The Anatomy & Physiology of Blood Pressure

Blood pressure, although commonly checked during doctors appointments using an instrument known as a sphygmomanometer on the brachial artery, is not usually well understood from a biological standpoint. Understanding the controlling physiological forces behind blood pressure is an important part of understanding how the circulatory system, and the human body, works.

Defining and understanding blood pressure
Blood pressure can be defined as the force, or pressure, exerted on the vessel walls by the blood as it is pumped and circulated throughout the body. This pressure within the vessels is created by the heart. As the heart pumps, blood is forced into the arteries in waves; these waves are strong, and push blood throughout the body’s circuit of arteries, veins and capillaries.

There are two types of blood pressure that are typically monitored and recorded; systolic and diastolic. The numerical difference between these two types of blood pressure is known as the pulse pressure. Systolic blood pressure is the blood pressure level at the peak of a ventricular contraction, or the point at which the heart has contracted during a beat, forcing blood out of its chambers. The second type of blood pressure, known as diastolic blood pressure, is measured during a phase of ventricular relaxation, or the time between heart beats where the ventricles have relaxed and are filling with blood once more.

Abnormal blood pressure
The average systolic blood pressure of a healthy individual between the ages of 20 to 30 years old, is approximately 120, while the average diastolic blood pressure is 75. This example of blood pressure would be read as 120/75 (one-hundred-twenty over seventy-five). This is a normal, healthy blood pressure.

When an individual’s blood pressure is too high, it is referred to as hypertension. Hypertension is typically diagnosed in individuals with blood pressures exceeding 140/90 and is common among Americans. Hypertension can cause damage to the vessel walls, an increase in cholesterol buildup within the vessels and can lead to cardiac disease and heart failure.

An individual with especially low blood pressure may be diagnosed as having hypotension. Hypotension is typically diagnosed when an individual’s blood pressure is recorded as lower than 80/60. Hypotension can pose risks to an individuals health, such as fainting, circulatory failure (shock), weak pulse and urinary suppression. Additionally, individuals suffering from hypotension often have blood pressures that are unable to be measured and recorded accurately.

Peripheral resistance
Peripheral resistance is best defined as the opposing forces acting on the flow of blood within the blood vessels. Pressure, such as in blood pressure, would not be possible without an opposing force to create the resistance that results in pressure. When speaking in terms revolving around blood pressure, blood viscosity, vessel length and vessel radius all have a direct impact on the amount of peripheral resistance.

Other factors that may affect blood pressure
A typical blood pressure reading is best taken at a relaxed state, as blood pressure readings taken during times of high physical activity may show elevated numbers. There are several factors that can affect a blood pressure reading, such as an individuals age or weight. Blood pressure typically increases as an individual ages due to the body’s decreased ability to accommodate systolic force. Additionally, an individual’s specific blood volume may contribute to their blood pressure. Medications, both prescription and over-the-counter, may affect blood pressure readings as well. Lastly, any resistance to the flow of blood throughout the body, such as that caused by excessive cholesterol buildup within the vessels, or constriction or stiffening of the vessels, may also contribute to poor blood pressure readings.

Saladin, Kenneth S.. Anatomy & physiology: the unity of form and function. 5th ed. New York: McGraw-Hill, 2010. Print.

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