chapter 26 lecture 5 is renal physiology production of urine hormonal regulation and the production of dilute and concentrated urine there are three major hormone systems that help to regulate fluid sodium chloride and potassium balance and they are the renin angiotensin aldosterone system the antidiuretic hormone which is also called vasopressin and the atrial naturetic peptide i want to talk first about the raa system the liver synthesizes angiotensinogen remember if it ends in gen or starts with pro it's inactive so this is in our blood all the time waiting to be activated when the cells of the maculidensa detect that there is high a high volume of water and solutes in the urine it causes renin which is a hormone to be released from the kidney renin is an enzyme and what renin does is it cleaves off this first part of angiotensinogen the gray part now we have angiotensin one this is still inactive so it needs another enzyme to cut the blue part off and that enzyme is ace ace is always around two in our bloodstream and so ace can only work if renin has already cleaved off part of the angiotensinogen so ace or angiotensin converting enzyme is what it stands for cleaves off that bit the blue bit and now we have active and active hormone so it takes two steps to cut it cut off the inactive parts to make this active renin and ace both have to work once renin once eighth cuts off this last part now we have angiotensin ii and that's the active form angiotensin ii is going to act on the um act first as a vasoconstrictor so remember back here where we had the glomerular filtration rate was was too high and we're losing too many things in the urine this is a vasoconstrictor and it constricts the afferent arteriole to make its diameter smaller so that not as much the filtration rate slows down and not as much is going to be lost in the urine it also activates the production of aldosterone which is a steroid hormone that's made in the adrenal cortex aldosterone is the major regulator of sodium in our body and aldosterone acts to increase sodium reabsorption so when more sodium is reabsorbed into the bloodstream then water follows and you have an increased blood volume and increased blood pressure there are drugs called ace inhibitors you may have heard of them and they act on this enzyme to prevent it from working if this doesn't work we don't produce the active form of angiotensin angiotensin ii if we don't produce angiotensin ii we don't produce aldosterone and blood pressure and blood volume stays low so the three sets of hormones antidiuretic hormone renin angiotensin ii aldosterone and atrial natural peptide are involved in regulating it now adh is released from the posterior pituitary when the hypothalamus detects a high osmolarity so that means a high concentration of solutes of which means you're dehydrated and this is the major regulator of water this is the major regulator the aldosterone is a major regulator of sodium and potassium so adh then acts on the principal cells in the collecting duct and it causes them its action is to cause them to put more aquaporin two channels into their membranes and that's going to increase water reabsorption in the collecting duct remember in the proximal convoluted tubule we had aquaporin one channels here these are aquaporin twos so that the final act of what adh does it increases blood volume and increases blood pressure the renin-angiotensin-aldosterone system renin's released when there's too much water and solutes in the filtrate renin and ace activate angiotensin too that decreases the filtration rate angiotensin ii activates aldosterone and aldosterone increases sodium reabsorption which increases water reabsorption so this acts also acts to increase blood volume and blood pressure the only one that doesn't is atrial natric peptide this is released from the a tree of the heart in response to high blood volume or blood pressure it acts on the mesengeal cells of the glomerulus to increase the filtration rate it causes them to relax when they relax the surface area is greater the the ability to filter is stronger so it's going to increase the filtration rate it also acts to inhibit anti-diuretic and hormone and aldosterone and it decreases sodium reabsorption and that it also decreases water reabsorption because if sodium doesn't leave water doesn't follow so the end result of atrial natural peptide is to decrease blood volume and decrease blood pressure it's really important