The kidneys themselves also serve as an endocrine gland. What hormones are produced by the kidney and what function do they serve? What other human body system do these hormones regulate?

The kidneys secrete a variety of hormones, including erythropoietin, calcitriol, and renin. Erythropoietin is released in response to hypoxia (low levels of oxygen at tissue level) in the renal circulation. It stimulates erythropoiesis (production of red blood cells) in the bone marrow. Calcitriol, the activated form of vitamin D, promotes intestinal absorption of calcium and the renal reabsorption of phosphate. Renin is an enzyme which regulates angiotensin and aldosterone levels.

Explanation:

Erythropoietin is a hormone that is produced predominantly by specialised cells in the kidney. Once it is made, it acts on red blood cells to protect them against destruction. At the same time it stimulates stem cells of the bone marrow to increase the production of red blood cells.

Calcitriol is the active form of vitamin D, normally made in the kidney. A manufactured form is used to treat kidney disease with low blood calcium, hyperparathyroidism due to kidney disease, low blood calcium due to hypoparathyroidism, osteoporosis, osteomalacia, and familial hypophosphatemia.

Renin also known as an angiotensinogenase, is an aspartic protease protein and enzyme secreted by the kidneys that participates in the body's renin–angiotensin–aldosterone system (RAAS)—also known as the renin–angiotensin–aldosterone axis—that mediates the volume of extracellular fluid (blood plasma, lymph and interstitial fluid) and arterial vasoconstriction. Thus, it regulates the body's mean arterial blood pressure.

The kidney secretes erythropoietin, calcitriol and renin hormone.

Explanation:

Hormones are chemical substances secreted in one part of the body ( endocrine gland) and secreted to other parts of the body where they exact specific function to body metabolism. Hormones serve as messengers, controlling and coordinating activities throughout the body.

The kidney secreted the following hormones:

- erythropoietin hormone

- calcitriol hormone

- renin hormone

Erythropoietin hormone helps to maintain good and healthy oxygen level in the tissue, it promotes the production of mature red blood cells by the bone marrow.

Calcitriol hormone is the active form of vitamin D, it helps to regulate serum calcium level by raising the level of calcium absorption in the gatrointestinal tract.

Renin hormone helps to increase the level of blood pressure which leads to a restitution of perfusion pressure in the kidney.

The hormones produced in the kidney also help to regulate functions such as stress response, blood pressure and heart rate.