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Primary FRCA > Physiology 18 > Flashcards

Physiology 18 Flashcards

1
Q

What are the two types of metabolic reaction? Give examples

A

Exergonic (energy-releasing)

  • Catabolism
  • Breaking bonds
  • Oxidation (Proton-producing reactions)

Endergonic (energy-consuming)

  • Anabolism
  • Maintenance of acid-base balance
  • Reduction (Proton-consuming reactions)
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2
Q

What are the components of total energy expenditure?

A

= work done + heat produced + energy stored

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3
Q

What is basal metabolic rate?

A

BMR = total energy liberated by a starved human body at complete rest at a comfortable ambient temperature

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4
Q

What factors affect metabolic rate?

A
  • Age (higher in children)
  • Gender (higher in males)
  • BSA
  • Stress levels
  • Muscle activity
  • Conscious level
  • Temperature
  • Hyperthyroidism
  • Pregnancy
  • Feeding
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5
Q

What is the average BMR of a young adult?

A

70-100 kcal/h

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6
Q

What are the main energy storing molecules used to drive reactions?

A

ATP
NAD+ (nicotinamide adenine dinucleotide)
FADH (flavin adenine dinucleotide)

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7
Q

How much ATP is produced by oxidation of NADH?

A

3x ATP

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8
Q

How much ATP is produced by oxidation of FADH2?

A

2x ATP

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9
Q

Break down the total ATP produced by metabolism of one glucose molecule

A

Glycolysis:
-2x ATP, 2x NADH

2x Pyruvate -> Acetyl CoA:
-2x NADH

2x Citric Acid Cycle:
-2x ATP, 6x NADH, 2x FADH2

Following the ETC this is a total of 38 ATP

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10
Q

Summarise the digestion of complex carbohydrates

A

Stage 1:
-Salivary and pancreatic amylases break polysaccharides into oligosaccharides

Stage 2:
-Maltase, lactase and sucrase in the small intestine convert oligosaccharides into absorbable monosaccharides

Absorption is driven by active transport with sodium

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11
Q

What are the daily requirements for carbohydrate, protein and fat for an adult?

A

Carb: 5-10 g/kg
Fat: 1-2 g/kg
Protein: 0.5-1 g/kg

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12
Q

What are the calorific values of protein, fat and carbohydrate?

A

Carbohydrate: 4 kcal/g
Fat: 9 kcal/g
Protein: 4 kcal/g

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13
Q

What is the common metabolite of proteins, fats and carbohydrates that allows the majority of energy production?

A

Acetyl CoA

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14
Q

What are the stages of glycolysis (broadly)?

A
  1. Phosphorylation to glucose-6-phosphate by glucokinase

2. Glycolysis pathway producing pyruvate

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15
Q

What is the energy balance of glycolysis?

A

Production of 4x ATP but consumption of 2x ATP = net 2x ATP

Production of 2x NADH

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16
Q

How is pyruvate prepared for the Krebs’ cycle?

A
  • Transported to mitochondria (when O2 present)

- Converted to Acetyl CoA, each pyruvate producing 1x Acetyl CoA, NADH and CO2

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17
Q

Where is glycogen stored?

A

Skeletal muscle and liver (3:1 ratio)

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18
Q

Outline the process of glycogenesis

A

Glucose -> Glucose-6-phosphate -> added to glycogen chains by glycogen synthetase + branching enzyme

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19
Q

What are the possible substrates for gluconeogenesis?

A
  1. Pyruvate
    - From deamination of amino acids
    - From lactate via the Cori cycle
  2. Glycerol
    - From breakdown of triglycerides in the liver

Both pyruvate and glycerol can undergo reverse glycolysis in the liver to produce glucose

20
Q

Summarise the Krebs cycle, naming important intermediates

A

Acetyl CoA (2C) + Oxaloacetate (4C) -> Citrate (6C) -> α-ketoglutarate (5C) -> Succinate (4C) -> Oxaloacetate (4C)

Produces 2x CO2, 3x NADH, 1x FADH2 and 1x ATP

21
Q

Outline the major concepts of oxidative phosphorylation / the Electron Transport Chain

A
  • System of electron and H+ carriers embedded in inner membrane of mitochondrion
  • These carriers oxidise FADH2 and NADH, pumping hydrogen ions into the interspace between the inner and outer mitochondrial membrane and passing along 2e-from each molecule of NADH/FADH2.
  • 1x NADH results in 10x H+ being pumped in to the interspace.
  • 1x FADH2 results in 6x H+ being pumped into the interspace.
  • At the end of the chain, cytochrome A3 combines 2e- + 1/2O2 + 2H+ to make water
  • The generated transmembrane flow of H+ down its gradient is used to drive ATP synthase
22
Q

How is CO2 carried in the blood?

A

Three ways:

  1. In solution
  2. Carbamino carriage (protein bound)
  3. As HCO3-
23
Q

How is total CO2 in solution calculated?

A

TCO2 = pCO2 x solubility coefficient

At 37°C the CO2 coefficient is 0.231

24
Q

What is the relative proportion of different modes of CO2 transport in the blood?

A

In solution: ~5%
Carbamino CO2: ~5%
HCO3-: ~90%

25
Q

What are the stages of bicarbonate production from CO2?

A

1: CO2 + H2O >< H2CO3

Equilibrium lies far to left - <1% of CO2 is as carbonic acid

2: H2CO3 >< H+ + HCO3-

[3: HCO3 + H+ >< 2H+ + CO32-]
Only occurs >pH 9

26
Q

How many isoenzymes of carbonic anhydrase exist in humans?

27
Q

Where is carbonic anhydrase found in humans?

A
  • RBCs
  • Lung cell tissue and capillary membrane
  • Muscle tissue
  • Bowel cell tissue and stomach membrane
  • Nasal mucosal membrane
  • Salivary glands
  • Mitochondria
28
Q

What metal does carbonic anhydrase contain?

29
Q

What is the mechanism of action of carbonic anhydrase?

A

H2O + Zn -> H+ + ZnOH-

ZnOH- + CO2 -> ZnHCO3-

ZnHCO3 -> Zn + HCO3-

30
Q

How quickly does carbonic anhydrase catalyse the formation of HCO3-?

A

Very quickly

The rate-limiting step is the availability of a buffer to accept the proton produced

31
Q

What is acetazolamide?

A

A non-selective carbonic anhydrase inhibitor

32
Q

How does acetazolamide help in the treatment of AMS?

A

Slows down CO2 transport, increasing intracellular CO2 and driving ventilation, thus ‘accelerating’ acclimatisation

33
Q

Can the body function without carbonic anhydrase?

A

Yes

It takes a level of inhibition above 98% to cause significant resting physiological change (increase in CO2 gradient between tissues and alveoli)

34
Q

Summarise carbamino carriage

A

Uncharged amino groups (R-NH2) can combine with CO2 -> carbamic acid

Carbamic acid can then dissociate -> carbamate + H+

Carbamino carriage requires that the uncharged amino group is not involved in a peptide bond and thus must be a terminal or side chain amino group (eg. arginine, lysine)

35
Q

What is the major factor limiting carbamino carriage?

A

Competition with H+ ions for uncharged amino groups.

Thus carbamino carriage is highly pH - dependent

36
Q

Where does carbamino carriage take place?

A

Almost exclusively in Hb - deoxyHb is 3.5x more effective than oxyHb - leads to the Haldane effect (along with the increased buffering capacity of deoxyHb)

Carbamino carriage capacity is responsible for 1/3 of the total arteriovenous difference in CO2 carriage

37
Q

What is the major factor affecting the buffering ability of proteins in the blood?

A

The imidazole group of the amino acid Histidine is the only group that acts as an effective buffer at physiological pH, therefore buffering capacity of plasma proteins/Hb is directly proportional to Histidine content

38
Q

How many histidine residues can be found in a Hb tetramer?

39
Q

How does Hb oxygenation affect protein buffering?

A

DeoxyHb -> Basic imidazole -> more H+ acceptance -> more HCO3- production

OxyHb -> Acidic imidazole -> less buffering

40
Q

How does the state of histidine affect Hb-O2 binding?

A

DeoxyHb -> Basic histidine -> Increased affinity of Hb for O2

This contributes to the Bohr effect

41
Q

How do RBCs avoid accumulation of H+ and HCO3-?

A
  1. Hb buffering of H+
  2. Hamburger shift:
    - Active export of HCO3- in exchange for Cl- by the membrane-bound proetin Band 3
42
Q

What is known about Band 3?

A
  • In addition to driving the Hamburger shift, band 3 also provides an anchoring site for the RBC cytoskeleton and band 3 defects may lead to hereditary spherocytosis.
  • Band 3 may have a role in the deformabiltiy of RBCs seen in the capillary
  • Band 3 is bound to carbonic anhydrase, facilitating rapid export of produced HCO3-
43
Q

What is the effect of hypothermia on CO2 carriage?

A
  • Solubility increases
  • Thus maintenance of pCO2 requires greater total content
  • Hypothermia also reduces the rate of dissociation of water, reducing production of H+ ions and increasing pH
44
Q

Outline the hypotheses for the physiological response to hypothermia

A

pH-stat vs. alphastat

pH-stat:

  • Response to hypothermia is to maintain pH 7.4 regardless of body temperature.
  • Achieved in hibernating mammals by hypoventilation
  • The resultant high pCO2 and intracellular acidosis may contribute to the hibernating ‘sleep’ state

alphastat:

  • Response to hypothermia is to allow pH to change accordingly
  • Ionisation state (and buffering function) of histidine changes to similar degree as dissociation of water, thus protein function remains close to normal
  • alphastat compensation is common in cold-blooded animals to good effect
45
Q

How do the different methods of managing pH in hypothermia differ on a practical level?

A

pH-stat:

  • pCO2 measured at 37°C then mathematically corrected for temperature
  • CO2 is administered to achieve pH of 7.4 (corrected for temperature)
  • High pCO2 may help to improve cerebral function, but no clinical evidence to support overall benefit (or harm) vs. alphastat

alphastat:

  • pCO2 measured at 37°C
  • Management adjusted to maintain uncorrected pH 7.4

Primary FRCA (34 decks)

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