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Urinary (Semester 3) > Controlling Osmolarity > Flashcards

Flashcards in Controlling Osmolarity Deck (15)
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1
Q

What defines osmolarity?

What drives osmotic movement?

A

The total concentration of solute in a solution (that can’t cross cell membranes)

Water will move across semi-permeable membranes according to the osmotic gradient: from areas of low –> high osmolarity

2
Q

Name 2 semi-permeable membranes

A
  1. Cell membranes

2. Capillary walls

3
Q

What generates oncotic pressure?

A

Large molecules that accumulate in the capillaries, as capillary walls don’t allow passage of large molecules, i.e; proteins or cells

4
Q

Name 3 ways you can uncontrollably lose water, one way you can lose water controllably and 2 methods that will increase the water in your body.

A

Uncontrollably lose:

  1. Evaporation from the lungs
  2. skin and sweating
  3. lose it from the gut

Controllably lose:
The kidney can variably lose water (but can’t replace it)
Thirst

Increasing water: thirst and ADH (more on that later)

5
Q

When would you require diuresis and anti-diuresis?

A

Diuresis: diluting urine to lose excess water, used when the fluid is hypotonic

Anti-diuresis: when fluid is hypertonic need to retain more fluid to balance the solute: solution ratio and keep the fluid at the right osmolarity. Stimulates more water resorption and thirst

6
Q

Which parts of the nephron are diluting segments?

A

The LOH, DCT and the CT

7
Q

How does the LOH dilute the urine?

A

Variable sodium and water resorption in the descending segment. The ascending segment is impermeable to water and ions are pumped out. This creates hypotonic filtrate and a hypertonic medullary interstitium

8
Q

How do the DCT and the CT concentrate urine?

What is the typical osmolarity in the DCT vs the medullary interstitium surrounding the LOH?

A

When you need to concentrate urine, the DCT and CT would have more ADH/aquaporins so water can be resorbed, and water will leave the CT as it passes through the hypertonic medullary interstitium

The osmolarity is typically 300 milli osmoles/L whereas in the medullary interstitium is typically 1200 milli osmoles/L

9
Q

Which hormone makes walls more and less permeable to water in the DCT and CT?

Why isn’t this permanent?

A

ADH/Vasopressin: stimulates aquaporins which are holes in the membrane walls that allow water to leave the filtrate and follow the osmotic gradient

Aquaporins aren’t permanent due to quick membrane turnover.

10
Q

How do the DCT and CT dilute urine?

A

Their walls become less permeable to water leaving the filtrate

11
Q

What stimulates ADH?

A

Osmoreceptors in the hypothalamus are sensitive to their own size: if they shrink this signals a need for anti-diuresis as the plasma has become too hypertonic, so they fire AP’s (if they swell, they don’t). This signals thirst and ADH

12
Q

What is counter-current multiplication?

A

The ascending LOH is impermeable to water and actively pumps out ions due to the Na-K-Cl cotransporter and Na-K-ATPase - creating a hypertonic medullary interstitium: generating a local gradient of 100-200 milli osmoles. Since the descending LOH is permeable to water, water can leave the filtrate due to this osmotic gradient

13
Q

Is counter-current multiplication enough to keep an extreme hypertonic medullary interstitium?

A

Urea is also recovered into the interstitial fluid in the DCT to further concentrate the medulla

14
Q

Explain how the blood supply fuels the kidneys without interrupting the process?

How much blood supply does the kidney require at rest, why?

A

Countercurrent multiplication requires a lot of ATP, so kidney needs 25% of cardiac output at rest

The blood vessels are arranged in a U shaped vasa recta from the cortex - down into the medulla and back again

15
Q

What determines the volume of the ECF and circulating fluid?

A

As long as the patient can drink, the ECF volume/circulating fluid is determined by the amount of solute.