PHYSIO FINAL: Renal Pt. 2

What is reabsorbed by the DCT and collecting duct?

• Water

• Na+

• Ca++

What regulates water reabsorption in the DCT and collecting duct?

• Antidiuretic hormone

• ADH

What regulates Na+ reabsorption in the DCT and collecting duct?

• Aldosterone

• Atrial natriuretic peptide (ANP)

What regulates Ca++ reabsorption in the DCT and collecting duct?

• Parathyroid hormone

• PTH

List of hormones that regulates reabsorption in DCT and collecting ducts

• Aldosterone

• ANP (atrial natriuretic peptide, ANP)

• ADH (antidiuretic hormone, ADH)

• PTH (parathyroid hormone, PTH)

What leads to increased renin?

• Decreased Na+

• Increased K+

• Decreased BP

What does increased renin lead to?

Increased aldosterone

What does aldosterone do?

• Promotes Na+ reabsorption and K+ secretion in DCT and collecting duct

  • Insertion of sodium-potassium pumps on basolateral membrane

What does aldosterone lead to?

• Increased plasma N+ and decreased K+

  • Water reabsorption increases

  • Decreases urine output

• Increased BV and BP

What does ANP lead to?

• Released due to high blood volume and pressure

• Antagonizes aldosterone

• Decreases Na+ reabsorption by collecting ducts

• Decreased plasma Na+

• Decreased water reabsorption

• Decreased blood pressure

What is another name for ADH?

Vasopressin

What causes an increase in ADH release?

• Increased plasma osmolarity

• Increased plasma Na+

• Decreased BV

What does ADH do?

• (Collecting ducts are relatively impermeable to water without ADH)

• Promotes water reabsorption in collecting duct via insertion of aquaporins

What does ADH lead to?

• Results in scant (small amounts) urine and increases blood volume

  • Urine is concentrated

Affect of Diuretics on ADH

• Cause diuresis (enhanced urine output)

• Block ADH

  • Alcohol, caffeine, osmotic diuretics

What does PTH do?

• Increases Ca2+ reabsorption by DCT (has other actions as well)

• Increased Ca++ plasma levels

Summary of tubular reabsorption

• Reabsorption by PCT

  • Water, ions, glucose, AA, vitamins, HCO3-, urea

• Reabsorption by LOH

  • D Loop: Water

  • A Loop: Na+, Cl-

• Reabsorption by DCT and collecting tubules

  • Water (ADH)

  • Na+ (Aldosterone)

  • Ca++ (PTH)

Tubular Secretion

• Selectively moves substances from blood to filtrate in renal tubules and collecting ducts

• Active transport from blood into lumen of PCT, DCT, or collecting ducts

Purpose of tubular secretion

• To rid the body of substances that:

  • Were not initially filtered in the capsule

  • Are in excess

What are the most important substances secreted?

• H+ ions

• K+ ions

• Substances (both foreign and non-foreign) too big to cross filtration membrane: Hormones, Drugs, Food additives (penicillin, saccharin, eg.)

Where does secretion of H+ occur?

Mostly PCT

What happens if ECF [H+] is too high (low plasma pH)?

• H+ secretion increases

• Increased HCO3- reabsorption

• Leads to decreased H+ in blood and increased plasma pH

What happens if ECF [H+] is too low (high plasma pH)?

• H+ secretion deceases

• Decreased HCO3- reabsorption

• Leads to increased H+ in blood and decreased plasma pH

What is the secretion of H+ important for?

Acid-base balance

K+ Secretion

• Usually most filtered K+ is reabsorbed

• However, if L+ is elevated in ECF, K+ is secreted via aldosterone

DRAW ON DIAGRAM OF NEPHRON THE DIRECTION IN WHICH PROTONS AND POTASSIUM MOVE AND WHERE

Pls.

What is the goal of regulation of concentration and volume of urine?

Keep total body water (TBW) constant

• Maintains osmolarity and BP

Mechanism of regulation of concentration/volume or urine

• Kidneys produce dilute urine if there is excess water

• Kidneys produce concentrated urine when we need to retain water

How is dilute urine made?

• Overhydration

• Leads to decreased ADH

• Water not reabsorbed from collecting duct

  • Large volume of dilute urine is excreted

How is concentrated urine made?

• Dehydration

• Leads to increased ADH

• Water is reabsorbed from collecting duct

  • Small volume of concentrated urine is excreted