Blood Pressure Regulation

Blood Pressure Regulation

The pressure created by ventricular contraction is the driving force for blood flow through the cardiovascular system. As blood is ejected from the left ventricle, the aorta and arteries expand to accommodate entering blood flow. When the ventricle relaxes and the semilunar valves close, the elastic arterial walls recoil, propelling the blood forward into smaller arteries and arterioles. By sustaining the driving pressure for blood flow during ventricular relaxation, the arteries create continuous blood flow through the vessels. While total blood flow is determined by cardiac output, blood flow to specific body areas can vary dramatically in a given time period. Organs differ in their requirement from moment to moment, and blood vessels constrict or dilate to regulate local blood flow to various areas in response to the tissue’s demands.

Blood pressure is highest in the arteries and decrease as blood flows through the circulatory system. The decrease in pressure occurs because energy is lost as a result of the resistance to flow from friction between blood cells. The resistance to blood flow (R) is directly proportional to the length of the tubing through which the fluid flows (L) and to the viscosity (η) of the fluid, and inversely proportional to the fourth power of the tubing radius (r): R Lη / R^4. The flow through individual arterioles depends on their resistance. The higher the resistance in the arterioles, the lower the blood flow through it. If an arteriole constricts and resistance goes up, blood flow through that arteriole goes down.

The CNS coordinates the reflex control of blood pressure. Its main function of the cardiovascular control center is to maintain blood flow to the brain and heart. Stretch – sensitive mechanoreceptors known as baroreceptors are located in the walls of the carotid arteries and aorta, where they monitor the pressure of blood flowing to the brain and to the body. The...