Physiology BIOL224 Chapter 17 - Respiratory Gas Exchange

What are the normal resting values of Partial Pressure of Oxygen (PO2) and Partial Pressure of Carbon Dioxide (PCO2) in Blood leaving the lungs entering systemic capillaries?

(PO2) 104 mm Hg (PCO2) 40 mm Hg

What is the normal resting Partial Pressure of Oxygen (PO2) and Partial Pressure of Carbon Dioxide (PCO2) in the Alveoli?

(PO2) 104 mm Hg (PCO2) 40 mm Hg

What are the normal resting values of Partial Pressure of Oxygen (PO2) and Partial Pressure of Carbon Dioxide (PCO2) in Blood leaving tissues and returning to lungs?

(PO2) 40 mm Hg (PCO2) 45 mm Hg

What is the normal resting Partial Pressure of Oxygen (PO2) and Partial Pressure of Carbon Dioxide (PCO2) in Blood entering the pulmonary capillaries?

(PO2) 40 mm Hg (PCO2) 45 mm Hg

What percentage of the oxygen transported in the blood is dissolved in the plasma? What percentage of oxygen is transported by hemoglobin?

1.5% 98.5%

Approximately what percentage of CO2 is transported by being dissolved in plasma?

10%

Approximately what percentage of CO2 is transported by being combined with hemoglobin as carbaminohemoglobin?

20%

What percentage of O2 carried by Hemoglobin (Hb) is released to resting tissues?

20-25%

Oxygen amounts to what percentage of air pressure at sea level? What is atmospheric pressure at sea level?

21% (159 mmHg) 760 mmHg

Approximately what percentage of CO2 is transported by Bicarbonate ions?

70%

Under normal resting conditions, what is the saturation percentage of Hemoglobin (Hb) in the tissues?

75%

Under normal resting conditions, what is the saturation percentage of Hemoglobin (Hb) in the lungs?

98%

How does the composition of alveolar gas differ from that of atmospheric air?

Alveolar gas = Less Oxygen, More Carbon Dioxide, and More Water.

What is the reaction by which CO2 reversibly combines with H2O to form carbonic acid (H2CO3), which dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3¯)?

CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3

How does the solubility of oxygen in body fluids compare to the solubility of carbon dioxide?

Carbon dioxide is 20 times more soluble than oxygen

What enzyme is involved in catalyzing the reaction between CO2 and H20 to form Carbonic Acid?

Carbonic Anhydrase

Which chemoreceptors are most important for responding to rising CO2 levels?

Central Chemoreceptors

The total pressure exerted by a mixture of gases is equal to the sum of the partial pressure of individual gases refers to what Law?

Dalton's law of partial pressures

What are the three ways CO2 is transported in the blood?

Dissolved in Plasma Combined with hemoglobin as Carbaminohemoglobin Bicarbonate ions

How would external respiration be affected by a decrease in the surface area of the respiratory membrane?

External respiration would decrease

How would external respiration be affected by an increase in the thickness of the respiratory membrane?

External respiration would decrease

In metabolically active tissues, the PO2 may drop to 20 mm Hg. How does this affect O2 unloading and Hemoglobin (Hb) saturation?

Hb saturation declines sharply = additional oxygen unloading

The relationship between the amount of a gas that dissolves in a liquid being directly proportional to the partial pressure of the gas above the liquid describes what Law?

Henry's law

What would be the effect on the oxygen-hemoglobin dissociation curve by a decrease in temperature, PCO2, or H+??

It would shift to the left

What is the effect of metabolically active tissues (low PO2) on the oxygen-hemoglobin dissociation curve?

Low PO2: Large changes in PO2 = Large changes in Hb saturation

Metabolically active tissues generate large amounts of CO2, H+, and heat. What is the effect on O2 unloading?

Metabolically active tissues = additional 35% of oxygen unloaded. vs Resting tissues = only 23% of oxygen carried by Hb is released.

What is the direction of movement for O2 and CO2 between the blood and the alveoli?

O2 = into blood CO2 = into Alveoli

What is the direction of movement for O2 and CO2 between the blood and tissue cells?

O2 = into tissues CO2 = into blood

How would O2 unloading be affected by a decrease in temperature, PCO2, or H+?

Oxygen unloading would decrease

What does it mean to say that hemoglobin is partially saturated or fully saturated?

Partial = 1-3 heme groups are bound to oxygen Full = all 4 heme groups are bound to oxygen

Besides the medulla oblongata, what other part of the brain stem contains respiratory centers?

Pons

What determines the direction of diffusion of each gas between alveoli-blood and blood-tissue?

Pressure gradients

Where does the reaction between CO2 and H2O to form Carbonic Acid occur most frequently?

Red Blood Cells

Which chemical factor in blood normally provides the most powerful stimulus to breathe?

Rising carbon dioxide levels

At high altitude, the PO2 in the lungs may drop to 80 mm Hg. How would this affect Hemoglobin (Hb) saturation?

Slightly change the Hb saturation. 95% instead of 98%

At sea level, the partial pressure of oxygen in air is 159 mm Hg. What does this statement mean?

That means that at sea level, Oxygen accounts for 21% of the pressure How was this value determined? 159/760 x 100 = 21%

Assuming a constant temperature, what determines the amount of a gas that will dissolve in a liquid?

The amount of a gas that dissolves in a liquid is directly proportional to the partial pressure of the gas above the liquid

Which respiratory area of the brain stem is thought to generate the basic respiratory rhythm?

Ventral Respiratory Group (VRG)

What are the two respiratory groups in the medulla oblongata?

Ventral respiratory group (VRG) and Dorsal respiratory group (DRG)

Where are the central chemoreceptors located?

Ventral surface of the medulla close to the exit site of the 9th and 10th cranial nerves. They primarily respond to changes in [H+] in the adjacent brain ECF.

Normally, arterial PO2 levels have little effect on breathing. Under what conditions does arterial PO2 become the major stimulus for respiration? Which chemoreceptors are involved?

When arterial PO2 falls below 60 mm Hg Peripheral Chemoreceptors

Where are the peripheral chemoreceptors located?

carotid arteries and aortic arch supplied with sensory fibres coursing in the sinus and aortic nerves receive sympathetic and parasympathetic motor innervations.

The relationship between local partial pressure of oxygen, and hemoglobin saturation, describes what curve?

oxygen-hemoglobin dissociation curve