Describe the thirst mechanism, indicating how it is triggered and terminated.

Video transcript

Welcome everyone. Here's our next question. Which of the following stimuli activates the hypothalamic thirst center. A increased osmolality of ECFB, decreased blood volume. C, decreased osmolality of ECF the increased blood volume, E both A and B or F, both C and D. So let's think about the purpose of the hypothalamic thirst center. And what would cause it to activate? And the two factors that we're being asked about is os morality of the ECF so extracellular fluid including the blood and blood volume. So, osmolality of course, is the measure of the solute concentration. And so increased osm morality means there's less water essentially. And that extracellular fluid because the solutes are more concentrated, decreased osm would mean the blood extracellular fluid is more dilute. And of course blood volume in general would increase when the amount of water in the body increases. So what is the purpose of the hypothalamic thirst center? Well, pretty straightforwardly to create a sensation of thirst, stimulating water intake. So any factor that means the body needs more water should activate this third center. So let's think this through. So factors that mean the body needs more water would be increased osmolality, the blood or extracellular fluid has become more concentrated or decreased the lead volume. So with that in mind, that leads us pretty clearly to our answers. A increased osmolality of ECF so that will activate the hypothalamic, their center and B decreased blood volume. Choice of C and D will have the opposite effect. Decreased osmolality of the ECF means blood is more dilute and the body wouldn't need any more water. And same with choice D increased blood volume. You don't need any more water. You've already got more water in the blood. So choice, F both C and D is incorrect and our answer choice will be E both A and B and just to be a little more thorough, how does this hypothalamic thirst center activate? It's activated through the means of osmo receptors, which sense changes in the plasma membrane stretch. So that is able to sense increased osmolality or decreased osmolality as the cells expand or contract and also changes in blood volume. So again, which stimuli activate the hypothalamic thirst center? Choice E both A and B. See you in the next video.