Synthesized by the combined action of the skin.kidneys, and liver, __ is important to the deposition of bone. estrogen calcitonin testosterone calcitriol growth hormone

## Step 1<br />The problem is asking us to identify the substance that is synthesized by the combined action of the skin, kidneys, and liver, and is important to the deposition of bone. The options provided are estrogen, calcitonin, testosterone, calcitriol, and growth hormone.<br /><br />## Step 2<br />Estrogen and testosterone are hormones that play a role in bone health, but they are not synthesized by the skin, kidneys, and liver. They are primarily produced in the ovaries and testes, respectively.<br /><br />## Step 3<br />Calcitonin is a hormone produced by the thyroid gland, not the skin, kidneys, or liver. It helps to regulate calcium levels in the blood, but it does not directly contribute to bone deposition.<br /><br />## Step 4<br />Growth hormone is produced by the pituitary gland and stimulates overall growth, including bone growth. However, it is not synthesized by the skin, kidneys, and liver.<br /><br />## Step 5<br />Calcitriol is the active form of vitamin D, which is synthesized by the skin, kidneys, and liver. It plays a crucial role in calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations, which are essential for normal bone mineralization.