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MBCHB3 RBF > Lecture 22-24: Acid:Base Part One > Flashcards

Lecture 22-24: Acid:Base Part One Flashcards

1
Q

What is a strong vs weak acid:

A
  • A strong acid is an acid that completely dissociates in solution i.e the [H+] equals the intial acid concentration. i.e fully ionised HCL-> H+ and Cl-
  • A weak acid is an acid that only partially dissociates in solution i.e H2CO3-> H+ and HCO3 (only a small amount of carbonic acid exists as H+ in solution
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2
Q

Describe pH in normal homeostasis

A

7.35-7.45 for cellular and enzyme function (tightly controlled)

This corresponds to a [H+] ranging from 35-45nMol/L

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3
Q

Where is the acid sources in the body?

A

Oxidative metabolism: Volatile acid i.e CO2 production

Protein catabolism: Non-volatile / fixed acids that MUST be excreted. Massively increased amounts i.e Lactic acid production (exercise), keto-acidosis = aceto-acetic acid and b-hydroxybutyric acid.

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4
Q

What are the bodies buffering systems?

A
  • Bicarb, instant but limited long term (ECF mainly and most important)
  • IC proteins, phosphates
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5
Q

What is acidaemia and alkalaemia?

A 
Acidaemia = pH\<7.35 
Alkalaemia = pH\>7.45
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6
Q

Write some notes on acidosis:

A

pH < 7.35

  • pH < 7.2 = severe acidosis
  • pH < 6.9 = Usually incompatible with life
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7
Q

Write some notes on alkalosis

A

pH < 7.45

  • pH < 7.6 = severe alkalosis
  • pH < 7.9 = Usually incompatible with life
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8
Q

What are the components of acid base balance?.

A
  • Diet
  • Blood
  • Liver
  • Lungs
  • Kidneys

i.e Many facets

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9
Q

What are the three mechanisms in which the body prevents dangerous changes in pH?

A
  1. Buffers
  2. Respiratory control of ventilation
  3. Excretion of acids (or bases) by the kidneys

** Every change of 0.3pH represents a change in [H+] by a factor of 2

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10
Q

What is a buffer?

A

Buffers are a solution consisting of a weak acid and its conjugate base

  • A buffer is a chemical in solution that resits changes in pH i.e mopping up H+
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11
Q

How does a buffer work?

A
  1. H+ is added, increasing H+ and lowering pH
  2. Equilibrium is right shifted
  3. H+ are consumed by the buffer conjugate base/anion, forming the buffer conjugate weak acid
  4. [H+] reduces, restoring pH to(wards) normal
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12
Q

What are the four buffers of blood?

A

Bicarbonate
Haemoglobin
Phosphate (also celllular)
Proteins (also cellular)

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13
Q

Describe how bicarbonate acts as a buffer:

A

H+ (+) HCO3- H2CO3 H2O (+) CO2

  • Carbonic acid only exists in very small amounts
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14
Q

Describe how Hb acts as a buffer:

A

Hb

  • Dissolved CO2 enters RBC, some binds Hb
  • Rest becomes HCO3 and H, the H produced is buffered by the Hb whilst HCO3 diffuses into the plasma in exchange for chloride
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15
Q

Describe how phosphate acts as a buffer

A

H + HPO4 H2PO4

Both phosphate and proteins contribute relatively little to buffering by blood and ECF due to their relatively low concentrations in plasma

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16
Q

Describe how proteins act as a buffer:

A

H + i.e albumin HA

Both phosphate and proteins contribute relatively little to buffering by blood and ECF due to their relatively low concentrations in plasma

17
Q

What are other buffers aside from the ones in blood and ECF?

A

Muscle + liver (H+Cl enter cell and exchanged for cation)
Bone (Usually only in chronic acidosis, but CaCO3 accepts H+ and forms Ca and HCO3)

18
Q

What equation determines the pH

A

Henderson-hasselbach equation

pH = 6.74 + log (HCO3/CO2)

19
Q

Describe the contribution of respiration to acid-base regulation

A
  • CO2 is removed via ventilation
  • Oxidative metabolism produces CO2 which forms HCO3 + H in the blood.
  • Low pH stimulates ventilation
  • Increased ventilation blows off CO2

Increased pCO2 causes acidosis
Decreased pCO2 causes alkalosis

20
Q

Describe the role of the kidneys in acid- base balance

A

Metabolism produces H+ and these are excreted into the kidney to balance non-volatile acid generated through metabolism

Kidneys also reabsorb HCO3 and produce HCO3 .

Excess H is buffered by:

  • > Phosphate buffers
  • > Ammonia buffers
21
Q

What are the two main renal processes in acid-base balance

A
  1. Reabsorption of filtered bicarbonate (includes generation of ‘new’ bicarbonate
  2. H+ Secretion in distal nephron (DT and CD), principally via ammonia, phosphate

Refer to previous lecture for detailed notes // explain this here

22
Q

Describe the response of the kidney to an acid load:

A
  • Increased HCO3 and H+ transport along the nephron
  • Increased ammoniogenesis
  • Increased availability of urinary buffers (mainly via ammonia)
23
Q

Describe in detail the generation of new bicarb production in the kidney and H secretion:

A

PCT: CA present on microvilli convert bicarb and acid into CO2 and water. CO2 crosses and in cell is converted back by CA. HCO3+Na symporter on basaloteral reasborbs these into blood. Na/H exchanger pump H back into tubule. (PCT+DCT and CD do this) [reabsorbed]

Production of new HCO3 comes from cellular CO2 production: H is secreted. into tubule lumen. HCO3/Cl exchanger on basolateral membrane. (DCT and CD)

H in tubule combines with HPO4 and NH3.

NH3 is produced by renal cells from glutamine.

24
Q

What is the rate of HCO3 reabsorption related to?

VIP

A

Related to arterial PCO2 and is increased by increased adrenal corticosteroids.

i.e in cushings, HCO3 is inversely related to plasma K and Cl.

25
Q

What is the rate of acid secretion by the kidney influenced by?

A
  • Availability of urinary buffers
  • Dissociation constants for those buffers and degree of acidosis
26
Q

What is the mantra of acid base physiology

A

Acidity = Bicarbonate / Carbon Dioxide

27
Q

What happens with respiratory disturbance in acid/base:

A

Respiratory acidosis = CO2 retention

Respiratory alkalosis = Hyperventilation

28
Q

What happens in metabolic disturbances acid base physiology

A

Metabolic acidosis: Increased acid production (low pH) (Low HCO3 as it buffers it)

Metabolic alkalosis: Loss of acid due to vomiting (stomach acid = HCl) (high pH and high HCO3 (from CO2, limitless supply))

29
Q

If the disorder is respiratory where does compensation occur?

A
  • Compensation is by the kidneys
  • This takes days
30
Q

If the disorder is metabolic where does compensation occur?

A
  • Compensation is by the lungs (+/- kidneys)
  • This takes hours

ECF buffering corresponds to the HCO3 bicarb buffer system

31
Q

Describe the compensation for respiratory disorders:

A

Ventilatory failure -> Inc. pCO2 -> Dec. pH -> Inc. H+ secretion and NH3 synthesis (Inc. HCO3)

Results in: Acid excretion as NH4

NB: Immediate effect of buffers has been omitted as these would have already occurred

(Process reversed for metabolic alkalosis)

32
Q

Describe compensation for (non-renal) metabolic disorders:

A

H+ accumulation via addition of acid or loss of HCO3 (i.e from gut)

Decreased pH, (HCO3 buffers and blunts this) this results in:

-> Inc. ventilation, decreasing pCO2 (develops over hours)

–> Renal compensation develops over days (inc. H+ secretion, inc NH3 secretion = acid excretion as NH4)

= pH return towards normal

(Process reversed for metabolic alkalosis)

33
Q

Describe compensation for renal metabolic disorders

A

Loss of HCO3 from kidneys results in H+ accumulation

Decreased pH (HCO3 buffers and blunts this)
=
Increased ventilation (dec. pCO2), pH returns towards normal

RENAL COMPENSATION LIKELY ABSENT FOR RENAL METABOLIC DISORDERS

(Process reversed for metabolic alkalosis)

34
Q

What is it called be low pH stimulates breathing?

A

Acidotic breathing

35
Q

In metabolic acidosis, how does the respiratory compensation function?

A

Reduction in pCO2 (hours)

Restores the pCO2/HCO3 ratio

36
Q

In respiratory acidosis, how does the renal compensation function?

A

Increase in bicarbonate (days)

Restores the pCO2/HCO3 ratio

37
Q

Summarise the changes in HCO3 and pCO2 in:

  • Metabolic alkalosis
  • Acute respiratory acidosis
  • Acute respiratory alkalosis
  • Metabolic acidosis
  • Mixed resp and metabolic acidosis
A
38
Q

Describe the compensation and pH changes of:

Metabolic acidosis
Resp. alkalosis
Resp. acidosis
Metabolic alkalosis

A
39
Q

Whats the role of aldosterone in acid base physiology?

A

Aldosterone acts on intercalated cells to promote H secretion

This is balanced by greater HCO3 reabsorption. (Cl loss to balance)

It also: ROMK (secretion) and ENAC (Na reabsorption) but these are principle cells

MBCHB3 RBF (39 decks)

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