Skeletal System
Chapter 7
Objectives
1. Identify the different structures and fuctions
of the Skeletal system.
2. Label a long bone and internal structures of
bone.
3. Explain bone development and growth.
4. Apply knowledge of homeostatic
mechanisms to explain the regulation of
blood calcium levels.
Introduction
• Bones are very active tissues
• Each bone is made up of several types of
tissues and is an organ
Skeletal System
Components
• Bone
• Tendons- connect
bones to muscle
• Ligaments- connect
bones to bones
Functions
• Muscle attachment
• Protection
• Contain blood-producing
cells
• Storage of inorganic salts
• Passageway for nerves &
blood vessels
Types of Bone Tissue
• Compact bone: homogeneous
• Spongy bone: small needle-like pieces of
bone; many open spaces
Classification of Bones
Long Bones
• Characteristics: Typically
longer than they are wide,
have a shaft with heads at
both ends
• Structure: contain mostly
compact bone
• Examples:
– Humerus, Femur, Ulna, Radius,
Clavicle, Phalanges
Short Bones
• Characteristics: Generally
cube-shaped
• Structure: contain mostly
spongy bone
• Examples:
– Wrist bones
– Foot bones
Flat Bones
• Characteristics: thin,
flattened, and usually
curved
• Structure: two thin
layers of compact bone
surrounding a layer of
spongy bone
• Example:
– Scapula
– Sternum
Irregular Bones
• Characteristics: irregular
shape, do not fit into
other bone
classification categories
• Example:
– Pelvis
– vertebra
Bone Classification
• Sesmoid
Long Bone Anatomy
Bone Structure
• Bones differ in size and shape, yet are similar
in several ways
• Parts of a long bone
– Epiphysis – expanded ends of bones that form
joints with adjacent bones
– Articular cartilage (hyaline cartilage) – covers the
epiphysis
– Diaphysis – the shaft of the bone
– Periosteum – a tough layer of vascular connective
tissue that covers the bone and is continuous with
ligaments and tendons
Parts of a long bone
• A bone’s shape makes possible its function
• Bony processes or grooves indicate places of
attachment for muscles
• Compact bone makes up the wall of the
diaphysis
• The epiphyses are filled with spongy bone to
reduce the weight of the skeleton
• The diaphysis contains a hollow medullary
cavity that is filled with marrow
Microscopic Structure
• Compact (Cortical)
Bone: osteocytes and
layers of ECM are
concentrically clustered
around a Haversian
Canal (Osteon).
– Haversian Canals contain
blood vessels and nerve
fibers which nourish the
bone cells.
Microscopic structure
• Osteocytes – bone cells that are located
within lacunae that lie in concentric circles
around osteonic canals
• Intercellular material consists of collagen and
inorganic salts
• In compact bone, osteocytes and intercellular
material are organized into osteons that are
cemented together.
Microscopic structure
• Osteonic canals contain blood vessels and
nerve fibers and extend longitudinally through
bone.
• Osteonic canals are interconnected by
transverse perforation canals.
• Unlike compact bone, the osteocytes and
intercellular material in spongy bone are not
arranged around osteonic canals.
Microscopic structure
Microscopic Structure
Bone Growth and
Development
• Osteoclasts – break down cartilage and bone
• Osteoblasts – bone-building cells
• Osteocytes – bone cells
Bone Development
• Intramembranous
Bones:
– Originate between
sheetlike layers of
connective tissue.
• Endochondral Bones:
– Begin as masses of
cartilage that bone tissue
replaces.
Bone Development
• Intramembranous Ossification:
1. Connective tissue appears at the sites of future
bones.
2. Connective tissue cells differentiate into osteoblasts.
3. Osteoblasts deposit bony material around
themselves and form spongy bone.
4. Membranous tissue cells give rise to the periosteum.
5. Osteoblasts inside the periosteum form compact
bone.
Intramembranous Bones
Bone Development
• Endochondral Ossification (Condensed Version):
1.
2.
3.
4.
5.
6.
7.
Cartilage breaks down in the center of the diaphysis. (primary
ossification center)
Periosteum forms around the developing dipahysis from connective
tissue.
Blood vessels and osteoblasts from periosteum invade the cartilage and
form spongy bone.
Epiphysis remain cartilaginous and later secondary ossification centers
appear and form spongy bone.
Epiphyseal plate undergoes mitosis and produces new cells which
enlarge , while calcium salts accumulate in the extracellular matrix, they
calcify, and the cartilage cells die.
Osteoclasts secrete acid that dissolves part of the calcified matrix and
osteoblasts deposit new bone tissue in place of the calcified cartilage.
Bone continues to grow at the epiphyseal plate until adulthood.
Endochondral
Ossification
Objectives
• To explain the different functions of bone in
detail.
• To apply your knowledge of homeostasis and
negative feedback loops to explain hormonal
regulation of bone calcium resorption and
deposition.
Bone Functions
• Support and Protection
– Bones give shape to the head, thorax, and limbs
– The pelvis and lower limbs provide support for the
body
– Bones of the skull protect the brain, ears and eyes
• Movement
– Muscles attach to bones
– Push and pull bones for movement
Bone Functions
• Blood cell Formation
– Two kinds of marrow occupy the medullary cavities of
bone
• Red marrow – formation of red blood cells, white blood cells
and platelets
• Yellow marrow – stores fat
• Storage of Inorganic Salts
– Bone stores inorganic mineral salts in the form of
calcium phosphate
– Calcium in bone is a reservoir for body calcium
• When blood levels of calcium are low, osteoclasts release
calcium from bone.
• Calcium is stored in bone under the influence of calcitonin
when blood levels of calcium are high.
Hematopoiesis
• Hematopoeiesis=Red blood cell formation
• RBC’s form in the liver, spleen, and bone marrow
– Red Marrow:
• Found in infants as well as in spongy bone of skull, ribs,
sternum, clavicles, vertebrae, and hip bones of adults
• Produces red blood cells (erythrocytes), white blood cells
(leukocytes), and platelets.
– Yellow Marrow:
• In adults
• Stores fat
• *doesn’t produce RBC’s
Inorganic Salt Storage
• ECM of bone is rich in calcium
• Calcium is required for muscle contraction,
nerve impulse conduction, blood clotting, and
other physiological processes.
• Our bodies must maintain a sufficient bloodcalcium level using a homeostatic mechanism.
Calcium Regulation
Low calcium levels
• Causes Parathyroid Hormone (PTH) to be
released
– PTH causes stored calcium in bone to be released
– PTH causes calcium reabsorption in the kidney
(not excreted in urine)
– PTH causes the synthesis of Vit. D. which increases
Ca+ absorption in the small intestines.
High calcium levels
• Causes the release of calcitonin from the
thyroid gland
– Calcitonin Inhibits Ca2+ absorption by the
intestines
– Inhibits osteoclast activity in bones
– Inhibits renal tubular cell reabsorption of Ca2+
allowing it to be excreted in the urine
Hypo vs. Hypercalcemia
• Hypocalcemia: can cause muscle stiffness and
seizures
• Hypercalcemia: too much calcium, causes
kidney stones or even kidney failure, could
cause heart problems
Bone Fractures
• Definition: break in a bone
• Types of bone fractures
– Closed (simple) fracture – break that does not
penetrate the skin
– Open (compound) fracture – broken bone
penetrates through the skin
• Treatment: reduction and immobilization
Common types of
Fractures
Repair of Bone fractures
• Steps in repair of bone fractures
1. Hematoma: blood-filled swelling is formed
2. Fibrocartilage callus: break is connected by
fibrocartilage
3. Bony Callus: fibrocartilage replaced by
spongy bone
4. Bone remodeling: permanent healing
Repair of Bone fractures
Hematoma
Internal
callus
(fibrous
tissue and
cartilage)
External
callus
Bony
callus of
spongy
bone
New
blood
vessels
Healed
fracture
Spongy
bone
trabecula
Hematoma
formation
Fibrocartilage
callus formation
Bony callus
formation
Bone remodeling
Curve of the Spine
• The spine has a normal curvature
• Primary curvatures: curvatures of the thoracic
and sacral regions
– Present from birth
• Secondary curvatures: spinal curvatures of the
cervical and lumbar regions
– Develop after birth
Skeletal changes
throughout life
• Osteoporosis
– Bone-thinning disease afflicting
• 50% of women over age 65
• 20% of men over age 70
– Disease makes bones fragile and bones can easily
fracture
– Vertebral collapse results in kyphosis (also known
as dowager’s hump)
– Estrogen aids in health and normal density of a
female skeleton
Skeletal changes
throughout life
Skeletal changes
throughout life
Objectives
• To Identify the major bones of the skull.
• To label the major features of the bones of the
skull.
Skeletal Organization
• Axial Skeleton
– Consists of the skull, hyoid bone, vertebral column
and thorax (ribs and sternum)
• Appendicular Skeleton
– Consists of the pectoral girdle (scapula and
clavicle), upper limbs, pelvic girdle (coxal bones)
and lower limbs
Skeletal Organization
The Skull!!
• Structure: made up of two sets of bones
– Cranium
– Facial bones
• Bones are joined by sutures
Human Skull, Lateral
View
Human Skull, Superior
View
Human Skull, Inferior
View
Human Skull, Anterior
View
Paranasal Sinuses
• Structure: hollow portions of bones
surrounding the nasal cavity
• Functions:
– Lighten the skull
– Amplify voice
Paranasal Sinuses
The Vertebral Column
• Structure: 24 single vertebral bones separated
by intervertebral discs
– Cervical vertebrae: 7 in neck
– Thoracic vertebrae: 12 in chest region
– Lumbar vertebrae: 5 in lower back
– Sacrum and coccyx: 9 fused vertebrae in gluteal
region
The Vertebral Column
Superior view of
vertebrae
Atlas and Axis
• Structure: most superior vertebrae
– Atlas: C1
– Axis: C2
• Function: form joint connecting skull and
spine; allow for movement of head
Regional characteristics
of vertebrae
Regional characteristics
of vertebrae
Regional characteristics
of vertebrae
Regional characteristics
of vertebrae
Sacrum and coccyx
The Bony Thorax
• Structure: made of three parts
1. Sternum
2. Ribs
• True ribs (pairs 1-7)
• False ribs (pairs 8-12)
• Floating ribs (pairs 11-12)
3. Thoracic vertebrae
• Function: forms a cage to protect major
organs
The Bony Thorax
Male and Female Pelvis
• Differences in male and female pelvis aid in
childbirth
– Female inlet is larger and more cicular
– Female pelvis as a whole is shallower and the bones
are lighter and thinner
– Female ilia flare more laterally
– Female sacrum is shorter and less curved
– Female ischial spines are shorter and further apart
– Female pubic arch is more founded because the angle
of the pubic arch is greater
Joints
• The functional junctions (articulations)
between bones
• Enable a wide variety of body movements
• Can be classified according to the degree of
movement possible:
– Immovable
– Slightly movable
– Freely movable
Joints
• Can also be classified according to the type of
tissue that binds them together:
– Fibrous
– Cartilaginous
– Synovial
Fibrous Joints
• Held together by dense
connective tissue
• Immovable or only
slightly moveable
– Examples:
• Sutures of the skull
(immovable)
• Joint between the
distal tibia and fibula
(slightly movable)
Cartilaginous Joints
• Hyaline cartilage or
discs of fibrocartilage
unite the bones in
cartilaginous joints
– Example: intervertebral
disks
Synovial Joints
• Makes up most joints of the skeletal
• More complex than fibrous or cartilaginous
joints
• Articular ends of bone in a synovial joint are
covered with hyaline cartilage
• Articulating surfaces within the joint are
lubricated with synovial fluid
• Are classified (and named) based on the
shapes of their parts and the movements they
permit
Ball and Socket Joint
• Consists of a bone with
a globular or egg-shaped
head articulating with
the cup shaped cavity of
another bone
• Permits a very wide
range of motion
• Examples:
– Hip and Shoulder Joints
Condyloid Joint
• Consists of an ovoid
condyle fitting into an
elliptical cavity
• Permits a wide variety
of motions
• Example:
– Joint between a
metacarpal and a
phalange
Gliding Joints
• Occur where
articulating surfaces are
nearly flat or slightly
curved
• Permits a “back and
forth” motion
• Example:
– Joints of the wrist and
ankle
Hinge Joint
• Occurs where a convex
surface fits into a
concave surface
• Movement is in one
plane only
• Example:
– Elbow and phalange
joints
Pivot Joint
• Occurs where a
cylindrical surface
rotates within a ring of
bone and fibrous tissue
• Example:
– Joint between the
proximal ends of the
radius and ulna
Saddle Joint
• Forms where
articulating surfaces
have both concave and
convex areas
• Permits a wide range of
movements
• Example:
– The metacarpal of the
thumb
Inflammatory Disorders
of the Joints
• Bursitis: inflammation
of bursa (synovial
membrane); water on
the knee
Inflammatory Disorders
of the Joints
• Sprain
– Ligaments or tendons reinforcing joint are
damaged by excessive stretching or are torn away
from bone
– Slow to heal because of poor blood supply
• Dislocation
– When a bone is forced out of normal position in
the joint cavity
Inflammatory Disorders
of the Joints
• Arthritis
– Most widespread, crippling disease in the U.S.
– 1 in 7 Americans suffer with it
– Initial symptoms: Pain, stiffness, and swelling of
the joint
– Acute and Chronic forms of Arthritis
Inflammatory Disorders
of the Joints
• Acute Arthritis
– Result from bacterial invasion
– Treated with antibiotic
– Synovial membrane thickens and fluid production
decreases, leading to increased friction and pain
Inflammatory Disorders
of the Joints
• Chronic Arthritis
– Osteoarthritis
•
•
•
•
Most common form
Degenerative condition, usually affects the aged
Wear and tear affects
Can cause bone spurs which restrict joint movement
– Rheumatoid arthritis
• Occurs between 40-50 years of, but can occur at any age
• Affects more women than men
• Many joints affected at the same time and usually in symmetrical
manner (left elbow then right elbow)
• Marked by remission (goes away) and flare ups (comes back)
• Autoimmune disease – body attacks its own tissues
– Gouty arthritis