Renal Failure Physiology Notes

Renal Failure Introduction

The term renal failure refers to the failure of excretory functions of the kidney. It is usually, characterized by a decrease in GFR. So GFR is considered the best index of renal failure. However, a decrease in GFR is not affected much during the initial stages of renal failure.

• If 50% of the nephrons are affected, GFR decreases only by 20-30%. It is because of the compensatory mechanism by the unaffected nephrons.
• The Renal failure may be either acute or chronic.

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Renal failure is always accompanied by other complications such as:

1. Deficiency of calcitriol (activated vitamin D) – resulting in the reduction of calcium absorption from the intestine and hypocalcemia.
2. Deficiency of calcitriol and hypocalcemia may cause secondary hyperparathyroidism in some patients. Deficiency of erythropoietin – resulting in anemia
3. Disturbances in acid-base balance.

Acute Renal Failure

• Acute renal failure is the abrupt stoppage of renal functions.
• It is often reversible within a few days to a few weeks.
• Acute renal failure may result in sudden life-threatening reactions in the body with the need for emergency treatment.

Acute Renal Failure Causes

1. Acute nephritis (inflammation of kidneys), which usually develops by an immune reaction
2. Damage of renal tissues by poisons like lead, mercury arid carbon tetrachloride
3. Renal ischemia, which develops during circulatory shock
4. Acute tubular necrosis (necrosis of tubular cells in the kidney) caused by burns, hemorrhage, snake bite, toxins (like insecticides, heavy metals, and carbon tetrachloride), and drugs (like diuretics, aminoglycosides, and platinum derivatives)
5. Severe transfusion reactions
6. Sudden fall in blood pressure during hemorrhage, diarrhea, severe burns, and cholera
7. Blockage of ureter due to the formation of calculi (renal stones) or tumors.

Acute Renal Failure Features

1. Oliguria (decreased urinary output)
2. Anuria (cessation of urine formation) in severe cases
3. Proteinuria (appearance of proteins in the urine) including albuminuria (excretion of albumin in the urine)
4. Hematuria (presence of blood in urine)
5. Edema due to increased volume of extracellular fluid caused by retention of sodium and water
6. Hypertension within a few days because of increased ECF volume
7. Acidosis due to the retention of metabolic end products
8. Coma due to severe acidosis (if the patient is not treated in time) resulting in death within 10-14 days.

Chronic Renal Failure

• Chronic renal failure is the progressive, long-standing, and irreversible impairment of renal functions.
• When some of the nephrons lose their function, the unaffected nephrons can compensate it.
• However, when more and more nephrons start losing function over the months or years, the compensatory mechanism fails and chronic renal failure develops.

Chronic Renal Failure Causes

1. Chronic nephritis
2. Polycystic kidney disease
3. Renal calculi (kidney stones)
4. Urethral constriction
5. Hypertension
6. Atherosclerosis
7. Tuberculosis
8. Slow poisoning by drugs or metals.

Chronic Renal Failure Features

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