Download Basic Structure of the Human Body

Human Anatomy
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
Total: 80 bones
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