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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
Q

How much bicarbonate if freely filtered out at the glomerulus each day?

A

4320Eq is delivered to the nephrons and is then reabsorbed

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26
Q

How much bicarbonate is filtered on the PCT?

A

80%

27
Q

How much bicarbonate s filtered in the DT, TAL and CD?

A

DT = 6%, TAL = 10% and CD = 4%

28
Q

How is H+ secretion across the apical membrane occurred by?

A

By both the Na+/H+ antiporter and H+ ATPase (vascular type)

29
Q

What is the predominant pathway for H+ secretion?

A

The Na/H+ antiporter (NEH3) it uses lumen to cell (Na+) gradient to drive the process

30
Q

How are H+ and bicarbonate produced in a cell?

A

They are produced in a reaction catalysed by carbonic anhydrase

31
Q

What is h+ secreted into?

A

The tubular fluid while bicarbonate is exits the cell across the basolateral membrane and returns to the blood

32
Q

How does bicarbonate exit?

A

Via a symporter that couples with the efflux of Na+ with HCO3- (NBC1)

33
Q

Where is carbonic anhydrase also present?

A

In the brush boarder of the basolateral membrane.

34
Q

What do enzymes in the brush boarder do?

A

They catalyse dehydration of H2CO03 in the luminal fluid

35
Q

What is the movement of CO2 out of the cell facilitated by?

A

AQP1 (aquaporin), which is located to both the luminal and basolateral membranes

36
Q

What is bicarbonate reabsorption like in the thick ascending limb (TAL)?

A

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
Q

How does bicarbonate exit the cell In the TAL?

A

It invokes the Na/HCO3- symporter (NBC1) and also a Cl-/HCO3- antiporter (AE2)

38
Q

Where can some Bicarboante also exit in the TAL?

A

Through Cl- channels present in the basolateral membrane

39
Q

What is bicarbonate reabsorption like in the distal tubule (DT)?

A

It involves an apical membrane Na+/H+ antiporter (NEH2) and a basolateral Cl-/HCO3- antiporter (AE2)

40
Q

How much does the collecting duct (CD) reabsorb bicarbonate?

A

A very small amount of 4%, it only reabsorbs the bicarbonate that has escape reabsorption by the PCT and loop of henle

41
Q

What are the type of intercalated cells are used for reabsorption and secretion of bicarbonate in the distal tubule and collecting duct?

A

Alpha and beta intercalated cells

42
Q

What do the alpha intercalated cells do?

A

They secrete H+ and reabsorb bicarbonate.

43
Q

What happens in intercalated cells?

A

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
Q

what are the two ways that H+ is secreted into the tubular fluid?

A

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
Q

What does bicarbonate exits across the basolateral membrane in exchange for?

A

Cl- via AE1 and it enters the capillary blood.

46
Q

What do beta-intercalated cells do?

A

They secrete HCO3- rather than H+ into the tubular fluid

47
Q

What is ammonia produced by?

A

It is produced by the kidney and its excretion adds bicarbonate to the ECF

48
Q

What is the production of ammonia from the kidneys regulated by?

A

It is regulated in response to the acid-base balance

49
Q

How is ammonia produced in the kidneys?

A

Via metabolism of glutamine, the kidneys metabolise glutamine, excrete ammonia and add bicarbonate to the body

50
Q

What does the formation of new ammonia depend on?

A

It depends on the excretion of ammonia

51
Q

What happens if ammonia is not excreted in the urine but instead enters the systemic circulation?

A

It is converted into urea but the liver.
This conversation process generates H+ which is then buffered by bicarbonate

52
Q

What is ammonia produced by?

A

It is produced by glutamine in the cells of the PCT - a process termed ammonia genesis

53
Q

What do each glutamine molecules produce?

A

Two ammonia molecules and a divalent anion 2-oxoglutarate

54
Q

What does the metabolism of 2-oxoglutarate provide?

A

It provides two molecules of bicarbonate

55
Q

Where does ammonia exit the cell?

A

Via the apical membrane and it enters the tubular fluid

56
Q

What does the primary mechanism for ammonia Involve?

A

It involves ammonia secretion into the tubular fluid by the Na+/H+ antiporter with ammonia substituting for H+

57
Q

What is the primary site of ammonia reabsorption with ammonia substituting for H+?

A

The thick ascending limb

58
Q

What is ammonia secreted by?

A

It is secreted into the tubular fluid by the collecting duct

59
Q

How does the bicarbonate buffer system differs from all other buffer systems?

A

It is regulated by both the kidneys and the lungs

60
Q

What is considered the rate limiting step in the bicarbonate buffer system?

A

The first reaction with the hydration and dehydration of CO2 - it is slow and is accelerated in the present of carbonic anhydrase

61
Q

What is the equation used for he bicarbonate buffer system?

A

CO2 + H20 <-> H2CO3 <-> H+ + HCO3-

62
Q

If acid addition exceeds excretion what does it equal?

A

Acidosis

63
Q

If acid excretion exceeds addition what does it =

A

Alkalosis

Renal Module (10 decks)

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