Final answer:
Vitamin D3, or calciferol, is produced in the body through synthesis. When the skin is exposed to sunlight, cholecalciferol is produced from cholesterol in the skin. This compound is converted to calcitriol in the kidneys, which is the active form of vitamin D.
Step-by-step explanation:
Vitamin D3, also known as calciferol, is produced in the human body through a process called synthesis. When the skin is exposed to UV radiation from sunlight, a compound known as cholecalciferol is produced from cholesterol in the skin. This compound is then converted to calcidiol in the liver and finally to the active chemical form of vitamin D, called calcitriol, in the kidneys. The production of calcitriol is regulated by various factors, including the individual's vitamin D status and the body's calcium and phosphate levels.