Hypertension is elevation of blood pressure above 140/90 mmHg. The pumping of the heart results in a high pressure peaks and troughs. When the left ventricle of the heart contracts and sends blood into the aorta, the blood pressure peak occurs. This peak is maintained for a brief time with the help of elastic recoil of great vessels. This peak is called systolic blood pressure. In a healthy young adult, the systolic blood pressure is below 140 mmHg. When the ventricles relax the blood pressure drops below the peak, but does not reach zero because of the elastic recoil of great vessel walls. This trough is called diastolic blood pressure. In a healthy young adult, diastolic blood pressure is below 90 mmHg. (Read more: Difference Between Systolic and Diastolic Blood Pressure)
Blood pressure is tightly controlled by the autonomic nervous system. There are specialized pressure sensors in blood vessels. Low pressure sensors are located in the right atrium, and superior and inferior vena cava. When blood pressure drops, these sensors get stimulated and send nerve impulses along the sensory nerves to the midbrain. Return signals from the midbrain increase the heart rate and the force of contraction of the left ventricle. This sends more blood into the systemic circulation, increasing the net venous blood return to the right atrium, and superior and inferior vena cava. High pressure sensors are located in the carotid bodies. When these are stimulated due to high blood pressure, the sensory input send from these sensors to the midbrain results in slower heart rate and less forceful ventricular contractions. Blood pressure depends upon several factors. They are chiefly heart rate, force of ventricular contraction, blood volume in circulation, nerve impulses, chemical signals, and vessel wall condition.
Primary Hypertension
Primary hypertension is elevation of blood pressure above normal for the age due to effects of ageing. This accounts for more than 95% of the cases. Loss of elastic recoil of the vessel wall is a marked feature in essential hypertension. Many individuals find that they have high blood pressure even though they have no previous history, no family history or risk factors. This type of high blood pressure is idiopathic, and it responds to simple lifestyle modifications and drug treatment.
Secondary Hypertension
Secondary hypertension is elevation of blood pressure above normal for the age due to a clinically detectable preceding cause. Common primary causes of secondary high blood pressure are, renal diseases, endocrine diseases, coarctation of aorta, pregnancy, and medications. Chronic and acute renal failures are characterized by failure of fluid removal. Therefore, there is fluid accumulation, increase of blood volume, and elevation of blood pressure. Cortisol is the flight, fright, and fight hormone. It makes the body ready for action. Cortisol elevates blood pressure, heart rate and relocates blood from peripheral circulation into vital organs. Cushings disease is due to excessive secretion of cortisol. Conns syndrome is due to excessive secretion of aldosterone. Aldosterone retains fluid. Coarctation of aorta results in poor venous return towards low pressure sensors and secondary rise of blood pressure. Pregnancy creates a fetal circulation and fluid retention. Steroids have a similar effect to Cushings syndrome. Oral contraceptive pill also retains fluid.
What is the difference between Primary and Secondary Hypertension?
• Primary hypertension has no detectable cause while secondary hypertension has.
• Primary hypertension is common while secondary hypertension is not.
• Primary hypertension is easier to treat while secondary hypertension is resistant to treatment unless the underlying pathology is treated.
Read more:
Difference Between Hypertension and Hypotension