Disorders of the Circulatory System

Because the circulatory system operates continuously throughout a person's entire life, without rest, it is also a system in which disorders are both common and clinically significant. Four such disorders are named in this chapter, and, taken together, they illustrate how a single underlying problem — the gradual narrowing of blood vessels — can progress through a chain of increasingly serious clinical stages.

Hypertension, or sustained high blood pressure, is a resting blood pressure that remains persistently above the normal range, conventionally taken as above approximately one hundred and forty millimetres of mercury systolic pressure or ninety millimetres of mercury diastolic pressure. Hypertension forces the heart to work harder than normal with every single beat, and over months and years this sustained extra strain damages the inner lining of artery walls throughout the body, making hypertension one of the principal risk factors for the other, more serious disorders described below, as well as for stroke.

Coronary artery disease, sometimes called atherosclerosis when referring to the underlying process, is a narrowing of the coronary arteries — the specific small arteries that branch off the aorta almost immediately and supply oxygenated blood to the heart muscle itself, rather than to the rest of the body. This narrowing results from the gradual build-up, on the inner wall of the artery, of plaques made of cholesterol, other fatty material and calcium deposits, which progressively reduce the internal diameter of the vessel and, with it, the volume of oxygenated blood able to reach the heart muscle it supplies.

Angina pectoris is not itself a separate disease but a symptom that results directly from coronary artery disease: a gripping, often severe pain in the chest (sometimes radiating to the left arm, neck or jaw) that occurs whenever narrowed coronary arteries fail to deliver enough oxygenated blood to keep pace with the heart muscle's momentary demand for oxygen. Angina is typically triggered by physical exertion or emotional stress, both of which increase the heart's oxygen demand, and it is characteristically relieved fairly quickly by resting, which brings the heart's oxygen demand back down within the reduced supply the narrowed arteries can still provide. Because the reduced blood flow in angina is temporary and reversible with rest, an attack of angina does not, on its own, cause any permanent damage to the heart muscle — this is what principally distinguishes it from a heart attack, in which a coronary artery becomes completely blocked and the heart muscle it supplies is permanently damaged from lack of oxygen. …