Your body has complex mechanisms that help control your blood pressure, which is is the force against your blood vessel walls (ref 1). Pressure sensors located in the walls of your blood vessels detect changes in blood pressure, and send messages to your brain, directing it to make adjustments in your body that will affect your blood pressure (ref 3).
Major Factors that Affect Blood Pressure
The major ways your body can regulate your blood pressure include: - Changing your heart beat: When your heart beats faster, more blood pumps through your vessels and blood pressure is higher. Similarly, when your heart beats with more forceful contractions, it pumps more blood with each beat, and pressure rises. - Contracting or expanding blood vessel walls: Blood vessel walls are muscular, which allows them to expand or contract. More narrow vessels cause faster blood flow and higher blood pressure (ref 4). Dilated vessels are wider, allowing blood to flow easily (ref 4). - Kidney function: Your body can also adjust your blood volume by controlling water retention and urination through kidney function (ref 2). The higher your blood volume, the higher your blood pressure.
Everyday Blood Pressure Control
Blood pressure changes throughout the day. It's lower when you are asleep or resting, and higher when you are active or excited (ref 1). Your body quickly adjusts to these changes by controlling your heart beat and blood vessel diameter (ref 5). For example, when you begin exercising, blood pressure increases (ref 5). The pressure sensors in your blood vessels detect this increase and send messages to your brain to slow the beating of your heart, lower the strength of your heart's contractions and relax blood vessel walls to reduce blood pressure (ref 5). Or, when you quickly move from a lying to a standing position, blood pressure drops (ref 5). Your body senses this and increases heart rate and force of contractions, and constricts blood vessel walls to increase your blood pressure (ref 5).
Blood Pressure Control in Times of Stress
In other cases, your blood pressure may fall suddenly, such as when you are injured and lose a lot of blood (ref 5). In addition to triggering changes in your heart beat and blood vessel walls, the sudden drop in blood pressure will also trigger the release of hormones that affect your kidney function (ref 5). If you lose a lot of blood, your body senses the drop in blood volume and triggers the productions of hormones that signal the kidneys to retain salt and water (ref 5). This increases your blood volume, thereby increasing blood pressure (ref 2).
Regulating Your Blood Pressure Over the Long Term
Over the long term, your kidneys are primarily responsible for blood pressure. In fact, many blood pressure lowering medications work by triggering the kidneys to release excess sodium and fluid. When working properly, this fluid regulation system keep blood pressure relatively constant over the years (ref 5). When your blood pressure is high, hormones are released to signal increased urination, lowering blood volume and blood pressure (ref 2). When blood volume and pressure is too low, hormones secreted from your brain tell your kidneys to retain sodium and water, increasing blood volume and blood pressure (ref 5). Problems with this system can lead to high blood pressure, which increases your risk of heart attack and stroke.
REFERENCES & RESOURCES
- National Heart, Lung, and Blood Institute: Description of High Blood Pressure
- New Human Physiology: Chapter 9: Systemic Resistance and Hypertension
- Get Body Smart: Autonomic Pathways
- Essentials of Medical Physiology; by Indu Khurana
- Disorders of Cardiovascular Function: Chapter 23: Disorders of Blood Pressure Regulation; by Carol M. Porth
- Merck Manuals Medical Library: High Blood Pressure