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Physiology- CP > Carriage of Gases > Flashcards

Carriage of Gases Flashcards

1
Q

What is the equation for pressure?

A

Pressure = Force/Area

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2
Q

What units can be used for pressure?

A
  • kPa (kiloPascal)
  • N/m²
  • mmHg (millimetres of mercury)
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3
Q

What is partial pressure?

A
  • In a mixture of gases, each one exerts an individual pressure- partial pressure
  • Partial pressure of any gas is independent of other gases in a mixture
  • If other gases were removed, the partial pressure would equal total pressure
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4
Q

What is Dalton’s law?

A
  • Total pressure is equivalent to sum of component partial pressures
  • E.g. Atmospheric pressure is 100kPa and oxygen constitutes 21% of air, there oxygen partial pressure = 21kPa
  • In lower altitude oxygen partial pressure is also lower
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5
Q

What is the relationship between partial pressure and solubility?

A
  • Gases dissolve in aqueous solutions

- At equilibrium, partial pressure of a gas in solution is equal to that of gaseous form

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6
Q

What is Henry’s Law?

A

[Gas]= partial pressure x solubility coefficient

  • Each gas has its own solubility coefficient
  • Also dependent on factors like temperature
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7
Q

How is oxygen carried in the blood?

A
  • Dissolved in plasma

- Bound to haemoglobin (found in erythrocytes)

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8
Q

What is the normal range of haemoglobin in females?

A
  • 11.5-16.0g/100 ml
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9
Q

What is the normal range of haemoglobin in males?

A
  • 13.5-18.0g/100ml
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10
Q

What is the importance of haemoglobin?

A
  • Haemoglobin is important because otherwise we would need a large cardiac output
  • 99% of oxygen carriage comes from haemoglobin
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11
Q

How does oxygen enter the blood from the lungs?

A
  • Diffusion from alveoli to the blood

- High pressure to low pressure

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12
Q

How is oxygen delivered to tissue?

A
  • Oxygen travels from blood into interstitium
  • From interstitial into cells
  • From cells into mitochondria for oxidative phosphorylation
  • Partial pressure from blood to mitochondria is decreasing so oxygen moves down a gradient
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13
Q

Describe the structure of haemoglobin

A
  • 4 sub- units each with global chain (peptide) and haem group (porphyrin ring)
  • Each subunit will bind to 1 molecule of oxygen
  • Saturated haemoglobin therefore will bind to 4 oxygen molecules
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14
Q

How much oxygen does 1g of haemoglobin bind to?

A
  • 1.36ml of oxygen at body temperature and pressure

- Hb is then saturated

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15
Q

What is anaemia?

A
  • Anaemia is the lack of Hb in the blood

- Less haemoglobin means less total oxygen content regardless of saturation

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16
Q

What does anaemia result from?

A
  • Impaired production (iron deficiency etc.)
  • Increased breakdown (haemolysis)
  • Blood loss (haemorrhage)
  • Fluid overload (haemodilution)
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17
Q

Describe the structure of adult haemoglobin (HbA)

A
  • 2 alpha chains of 141 amino acids

- 2 beta chains of 146 amino acids

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18
Q

What percentage of adult haemoglobin in HbA₂?

A

2%

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19
Q

Describe the structure of HbA₂

A
  • 2 alpha chains

- 2 delta chains replace the beta chains

20
Q

What percentage of adult Hb is HbF (foetal haemoglobin)?

A

1%

21
Q

Describe the structure of foetal haemoglobin

A
  • 2 alpha chains

- 2 gamma chains replace beta chains

22
Q

What is foetal haemoglobin?

A
  • Embryonic forms replaced by HbF from 13 weeks of gestation
  • At birth, majority of Hb is still HbF (80%)
  • Switched to adult forms occurs between 3-6 months of age
  • HbF not fully replaced and is approximately 1% adult Hb
23
Q

What are some genetic defects that can occur in globin chains?

A
  • Commonest of all genetic disorders
  • Thalassaemia- defect in synthesis of globin chains
  • Sickle cell disease- defect in structure of globin chains
24
Q

What is Thalassaemia?

A
  • Inherited defects in globin chain synthesis
  • Can either be alpha or beta thalassaemia depending on chain affected, Hb not made properly
  • Leads to imbalance of chains result in decreased erythropoiesis and increased haemolysis of mature cells
25
Q

What causes sickle cell disease?

A
  • Specific mutation in the beta chain

- A to T- valine for glutamine at codon 6

26
Q

What are the two types of sickle cell disease?

A
  • Heterozygous (HbAS)- leads to sickle cell trait

- Homozygous (HbSS)- leads to sickle cell anaemia

27
Q

Describe heterozygous sickle cell disease (HbAS)

A
  • Generally asymptomatic
  • Anoxia manifesting in stress (e.g. air travel)
  • Confers protection against malaria
28
Q

What does sickle shaped cell mean for the circulation?

A
  • Decreases flexibility of the cell leading to characteristic sickle shape
  • Sickling leads to shortened erythrocyte survival and impaired flow through microcirculation
  • Impaired blood flow and infarctions
29
Q

Describe homozygous sickle cell disease (HbSS)

A
  • Symptoms variable from asymptomatic to death
  • Increased turnover of cells can lead to severe haemolytic anaemia
  • Severe pain (bone and spleen common) due to vast-occlusive crises and infarction
30
Q

How long do sickle cell abnormalities take to manifest?

A
  • around 6 months

- Due absence of beta globin chains

31
Q

How does oxygen bind to haem?

A
  • Haem group has 4 pyrrole groups arranged in porphyrin ring, centre is Fe²⁺
  • Oxygen binds to Fe²⁺ and interacts with iron
  • Fe³⁺ is unable to do this
32
Q

Describe how haemoglobin saturation works

A
  • Each haemoglobin can carry 4O₂
  • Saturation 50\5 means half haemoglobin in the blood is fully saturated
  • Haemoglobin only exists in two states
33
Q

Describe cooperative binding of oxygen

A
  • Each oxygen increases haemoglobin affinity for oxygen
  • Cooperative binding means that once oxygen has bound, more likely for oxygen to continue to bind
  • Increasing affinity of Hb to bind to oxygen
34
Q

What are the relative oxygen affinities for two Hb sub-species?

A
  • Haemoglobin with three oxygens bound to it has 100x more affinity for oxygen than Hb with no oxygen bound to it
  • Haemoglobin with less bound oxygen makes blood appear blue
35
Q

Describe a normal oxygen-haemoglobin dissociation curve

A
  • Sigmoidal curve
  • Loading in lungs
  • Unloading in tissues
36
Q

Describe oxygen-haemoglobin dissociation in the heart

A
  • Heart extracts most oxygen available
  • As there is little functional reserve
  • To increase oxygen delivery, blood flow must increase
  • Cardiac muscle is sensitive to ischaemic stress
37
Q

Describe oxygen-haemoglobin dissociation in the kidneys

A
  • Kidney receives ~25% of cardiac output due to its excretory role rather than demand
  • Therefore, renal outflow has high Hb saturation
38
Q

What factors affect the dissociation curve?

A
  • Factors that affect haemoglobin affinity
    E.g. Hb affinity to bind to oxygen decreases
  • Dissociation curve shifts to right
  • At any given PO₂ now, Hb saturation is lower
  • Increased O₂ delivery to tissues
39
Q

What factors affect Hb affinity?

A
  • Temperature
  • [H+]- Bohr effect
  • 2,3 Biphosphoglyceric Acid (BPG)
40
Q

How does temperature affect oxygen-haemoglobin dissociation?

A
  • Increased temperature decreases the affinity for oxygen

- Reduced affinity can occur during exercise (metabolism)

41
Q

What is the Bohr Effect?

A
  • Related to pH changes- H+ and CO₂
  • H+ stabilises deoxy-Hb, decreasing affinity for O₂ and increasing tissue delivery- binds protein and change conformation shape
  • Chronic change in Ph from 7.4 to 7.2 can increase O₂ delivery by approx. 15%
  • Acute pH changes occur often and change O₂ delivery
  • Metabolically active tissue produces CO₂ and require more O₂ to respire aerobically
  • Anaerobic respiration will also increase pH
42
Q

What is BPG?

A
  • 2,3 Bisphosphoglyceric Acid
  • 1,3 BPG in glycolysis converted to 2,3 BPG (enzyme BPG maltase increases [H+])
  • 2,3BPG can be converted to 3-phosphoglycerate in glycolysis (enzyme BPG phosphate- decreases [H+])
43
Q

What factors increase BPG production?

A
  • High altitude
  • Chronic hypoxia states
  • -> Lung disease, heart disease and anaemia
44
Q

How does BPG stabilises Deoxy-Hb?

A
  • BPG stabilises the deoxy-Hb
  • BPG binds between lysine and histidine residues of B-globin chains
  • Oxygenated Hb has a different conformation and prevents binding
  • Does not stabilises Oxy-Hb
45
Q

Describe BPG and Foetal Haemoglobin

A
  • As BPG binds to beta chains it does not affect HbF, which has gamma chains
  • As such HbF has a greater affinity for O₂ than HbA in the presence of BPG
  • Without increased affinity, foetal haemoglobin has a higher affinity for any given PaO₂

Physiology- CP (19 decks)

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