(Slides 21-28) Tubular Reabsorption & GFR regulation

What occurs in the proximal convoluted tubule?

• Secretion

  • Urea

    Uric acid

    Creatinine

    Some drugs

• Reabsorption

  • Glucose

    Amino acids

    Protein

    Vitamins

    Lactate

    Urea

    Uric acid

What occurs in the distal convoluted tubule?

• Secretion

  • Urea

  • Amino Acid

  • Uric Acid

• Reabsorption

  • Glucose

  • Lactate

  • Urea

  • Uric Acid

What occurs in the descending loop of henle?

Reabsorption

• Water

What occurs in the ascending loop of henle?

• Secretion

  • Urea

• Reabsorption

  • Glucose

  • Amino Acid

  • Lactate

Which part of the tubule does reabsorption occur the most?

Proximal convoluted tubule

What are things we 100 percent reabsorb in the PCT?

• Glucose

  • unless person is diabetic

• Oligopeptides

• Proteins

• Amino Acids

• Vitamins

• Lactate

What are things we 100 percent secrete?

• Creatinine

• H+ (Hydrogen Ion)

• NH4+ (ammonia)

• Some drugs

We secrete and reabsorb what things depending on what the body needs?

• Sodium

• Chloride

• Water

• HCO3- (Bicarbonate)

• Potassium

• Calcium

• Magnesium

• Phosphate

What only reabsorbs water?

Descending loop of henle

• ocassional urea

What only reabsorbs ions like:

• Na+

• Cl-

• Mg

Ascending loop of henle

What ion is 50/50 with reabsorption and secretion?

Urea

• 50% stays in the tubule → becomes urine

• 50% is reabsorbed → used to maintain medullary gradient

What are the two major categories that regulate Glomerular Filtration Rate?

• Renal autoregulation (intrinsic)

• Neural/hormonal control (extrinsic).

What is the purpose of Glomerular Filtration Rate regulation?

To keep GFR stable when blood pressure changes

What is renal autoregulation?

The kidney’s intrinsic ability to maintain constant GFR despite changes in systemic blood pressure.

What are the two mechanisms of renal autoregulation?

• Myogenic response

• Tubuloglomerular feedback.

What are intrinsic controls?

Process within the kidney that change GFR

What are extrinsic controls?

Processes outside the kidney that change GFR.

Neural and hormonal control: Extrinsic controls involve?

Physiologic processes to change GFR

What happens to GFR with extensive sympathetic stimulation?

GFR decreases.

What are two hormones that contribute to regulating GFR?

• Angiotensin ll

• Atrial natriuretic peptide (ANP)

What does angiotensin II do to the arterioles?

Constricts both afferent and efferent arterioles.

• decreases GFR

What does ANP do to mesangial cells?

Relaxes them

• increases GFR

When mesangial cells are relaxed their filtration surface area?

increases

What is the myogenic mechanism?

Increased BP → stretches afferent arteriole → afferent arteriole constricts

→ restores GFR

What is the tubuloglomerular feedback?

Macula densa on DCT monitors tubular fluid and signals juxtaglomerular

cells (smooth muscle, surrounds afferent arteriole) to constrict afferent

arteriole to decrease GFR.

• RAA pathway

What happens to ATP/adenosine when GFR increases?

They increase.

What do ATP and adenosine do to the afferent arteriole?

Cause vasoconstriction.

What is the effect of ATP/adenosine on GFR?

Vasoconstriction slows GFR.

What happens to NO when GFR increases?

NO increases.

What does NO do to the afferent arteriole?

Causes vasodilation.

What is the effect of NO on GFR?

Vasodilation increases GFR.

What happens to NO when GFR decreases?

NO decreases → vasoconstriction → GFR decreases further.

Why does sympathetic stimulation decrease GFR?

Constricts afferent arteriole to preserve blood volume and BP.

What tubules does aldosterone act?

Collecting tubule and collecting duct.

What does aldosterone do in Collecting tubule and collecting duct?

• ↑ NaCl reabsorption

• ↑ water reabsorption

• ↑ K⁺ secretion

• ↑ H⁺ secretion.

What tubule does angiotensin II act?

PCT, thick ascending limb, DCT, collecting tubule.

What does angiotensin II do in the PCT, thick ascending limb, DCT, collecting tubule.?

• ↑ NaCl and water reabsorption

• ↑ H⁺ secretion.

What tubules does ADH act?

DCT and collecting duct.

What does ADH do in the DCT and collecting duct.?

↑ water reabsorption.

What tubules does ANP act?

DCT and collecting duct.

What does ANP do in the DCT and collecting duct.?

↓ NaCl reabsorption.

Where does PTH act in the tubule?

PCT, thick ascending limb, DCT.

What does PTH do in the PCT, thick ascending limb, DCT.?

• ↓ phosphate reabsorption

• ↑ calcium reabsorption.

Water always follows?

Salt