How the Kidneys Control Blood Pressure
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How the Kidneys Control Blood Pressure

What are the kidneys? How the kidneys control blood pressure? the kidneys regulate the amount salt in the body and produce a hormone called renin.The level of renin depends upon the level of salt, which in turn is controlled by the action of the adrenal hormone, aldosterone, on the tubules.

How The Kidneys Control Blood Pressure

By Mr Ghaz, January 16, 2011

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The Kidneys

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We have two kidneys, lying on the back wall of the abdomen. From the inner side of each kidney a tube called the ureter runs down the back of the abdominal cavity and enters the bladder. The tube leading from the bladder is called the urethra. In women, its opening is in front of the vagina, and in men at the tip of the penis.

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The kidneys contain thousands of tiny filtering units, or nephrons. Each nephron can be divided into two important parts - the filtering part, or glomerulus, and the tubule, where water and essential nutrients are extracted from the blood.

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The glomerulus consists of a knot of tiny blood capillaries which have very thin walls. Water and the waste dissolved within it can pass freely across these walls into the collecting system of tubules on the other side. So large is this network of blood capillaries that it may contain - at any one moment - almost a quarter of the circulating blood throughout the whole body, and filters about 130 ml (4.6 fl oz) from the blood each minute.

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The holes in the capillary wall form a biological sieve, and are so small that molecules beyond a certain size cannot pass. When the kidneys become infected, the glomeruli inflame and the sieve fails to be so selective, allowing larger molecules to escape into the urine. One of the smallest protein molecules to find its way into the urine is albumin. This is why your doctor tests your urine for protein to see whether the kidneys are functioning properly.

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Kidney Tubules

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The tubules run between the glomeruli to a collecting system which ultimately drains into the bladder. Each glomerulus is surrounded by a Bowman’s capsule, which is the beginning of its tubule. It is here that almost all the filtered water and salt is reabsorbed, so that the urine is concentrated. To reabsorb all this water, the body has a highly sophisticated system in which a hormone secreted into the blood from the pituitary gland in the brain changes the permeability of the tubule (its ability to reabsorb water).

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While the hormone is in the blood, the tubule allows a great deal of water to be reabsorbed. When the hormone is ‘turned off, however, the tubule become less permeable to water and more is lost in the urine-this is called diuresis and the hormone concerned is known as antidiuretic hormone (ADH). In certain conditions, such as diabetes insipidus (not to be confused with ‘sugar diabetes’ or diabetes mellitus), this hormone may be totally lacking. When this happens the patient cannot conserve water, and so loses large quantities in the urine, which have to be replaced by drinking.

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Another hormone, aldosterone, secreted by the adrenal glands just above the kidneys, is responsible for exchanging sodium salt potassium salt-so helping to control blood pressure and the balance of salt in the body. Parathormone, another hormone made by four small glands buried behind the thyroid gland, regulates the reabsorption of the essential mineral calcium, from which our bones and teeth are made.

High Blood Pressure

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The kidneys regulate the amount of salt in the body and produce a hormone called renin. The level of renin depends upon the level of salt, which in turn is controlled by the action of the adrenal hormone, aldosterone, on the tubules. Renin activates another hormone, angiotensin. This has two effects: firstly, it constricts the arterioles and raises the blood pressure; secondly, it causes the adrenal gland to release aldosterone, making the kidneys retain salt and causing the blood pressure to rise.

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How the kidneys control blood pressure

Above: Kidneys secrete renin which produces angiotensin when pressure is low; this constricts the arteries and raises pressure. At the same time, adrenal glands produce aldosterone; this causes salt retention which also raises pressure and stops renin production.

 

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The kidney's filtering system

Above: A kidney and its components. The renal artery carries blood to the kidney, split into arcuate arteries and finally into afferent arterioles. Each of these ends in a glomerulus (inset). Blood is filtered through the glomerular wall and enters the renal tubule. The basic components of blood (plasma, protein, red and white corpuscles) are too large to cross the semi-permeable membrane of the glomerulus, but most of the other materials (e.g. water, salts and hormones) can pass across it. The next stage is called selective reabsorpton. Materials essential to the body are reabsorbed into the efferent arterioles, across the tubule wall. Once the blood has been thoroughly filtered, it leaves the kidney in the renal vein; waste products are excreted in the urine.

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Comments (7)

This article, like all its predecessors are physiology textbook quality. I would recommend them as a starting point for anyone studying human physiology. Liked. Tweeted. Buzzed Up. Voted up.

I agree with Jerry my friend, thank you.

This is a very thorough and professional article - thanks!

Through and educational article. This is very detail.

Great article

Wonderfully researched and written. Since I have hypertension, I found this relevant and helpful.

Very Informative!

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