Learning that the kidneys are involved in blood pressure regulation is a concept that is new to many who are diagnosed with high blood pressure. Most are familiar with the kidney’s function of producing urine from waste products in the blood, but not a lot is know by the general public about the important function of the kidneys in regulating blood pressure. Blood pressure regulation is an important function of the kidney and understanding this process will help patients learn the importance of taking their blood pressure medications.
In the average human, there are two kidneys that are located on each side of the lower back. These two bean shaped organs provide a filtration system for the blood circulation of the body. As fresh blood is brought into the kidney, substances are absorbed into the kidney. Anything that the body needs will then be reabsorbed into the blood stream, while waste products will be sent eventually to the bladder in the form of urine.
How the Kidneys Regulate Blood Pressure
The kidneys play a role in maintaining and regulating blood pressure by controlling how much urine is passed from the body. Blood volume, or how much total plasma and blood cells are in the body, has a direct influence on the kidneys to regulate urine production. In combination with hormones that are produced from several body organs and the kidneys, a feed-back mechanism results in changes in the amount of water and salts that are reabsorbed by the kidneys.
The hormones involved in blood pressure regulation are Renin, Angiotensin, Aldosterone, and Antidiuretic Hormone. Each has a specific job in regulating blood pressure and is produced in different areas of the body. These hormones react differently depending on the drugs that are prescribed for lowering high blood pressure. Your doctor will choose a medication taking into consideration your other health issues.
How Hormones Act on the Kidney to Raise Blood Pressure
Renin is produced by the kidneys as a result of decreases in blood pressure that are noted by special cells in the kidneys as the blood is traveling through them. Renin then stimulates a hormone from the liver called Angiotensin. Angiotensin then travels to the lungs where it becomes Angiotensin II. Angiotensin II goes on to act on the adrenal glands to release Aldosterone, which constricts blood vessels and increases reabsorbtion of salt and water back into the body by the kidneys. This mechanism can increase blood pressure quite sufficiently and is altered by prescription medications used to decrease high blood pressure.
An easy way to remember this complex system of increasing blood pressure is to memorize the following bullet points:
- Decreased blood pressure = Increased kidney production of Renin· Renin acts on Angiotensin I from the liver.
- Angiotensin I becomes Angiotensin II in the lungs.
- Angiotensin II causes constricted blood vessels throughout the body and increased salt and water reabsorbtion in the kidneys.
A final hormone used in blood pressure regulation is Antidiuretic Hormone or ADH. ADH is produced by the hypothalamus in the brain. The main function of this hormone is to increase salt and water reabsorbtion by the kidneys much like aldosterone.
How the Kidneys Lower Blood Pressure
You may be wondering how this process reverses if the blood pressure is too high. When the pressure is high, the kidneys will work harder to increase the amount of water that is made into urine, thereby decreasing blood volume. However, if the arteries are coated with atherosclerotic plaques, even the kidneys will not be able to keep up and lower the blood pressure sufficiently. In these cases, there is a greater risk of heart attack.
If you have been newly diagnosed with high blood pressure, your doctor may prescribe medications that will act on the Renin-Angiotensin mechanism, Aldosterone production, or Antidiuretic Hormone. By understanding the great role that these chemicals have on your blood pressure, you can get a better grasp on why you need to take your medications and how they affect your body. If you have any questions or concerns about your health condition, contact a licensed healthcare provider.
Works Cited:
Abrams, Peter. Physiology, All you need to know about how your body works. Bright Star Publishing, 2007.
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