BIO 238
THE SKELETAL SYSTEM
BONE FUNCTION
Support
 Protection
 Leverage- for motion
 Mineral Homeostasis
 Blood cell production

 Hemopoiesis

in red bone marrow
Triglyceride Storage
MACROSCOPIC STRUCTURE
Parts of a long bone:
 Diaphysis
 Epiphysis
 Metaphysis
 Articular cartilage
 Periosteum
 Medullary cavity
 Endosteum

FIGURE 6.1A
FIGURE 6.1B
MICROSCOPIC STRUCTURE

Matrix=


25% water, 25% collagen fibers, 50% crystallized mineral
salts
Osteogenic cells- in periosteum; Osteoblastssecrete collagen fibers
Build matrix and become trapped in lacunae
Become osteocytes- maintain bone
 Osteoclasts –formed from monocytes


Digest bone matrix for Normal bone turnover
COMPACT BONE STRUCTURE
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
SPONGY BONE
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
BONE FORMATION
Ossification- formation of bone
 1. initially in embryo & fetus
 2. Growth
 3. remodeling
 4. repair of fractures
BONE FORMATION
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
GROWTH
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
REMODELING

The adult skeleton:
 maintains
itself
 replaces mineral reserves

Remodeling:
 recycles
and renews bone matrix
 involves osteocytes, osteoblasts, and osteoclasts
EFFECTS OF EXERCISE ON BONE
Mineral recycling allows bones to adapt to
stress
 Heavily stressed bones become thicker and
stronger

BONE DEGENERATION
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

MINERALS

A dietary source of calcium and phosphate
salts:
 plus
small amounts of magnesium, fluoride, iron,
and manganese
VITAMINS
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.

OTHER HORMONES
Growth hormone and thyroid hormones
stimulate bone growth
 Estrogens and androgens stimulate osteoblasts
 Calcitonin and parathyroid hormone regulate
calcium and phosphate levels

THE SKELETON AS CALCIUM RESERVE
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 REGULATION

Calcium ions in body fluids:
 must

be closely regulated
Homeostasis is maintained:
 by
calcitonin and parathyroid hormone
 which control storage, absorption, and excretion
CALCITONIN AND PARATHYROID HORMONE
CONTROL

Bones:
 where

Digestive tract:
 where

calcium is stored
calcium is absorbed
Kidneys:
 where
calcium is excreted
PARATHYROID HORMONE (PTH)
PARATHYROID HORMONE (PTH)
Produced by parathyroid glands in neck
 Increases calcium ion levels by:

 stimulating
osteoclasts
 increasing intestinal absorption of calcium
 decreases calcium excretion at kidneys
CALCITONIN
CALCITONIN
Secreted by C cells (parafollicular cells) in
thyroid
 Decreases calcium ion levels by:

 inhibiting
osteoclast activity
 increasing calcium excretion at kidneys
HOMEOSTASIS
Copyright 2010, John Wiley & Sons, Inc.
BONES ROLE IN BLOOD CALCIUM
REGULATION




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
JUST SO YOU WILL KNOW…




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
WHAT ARE THE TYPES
OF FRACTURES, AND
HOW DO THEY HEAL?
FRACTURES

Fractures:
 cracks
or breaks in bones
 caused by physical stress

Fractures are repaired in 4 steps
Copyright 2010, John Wiley & Sons, Inc.
STEPS IN
REPAIR OF A
BONE
FRACTURE
Copyright 2010, John Wiley & Sons, Inc.
TYPES OF
BONE
FRACTURES
THE MAJOR TYPES OF FRACTURES

Pott’s fracture
THE MAJOR TYPES OF FRACTURES

Comminuted fractures
THE MAJOR TYPES OF FRACTURES

Transverse fractures
THE MAJOR TYPES OF FRACTURES

Spiral fractures
THE MAJOR TYPES OF FRACTURES

Displaced fractures
THE MAJOR TYPES OF FRACTURES

Colles’ fracture
THE MAJOR TYPES OF FRACTURES

Greenstick fracture
THE MAJOR TYPES OF FRACTURES

Epiphyseal fractures
THE MAJOR TYPES OF FRACTURES

Compression fractures
BONE DISORDERS
ABNORMAL CURVATURES
Kyphosis – exaggerated thoracic curvature
(humpback)
 Lordosis – exaggerated lumbar curvature
(swayback)
 Scoliosis – exaggerated lateral curvature

KYPHOSIS, LORDOSIS, SCOLIOSIS
AGE AND BONES
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%

EFFECTS OF BONE LOSS

The epiphyses, vertebrae, and jaws are most
affected:
 resulting
in fragile limbs
 reduction in height
 tooth loss
OSTEOPOROSIS

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.
OSTEOPOROSIS



Severe bone loss
Affects normal function
Over age 45, occurs in:


29% of women
18% of men
HORMONES AND BONE LOSS
Estrogens and androgens help maintain bone
mass
 Bone loss in women accelerates after
menopause

CANCER AND BONE LOSS

Cancerous tissues release osteoclast-activating
factor:
 that
stimulates osteoclasts
 and produces severe osteoporosis