The intestines contain endocrine cells that produce hormones that are responsible in aiding digestion, while the endocrine role of the kidneys includes the release of hormones specific to Na+ and water retention in the body; another kidney hormone (EPO) is involved in red blood cell formation.
Thymosin, involved in the development of the immune response, is a hormone produced by the thymus.
Adipose tissue is responsible for the production of leptin, which is generated in response to food intake.
a strong vasodilatory, peptide hormone, secreted by the cardiac muscle cells
Organs with Secondary Endocrine Functions
There are several organs whose primary functions are non-endocrine, but that also possess endocrine functions. These include the heart, kidneys, intestines, thymus, and adipose tissue.
The heart possesses endocrine cells in the walls of the atria that are specialized cardiac muscle cells. These cells release the hormone atrial natriuretic peptide (ANP) in response to increased blood volume . High blood volume causes the cells to be stretched, resulting in hormone release. ANP acts on the kidneys to reduce the reabsorption of sodium (Na+), causing Na+ and water to be excreted in the urine. ANP also reduces the amounts of renin released by the kidneys and aldosterone released by the adrenal cortex, further preventing the retention of water. In this way, ANP causes a reduction in blood volume and blood pressure, while reducing the concentration of Na+ in the blood.
The gastrointestinal tract produces several hormones that aid in digestion. The endocrine cells are located in the mucus of the GI tract throughout the stomach and small intestine. Some of the hormones produced include gastrin, secretin, and cholecystokinin, which are secreted in the presence of food. They also act on other organs, such as the pancreas, gallbladder, and liver, by triggering the release of gastric juices, which help to break down and digest food in the GI tract.
While the adrenal glands associated with the kidneys are major endocrine glands, the kidneys themselves also possess endocrine function. Renin, released in response to decreased blood volume or pressure, is part of the renin-angiotensin-aldosterone system that leads to the release of aldosterone. Aldosterone then causes the retention of Na+ and water, raising blood volume. The kidneys also release calcitriol, which aids in the absorption of calcium (Ca2+) and phosphateions. Erythropoietin (EPO), a protein hormone produced by the kidney, triggers the formation of red blood cells in the bone marrow. EPO is released in response to low oxygen levels. Because red blood cells are oxygen carriers, increased production results in greater oxygen delivery throughout the body. EPO has been used by athletes to improve performance as greater oxygen delivery to muscle cells allows for greater endurance. Because red blood cells increase the viscosity of blood, artificially high levels of EPO can cause severe health risks.
The thymus is found behind the sternum. It is most prominent in infants, becoming smaller in size through adulthood. The thymus produces hormones referred to as thymosins, which contribute to the development of the immune response .
Adipose tissue is a connective tissue found throughout the body. It produces the hormone leptin in response to food intake. Leptin increases the activity of anorexigenicneurons and decreases that of orexigenic neurons, producing a feeling of satiety after eating, thus affecting appetite and reducing the urge for further eating. Leptin is also associated with reproduction. It must be present for GnRH and gonadotropin synthesis to occur. Extremely thin females may enter puberty late; however, if adipose levels increase, more leptin will be produced, improving fertility.