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Dentistry Biological Science > Respiration 2 > Flashcards

Respiration 2 Flashcards

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1
Q

Give the composition of atmospheric air

A

79% nitrogen
21% oxygen
trace co2

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2
Q

What are volumes for oxygen consumed at rest and carbon dioxide produced?
Why are they different?

A

250ml O2
200ml CO2

Different as oxidation of organic fuel produces water as well as CO2 and the water is a dilution factor.

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3
Q

How much oxygen do we have travelling around the blood per minute?
What is alveolar ventilation at rest?

A

1L (250ml breathed in and 750ml reservoir)

4.2L/min (21% of this will be oxygen)

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4
Q

What is the value for the reservoir of carbon dioxide we have and how many is expelled?

A

2400ml and 200ml per min

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5
Q

What two things affect pressure of a gas?

Explain Daltons law

A

Temperature + concentration of gas molecules

Individual pressure of a particular gas in a mixture of chemically non-reactive gases is called partial pressure.

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6
Q

Why does the oxygen concentration decreases rom the atmosphere to the upper airway?
Why is the oxygen expelled higher than that in the alveoli?

A

The air in the upper airway gets humidified which partially dilutes the oxygen.

Mixing of alveolar gas with air in the anatomical dead space.

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7
Q

Why is Henry’s law applicable to this?

A

Amount of gas dissolved in a liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.
Gases diffuse from higher to lower partial pressures.
So direction of diffusion depends on direction of partial pressure difference not on concentration difference.

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8
Q

Why use partial pressures instead of concentrations of the gases?

A

1) . Partial pressure is a better indication of how a gas will diffuse from one compartment to another
2) . Content (concentration) of gas dissolved in liquid depends on solubility as well as partial pressure - while concentration of a gas in a mixture of gases does not.

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9
Q

Give the keys points on systemic and alveolar blood gas concentrations

A

During gaseous exchange:
Systemic blood PO2 equilibrates to (almost) match alveolar PO2
Systemic PCO2 equilibrates to (exactly) match alveolar PCO2

After gaseous exchange:
Systemic blood p02 equilibrates to almost match alveolar pO2.
Alveolar pC02 equilibrates to exactly match systemic blood pCO2.

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10
Q

What is the rate of transfer of gas between air and blood determined by?

A
  • partial pressure difference
  • solubility
  • thickness of diffusion barrier (alveolar epithelium and capillary endothelium)
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11
Q

What provides the driving force for diffusion and what limits this?

A

Driving = partial pressure difference

Limited by solubility of the gas in water and the diffusion barrier.

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12
Q

High or low?

Solubility and partial pressure differences for oxygen and carbon dioxide

A

Oxygen:
Partial pressure difference = high
solubility = low

Carbon dioxide:
pp difference = low
solubility = high

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13
Q

Because transfer is rapid, where is equilibrium achieved in the pulmonary capillary?

A

1/3 along

other 2/3 is for when more oxygen is needed

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14
Q

What is systemic and alveolar levels of these gases controlled by?

A

systemic blood PO2 is determined by alveolar PO2 and alveolar PCO2 is determined by capillary blood PCO2

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15
Q

Why is systemic arterial pO2 less than alveolar pO2?

A

1) . The anatomical right-to-left shunt (next slide) of deoxygenated bronchial vein blood mixing with oxygenated pulmonary vein blood, lowers PO2 entering left atria
2) . Drainage of part of the coronary venous blood directly into the left ventricle, further lowers PO2 of blood flowing from left ventricle into aorta

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16
Q

Explain the left-to right shunt

A

Mixing of deoxygenated and oxygenated blood.
Systemic bronchial arteries supply bronchioles with blood. Deoxygenated blood from these drains into the pulmonary vein (oxygenated blood).

Also in the heart, part of the coronary venous blood drains directly into the left ventricle.

17
Q

How is oxygen in blood carried to tissues?

A

By bulk flow.
A change in partial pressure.
Capillary oxygen must be sufficient to maintain the gradient and supply the mitochondria with this oxygen for glycolysis.

18
Q

What are the 4 measurements of oxygen transport?

A
  1. Percentage of haemoglobin saturation
  2. Amount of gas in Hb and plasma
  3. Max that could be carried if all Hb is saturated.
  4. Partial pressure and the difference which drives diffusion and the uptake and release of oxygen by haemoglobin
19
Q

Why do we need Hb?

A

Oxygen carrying capacity of blood is greatly increased with it.

20
Q

What is the % saturation of oxygen entering pulmonary capillaries?

A

75%

21
Q

Explain the structure of haemoglobin and haem?

Why is this oxygenation and not oxidation?

A

Haemoglobin:
4 protein subunits (2 alpha and 2 beta) each with own haem group
Each hb can carry 4 O2

Haem:
Each contains a Fe2+ ion which binds both a histidine of the globin protein and a molecule of oxygen

Fe2+ ion remains in ferrous state when binding oxygen.

22
Q

What is binding to hb affectd by?

A

Co-operativity
temperature
pCO2
pH

it can either facilitate uptake of oxygen in lungs or release of oxygen in tissues where it is needed.

23
Q

Explain the key points on an O2-Hb dissociation curve

A

Curve is sigmoidal due to cooperatively of Hb - binding of one oxygen increases affinity.

Exponential phase: small increases in pO2 causes large increases in saturation. Oxygen consumption in tissues lowers pO2, small drop in pO2 causes large drop in % saturation, aiding unloading of oxygen where needed.

Plateau phase: Further changes in pO2 have little affect on % saturation. Large drop in pO2 causes only a small drop in % saturation so supports oxygen uptake in low atm

24
Q

What blood are we considering at the exponential and the plateau phase?

What does the difference between the oxygen content in the blood at each of these stages show?

A

Exponential - mixed venous blood

Plateau - normal arterial blood

Shows the blood normally extracted by tissues at rest.

25
Q

Explain the shift of the oxygen dissociation curve to the left

  • what causes it
  • where it occurs

What happens at the tissues?

A

Left means an increased affinity for oxygen (oxygen binds more readily).
In alveoli: loss of co2 raises pH - evaporation lowers temp, left-ward shift aids uptake of oxygen by haemoglobin

In tissues, co2 is being produced, lowering pH. Metabolism raises temp. rRight-ward shift triggers unloading of oxygen from Hb where it is needed.

26
Q

Explain the changes in oxygen concentration during gaseous exchange.

A

Decreased from dry air to trachea and the air gets moistened.
Decreases again after oxygen extraction in alveolar which then is the same in the pulmonary capillary as they equilibrate.
Slight decrease again as arterial blood is mixed with oxygenated blood,

Two more decreases as it goes into the mean tissue capillary and mitochondria and then an increase in mixed venous blood.

27
Q

What are the 3 ways that carbon dioxide is transported?

A
  • Dissolved in plamsa
  • As bicarbonate
  • As carbamino compounds
28
Q

Co2 + water to bicarbonate reaction:
Where is it fast?
What is a rightward shift in equilibrium aided by?

A

Fastest in erythrocytes

rightward shift:

1) Exchange of bicarbonate for Cl- (chloride shift)
2) Buffering of H+ by deoxy-Hb
3) Carbon dioxide reactions with Nh2 groups on lysine and arginine residues of Hb amino acids to reduce Co2 conc.

29
Q

What is the haldane effect?

A

At any given pCO2, the quantity of CO2 carried is greater in partially deoxygenated (venous) blood than in oxygenated (arterial) blood.
Due to:
1) Better buffering of H+ by oxy-Hb promotes formation of HCO3-
2) Hb forms carbamino compounds with CO2 more readily when deoxygenated

30
Q

How does the haldane effect work in the lungs?

A

Hb becomes oxygenated.

CO2 released from carbamino compounds & HCO3- converted back to CO2.
Diffusion of CO2 out blood into alveoli.

31
Q

Give details on the C02 dissociation curve

A

Curve is semi-linear.
Has a small range of partial pressures.
For a given pCO2, the CO2 content of oxygenated blood is less than that of deoxygenated blood.

32
Q

Why is alveolar ventilation (V , ~4.2 L/min) always less than a minute ventilation (VM, ~6.0 L/min)?

A

Anatomical dead space

Dentistry Biological Science (88 decks)

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