A variety of hormones and local growth factors control bone and mineral metabolism. Growth hormone (GH) enhances bone turnover by increasing osteoblast quantity and function, either directly or indirectly through local IGF1 and IGF2 synthesis. It also promotes bone resorption via unknown methods. In contrast, thyroid hormone, calcitriol, and corticosteroids inhibit bone formation and increase bone resorption.
Growth hormone acts on bone to enhance bone growth in children and decrease risk of fracture in adults. The effect of growth hormone on bone growth is due to its action on cells called osteoblasts which make up a portion of the bone matrix. Osteoblasts are responsible for building new bone tissue. They do this by producing collagen and calcium phosphate proteins that provide structure to the growing bone mass. Osteoblasts also release chemicals that help destroy old bone so that newer, stronger bone can replace it. Osteoblasts need oxygen and nutrients delivered by blood vessels to work properly. Growth hormone stimulates new blood vessel development within the bone which allows oxygen and nutrients to reach the osteoblasts more effectively.
Osteoclasts are large multinucleated cells which dissolve bone tissue. They play an important role in removing damaged or old bone so that new bone can grow in its place. Osteoclasts develop from hematopoietic stem cells which are found in the bone marrow.
The primary tropic function of growth hormone is to increase the production of insulin-like growth factors (IGFs) from the liver, which stimulates bone development. Growth hormone also activates a variety of organs by non-tropic methods, influencing metabolism and increasing blood glucose levels. These non-tropical effects are important in treating chronic disease such as diabetes and heart failure.
The growth hormone/IGF-1 system stimulates both bone-resorbing and bone-forming cells, although bone creation is the predominate impact, resulting in increased bone mass. Thyroid hormones boost the energy generation of all cells in the body, including bone cells. A decrease in thyroid function can lead to osteoporosis by reducing the energy supply for bone cell activity.
Osteoclasts are special types of cells that break down bone. Osteoblasts are similar cells that build bone. The two types of cells work together to allow for strong bones throughout life. Osteoclasts help control calcium levels in the blood by absorbing some and re-depositing others into the bone. Osteoblasts produce the substance that osteoclasts eat so that there is no buildup of bone material.
Thyroid hormone affects most organs in the body, but its main role is within the skeletal system. The thyroid gland produces two hormones: thyroxine (T4) and triiodothyronine (T3). T4 is the predominant form in adults; T3 is primarily responsible for triggering muscle contraction and brain function. The thyroid also plays a vital role in metabolism. It controls the rate at which we burn calories - whether we need them for energy or not. Too little thyroid hormone causes your body to slow down its metabolic rate so that it doesn't have to work as hard.
Many hormones are produced by the pituitary gland, including growth hormone, which encourages the development of bone and other bodily tissues and plays a role in the body's management of nutrients and minerals. The thyroid gland produces two important hormones that play major roles in skeletal development and function: thyroxine (T4) and triiodothyronine (T3). The pancreas also releases hormones that affect bone density: insulin and glucagon. Finally, the adrenal glands produce hormones that help regulate calcium levels in the blood; when they release too much cortisol, this can have negative effects on bone health.
The growth plate is the cartilage that connects each end of a long bone (such as the femur or humerus) with muscles and other connective tissue. It allows for complete bone growth, but because it is so sensitive to growth hormones, it must be protected from excessive strain during puberty when bone growth is most active. The growth plate controls the direction of bone growth as well as the rate at which it occurs. If sufficient stress is applied to the bone toward the end of growth, the growth plate will close up completely, preventing any further lengthening of the bone. Once this has happened, even if the load on the bone remains the same, then it will grow no longer than its original length.
Growth hormone (GH), commonly known as somatotropin or human growth hormone, is a peptide hormone released by the pituitary gland's anterior lobe. It promotes the development of virtually all tissues in the body, including bone. It is also responsible for increasing the size of many organs, such as the heart, lungs, and liver.
Growth hormone acts on cells of the immune system and stimulates the production of antibodies which help fight infection. It also has many other functions, such as regulating blood sugar levels and producing certain chemicals that are necessary for tissue repair. The absence of growth hormone leads to severe dwarfism called Laron dwarfism due to absent or reduced activity of growth hormone receptors in various tissues. Hormone therapy, using exogenous growth hormone, can be an effective treatment for short stature due to other conditions such as AIDS or cancer.
Growth hormone is used for treatment of chronic kidney disease patients who need extra protein to build healthy bones and muscles. It can also be used during pregnancy to prevent fetal loss and improve physical condition of the mother. Growth hormone injections are given daily or every other day.
Growth hormone releasing hormones are found in both the brain and the gut. When the hypothalamus in the brain releases growth hormone releasing hormones, this signals the release of growth hormone from the pituitary gland.