the skeletal system

骨骼系统包含定义，功能，类型，更新等

The Skeletal System

• Definition
  • The framework of bones and cartilage that protects our organs and allows us to move is called the skeletal system.
• Functions
  • Support
    • The skeletal system provides a framework for the body and, as such, it supports soft tissues and provides a point of attachment for many muscles.
  • Protection
    • Many internal organs are protected from injury by the skeleton.
  • Movement
    • Bones serve as levers to which muscles are attached. When the muscles contract, the bones acting as levers produce movement.
  • Mineral storage
    • Bones store several minerals that can be distributed to other parts of the body on demand. The principal stored minerals are calcium and phosphorus.
  • Blood cell production
    • Red marrow in certain bones is capable of producing blood cells, a process called hematopoiesis or hemopoiesis.
• Types of bones
  • Shape
    • long
      • Long bones have greater length than width and consist of a diaphysis and a variable number of epiphyses. Long bones are slightly curved for strength.
    • short
      • Short bones are somewhat cube-shaped and nearly equal in length and width. Their texture is spongy except at the surface, where there is a thin layer of compact bone.
    • flat
      • Flat bones are generally thin and composed of two more or less parallel plates of compact bone enclosing a layer of spongy bone. Flat bones afford considerable protection and provide extensive areas for muscle attachment.
    • irregular
      • Irregular bones have complex shapes and cannot be grouped into any of the three categories just described.
  • Additional types
    • sutural or wormian bones
      • Small bones between the joints of certain cranial bones.Number varies greatly from person to person.
    • sesamiod bones
      • Small bones in tendons where considerable pressure develops. variable in number yet at least 2.
• Bone Replacement
  • Bones are continually remodeled.
  • Remodeling is the replacement of old bone tissue by new bone tissue.
  • Bones are never metabolically at rest.
  • Normal bone growth in the young and bone replacement in the adult depend on several factors.
    • First, sufficient quantities of calcium and phosphorus.
    • Second, the individual must obtain sufficient amounts of vitamins, particularly vitamin D.
    • Third, the body must manufacture the proper amounts of the hormones responsible for the general growth of bones.
• Aging and the Skeletal System
  • I. principal effects of aging on the skeletal system
    • The loss of calcium from bones
    • A decrease in the rate of protein formation.