The Skeletal System
Bones and Skeletal Tissues
Skeletal System
• Bone, cartilage, tendons, ligaments
• Bones are organs, consisting of several
tissues
– Bone, cartilage, blood forming tissue, blood,
nerves, fat, epithelium
• Dynamic
• Strong and light
• Approx. 206 bones in an adult, 270 for
infant
Functions of the Skeletal System
• Support
– Framework to support body and soft organs
• Protect
– Rib cage protects lungs, heart, etc.
• Body Movement
– Lever system
• Blood Cell Formation
– Hematopoiesis switches from infancy to adult
• Mineral Storage
– Calcium and Phosphorous
Support – feet and legs support pelvis and body
trunk, pelvic bowls supports pelvic organs, ligaments
lash bones together, cartilage (firm flexible support)
Protect – cranium protects eyes, hearing organs,
brain
Blood cell formation – Hematopoiesis occurs in liver
and spleen in infants. After infancy to spongy bone
tissue in hip bones, ribs, breast bone, back bones,
skull, ends of long bones.
Storage – 50% of bone is mineral tricalcium
phosphate called hydroxyapatite. Deposition and
reabsorbtion is regulated by hormones. The calcium
and phosphorous is important in muscle contraction
and nerve activity. Maintenance of minerals in body.
Composition of Bone Matrix
• Collagenous fibers
– 25% of bone is collagen
– If hydroxyapatite were disolved the bone
would be rubbery…..keeps bone from being
brittle.
• Calcium salts
– Tricalcium phosphate (hydroxyapatite) and
some calcium carbonate.
– These salts crystallize and become hardened
Bone Cells
• Osteoblast
– A bone-forming cell
• Osteocyte
– Mature bone cell, shaped like a
spider web with a body and
long processes, that occupies a
lacuna in the bone matrix
• Osteoclasts
– Large cell that reabsorbs or
breaks down the bone matrix
Types of Bone
• Dense outer layer…Compact Bone….long
bones
– Dense and solid, however microscopic exam reveals
a structure with many passageways for blood vessels,
lymph vessels, and nerves
– Provides protection, support and helps long bones
resist the stress of weight placed on them
• Internal to this is Spongy Bone…short, flat,
irregular bones
– The open network is filled with red or yellow marrow
– Thin plates are trabeculae
Spongy Bone
Classification of Bones
• Long
– Longer than wide
– Mostly compact bone
• Short
– Roughly cubed shaped
– Primarily spongy bone
– Sesamoid bone,
connects with a tendon
• Flat
– Thin, flattened, somewhat
curved
• Irregular
– Various shapes
Red marrow - Forms blood cells and platelets. Found in spongy bone.
Yellow marrow – Primarily consists of adipose cells. Found in shaft of long bones.
Membranes of Bone
• Periosteum
– A white membrane of connective tissue
covers the entire outer surface of each bone
except where bones articulate.
– It is tough, vascular, fibrous membrane, and
continuous with tendon.
• Endosteum
– A thin inner membrane of connective tissue.
– Covers trabeculae of spongy bone and central
canals of osteons.