BIOL 318: CH. 22 - GAS EXCHANGE & PULMONARY CIRCULATION

What is partial pressure?

Partial pressure is the contribution of one gas to the total pressure in a mixture of gases.

What is atmospheric pressure?

Atmospheric pressure is the sum of the pressure of all gases in a mixture.

What does Dalton’s Law state about total atmospheric pressure?

Dalton’s Law states that the total atmospheric pressure is the sum of the partial pressures of all gases in the mixture.

What percentage of the atmosphere is oxygen?

Oxygen makes up 20.9% of the atmosphere.

• nitrogen is the most abundant

What is the atmospheric pressure at sea level?

The atmospheric pressure at sea level is 760 mm Hg.

How is the partial pressure of oxygen (PO₂) calculated?

The partial pressure of oxygen (PO₂) is calculated by taking 20.9% of the atmospheric pressure, which results in 159 mm Hg.

How do gases travel in relation to pressure?

Gases travel down the pressure gradient, moving from areas of higher pressure to areas of lower pressure.

How do gases travel in relation to partial pressure?

Gases travel down their partial pressure gradient, moving from areas of higher partial pressure to areas of lower partial pressure.

What happens to atmospheric pressure as altitude increases?

Atmospheric pressure decreases with altitude.

How does a decrease in atmospheric pressure affect partial pressure gradients in the lungs?

A decrease in atmospheric pressure reduces partial pressure gradients in the lungs, which affects gas exchange.

Do oxygen levels change at different altitudes?

Oxygen levels do not change at different altitudes, but the lower atmospheric pressure reduces the availability of oxygen for gas exchange.

What are the effects of reduced partial pressure gradients in the lungs?

Reduced partial pressure gradients in the lungs lead to decreased gas exchange and slower diffusion of oxygen into the blood.

What is alveolar gas exchange?

Alveolar gas exchange is the process by which oxygen and carbon dioxide are exchanged between the alveoli and the blood in the lungs.

What produces the water film on the surface of the epithelium in the alveoli?

The water film is produced by Type II cells in the alveoli.

Where is the water film located in the alveoli?

The water film lines the lumen of the alveoli on the surface of the epithelium.

Why must oxygen be dissolved in water before entering tissues and blood?

Oxygen must be dissolved in water to facilitate its diffusion across the respiratory membrane into the blood.

What is the pathway of oxygen during alveolar gas exchange?

Oxygen moves from alveolar air into the water film and then across the respiratory membrane into the blood.

How does partial pressure influence gas diffusion in alveolar gas exchange?

Gases diffuse based on their partial pressure, with oxygen moving into the water film because its partial pressure is greater in the alveolar air than in the blood.

What happens to oxygen when it enters the alveolus?

The partial pressure of oxygen (PO₂₎ in the alveolus is greater than in water and blood, so oxygen enters the water and then moves into the blood.

What happens to carbon dioxide at the alveolus?

The partial pressure of carbon dioxide (PCO₂) in the blood at the alveolus is greater than in water, so carbon dioxide moves from the blood into the water and then into the alveolus.

Is blood fully saturated with oxygen when leaving the alveoli?

No, blood is not 100% saturated with oxygen when leaving the alveoli.

How do pulmonary veins interact with bronchial veins?

Pulmonary veins anastomose with bronchial veins, allowing for a connection between the two.

What gas has the highest partial pressure in the pulmonary circuit?

Nitrogen has the highest partial pressure.

Which gas has the lowest partial pressure in the pulmonary circuit?

CO₂ has the lowest partial pressure.

Where is PO₂ the highest in the body?

PO₂ is highest in the atmosphere.

Where is PO₂ the lowest in the body?

PO₂ is lowest in the tissues.

What does gas exchange efficiency depend on?

Gas exchange efficiency depends on:

• pressure gradients

• solubility of gases

• membrane thickness

• membrane area

• ventilation-perfusion coupling

How do pressure gradients affect gas exchange?

Pressure gradients drive gas exchange, and changes in altitude can impact them by altering atmospheric partial pressure.

Where is the lowest atmospheric partial pressure found?

The lowest atmospheric partial pressure is found at high altitudes.

How does solubility of gases affect gas exchange?

The solubility of gases affects how easily they dissolve in blood, with CO₂ being more soluble than O₂.

Why is oxygen less soluble in blood?

Oxygen is not very soluble in water, which limits its ability to dissolve directly into blood.

How does membrane thickness impact gas exchange?

Increased membrane thickness reduces gas exchange efficiency.

Why is membrane area important for gas exchange?

A larger membrane area allows for more gas exchange, while a reduced area, such as in emphysema, decreases efficiency.

How does emphysema affect gas exchange?

Emphysema leads to the loss of alveolar walls, reducing surface area for gas exchange.

What is ventilation-perfusion coupling?

Ventilation-perfusion coupling ensures that blood flow matches oxygen supply for efficient gas exchange.

What happens when PO₂ is low?

Low PO₂ causes vasoconstriction, reducing blood flow to poorly ventilated areas.

What happens when PO₂ is high?

High PO₂ causes vasodilation, increasing blood flow to well-ventilated areas.

What type of cells are present in the alveoli?

The alveoli have thin, simple squamous cells.

Are blood vessels present around the alveoli?

Yes, blood vessels are present around the alveoli.

What is the oxygen concentration in the alveoli relative to the blood returning to the lungs during inspiration?

During inspiration, the alveoli have high oxygen concentration, and the blood returning to the lungs has low oxygen concentration.

What is the carbon dioxide concentration in the alveoli relative to the blood returning to the lungs during inspiration?

During inspiration, the alveoli have low carbon dioxide concentration, and the blood returning to the lungs has high carbon dioxide concentration.

How does oxygen diffuse in the alveoli?

Oxygen diffuses from the air to the water, through the epithelium, and into the blood.

What happens when oxygen enters RBCs?

Oxygen enters red blood cells (RBCs) and binds to hemoglobin.

Where does the oxygen go after binding to hemoglobin in RBCs?

The oxygen travels to other tissues of the body for delivery.

What is the concentration of oxygen in the blood when it reaches the tissues?

The oxygen concentration in the blood is high when it reaches the tissues.

What is happening in the tissues at this point?

Many tissues are aerobically metabolizing, which uses oxygen and produces carbon dioxide and water.

What is the difference in oxygen concentration between the blood and tissues?

The blood has a high oxygen concentration, while the tissues have a low oxygen concentration.

What is the difference in carbon dioxide concentration between the blood and tissues?

The blood has a low carbon dioxide concentration, while the tissues have a high carbon dioxide concentration.

What happens to oxygen when it reaches the tissues?

Oxygen unbinds from hemoglobin and diffuses into the tissue cells.

What conditions in the tissues favor the unloading of oxygen from hemoglobin?

Low pH, high carbon dioxide, and low oxygen in the tissues favor the unloading of oxygen from hemoglobin.

Why are the tissues more acidic?

The tissues are more acidic because they are producing carbon dioxide, which lowers the pH.

What happens to carbon dioxide in the tissues?

Carbon dioxide diffuses out of the tissue cells and enters the blood.

What happens when CO₂ enters red blood cells (RBCs)?

CO₂ binds to hemoglobin in red blood cells.

Where is CO₂ traveling when it binds to hemoglobin in RBCs

CO₂ is traveling towards the lungs.

What is the chemical equation for the conversion of CO₂ in the RBC?

CO₂ + H²O ⇄ H₂CO₃ ⇄ H+ + HCO3-.

What forms from the combination of CO₂ and water in red blood cells?

Carbonic acid (H2CO3) forms and dissociates into H+ and bicarbonate (HCO3-).

What is the majority form in which CO₂ is carried in the blood?

The majority of CO2 is carried as bicarbonate (HCO3-).

Which enzyme is responsible for the conversion of CO₂ and H2O in red blood cells?

The enzyme carbonic anhydrase is responsible for the conversion.

What happens to bicarbonate (HCO3-) after it forms in the RBC?

Bicarbonate (HCO3-) leaves the RBC to act as a buffer against low pH.

What compensates for the charge when bicarbonate leaves the red blood cell?

Chloride ions (Cl-) enter the RBC to balance the charge, a process known as the chloride shift.

How does gas exchange occur in the lungs with respect to temperature?

Gas exchange in the lungs occurs at a colder temperature.

What is the oxygen concentration in the alveoli compared to the blood?

The alveoli have high oxygen (O2) concentration, while the blood has low oxygen concentration.

What is the carbon dioxide concentration in the alveoli compared to the blood?

The alveoli have low carbon dioxide (CO2) concentration, while the blood has high carbon dioxide concentration.

What happens when bicarbonate (HCO3-) enters red blood cells (RBCs)?

When bicarbonate (HCO3-) enters RBCs, chloride (Cl-) leaves the RBCs in a process called the reverse chloride shift.

What role does carbonic anhydrase play in the formation of water (H2O) and carbon dioxide (CO2)?

Carbonic anhydrase drives the formation of water (H2O) and carbon dioxide (CO2).

What is the chemical equation that describes the formation and reversal of CO2 and H2O in red blood cells?

The chemical equation is: CO2 + H2O ⇄ H2CO3 ⇄ H+ + HCO3-.

How does CO2 leave the RBCs and exit the body?

CO2 leaves the RBCs, diffuses out of the blood into the alveoli, and is then exhaled.

How does oxygen move from the alveoli to the blood?

Oxygen diffuses from the alveoli into the blood.

How often does the cycle of gas exchange occur?

The cycle of gas exchange occurs approximately three times per minute.

Where does deoxygenated blood enter the heart?

Deoxygenated blood enters the heart through the right atrium.

How does blood reach the right atrium?

Blood reaches the right atrium via the superior vena cava, inferior vena cava, and coronary sinus.

What happens when the atria contract?

When the atria contract, blood is pushed into the right ventricle.

What happens when the ventricles contract?

When the ventricles contract, blood is forced up the pulmonary trunk.

Where does blood go after being forced up the pulmonary trunk?

After being forced up the pulmonary trunk, blood travels to the pulmonary arteries, which carry it to the lungs.

What do arteries and veins do in pulmonary circulation?

Arteries carry blood away from the heart, while veins carry oxygen-rich blood to the heart.

Where does oxygen-rich blood go after leaving the lungs?

Oxygen-rich blood from the lungs travels through the pulmonary veins to the left atrium.

What happens when the left atrium contracts?

When the left atrium contracts, blood is pushed into the left ventricle.

What is the next step for blood after the left ventricle contracts?

After the left ventricle contracts, blood is pushed into the aorta.

What does the aorta do in the circulatory system?

The aorta distributes blood to systemic and coronary circulation.