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(LUSUMA) Urinary System > S4) Basic Renal Processes > Flashcards

S4) Basic Renal Processes Flashcards

1
Q

Which ion is transport together with Na+?

A

Cl-

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2
Q

How much sodium is reabsorbed in the kidney?

A

Up to ~99% Na+ ions, Cl- ions and H2O are reabsorbed in kidney

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3
Q

Sodium reabsorption varies with the ingestion of sodium.

Why?

A

The kidney needs to match excretion of sodium to ingestion to remain sodium balance

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4
Q

What happens if the amount of Na+ ions in ECF changed due to diet changes?

A

⇒ Amount of water in the ECF would change

⇒ ECV would change

⇒ BP would change

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5
Q

Sodium input only occurs through ingestion of food.

Identify 3 means of sodium output

A
  • Sweat
  • Faeces
  • Urine
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6
Q

What is the main site of absorption in the nephron?

A

Proximal convoluted tubule – absorbs Na+ (67%) and H2O (65%)

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7
Q

What is absorbed by the following:

  • Descending LoH
  • Ascending LoH
A
  • Descending thin limb of LoH: H2O (10-15%)

- Ascending thin and thick limb of LoH: Na+ (25%)

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8
Q

What stimulates proximal tubule reabsorption?

A

RAAS

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9
Q

Which cells are the target for aldosterone?

A

Principal cells of distal convoluted tubule and collecting duct

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10
Q

What happens when renal artery blood pressure increases?

A

In proximal tubule:

  • Number of Na-H antiporter reduces
  • Activity of Na-K ATPase reduces
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11
Q

What effect does an increased renal artery BP have on reabsorption?

A
  • Pressure natriuresis:

I. Reduction in sodium reabsorption in PCT

II. Increased Na+ excretion

  • Pressure diuresis:

I. Reduction in water resorption in PCT

II. Increased H2O excretion

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12
Q

What is the significance of the pressure diuresis and natriuresis that follow increased BP?

A
  • ECF volume decreases
  • Initial BP rise diminishes
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13
Q

Distinguish between paracellular and transcellular reabsorption

A
  • Paracellular reabsorption: lumen → tight junction → capillary
  • Transcellular reabsorption: lumen → apical membrane → basal membrane → capillary
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14
Q

Distinguish between paracellular and transcellular secretion

A
  • Paracellular secretion: capillary → tight junction → lumen
  • Transcellular secretion: capillary → basal membrane → apical membrane → lumen
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15
Q

What are aquaporin channels and what do they do?

A

- Aquaporins are channels which selectively conduct water molecules in and out of the cell

  • They prevent the passage of ions/other solutes hence solely increase permeability to H2O
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16
Q

Briefly distinguish between Cl- and Na+ reabsorption

A
  • Na+ reabsorption: active, transcellular process, driven by 3Na-2K-ATPase pumps
  • Cl- reabsorption: active, transcellular and also passive paracellular process, coupled to 3Na-2K-ATPase pumps
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17
Q

Identify the substances that are reabsorbed in the PCT and how this is achieved

A
  • PCT reabsorbs:

I. 65% H2O

II. 100% glucose and AA

III. 67% Na+

  • Proximal tubule is highly permeable to H2O and reabsorption is isosmotic with plasma
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18
Q

Which 3 factors govern sodium uptake into renal capillaries in the PCT?

A
  • Osmotic gradient established by solute absorption (osmolarity in interstitial spaces increases)
  • Hydrostatic force in interstitium increases
  • Oncotic force in peritubular capillary increases (loss of 20% glomerular filtrate leaving cells & proteins in blood)
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19
Q

Identify the 4 different transporters which facilitate sodium reabsorption in the apical membrane in S1 of the PCT

A
  • Na-H (antiporter)
  • Na-Glucose (symporter)
  • Na-AA (cotransporter)
  • Na-Pi
20
Q

Identify the 2 different transporters which facilitate sodium reabsorption in the basolateral membrane in S1 of the PCT

A
  • Basolateral 3Na-2K-ATPase
  • NaHCO3- cotransporter (acids and bases)
21
Q

Describe the movement of chloride ions in S1 of the PCT

A
  • Urea and Cl- move down S1 compensating for loss of Glucose
  • Increasing Cl- concentration creates a conc. gradient for chloride reabsorption in S2-3
22
Q

How is water transported in S1 of the PCT?

A

Using aquaporins

23
Q

How is sodium reabsorbed in the apical and basolateral membranes of S2-S3 in the PCT respectively?

A
  • Basolateral: 3Na-2K-ATPase
  • Apical: Na-H exchange
24
Q

How are chloride ions reabsorbed in S2-S3 of the PCT?

A

Paracellular and transcellular Cl- transport

25
Q

How is water reabsorbed in S2-S3 of the PCT?

A
  • Aquaporins
  • ~4mOsmol gradient favours water uptake from lumen
26
Q

Describe sodium and chloride uptake in the late PCT

A
27
Q

Describe, briefly, how the concentration of the following molecules change to establish an iso-osmotic solution in the PCT:

  • Cl-
  • Pi
  • Glucose, AA, lactate
  • HCO3-
A
28
Q

Identify the sodium transporter in the Loop of Henle

A

NaKCC (symporter)

29
Q

Distinguish between the general actions of the descending and ascending limbs of the Loop of Henle

A
  • Descending limb reabsorbs H2O but not NaCl
  • Ascending limb reabsorbs NaCl but not H2O
30
Q

Describe the reabsorption that occurs in the descending and ascending limbs of the Loop of Henle

A
  • Increase in [Na+]i allows paracellular reuptake of H2O from descending limb
  • Na+ and Cl- are concentrated in the lumen of the descending limb ready for active transport in the ascending limb
31
Q

Describe the reabsorption that occurs in the thin ascending limb of the Loop of Henle

A
  • H2O reabsorption in descending limb creates a gradient for passive Na+ reabsorption in thin ascending limb
  • This occurs through the paracellular route
32
Q

Describe the 4 active transport processes which occur in the thick ascending limb of the Loop of Henle

A
  • Active transport from lumen to cells via NaKCC transporter
  • Na+ move into interstitium via 3Na-2K-ATPase
  • K+ diffuse via ROMK back into lumen (maintain activity of NKCC2 transporter)
  • Cl- move into interstitium
33
Q

What is unique about the thick ascending limb of the Loop of Henle?

A
  • Region uses the most energy in the nephron
  • Sensitive to hypoxia
34
Q

Describe the osmolarity of the tubule fluid leaving the Loop of Henle

A

Tubule fluid leaving loop is hypo-osmotic compared to plasma

35
Q

Identify the 2 regions of the distal convoluted tubule

A
  • DCT 1 (early)
  • DCT2 ( late)
36
Q

Describe the general reabsorption that happens in the DCT as a whole

A
  • Hypo osmotic fluid (from LoH) enters
  • Active transport of Na+ (5-8%)
  • Low H2O permeability
37
Q

Identify the sodium transporter in the early DT

A

NaCC (symporter)

38
Q

Describe the reabsorption that occurs in DCT1

A
  • NaCl enters apical membrane via electro-neutral NCC transporter
  • NaCl leaves via 3Na-2K-ATPase in basolateral membrane
  • More hypo-osmotic fluid leaves, so further dilution occurs
39
Q

Identify the sodium transporter in the late DT & CD

A

ENaC (epithelial sodium channels)

40
Q

Describe the reabsorption that occurs in DCT2

A
  • NaCl enters apical membrane via NCC and ENaC
  • NaCl leaves 3Na-2K-ATPase in basolateral membrane
  • Electrochemical gradient from ENaC drives paracellular Cl- reuptake
41
Q

Describe the action of diuretics on membrane transporters in the DCT

A
  • NCC transporter: sensitive to Thiazide diuretics
  • ENaC transporter: sensitive to Amiloride diuretics
42
Q

Describe calcium reabsorption across the DCT

A
  • Cytosolic Ca2+ is bound by calbindin, shuttling it to the basolateral membrane
  • It is transported out by NCX
  • Tightly regulated by hormones e.g. PTH and 1,25- dihydroxy vitamin D
43
Q

How can the collecting duct be divided into segments?

A
  • Cortical region (CCD)
  • Medullary region (MCD)
44
Q

Identify 2 cell types found in the CCD

A
  • Principal cells (70%)
  • Intercalated cells
45
Q

Describe reabsorption in the principal cells of the collecting duct

A
  • Reabsorption of Na+ via ENaC on apical membrane
  • Driving force: 3Na-2K-ATPase in basolateral membrane
  • Lumen(–) charge drives paracellular Cl- uptake
46
Q

Identify the 2 types of intercalating cells

A
  • Acid-secreting Type A intercalating cells
  • Bicarbonate-secreting Type B intercalating cells
47
Q

Describe the different membrane transporters found in Type A intercalating cells of the collecting duct

A
  • Express H+-ATPase and H+/K+-ATPase on apical membrane
  • Express Cl−/HCO3− exchanger on basolateral membrane

(LUSUMA) Urinary System (23 decks)

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