Controls of Blood Pressure

Short Term Neural Control

The heart influences blood pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. by generating systole, and the vessels contribute through resistanceThe opposition to airflow in the respiratory tract, influenced by airway diameter.. Other physical factors include cardiac output, which refers to blood volume per minute. Peripheral resistance is another factor, involving vascular resistanceThe resistance blood encounters as it flows through vessels, primarily determined by vessel diameter, viscosityThe thickness or resistance to flow in a fluid, such as blood., and turbulenceIrregular, chaotic blood flow that increases resistance and can contribute to clot formation.. Blood volume is also a key determinant. Blood volume changes. For example, it increases when you’re bloated. It decreases when you’re dehydrated. Both situations affect blood pressure.

. The most important mechanisms to regulate are peripheral resistance and blood volume. This occurs through the cooperation of the heart, blood vessels, and kidneys.

Short-term neural control mechanisms all function by altering peripheral blood resistance and consequently, cardiac output. They insure that MAP is adequate by altering blood vessel diameter. In addition, they can redirect flow based on organ demand. So while you work out, blood flow to the digestive system decreases and increases to the skeletal muscles. These changes are regulated by the vasomotor centerA brainstem region that regulates blood pressure by controlling blood vessel diameter. located in the medulla of the brain.

Short Term Hormonal Control

The heart influences blood pressure by generating systole, and the vessels contribute through resistance. Several physical factors affect blood pressure. These include cardiac output, which is the blood volume per minute. Peripheral resistance also plays a role, encompassing vascular resistance, viscosity, and turbulence. Blood volume is another factor. Blood volume changes. For example, it increases when you’re bloated. It decreases when you’re dehydrated. Both of these variations affect blood pressure.

Short term mechanisms for regulating blood pressure involve hormonal control and neural mechanisms. Many hormones are involved in BP regulation, including norepinephrineA neurotransmitter involved in attention, arousal, and the fight-or-flight response. and epinephrineadrenaline): Fight-or-flight hormone from the adrenal medulla., antidiuretic hormoneADH A hormone that increases water reabsorption in the kidneys to concentrate urine and reduce water, angiotensin two, erythropoietin(EPO): A hormone produced by the kidneys that stimulates erythropoiesis., and natriuretic peptides. Norepinephrine and epinephrine predominate during periods of stress. These hormones enhance the sympathetic fight-or-flight response. This response occurs in stressful situations, like finding out that you didn’t prepare properly for your biology test. Antiduretic hormone, or ADH, stimulates waterThe universal solvent essential for life. conservation at the kidneys. When blood pressure falls dangerously low, like when you cut yourself very badly, ADH is released. It increases pressure by causing dramatic vasoconstrictionThe narrowing of blood vessels due to contraction of smooth muscle, increasing blood pressure and re in your peripheral arteriolesSmall arteries that regulate blood flow into capillaries through vasoconstriction and vasodilation.

Erythropoietin is a hormone secreted by the kidneys that causes an increase in red blood cell production. This increases blood viscosity, which causes BP to increase.

Atrial natriuretic peptide reduces blood volume and blood pressure. It does this by blocking reninAn enzyme secreted by the juxtaglomerular cells that helps regulate blood pressure by triggering the and aldosteroneA hormone that increases sodium and water reabsorption in the kidneys, helping regulate blood pressu. This action causes the kidneys to excrete more sodium(Na⁺): Major ECF cation; important for fluid balance, nerve function. and water. This lowers the blood volume and consequently causes the blood pressure to drop.

Long Term

Now that we’ve examined these three factors that affect vessels and blood pressure, let’s consider the organs that regulate it. The kidneys are the master controllers of blood pressure. Acting like a bottleneck, they contain many tiny capillariesThe smallest blood vessels where gas, nutrient, and waste exchange occurs between blood and tissues. under high pressure. These capillaries receive about 25% of cardiac output. This makes them a key determinant of blood pressure.

Long term control of blood pressure is mediated by the kidneys and targets blood volume as the regulatory mechanism. To maintain a constant blood volume, the kidneys keep the average blood volume at about five liters. This volume can vary slightly depending upon age, size, and gender.

Kidneys can act directly and indirectly to stabilize the mean arterial pressureThe average pressure in the arteries during one cardiac cycle, ensuring adequate blood flow to organ. First let’s look at direct mechanisms. Direct action by the kidneys involves increasing the filtrationThe process by which fluid moves out of capillaries into surrounding tissues due to hydrostatic pre rate through the kidneys. If the blood volume and consequently the blood pressure rise, the filtrateThe fluid that is filtered from the blood into the nephron and will eventually become urine. is rushed through the kidney tubules quickly. The result is an increase in the volume of filtrate lost in the urineThe liquid waste excreted by the kidneys.. This decrease in blood volume leads to a parallel decrease in blood pressure. As a result, the kidneys resume their normal filtration rate.