The human skeletal system is well-known as a hard structure that gives the human its shape. The bones allow one to stand upright and give support for movements such as walking and running. The bones are not just collections of calcium and other minerals sitting within the body, however. They are also involved in important physiological processes.
Support, Protection, and Movement
The skeleton protects the inner organs of the body and gives it structural support. The vertebral column supports the upright position of the human, and it also protects the spinal cord. The ribs protect the lungs and heart, and the pelvis protects the pelvic organs, including the female reproductive organs and intestines.
The bones are necessary for movement and are used as levers. While muscles contract and relax to facilitate movement, this could not happen if they were not attached to the bones.
Blood Cell Formation
Bone marrow can be found in different types of bone tissue. Red marrow is responsible for the creation of erythrocytes (red blood cells), leukocytes (white blood cells), and platelets. The presence of hemoglobin gives the marrow its red appearance. As one ages, the red marrow is replaced by yellow marrow, which is comprised mostly of fat and does not produce blood cells.
Blood Calcium Level - Calcium Hydroxyapatite
Calcium is used for several processes within the body, including muscle contraction, metabolism, nerve impulses, and the formation of blood clots. There are specialized bone cells that are involved with maintaining normal blood calcium levels so these processes can be carried out.
Bone cells are called osteocytes. Within a bone, inorganic salts (salts that do not contain carbon) and collagen surround the osteocytes. This is called the intercellular matrix. Cylindrical sections of matrix and osteocytes are called osteons, and each osteon has a central canal containing blood vessels and nerves.
The salts of the matrix are mostly hydroxyapatite, which is a form of calcium phosphate. Osteoclasts are a type of bone cell that breaks down hydroxyapatite to release calcium into the blood. Osteoblasts build intercellular matrix from the excess calcium in the blood. These bone cells are stimulated by different hormones.
When blood calcium levels are too low to sustain the physiological processes of the body, parathyroid hormone is released and osteoclasts are stimulated to break down the hydroxyapatite. When blood calcium levels are high, the thyroid releases calcitonin. Calcitonin stimulates osteoblasts to store calcium in the bone matrix.
While the bones are necessary for movement and structural support, they greatly affect other physiological processes as well. Red marrow is the site of blood cell formation. Blood calcium levels dictate the calcium content of bones. Specialized osteocytes release calcium into the blood and build bone matrix from excess blood calcium.
Reference
Shier, D., Butler, J., Lewis, Ricki. Hole's Human Anatomy & Physiology. New York: McGraw-Hill, 2002.
Diane Ursu - Diane Ursu joined Suite101 as a contributing writer in August 2009 and became a Feature Writer in January 2010. She is a freelance writer ...
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