Diuretics Introduction
Diuretics or diuretic agents are substances, which enhance the output of urine. These substances increase the excretion of water, sodium, and chloride through urine. The diuretic agents increase urine formation by influencing any of the processes involved in urine formation. Diuretics are commonly called water pills.
Table of Contents
General Uses Of Diuretics
Diuretics are generally used for the treatment of disorders involving an increase in extracellular fluid volume:
- Hypertension
- Congestive cardiac failure
- Edema.
The diuretic agents prevent hypertension, congestive cardiac failure, and edema by increasing urinary output and reducing ECF volume.
Read And Learn More: Medical Physiology Notes
Abuses And Complications Of Diuretics
- Nowadays, diuretics are misused in order to reduce body weight and keep the body slim. Even persons suffering from eating disorders attempt to reduce body weight by misusing diuretics.
- However prolonged use of these substances leads to complications syndrome of diuretic dependant sodium retention characterized by edema.
The adverse effect depends upon the type of diuretic agents used. Tic common adverse effects of diuretics are:
- Dehydration
- Electrolyte imbalance
- Potassium deficiency
- Headache
- Dizziness
- Renal damage
- Cardiac arrhythmia
- Heart palpitations
Types Of Diuretics
Diuretics are classified into seven types:
- Osmotic diuretics
- Diuretics that inhibit the active reabsorption of electrolytes
- Diuretics that inhibit the action of aldosterone
- Diuretics that inhibit the activity of carbonic anhydrase
- Diuretics which increase the glomerular filtration rate
- Diuretics that inhibit secretion of ADH
- Diuretics inhibit ADH receptors.
1. Osmotic Diuretics
- Osmotic diuretics are the substances that induce osmotic diuresis. Osmotic diuresis is the type of diuresis that occurs because of increased osmotic pressure.
- Some of the osmotically active substances are not reabsorbed from renal tubules.
- When injected in large quantities into the body, these substances increase the osmotic pressure in the tubular fluid.
- The increased osmotic pressure in tubular fluid in turn reduces water reabsorption. It leads to the excretion of excess water through urine.
- The elevated blood sugar level in diabetes can also cause osmotic diuresis in the same manner.
The osmotic diuretics are:
- Urea
- Mannitol
- Sucrose
- Glucose.
2. Diuretics Which Inhibit Active Reabsorption Of Electrolytes
- This type of diuretic inhibits the active reabsorption of electrolytes like sodium and potassium from the renal tubular fluid.
- Inhibition of electrolyte reabsorption causes osmotic diuresis.
These diuretic agents are of three types:
- Loop Diuretics – Diuretics which Inhibit the Electrolyte Reabsorption in the Thick Ascending Limb of Henle’s Loop
- Loop diuretics are the substances that inhibit electrolyte reabsorption in Henle’s loop.
- These diuretics inhibit the sodium and chloride reabsorption from the thick ascending limb of Henle’s loop.
- So, the osmotic pressure in the tubular fluid increases leading to diuresis. The osmolarity of medullary interstitial fluid also decreases due to the inhibition of sodium reabsorption into the medullary interstitium.
- So, the medullary interstitium fails to concentrate the urine resulting in the loss of excess fluid through urine.
Some of the loop diuretics are:
- Furosemide
- Torasemide
- Bumetanide.
Diuretics that Inhibit Active Transport of Electrolytes In Proximal Part of Distal Convoluted Tubule. Diuretics of this type inhibit sodium reabsorption in the proximal part of distal convoluted tubules.
These diuretics are usually called thiazide and related diuretics. Examples:
- Chlorothiazide
- Metolazone
- Chlortalidone.
- Diuretics that Inhibit the Active Transport of Electrolytes in the Distal Part of the Distal Convoluted Tubule and Collecting Duct
- Some of the diuretics inhibit the reabsorption of sodium and excretion of potassium in the distal portion of the distal convoluted tubule and collecting duct.
Such substances are called potassium-retaining diuretics or potassium-sparing diuretics which are:
- Triamterene
- Amiloride.
3. Diuretics Which Inhibit the Action Of Aldosterone: Some diuretics inhibit sodium reabsorption and potassium excretion in the distal convoluted tubule and collecting duct by inhibiting the action of aldosterone.
These substances are also called potassium-retaining diuretics or ajocAv-rone antagonists. Examples:
- Spironolactone
- Everyone
4. Diuretics Which Inbiht The Activity Of Carbonic Anhydrase
- Some diuretics inhibit the activity of carbonic anhydrase in proximal convoluted tubules and prevent the reabsorption of bicarbonates from renal tubules resulting in osmotic diuresis.
- Such diuretic agents are called carbonic anhydrase inhibitors. Acetazolamide is a carbonic anhydrase inhibitor.
5. Diuretics That Increase Glomerular Filtration Rate: Some xanthines (alkaloids used as mild stimulants) cause diuresis by increasing the glomerular filtration rate and to some extent by decreasing the sodium reabsorption.
Diuretic xanthines are:
- Caffeine
- Theophylline
6. Diuretics Which Inhibit the Secretion Of Adh: Some diuretics produce diuresis by inhibiting the secretion of ADH.
The inhibitors of ADH secretion are:
- Water
- Ethanol.
7. Diuretics Which Inhibit Adh Receptors: The antagonists of V2 receptors cause diuresis by inhibiting the receptors of antidiuretic hormone thereby preventing the activity of this hormone.
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