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Year 2 Uro > Renal regulation of water and acid-base balance > Flashcards

Renal regulation of water and acid-base balance Flashcards

1
Q

What is osmotic pressure proportional to?

A

Number of solute particles

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2
Q

What is osmolarity equal to?

A

Concentration x No. of dissociated particles

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3
Q

What are the units of osmolarity?

A

Osm/L OR mOsm/L

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4
Q

Calculate the osmolarity for 100 mmol/L glucose and 100mmol/L NaCl?

A

Osmolarity for glucose = 100 x 1 = 100 mOsm/L

Osmolarity for NaCl = 100 x 2 = 200 mOsm/L

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5
Q

What is the total fluid volume of the body?

A

60% of body weight

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6
Q

What proportion is extracellular and intracellular?

A

1/3 extracellular

2/3 intracellular

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7
Q

Give examples of trans-cellular fluid?

A

CSF

Periotoneal fluid

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8
Q

What comprises extracelllular fluid?

A

Transcellular
Interstitial
Plasma

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9
Q

What are the unregulated forms of water loss?

A

Sweat
Feces
Vomit
Water evaporation from respiratory lining and skin

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10
Q

What is the regulated form of water loss?

A

Renal regulation – urine production

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11
Q

What happens when there is a positive water balance?

A

High water intake enters EC compartment

ECF volume increases

Sodium conc decreases

Osmolarity decreases

Hypo-osmotic urine production

Osmolarity normalises

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12
Q

What happens when there is a negative water balance? (low water intake)

A

Low water intake

Low ECF volume

High sodium conc

Osmolarity increases

Hyper-osmotic urine production

Osmolarity normalises

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13
Q

What percentage of water is absorbed in the PCT?

A

67%

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14
Q

What occurs in the descending limb of the loop of henlé?

A

Water is passively absorbed

Salt is not reabsorbed

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15
Q

Why is an osmotic gradient in the loop of henle essential?

A

Since water is reabsorbed through the passive process of osmosis, it requires a gradient.
The medullary interstitium needs to be hyperosmotic for water reabsorption to occur from the Loop of Henle and Collecting duct.

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16
Q

What is countercurrent multiplication?

A

Filtrate arrives at loop of henle at osmolarity equal to plasma

Salt is actively reabsorbed into interstitial from ascending

Water passively flows into interstitial from thin descending

Fresh filtrate arrives

Active salt reabsorbed into interstitium again from ascending

Water from descending equilibrates by passively moving into interstitium

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17
Q

What is the gradient that can be achieved via countercurrent mulitplcation?

A

300 at top

1200 at bottome

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18
Q

What is urea recycling?

A

Urea contributes to the concentrating of the interstitium

Filtrate arrives at collecting duct where there are two urea transporters on basolateral (UT-A3) and on apical membrane (UT-A1)

Urea pumped out to medullary interstitum, increases osmolarity

Can be reabsorbed by vasa recta by UTB-1 transporter

But also reabsorbed to filtrate by descending limb of loop (UT-A2) aka urea recycling

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19
Q

What are the two goals of urea recycling?

A

Urea excretion requires less water due to high osmolarity at bottom

Increases interstitium osmolarity to aid water reabsorption process

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20
Q

Where does IV fluid infusion first enter?

A

Extracellular compartment

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21
Q

What is the main function of ADH?

A

Promote water reabsorption from collecting duct

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22
Q

Where is ADH produced?

A

Hypothalamus (neurons in supraoptic & paraventricular nuclei)

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23
Q

Where is ADH stored?

A

Posterior pituitary

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24
Q

What happens when you are dehydrated?

A

Rise in plasma osmolarity is detected by osmoreceptors

Stimulates ADH production and release

25
Q

What happens to inhibit ADH?

A

Decreased osmolarity

Hypervolemia

Increase in blood pressure

26
Q

What other substances inhbit ADH?

A

Ethanol

ANP

27
Q

How does ADH support water reabsorption?

A

ADH binds to V2 receptor

G-protein mediated signalling cascade activates cAMP

cAMP activates protein kinase A

28
Q

What does ADH do with regards to aquaporins?

A

ADH up/downgrades AQP2 & AQP3 numbers as required
AQP2 on apical cell membrane (lumen side) AQP3 on basolateral (to blood)

also effects on UT-A3 and UT-A1 - icnreased permeability to urea - more reabsorption (less excretion)

29
Q

How is sodium actively reabsorbed in PCT

A

NaK2CL triple transporter from lumen to tubular cell
Na+/K+ ATPase pump from tubular cell to blood

K+CL- symporter into blood

30
Q

What is the conc of the fulid in DCT?

A

Hyposomotic

31
Q

Why is some water reabsorbed in diuresis?

A

Paracelluar pathways

Some aquaporins function

32
Q

How does ADH support Na+ reabsorption in the kidney?

A

Thick ascending limb: ↑Na+ - K+ - 2Cl- symporter
Distal convoluted tubule: ↑Na+ - Cl- symporter
Collecting duct: ↑Na+ channel

33
Q

What are some ADH-related clinical disorders?

A

Central diabetes insipidus

Syndrome of inappropriate ADH secretion

Nephrogenic diabetes insipidus

34
Q

What is the primary excretion of base?

A

Faeces

35
Q

What does the excretion of bicarbonate lead to?

A

Net addition of Metabolic Acid

36
Q

How are metabolic acids neutralised?

A

𝐻2𝑆𝑂𝟒+2𝑁𝑎𝑯𝑪𝑶𝟑↔𝑁𝑎2𝑆𝑂4+2𝐶𝑂2+2𝐻2𝑂

𝐻𝐶𝑙+𝑁𝑎𝑯𝑪𝑶𝟑↔𝑁𝑎𝐶𝑙+𝐶𝑂2+𝐻2𝑂

37
Q

What is the ECF conc of bicarbonate?

A

ECF [HCO3-] = ~350mEq

38
Q

What is the role of the kidneys to maintain acid-base balance?

A

Secretion & excretion of H+
Reabsorption of HCO3-
Production of new HCO3-

39
Q

How does bicarbonate act as a buffer?

A

𝑪𝑶𝟐+𝑯𝟐𝑶↔𝑯𝟐𝑪𝑶𝟑↔𝑯++𝑯𝑪𝑶𝟑−

40
Q

What is the Henderson-hasselbalch equation?

A

𝒑𝑯=𝒑𝑲^′+𝒍𝒐𝒈 (𝑯𝑪𝑶𝟑−)/𝜶𝑷𝑪𝑶𝟐

[𝑯+]= (𝟐𝟒 𝐱 𝑷𝑪𝑶𝟐)/([𝑯𝑪𝑶𝟑−])

41
Q

What is a disorder caused by pCO2 called?

A

Respiratory

42
Q

What is a disorder caused by bicarbonate called?

A

Metabolic

43
Q

How is bicarbonate reabsorbed to the blood in the PCT?

A

H+ and HCO3- are converted to H2CO3 then H2O and CO2 by carbonic anhydrase
CO2 diffuses into the PCT cell
carbonic anhydrase converts this back to H+ and HCO3-
the Na+ HCO3- symporter drives this back into the blood through the basolateral membrane
H+ goes back into the tubular fluid by Na+/H+ antiporter and via H+ ATPase transporter (apical side)

44
Q

How is bicarbonate reabsorbed in DCT and collecting duct?

A

H+ and HCO3- are converted to H2O and CO2 in the tubular fluid (carbonic anhydrase)
CO2 diffuses into DCT/collecting duct, converted back by carbonic anhydrase
HCO3- pumped to blood by Cl- HCO3- antiporter
H+ secreted by H+ ATPase pump and H+ K+ATPase
all within alpha intercalated cells

45
Q

How are new bicarbonate ions produced?

A

PCT - ammoniogenesis

DCT and collecting duct - carbonic anhydrase

46
Q

Describe the process of ammioniogenesis?

A

In PCT : glutamine broken down to NH4+ and A2- (A2 gives rise to two HCO3- which is reabsorbed)
NH4+ needs to be excreted so that the bicarb created is not wasted
Either becomes NH3 gas and diffuses out or forced out by Na+ NH4+ antiporter

47
Q

What the characteristics of metabolic acidosis?

A

Reduced bicarbonate

Reduced pH

48
Q

What the characteristics of metabolic alkalosis?

A

Increased bicarbonate

Increased pH

49
Q

What is the compensatory mechanisms of metabolic acidosis?

A

Hyperventilation

Increased bicarbonate reabsorption and production

50
Q

What is the compensatory mechanisms of metabolic alkalosis?

A

Decreased ventilation

Increased bicarbonate excretion

51
Q

What the characteristics of respiratory acidosis?

A

Increased pCO2

Reduced pH

52
Q

What the characteristics of respiratory alkalosis?

A

Decrease pCO2

Increased pH

53
Q

What is the compensatory mechanisms of respiratory acidosis?

A

Acute intracellular buffering

Chronic Increased bicarbonate reabsorption and production

54
Q

What is the compensatory mechanisms of respiratory alkalosis?

A

Acute Intracellular buffering

Chronic Decreased bicarbonate reabsorption and production

55
Q

describe the process of forming new bicarbonate using carbonic anhydrase?

A

In DCT/collecting duct alpha intercalated cell: same process as in reabsorption but H+ in tubular fluid is bound to HPO42- to create H2PO4- which acts as a buffer and produces a net gain of HCO3 (reduced amount of H+)

56
Q

describe the process of bicarbonate excretion in the DCT/collecting duct

A

H+ and HCO3- are converted to H2O and CO2 in the tubular fluid (carbonic anhydrase)
CO2 diffuses into DCT/collecting duct, converted back by carbonic anhydrase
HCO3- secreted into tubular fluid by CL- HCO3- antiporter
H+ reabsorbed to blood by H+ ATPase pump on basolateral membrane (b intercalated cells only)

57
Q

how is sodium actively reabsorbed in DCT

A

NaCl symporter from lumen to tubular cell
NaKATPase pump to blood

K+Cl- symporter to blood

58
Q

how is sodium actively reabsorbed in collecting duct

A

principal cells
passively enters cell
Na+K+ATPase pump into blood

Year 2 Uro (5 decks)

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