Final answer:
Thiazide diuretics treat hypertension by inhibiting Na+/Cl- reabsorption in the DCT, increasing urine volume and reducing blood pressure, not by affecting contractility or immediately increasing GFR.
Step-by-step explanation:
Thiazide diuretics are medications used to treat hypertension by reducing blood volume and pressure. These diuretics inhibit the Na+/Cl- symporter primarily in the distal convoluted tubule (DCT) of the nephron. Consequently, this inhibition leads to increased excretion of sodium (Na+) and chloride (Cl-) ions, which in turn pulls water into the urine by osmosis, thus increasing urine volume and reducing blood volume. The result is a decrease in blood pressure, which makes thiazide diuretics effective antihypertensive agents. However, they are not effective in patients who are severely sodium-depleted because there is already less sodium present for the drugs to act upon. Thiazide diuretics' action is somewhat dependent on the acid-base balance and they do not immediately increase the glomerular filtration rate (GFR) or decrease blood pressure by affecting heart contractility.