Acid-Base Homeostasis Flashcards Preview

Year 2 EMS MoD > Acid-Base Homeostasis > Flashcards

Flashcards in Acid-Base Homeostasis Deck (41)
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1
Q

What is the total CO2 produced in a day on average?

A

25mol/day

2
Q

Name 6 buffering systems in the body?

A

1) Hb
2) Bicarbonate
3) Phosphate
4) Proteins
5) Ammonia
6) Misc organic acids

3
Q

What is the reference range for blood pH?

A

7.45-7.35

4
Q

What is the reference range for plasma [H+]?

A

35-45mmol/L

5
Q

What is the Henderson-Hesselbalch equation and whatr does it show?

A

pH = pK + log([HCO3]/[pCo2}xa)
Says the pH and thus [H+] is determined by the balance between H+ and HCO3 so [H+] homeostasis requires a balance between H+ production and regeneration of HCO3-

6
Q

Give 4 sites of acid-base metabolism?

A

Lungs
Kidneys
GI tract
Liver

7
Q

Which are the 2 main sources of excretion of acid from the body?

A

Lungs (as CO2)

Kidneys (H+)

8
Q

Describe how reactions of CO2 within the RBC cause O2 to be released to tissues in tissue gas exchange?

A

CO2 is released from the tissues and is non polar so passes straight across the RBC membrane
CO2 reacts within the RBC to become H+ and HCO3-
H+ sticks to the Hb molecule (a protein), this acidifies the protein causing it to change shape and release the O2
Thus O2 is released from the RBC to the tissues

9
Q

Describe how reactions within the RBC cause O2 to be taken up and CO2 to be released by RBC’s at the lungs?

A

More O2 outside the RBC enters the RBC
The O2 binds to the Hb molecule causing H+ to be released which binds to HCO3- to form H20 and CO2 which is released into the lungs

10
Q

Name the 3 things which cause a right shift of the O2-Hb dissociation curve?

A

You get a right shift (O2 released more readily) with:

1) Increased temp
2) Acidosis
3) Increased 2,3 DPG

11
Q

Which 2 buffering systems are considered to be most important in the body?

A

1) Bicarbonate

2) Hb

12
Q

What role does the kidneys play in acid-base homeostasis (3 mechanisms)?

A

1) Renal reclamation of bicarbonate
2) Renal generation of bicarbonate
3) Mineralocorticoid action in kidney in excreting H+

13
Q

What is the mechanism of renal reclamation of bicarbonate?

A

1) Bicarbonate is a small molecule so is filtered out of the blood into the renal tubule
2) Its combined with H+ pumped into the renal tubule in exchange for Na+ to form CO2 and H2O
3) CO2 is reabsorbed and converted back into bicarbonate

14
Q

What is the mechanism for renal generation of bicarbonate?

A

Renal tubular cells produce bicarbonate and in doing so produce H+ which is lost in the urine

15
Q

How does mineralocorticoid action in the kidney affect acid-base homeostasis?

A

Occurs in the distal tubules
Under endocrine control via the hormone aldosterone
Either K+ or H+ can be excreted from the kidneys in exchange for Na+
If [H+] is high then H+ is excreted under the control of aldosterone

16
Q

What role does the GI tract have in acid base homeostasis?

A

Stomach excretes acid, this needs to be balanced by alkaline excretion
Bicarbonate is excreted in pancreatic juices to neutralise this acid, this has to be balanced to prevent disturbances

17
Q

What role does the liver have in acid-base homeostasis?

A

1) Dominant site of lactate metabolism

2) Only sight of urea synthesis

18
Q

What role does the urea cycle have in acid-base homeostasis?

A

1) Proteins catabolised to NH4+ and HCO3-
2) The average protein produces an excess of NH4+
3) The role of the urea cycle is to combine NH4+ and CO2 to neutralise HCO3-
HCO3- can be converted to H+ and Urea, this is inhibited by acidosis
NH4+ is converted to NH3 which is excreted in the urine (loses a H+) and this is stimulated by alkalosis

19
Q

How can severe liver failure lead to metabolic alkalosis and NH4+ toxicity?

A

Because these 2 reactions do not occur:

1) NH4+ + oxo-glutarate -> glutamine
2) NH4+ + CO2 -> urea + H+

20
Q

Which are the 2 important reversible reactions involved in acid-base homeostasis?

A

CO2 HCO3- + H+
2NH4+ + HCO3- (NH2)2CO2 + H+
acidosis alkalosis

21
Q

What are the 2 kind of acid base states that can occur?

A

Metabollic acidosis/alkalosis

Respiratory acidosis/alkalosis

22
Q

What are the 3 main compensatory mechanisms for acidosis/alkalosis?

A

1) Respiratory
2) Renal bicarbonate regeneration
3) Hepatic shift between urea synthesis and ammonia excretion

23
Q

What are the 5 possible causes of metabolic acidosis?

A

1) Increased H+ formation
2) Acid ingestion
3) Reduced renal H+ excretion
4) Loss of bicarbonate
5) Inability to excrete H+ through expiration of CO2

24
Q

What happens to H+ levels, pCO2 and pO2 in metabolic acidosis?

A

H+ increases (because its acidosis)

pCO2 decreases and pO2 increases (respiratory compensation causes hyperventilation)

25
Q

Give 3 possible basic reasons for metabolic alkalosis?

A

1) Generation of bicarbonate by gastric mucosa
2) Renal generation of HCO3- in hypokalaemia
3) Administration of bicarbonate

26
Q

What happens to H+ levels, pCO2 and pO2 in metabolic alkalosis?

A

H+ decreases (because its alkalosis)

pCO2 increases and pO2 decreases (breathing rate decreased as respiratory compensation so blow off less CO2)

27
Q

What are the 3 main consequences of metabolic alkalosis?

A

1) K+ moves into the cells and urine
2) PO4 moves into cells
3) Respiratory suppression

28
Q

What acid-base disorder does excessive vomiting lead to?

A

Metabolic alkalosis

29
Q

What kind of acid-base disorder to ectopic ACTH lead to and why?

A

Metabolic alkalosis
Causes body to produce too much cortisol from the adrenals which stimulates the mineralcorticoid receptors which leads to loss of potassium and H+ and absorption of Na+

30
Q

Give 3 examples of conditions which lead to respiratory acidosis?

A

CO2 retention due to:

1) inadequate ventilation
2) parenchymal lung disease
3) inadequate perfusion

31
Q

What happens to the levels of H+ and pCO2 and pO2 in respiratory acidosis?

A
increased H+ (because its acidosis)
increased pCO2 (its Co2 retention which is leading to the acidosis)
pO2 decreased because of reduced ventilation
32
Q

What causes respiratory alkalosis?

A

Increased CO2 excretion due to excessive ventilation producing alkalosis

33
Q

What happens to the levels of H+, pCO2 and pO2 in respiratory alkalosis?

A

H+ decreases because its alkalosis
pCO2 decreases (its the excessive excretion leading to alkalosis)
pO2 increases because of hyperventilation

34
Q

Give 4 possible basic causes of metabolic acidosis?

A

1) Increased H+ formation
2) Acid ingestion
3) Reduced renal H+ excretion
4) Loss of bicarbonate

35
Q

Give 4 possible reasons for increased H+ formation leading to metabolic acidosis?

A

1) Ketoacidosis, diabetic or alcoholic
2) lactic acidosis
3) poisoning
4) inherited organic acidoses

36
Q

Give the 4 mechanisms leading to acidosis in diabetic keto-acidosis?

A

1) Hyperglycaemia
2) osmotic diuresis -> to pre-renal uraemia
3) hyperketonaemia
4) increase FFA
All 4 lead to acidosis

37
Q

Give the 2 causes of lactic acidosis?

A

Type a = shock

Type b = metabolic and toxic causes

38
Q

How does acidosis occur in an alcoholic?

A

Get NAD+ depletion and thiamine deficiency
Enhanced glycolysis for ATP formation
Keto-acids to counter regulatory hormones
Profuse vomiting

39
Q

Can high lactate occur in alkalosis?

A

Yes
Get increased glycolysis
Reduced O2 delivery due to shift in O2 dissociation curve
Lactate induced vasoconstriction
Impaired mitochondrial respiration
Also get a O2 debt leading to further anaerobic lactate production leading to hyperventilation

40
Q

Give 2 reasons for reduced H+ excretion?

A

1) Renal tubular acidosis

2) Generalised renal failure

41
Q

What 4 steps lead to metabolic acidosis in renal failure?

A

Due to reduced volume of nephrons:

1) Increased bicarbonate loss
2) Reduced NH4+ excretion
3) NH4+ to liver for urea and H+ synthesis
4) Only fraction of NH4+ derived from glutamine (normally approx. 100%)