Hypertension

Hypertension or high blood pressure is a medical condition where the blood pressure in the arteries is chronically elevated. While it is formally called arterial hypertension, the word "hypertension" without a qualifier usually refers to arterial hypertension.

Pathophysiology

The mechanisms behind the factors associated with inessential hypertension are generally fully understood, and are outlined below. However, those associated with essential hypertension are far less understood. What is known is that cardiac output is raised early in the disease course, with total peripheral resistance normal; over time cardiac output drops to normal levels but TPR is increased. Three theories have been proposed to explain this:

Related Topics:
Cardiac output - Total peripheral resistance

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• Inability of the kidneys to excrete sodium, resulting in natriuretic factor (note: the existence of this substance is theoretical) being secreted to promote salt excretion with the side-effect of raising total peripheral resistance.
• An overactive renin / angiotension system leads to vasoconstriction and retention of sodium and water. The increase in blood volume leads to hypertension.
• An overactive sympathetic nervous system, leading to increased stress responses.

Inessential hypertension

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• Pregnancy: unclear.
• Kidney disease / renal artery stenosis: the normal physiological response to low blood pressure in the renal arteries is to increase cardiac output (CO) to maintain the pressure needed for glomerular filtration. Here, however, increased CO cannot solve the structural problems causing renal artery hypotension, with the result that CO remains chronically elevated.
• Cancers: tumours in the kidney can operate in the same way as kidney disease. More commonly, however, tumors cause inessential hypertension by ectopic secretion of hormones involved in normal physiological control of blood pressure.
• Drugs: anything with an adrenergic effect causes vasoconstriction at sites with alpha-adrenoceptors, increasing total peripheral resistance.
• Malformed aorta, slow pulse: these cause reduced blood flow to the renal arteries, with physiological responses as already outlined.
• Anemia: unclear.
• Fever: unclear.
• Aortic valve disease: unclear.