Physiology Topics
Functions of the skeletal system include body support, protection of internal organs, assistance in movement, storage of calcium and phosphate, blood cell formation and lipid storage in adults.
Bones are organs made of connective tissue, vascularized and innervated. They originate as fibrous connective tissue membranes formed by condensed embryonic connective tissue (mesenchyme), including four types of cells: fibroblasts, chondroblasts, osteoblasts and hemocytoblasts. Bone starts forming at about six weeks of gestation with the formation of fibrous and hyaline membranes.
The periosteum is a tough sheet of dense irregular connective tissue that surrounds the bone surface were it is not covered by cartilage. It contains bone forming cells that allow the bone to grow thicker. The endosteum is a similar membrane that lines the medullary cavity.
Osteogenic cells are derived from mesenchyme, and can undergo cell division and differentiation into osteoblasts. Osteoblasts are bone-building cells that secrete collagen and other components of the bone matrix, and initiate calcification. Osteocytes are derived from osteoblasts that have become entrapped in the matrix secretions, and their function is to maintain bone by exchanging nutrients and waste with blood. Osteoclasts are derived from immune cells and concentrate in the endosteum, their function being to destroy bone matrix as part of the normal development, maintenance and repair of bone.
Continue to "Bone Formation" or take a quiz: [Q1] [Q2].
Need more practice? Answer the review questions below.
1- List the functions of the skeletal system.
2- What are the basic characteristics of bone?
3- How do bone originates in the embryo?
4- What is the periosteum?
5- What is the endosteum?
6- What are Osteogenic cells?
7- What are osteoblasts?
8- What are osteocytes?
9- What are osteoclasts?