

 Compression fractures

 Kyphosis – exaggerated thoracic curvature (humpback)  Lordosis – exaggerated lumbar curvature (swayback)  Scoliosis – exaggerated lateral curvature

 Bones become thinner and weaker with age  Osteopenia (A condition of bone in which decreased calcification, decreased density, or reduced mass occurs) begins between ages 30 and 40  Women lose 8% of bone mass per decade, men 3%

 The epiphyses, vertebrae, and jaws are most affected:  resulting in fragile limbs  reduction in height  tooth loss

 a disorder in which the bones become increasingly porous, brittle, and subject to fracture, owing to loss of calcium and other mineral components, sometimes resulting in pain, decreased height, and skeletal deformities: common in older persons, primarily postmenopausal women, but also associated with long-term steroid therapy and certain endocrine disorders.

 Severe bone loss  Affects normal function  Over age 45, occurs in:  29% of women  18% of men

 Estrogens and androgens help maintain bone mass  Bone loss in women accelerates after menopause

 Cancerous tissues release osteoclast-activating factor:  that stimulates osteoclasts  and produces severe osteoporosis