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

FIGURE 6.4

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 B12 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.

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