MCAT Content / Circulatory System / Systolic And Diastolic Pressure

Systolic and diastolic pressure

Topic: Circulatory System

Blood pressure is the pressure of the fluid (blood) against the walls of the blood vessels. It is of two types: systolic and diastolic. The normal value of systolic blood pressure is 120 mm Hg and of diastolic blood pressure is 80 mm Hg.

Blood pressure is the pressure exerted by blood on the walls of a blood vessel that helps to push blood through the body. Systolic pressure measures the amount of pressure that blood exerts on vessels while the heart is beating. The optimal systolic blood pressure is 120 mmHg. Diastolic pressure measures the pressure in the vessels between heartbeats. The optimal diastolic blood pressure is 80 mmHg. Many factors can affect blood pressure, such as hormones, stress, exercise, eating, sitting, and standing. Blood flow through the body is regulated by the size of blood vessels, by the action of smooth muscle, by one-way valves, and by the fluid pressure of the blood itself. During systole, when new blood is entering the arteries, the artery walls stretch to accommodate the increase of pressure of the extra blood. During diastole, the walls return to normal because of their elastic properties.

The pressure of the blood flow in the body is produced by the hydrostatic pressure of the fluid (blood) against the walls of the blood vessels. The fluid will move from areas of high to low hydrostatic pressures. In the arteries, the hydrostatic pressure near the heart is very high, and blood flows to the arterioles where the narrow openings of the arterioles slow the rate of flow. During systole, when new blood is entering the arteries, the artery walls stretch to accommodate the increase of pressure of the extra blood; during diastole, the walls return to normal because of their elastic properties.

Blood pressure values are universally stated in millimeters of mercury (mm Hg). The blood pressure of the systole phase and the diastole phase gives the two readings for blood pressure. For example, the typical value for a resting, healthy adult is 120/80, which indicates a reading of 120 mm Hg during the systole and 80 mm Hg during diastole.

 

Practice Questions

 

Khan Academy

 

MCAT Official Prep (AAMC)

Practice Exam 2 C/P Section Question 44

Practice Exam 4 C/P Section Question 57

 

Key Points

• The systolic pressure is defined as the peak pressure in the arteries during the cardiac cycle; the diastolic pressure is the lowest pressure at the resting phase of the cardiac cycle.

• Normal blood pressure for a healthy adult is 120 mm Hg during systole (peak pressure in the arteries ) and 80 mm Hg during diastole (the resting phase).


Key Terms

Blood pressure: the pressure exerted by the blood against the walls of the arteries and veins; it varies during the heartbeat cycle and according to a person’s age, health, and physical condition

Systolic pressure: the peak arterial pressure during heart contraction

Diastolic pressure: the minimum arterial pressure between contractions, when the heart expands and refills

Hydrostatic pressure: the force when blood moves along the capillary, fluid moves out through its pores and into the interstitial space

Smooth muscle: involuntary muscle



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