Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Renal and Endocrine Biology > REB 23. Countercurrent Mechanism > Flashcards

REB 23. Countercurrent Mechanism Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

What type of urine is produced when an individual is dehydrated?

A

highly concentrated, low volume of urine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What type of urine is produced when an individual is over-hydrated?

A

dilute, large volume of urine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the osmotic concentration of 1 mmol of glucose?

A

1 mOsm/L

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the osmotic concentration of 1 mmol of NaCl?

A

NaCl

  • can be split into Na and Cl
  • therefore, 1 mmol of Na+ and 1 mmol of Cl-
  • in total, 2 mOsm/L
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the definition of Osmotic Pressure?

A

the pressure that must be applied to a solution to prevent the movement of solvent into it when solution and solvent are separated by a semi-permeable membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is reabsorbed in the proximal convoluted tubule?

A
  • Na+ [part of 65%]
  • HCO3-
  • glucose
  • amino acids
  • H2O [part of 65%]

basically all constituents of blood minus cells + proteins
(returns most of filtrate back to blood)
- around 70% of the filtrate is reabsorbed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the osmolarity of the proximal convoluted tubule?

A

around 300 mOsm/L

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Which part of the renal tubules has NO regulatory role?

A

the proximal convoluted tubule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is mainly absorbed in the early Proximal Convoluted Tubule?

A
  • HCO3- (90%) is a major anion reabsorbed with Na+

- due to counter transport of H+ (?)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is mainly absorbed in the Distal Convoluted Tubule?

A
  • some Na+ is reabsorbed by simple diffusion and bulk flow

- Cl- lags behind and is helped by bulk flow so it catches up

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What percentage of filtrate is reabsorbed in the loop of Henle? What mechanism is this done through?

A
  • 20% of the filtrate is reabsorbed through the loop of henle
  • reabsorption is part of the countercurrent mechanism
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What percentage of filtrate is reabsorbed in the distal tubules and collecting duct?

A
  • around 10% of filtrate is left
  • this region deals with VARIABLE salt and water reabsorption

Low Water Intake = High Water Reabsorption
- to ensure enough water in body

High Water Intake = Low/No Water Reabsorption
- to get rid of excess water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the part of the tubule which has VARIABLE resorption?

A

distal tubules + collecting duct

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is sodium reabsorption controlled by in the distal tubules and collecting duct?

A

Aldosterone

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is water resorption controlled by in the distal tubules and collecting duct?

A

Anti-Diuretic Hormone (ADH)

- aka Vasopressin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the normal urinary output?

A

1 mL/min

17
Q

If there is a high water intake, what does this lead to? How does this effect urinary output?

A
  • high water intake leads to no water reabsorption

- the urinary output is around 12 mL/min

18
Q

If there is a low water intake, what does this lead to? How does this effect urinary output?

A
  • low water intake leads to high (maximal) water reabsorption
  • the urinary output is around 0.5 mL/min
19
Q

What are the 2 requirements for adjustable water reabsorption in the collecting duct?

A

[1] Presence of ADH

  • ADH inserts aquaporins
  • without ADH, collecting duct is impermeable to water

[2] Hypertonic Interstitium

  • surrounds the collecting duct
  • this provides the osmotic gradient to reabsorb water
20
Q

What is the function of the hypertonic interstitium in the collecting duct?

A

it provides the OSMOTIC GRADIENT to reabsorb the water

21
Q

What is the main function of the Loop of Henle?

A

it generates and maintains the hypertonic interstitium
- this allows water to leave the tubules through osmosis!

aka it creates a concentration gradient (countercurrent) in the medulla of the kidney

22
Q

What are the characteristics of the Loop of Henle? [3]

A

[1] Countercurrent Flow

  • filtrate flows down in descending limb
  • filtrate flows up in ascending limb

[2] Descending Limb Permeable to Water

[3] Ascending Limb Impermeable to Water

  • lined with salt pumps which deposit salt into the interstitium
  • there is a difference of around 200 mOsm/L between the ascending limb + surrounding interstitium
23
Q

What are the 2 parts of the Countercurrent Mechanism?

A

[1] Countercurrent Exchange System

[2] Countercurrent Multiplier

24
Q

What is the countercurrent exchange system?

A

it is the anatomical arrangement of vessels so that flow in one vessel is in the opposite direction from flow in the adjacent vessel

25
Q

What is the countercurrent multiplier?

A

it is the anatomical arrangement of the loop of Henle that concentrates solute in the renal medulla

26
Q

What are the 3 distinct regions of the Loop of Henle?

A

[1] Thin-Walled Descending
[2] Thin-Walled Lower Portion of Ascending
[3] Thick-Walled Upper Portion of Ascending

27
Q

What is the thin-walled descending loop of henle permeable to?

A
  • highly permeable to H2O, but NOT solutes

- H2O will flow from the loop into the surrounding medium via osmosis

28
Q

What is the thin-walled lower portion of ascending loop of henle permeable to?

A
  • highly permeable to Na+ and Cl-
  • moderately permeable to urea
  • almost completely impermeable to H2O
29
Q

What is the thick-walled upper portion of the ascending loop of henle permeable to?

A
  • Na+ and Cl- are actively pumped out of the filtrate into the surrounding medium
30
Q

** What is the countercurrent mechanism? List and explain the steps. **

A

[1] the active salt pump in the ascending lumb transports NaCl out of the lumen
- this happens until the surrounding interstitium is 200 mOsm/L more concentrated than tubular fluid

[2] water moves passively out of the descending limb until the osmolarities become equal (equilibrium)

[3] the entire column of fluid then goes around the loop of henle

[4] ascending limb again transports salt out while water passively diffuses from the descending limb until a 200 mOsm/L difference is re-established between ascending limb and interstitium at each level

[5] now advance the entire column of fluid around the loop of Henle

[6] again, active extrusion of salt from ascending limb coupld with diffusion of water out of descending limb re-establishes the 200 mOsm/L gradient at all levels

[7] as the process continues, the fluid in the descending limb becomes increasingly hypertonic until it reaches a max. of 1200 mOsm/L at bottom of loop

[8] interstitial fluid achieves equilibrium in medulla

[9] concentration of tubular fluid in ascending limb progressively decreases as salt is pumped out

31
Q

What may the osmotic concentration of urine be as it leaves the collecting tubule during LOW water intake?

A

it can go up to 1200 mOsm/L

- there is only a small volume of concentrated urine excreted

32
Q

What may the osmotic concentration of urine be as it leaves the collecting tubule during HIGH water intake?

A
  • it can go down to around 100 mOsm/L
  • there is a large volume of dilute urine
  • there is barely any H2O reabsorption (water is eliminated)
33
Q

What is the salt pump in the thick ascending loop of Henle? What is the carrier protein involved? What is it inhibited by? What does inhibition do?

A
  • carrier protein (NKCC2) transports 1Na+, 1K+ and 2Cl-
  • inhibited by loop diuretics (e.g. furosemide + bumetanide)
  • inhibition reduces hypertonic interstitium
  • – reduces ability to reabsorb by osmosis
  • – salt and water excretion increases
  • – aka ions do not move into the interstitium
34
Q

How is urea handled in the nephron?

A
  • urea is mainly absorbed by the thin descending loop of henle
  • thick ascending + DT is highly impermeable to urea
  • so tubular [urea] increases
  • in the final collecting duct/loop, the urea concentration increases
  • ADH also increases urea permeability by promoting UT-A1 and UT-A3 urea transporters
35
Q

How does ADH increase urea permeability?

A
  • it increases urea permeability by promoting UT-A1 and UT-A3 urea transporters
36
Q

How much urea is left remaining as the urine leaves the tubules?

A

around 20%

37
Q

Why isn’t the hypertonic interstitium “washed away”? **

A

[1] blood flow to the medulla interstitium is very low
- only about 2% of flow in the inner medulla

[2] vasa recta capillaries “hairpin” operates as a countercurrent flow

38
Q

What are the pressures in the vasa recta?

A
  • net inward pressure of 15 mmHg in the vasa recta (as in the other peritubular capillaries)

[[ NaCl and water in the interstitium is therefore drawn into the vessels ]]

Blood Pressure: 20 mmHg
Oncotic Pressure = 35 mmHg
Net Pressure = 15 mmHg
- flow is directed INTO the vessel

Renal and Endocrine Biology (25 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions