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Renal Module > Lecture 6 - Acid Base Balance > Flashcards

Lecture 6 - Acid Base Balance Flashcards

1
Q

What are the normal ranges of plasma conc in Na+, K+ and H+?

A

Na+ = 140mmol,
K+ = 4.5mmol
H+ =40nmol (smallest)

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2
Q

What do protons do in buffer reactions?

A

Change the % of dissociation of buffers

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3
Q

What is H20 and CO2 catalysed by?

A

Carbonic anhydrase - enzyme

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4
Q

When does carbonic anhydrase catalyse H20 and CO2?

A

In the rate limiting step which is the slowest part of

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5
Q

What is the equation used for acid-base balance?

A

The Henderson-Hasselbalch equation

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6
Q

What varies as bicarbonate concentration of PCO2 change?

A

H+ and pH

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7
Q

What is the concentration of CO2 primary regulated by?

A

Breathing

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8
Q

What are H+ and bicarbonate managed by?

A

The kidney, bicarbonate is generates and reabsorbed, acid is excreted

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9
Q

What are three changes that can affect acid-base balance?

A

Diet - acidic and alkaline components
Metabolism - produces acid and alkali
Egestion - bicarbonate loss in faeces

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10
Q

What is the net result of acid base balance?

A

It is usually daily addition of acid to the body - has to be corrected by excretion or buffering

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11
Q

What process can lose acid?

A

Vomiting

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12
Q

What state is the body usually in?

A

An acidic state

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13
Q

What is volatile acid?

A

It is acid that is secreted from CO2 and can be excretes as CO2

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14
Q

What is a non volatile acid?

A

It is an acid that is not secreted by CO2 e.g. lactic acid

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15
Q

What does renal acid excretion (RAE) =

A

Endogenous acid production (EAP)

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16
Q

What does H+ concentration gradient promote?

A

Lumen movement

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17
Q

What does conformational changes of transport proteins alter?

A

Kinetics to favour secretion

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18
Q

What does endothelin 1 do (ET)?

A

Increases number of NBC1 and NHE3 transporters in cell membrane

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19
Q

What does the parathyroid hormone do?

A

Inhibits phosphate reabsorption in the PCT so there is more available for H+ buffering in the distal nephron.

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20
Q

What does cortisol increase?

A

Increases transcription of NBC1 and NHE3 genes

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21
Q

What does angiotensin II increase?

A

Increases nHE3 activity and stimulus ammonia production and secretion

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22
Q

What does aldosterone do?

A

Acts in distal regions of nephrons and is increases during acidosis to increase proton secretion

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23
Q

What does dietary acid stimulate?

A

Renal and adrenal ET-1 production, ET-1 increases aldosterone which stimulates distal nephron H+ secretion

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24
Q

What happens if you increase nitric oxide production?

A

There is an increase in Na+ protons exchange in the proximal and distal nephron

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25
How much bicarbonate if freely filtered out at the glomerulus each day?
4320Eq is delivered to the nephrons and is then reabsorbed
26
How much bicarbonate is filtered on the PCT?
80%
27
How much bicarbonate s filtered in the DT, TAL and CD?
DT = 6%, TAL = 10% and CD = 4%
28
How is H+ secretion across the apical membrane occurred by?
By both the Na+/H+ antiporter and H+ ATPase (vascular type)
29
What is the predominant pathway for H+ secretion?
The Na/H+ antiporter (NEH3) it uses lumen to cell (Na+) gradient to drive the process
30
How are H+ and bicarbonate produced in a cell?
They are produced in a reaction catalysed by carbonic anhydrase
31
What is h+ secreted into?
The tubular fluid while bicarbonate is exits the cell across the basolateral membrane and returns to the blood
32
How does bicarbonate exit?
Via a symporter that couples with the efflux of Na+ with HCO3- (NBC1)
33
Where is carbonic anhydrase also present?
In the brush boarder of the basolateral membrane.
34
What do enzymes in the brush boarder do?
They catalyse dehydration of H2CO03 in the luminal fluid
35
What is the movement of CO2 out of the cell facilitated by?
AQP1 (aquaporin), which is located to both the luminal and basolateral membranes
36
What is bicarbonate reabsorption like in the thick ascending limb (TAL)?
It is very similar to the PCT. H+ is secreted by a Na+/H+ antiporter and H+ ATPase. Also has NEH3 antiporter for the predominant pathway for H+ secretion
37
How does bicarbonate exit the cell In the TAL?
It invokes the Na/HCO3- symporter (NBC1) and also a Cl-/HCO3- antiporter (AE2)
38
Where can some Bicarboante also exit in the TAL?
Through Cl- channels present in the basolateral membrane
39
What is bicarbonate reabsorption like in the distal tubule (DT)?
It involves an apical membrane Na+/H+ antiporter (NEH2) and a basolateral Cl-/HCO3- antiporter (AE2)
40
How much does the collecting duct (CD) reabsorb bicarbonate?
A very small amount of 4%, it only reabsorbs the bicarbonate that has escape reabsorption by the PCT and loop of henle
41
What are the type of intercalated cells are used for reabsorption and secretion of bicarbonate in the distal tubule and collecting duct?
Alpha and beta intercalated cells
42
What do the alpha intercalated cells do?
They secrete H+ and reabsorb bicarbonate.
43
What happens in intercalated cells?
H+ and HCO3- are produced by hydration of CO2 - this reaction is catalysed by carbonic anhydrase and h+ is secreted into the tubular fluid.
44
what are the two ways that H+ is secreted into the tubular fluid?
1 - by the apical membrane H+ ATPase (V-type 2 - couples secretion of H+ with the reabsorption of K+ via an H+/K+ ATPase
45
What does bicarbonate exits across the basolateral membrane in exchange for?
Cl- via AE1 and it enters the capillary blood.
46
What do beta-intercalated cells do?
They secrete HCO3- rather than H+ into the tubular fluid
47
What is ammonia produced by?
It is produced by the kidney and its excretion adds bicarbonate to the ECF
48
What is the production of ammonia from the kidneys regulated by?
It is regulated in response to the acid-base balance
49
How is ammonia produced in the kidneys?
Via metabolism of glutamine, the kidneys metabolise glutamine, excrete ammonia and add bicarbonate to the body
50
What does the formation of new ammonia depend on?
It depends on the excretion of ammonia
51
What happens if ammonia is not excreted in the urine but instead enters the systemic circulation?
It is converted into urea but the liver. This conversation process generates H+ which is then buffered by bicarbonate
52
What is ammonia produced by?
It is produced by glutamine in the cells of the PCT - a process termed ammonia genesis
53
What do each glutamine molecules produce?
Two ammonia molecules and a divalent anion 2-oxoglutarate
54
What does the metabolism of 2-oxoglutarate provide?
It provides two molecules of bicarbonate
55
Where does ammonia exit the cell?
Via the apical membrane and it enters the tubular fluid
56
What does the primary mechanism for ammonia Involve?
It involves ammonia secretion into the tubular fluid by the Na+/H+ antiporter with ammonia substituting for H+
57
What is the primary site of ammonia reabsorption with ammonia substituting for H+?
The thick ascending limb
58
What is ammonia secreted by?
It is secreted into the tubular fluid by the collecting duct
59
How does the bicarbonate buffer system differs from all other buffer systems?
It is regulated by both the kidneys and the lungs
60
What is considered the rate limiting step in the bicarbonate buffer system?
The first reaction with the hydration and dehydration of CO2 - it is slow and is accelerated in the present of carbonic anhydrase
61
What is the equation used for he bicarbonate buffer system?
CO2 + H20 <-> H2CO3 <-> H+ + HCO3-
62
If acid addition exceeds excretion what does it equal?
Acidosis
63
If acid excretion exceeds addition what does it =
Alkalosis

Renal Module (10 decks)

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