5 - Renal Tubular Transport 2 Flashcards
(30 cards)
What is responsible for regulation of tubular reabsorption?
Neuronal, hormonal, and physical factors alter tubular fluid and solute reabsorption.
What effect can a change in the filtration fraction in the glomerular capillaries of change in vascular resistance un the upstream segments of the renal arterial vasculature have?
These will alter the postglomerular plasma oncotic pressure and the peritubular capillary hydrostatic pressure, which will alter the rate of fluid reabsorption in the capillary bed.
What is backleak?
Alterations in physical factors such as hydrostatic and oncotic pressure that alter the tubular reabsorption of fluid and solute.
What effect does Aldosterone have on tubular reabsorption? Where does it act?
Acts in principal cells of late distal tubule and collecting duct.
Increases Na+ reabsorption and K+ secretion.
What effect does angiotensin II have on tubular reabsorption? Where does it act?
Acts primarily in the PT.
Increases Na+ and water reabsorption, increases H+ secretion.
What effect does antidiuretic hormone (vasopressin, ADH) have on tubular reabsorption? Where does it act?
Acts in principal cells of the late distal tubule and collecting duct, inner medullary collecting duct.
Increases water reabsorption.
What is the effect of Atrial natriuretic peptide (ANP, ANF) on tubular reabsorption? Where does it act?
Acts in the distal tubule and collecting duct.
Decreases Na+ reabsorption.
What is the effect of parathyroid hormone (PTH) on tubular reabsorption? Where does it act?
In PT: decreases PO43-
reabsorption.
In thick ascending loop of henle and distal tubule: increases Ca++ reabsorption.
What is the pattern of calcium reabsorption in the kidneys?
The percentage of filtered calcium that’s reabsorbed follows the same pattern as sodium.
How is calcium reabsorbed in the PT, thick ascending loop of henle, and the early distal tubule?
PT: mainly paracellular, not under hormonal control, largely parallels Na reabsorption.
Thick ascending: mainly paracellular, stimulated by PTH.
Early distal tubule: Distal tubular mechanism stimulated by PTH.
What is the primary controller of calcium reabsorption?
PTH, regulated by plasma calcium, increases calcium reabsorption.
It acts mainly in the loop of henle and distal tubule to influence calcium.
Kidney plays important role in body’s compensation to decreased plasma calcium.
What are the compensatory responses to decreased plasma calcium concentration?
Increased PTH, which increases vit D3 activation which increases intestinal Ca2+ reabsorption, increased renal Ca2+ reabsorption, and increased Ca2+ released from bones.
What is the result of decreased calcium excretion?
Increased Parathyroid hormone, decreases extracellular fluid volume, decreased BP, increased plasma phosphate, metabolic alkalosis, and vitamin D3 activation.
What is the result of increased calcium excretion?
Decreased PTH, increased extracellular fluid volume, increased BP, decreased plasma phosphate, and metabolic acidosis.
How is phosphate handled by the kidneys?
It it not freely filtered b/c 10% of phosphate in plasma is protein bound.
80 % of filtered phosphate is reabsorbed in the PT via a Na/Pi co-transporter
20% reabsorbed in the distal tubule.
What is the renal overflow mechanism for phosphate?
The kidney will completely reabsorb the filtered phosphate if plasma phosphate concentration is less than 0.8 mM/L.
Kidney will excrete any phosphate above this threshold.
What causes increased urinary phosphate excretion?
Increased PTH, PO4 loading, ECV expansion, acidosis, and glucocorticoids.
What causes decreased urinary phosphate excretion?
Decreased PTH, PO4 depletion, ECV contraction, alkalosis, growth hormone.
What is the most important phosphate controlling hormone? How does it work?
PTH. It increases cAMP in the PT and inhibits reabsorption.
How do the kidneys handle magnesium? What percentage is protein bound? Where it is reabsorbed?
It is not freely filtered b/c ~50% of plasma magnesium is bound to protein.
30% filtered Mg reabsorbed in the PT
65% thick ascending limb
What is the mechanism by which Mg is handled by the kidneys? What increases Mg excretion?
Not well known.
Mg excretion increases in response to increased extracellular Mg, ECV expansion, and increased extracellular calcium.
Where is water reabsorbed in the kidneys?
65% PT: isosmotic reabsorption with Na and electrolytes.
20% loop
5% distal tubule (ADH)
9.5% collecting duct (ADH)
Why are the PT and thin descending loop of henle known as “leaky epithelia”?
They have a relatively low resistance across the tight junctions and these layers are highly permeable to water.
Here water is reabsorbed both paracellularly and transcellularly.
What portions of the nephron are impermeable to water?
Thin ascending loop, thick ascending loop, and the early distal tubule.
