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1k. Renal System > L106: Kidney 2 > Flashcards

L106: Kidney 2 Flashcards

1
Q

Where does reabsorption occur?

A

Renal tubule

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2
Q

What does the renal tubule comprise of?

A
  • PCT;
  • LoH;
  • DCT;
  • Collecting duct.
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3
Q

What part of the kidney are the PCT and DCT located?

A

Cortex

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4
Q

What part of the kidney are the LoH located?

A

Medulla

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5
Q

What is the primary location for reabsorption?

A

PCT (~65%)

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6
Q

How is reabsorption in the PCT facilitated?

A

Sodium active transport (primary active transport), everything follows sodium (aka sodium handling)

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7
Q

What process occurs at the LoH?

A

Countercurrent multiplication

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8
Q

What is the main function of countercurrent multiplication?

A

Water reabsorption, concentration of urine

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9
Q

What part of the nephron is responsible for fine-tuning of the filtrate?

A

DCT

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10
Q

What three hormones modulate water reabsorption in the DCT?

A
  • Anti-diuretic hormone;
  • Aldosterone;
  • Atrial-natriuretic hormone.
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11
Q

What direction do water and nutrients move when reabsorbed?

A

From tubule to blood

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12
Q

What direction do water and nutrients move when secreted?

A

From blood into tubule (form urine)

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13
Q

What structural specialisation facilitates maximal reabsorption in the PCT?

A
  • Microvilli;
  • Convoluted (winding);
  • Closely located to peritubular capillaries.
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14
Q

How are water and nutrients reabsorbed in the PCT?

A

Passive diffusion (and secondary active transport to sodium) (50%)

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15
Q

Why do nutrients diffuse from the tubule lumen to the peritubular capillaries? (in PCT)

A

Higher concentration in lumen than blood, therefore they move down a concentration gradient

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16
Q

What do nutrients/ molecules require to passively diffuse into the capillaries in the PCT?

A
  • Pores/ carrier proteins to cross phospholipid bilayer;
  • Water: aquaporins;
  • No ATP.
17
Q

What molecules are co-transported via sodium? (PCT)

A

Glucose and amino acids (passive but facilitated)

18
Q

What ion exchange occurs on the basolateral membrane during sodium reabsorption? (PCT)

A

3 x Na+ OUT, 2 x K+ IN

19
Q

What direction does sodium move during active transport?

A

Against a concentration gradient

20
Q

What process results in water being reabsorbed as a result of sodium active transport? (PCT)

A

Osmosis

21
Q

What process results in Cl- and other -ve ions being reabsorbed as a result of sodium active transport? (PCT)

A

Electrical gradient

22
Q

How much sodium reabsorption occurs in the LoH?

A

~25%

23
Q

What type of nephrons are specialised for countercurrent multiplication and why?

A

Juxtamedullary, due to long LoH

24
Q

How is the LoH specialised to facilitate countercurrent multiplication?

A
  • Thin descending limb: permeable to water and no sodium reabsorption;
  • Thick ascending limb: impermeable to water (no aquaporins), active sodium reabsorption.
25
Q

What is the purpose of active sodium reabsorption in the thick, ascending limb?

A
  • Pumped into interstitium of medulla;
  • Leads to ‘salty’ medulla;
  • Leads to high osmotic pressure and osmotic gradient;
  • Water moves freely from thin descending limb into salty medulla.
26
Q

Explain sodium reabsorption in the thick, ascending limb.

A
  • Na+/K+ pump on the basolateral membrane;
  • Na+ AGAINST concentration gradient into interstitial space of medulla;
  • NKCC2 co-transporter pump on apical membrane;
  • For every Na+, 2 x Cl- and 1 x K+ follow (passive from lumen);
  • Increases sodium reabsorption.
27
Q

Where is the NKCC2 co-transporter pump located?

A

Exclusive to thick ascending limb

28
Q

What is one target of diuretic drugs?

A

NKCC2

29
Q

How do diuretic drugs work via the NKCC2 pump?

A
  • Block pump;
  • Prevent Na+ reabsorption and therefore water;
  • Increased volume of urine;
  • Decreased BP.
30
Q

What is the main process at the DCT?

A

Fine-tuning of filtrate

31
Q

Name three hormones which act at the DCT.

A
  • ADH (anti-diuretic hormone);
  • Aldosterone;
  • Artial natriuretic peptide hormone.
32
Q

Which hormones stimulate water (and salt) reabsorption?

A

ADH and aldosterone

33
Q

How does ADH work?

A
  • Released from pituitary gland upon dehydration;
  • Leads to insertion of aquaporins (DCT);
  • Water leaves DOWN a gradient into cortex;
  • Less water lost in urine.
34
Q

How does aldosterone work?

A
  • Works with ADH upon dehydration;
  • Released by adrenal gland;
  • Stimulates the up regulation by Na+/ K+ pumps;
  • [Na+] increases and therefore water follows due to osmosis;
  • Less water lost in urine;
  • K+ rich urine (exchanged for Na+ by blood plasma).
35
Q

How does ANH work?

A
  • Works against ADH and aldosterone;
  • Released by smooth muscle cells in the atrium of the heart upon high BP;
  • Inhibits ADH and aldosterone;
  • Prevents reabsorption of water and salt;
  • Large amount of urine.

1k. Renal System (4 decks)

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