Medical
Terminology
AHS 115
Skeletal System
Functions
• Support: body structure and shape
• Protection for vital organs (brain, heart, etc.)
• Movement for attached skeletal muscles
– Tendons: attach muscle to bone
– Ligaments: attach bone to bone
• Mineral storage: calcium and phosphorus
• Blood cell formation - hematopoiesis
Types of Bone
Compact Bone
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Very dense, stress bearing
Haversian systems –basic unit
of compact bone
Lamellae: concentric cylinder
shaped calcified structure
Lacunae: small spaces
containing tissue fluid
Osteocytes: facilitate exchange
of calcium between blood and bone
Canaliculi: canals connecting the lacunae
together and to the haversian canal which
carries nutrients and wastes to and from the
osteocytes
Cancellous Bone
• Light, spongy
• Found at ends of long bones, ribs,
sternum, hips, vertebrae, cranium
• No haversian systems
• Web-like arrangement
• Highly vascular
Classification of Bones
Long bones
• Found in the extremities
• Act as levers
• Includes:
– Epiphysis
• End of long bones
• Covered with hyaline cartilage for articulation
• Filled with cancellous bone
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Diaphysis
Shaft
Covered with periosteum
Medullary canal
Compact bone
• Examples: femur, tibia, fibula, humerus,
radius, clavicle, metacarpals, phalanges
Short Bones
• Cube shaped
• Allows flexible movement
• Cancellous bone covered by compact
bone
• Examples:
– Carpals
– Tarsals
Flat Bones
• Protect vital organs and provide broad
surface area for muscle attachment
• Examples:
– Cranial bones
– Scapula
– Sternum
– Ribs
Irregular Bones
• Peculiarly shaped to provide support and
protection, yet allow flexibility
• Examples:
– Vertebrae
– Ear
– Hyoid
– Mandible
Sesamoid Bones
• Extra bones found in certain tendons
• Example:
– Patella
Composition
• Collagen: chief organic constituent (protein)
• Inorganic calcium salts (Vitamin D essential for absorption
of minerals i.e. calcium)
• Deposition favored by
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a. Estrogen, testosterone
b. Alkaline phosphatase
c. Thyrocalcitonin
d. Mechanical stress i.e. traction
• Withdrawal favored by
– a. Alkaline phosphatase
– b. Parathormone
– c. Inactivity
Composition
Cells
• Osteoblasts: bone building, bone repairing cells in the
periosteum
• Osteocytes: mature bone cells within the bone matrix
• Osteoclast: causes reabsorption of bone
Periosteum
• 1. Dense, fibrous membrane covering bone
• 2. Contains blood vessels
• 3. Essential for bone cell survival and bone formation
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Cells that Aid in Bone Formation
Osteoblast
Builds new bone
Mature bone cell
Osteocyte
Osteoclast
Eats bone
Bone Formation
• Initially collagen fibers secreted by fibroblasts
• Cartilage deposited between fibers
• Skeleton fully formed by 2nd month of fetal development (all
cartilage)
• After 8th week of fetal development ossification (mineral matter
deposited and replaces cartilage) begins
• Childhood and adolescence:
– ossification exceeds bone loss
• Early adulthood thru middle age:
– ossification equals bone loss
• After age 35:
– bone loss exceed ossification
Fetal Skeleton
275 bones
12 weeks
(6-9 inches long)
Anatomy of Long Bone
• Diaphysis
– Shaft
– Composed of compact bone
• Epiphysis
– Ends of bone composed mostly
of spongy bone
• Periosteum
– outside covering of diaphysis
• Endosteum
– Lines medullary cavity
• Arteries
• Articular cartilage
• Medullary cavity
– Cavity inside the shaft
– Contains yellow marrow (mostly fat) in adults
Bone Marrow
• Red bone marrow
– Found in vertebrae, ribs, sternum, cranium,
ends of humerus and femur
– Produces:
• Erythrocytes – red blood cells
• Plateletes - thrombocytes – clotting cells
• Some leukocytes – white blood cells
• Yellow bone marrow
– Found in medullary cavity of long bones
– Fat storage
Bone Marrow
Yellow marrow
• Medullary cavity of long bones
• Fat storage
Red marrow
• Hematopoietic tissue
• In all cancellous bone in children
• In adults: cancellous bone of vertebrae, hips, sternum,
ribs, cranial bones, proximal ends of femur and humerus
• Forms RBCs, platelets, some WBCs, and destroys old
RBCs and some foreign materials
Divisions of the
Skeletal System
Axial Skeleton
Forms the longitudinal axis of the body
Divided into three parts:
• Skull
• Vertebral Column
• Thorax
Appendicular Skeleton
• Composed of 126 bones
• Includes bones of the:
– Limbs (appendages)
– Pectoral (shoulder) girdle
– Pelvic (hip) girdle
Joints
Classification
• Synarthrotic: immovable - cranium
• Amphiarthrotic: limited movement i.e.
pubic symphysis, vertebral joints,
sacroiliac joint
• Diarthrotic: freely movable
– Gliding: bones of the wrist
– Pivot: between radius and ulna
– Ball and socket: hip
– Hinge: elbow
Immovable Joints
Synarthrosis
Slightly Movable Joint
Ampharthrosis
Freely Movable Diarthrosis
Synovial Joint Movement
Extension
Flexion
Rotation
Adduction
Abduction