Anatomy And Physiology

What is Blood Pressure



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In the face of our obesity epidemic, the media, scientists, even our next door neighbours are constantly reminding us of the health risks that are related to obesity. Most of us have heard of blood pressure and how it is critical for us to maintain it within the normal range. We all have a vague idea of what could increase our blood pressure just as most of us know that the reading "120/80" is ideal. However, do most people really know what blood pressure is? What the reading "120/80" actually represents? Probably not.

As its name suggests, blood pressure is the pressure exerted by the circulating blood on the blood vessel walls. Arterial blood pressure (exerted by blood that is travelling away from the heart) is primarily produced by the contractions of the heart. However, hydrostatic pressure (exerted by gravity from the column of blood) adds to it, resulting in the final blood pressure reading. As blood moves through the circulatory system, the contractile force from the heart decreases. Naturally, the pressure decreases as the blood travels from arteries to arterioles, capillaries, venules and eventually veins. The blood pressure measured in the medical context is the arterial blood pressure.

There are two elements to the arterial blood pressure, hence why the reading consists of two values - systolic and diastolic. Systolic pressure, the larger value in the blood pressure reading, is produced by the expulsion of blood from the heart into the arteries when the heart contracts. On the other hand, diastolic pressure is produced when the heart refills with blood, ready for the next contraction. Pressure is generally measured in millimetres of mercury (mmHg), which is sort of ironic since most medical equipments don't contain mercury anymore.

As most of us already know, the reading 120/80 (spoken as "120 over 80") belongs to a resting, healthy adult human. However, our arterial blood pressure is not static, it is influenced by a wide range of factors and cycles throughout the day (known as the circadian rhythm). Factors that are able to influence the blood pressure include:

- Heart beat: The more often the heart contracts, the higher the blood pressure.
- Blood volume: The more blood within the circulation, the higher the cardiac output and thus, higher blood pressure.
- Blood viscosity: If the thickness of the blood is increased somehow (by excess amounts of sugar, for example), it would naturally result in a higher blood pressure.
- Vessel wall resistance: If the blood vessel wall is smooth, blood will be able to travel through the wall with little resistance, resulting in a lower blood pressure.

After all that scientific explanation, it seems as though there is no point in measuring blood pressure. However, blood pressure is one of the four principal vital signs for good valid reasons. Although, we do not completely understand how blood pressure is regulated, physiologically, that exist three mechanisms for regulating blood pressure: baroreceptor reflex, renin-angiotensin system and aldosterone release. With these regulatory mechanisms functioning to keep a person's blood pressure within the acceptable range, measurements outside the normal range is an indication of potentially deadly consequences.

High blood pressure, often referred to as hypertension, puts excessive amounts of pressure on the blood vessel walls. This increases the heart's workload and over time, causes the cardiac muscles to thicken, enlarge and weaken. If left untreated, persistent hypertension increases the risks of stroke, heart attacks, heart failure amongst other fatal health problems. On the other hand, low blood pressure (or hypotension) indicates problems such as excessive blood loss and congestive heart failure.

Thus, what seemed to be just two random numbers measured by your doctor is actually very important in monitoring your health. Once a problem is detected, it is vital to follow your doctor's recommended medication and treatment. It is not just a problem that if left ignored for long enough will go away. For the sake of your life, blood pressure is vital and thus, should be understood clearly.

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