Week 7 - Respiration during exercise (p3) Flashcards

1
Q

What is Dalton’s law?

A

total pressure of a gas mixture is equal to the sum of the pressure that each gas would exert independently

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2
Q

How is the partial pressure of a gas worked out?

A

fraction of gas within air x barometric pressure (x 750mmHg at sea level)

Oxygen 159 mmHg
Carbon dioxide 0.3 mmHg
Nitrogen 600.7 mmHg
(Inspired air)

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3
Q

Identify the difference between arterial partial pressure of oxygen and alveolar partial pressure of oxygen.

A

Arterial PO2 (100mmHg) is slightly less than alveolar PO2 (105mmHg) due to a very small gas exchange impairment.

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4
Q

Identify the difference between arterial PCO2 and alveolar PCO2.

A

both 40mm Hg

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5
Q

At rest, what is PO2 and PCO2 in deoxygenated blood?

A

PO2 40mmHg
PCO2 46mmHg

Venous PO2 is decreases whereas venous PCO2 is increases as tissues consume oxygen but produce CO2.

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6
Q

What happens to partial pressure of O2 and CO2 in the alveolar when inspired?

A

PO2 decreases to 105mmHg (from 159)
PCO2 increases to 40mmHg (from 0.3)

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7
Q

What are the four steps of pulmonary circulation?

A
  1. Pulmonary artery carries deoxygenated blood from
    the right ventricle to the lungs
  2. Gas exchange between the alveoli and pulmonary
    capillaries occurs
  3. Oxygenated blood is returned to the left atrium via
    the pulmonary vein
  4. Oxygenated blood is pumped around the systemic
    circulation to systemic cells
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8
Q

What is the pressure and resistance of the pulmonary circuit like?

A

low pressure, low resistance

mean pulmonary artery pressure is 15mmHg

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9
Q

What is the mean pulmonary artery pressure compared to systemic arterial pressure?

A

15mmHg compared to 100mmHg

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10
Q

Why is the pulmonary circulation low resistance?

A

its thin walled and has little smooth muscle - this is it accepts the entire cardiac output so it doesn’t need to redistribute the blood.

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11
Q

During exercise, what happens to pulmonary vascular resistance?

A

decreases due to recruitment and distension (enlarge) of pulmonary capillaries which increases flow and decreases resistance

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12
Q

What does gas exchange require a matching of?

A

Ventilation to blood flow (V/Q)

  • The ideal V/Q is 1
  • V/Q > 1 = under perfused (apex of lung)
  • V/Q < 1 = over perfused (base of lung)
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13
Q

Upon exercise, why does V/Q improve?

A

o Increased tidal volume
o Increased pulmonary artery pressures

In some cases, V/Q worsens, especially during heavy exercise

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14
Q

What are the two forms in which oxygen is carried in the blood?

A
  1. Dissolved into plasma (2%)
  2. Bind with haemoglobin (98%)
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15
Q

What is Henry’s law?

A

the amount of gas dissolved in blood is proportional to the partial pressure of that gas

o The amount of O2 dissolved is 0.003 mL O2/100 mL blood/mmHg.
o At an arterial PO2 of 100 mmHg, this results in 0.003*100=0.3 mL O2/100 mL blood.

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16
Q

Each molecule of haemoglobin (Hb) can transport how many molecules of oxygen?

A

4

17
Q

How many mL of oxygen do we have per gram of haemoglobin?

A

1.34mL per gram of Hb

18
Q

How many grams of haemoglobin do you have per 100mL of blood?

A

15

19
Q

How do you work out arterial oxygen content?

A

1.34 x haemoglobin mass x oxygen saturation/100 + (0.003 x PO2)

1.34 x 15 x 1 + (0.003 x 100) = 20.3mL O2/100ml of blood

20
Q

What is the total oxygen content in venous blood?

A

15

less than oxygen content in arterial blood which is 20

21
Q

When venous P02 decreases during exercise, what is the effect?

A

the amount of 02 unloaded to tissues becomes significantly greater

22
Q

What is the “Bohr effect”?

A

exercise causes an increase in H+, CO2 and core body temperature, causing a rightward shift of the oxyhemoglobin dissociation curve (ODC) - so haemoglobin is less saturated with oxygen which facilitates the unloading of O2 to active tissue

23
Q

What is the protein that carries oxygen in the muscle?

A

Myoglobin - an oxygen binding protein found in skeletal muscle

24
Q

What is the role of myoglobin?

A
  • High O2 affinity; unloads at very low PO2 (less than 20)
  • Shuttles O2 from muscle cell membrane to mitochondria for aerobic respiration
  • Provides intramuscular O2 storage for when its needed during exercise (its a reserve)
25
Q

What are the 3 forms in which carbon dioxide is carried in the blood?

A
  1. Dissolved in plasma (10%)
  2. Bound to deoxygenated haemoglobin to form carboamino haemoglobin (20%)
  3. Bicarbonate (70%)
26
Q

What is the principal way that carbon dioxide is transported?

A

by bicarbonate

27
Q

Is CO2 more soluble or is O2 more soluble?

A

CO2 20x more soluble than 02

28
Q

Carbon dioxide binds with oxygen to form carbonic acid which dissociates into bicarbonate and a hydrogen ion. What happens next?

A

bicarbonate leaves the RBC and chlorine moves into the cell to maintain neutrality

29
Q

What is the equation for bicarbonate and hydrogen ion?

A

CO2 + water –> carbonic acid –> bicarbonate + H+

30
Q

How does CO2 production during exercise stimulate breathing via a feedback loop?

A

causes an increase in H+ and thus a decrease in arterial pH - this stimulates breathing

31
Q

What form is most of the oxygen contained in blood?

A

oxyhemoglobin as oxygen binds to hemoglobin