Kidney Function and Regulation: Electrolytes, Hormones, and Nephron Segments

What is the primary function of the kidney in electrolyte regulation?

To regulate plasma levels of electrolytes, especially sodium.

What membrane protein creates the sodium gradient that drives reabsorption?

Na⁺/K⁺-ATPase located on the basolateral membrane.

How is water primarily reabsorbed in the kidney?

Secondarily to sodium reabsorption via osmosis.

At what parts of the nephron does regulated sodium/water reabsorption occur?

Late distal tubule and collecting duct.

What regulates afferent arteriole diameter?

Smooth muscle contraction/relaxation.

How does sympathetic activation affect the afferent arteriole?

Causes constriction, decreasing renal blood flow and GFR.

What is tubuloglomerular feedback?

Increased flow/NaCl to distal tubule causes afferent arteriole constriction and reduced GFR.

What is the normal GFR value?

120 mL/min.

How much sodium/water is reabsorbed in the proximal tubule?

~60%.

What transporters are key in the proximal tubule?

SGLT and sodium-hydrogen exchanger (NHE).

How much sodium/water is reabsorbed in the Loop of Henle?

~25%.

What major transporter is in the thick ascending limb?

Na-K-2Cl cotransporter.

How much sodium/water is reabsorbed in the distal tubule?

~10%.

What transporter functions in the distal tubule?

NaCl cotransporter.

What channels are regulated in the collecting duct?

ENaC (Aldosterone target) and Aquaporin (ADH target).

What triggers renin release?

Low blood pressure.

What does renin convert angiotensinogen into?

Angiotensin I.

What enzyme converts Angiotensin I to Angiotensin II?

ACE (Angiotensin-Converting Enzyme).

What are the effects of Angiotensin II?

Vasoconstriction and stimulates aldosterone release.

What does aldosterone do in the kidney?

Increases ENaC expression, increasing Na⁺ reabsorption and K⁺ secretion.

What is the main stimulus for ADH release?

Increased plasma osmolality.

What does ADH do in the kidney?

Inserts aquaporin channels in the collecting duct, increasing water reabsorption.

What percentage of potassium is inside cells?

Most of it (very high intracellular concentration).

What moves potassium into cells?

Insulin and epinephrine.

What relationship exists between H⁺ and K⁺?

Reciprocal; disturbances in H⁺ affect K⁺ movement and vice versa.

How is potassium handled in the proximal tubule?

Paracellular reabsorption.

What regulates potassium secretion in the distal nephron?

Aldosterone-mediated sodium reabsorption through ENaC.

What triggers PTH secretion?

Low plasma calcium.

What are PTH's effects on the kidney?

Increases calcium reabsorption, decreases phosphate reabsorption, and activates vitamin D.

How does vitamin D affect calcium?

Increases intestinal absorption of calcium.

What hormone lowers blood calcium?

Calcitonin.

What is the relationship between calcium and phosphate regulation in the kidney?

Reciprocal; when calcium reabsorption increases, phosphate is excreted.