Are there other substances that affect bone development What about hormones

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Bone development is a complicated process and requires many different substances and hormones, even a specific gene. Scientists have discovered that there is a gene that is required for the formation of the body's skeleton. If this gene is not present in the embryo stage of development, bones cannot form correctly.

Vitamin K

Associated with blood clotting, it helps in the production of osteocalcin, another protein that is part of the process of bone remodeling; this vitamin also helps to prevent bone from being broken down and calcium from being excreted in urine.

Osteocalcin

A type of protein that is part of the bone remodeling process.

Folate

A vitamin known to prevent spinal defects in developing fetuses; also important in reducing homocys-teine levels, which have been associated with an increase in osteoporosis-related fractures.

Magnesium

An alkaline earth element that contributes to the hardening of the bone in the process of remodeling.

Phosphorus

A salt or ester of phosphoric acid that contributes to the hardening of the bone in the process of remodeling.

Calcitonin

A hormone naturally secreted by the thyroid gland that binds with osteoclasts, making them less active and allows the osteoblasts to form more bone.

Parathyroid hormone (PTH)

Secreted by the parathyroid glands (located by the thyroid gland), PTH assists in the regulation of calcium by promoting the absorption of calcium from the intestine and reducing loss of calcium from the urine by the kidney; excessive amounts can lead to bone loss.

Cortisol

Secreted by the adrenal glands (located by the kidneys), is needed in small amounts for bone growth. Large amounts of cortisol can interfere with bone growth. The synthetic form of cortisol, or steroids, used in the treatment of some diseases, can cause bone loss.

Growth hormone

Secreted by the pituitary gland (located in the brain), is important to both bone formation and bone resorption (destruction of the bone), but is most important in its role of increasing the speed of bone formation during puberty.

In addition to this gene, the following other substances and hormones are needed for normal bone formation:

• Calcitonin, a hormone naturally secreted by the thyroid gland (located in the neck), binds with the osteoclasts making them less active, which allows the osteoblasts to form more bone.

• Parathyroid hormone (PTH), secreted by the parathyroid glands (located by the thyroid gland), assists in the regulation of calcium by promoting the absorption of calcium from the intestine and reducing loss of calcium from the urine by the kidney. Interestingly, while PTH is necessary and important at normal levels, excessive amounts can lead to bone loss.

• Cortisol, secreted by the adrenal glands (located by the kidneys), is needed in small amounts for bone growth. Large amounts of cortisol can interfere with bone growth. The synthetic form of cortisol, or steroids, used in the treatment of some diseases (see Question 16), can cause bone loss.

Growth hormone, secreted by the pituitary gland (located in the brain), is important to both bone formation and bone resorption (destruction of the bone) but is most important in its role of increasing the speed of bone formation during puberty.

Thyroid hormones, secreted by the thyroid gland, regulate the body's metabolism and help to control the rate at which bone remodeling occurs. However, too much thyroid hormone (hyperthyroidism) can cause excessive bone destruction.

Insulin, a hormone secreted by the pancreas to help the body use carbohydrates and sugar, and leptin, a newly identified hormone that is found in fat cells, both have effects on bone growth.

• Sex hormones, such as estrogen and testosterone, are important for bone growth and for maintaining bone mass. The estrogen produced in adolescents at the end of puberty is important for closing the bone growth plates, which prevents further growth in height. Estrogen and testosterone, both produced in men and women, stimulate bone formation. Testosterone also aids in muscle growth, which increases the mechanical stress on bones, which in turn, encourages more bone formation by the osteoblasts.

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