Anatomy and Basic Physiology

What are the 3 major functions of the kidneys?

Fluid/acid-base/electrolyte homeostasis; waste excretion; endocrine production

What endocrine products are made by the kidneys?

1,25-dihydroxy vitamin D; renin; erythropoietin

How much water do adult glomeruli filter per day?

~180 L/day

What fraction of filtered water is normally excreted?

~1%

What fraction of filtered Na+ is normally excreted?

~0.5% to 1%

Normal filtration fraction?

~20%

What is Bowman space?

Potential space around glomerular capillary tuft that receives filtrate

What is the blood flow sequence through the nephron?

Afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries/vasa recta

What cells are the specialized epithelial cells of the glomerulus?

Podocytes

What makes up the glomerular filtration barrier?

Endothelium; glomerular basement membrane; filtration slits between podocytes

What normally crosses the glomerular filter?

Water; electrolytes; glucose; amino acids; lactate; urea

What normally does not cross the glomerular filter?

Blood cells; most large proteins

Which nephron segment does the bulk of reabsorption?

Proximal tubule

How much filtrate is reabsorbed by the proximal tubule?

~65% to 70%

What are the 3 segments of the proximal tubule?

S1; S2; S3

Main role of the thin limb of the loop of Henle?

Maintains corticomedullary concentration gradient

Main role of the thick ascending limb?

Urine dilution/concentration; Na+; Ca2+; Mg2+ handling

What does the distal convoluted tubule reabsorb?

Na+ and Ca2+

Which nephron segments fine-tune water, urea, K+, and H+ handling?

Distal nephron and collecting ducts

Why is sodium reabsorption considered the kidney's most important role?

Maintains cardiac preload and cardiac output

How is proximal tubular Na+ reabsorbed paracellularly?

Hydrostatic and oncotic pressure forces

How is proximal tubular Na+ reabsorbed transcellularly?

Na+-H+ exchanger

Which hormone stimulates the proximal tubular Na+-H+ exchanger?

Angiotensin II

What mainly controls distal tubular sodium transport?

Aldosterone and kinases

What creates dilute tubular fluid?

Ascending limb reabsorbs solute without water

What happens to aquaporins when ADH is suppressed?

They disappear from the collecting duct

What is the effect of ADH on the collecting duct?

Aquaporin insertion → water reabsorption

Which ions are secreted by the distal nephron under aldosterone?

K+ and H+

Which hormones regulate Ca2+ and phosphate balance?

PTH; activated vitamin D; FGF23

What kinds of substances can renal tubules secrete?

Drugs; diuretics; uric acid; organic anions