Lecture 2 – Gas Exchange and Transport

1) How do the pulmonary circulation and the bronchial circulation to the lungs differ? Are these two circulations connected at all?

Pulmonary circulation carries oxygen-poor blood from the right ventricle to the lungs and back to the left atrium, while bronchial circulation supplies oxygen-rich blood to the lung tissues themselves. They are connected because some deoxygenated bronchial blood drains into pulmonary veins, slightly lowering oxygen levels entering the left atrium.

2) What type of cell makes up 95% of the surface area of our alveoli?

Squamous alveolar cells (Type I) make up 95% of the alveolar surface area.

3) Why are our lungs prone to collapsing and what do septal cells secrete to keep them from doing so?

The lungs are prone to collapse due to surface tension in moist alveoli. Septal (Type II) cells secrete pulmonary surfactant to prevent this.

4) What is a partial pressure? Gas will move from where it is in a _________ partial pressure to where it is in a ______________ partial pressure.

A partial pressure is the pressure each gas exerts in a mixture. Gas moves from high partial pressure to low partial pressure.

5) What is gas solubility and what two things affect the solubility of a gas?

Gas solubility is how much gas dissolves in a liquid, affected by partial pressure and the solubility coefficient of the gas.

6) If a gas has a low solubility, what is needed to push the gas into the liquid?

A gas with low solubility needs a larger pressure gradient to be pushed into the liquid.

7) What are the three reasons the partial pressures within the alveoli differ from those in the atmosphere?

Alveolar pressures differ because air mixes with dead space air, continuous gas exchange occurs, and there is more water vapor in the alveoli.

8) Explain the movement of gas that occurs during alveolar respiration? (be sure to include the partial pressures and which gas is moving in which direction)

During alveolar respiration, O2 (104 mm Hg) moves from the alveoli to the blood (40 mm Hg), and CO2 (45 mm Hg) moves from the blood to the alveoli (40 mm Hg)

9) The efficiency of gas diffusion across the respiratory membrane is dependent upon what two things? How do you think gas diffusion would be affected if a person had pneumonia (alveoli filled with fluid and mucus)?

Diffusion depends on large surface area and thin membrane. In pneumonia, fluid thickens the barrier, reducing gas exchange efficiency.

10) Define ventilation and perfusion. 

Ventilation is the movement of air into and out of lungs; perfusion is the movement of blood through pulmonary capillaries.

11) What effect would an increase in PCO₂ within the blood have on perfusion? How would this then affect ventilation?

Increased PCO2 in blood causes vasodilation of pulmonary arterioles, improving perfusion, and also bronchodilation, enhancing ventilation.

12) Why is there a lower PO₂ and higher PCO₂ within the systemic cells than in the blood? (What are the cells doing with the oxygen and where is the CO2 coming from?)

Systemic cells use O2 for energy (cellular respiration) and produce CO2 as waste, leading to low PO2 and high PCO2.

13) Why is PO₂ lower within the systemic capillaries than it is within the pulmonary capillaries?

PO2 is lower in systemic capillaries because deoxygenated bronchial blood mixes with oxygenated pulmonary blood.

14) How much of our oxygen is carried by hemoglobin?

About 98% of oxygen is carried by hemoglobin.

15) What chemical is most of our carbon dioxide converted into to, so it can be carried from the systemic tissues to the lungs within our blood?

Most CO2 is converted into bicarbonate (HCO3–) for transport.

16) Explain the conversion of carbon dioxide into bicarbonate.  What enzyme is necessary for this process and what is its specific function? 

In systemic capillaries, CO2 + H2O → H2CO3 → HCO3– + H+, catalyzed by carbonic anhydrase, which speeds up the conversion.

17) What is the chloride shift and why is it important?

The chloride shift is when Cl– enters RBCs as HCO3– leaves, maintaining electrical balance in the cell.

18) What three substances can be transported by attaching to hemoglobin and what part of the hemoglobin do they bind with?

Oxygen binds to iron, CO2 binds to globin, and H+ also binds to globin within hemoglobin.

19) What is hemoglobin saturation?  What has the greatest effect on hemoglobin saturation?

Hemoglobin saturation is the percentage of Hb bound to O2, mainly affected by PO2 levels.

20) What is the cooperative binding affect?

The cooperative binding effect means each bound O2 makes it easier for the next one to bind.

21) The OHSC is relating what two things to each other?

The OHSC relates PO2 to percent O2 saturation of hemoglobin.

22) When climbing up in altitude the partial pressure of oxygen decreases. How does this affect hemoglobin saturation? How would this change in hemoglobin saturation then affect the amount of oxygen available to the cells of the body?

At higher altitudes, PO2 decreases, lowering hemoglobin saturation and thus reducing oxygen available to body cells.

23) What is oxygen reserve and how is it affected by the metabolic needs of the systemic tissues?

The oxygen reserve is the O2 left bound to hemoglobin after systemic exchange; it decreases when metabolic demand increases.

24) What four things can cause in increased release of oxygen to the tissues of the body?

Increased temperature, low pH (high H+), 2,3-BPG, and CO2 binding all increase O2 release to tissues.

25) If more oxygen is released to the tissues, which type of shift in the OHSC curve will we see?

More oxygen release to tissues causes a right shift in the OHSC curve.