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Osteology
• Osteology: The study of the anatomy,
physiology and related diseases of bone is
referred to as osteology.
Bone
• Bone: A specialized type of connective
tissue that consists of living cells held in
place by a rigid intercellular matrix of
collagen fibers embedded with calcium
salts.
Matrix of Bone
• Inorganic mineral salts provide bone’s hardness
– hydroxyapatite (calcium phosphate) & calcium
carbonate
• Organic collagen fibers provide bone’s flexibility
– their tensile strength resists being stretched or torn
– remove minerals with acid & rubbery structure
results
• Mineralization (calcification) is hardening of tissue
when mineral crystals deposit around collagen fibers
• Bone is not completely solid since it has small
spaces for vessels and red bone marrow
– spongy bone has many such spaces
– compact bone has very few
Exercise, Hormones, and
Nutrition
• Normal bone growth and maintenance depend
on nutritional and hormonal factors
– Vitamin C is required for collagen synthesis, and
stimulation of osteoblast differentiation
– Vitamin A stimulates osteoblast activity
– Vitamins K and B12 help synthesize bone proteins
– Growth hormone and thyroxine stimulate bone growth
– Estrogens and androgens stimulate osteoblasts
– Calcitonin and parathyroid hormone regulate calcium
and phosphate levels
Factors Affecting Bone Growth
• Nutrition
– adequate levels of minerals and vitamins
• calcium and phosphorus for bone growth
• vitamin C for collagen formation
• vitamins K and B12 for protein synthesis
• Sufficient levels of specific hormones
– during childhood need insulin like growth factor
• promotes cell division at epiphyseal plate
• need hGH (growth), thyroid (T3 &T4) and insulin
– sex steroids at puberty
• growth spurt and closure of the epiphyseal growth
plate
• estrogens promote female changes -- wider pelvis
Exercise, Hormones, and Nutrition
Hormonal Abnormalities
• Oversecretion of HGH during childhood
produces giantism ( in adults=acromegally)
• Undersecretion of HGH or thyroid hormone
during childhood produces short stature
(dwarfism)
• Both men or women that lack estrogen
receptors on cells grow taller than normal
– estrogen responsible for closure of growth plate
Exercise, Hormones, and
Nutrition
FIGURE 6–14 Examples of Abnormal Bone Development.
Calcium Homeostasis & Bone Tissue
• Skeleton is reservoir of Calcium & Phosphate
• Calcium ions involved with many body
systems
– nerve & muscle cell function
– blood clotting
– enzyme function in many biochemical
reactions
• Small changes in blood levels of Ca+2 can be
deadly (plasma level maintained 9-11mg/100mL)
– cardiac arrest if too high
– respiratory arrest if too low
Calcium Homeostasis
• 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
Calcium Homeostasis
• Calcitonin and parathyroid hormone control and
affect
– Bones
• Where calcium is stored
– Digestive tract
• Where calcium is absorbed
– Kidneys
• Where calcium is excreted
Calcium Homeostasis
• Parathyroid Hormone (PTH)
– Produced by parathyroid glands in neck
– Increases calcium ion levels by
• Stimulating osteoclasts
• Increasing intestinal absorption of calcium
• Decreasing calcium excretion at kidneys
• Calcitonin
– Secreted by C cells (parafollicular cells) in thyroid
– Decreases calcium ion levels by
• Inhibiting osteoclast activity
• Increasing calcium excretion at kidneys
Hormonal Influences
• Parathyroid hormone (PTH) is
secreted if Ca+2 levels falls
– PTH gene is turned on & more
PTH is secreted from gland
– osteoclast activity
increased, kidney retains
Ca+2 and produces
calcitriol
• Calcitonin hormone is secreted
from parafollicular cells in
thyroid if Ca+2 blood levels get
too high
– inhibits osteoclast activity
– increases bone formation
by osteoblasts
Calcium Homeostasis
Figure 6–15 A Chemical Analysis of Bone.
Calcium Homeostasis
Figure 6–16a Factors That Alter the Concentration of Calcium Ions in
Body Fluids.
Calcium Homeostasis
Figure 6–16b Factors That Alter the Concentration of Calcium Ions in
Body Fluids.
Exercise & Bone Tissue
• The pull on bone by skeletal muscle and
gravity is mechanical stress .
• Stress increases deposition of mineral
salts & production of collagen (calcitonin
prevents bone loss)
• Lack of mechanical stress results in bone
loss
– reduced activity while in a cast
– astronauts in weightlessness
– bedridden person
• Weight-bearing exercises build bone
mass (walking or weight-lifting)
Osteopenia
• Bones become thinner and weaker with
age
– Osteopenia begins between ages 30 and 40
– Women lose 8% of bone mass per decade,
men 3%
Osteopenia
• The epiphyses, vertebrae, and jaws are most
affected:
– Resulting in fragile limbs
– Reduction in height
– Tooth loss
• Osteoporosis
– Severe bone loss
– Affects normal function
– Over age 45, occurs in
• 29% of women
• 18% of men
Osteopenia
Figure 6–19 The Effects of Osteoporosis on Spongy Bone.
Aging
• 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
Osteoporosis
• Decreased bone mass resulting in porous bones
• Those at risk
– white, thin menopausal, smoking, drinking female
with family history
– athletes who are not menstruating due to
decreased body fat & decreased estrogen levels
– eating disorders whose intake of calcium is too low
• Prevention or decrease in severity
– adequate diet, weight-bearing exercise
– behavior when young may be most important factor
Osteoporosis
• Osteoporosis is a disorder characterized by a decrease in total
bone material which is experienced primarily by females. It is
theorized that osteoporosis is caused primarily by an estrogen
deficiency. Estrogen is a parathyroid antagonist. When insufficient
estrogen is produced by the female, the parathyroid hormone that is
present can significantly de-mineralize the skeletal system.
Osteoporosis begins at about the age of 18 years, where lifestyle
factors (smoking, poor diet and sedentary lifestyle) play the most
significant roles. At age 35 years, the amount of estrogen produced by
most females begins to decrease and bone demineralization
accelerates. After menopause, osteoporosis progresses rapidly
because of the absence of estrogen. Osteoporosis is visible on
an x-ray only after at least 30% of the bone mass has been lost.
Patients, however, only experience symptoms after at least 50% of
the total bone mass has been lost. It is necessary for individuals at
risk to undergo early diagnostic imaging tests (single/dual photon
absorptiometry) in order to detect osteoporosis in its earliest stages.
The most effective therapy for osteoporosis is prevention. Individuals
should attempt to maintain a healthy skeletal system in their youth.
Causes of osteoporosis include: genetic factors, estrogen
deficiencies, poor diet (high phosphate/low calcium), smoking, and
environmental factors.
Lateral View of Osteoporotic
Thoracic Spine
Normal Bone VS Osteoporotic
Bone (Cod Fish Vertebra)
Hyperkyphosis
Disorders of Bone Ossification
• Rickets
• calcium salts are not deposited properly
• bones of growing children are soft
• bowed legs, skull, rib cage, and pelvic deformities
result
• Osteomalacia
• new adult bone produced during remodeling fails
to ossify
• hip fractures are common
Functions of Bone
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1) Support
2) Protection
3) Locomotion
4) Mineral homeostasis
5) Hematopoiesis
6) Triglyceride storage
Anatomy of a Long Bone
• Diaphysis: The long cylindrical portion (shaft/bone) of a long bone.
• Epiphysis: The proximal and distal ends of a long bone.
• Metaphysis: In a mature/adult bone, the metaphysis represents the
region of the bone where the diaphysis joins to the epiphysis. In
a growing bone, the metaphysis contains the epiphyseal (growth)
plate. The epiphyseal plate is a layer of hyaline cartilage existing
within the metaphysis of a long bone that allows the diaphysis of
the bone to grow in length, but not width.
• Articular Cartilage: Articular cartilage is a thin layer of hyaline
cartilage that covers the proximal and distal epiphyses where the
bone forms articulations/joints. Articular cartilage reduces friction
in moveable joints, and assists in shock absorption
Typical Long Bone
Articular Cartilage
• Articular Cartilage: Articular cartilage is a
thin layer of hyaline cartilage that covers
the proximal and distal epiphyses where
the bone forms articulations/joints.
Articular cartilage reduces friction in
moveable joints, and assists in shock
absorption
Periosteum
• Periosteum: The periosteum is a tough sheath
of dense irregularly arranged connective
tissue that covers the surface of bone except
where articular cartilage exists. The periosteum.
The periosteum contains cells which are
involved in bone formation and allows the bone
to grow in diameter/thickness. The periosteum
also helps to nourish the bone, assist in
fracture repair, protects the bone and acts as
an attachment site for tendons and
ligaments.
Periosteum and Endosteum
Medullary Cavity
• Medullary Cavity: The space within the
diaphysis of a long bone that contains the
red (infant) or yellow (adult) bone
marrow.
Endosteum
• Endosteum: The membrane that
contains bone forming cells that lines
the internal surface of the medullary cavity
and external surface of the boney
trabeculae.
Spongy Bone and the
Endosteum
Histology of Bone
• Bone is a typical connective tissue. It contains a
small number of cells existing in a large amount
of intercellar matrix. The matrix of bone is
approximately 25% water, 25% protein fibers,
and 50% crystallized mineral salts. There are
four types of cells that can be found in bone:
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a) osteogenic cells
b) osteoblasts
c) osteocytes
d) osteoclasts.
Osteogenic Cells
• Osteogenic Cells: Osteogenic cells are
undifferentiated stem cells that are
found in the inner surface of the
periosteum, the endosteum and in the
canals that transmit
blood vessels within the bone. These
cells are the only bone cells that are
capable of reproduction and ultimately
differentiate into osteoblasts.
Bone Cells
Osteoblasts
• Osteoblasts: Osteoblasts synthesize and
secrete collagen fibers as well as other
organic compounds that are needed to
build bone. They are also involved in
initiating the calcification of these organic
components of bone.
Osteocytes
• Osteocytes: Osteocytes represent the
principle type of bone cell in bone tissue.
Osteocytes are mature cells that arise
from osteoblasts that have been
trapped in the mineral intercellular
matrix of bone. Osteocytes essentially
maintain bone tissue.
Osteoclasts
• Osteoclasts: Osteoclasts are large cells
which result from the fusion of as many as
50 monocytes. Osteoclasts exist primarily
within the endosteum of bone. These
cells
contain a ruffled
border that faces the bone, from which
powerful lysosomal
enzymes and acids are released that
break bone down.
Types of Bone
• Bone essentially occurs as either:
• a) compact bone or
• b) spongy bone.
Compact VS Spongy Bone
Haversian System
• Compact bone is dense and smooth in
appearance. It forms the external layer of all of
the bones of the body and makes up the
principle portion of the diaphysis of the long
bones. Compact bone contains few spaces
between its mineralized components and is
arranged in units called Haversian
systems/osteons. Compact bone provides
bone with protection, support and the ability
to resist weight bearing stresses.
Three Dimensional Structure of the Haversian
System/Osteon
Micrograph of the Osteon
Histology of Bone
The Haversian System
• The Haversian system is the basic unit of compact bone.
Blood vessels, lymphatic vessels and nerves penetrate through
the compact layer of bone through small openings known as
Volkmann’s/perforating canals. These blood vessels will
connect with the blood vessels of the periosteum, medullary
cavity, and the central canal of the Haversian system. The
central canals of the Haversian system and the blood
vessels which are contained within them, run in a
longitudinal direction through the compact bone.
Surrounding these canals/blood vessels, are concentric rings
composed of the mineralized intercellular matrix of bone.
Contained within these rings, are small spaces known as
lacunae which contain the osteocytes. Extending from each
osteocyte are cytoplasmic projections referred to as
canaliculae. The canaliculae of the osteocytes from each
successive ring contact each other and allow the osteocytes
to pass/exchange material between themselves and the
blood vessels within the Haversian canal. The exchange of
materials via the canaliculae of the osteocytes allows the
passage of substances such as nutrients, hormones, dissolved
gases, and wastes through the calcified intercellular matrix of
bone.
Histology of Spongy Bone
• The histological architecture of spongy bone is different
than that of compact bone. Spongy bone does not
contain true Haversian systems. Instead, spongy bone
consists of a lattice work of thin boney trabeculae. The
strength of a bone is actually determined by the density
and arrangement of the components making up the spongy
bone. The trabeculae making up the bones of an individual
are arranged in such a way as to allow the bone to
withstand the maximum amount of stress that they would
encounter in their particular lifestyle. If the lifestyle of an
individual changes, the boney trabeculae will be
broken down and remodeled in a new architectural
arrangement that will allow the bon to withstand the
maximum amount of stress that will be encountered in
these new activities. This structural relationship between
compact and spongy bone allows the bones to be both light
and strong. The spaces contained between the boney
trabeculae contain bone marrow. The osteoblasts,
osteocytes and osteoclasts of the spongy bone
exchange substances directly with the blood vessels in
the bone marrow.
Bone Remodeling
• Bone, especially spongy bone, remodels
itself throughout life in order allow the
skeletal system to adapt to changing
anatomical and physiological stresses.
• Woolfes Law: The more physical stress
that is put on a bone, the denser and
stronger the bone becomes.
Aneurysmal Bone Cyst
Aneurysmal Bone Cyst of the
Fibula
Aneurysmal Bone Cyst of the
Spine (Vertebra)
Types of Fractures
Comminuted and Compression
Fractures
Spiral and Epiphyseal Fractures
Depressed and Greenstick
Fractures
Stages of Healing In a Bone
Fracture
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Hematoma Formation
Fibrocartilage Callus Formation
Bony Callus Formation
Bone Remodeling
Hematoma Formation
• Hematoma formation
– Torn blood vessels
hemorrhage
– A mass of clotted
blood (hematoma)
forms at the fracture
site
– Site becomes swollen,
painful, and inflamed
Fibrocartilage Callus Formation
• Fibrocartilaginous
callus forms
• Granulation tissue
(soft callus) forms a
few days after the
fracture
• Capillaries grow into
the tissue and
phagocytic cells
begin cleaning
debris
Bony Callus Formation
• Bony callus formation
– New bone trabeculae
appear in the
fibrocartilaginous callus
– Fibrocartilaginous callus
converts into a bony
(hard) callus
– Bone callus begins 3-4
weeks after injury, and
continues until firm
union is formed 2-3
months later
Bone Remodeling
• Bone remodeling
– Excess material on
the bone shaft exterior
and in the medullary
canal is removed
– Compact bone is laid
down to reconstruct
shaft walls
Long Bones
Short Bones
Flat Bones
Irregular Bones