Bones and Skeletal Tissues
Major Function of Bones
• Support – form the framework that supports the
body and cradles soft organs.
• Protection – provide a protective case for the
brain, spinal cord, and vital organs.
• Movement – provide levers for muscles.
• Mineral storage – reservoir for minerals
especially calcium and phosphorus
– that can be released into the blood if the body needs
them.
• Blood cell formation – hematopoiesis occurs
within the marrow cavities of bones
Minor Functions of Bones
• Acid/Base Balance: Absorbs or releases
alkaline mineral salts if blood pH changes
drastically.
• Detoxification: Helps remove heavy metals
and foreign elements from the blood to
protect other vitals organs.
– It will try to release them slowly to prevent
excessive stress on the kidneys who must
excrete them.
Bone: Cell Types
• Bone is considered connective tissue that contains several
types of cells make it capable of adapting and changing
according to stresses placed on it.
– Osteoblast (build): Produced by osteogenic cells if there is
an increase in stress or fracture to the bone.
• They lay down building blocks of bone matrix (collagen
and glycoaminoglycans) ( GAGs). This plays an important
role in mineralization of bone.
– Osteocyte: As the osteoblast deposit matrix they become
trapped in lacunae. They stop producing matrix and assume
a role in maintaining calcium and phosphate balance
between bone and blood.
Bone: Cell Types
– Osteoclast: (Break) break down bone matrix by
secreting acids and enzymes . Components of the
matrix mainly Calcium and Phosphorus are released
in the blood.
– Osteoid – unmineralized bone matrix composed of
proteoglycans, glycoproteins, and collagen
Bone Membranes
• Periosteum – double-layered protective
membrane
– Outer fibrous layer is dense regular connective
tissue
– Inner osteogenic layer is composed of
osteoblasts and osteoclasts
– Richly supplied with nerve fibers, blood, and
lymphatic vessels, which enter the bone via
nutrient foramina
• Endosteum – delicate membrane covering
internal surfaces of bone
Microscopic Structure of Bone:
Compact Bone
Figure 6.6a, b
Gross Anatomy of Compact Bone
• Compact bone
– dense and heavy bone designed for compressive
forces
• Haversian system, or osteon – the structural unit of
compact bone
– Lamella – weight-bearing, column-like matrix tubes
composed mainly of collagen
– Haversian, or central canal – central channel
containing blood vessels and nerves
– Volkmann’s canals – channels lying at right angles
to the central canal, connecting blood and nerve
supply of the periosteum to that of the Haversian
canal
– Canaliculi – hairlike canals that connect lacunae to
each other and the central canal
Microscopic View of Compact Bone
Histology of Compact Bone
Structure of Spongy Bone
Spongy bone
Trabeculae: Light weight
porous bone that’s
arrangement is aligned to
the stresses placed on
them.
part of the bone that
weakens and fractures
with osteoporosis.
Red bone marrow is found
within the trabeculae
cavities
Structure of Long Bones
Structure of Long Bone
Red Marrow
• In infants
– Found in the
medullary cavity
and all areas of
spongy bone
• In adults
– Found in the diploë
of flat bones, and
the head of the
femur and humerus
The Skeleton
• The human adult
skeleton has 206
bones.
– Axial skeleton – bones
of the skull, vertebral
column, and rib cage
– Appendicular skeleton
– bones of the upper
and lower limbs,
shoulder, and hip
Shapes of Bones
Response to Mechanical Stress
• Trabeculae form
along lines of stress
• Large, bony
projections occur
where heavy, active
muscles attach
Remodeling of Bone
• Mechanical and gravitational forces acting on the
skeleton influence bone remodeling.
– Less stimulation on bone increases osteoclasts
activity resulting in the resorption of bone matrix
which:
• Demineralization of bone
• releases the calcium and phosphate into the blood
• Increasing stress levels stimulate of osteoblasts resulting
in the deposition of bone matrix which:
– removes calcium and phosphate from the blood
– increases bone density
• Hormonal mechanism maintains calcium homeostasis in
the blood
Hormonal Mechanism
• Rising blood Ca2+ levels trigger the thyroid
to release calcitonin
• Calcitonin stimulates calcium salt deposit
in bone
• Falling blood Ca2+ levels signal the
parathyroid glands to release PTH
• PTH signals osteoclasts to degrade bone
matrix and release Ca2+ into the blood
Hormonal Mechanism
Response to Mechanical Stress
• Wolff’s law – a bone grows or remodels in
response to the forces or demands placed upon
it.
• Observations supporting Wolff’s law include
– Who will have a higher bone density.
• A 32 year old astronaut how has been in space for 6
months.
• A 55 year old active female
• An 18 year old female who has been paralyzed from the
waist down for 6 months.
Osteoporosis
• In premenopausal women the hormone Estrogen has a
protective effect on the bone by increasing osteoblastic
activity and limiting osteoclastic activity.
• When levels of estrogen drop( menopause) there is a
shift is towards osteoclastic. This weakening of the bone
leads to a condition called Osteoporosis.
• It is critical to consume most of your dietary calcium
between the years of 14-24.
• This is when you deposit most of the calcium that will
protect your bone for the rest of your life.
Osteoporosis
The spongy bone in the thoracic spine is very susceptible to osteoporosis.
Female Athlete Triad
• Disordered eating:
– Energy output is greater than energy input.
• Loss of menstrual period (Amenorrhea)
– Females who loose to much weight or have a body fat
percentage less than 12% often experience
hormonal irregularities secondary to inhibition of
hypothalamic function.
• Osteoporosis
– The hypothalamus is needed to produce estrogen
which has important for bone health.
– The lack of this hormone leads to the premature
weakening of bones.
• Stress fractures in the young is a red flag !
Table 6.2.1
Table 6.2.2
Common Types of Fractures
Table 6.2.3
Joints and Their Classification
• Arthrology = study of the joints
• Kinesiology = study of musculoskeletal
movement
• Classified by freedom of movement
– diarthrosis (freely movable)
– amphiarthrosis (slightly movable)
– synarthrosis (little or no movement)
• Classified how adjacent bones are joined
– fibrous, cartilaginous, bony or synovial
Fibrous Joint -- Sutures
• Immovable fibrous
joints
– bind skull bones together
– Considered a
synarthrosis
Fibrous Joint -- Syndesmosis
• Two bones bound
by ligament only
– interosseus
membrane
• Most movable of fibrous
joints
– Amphiarthrosis
• Interosseus membranes
unite radius to ulna and
tibia to fibula
Cartilaginous Joint -- Symphysis
• 2 bones joined by
fibrocartilage
– pubic symphysis
and intervertebral
discs
• Only slight amount
of movement is
possible
– Amphiarthrosis
General Anatomy of Synovial Joint
• Articular capsule encloses joint cavity
– continuous with periosteum
– lined by synovial membrane
• Synovial fluid = slippery fluid; feeds cartilages
• Articular cartilage = hyaline cartilage covering the joint
surfaces
• Articular discs and menisci
– jaw, wrist, sternoclavicular and knee joints
– absorbs shock, guides bone movements and distributes forces
• Tendon attaches muscle to bone
• Ligament attaches bone to bone
Synovial Joint
• Joint in which two bones are separated by a space called a joint cavity
• Most are freely movable
– diarthrosis
Tendon Sheaths and Bursae
• Bursa = saclike extension of joint capsule
– between nearby structures so slide more easily past each other
• Tendon sheaths = cylinders of connective tissue lined with
synovial membrane and wrapped around a tendon
Types of Synovial Joints
Arthritis
• Arthritis ( Arthro= Joint) itis =inflammation
• Osteoarthritis results from years of joint wear
– articular cartilage softens and degenerates
– accompanied by crackling sounds called crepitus
– bone spurs develop on exposed bone tissue
causing pain
What Joint is this? Which has
Arthritis?
Osteoarthritis
Total Hip Replacement.
Arthritis and Artificial Joints
• Rheumatoid arthritis is autoimmune attack
on joint
– antibodies attack synovial membrane,
enzymes in synovial fluid degrade the
cartilage, bones ossify
– remissions occur, steroids and aspirin control
inflammation
• Arthroplasty is replacement of diseased
joint with artificial device called prosthesis
Rheumatoid Arthritis