Sweep 1.3 Flashcards by Tyler Brown

Reabsorption in the proximal tubule

1. Glucose and amino acids are rebsorbed with

Na+ using symporters

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Reabsorption in the proximal tubule

2. Active transport on ——–, keeps intracellular —– low

basal side

Na+

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Reabsorption in the proximal tubule

3. Water (and solutes) move via ——–; keeps the osmolarity of the tubular fluid —-

paracellular transport

constant

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Reabsorption in the proximal tubule

4. Na+ reabsorption also occurs in conjunction with bicarbonate reabsorption using a ———-

Na+/H+ antiporter

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reabsorption is not direct……

H+ secretion = HCO3- reabsorption

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To summarize: by the end of the proximal tubule –

K+ and divalent cations reabsorbed by solvent drag

bicarbonate reabsorbed due to activity of Na+ / H+ transporter

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In the ascending thick limb (ATL; see diagram at right), fluid is diluted via

Na+ K+ 2Cl- symporter in apical membrane

Na+ K+ ATPase in basolateral membrane

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ascending thick limb

paracellular transport of monovalents and divalents NOT due to

solvent drag. Tubular fluid becomes positive when Cl- reabsorbed so cations diffuse along an electrical gradient

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ATL
Fluid leaving loop is ——–, but the renal countercurrent mechanism has established an osmotic gradient required for formation of hyperosmotic urine. Concentration of the tubular fluid will occur in the collecting duct if antidiuretic hormone (ADH/vasopressin) is present.

hyposmotic

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More NH4+ can be added to the urine by diffusion trapping.

Much of the NH4+ leaving the proximal tubule is

reabsorbed by the ascending limb of the loop of Henle

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More NH4+ can be added to the urine by diffusion trapping.

NH4+ substitutes for———- and enters the interstitial fluid in the ——— where it is in equilibrium with NH3

K+ in the Na+K+2Cl- symporter

medulla

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NH4+ is produced in the ———- by metabolism of glutamine. The NH4+ that is produced is transported into the ———– and the HCO3- moves into blood.

proximal tubules

tubular fluid

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The peritubular capillaries are permeable to ——- so plasma osmolarity changes as the

NaCl and water

capillaries follow the loop, but the osmolarity of the blood leaving the kidney (to veins) is normal.

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The initial segment of the distal tubule, reabsorbs ~8% of filtered NaCl via a————- and———–

Na+ Cl- symporter in apical membrane

Na+ K+ ATPase in basolateral membrane

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There are two cell types in the collecting duct and late distal tubule

principal cells have

epithelial sodium channels (ENaC) that reabsorb Na+ and secrete K+

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There are two cell types in the collecting duct and late distal tubule

Principal cells
K+ secreted due to

Na+ K+ ATPase activity in basal membrane

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Principal cells

Na+ reabsorption drives

paracellular Cl- reabsorption

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There are two cell types in the collecting duct and late distal tubule

intercalated cells involved with acid-base balance; can also

reabsorb K+

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Hormonal regulation of blood volume -

ADH

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Actions of ADH
increases the permeability of the late ———— to water by increasing ——— into the apical membrane (basolateral membrane is freely permeable to water)

distal tubule and the collecting duct

aquaporins

ADH

also increases permeability of

medullary collecting duct to urea

ADH

If ADH low (diuresis) –

solutes reabsorbed in distal tubule and collecting duct, but no water reabsorption; urine as dilute as 50 mOsm/kg H2 O 18L pee

If ADH high (antidiuresis) –

water reabsorbed as fluid passes through collecting duct; urine can be concentrated up to 1200 mOsm/kg H2O ½ L pee

Alcohol inhibits

ADH secretion**

How the system works….. | renin released in response to a drop in

perfusion pressure, decreased NaCl delivery to macula densa, or sympathetic input to juxtaglomerular cells

aldosterone from the adrenal cortex acts to increase ------------ in the distal tubule and collecting duct by increasing ------------

NaCl reabsorption transport protein synthesis

Natriuretic peptides are hormones secreted when the

heart dilates (during volume expansion)

Natriuretic peptides

Atrial natriuretic peptide from the atria Brain natriuretic peptide from the ventricles (first found in brain)

The effects of natriuretic peptides include

vasodilation of afferent arterioles vasoconstriction of efferent arterioles inhibition of renin (and aldosterone) inhibition of ADH secretion

Natriuretic peptide | Net effect is to increase the

excretion of NaCl and water.

Why is potassium regulation important? hyperkalemia will

depolarize Vm

hypokalemia will

hyperpolarize Vm

In the thick ascending limb have reabsorption of K+ by

Na+K+2Cl- symporter and paracellular transport (non-solvent drag)

In the late distal tubule and collecting duct | K+ secreted by

principal cells depending on ATPase activity, K+ gradient, and/or apical K+ permeability

Late distal tubule and collecting duct ---------------- reabsorb K+ when potassium is depleted

intercalated cells

Cells of the proximal tubule detect -------- can alter ------------ accordingly.

intracellular pH and CA activity

Factors affecting excretion of potassium include plasma [K+] - increased K+ stimulates

aldosterone release, and aldosterone increases Na+ K+ ATPases in principal cells

Factors affecting excretion of potassium include | flow rate of tubular fluid –

increased flow rate increases K+ secretion | -local response to bending of cilia

↑ flow -----> ↑ ------ in collecting duct ---> ↑ ----- reabsorption -----> favors ↑ ---------

Na+ Na+ K+ secretion

nonvolatile acids | must be neutralized with

HCO3-

nonvolatile acids --------- within tubular cells eliminates H+ and produces an HCO3- that is reabsorbed

ammonium production

Bicarbonate reabsorption begins in the ---------, and ----- of filtered HCO3- is reabsorbed here.

proximal tubule 80%

CA activity in the tubular epithelium produces H+ and HCO3- H+ is secreted via ---------- also have ------------ operating to secrete H+ (not illustrated)

Na+ / H+ antiporter H+ ATPase pumps and H+/K+ ATPase pumps

HCO3- is transported/reabsorbed across

basolateral membrane

In the late distal tubule and the collecting duct CA activity in the --------- cells produces bicarbonate and H+

intercalated

Intercalated cells | H+ is secreted via an

H+ ATPase pumps and an H+/K+ ATPase pump (not illustrated)

A less common type of intercalated cell reverses the position of the

H+ and HCO3- transporters to the basolateral and apical membranes, respectively. These cells reabsorbs H+ and secretes HCO3- ; activity of this cell type is normally very low.

If the body is alkaline, the kidney must produce alkaline urine which requires

incomplete reabsorption of HCO3- (figure on right) | increase excretion of HCO3- by not neutralizing all the HCO3- that is in the tubular fluid