Maintaining blood pressure is critical to maintaining proper bodily functions. The kidney filters blood only when there is sufficient blood pressure to push blood through the glomerulus where it is filtered. Filtration of the blood occurs under pressure.
Osmoregulation is the process of regulating the water content and solutes of the blood and ultimately has a direct correlation to blood pressure. As the amount of water in the body varies so does blood pressure. The lower the water content of the blood, due to dehydration, the lower the blood pressure, whereas high water content causes high blood pressure.
Below is an animation that simply outlines the role of the hormones renin and vasopressin in maintaining blood volume and blood pressure..
Vasopressin is a hormone produced by nerve cells in the hypothalamus, called neurosecretory cells and stored at the ends of axons, which extend into the pituitary gland. Neurosecretory cells are activated by special receptors in the hypothalamus, called osmoreceptors, that monitor the blood concentration of certain solutes. Osmoreceptors will fire off when blood water content falls and solute concentrations rise due to excessive water loss or insufficient intake of water.
Excitation of the osmoreceptors triggers the release of vasopressin from the pituitary gland into the blood. The hormone than travels to the kidney where it causes increased reabsorption of water from the collecting and distal tubules. Without vasopressin in the blood the collecting tubules are almost impervious to water. Vasopressin also acts on the muscles, lining the walls of blood vessels, to constrict them.
Osmoreceptors trigger sensations of thirst, as do hormones related to water regulation as discussed below, which increases the uptake of water through drinking
Renin is released in response to low blood pressure. It is an enzyme the clips a small section from an inactive substance in the blood known as angiotensinogen and converts it to the active form known as angiotensin I. Pressure sensitive receptors in the kidney trigger the release of renin by the kidney. Renin flows through the blood where it stimulates the production of a chemical called angiotensin II. Click to see on overview of the renin -angiotensin-aldosterone pathway. Angiotensin II is a powerful vasoconstrictor and also promotes the secretion of aldosterone from the adrenal gland. Aldosterone is a hormone that promotes the active reabsorption of sodium in the distal tubule of the nephron which in turn causes the reabsorption of water.
The main trigger for the secretion of vasopressin is an increase in blood concentration where as the main trigger for the release of renin from the kidney is low blood pressure.
1) ADH is produced in the
2) A person with an elevated level of aldosterone in their blood would most likely be suffering from
3) When blood levels of ADH are elevated the
4) Which of the following hormones promotes sodium reabsorption through the walls of the distal tubule?
5) A drug is taken by a patient that inhibits sodium reabsorption in the distal tubule of the nephron. Which comment is likely to be true?
6) A person suffering from high blood pressure is most likely to be given
7) A patient's urine was analysed and found to contain unusually low levels of sodium. What is the likely cause of this?
8) Which one of the following is incorrect about ADH?
9) Renin is produced by the
10) The kidney is involved in regulating blood pressure by
11) If the level of aldosterone was decrease in the blood
12) A patient suffering from dehydration would have elevated blood levels of
13) Which one of the following is secreted by the kidney and is a hormone that acts as an enzyme?
14) The target cells of angiotensin II are found in the
and the
