[Music] hi everyone my name is andre welcome back to med school eu and in today's lecture we are going to discuss the homeostasis and the control of water osmoregulation is the proper term for the control of water within our our body and so let's first discuss the organs that will be involved so there's going to be three primary body parts that will be involved with osmoregulation one of them the most important guidance of homeostasis is the hypothalamus and just beneath that the hypothalamus will have a pituitary gland so the hypothalamus is basically going to be this mastermind and the pituitary gland is going to be the part that releases hormones that will stimulate osmo regulation and of course the stimulation will be occurring in the kidneys because the kidneys primarily control how much water is going to be excreted and so the monitor system will of course reside within the kidneys now let's zoom in a little bit of what's going on uh within our hypothalamus and the pituitary gland structure so the water potential is monitored by the hypothalamus which is located right here on this diagram because the hypothalamus is going to contain osmoreceptors and so these osmoreceptors are going to detect whether or not the water levels are at homeostasis so if the water levels are low then the hypothalamus is going to react by triggering signals that go down to the pituitary gland now this side the right side of the pituitary gland right side on the diagram which will be depending on the view that you're looking at it will have the posterior pituitary gland and of course on the other side we'll have the anterior pituitary gland so now let's discuss how all of this will be regulated so if we have a decrease in water within our blood the hypothalamus osmoreceptors will be able to sense it because of course the blood travels everywhere it of course touches the hypothalamus and these osmoreceptors are going to be sensitive to see how much what is the concentration of water within the blood plasma and if the concentration of water is decreased to the levels that it has measured then it's going to send the signal through some of these neurons that will send the signal to the posterior pituitary gland not the anterior the anterior pituitary gland has nothing to do with water regulation it's all about the posterior pituitary gland so it will send signals to posterior pituitary gland which will release a hormone called adh which is which is a peptide hormone and which then will this hormone will travel all over the body because it will be in the blood but it will have a special effect on the kidneys which we're going to discuss next so let's summarize this if we have a low water potential or low concentration of water within our blood that is going to be sensed by the osmo receptors which will then stimulate the posterior pituitary gland which will then release the adh peptide hormone and it's made up of i believe nine amino acids so it's a quite a small peptide but it does have a tremendous effect on the kidneys in terms of reabsorbing more water and we're going to discuss this in a little bit more detail in the next slide but before we get there i wanted to discuss what happens if we have a higher a water potential than normal because sometimes we can drink more water than needed and so we're going to be over saturated with water in the blood plasma now what occurs is the osmoreceptors are simply going to stop firing and they're going to stop stimulating the posterior pituitary gland so the hypothalamus will just stop its signals that are supposed to be going down these neurons they will all stop they will not be happening and therefore the posterior pituitary gland will not be releasing adh hormone and then over time in about 15 to 20 minutes the adh hormone will then the concentration of adh hormone in the blood will decrease and therefore it will cycle through several times and then the kidneys will not have will not be affected by the adh hormone which will then make the kidney less reabsorb its water much less which will then create a more of a dilute solution of urine however when it's the opposite when the water saturation is low within the blood then these neurons will continuously be firing for the posterior to the pituitary gland to increase the concentration of adh within the blood and they will continue to circulate until we have enough water within our system now other things happen as well so this is not the only regulatory mechanism physiologically yes however there are other mechanisms that regulate our water consumption so for example hypothalamus will be sending other signals to different parts of the brain that will make us feel thirsty that will make us feel like we need to we need to get some water we haven't had water dry mouth so all of these symptoms will be happening because of the action of the hypothalamus which is kind of the brain of all of the operations involving homeostasis so let's discuss the action of adh it will be released from the posterior pituitary gland that will go into the blood circulate all over the body and once it does reach the kidneys it's going to have a special effect on the collecting duct and more specifically it will have an effect on the permeability of water of the walls of the collecting duct so normally with low adh levels in the blood the the collecting duct will be impermeable to water it will not be reabsorbing water and the water will just go out as you can see with this fatter arrow so this is going to be impermeable whereas if we're looking at the other side with high adh now the the collecting ducts walls will now be more permeable to water it will increase its permeability and the water as you can see here will be reabsorbed back in to the medulla or the tissue fluid and so it's going to easily flow into the medulla without anything any active transport it will be done passively because there's a huge concentration of n a plus and other solutes remember the medulla especially the the further you go the further down you go in the medulla you're going to have a higher concentration of sodium higher concentration of chloride and all the other ions and because you have a higher concentration there naturally water will flow towards where the solutes are and so this is exactly what's happening with passive transport from high concentration of water inside the filtrate to the low concentration of water within the tissue fluid of the medulla and so because of the the action of adh we're going to have more water absorbed and we're going to have a more concentrated urea or more concentrated urine whereas without the adh or low levels of dh we're going to have dilute urine and and in a nutshell this is the action of adh that is released from the posterior pituitary gland due to the impulse of the hypothalamus now let's discuss how the adh actually does make the collecting duct more permeable how does this really work and this is not something that is required for the imats however i believe it is a very fascinating topic to discuss because it's pretty cool how these things are done so the first thing that occurs is that of course the adh must reach the collecting duct within the blood within the capillaries that run by the collecting duct and the adh is going to bind two receptors in the cell surface membrane of the cells lining the collecting ducts so over here it's going to bind to its receptors and that is going to cross into the collecting duct and now because of this binding it activates a series of reactions which just end up with the production of an active phosphorylase enzyme so the reactions occur right here at step two and this phosphorylase enzyme causes vesicles that are surrounded by membrane containing water permeable channels in other words aquaporins so we've talked about aquaporins before and what they're going to do is is these channels are already they're already made they're just sitting there idle waiting for the adh to interact with them and so once this enzymatic reaction occurs it is going to release the vesicle and cause the vesicle to fuse with the other side of the membrane and now because it fuses as you can see we got aquaporin aquaporin aquaporin a lot more aquaporins on the surface so then this specialized water channel will make the water just seep through and the water will then go out in to the blood instead of going out as urine so just to conclude our video with this little graph here to highlight the significance of adh in its regulation of water and keeping the homeostasis because what we have occurring is that with adh there's going to be a huge spike in the reabsorption of water in the loop of henle but additionally what's most important is there's going to be a huge spike in the reabsorption of water in the collecting duct and this reabsorption of water will create a more concentrated fluid so your urine will be more concentrated rather than being more dilute which is in the case of not having much adh inside the blood so this concludes our video for today in the next lecture we're going to take a look at the homeostasis and control of glucose concentration [Music] you