Causes

In 90-95% of patients of suffering from hypertension there is no identifiable cause and this is referred to as essential or primary hypertension. Where hypertension occurs as a result of a pre existing medical condition or medication it is known as secondary. The actual rise in pressure occurs with either an increase in cardiac output or an increase in systemic vascular resistance.

Primary Hypertension

The cause of essential hypertension is not fully understood but there are lifestyle factors which can contribute to the condition. By rectifying these possible factors blood pressure can be reduced but medication may still be required.

It has also been postulated that primary hypertension has a strong genetic link and may be hereditary

Seconday Hypertension

Secondary hypertension can be grouped into different  catergories according to which systems are affected.

• Cardiovascular Hypertension

Caused by for example atherosclerosis where the blood vessels become partially blocked by plaques which increase peripheral resistance.  Another disease which causes hypertension in this system is aortic coarctation where the aorta narrows which means there are higher levels of vascular resistance and therefore a higher blood pressure

 Diagram courtesy of https://commons.wikimedia.org/wiki/File:Atherosclerosis_diagram.gif under public domain 

•  Renal Hypertension

Partial blockage of the renal artery possibly through atherosclerotic plaques reduces blood flow and stimulates the renin-angiotensin system to increase blood volume and ultimately blood flow, this in turn increase blood pressure.

Renal disease can cause hypertension as nephrons in the kidney become damaged and sodium excretion becomes impaired.

• Endocrine Hypertension

80% of patients with Cushing’s disease have hypertension. In this condition there is an over production of cortisol (also involved in stress) which elevates Blood pressure

Pheochromocytoma- tumour that increases the secretion of noradrenaline and adrenaline which increase blood pressure by increasing cardiac output and stimulating vasoconstriction

• Neurogenic Hypertension

Occurs after damage to the baroreceptors.  Baroreceptors regulate blood pressure and sense changes in pressure. In hypertension the baroreceptors no longer bring blood pressure under control instead the normal blood pressure is reset at a higher pressure and so blood pressure remains at a constant high

Neurogenic hypertension also occurs when there is a reduction in blood flow through the cerebral artery, when blood flow is low there is a compensatory mechanism to increase blood pressure 

• Other causes of secondary hypertension

 Drugs -There are many drugs which can increase blood pressure including the osetrogen component of the combined oral contraceptive pill, decongestants, St Johns wort to name a few.  The sudden withdrawal of certain antihypertensives can actually cause rebound hypertension also.

Pregnancy

Gestational hypertension- present in 5 to 10% of pregnancies but most common in a womans first pregancy where it is prevalent in up to 25% of cases

A more serious form of hypertension in pregancy is preclampsisa where the mother blood pressure reaches 180/110mmHg . Preeclampsia is most common in a womans first preganancy and occurs in the third trimester. 4% of these women go onto develop the lifethreatening condition  eclampsia where there is an onset of convulsions for 1-2 minutes followed by a coma of these 5% die.  The only way to reduce the blood pressure is to deliver the baby and placenta

Sleep Apnea

The sufferer often stops breathing for short periods of time during sleep, resulting in oxygen depravation to some blood vessesl.  When the vessels are not supplied efficeintly wit oxygen they beocme less efective at regualting blood pressure.