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REN > Osmoregulation > Flashcards

Osmoregulation Flashcards

1
Q

Where is osmolality detected?

A

Within the AV3V where the BBB is incomplete.

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2
Q

Where do the neurons of AV3V project to and what do they detect?

A

Neurons project to supraoptic and paraventricular nuclei of the hypothalamus.

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3
Q

How will the nuclei respond to an increased osmolality in the blood?

A

Neurons respond to an increased osmolality by increasing ADH release form the posterior pituitary.

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4
Q

Where is ADH/vasopressin sythesised?

A

In the cell bodies of the neurons of the hypothalamus as a prehormone which is cleaved as it descends to the pituitary via axons.

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5
Q

What products result from prehormone cleaving to produce ADH?

A

ADH and other peptides

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6
Q

Where does ADH act systemically?

A

Travels in circulation to V2 receptors on the basolateral membrane of the CCT.

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7
Q

What are V2 receptors? What is there function when activated?

A

GsPCR that use the AC pathway to activate PKA for phosporylation and exocytosis of vesicles containing AQP2 on to the apical membrane of CCT for increased water reabsorption.

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8
Q

What is the structure of an AQP and how does it allow water to pass?

A

Multisubunit oligomer that is arranged into a tetramer of identical units, on which has a glycon attached. Water passes through its pour.

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9
Q

Where are the different AQPs located?

A

AQP1 - PT and DL
AQP2 - Apical of CCT and MCD
AQP3 - Across basolateral

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10
Q

Why is oxytocin released alongside ADH? Where does oxytocin act?

A

To increase thirst.
AV3V neurons projecting to the median preoptic area stimulate thirst through oxytocin release which acts as an agonist on V1 and V2 receptors.

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11
Q

What effect does the combination of ADH and oxytocin produce?

A

Decreased output and increased input

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12
Q

Why is osmoregulation response activated frequently in humans?

A

Due to binge drinking rather than drinking small continuous infusions.

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13
Q

What is the concentration of ADH proportional to?

A

Rate of secretion of water in the kidney.

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14
Q

In what fashion is ADH released?

A

Tonic release that is slow and graded

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15
Q

What will MAX ADH cause?

A

HIGH osmolality, low volume urine

1400mOsm , 300ml.day

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16
Q

What will no ADH cause?

A

LOW osmolality, high volume urine

60-90mOsm , 25L.day

17
Q

What is a normal daily urine output?

A

1.8L.day

18
Q

Why does sea water cause dehydration?

A

It has a high osmolality of 2000mOsm. To removed a solution of this osmolality at a max of 1400mOsm, it would require 1.4L of water to be excreted. (2000/1400)

19
Q

What is the max osmolality of urine that the kidney can produce?

A

1400mOsm per Litre (finite range of water excretion) - Any substance above this osmolality will cause dehydration

20
Q

What is the max. renal osmolality of a neonate? Why does this put them at risk?

A

500mOsm - If a formula feed exceeds this it will draw more water into the renal tubules and cause dehydration.

21
Q

What are the most dominant osmolytes of the circulation?

A

Na and Cl

22
Q

Why do proteins, fats and carbohydrates that are consumed in large amounts have less of an effect on osmolality than the two dominant osmolytes?

A

The substances are broken down into products that are used for other functions or are less water soluble.

23
Q

What are carbohydrates broken down into? What are they used for?

A

Simple sugars - transported into cells.

Glucose is oxidised to CO2 and H2O.

24
Q

What are proteins broken down into? What are they used for?

A

AA - rapidly taken up into cells

N2 is removed as urea which has a HIGH FLUX but low contribution to osmolality.

25
Q

Why is K not an effective osmolyte?

A

Cells are relatively more permeable to K, creating an intracellular K reservoir.
K is cleared more rapidly than Na so has a HIGH FLUX but low effect on osmolality due to its high clearance.

26
Q

What is a hyperosmolar hyperglycaemic state?

A

In DM, glucose can become high enough to contribute to osmolality if >320mOsm. The hyperosmolality stimulates thirst to prevent dehydration but excess intake will cause hyponatraemia.

27
Q

What are the effects of hyponatraemia?

A

Affects mental status, seizures, neurology, increased blood viscosity and clotting risk.

28
Q

What are the side effects of delivering ADH intranasally?

A

Nasal necrosis as a result of V1 mediated vasoconstrction, limiting the blood supply to the nasal tissue.

29
Q

What ADH analogue is used to treat high osmolality?

A

Desmopressin

30
Q

What is the bodies main priority?

A

Body will correct BP / Volume changes before correcting osmolality.

31
Q

What contributes to correcting a volume change?

A

Increased osmolality = increased ADH = Increased thirst = Increased volume

32
Q

What is the issue with correcting osmolality in regards to volume?

A

Solute content changes will disturb volume to regulate the concentrations.

REN (14 decks)

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