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GU 1 > 6/7 - Integration of salt and water balance > Flashcards

6/7 - Integration of salt and water balance Flashcards

1
Q

What should I know

A
  1. Hormonal mechanisms that control fluid and sodium balance
  2. Know the control and actions of ADH (anti-passing urine) and ang ll
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2
Q

Why do we need a kidney?

A
  • There is always a gap between intake and output of body fluids. The kidney allows you to maintain a large range of fluid intakes and keep osmolality and volume relatively constant
  • the kidneys are important for BP, acid base, osm, blood filtering and hormone release
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3
Q

What hormones do the kidneys release?

A
  • renin (RLS for ang ll production)

- erythropoietin to stimulate RBC production and so is important in determining the O2 carrying capacity of the blood

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4
Q

What happens with dehydration summary

A
  1. water deficit OR increase in salt
  2. increase in ECF osmolality
  3. osmoreceptors sense increase and signal adh secretion from post pit
  4. increase in adh permeability in distal tubules and collecting ducts
  5. increased water retention reduced excretion
    > feel thirsty when either salt increases or fluid decreases
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5
Q

Do barorecptors influence osmoreceptors?

A

Yes

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6
Q

Where do you find osmoreceptors?

A

Osmoreceptors are found in supraoptic and paraventricular nuclei

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7
Q

How do osmoreceptors work?

A

They sense both changes in osmolality and circulating blood volume and result in adh release.
Inputs to the hypothalamus from the medullary vasomotor center which receive input from the baroreceptors increase adh release in response to a reduced circulating volume.

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8
Q

How do changes in omsol cause a response from osmoreceptors

A

Small changes in osmol cause small deformations of neurons. In hyperosmotic fluid the size of the neuron changes and opens gap junction channels which causes the neuron to depolarise or repolarise and hence send a signal to the hypothal (if structures are cross-linked)

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9
Q

What is adh released in response to

A

An increase of less than 1% osmolarity or decreased volume (greater than 10%) of the ECF

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10
Q

What is ADH secretion most sensitive to?

A

Secretion of ADH in response to increased osmolarity has a LOWER threshold and higher sensitivity/slope than its response to a decreased EC volume

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11
Q

Physiological stimuli to adh secretion

A
  1. Increased plasma osmol 1-2%

2. Decreased ECF vol 7-10%

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12
Q

Non-physiological stimuli to adh secretion

A
  • pain, stress
  • drugs: nicotine, SSRIs
  • Carcinomas
  • CNS disorders
  • alcohol inhibits ADH secretion
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13
Q

How does ADH work?

A

Enters the blood/renal interstitial fluid and causes insertion of AQP2 on the tubular lumen causing increased water reabsorption and reduced ECF osmol until the signal decreases (FB loop)
Occurs by ADH stimulating V2 receptor > cAMP > PKA > protein phosp

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14
Q

What is thirst driven by?

A

High osmol not vol

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15
Q

What senses changes in BV?

A

Cardio-pulmonary volume receptors - also sends info to osmoreceptors

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16
Q

Where does adh act?

A

Distal tubule, cortical collecting tubule and outer and inner medullary collecting ducts

17
Q

What is it called if ADH levels are low

A

Either central or nephrogenic diabetes insipidus

18
Q

Central Diabetes Insipidus (neurogenic or pituitary DI)

A
  • inadequate ADH secretion/production
  • is a problem with hypothal or pp
  • may be due to brain injury, tumor or infection
  • rarely hereditary
  • can be treated with ADH analogues as receptors work fine
  • ADH is absent
19
Q

Nephrogenic DI

A
  • collecting tubule is unresponsive to ADH
  • conc urine cannot be produced
  • can be caused by certain drugs i.e. lithium
  • less commonly hereditary i.e. congenitial defect in the V2 receptor or Aquaporin2
  • is NOT currently treatable
  • sufficient ADH is being released by kidney is unresponsive
20
Q

What receptor does ADH work on?

A

V2

21
Q

How to tell apart neurogenic/central diabetes insipidus and nephrogenic?

A
  • is there ADH circulating
  • Are they responsive to ADH
  • water deprivation test
22
Q

What is the water deprivation test?

A

Used to decipher between the 2 types of DI. An ADH analogue is given. If urine osmol increases i.e. there is a response to ADH and more water is reabs then it is central DI

23
Q

What is SIADH

A

Syndrome of inappropriate ADH secretion

24
Q

SIADH

A
  • defect in appropriate ADH secretion
  • higher than normal ADH levels and so patient reabsorbs and retains water inappropriately and their ECF omsol decreases.
  • if their water intake is not tightly controlled then a hypo-osmolar state can result which is not good
25
Q

What is SIADH commonly caused by?

A
  • brain injury or tumour
  • anti-cancer drugs
  • cancer
26
Q

SIADH treatment

A

Restrict water intake instead give an isotoinc fluid so their osmol doesn’t drop

27
Q

What results did they see when they injected kidney into a rabbit?

A

Increase in BP. Due to RAAS (something produced by kidney that led to a increased BP)

28
Q

What 3 factors promote renin secretion by JG cells in the afferent arteriole?

A
  1. Decrease in afferent arteriole pressure
  2. Increase in sympathetic activity
  3. Reduction in NaCl delivery to macula densa cells (reduced renal perfusion)
29
Q

Where are MD cells

A

TAL/distal convoluted tubule

30
Q

Primary difference between ADH and ang 2

A

ADH just affects water reabs while ang 2 primary increases Na reabsorption in the prox tubule which then brings water with it usually

31
Q

How to correct osmol

A

ADH > drag in water

- why adh is very sensitive to osmol changes

32
Q

Correct vol

A

Usually to bring salt back and forth which brings water with it via ang 2
- renin is released in response to smaller changes in BP or BV

33
Q

If the right renal artery becomes abnormally constricted, what will happen to renin secretion by each of the kidneys?

A

R: the right kidney receives reduced renal perfusion and afferent arteriole pressure and so renin secretion will increase. Sensed by the infrarenal baroreceptor and reduced flow to MD cells. The increase in renin secretion will increase ang 2 and increase arterial BP both of which will act on the L kidney to REDUCE renin secretion.

GU 1 (19 decks)

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