Head, Shoulders, Knees
and Toes
The Skeletal System
Outline
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Intro
Bone Structure
Bone Development
Bone Function
Skeletal Organization
– Axial and appendicular skeleton
• Joints
• Joint Movements
Bone is ALIVE
May appear dead…but is actually
composed of very active tissues
Functions include:
1. Muscle attachment
2. Protection and support
3. Blood cell production
4. Storage of minerals
General Bone Structure
Bones differ greatly in size
and shape, but they have a
lot in common too!
Microscopic Structure
Microscopic Structure
Microscopic Structure
Microscopic Structure
Microscopic Structure
• Osteocytes (bone cells) are located in
lacunae (spaces) that lie in concentric
circles, called lamella, around osteonic
canals
• Osteocytes pass nutrients and gases in
the matrix through canaliculi
• What’s between the cells?
– Collagen (structural protein), inorganic salts
(eg. Calcium Phosphate)
“osteogenic
potency”
“osteogenic
potency”
Section through head of femur
Compact bone
Spongy bone
Yellow Marrow
Red Marrow
Important cells of bone tissue
– Osteoblasts – cells that deposit bone tissue
around themselves; contain receptors for hormones that
regulate bone growth
– Osteocytes – former osteoblasts that have become
trapped in the bony matrix they just secreted; stop
depositing bone but still involved in cellular activities in
their local area
– Osteoclasts – cells that can degrade bone back
into its mineral components; these mineral ions are used in
the body for muscle contraction, nerve transmission,
energy transfer reactions, etc.
Bone Development and Growth
• Bones form by replacing connective
tissue in the fetus
• Some form within sheet-like layers of
connective tissue (intramembranous
bones), while others replace masses of
cartilage (endochondral bones)
Intramembranous Ossification
The flat bones of the skull form as
intramembranous bones that develop from
layers of connective tissue
Endochondral Ossification
First develop as hyaline cartilage models in
the fetus, which is later replaced with bone
Most bones in the body form
this way
Growth in LENGTH
Endochondral Ossification
Growth in diameter? Osteoblasts of the periosteum lay down new
compact bone while osteoclasts resorb bone in the medullary cavity
Homeostasis of Bone Tissue
Depending on the body’s needs, osteoclasts
tear down and osteoblasts build bone
Under Hormonal control:
1. Calcitonin – released when
supply of calcium in blood is
plentiful or high; calcium
deposited in bone (osteoblasts)
2. Parathyroid Hormone –
released when blood supply of
calcium is low; bone resorbed
into bloodstream (osteoclasts)
Bone Functions
1. Muscle attachment
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Movement of the body
•
Bones act as levers
2. Protection and support
3. Blood cell production
•
Red blood cells, white blood cells, and platelets are formed in the RED
MARROW
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RM found in spongy bone of skull, ribs, sternum, clavicles, vertebrae,
and pelvis
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Fat is stored in the YELLOW MARROW; found in most bones
4. Storage of minerals
•
Store calcium, but also magnesium, sodium, potassium, and carbonate
ions
•
Released or stored according to body needs
Skeletal
Organization
Axial
Appendicular
Major Bones of the Human Skeleton
Orange = Axial Skeleton
Yellow = Apendicular Skeleton
Axial Skeleton
Skull
1. Cranium
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Encloses and protects the brain
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Attachment point for muscles for
chewing and head movement
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Air-filled sinuses reduce its weight
2. Facial skeleton
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13 immovable facial bones and mandible
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Attachment point for muscles – facial expressions, mastication
CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display.
CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display.
CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Vertebral Column
1. Cervical vertebrae
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7 bones, comprise the neck and
support the head
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Atlas – 1st vertebra, supports head
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Axis – 2nd vertebra, has dens that
pivots within the atlas
2. Thoracic vertebrae
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12 bones, articulate with the ribs
3. Lumbar (see later slides)
4. Sacrum (see later slides)
3. Lumbar vertebrae - 5 massive bones support the majority of
the body weight
4. Sacrum – triangular structure at base of vertebral column;
composed of 5 fused vertebrae
5. Coccyx – lowermost portion; four fused vertebrae
The Thoracic Cage
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Includes the ribs, thoracic vertebrae, sternum, and costal cartilages
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Breathing, support and protection
Appendicular Skeleton
The Pectoral Girdle
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Forms incomplete ring that supports the upper limbs
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Made of two clavicles and two scapulae
The Upper Limb
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Bones of the upper limb form the framework for the arm, forearm, and
hand
CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Pelvic Girdle
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Composed of the two coxal bones and the sacrum
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Protection of lower body organs, supports weight on lower limbs
The Lower Limb
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Bones of the upper limb form the framework for the thigh, lower leg, and
foot
Joints
1. Fibrous
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Joint composed of dense connective tissue
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No movement, or only very little movement
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Ex: Sutures in the skull
2. Cartilaginous
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Joint composed of hyaline cartilage or
fibrocartilage
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Ex: Intervertebral disks, pubic symphysis
3. Synovial
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Most joints are synovial
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Articular ends covered in hyaline cartilage
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Joint capsule: connective tissue, synovial
membrane, and synovial fluid
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Ex: knee, hip, shoulder, elbow
5 Types of synovial Joints
Bone Fractures pg. 136
Bone Healing