Pressure in the Human Circulatory System

Pressure is defined as force per unit area and is measured in pascals [Pa = N/m²]. The term pressure is used when describing fluids (gases or liquids). If a fluid is at rest, pressure is transmitted equally to all its parts and, at any one point, is the same in all directions. This fact was discovered by the French scientist Blaise Pascal. Pressure plays an important role in our health, as for example blood pressure in the human circulatory system. Blood pressure is the pressure that is exerted by blood against the walls of the arteries as it travels through the body. When the volume of blood pumped through the arteries or the pressure that the blood puts against the walls of the arteries increases, the delicate tissues in the artery walls wear thin and may tear. Fat and cholestrol deposits further obstruct blood flow, narrowing the arteries, and thereby accelerating damage by raising blood pressure even more. Elevated blood pressure speeds up the progress of atherosclerosis, and wears out the coronary arteries faster than normal. High blood pressure may cause heart failure, kidney failure, and strokes.

As blood travels through the arterial system, the heart contracts and relaxes. When blood pressure is measured, two values are given. The first, called the systolic pressure, refers to the pressure on the arterial walls when the heart contracts and the second, called the diastolic pressure, is the measure of the pressure when the heart relaxes. For adults normal blood pressure is less than 19 kPa systolic, and 12 kPa diastolic. Blood pressure above this value is considered unhealthy and should be treated.

Irina Vinar -- 1999

Editor's Supplement -- 2001

• Factors influencing the diameter of human anterior and posterior intercostal arteries. David R. Kuhlman, Sadik A. Khuder, Richard D. Lane. Clinical Anatomy. Vol. 28, No. 2 (March 2015): 219–226.