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BRS 1b > Renal regulation of water and acid-base balance > Flashcards

Renal regulation of water and acid-base balance Flashcards

1
Q

What is osmolarity?

A

Osmolarity: The concentration of osmotically active particles in solution, which maybe quantitatively expressed is osmoles of solute per litre of solution.

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2
Q

What does osmolarity depend upon?

A

• Osmolarity depends on the intrinsic property of the substance, and dissociation capacity – Ionic compounds have the ability to dissociate into respective ions.

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3
Q

What are the 2 compartments of fluid?

A 
Intracellular fluid (2/3)
Extracellular fluid (1/3)
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4
Q

How is extracellular fluid divided?

A

3/4 Extravascular

1/4 intravascular

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5
Q

What is transcellular fluid?

A

Refers to fluid that resides within epithelial lined spaces (cerebrospinal fluid and peritoneal fluid)

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6
Q

What are four forms of unregulated water loss?

A

Sweat
Faeces
Vomit
Water evaporation from respiratory lining and skin

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7
Q

What happens in a positive water balance?

A

High water intake,

ECF volume increases

This reduces the concentration of sodium and thus osmolarity

Hypo-osmotic urine production

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8
Q

Which channels are integrated within the descending limb to facilitating water leaving the loop of henle and entering into the hyperosmolar interstititum?

A

Aquaporin channels

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9
Q

Describe the permeability to water in the ascending limb

A

Impermeable to water to the absence of aquaporin channels

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10
Q

Describe sodium transport within the thick ascending loop

A

ATPase pumps actively remove sodium from the tubular cells into the juxtamedullary fluid

Have a high mitochondria density to supply ATP

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11
Q

Describe the interstitial osmolarity gradient progressing downwards of the nephron

A

Increasingly hyperosmolar

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12
Q

Why is the ascending limb impermeable to water?

A

Presence of tight junctions reduces paracellular transport of water

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13
Q

Which urea transporters are located on the apical cell surface membrane of the collecting duct, allowing the passage of urea into the tubule cells?

A

UT-A1

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14
Q

What is the UT-A3 transporter?

A

Present on the basolateral cell membrane of the collecting duct, facilitating the passage of urea from the tubule cells into the medullary interstitium

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15
Q

Which hormone influences the permeability of the collecting duct to urea?

A

Vasopressin

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16
Q

What impact does urea have on the osmolarity of the interstitial fluid?

A

Increases the osmolarity by a significant magnitude

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17
Q

How is urea reabsorbed into the vasa recta?

A

Via UT-B1 transporters

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18
Q

What effect does vasopressin have on urea transporter?

A

Vasopressin up-regulates UT-A1 and UT-A3, potentiating the increase of urea transport into the medullary interstitial fluid

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19
Q

Which transporters allow urea into the thin descending limb of the loop of Henle?

A

UT-A2

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20
Q

Which neurones synthesise vasopressin?

A

Hypothalamic magnocellular neurones originating from the supraoptic and paraventricular nuclei

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21
Q

How many amino-acids long is vasopressin?

A

9 amino acids

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22
Q

What is the overall function of vasopressin?

A

Promotes water reabsorption from the DCT and collecting duct

23
Q

What is the normal plasma osmolarity in a healthy adult?

A

275-290mOSm/kg

24
Q

What % range change in osmolarity is required for the detection of baroreceptors?

A

5-10%

25
Q

What factors stimulate ADH production?

A 
Increase in plasma osmolarity 
Decrease in blood pressure
Nausea
Angiotensin II
Nicotine 
Hypovolaemia
26
Q

What factor inhibit ADH production?

A

Decreased plasma osmolarity
Hypervolaemia, increased blood pressure
Ethanol
ANP

27
Q

Which receptors does AVP bind to on tubule cells?

A

G-protein linked V2 receptors on the basolateral cell surface membrane of principal tubule cells of the collecting duct

28
Q

What happens upon AVP binding to G-protein linked V2 receptors within principal tubule cells?

A

Activates adenylate cyclase activity, generating cAMP - protein kinase promotes the migration of AQP 2 molecules towards the basolateral membrane

29
Q

Which transporter pumps sodium ions out of the thick ascending limb?

A

Na+/K+ ATPase pump

30
Q

What are the two effects of the Na-K-ATPase pump?

A

Removal of sodium while retaining water leads to hypotonic filtrate to the distal convoluted tubule

Pumping of sodium into the interstitial space generates a hyperosmotic interstitial fluid environment in the kidney medulla.

31
Q

What is diuresis?

A

Increased dilute urine excretion
There is minimal ADH influence
Overall reduced water reabsorption and hyposmolar urine

32
Q

What is anti-diuresis?

A

Antidiuresis (Concentrated urine in low volume excretion)
In response to low plasma osmolarity or low blood pressure.
-Vasopressin supports sodium reabsorption in the thick ascending limb, distal
convoluted tubule and collecting duct – increasing hyperosmolar juxtamedullary
fluid concentration.

33
Q

What are the main causes of central diabetes insipidus?

A

Decreased/negligent production and release of ADH (stroke, organic brain disease)

34
Q

What are the clinical features of CDI?

A

Polyuria and polydipsia
Water deprivation test to
confirm & measure
HbA1C.

35
Q

What is the treatment of CDI?

A

External ADH

36
Q

What is SIADH?

A

Increased production and

release of ADH

37
Q

What are the clinical features of SIADH?

A

Hyperosmolar urine
Hypervolaemia
Hyponatremia

38
Q

What is the treatment for SIADH?

A

Non-peptide inhibitor of
ADH receptor (Conivaptan
and tolvaptan).

39
Q

What is the treatment of NDI?

A

Mutant V2 receptor
unresponsive to
ADH stimulation

40
Q

What are the clinical features of NDI?

A

Polyuria

Polydipsia

41
Q

What is the treatment of NDI?

A

Thiazide diuretics +

NSAIDs.

42
Q

What does carbonic acid dissociate into?

A

Bicarbonate and hydrogen ions

43
Q

How is bicarbonate transported into the interstitium through the basolateral surface?

A

NBC-1 transporter

44
Q

Which transporters secrete hydrogen ions into the tubular fluid?

A

NHE2 transporters

45
Q

What are the roles of principal cells?

A

Sodium reabsorption & potassium secretion. Principal cells have a low
mitochondrial density due to the passive diffusion of sodium ions intracellularly,
and potassium efflux.
 Aldosterone regulates Na+ reabsorption by increases apical Na+ channels &
basolateral Na+-K+ ATPase pumps.
 Anti-diuretic hormone (ADH) regulates water reabsorption by increasing
apical aquaporins (Present within intracellular vesicles, ADH signals increased
vesicle fusion to embed aquaporins).

46
Q

What are the two types of intercalated cells?

A

Alpha

Beta

47
Q

What is the function of the alpha intercalated cells?

A

HCO3- reabsorption & H+ secretion.

48
Q

What is the function of beta intercalated cells?

A

HCO3- secretion & H+ reabsorption.

49
Q

What is an intercalated cell?

A

Intercalated cell: Secretes or absorbs acid/bicarbonate  Regulation of blood
pH. Intercalated cells reabsorb K+ & HCO3-, while secreting H+. This function
reduces the acidity of the plasma, and subsequently increases urine acidity; this
mechanism is achieved by carbonic anhydrase activity.
 Mitochondrial rich

50
Q

Which amino acid within intercalated cells is used as a mediator for ammonia release?

A

Glutamine

51
Q

How is ammonia transported into the filtrate?

A

NHE3 anti-porter

52
Q

What happens to ammonia when in the filtrate?

A

Ammonia is protonated by hydrogen ions in the filtrate to form ammonium ions

The bicarbonate that dissociated from glutamine enters circulation

53
Q

Which ion behaves as a urinary buffer in the tubular fluid?

A

Phosphate ions

BRS 1b (62 decks)

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