Baroreceptor reflex

Another reflex we have in our body that is almost similar to the diving reflex is the baroreceptor reflex. If you lay down and you want to stand up real quick, all the blood goes down due to gravity. The mean arterial blood pressure goes down. This is seen by the baroreceptors in the carotis and the aorta. These give a signal to the medulla and this control center makes sure that the sympathetic output goes up and the parasympathetic output goes down. In the arterioles and the veins there is vasoconstriction, by the ventricles the force of contraction goes up and the SA node makes sure the heart rate goes up. Because of the vasoconstriction the peripheral resistance goes up and because of the actions of the venctricles and the SA node the cardiac output goes up. These two have an effect on the blood pressure and in this case the blood pressure goes up. This is a negative feedback loop. 

In the image below we see a schematic representation of what the baroreceptor reflex looks like. In the case below, we start with high blood pressure and we must therefore ensure that the blood pressure decreases.