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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
What are the stages of bicarbonate production from CO2?
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
How many isoenzymes of carbonic anhydrase exist in humans?
11
27
Where is carbonic anhydrase found in humans?
- RBCs - Lung cell tissue and capillary membrane - Muscle tissue - Bowel cell tissue and stomach membrane - Nasal mucosal membrane - Salivary glands - Mitochondria
28
What metal does carbonic anhydrase contain?
Zinc
29
What is the mechanism of action of carbonic anhydrase?
H2O + Zn -> H+ + ZnOH- ZnOH- + CO2 -> ZnHCO3- ZnHCO3 -> Zn + HCO3-
30
How quickly does carbonic anhydrase catalyse the formation of HCO3-?
Very quickly The rate-limiting step is the availability of a buffer to accept the proton produced
31
What is acetazolamide?
A non-selective carbonic anhydrase inhibitor
32
How does acetazolamide help in the treatment of AMS?
Slows down CO2 transport, increasing intracellular CO2 and driving ventilation, thus 'accelerating' acclimatisation
33
Can the body function without carbonic anhydrase?
Yes It takes a level of inhibition above 98% to cause significant resting physiological change (increase in CO2 gradient between tissues and alveoli)
34
Summarise carbamino carriage
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
What is the major factor limiting carbamino carriage?
Competition with H+ ions for uncharged amino groups. Thus carbamino carriage is highly pH - dependent
36
Where does carbamino carriage take place?
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
What is the major factor affecting the buffering ability of proteins in the blood?
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
How many histidine residues can be found in a Hb tetramer?
38
39
How does Hb oxygenation affect protein buffering?
DeoxyHb -> Basic imidazole -> more H+ acceptance -> more HCO3- production OxyHb -> Acidic imidazole -> less buffering
40
How does the state of histidine affect Hb-O2 binding?
DeoxyHb -> Basic histidine -> Increased affinity of Hb for O2 This contributes to the Bohr effect
41
How do RBCs avoid accumulation of H+ and HCO3-?
1. Hb buffering of H+ 2. Hamburger shift: - Active export of HCO3- in exchange for Cl- by the membrane-bound proetin Band 3
42
What is known about Band 3?
- 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
What is the effect of hypothermia on CO2 carriage?
- 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
Outline the hypotheses for the physiological response to hypothermia
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
How do the different methods of managing pH in hypothermia differ on a practical level?
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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