The Skeletal System
Orthopedics – field of medicine associated with
A. Functions
1. Support – framework for the body,
support for soft tissue, attachment for
skeletal muscle.
2.
Protection – of internal organs
(skull – brain , rib cage – heart and
lungs)
3.
Movement – skeletal muscles
4. Mineral storage – calcium and
phosphate
5. Blood cell production – Hemopoiesis
– red bone marrow  red blood cells
6. Energy storage – yellow bone
marrow – lipid storage, made mostly of
adipose tissue, chemical energy storage
7.
Immune system - WBCs
B. Types of bones – Each bone is an organ
1. Long bones – greater length than width
a. Mostly compact bone tissue, some
spongy
b. Thigh, legs, toes, arms, forearms,
fingers
2. Short bones – cube-shaped
a.
mostly spongy
b.
equal length and width
c.
wrist and ankle
3. Flat bones – thin
a.
Composed of two or more
parallel plates of compact bone
b.
Cranium, sternum, ribs,
scapula
4. Irregular bones – complex shape
vertebrae, facial bones
5. Sutural bones (wormian bones)
Small bones between the joints of
the cranium, numbers vary from
person to person
6. Sesamoid bones
a. Small bones located in
tendons where pressure develops
b. wrist and patellas
C. Structure of the long bone
1. Diaphysis – shaft, long, main
cylindrical portion
2. Epiphysis – ends of the bone
3. Metaphysis – where diaphysis and
epiphysis meet in mature bones,
contains epiphyseal (growth) plate
4. Articular cartilage – thin layer of
hyaline cartilage covering the
epiphysis at the joint, reduces
friction (shock absorption)
5. Periosteum – around the bone,
membrane around surface, two
layers of outer dense connective
tissue with blood vessels and nerves
6. Medullary – marrow cavity, within
diaphysis, consists of yellow marrow
7. Endosteum – lining medullary cavity
consisting of osteoprogenitor cells
D. Histology – four types of connective tissue – cartilage, bone,
marrow, periosteum
1. Matrix – consists of an inorganic component (mineral
salts) and organic collagen fibers – responsible for
calcification
2. Cell types
a. Osteoprogenitor cells – undergo
mitosis to become osteoblasts
b. Osteoblasts – cells to form new
bone (osteogenesis) – no mitosis, form
collagen and compounds to build bone
and will become osteocytes
c. Osteocytes – most abundant,
mature bone cells, recycle calcium
salts and assist in repair
d. Osteoclasts – giant cells with 50 or
more nuclei, develop from a type of
WBC called a monocyte, function in
bone resorption by secreting acids to
release stored minerals (regulates
calcium and phosphate in body fluids)
3. Bone tissue
a. Compact bone tissue – few
spaces, withstand forces
applied at either end
• Forms external part of all
bones
• Forms bulk of long bones
• Form concentric rings
• Arteries penetrate through
Volkmann’s canal
• Haversian canal – central canal
b. Spongy bone tissue – not heavily
stressed, lighter
• No true osteon
• Latticework of rods or plates
called trabeculae
• Spaces filled with red marrow
Ossification: bone formation – human embryonic
skeleton is composed of fibrous connective tissue and
hyaline cartilage – ossification begins 6th or 7th week of
embryonic development through adulthood
A. Intramembranous Ossification – within fibrous tissue –
most of skull and clavicles
1. cells within mesenchyme –
differentiate into
osteoprogenitor cells and
then osteoblasts
2. clusters of osteoblasts are
surrounded by a calcified
matrix and it becomes a
trabecula
3. trabeculae fuse to form
latticework (spongy)
4. osteoblasts become
osteocytes – can no longer
form bone
B. Endochondral ossification – replacement of cartilage by
bone – most bones
1. Mesenshyme comes together
2. Cells form chondroblasts that
become hyaline cartilage
3. Cartilage grows in length by cell
division
4. Chondrocytes burst changing pH
in matrix causing calcification
5. Cartilage cells die
6. Blood vessels penetrate the
perichondrium and the bond
causing osteoprogenitor cells to
change into osteoblasts
7. These form compact bone
8. Epiphyseal plates continue to be
active because of hGH (human
growth hormone
9. Secondary ossification occurs from
the epiphyseal plate to the diaphysis
Homeostasis – remodeling is the replacement of old bone
tissue ( 18% of protein and minerals removed and replaced
per year)
A. Bone growth and maintenance – diameter is increased
by destruction of bone internally and construction
externally (osteoclasts) – need calcium, pjosphorus
and collagen
B.Minerals – calcium and phosphorus from diet
C. Vitamins
1. Vitamin D – calcium absorption from GI tract as well as
from the removal of bone
2. Vitamin C regulates matrix
3. Vitamin A regulates osteoblasts and osteoclasts
4. Vitamin B12
D.Hormones
1.
hGH – tall or short
2.
estrogen, testosterone – promote bone growth
3.
insulin, thyroid hormones – growth and maturity
E. Mineral storage
1. calcium – in bone, but also for muscular function,
nerve function, blood clotting (calcitonin regulates
calcium)
2.
phosphate – DNA, RNA, ATP
F. Exercise and bone - bone becomes stronger when under
mechanical stress by increasing mineral deposition and
production of collagen (bone loss can be as much as 1%
per week – astronauts
G. Aging and bone – calcium loss, inadequate ossification
(osteopenia)
FEMALES – begins after 30 and accelerates around 40-50
(30% lost by age 70)
MALES – begins after 60