Human Skeletal System

Study Notes

Structure of Bone

Articular cartilage provides a smooth gliding surface for tendons and ligaments to move.
Epiphyseal line is a remnant of the epiphyseal plate where the bone grows in length.
Epiphysis is the rounded end of the long bone, formed by a secondary ossification center.
Diaphysis is the shaft of the long bone.
Medullary cavity contains yellow marrow in adults and red marrow in infants.
Periosteum is a tough connective tissue sheath that surrounds the bone and anchors tendons and ligaments.
Compact bone is made up of tightly packed osteons (cylindrical structures containing Haversian canals).
Cancellous (spongy) bone is made up of a network of thin, plate-like trabeculae that form a honeycomb-like structure.

Histology of Bone (Osseous Tissue)

Osteocytes are mature bone cells that maintain the bone matrix.
Osteoblasts are bone-forming cells that secrete the organic matrix of bone.
Osteogenic cells are stem cells that develop into osteoblasts.
Lacunae are small spaces in the bone matrix that house the osteocytes.
Canalliculi are tiny channels that connect the lacunae and allow nutrients and waste products to pass through.
Haversian canals are central canals in the osteons that contain blood vessels and nerves.
Volkmann's canals are channels that connect the Haversian canals and allow blood vessels and nerves to pass through the bone.

Factors Affecting Bone Growth

Minerals: calcium and phosphorus are needed for bone growth.
Vitamins:
- Vitamin A stimulates osteoblast activity.
- Vitamin C is required for collagen synthesis.
- Vitamin D is required for calcium absorption from foods.
- Vitamin K and B12 are needed for bone protein synthesis.
Hormones:
- Growth hormone (GH) is produced by the pituitary gland.
- Insulin-like growth factors are produced by the liver and bone.
- Sex hormones: estrogen and testosterone.

Calcium Homeostasis

Parathyroid hormone (PTH) is secreted by parathyroid glands and increases blood calcium levels by:
- Increasing bone resorption (release of calcium from bone into the blood).
- Decreasing calcium excretion by the kidneys.
Calcitonin (CT) is secreted by parafollicular cells of the thyroid gland and decreases blood calcium levels by:
- Decreasing bone resorption.
- Increasing calcium excretion by the kidneys.

Divisions of the Skeletal System

The Axial skeleton consists of bones arranged along the longitudinal axis of the body and consists of 80 bones.
The Appendicular skeleton consists of 126 bones in the upper and lower extremities (limbs) and pectoral (shoulder) and pelvic (hip) girdles.

Types of Bones

Long bones: mostly compact bone tissue in their diaphyses, but have considerable amounts of spongy bone tissue in their epiphyses.
Short bones: cube-shaped, consists of spongy bone tissue except at the surface, which has a thin layer of compact bone.
Flat bones: generally thin, composed of two parallel plates of compact bone tissue enclosing a layer of spongy bone tissue, provide extensive areas for muscle attachment.
Irregular bones: complex shapes.
Sesamoid bones: develop in certain tendons, not always completely ossified, protect tendons from excessive wear and tear.

Description

This quiz covers the structure of bones, including articular cartilage, epiphyseal line, epiphysis, diaphysis, medullary cavity, and periosteum. Learn about the different components of the skeletal system.