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test 5 > Lecture 45 Tubular Mechansim II > Flashcards

Lecture 45 Tubular Mechansim II Flashcards

1
Q

What is simple diffusion?

A

Net movement represents molecules or ions moving down their electrochemical gradient, it does not require ATP

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2
Q

what is facilitated diffusion?

A

molecule or ion moving across a membrane down its concentration gradient, attached to a specific membrane bound protein
does not require energy

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3
Q

what is active transport?

A

protein mediated transport that uses ATP as a source of energy to move molecules or ions against its electrochemical concentration gradient

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4
Q

what is the difference between simple diffusion and facilitated diffusion?

A

facilitated requires a transporter, and relies on the amount of transporter and concentration of solute.. they reach a vmax if all available transporters are taken… to increase after vmax need more transporters

simple diffusion does not require a transporter so the line on the graph just increase

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5
Q

What is the difference between primary and secondary transport?

A

primary: ATP is consumed directly by the transporting protein ( Na/K atpase pump)
secondary: active transport depends indirectly on ATP as a source of energy ex Na-glucose symporter. this process depends on the concentration gradient for sodium allowing glucose to move.

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6
Q

What is the filtered load?

A

the amount of any substance that filters from the glomerulus and enters the bowman’s space per unit time

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7
Q

PCT- Sodium ( Na+) reabsorption

2/3 (67%) of the filtered sodium is reabsorbed in the proximal tubule by what?
The _______ creates the gradient for sodium entry into the cell and its removal from cell back into the bloodstream.

what stimulates the basolateral atpase and enhances the fraction of sodium reabsorbed in the proximal tubule?

A

SGLT and NHE transporters

basolateral Na/K ATpase

catecholamines and angiotensin II

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8
Q

PCT- water and electrolytes reabsorption

Proximal tubules have a high permeability for water and about 2/3 of the filtered water, potassium, and chloride follow ______.

why does the chloride concentration rise slightly through the proximal tubule?

Osmotic flow of water in the proximal tubules occurs through tight junctions between epithelial cells ________ pathway. and through the cells _____ pathway.

A

sodium

large percentage of bicarbonate is reabsorbed

paracellular, transcellular

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9
Q

PCT- Urea Reabsorption

what is BUN?

what does increased BUN cause?

As water is reabsorbed from the tubule, urea concentration in the tubule _________

This creates a concentration gradient favoring passive urea reabsorption _______.

A

blood urea nitrogen levels, ( urea is excreted form the body it is a nitrogenous waste. these levels can indicate renal health)

gout

increases

paracellularly.

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10
Q

All filleted glucose in the kidney is reabsorbed where?

via what kind of transport ?

Glucose molecules are recovered from the EARLY PCT by _______ transporter and from the LATER PT by the _______ transporter.

Glucose uptake by the epithelial cells generates a concentration gradient that drives facilitated diffusion via _____ and ______ transporters in the PCT and PST respectively.

A

the proximal tubule
secondary active transport linked to sodium

SGLT2, SGLT1

GLUT2 and GLUT 1

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11
Q

the apical surface of the proximal tubule contains two peptide transporters what are they?

what degrades these peptides

defects in the pathways can lead to what?

What should the concentration of glucose and amino acids leaving the PCT be?

A

PepT1 and PEPt2 ( they are H+ peptide transporters that transpire dipeptides and tripeptides)

peptides are degraded inside the cell by proteases and transported to the blood as free amino acids.

proteinuria

0

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12
Q

filtration of glucose is _______ to the plasma concentration. Filtration does not saturate.

Reabsorption of glucose is proportional to the plasma concentration until____ is reached.

glucose excretion is ____ until the ____ is reached.

what is renal threshold?

A

proportional
transport maximum ( Tm)
0, renal threshold

plasma concentration at which saturation occurs

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13
Q

the presence of unrecovered glucose within the renal tubule lumen causes osmotic diuresis as ______

A

polyuria ( diabetes mellitus has polyuria too)

urine output of more than 3 L per day

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14
Q

what occurs to PH when you excrete HCO3?

HCO3- is anionic and cannot be diffused freely through the membrane. what does the body do to solve this?

A

the ECF becomes acidic.

  • the proximal tubule secretes equal amounts of H+ to turn HCO3 into H2CO3 via carbonic anhydrase it is then converted to CO2 and H2O. the molecule is recovered by diffusion.

The proximal tubule also actively secretes H+ into the tubule using a H+ pump. it is a V-type H+ pump ( V-type H+ ATPase)

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15
Q

what stimulates the Na+/H+ antiport?

A

angiotensin II

in volume depleted states, the amount of bicarbonate reabsorption in the PCT increases

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16
Q

Generalized reabsorption defects in PCT because of hereditary defects nephrotoxins, lead poisoning do what?

A

increase excretion of amino acids, glucose, HCO3, PO4 and all substances reabsorbed by the PCT..

this may lead to metabolic acidosis hypophosphatemia and osteopenia

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17
Q

what is glomerulartubular balance?

what does this do?

A

when the proximal collecting tubule recaptures filtered sodium

capturing this sodium helps protect the extracellular volume despite any changes that may occur in GFR.

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18
Q

what is the most important driving force for reabsorption in the PCT?

A

peritublar capillary oncotic pressure (piC)

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19
Q

what do diuretics do?

A

they inhibit sodium reabsorption which increases sodium concentration in the lumen and more water remains in the lumen for excretion

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20
Q

if kidney excretes sodium what else is excreted?

A

aguaaaa

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21
Q

Why would you use diuretics for an individual with edema and hypertension?

A

reduce extracellular fluid volume

22
Q

What is Acetazolamide used for? what is the mechanism?

A

it is a carbonic anhydrase inhibitor, it reduces bicarbonate reabsorption and the activity of the Na/H+ antiporter in the Proximal convoluted tubule

this is a diuretic..

sodium remains in the lumen and therefore water does too so it is excreted in the urine

used in the treatment or prophylaxis of altitude sickness where urinary bicarbonate excretion is helpful to offset acute respiratory alkalosis, it is also used to reduce intraocular pressure associated with glaucoma

23
Q

Thin descending segment of the loop of henle is _____ to water and ________ to solutes

A

permeable to water ( water leaves)

impermeable to solutes

24
Q

The thin ascending segment is ______ to water

A

impermeable

25
Q

The thick ascending segment is _________ to water. what happens to solutes here?

A

impermeable to water
solutes come out at this point.
sodium, potassium and chloride are absorbed.

26
Q

How does reabsorption work in the thick ascending segment of the loop of Henle?

A

Na/k Atpase pump creates a relative Na+ deficiency in the cell. it provides a favorable gradient for movement of Na+ across the luminal surface into the cell via Na/Cl/K cotransporter

  • low intracellular Na+ concentration also drives Na/H+ antiport causing H+ secretion and bicarbonate absorption.
  • K + channel of the luminal membrane causes diffusion of K+ back into the lumen and creates a positive luminal potential, promotes Na+ Ca2+ and Mg2+ reabsorption via paracellular pathway.
27
Q

what do loop diuretics do the the Na/CL/K cotransporter in the luminal membrane?

A
  • they block it and there is increased urine output of sodium, chloride and potassium and other electrolytes as well as water.
  • explosive increase in urine flow because this nephron segment usually reabsorbs 20-25% of filtered Na..

loop diuretics are useful when rapid diuresis is needed like in pulmonary edema.

examples of drugs: Furosemide, Ethacrynic acid, Bumetanide

  • loop diuretics can cause hypocalcemia
28
Q

Describe early distal tubule reabsorption

A

early distal tubule reabsorbs Na, Cl, and Ca. Na/K Atpase creates a low intracellular concentration NaCl crosses the apical membrane via a Na/Cl symporter.

Chloride diffuses out of the cell into the renal interstitial fluid through chloride channels in the basolateral membrane

This segment is impermeable to water— osmolalility decrease further.

29
Q

The ultrafiltrate in the early distal tubule has the ________ osmolality of the entire nephron.

A

lowest

30
Q

What is the job of parathyroid hormone in the early distal tubule ?

Calcium is actively extruded into the peritubular fluid via__________.

Calcium binding protein ______ facilitates calcium reabsorption.

Calbindin synthesis is increased by the active form of vitamin ____, therefore enhances PTH’s action on the distal tubule

A

lumen Ca2+ enters the cell passively through calcium channels by parathyroid hormone ( PTH)

Ca2+- Atpase or 3 Na/Ca2+ antiporter

calbindin

vitamin D

31
Q

What is a mutation of Na-Cl cotransporter?

A

salt wasting ( Gitelman’s syndrome). causes hypocalcuria and is the result of increased Ca2+ reabsorption in the distal nephron.

32
Q

What do thiazide diuretics do?

A

inhibit the Na-Cl symporter in the distal tubule and are widely used to treat hypertension and heart failure.

Thiazides are less potent than loop diuretics since a lower proportion of the filtered NaCl load is reabsorbed in the distal tubule compared to the loop of Henle.

33
Q

Why would thiazide diuretics lead to hypercalcemia?

A

inhibiting Na+ influx causes the DCT epithelial cell hyperpolarizatoin which increases the electrochemical gradient driving Ca2+ reabsorption resulting in hypercalcemia.

loop diuretics cause hypocalcemia

34
Q

what do principal cells do?

A

they reabsorb sodium and secrete potassium

35
Q

Principal cells of late distal tubule and collecting ducts:

luminal membrane contains sodium channels called ______,( influx or eflux) of sodium down its concentration gradient created by Na/K ATPase.

some chloride does not follow sodium creating a negative luminal potential causing potassium secretion.

________ activates the mineralocorticoid receptor on these cells having the following effects:
1.
2.
3.

what are they?

A

Enac

influx

Aldosterone

effects are

  1. increasing luminal Enac channels
  2. increase Enac opening time
  3. stimules/ augments Na/K ATpase
36
Q

over secretion of ADH results in the ___________.

A

Syndrome of Inappropriate Antidiuretic Hormone

37
Q

Principal cells express aquaporins which are are regulated by _________.

A

anti-diuretic hormone (ADH)

38
Q

ADH acts on ____ receptors to cause insertion of aquaporins which in turn cause water reabsorption.

A

V2

39
Q

is the medullary or the cortical collecting duct permeable to urea due to special transporters.

A

medullary collecting duct is permeable to urea with special urea transporters= facilitates urea diffusion across the luminal and basolateral membranes

40
Q

where are H+- ATPase found?

A

intercalated cells

41
Q

Intercalated cells:
Luminal membrane contains _____ which pumps H+ into the lumen. Most of the H+ is eliminated from the body via ___________.

H+ pumped into the lumen binds to prostate to form deprotonated phosphate which _____ reabsorbs, thus elminating H+.

When H+ combines with ammonia it forms __________ which is ________ reabsorbed and is excreted. for every H+ excreted by these buffers, bicarbonate is added to the body.

___________ stimulates H+-ATPase of intercalated cells and excess of this causes _____________.

A

H-ATPase
buffers, phosphate, ammonia

poorly

ammonium, poorly

aldosterone, Metabolic Alkalosis.

42
Q

How do sodium channel blockers and aldosterone antagonists work?

A

they reduce Na+ reabsorption so K+ secretion diminished and decreases urinary excretion of K+ and act as K+ sparing diuretics.

K+ sparing agents have a weak diuretic effect because less than 5% of the filtered Na is reabsorbed at this site.

43
Q

A tumor of the adrenal cortex can be treated with _________. this person has ________ syndrome.

A

spironolactone
Conn’s ( hyperaldosteronism)

this person can present with hypertension
( high plasma Na+), hypokalemia ( less plasma K+), and metabolic alkalosis ( plasma HCO3-)

44
Q

potassium sparing diuretics work by:
1.
2.
3.

what are examples of them aldosterone antagonists and Na+ blockers:

A
  1. Blocking Enac channels
  2. Blocking aldosterone receptors
  3. Blocking the production of aldosterone

aldosterone antagonists: spironolactone, epieronone,

Na+ blockers: amiloride, Triamterene.

45
Q

What are the effects of aldosterone?

A 
( collecting tubule and duct)
increase NaCl
 H2o reabsorption 
 increase K+ secretion
increase H+ secretion
46
Q

What are the effects of angiotensin II?

A

Proximal tubule, thick ascending loop of Henle/ distal tubule, collecting duct)
increase NaCl
H20 reabsorption
increase H+ secretion

47
Q

what are the effects of antidiuretic hormone?

A

Distal tubule, collecting tubule and duct

increase H2O reabsorbtion

48
Q

what are the effects of atrial natriuretic peptide?

A

Distal tubule, collecting tubule and duct

decrease NaCl reabsorption

49
Q

What are the effects of parathyroid hormone?

A

decrease PO4 reabsorption

increase Ca reabsorption

50
Q

_______ can be used to read head injuries to reduce intracranial pressure by producing a fluid shift out of the brain

A

mannitol

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