Major functions of nephron segments

Reabsorbs isosmotically 60 to 65 percent of the filtered NaCl and H2O

Reabsorbs 90 percent of the filtered HCO3-

Major site of ammonia production in the nephron

Reabsorbs almost all of filtered glucose and amino acids

Reabsorbs K+, phosphate, calcium, magnesium, urea, and uric acid

Secretes organic anions (such as urate) and cations (such as creatine); this pathway is also used for excretion of protein-bound drugs and toxins

Reabsorbs 25 to 35 percent of filtered NaCl

Countercurrent multiplier as NaCl reabsorbed in excess of water

Major site of active regulation of magnesium excretion

Reabsorbs about 5 percent of filtered NaCl but almost no water

Major site, with connecting segment, of active regulation of calcium excretion

Principal cells reabsorb Na+ and Cl- and secrete K+ under the influence of aldosterone

Intercalated cells secrete H+, reabsorb K+, and, in metabolic alkalosis, secrete HCO3-

Reabsorb water in the presence of antidiuretic hormone

Site of final modification of the urine

Reabsorb NaCl, the concentration of which can be reduced to less than 1 meq/L

Reabsorb water and urea relative to the amount of antidiuretic hormone present, allowing a concentrated or dilute urine to be excreted

Secrete H+ and NH3; urine pH can be reduced to as low as 4.5 to 5.0

Can contribute to potassium balance by reabsorption or secretion of K+