Compare and contrast the negative feedback regulation of blood pressure via short- term mechanisms and long-term mechanisms. Include in your discussion three different ways short- term mechanisms regulate blood pressure and two ways long-term mechanisms do. Also explain how local hormones signal changes, which result in localized blood pressure changes and the shunting of blood.
There are several different mechanisms that the body uses to regulate blood pressure. Depending on the circumstances, the body may use one of many short or long term mechanisms. The short-term mechanisms normally control pressure and resistance while the long-term mechanisms work to manipulate volume. First I will discuss the short-term mechanisms. There are reflexes at the brain stem (medulla) level that regulate blood pressure. One example of this is the body's fight or flight response. When the body senses stress that ignites the fight or flight response a message is relayed to the medulla causing a temporary rise in blood pressure.
The vasomotor center in the medulla also plays a role in blood pressure changes. Many vasomotor fibers release Norepinephrine, which increases heart rate and contractility, dilate coronary vessels and constrict skin and organ vessels. These factors, in turn, cause an increase in blood pressure. When blood pressure rises above its normal range the change is detected and stimulates the baroreceptors in carotid sinuses and in the aortic arch. Impulses travel along afferent nerves and stimulate the cardioinhibitory center, which results in vasodilation of arterioles and veins thus causing a decrease in blood pressure. There are also chemoreceptors that are located near the baroreceptors. When blood oxygen and pH levels drop or CO2 levels rise, these chemoreceptors transmit impulses to the cardioacceleratory center causing cardiac output to increase and impulses to the vasomotor center causing vasoconstriction. These events cause an increase in blood pressure.