 blood pressure is regulated by both short term and long term mechanisms. In the short term regulation of blood pressure, one of very important mechanisms is baroreflex. What is this baroreflex? Baroreflex is brought about by the stimulation of baroreceptors, that is the carotid sinus and aortic sinus. So, there are two baroreceptors, carotid sinus and aortic sinus and as the name suggests, carotid sinus is located in the carotid artery, actually just above the bifurcation of the common carotid artery. In the internal carotid artery, this carotid sinus is located and the aortic sinus. So, this is aortic sinus, it is located in the arc of the aorta. So, whenever there is increase in blood pressure, these baroreceptors are stimulated and what is the range in which they work? It is basically greater than 70 millimeter mercury up to 200 millimeter mercury. So, whenever mean arterial pressure is greater than 70 millimeter mercury, these baroreceptors are stimulated and actually this aortic sinus, this works at plus 30 millimeter higher range than that of the carotid sinus. So, that is the difference between the operations of carotid sinus and aortic sinus. Anyways, when these baroreceptors are stimulated, the information from these receptors goes via afferent neurons which are basically the glossopharyngeal nerve in case of carotid sinus and there is vagus nerve from the aortic sinus. So, these after neurons carry the information to medulla that is the nucleus tractus solutarius and basically cause the stimulation of nucleus tractus solutarius. So, increase in BP will lead to stimulation of the nucleus tractus solutarius. Now, this stimulation further leads to stimulation of a region, cordial ventral natural region of the medulla that is the CVLM and once this is stimulated, actually two things happen simultaneously actually here the CVLM causes stimulation of the nucleus ambiguis and dorsal motor nucleus of the vagus which is basically the center for the vagus nerve and it leads to parasympathetic system stimulation. So, parasympathetic system is stimulated and CVLM in turn inhibits the rostrum ventral region of the medulla which is responsible for the neurons which are reached to the intermediate lateral column of the styrochord that is the sympathetic system. So, you see when BP is increased what is happening the stimulation of CVLM is leading to the activation of the parasympathetic system and via the inhibition of the rVLM it is leading to the inhibition of the sympathetic system because rVLM is responsible for the sympathetic system. So, rVLM is inhibited and sympathetic system activation decreases. So, what is the end result that is very important because it is at this level that clinics operate the drugs are given at this level. So, we should know that what is the effect of activation of the sympathetic system sorry inhibition of the sympathetic system and activation of the parasympathetic system when BP increases. So, first we will see parasympathetic system it is simpler you see parasympathetic system basically supplies the SA node and the AV node and there it what it causes is it causes decrease in heart rate. So, you see here we have not written anything regarding the contractility of the heart it is may reach heart rate to which parasympathetic system is affecting and actually it is decreasing the heart rate because of which there is decrease in the cardiac output decrease heart rate will lead to decrease in cardiac output and hence decrease in systolic blood pressure. So, parasympathetic system has its effect mainly on heart and that to only on heart rate and in the conductivity of the signal also because it is affecting the conducting heart rate. But sympathetic system has varied effects and normally you see what sympathetic system supply in cardiovascular system it supplies heart. So, there is effect on the heart rate sympathetic system causes increase in the heart rate there is increase in the force of contraction then it has effect on vessels as well there is arterial it causes arterial constriction which causes in turn increase in the peripheral resistance and hence increase in the diastolic blood pressure because the main determinant of blood pressure are cardiac output. So, systolic blood pressure is determined by cardiac output and diastolic blood pressure is determined by peripheral resistance. So, you see here the effect of sympathetic system is on both there is increase in the peripheral resistance when there is activation of sympathetic system and increase in the diastolic blood pressure plus by its effect on heart it is causing increase in the cardiac output by increasing both heart rate and increasing the force of contraction. Also you see I have written one more it causes Veno constriction that is the constriction of the veins because of which there is increase in the venous return and hence further increasing the force of contraction by the panstallic mechanism. So, this is the effect of sympathetic and parasympathetic system on cardiovascular system it is very very important. So, now simply you see that whenever blood pressure increases because of the stimulation of the parasympathetic system and inhibition of the sympathetic system what happens ultimately the peripheral resistance is going to decrease because sympathetic system is not going to have its effect and hence there will be decrease in the diastolic blood pressure then the cardiac output is also going to decrease and hence there will be decrease in the systolic blood pressure and both if they see together there will be decrease in the mean arterial blood pressure and what will happen if for there is decrease in blood pressure decrease in blood pressure then the opposite events will happen because baroreceptors will be not that much stimulated what is known as unloading of the baroreceptors then this afferent activity will be reduced stimulation of NTS will be less and hence this inhibition of RVLM will not be that much. So, sympathetic system will become active and parasympathetic system will be less active and we will see opposite effects. So, that was about baroreffects. Thanks for watching the video if you like it do press the like button share the video with others and don't forget to subscribe to the channel physiology open. Thank you.