Urinary System 5 - Control of water balance Flashcards Preview

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Flashcards in Urinary System 5 - Control of water balance Deck (21)
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1
Q

What does your body need to remove in urine?

A
  • Excess volume to prevent bloating
  • Remove excess water to keep osmolarity up
  • Remove excess salt to stop osmolarity getting too high
2
Q

What is the normal plasma osmolarity?

A

285-295mosmol/l

3
Q

How is water lost?

A
  • Sweat (uncontrollable)
  • Faeces (uncontrollable)
  • Respiration (Uncontrollable)
  • Urine output (controllable)
4
Q

List the places where water is reabsorbed in the kidney

A
  • Proximal tubule
  • Descending loop of Henle
  • Distal tubule
  • Collecting duct
5
Q

List the places where salt is reabsorbed in the kidney

A
  • Proximal tubule
  • Ascending limb of the loop of henle
  • Distal tubule
6
Q

List the fraction of filtered load reaching the different parts of the nephron

A
  • 30% reaches descending loop of henle
  • 20% reaches the distal convoluted tubule
  • 1-10% enters the urine
7
Q

How is water reabsorption varied in different animals?

A
  • Length of the loop of henle

- Activity of the loop of henle

8
Q

Describe how the gradient is established by the loop of henle with regards to sodium

A
  • Salt is pumped out of the ascending limb to generate an osmotic gradient
  • Water follows from the descending limb
  • As more fluid enters the loop of henle, more salt is pumped out to get the same concentration gradient
  • The osmolarity is more different at the bottom of the loop than at the top
9
Q

Describe how urea increases the osmotic gradient

A
  • Collecting duct and the bottom of the loop of Henle are permeable to urea
  • Urea diffuses out of collecting duct and into the bottom of the loop of henle, then into the interstitial fluid increasing the osmolarity
10
Q

List the different urea transporters and their locations

A
  • UT-A1 is in the inner medullary collecting duct
  • UT-A2 In the thin descending limb
  • UT-A3 in the inner medullary collecting duct
  • UT-B1 in the descending vasa recta
11
Q

What happens if there is a fault in urea transporter A1 or 3?

A
  • Reduced urea in the inner medulla
  • Reduction in ability to concentrate urine
  • Increased water uptake by 20%
  • No ability to reduce urine output
12
Q

What happens if there is a fault in urea transporter B?

A
  • Increased urine production
  • Reduced urine concentrating ability
  • Weight loss
13
Q

How does blood flow through the vasa recta create a concentration gradient?

A
  • Permeable to water and solutes
  • Water diffuses out of the descending limb and salts diffuse in
  • In the ascending limb the reverse happens
  • This allows oxgen and nutrients to be delivered
14
Q

How is water reabsorption controlled in the collecting duct?

A
  • Vasopressin secreted from the posterior pituitary gland

- Binds to V2 receptors on the basolateral membrane of principal cells in the collecting duct

15
Q

List the actions of vasopressin in the kidney

A
  • Increases insertion of aquaporins in the cell membranes
  • Stimulates urea transport from the collecting duct to the ascending limb of loop of henle cy increasing UTA1 and UTA3 in the collecting duct
16
Q

What triggers ADH release?

A
  • 285-295mosmol/L plasma osmolarity
  • Detected by osmoreceptors in the hypothalamus
  • Stimulated by fall in blood volume
  • Inhibited by ethanol
17
Q

Describe the pathway that happens following decreased plasma osmolarity

A
  • ADH release decreases
  • Decreased water permiability
  • Increased urine flow rate
18
Q

Describe the pathway that happens in dehydration

A
  • Thirst increases
  • Plasma osmolarity increases
  • Increased ADH
  • Increased permiability to water
  • Decreased urine flow rate
19
Q

What is the main disorder of water balance?

A
  • Diabetes insipidus
  • Excretion of lots of urine
  • Due to Issues with ADH production, detection, or functon
20
Q

Describe the osmolarity of the fluid entering the loop of Henle

A

Isotonic - PCT is permeable to everything

21
Q

Describe the osmolarity of the fluid leaving the loop of Henle

A

Hypotonic as the ascending limb of the loop of Henle pumps out ions