The Heart as an Endocrine Gland
We are all familiar with the primary function of the heart in the human body, which is to pump blood to every cell in the body. However, the heart also provides another function in the body as an endocrine organ. It releases hormones in the bloodstream just like the other endocrine organs such as the adrenals, thyroid, parathyroids, ovaries, testes, thymus, hypothalamus, pancreas, pineal and the pituitary gland located deep within our brain. Even the stomach and our intestines are also part of this system because they also release hormones into the bloodstream.
The Endocrine System
The endocrine system controls relatively slow processes in the body by releasing hormones, chemical messengers, directly into the bloodstream from glands. They control such processes as growth and development of body structures, metabolism, mood changes, and sexual characteristics. Even though these hormones are released directly into the bloodstream they are specific only to the targeted organs or tissues.
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For example, insulin is released from the pancreas into the bloodstream to control the level of glucose in the blood. The insulin is only targeted to control specific receptors on the surface of cells. The insulin cause these receptors to activate certain molecules to transfer glucose from outside the cells into the interior of cells to generate cellular energy; thus maintaining the level of glucose in the blood within normal range. If there is a malfunction in this process, e.g. not enough insulin, glucose level will increase in the blood until the only way the body can get rid of it is by the kidneys with excessive loss of water. Consequently, being thirsty and experiencing frequent urination are two of the main symptoms of type one diabetes.
What Are Natriuretic Peptides
The two hormones are called natriuretic peptides because they behave as natriuretics, but at the same time they also behave as diuretics. Basically what it means is that these hormones increase the excretion of sodium in the urine (natriuresis) and increase the output of water (diuresis). They exert their effect on blood pressure in the same manner as the diuretic pills or water pills as people prefer to call them and other anti-hypertension pills prescribed by your doctor.
In essence, the body has it own mechanism for controlling blood volume and blood pressure located right in the heart as well as other parts of the cardiovascular system. This action is triggered when the muscles of the heart senses excessive blood pressure and higher than normal blood volume, especially in the atrial or upper chambers of the heart, but unfortunately this mechanism does not always bring blood pressure down into an acceptance range on its own. That is where prescription drugs come into play to help the body decreases its blood pressure.
The Endocrine Function of the Heart
The heart is not only considered to be a part of the circulatory or cardiovascular system as most people were taught in biology class but it is also a part of the endocrine system as well. An article published in Scientific American in 1986, The Heart As An Endocrine Gland, by Marc Cantin and Jacques Genest is an account of their discovery of two hormones secreted by the heart that have dramatic effects on the behavior of the cardiovascular system. Researchers have long suspected as far back as 1956 that the heart has other functions in the body besides pumping blood.
These hormones are released by the heart from granules located mostly in the muscular walls of the atrial ( upper chambers) and in lesser amount in the ventricles (lower chambers) of the mammalian heart. These granules, small clusters of particles, are similar to granules found in the cells of other endocrine glands. The hormones are A-type natriuretic peptides or atrial natriuretic peptides (ANP), sometimes called atrial natriuretic factor (ANF), and B-type natriuretic peptides or brain natriuretic peptides (BNP). The latter is also found in the brain hence the name since it was first discovered there and as well as in the central nervous system. But it is predominantly found in the ventricles of the heart. There is also a third hormone in this class called the C-type natriuretic peptides which is found mainly in the walls of the blood vessels.
How Do Natriuretic Peptides Work?
Natriuretic peptides work by targeting the receptors found in the smooth muscles of the arteries, and veins, and the receptors located in several regions in the kidneys. These hormones trigger the receptors in the wall of arteries and veins causing the muscles to relax with a resultant dilation of the arteries and veins. Consequently, this dilation causes a decrease in blood pressure because these hormones are vasodilators. Also, these hormones are potent inhibitor of another chemical in our bloodstream called renin-angiotensin. This chemical has the opposite effect of these hormones on the muscles in the wall of the arteries. It causes the arteries to constrict thus increasing blood pressure and it causes a decrease in the production of renin, chemicals secreted and released in the kidney, to control blood volume and blood pressure.
The specific region of the kidneys where natriuretic peptides target is the glomerulus located in the nephron region of the kidney where filtering of our blood first takes place. Researchers have determine that these hormones from the heart muscles suppresses the action of renin which are secreted within the kidney outside of the nephron region. This action causes an increase in the glomerular filtration rate (GFR) to filter out more sodium from the bloodstream (natriuresis) thus increasing urine output (diuresis).
Finally, natriuretic peptides affect the function of other endocrine glands such as the small pituitary gland at the base of our brain. It causes a decrease in the production of a hormone released from the pituitary gland called an anti-diuretic hormone (ADH). In other words when this happens there is an increase of urine output from the kidneys because the natriuretic peptides inhibit the production of ADH.
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Information gathered from research on the physiological effects of natriuretic peptides on several processes related to the functions of the cardiovascular system, shows a strong indication for further research on these hormones. The data clearly shows potential uses of these hormones as another and better way to manage hypertension, blood volume, cardiac related diseases, and kidney diseases. For example, measuring the level of brain natriuretic peptides in the blood is one way of determining the level of heart failure in a patient; the higher this hormone level is the greater the severity of the heart failure. The test determines how healthy your heart is pumping.
© 2012 Melvin Porter