Normal cutoff values for blood pressure are 120/80 mmhg (systolic/diastolic). A person with sustained and persistent elevated blood pressure levels than the cutoff values is said to be having Hypertension.
Generally hypertension is categorized into two depending on the etiology as follows;
- Primary Hypertension (Essential Hypertension)
- Secondary Hypertension
Primary hypertension is said to be developing mainly due to 2 reasons. First is the genetic make- up. It is said that familial aggregation or the genetic make up would explain the occurrence of hypertension among twins. Second would be the vascular causes which would result in vasoconstriction. It could be an inbuilt cause which would stimulate constriction of vessels, or stimuli from outside such as smoking, obesity, stress, etc.
Secondary hypertension develops as a result of malfunction in another system. Depending on the etiology, causes for above, can be discussed under 4 main categories;
- there are 3 main factors which would influence in increase in blood pressure such as activation of renin-angiostensin-aldesterone system, retention of sodium and water and Release of vasopressor materials. (Discussed mainly under “Quick look at physiology of Blood pressure regulation”)
- Hormonal imbalances causing elevated blood pressure levels are included under this topic. Eg :- Cushing’s syndrome, Primary aldosteronism, phaeochromocytoma, oral contraceptives, etc.
- Coartctation of Aorta
- Eg:- polyneuritis, Raised Intracranial pressure, etc..
There are various pathological changes occurring in hypertension in various organs. Many of these can be explained using the basic changes occurring in blood vessels, specially in arterial system.
In hypertension, due to increased haemodynamic stress, degenerative changes occurring in the large and small sized arteries will lead mainly to atherosclerosis. Also it would lead to aortic dissection, cerebrovascular hemorrhages and aneurysms.
Many of the pathological changes occurring in other oragns can be expalined using the changes occuring in arterioles.
- Hyaline arteriolosclerosis
- Hyperplastic arteriolosclerosis
Due to gradual elevation of blood pressure, over a long period would cause degenerative changes in the endothelial cells, which would lead to leakage of plasma proteins in to the intimal layer, causing aggregation of pink, glass like proteinacious material in the intimal layer of blood vessels, leading to intimal thickening, which would in turn cause luminal narrowing. Along with this as there would be an increase in synthesis of matrix of smooth muscle cells, in the Tunica media as a response to increased haemodynamic stress also contributes for luminal narrowing. These changes are called “Hyaline arteriolosclerosis”. Normally these changes occur in patients who have “Benign hypertension”, which develops slowly and gradually over years. These changes are mostly widespread and affects almost all the organs.
If the blood pressure suddenly and markedly elevated over 200/140mmhg, it is called “Malignant Hypertension”. Most acute change expected would be fibrinoid necrosis of blood vessels, due to marked increase in blood pressure. This would cause leakage of massive amount of fluid out in to the organs causing edema. If patient suffers from this type elevations in blood pressure, for a reasonable amount of time to call it a chronic condition, arterioles will show an adaptation where concentric laminated thickening of smooth muscles occurs with re-duplication of basement membranes. This would mimic the arrangement of an onion-skin. Therefore it is also called an Onion-Skin type thickening. These changes are known as “Hyperplastic Arteriolosclerosis”.