Unit 2: Skeletal System

Study Notes

Provides structural support by attaching to other organs.
Stores minerals, mainly 98% of calcium ions and phosphate ions.
Produces blood cells in bone marrow, including erythrocytes, leukocytes, and platelets.
Facilitates movement through leverage; muscles exert force on bones.
Offers protection for vital organs:
- Rib cage protects the heart.
- Skull safeguards the brain.
- Vertebrae protect the spinal cord.
- Pelvic bones safeguard reproductive organs.

Osteocyte: Mature bone cell found in lacunae; regulates calcium ion release.
Structure: Consists of a protein-mineral matrix; channels called canaliculi connect osteocytes to bone capillaries.
Osteoblast: Immature bone cell located on inner and outer surfaces; responsible for osteogenesis by secreting osteoid, building new bone.
Osteoclast: Multinucleated cell that performs osteolysis; secretes acid to dissolve bone, releasing calcium and phosphate into the bloodstream.

Compact (Dense) Bone:
- Strong bone that withstands stress along its long axis.
- Composed of osteons (Haversian system), including a central canal, canaliculi, and lamellae.
Spongy (Trabecular or Cancellous) Bone:
- Lightweight structure formed by a network of plates called trabeculae.
- Contains red bone marrow; located in epiphyses and surrounds the medullary cavity.

Epiphysis: Ends of long bones housing red bone marrow.
Diaphysis: Shaft or middle part of long bones; contains yellow marrow in the medullary cavity.
Metaphysis: Growth zone between the epiphysis and diaphysis.
Periosteum: Outer surface of bone; protects, isolates, and serves as an attachment for nervous tissue and blood vessels.
Endosteum: Inner surface lining the medullary cavity; contains osteoprogenitor cells for active repair and growth.

Ossification Types:
- Intramembranous Ossification:
  - Rapid development of bones like clavicle, mandible, and skull.
  - Occurs directly from embryonic membrane; involves differentiation of mesenchymal cells into osteoblasts.
- Endochondral Ossification:
  - Slower process, occurring in limbs, vertebrae, and hips, lasting years.
  - Bone develops from a hyaline cartilage model, with chondrocytes enlarging near the diaphysis.

Provides structural support by attaching to other organs.
Stores minerals, mainly 98% of calcium ions and phosphate ions.
Produces blood cells in bone marrow, including erythrocytes, leukocytes, and platelets.
Facilitates movement through leverage; muscles exert force on bones.
Offers protection for vital organs:
- Rib cage protects the heart.
- Skull safeguards the brain.
- Vertebrae protect the spinal cord.
- Pelvic bones safeguard reproductive organs.

Osteocyte: Mature bone cell found in lacunae; regulates calcium ion release.
Structure: Consists of a protein-mineral matrix; channels called canaliculi connect osteocytes to bone capillaries.
Osteoblast: Immature bone cell located on inner and outer surfaces; responsible for osteogenesis by secreting osteoid, building new bone.
Osteoclast: Multinucleated cell that performs osteolysis; secretes acid to dissolve bone, releasing calcium and phosphate into the bloodstream.

Compact (Dense) Bone:
- Strong bone that withstands stress along its long axis.
- Composed of osteons (Haversian system), including a central canal, canaliculi, and lamellae.
Spongy (Trabecular or Cancellous) Bone:
- Lightweight structure formed by a network of plates called trabeculae.
- Contains red bone marrow; located in epiphyses and surrounds the medullary cavity.

Epiphysis: Ends of long bones housing red bone marrow.
Diaphysis: Shaft or middle part of long bones; contains yellow marrow in the medullary cavity.
Metaphysis: Growth zone between the epiphysis and diaphysis.
Periosteum: Outer surface of bone; protects, isolates, and serves as an attachment for nervous tissue and blood vessels.
Endosteum: Inner surface lining the medullary cavity; contains osteoprogenitor cells for active repair and growth.

Ossification Types:
- Intramembranous Ossification:
  - Rapid development of bones like clavicle, mandible, and skull.
  - Occurs directly from embryonic membrane; involves differentiation of mesenchymal cells into osteoblasts.
- Endochondral Ossification:
  - Slower process, occurring in limbs, vertebrae, and hips, lasting years.
  - Bone develops from a hyaline cartilage model, with chondrocytes enlarging near the diaphysis.