For example, growth hormone is secreted from the anterior pituitary; is it also synthesized there?
Vitamin D is synthesized in multiple sites though classically it is said that final hydroxylation occurs in the kidneys.
Vitamin D is a hormone the kidneys produce that controls blood calcium concentration and impacts the immune system. It is also known as calcitriol, ergocalciferol, calcidiol and cholecalciferol. Of those, calcidiol is the form doctors most commonly focus on when measuring vitamin D levels in the blood.
The body makes vitamin D in a chemical reaction that occurs when sunlight hits the skin. This reaction produces cholecalciferol, and the liver converts it to calcidiol. The kidneys then convert the substance to calcitriol, which is the active form of the hormone in the body.