Disorders of the Circulatory System

Hypertension - persistently high blood pressure, defined here as systolic pressure above 150 mm Hg or diastolic pressure above 90 mm Hg, against a normal reading of about 120/80 mm Hg - is the most common circulatory disease, and if uncontrolled it can damage the heart, brain and kidneys. Coronary heart disease develops when arteries become lined with atheroma, a build-up of cholesterol, fibres, dead muscle and platelets; this process, called atherosclerosis, forms plaques that stiffen the artery wall, narrow its lumen and reduce blood flow, and plaques can also trigger clot formation (a coronary thrombus) that causes a heart attack. Stroke occurs when a blood vessel supplying the brain either bursts (a brain haemorrhage) or is blocked by atherosclerosis or a thrombus, starving the brain tissue it served of oxygen and causing tissue death (cerebral infarction). Angina pectoris is the ischaemic chest pain felt in early coronary heart disease, when an atheroma partially blocks a coronary artery and reduces the heart muscle's blood supply enough to cause tightness, choking and breathing difficulty, usually for a short duration. Myocardial infarction (heart attack/heart failure) occurs when blood supply to the heart muscle is severely cut - typically by a thrombus - killing muscle fibres; this is also called ischaemic heart disease, and if angina from it persists it can progress to death of heart muscle and outright heart failure, during which the Frank-Starling curve shifts downward and to the right, so a failing heart ejects a smaller stroke volume for any given filling volume than a healthy one would. Rheumatic heart disease is an autoimmune complication that appears 2-4 weeks after a streptococcal throat infection, when the antibodies raised against the bacteria mistakenly attack the heart itself, producing fibrous nodules on the mitral valve, connective-tissue fibrosis, and fluid build-up in the pericardial cavity. Other circulatory disorders include varicose veins (veins so dilated that their valves can no longer prevent backflow, most often in the legs, the rectal-anal region, the oesophagus or the …