• Support- framework that supports body and cradles its soft organs
• Protection- for delicate organs, heart, lungs, brain
• Movement- bones act as levers for muscles
• Mineral storage- calcium & phosphate
• Blood cell formation- hematopoiesis
The Skeletal System
Parts of the skeletal system·Bones (skeleton)·Joints·Cartilages·Ligaments (bone to bone)(tendon=bone tomuscle)
Divided into two divisions·Axial skeleton·Appendicular skeleton – limbs and girdle
Bones of the Human Body
The skeleton of an adult has 206 bones· Two basic types of bone tissue· Compact bone
· Homogeneous· Spongy bone
· Small needle-like pieces of bone· Many open spaces
275 bones12 weeks (6-9 inches long)
• Long Bones- metacarples, metatarsals, phalanges, humerus, ulna, radius, tibia, fibula
• Short Bones- carpals, tarsals
• Flat Bones- rib, scapula, skull, sternum
• Irregular Bones- vertebrae, some facial bones
• Sesamoid- patella
Classification of Bones
Long bones· Typically longer than wide· Have a shaft with heads at both ends· Contain mostly compact bone
•Examples: Femur, humerus
Classification of Bones
Short bones·Generally cube-shape·Contain mostly spongy bone
·Examples: Carpals, tarsals
Classification of Bones
Flat bones·Thin and flattened·Usually curved·Thin layers of compact bone around a layer of spongy bone
·Examples: Skull, ribs, sternum
Classification of Bones
Irregular bones·Irregular shape·Do not fit into other bone classification categories
·Example: Vertebrae and hip
Sesamoid bones
• Embedded within tendon where its passes over a joint
• Free surface covered with cartilage; the other part embedded within tendon; no periosteum
• Patella (within the tendon of m. quadriceps femoris)
Additional bones
• Mainly in the skull: ossa interfrontalis, coronalis, sagittalis, lambdoidalis, etc.
• Known also as ossa suturarum
Distalepiphysis
Proximal epiphysis
diaphysis
yellow marrow
epiphyseal line
periosteum
compact bone
spongy bone
Endosteum
hyaline cartilage
Sharpey’s fibers
Structures of a Long Bone
Periosteum·Outside covering ofthe diaphysis·Fibrous connectivetissue membrane
Sharpey’s fibers·Secure periosteum tounderlying bone
Arteries·Supply bone cellswith nutrients
Structures of a Long Bone
Articular cartilage· Covers the external surface of the epiphyses· Made of hyaline cartilage· Decreases friction at joint surfaces
Structures of a Long Bone
Medullary cavity·Cavity of the shaft·Contains yellow marrow (mostly fat) in adults·Contains red marrow(for blood cell formation) in infants
Components of Bone
• Cortical bone – Structural • Trabecular bone – Structural • Bone Marrow – Structural and RBC• Vessels – Nutritional and Innervation
Cortical Bone
• Osteon (Harvesian Canals)– Cylindrical tubes made of concentric lamellae– Central opening
• Blood vessels• Neural tissue• Lymphatic
• Periosteum– Fibrous tissue covering– Enables attachment of muscles and tendons
Cortical bone
• Lamellae– Concentric layers of
mineralized bone– Crisscross pattern at
90– Torsion and bending
strength• Osteoclasts
– Bone resorbing• Osteoblasts
– Bone forming
Trabecular Bone
• Cancellous or Spongy• Lattice structure• Pores filled with marrow• 20% Bone Mass• 80% Bone Surface
Trabecular Structure
• Plate and rod structure– Low loads - rod– Higher loads - plate
• Light yet spongy• Oriented in direction
of loads– “Wolff’s Law”
Bone Marrow
Consists of stroma, myeloid tissue, fat, lympatic tissuesRed marrow
Involved with the production of RBCConsists of haemopoetic tissueHighly vascularized
Yellow marrowNot as vascularized as red marrowLarge amount of fat cellsPercentage increases wrt red marrow with age (up
to20yrs)
Mechanisms of bone formation
• Membranous ossification how: direct differentiation of cells within mesenchymal condensations into bone forming cells (osteoblasts) flat bones of the skull, clavicle, periosteum
• Endrochondral ossification how: replacement of a cartilagenous template by bone endochondral bones:axial and appendicular skeleton, some bones in the skull
Membranous bone formation
Endochondral Ossification
cartilagecalcified cartilage
bone
epiphyseal plate
epiphyseal line
Endochondral Ossification
2o ossification center
Fetus: 1st 2 months
AdultChildhood
Just before birth
Types of bone cellsinvolved in bone homeostasis
How do cells look?
Origin of bone cells
hematoma callus bony callusbone remodeling
Diseases of the Skeletal System:
Osteoporosis- bone reabsorption outpaces bone deposit; bones become lighter and fracture easier
Factors: • age, gender (more in women)• estrogen and testosterone decrease• insufficient exercise (or too much)• diet poor in Ca++ and protein• abnormal vitamin D receptors• smoking
Osteoporosis
29 40 84 92
Rickets- vitamin D deficiency
Osteomalacia- soft bones, inadequate mineralization in bones, lack of vitamin D
Pagets Disease- spotty weakening in the bones, excessive and abnormal bone remodeling
Rheumatoid arthritis- autoimmune reaction
Diseases of the Skeletal System
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