Kidney Problems : A Cause Of High Blood Pressure - Secondary Hypertension (Part-I)
Kidney Diseases Are A Common Cause Of High Blood Pressure
Approximately 5% of people suffering from high blood pressure can be found to have specific causes.
The most likely candidates suffering from secondary hypertension include the following :
- Individuals who develop high blood pressure at an early age without a family member suffering from it (no heredity).
- Those who first exhibit high blood pressure when over age 50.
- Those whose blood pressure had been previously brought under control with medicines but then becomes resistant to treatment.
Kidneys Are A Pair Of Bean Shaped Excretory Organs
Kidney Disorders A Cause of High Blood Pressure - Renal Hypertension
The kidneys are a pair of bean shaped excretory organs situated in the lumbar region, one on each side of the vertebral column.
They remove waste products and excess water and salts from the blood, and maintain its pH.
Each kidney contains about one million nephrons (structural units) and each nephron is capable of forming urine by itself.
High blood pressure that is caused by kidney diseases, is a result of either of the following causes :
- Salt and water retention by the kidneys causing expansion of blood volume.
- An alteration in the removal of certain chemicals from the body, called vasoactive substances, whose basic function is to increase blood vessel tone and cause arterial constriction.
Renal hypertension can be further classified into the following types :
1. Renal Vascular Hypertension
Narrowing of renal artery supplying blood to the kidneys, leads to reduced renal perfusion. When blood flow to the kidneys becomes sufficiently scarce, it stimulates the Renin Angiotensin Aldosterone System (RAAS).
Specialized cells of juxta glomerular apparatus of the kidneys secrete the enzyme renin which acts on Angiotensinogen to cleave off peptide Angiotensin-I.
This peptide is then acted upon by Angiotensinogen Converting Enzyme (ACE) to create Angiotensin-II.
Circulating Angiotensin-II elevates arterial pressure by causing constriction of arteries, by stimulating Aldosterone hormone secretion from adrenal cortex with resulting salt retention, and/or stimulating Adrenaline release from the nerves.
Salt and water retention causes excess fluid volume, the blood vessels fill up with this additional fluid, and blood pressure rises.
Most common cause of narrowing or stenosis of renal arteries in young hypertensives is fibromuscular hyperplasia (or thickening of the muscle layer of renal artery) which is most common in women under age 50.
Remainder of the cases are due to cholesterol deposition and age-related hardening of renal arteries.
Symptoms of Renal Vascular Hypertension include the following :
- Blurry or double vision
- Blood in urine
- Nose bleed.
Vast majority of people will never experience any symptoms.
It can also cause chronic kidney disease or a slow decline in the function of kidneys.
This condition should be suspected in the following instances :
- If the documented onset is below age 20 or after age 50.
- If there are epigastric or renal artery bruits (a bruit is a turbulence in the blood flow that can be heard by placing a stethoscope lightly over the abdomen, best heard to the right or left of midline above umblicus or in the flanks).
- If there is atherosclerotic disease of aorta or Peripheral Vascular Disease (PVD).
- If there is an abrupt deterioration in the kidney functions after administration of Angiotensin Converting Enzyme inhibitors (ACE inhibitors), the medication for high blood pressure.
Diagnostic approach towards this condition includes the following interventions :
- Rapid Sequence Intra Venous Pyelogram(IVP).
- Renal Arteriography (the diagnostic test).
- Radio isotope renography.
- Duplex doppler studies.
- Non-invasive angiograms.
Pregnancy Associated High Blood Pressure - A Variant Of Renal Vascular Hypertension
Pre-eclampsia eclampsia or toxemia of pregnancy is a disease of late pregnancy (can occur any time after 20 weeks of pregnancy up to 6 weeks after delivery) and is defined as the presence of elevated blood pressure, proteins in urine, and swelling of entire body, particularly of face and hands.
It is also associated with jaundice and liver abnormalities, and is most common in first pregnancy.
Disturbances in vision, headache, and development of convulsions indicate the nervous system also getting involved, and is termed as eclampsia.
It is a disease unique to pregnancy, with the only cure being child birth and delivery of placenta.
In pure pre eclampsia, the cause resides in the cells of inner lining of blood vessels of glomeruli of kidneys.
These cells swell up due to an increase in cytoplasmic volume, are filled with vacuoles, and encroach the lumen of blood vessels, causing a scarcity of blood and nutrient supply in the enlarged glomeruli.
As a result of deficiency of oxygen and nutrients, the glomeruli suffer from damage, with fibrous deposits accumulating within them.
This causes decline in kidney function, salt and water retention, and the resultant increase in blood pressure.
This is a life threatening condition, and tends to recur in subsequent pregnancies.
In mild pre eclampsia, the diastolic blood pressure is less than 90-100 mm Hg. In moderate disease, the diastolic BP is in the range of 90-110 mm Hg. In severe pre eclampsia, the overall blood pressure levels may reach 160/110 mm Hg.
2.Renal Parenchymal Hypertension
Any disease that affects the kidney structure or renal parenchyma can cause high blood pressure.These conditions are the most common causes of secondary hypertension.
Polycystic kidney disease is an inherited condition in which cysts develop in kidneys, which prevent them from functioning normally, and raise the blood pressure.
Our kidneys filter waste and sodium using microscopic sized filters called glomeruli, that can sometimes become swollen. If the swollen glomeruli cannot work normally, it leads to high blood pressure (Glomerular diseases).
Certain other conditions like tubular interstitial diseases, Diabetic nephropathy (a complication of long standing diabetes) also damage the kidney's filtering system and cause an increase in blood pressure.
These diseases lead to severe damage and destruction of cells and result in inflammation and deposition of fibers in small arteries in the kidney.
These conditions lead to a rise in blood pressure by the following mechanisms :
- Fibrosis of small intrarenal vessels leading to activation of renin angiotensin system.
- Secretion of an unidentified vasoconstrictor substance other than renin, by the kidneys.
- Damaged kidneys fail to produce the vasodilator Bradykinin.
- Shrunken and diseased kidneys fail to inactivate vasoconstrictors circulating in the blood.
- Inability to excrete excess sodium, causing salt and water retention.
3. Tumors Of Kidney Causing High Blood Pressure
A rare form of secondary hypertension results from the excess secretion of renin by juxtaglomerular cell tumors or nephroblastomas.
This causes constriction of blood vessels and salt and water retention, leading to an increase in fluid volume, that is taken up in blood vessels and causes an increase in blood pressure.
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