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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
What happens to inhibit ADH?
Decreased osmolarity Hypervolemia Increase in blood pressure
26
What other substances inhbit ADH?
Ethanol | ANP
27
How does ADH support water reabsorption?
ADH binds to V2 receptor G-protein mediated signalling cascade activates cAMP cAMP activates protein kinase A
28
What does ADH do with regards to aquaporins?
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
How is sodium actively reabsorbed in PCT
NaK2CL triple transporter from lumen to tubular cell Na+/K+ ATPase pump from tubular cell to blood K+CL- symporter into blood
30
What is the conc of the fulid in DCT?
Hyposomotic
31
Why is some water reabsorbed in diuresis?
Paracelluar pathways | Some aquaporins function
32
How does ADH support Na+ reabsorption in the kidney?
Thick ascending limb: ↑Na+ - K+ - 2Cl- symporter Distal convoluted tubule: ↑Na+ - Cl- symporter Collecting duct: ↑Na+ channel
33
What are some ADH-related clinical disorders?
Central diabetes insipidus Syndrome of inappropriate ADH secretion Nephrogenic diabetes insipidus
34
What is the primary excretion of base?
Faeces
35
What does the excretion of bicarbonate lead to?
Net addition of Metabolic Acid
36
How are metabolic acids neutralised?
𝐻2𝑆𝑂𝟒+2𝑁𝑎𝑯𝑪𝑶𝟑↔𝑁𝑎2𝑆𝑂4+2𝐶𝑂2+2𝐻2𝑂 𝐻𝐶𝑙+𝑁𝑎𝑯𝑪𝑶𝟑↔𝑁𝑎𝐶𝑙+𝐶𝑂2+𝐻2𝑂
37
What is the ECF conc of bicarbonate?
ECF [HCO3-] = ~350mEq
38
What is the role of the kidneys to maintain acid-base balance?
Secretion & excretion of H+ Reabsorption of HCO3- Production of new HCO3-
39
How does bicarbonate act as a buffer?
𝑪𝑶𝟐+𝑯𝟐𝑶↔𝑯𝟐𝑪𝑶𝟑↔𝑯++𝑯𝑪𝑶𝟑−
40
What is the Henderson-hasselbalch equation?
𝒑𝑯=𝒑𝑲^′+𝒍𝒐𝒈 (𝑯𝑪𝑶𝟑−)/𝜶𝑷𝑪𝑶𝟐 [𝑯+]= (𝟐𝟒 𝐱 𝑷𝑪𝑶𝟐)/([𝑯𝑪𝑶𝟑−])
41
What is a disorder caused by pCO2 called?
Respiratory
42
What is a disorder caused by bicarbonate called?
Metabolic
43
How is bicarbonate reabsorbed to the blood in the PCT?
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
How is bicarbonate reabsorbed in DCT and collecting duct?
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
How are new bicarbonate ions produced?
PCT - ammoniogenesis DCT and collecting duct - carbonic anhydrase
46
Describe the process of ammioniogenesis?
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
What the characteristics of metabolic acidosis?
Reduced bicarbonate | Reduced pH
48
What the characteristics of metabolic alkalosis?
Increased bicarbonate | Increased pH
49
What is the compensatory mechanisms of metabolic acidosis?
Hyperventilation | Increased bicarbonate reabsorption and production
50
What is the compensatory mechanisms of metabolic alkalosis?
Decreased ventilation | Increased bicarbonate excretion
51
What the characteristics of respiratory acidosis?
Increased pCO2 | Reduced pH
52
What the characteristics of respiratory alkalosis?
Decrease pCO2 | Increased pH
53
What is the compensatory mechanisms of respiratory acidosis?
Acute intracellular buffering Chronic Increased bicarbonate reabsorption and production
54
What is the compensatory mechanisms of respiratory alkalosis?
Acute Intracellular buffering | Chronic Decreased bicarbonate reabsorption and production
55
describe the process of forming new bicarbonate using carbonic anhydrase?
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
describe the process of bicarbonate excretion in the DCT/collecting duct
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
how is sodium actively reabsorbed in DCT
NaCl symporter from lumen to tubular cell NaKATPase pump to blood K+Cl- symporter to blood
58
how is sodium actively reabsorbed in collecting duct
principal cells passively enters cell Na+K+ATPase pump into blood

Year 2 Uro (5 decks)

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