9.3:
Antihypertensive Drugs: Action of Diuretics
When the glomerular filtrate passes through the renal tubule, sodium ions are reabsorbed into the blood through ion transporters that are expressed across the tubule.
This reabsorption of ions is vital for overall body function. However, excess sodium in the blood can lead to water retention, resulting in expanded blood volume and increased blood pressure.
Diuretics inhibit the renal ion transporters, preventing the reabsorption of Na+.
This increases urine output, facilitating the elimination of water and sodium ions from the body and reducing the overall blood volume.
The decrease in blood volume lessens the pressure exerted on the arterial walls, leading to a drop in blood pressure.
In most patients, diuretics effectively reduce systolic blood pressure by 10–15 mmHg, serving as a standalone treatment for mild to moderate hypertension.
However, they may have several side effects, including hyperuricemia, which causes elevated uric acid levels.
Accumulation of insoluble uric acid crystals in the joints leads to painful gouty attacks with swelling and redness.
9.3:
Antihypertensive Drugs: Action of Diuretics
Diuretics are antihypertensive drugs used to treat hypertension resulting from sodium and water retention. Sodium, vital for fluid balance and nerve or muscle function, is regulated by the kidneys through millions of nephrons. Blood enters nephrons via afferent arterioles, which branch into capillaries called glomeruli. These filter blood plasma, allowing water and solutes, like sodium ions, to pass through capillary walls into Bowman's capsule. The filtrate then flows through various tubules and the collecting duct. Solutes and water are selectively reabsorbed or secreted throughout this journey using passive and active transport mechanisms. This maintains optimal sodium levels. However, excessive sodium intake or impaired renal excretion can raise sodium concentration in the bloodstream, triggering osmosis and water retention, thereby increasing blood volume and pressure on vessel walls. Diuretics control this pressure by inhibiting ion transporters, promoting sodium and water excretion through increased urine output. This reduces arterial wall pressure and blood pressure. Diuretics effectively decrease blood pressure by 10-15 mmHg in most patients, serving as a standalone treatment for mild to moderate hypertension. However, they may cause side effects like hyperuricemia, characterized by elevated uric acid levels, leading to gout attacks with pain, swelling, and redness.