Chapter 22: Respiratory System Check Your Understanding

List the three ways CO2 is transported in blood.

About 70% of CO2 is transported as bicarbonate ion (HCO3-) in plasma. Just over 20% is transported bound to hemoglobin in the RBCs, and 7-10% is dissolved in plasma.

What is the difference between respiratory volumes and respiratory capacities?

Respiratory capacities are combinations of two or more respiratory volumes.

Explain why slow, deep breaths ventilate the alveoli more effectively than do rapid, shallow breaths.

Slow, deep breaths ventilate the alveoli more effectively because a smaller fraction of the tidal volume of each breath is spent moving air into and out of the dead space.

Suppose a patient is receiving oxygen by mask. Are the arterioles leading into the O2-enriched alveoli dilated or constricted? What is the advantage of this response?

The arterioles leading into the O2-enriched alveoli would be dilated. This response allows matching of blood flow to availability of oxygen.

PO2 in the alveoli is about 56 mm Hg lower than in the inspired air. Explain this difference.

The difference in PO2 between inspired air and alveolar air can be explained by (1) the gas exchange occurring in the lungs (O2 continuously diffuses out of the alveoli into the blood), (2) the humidification of inspired air (which adds water molecules that dilute the O2 molecules), and (3) the mixing of newly inspired air with gases already present in the alveoli.

What causes the partial vacuum (negative pressure) inside the pleural cavity? What happens to a lung if air enters the pleural cavity? What is the clinical name for this condition?

The partial vacuum (negative pressure) inside the pleural cavity is caused by the opposing forces acting on the visceral and parietal pleurae. The visceral pleurae are pulled inward by the lungs' natural tendency to recoil and the surface tension of the alveolar fluid. The parietal pleurae are pulled outward by the elasticity of the chest wall. If air enters the pleural cavity, the lung on that side will collapse. This condition is called pneumothorax.

A 3-year-old boy is brought to the emergency department after aspirating (inhaling) a peanut. Bronchoscopy confirms the suspicion that the peanut is lodged in a bronchus and then it is successfully extracted. Which main bronchus was the peanut most likely to be in? Why?

The peanut was most likely in the right main bronchus because it is wider and more vertical than the left.

Premature infants often lack adequate surfactant. How does this affect their ability to breathe?

A lack of surfactant increases surface tension in the alveoli and causes them to collapse between breaths. (In other words, it markedly decreases lung compliance.)

Where is angiotensin converting enzyme found and why is this a good location for this enzyme? Name the blood pressure--increasing hormone cascade to which this enzyme belongs.

Angiotensin converting enzyme is found in the plasma membrane of lung capillary endothelial cells. This is a good location for it because all of the blood in the body passes through the lung capillaries about once every minute. Angiotensin converting enzyme is part of the renin-angiotensin-aldosterone hormone cascade, which increases blood pressure.

What is the relationship between CO2 and pH in the blood? Explain.

As blood CO2 increases, blood pH decreases. This is because CO2 combines with water to form carbonic acid. (However, the change in pH in blood for a given increase in CO2 is minimized by other buffer systems).

Your patient, Mr. Singh, has COPD. As a result, his pulmonary alveoli are poorly ventilated. Would you expect his pulmonary arterial blood pressure to be higher or lower than normal? Explain. Over the long term, this change in blood pressure may cause Mr. Singh to develop heart failure. Which side of the heart will fail? Edema is one sign of heart failure. Where would you expect to see edema in Mr. Singh?

Because Mr. Singh's alveoli are poorly ventilated, the local PO2 around those alveoli would be low. This low PO2 would cause the pulmonary artieroles to constrict (due to ventilation-perfusion coupling), increasing resistance and thereby increasing pulmonary pressure. In the long term, pulmonary hypertension and cause right heart failure. When one side of the heart fails, pressure increases upstream of the failing pump--in this case in the systemic capillaries. This causes peripheral edema, which would be noticeable in the extremities such as the feet and ankles.

Which chemical factor in blood normally provides the most powerful stimulus to breathe? Which chemoreceptors are most important for this response?

CO2 in the blood normally provides the most powerful stimulus to breathe. Central chemoreceptors are most important in this response.

Suppose you are given a sealed container of water and air. The PCO2 and PO2 in the air are both 100 mm Hg. What are the PCO2 and PO2 in the water? Which gas has more molecules dissolved in the water? Why?

In a sealed container, the air and water would be at equilibrium. Therefore, the partial pressures of CO2 and O2 (PCO2 and PO2) will be the same in the water as in the air: 100 mm Hg each. More CO2 and O2 molecules will be dissolved in the water (even though they are at the same partial pressure) because CO2 is much more soluble than O2 in water.

On the graph of intrapulmonary pressure below, label the periods of inspiration and expiration, and all of the points where air flow is zero. Explain.

Intrapulmonary pressure increases during expiration and decreases during inspiration. When intrapulmonary pressure is zero relative to atmospheric pressure, air flow is zero. This occurs at the three points labeled in the graph, which are between inspiration and expiration. After air flow stops, it changes direction.

What long-term adjustments does the body make when living at high altitude?

Long-term adjustments to altitude include an increase in erythropoiesis, resulting in a higher hematocrit; an increase in BPG, which decreases Hb affinity for oxygen; and an increase in minute respiratory volume.

What is the driving force for pulmonary ventilation?

The driving force for pulmonary ventilation is a pressure gradient created by changes in the thoracic volume.

Which structure seals the larynx when we swallow?

The epiglottis seals the larynx when we swallow.

Which structural features of the trachea allow it to expand and contract, yet keep it from collapsing?

The incomplete, C-shaped cartilage rings of the trachea allow it to expand and contract and yet keep it from collapsing.

An injured soccer player arrives by ambulance in the emergency room. She is in obvious distress, breathing rapidly. Her blood PCO2 is 26 mm Hg and pH is 7.5. Is she suffering from hyperventilation or hyperpnea? Explain.

The injured soccer player's PCO2 is low. (Recall that normal PCO2 = 40 mm Hg.) The low PCO2 reveals that this is hyperventilation and not hyperpnea (which is not accompanied by changes in blood CO2 levels).

What features of the alveoli and their respiratory membranes suit them to their function of exchanging gases by diffusion?

The many tiny alveoli together have a large surface area. This and the thinness of their respiratory membranes make them ideal for gas exchange.

Name the two types of mucous membrane found in the nasal cavity.

The nasal cavity contains both respiratory mucosa and olfactory mucosa.

What distinguishes the obstruction in asthma from that in chronic bronchitis?

The obstruction in asthma is reversible, and acute exacerbations are typically followed by symptom-free periods. In contrast, the obstruction in chronic bronchitis is generally not reversible.

The dotted lines in the two graphs below represent a shift in the oxygen-hemoglobin dissociation curve. Which shift would allow more oxygen delivery to the tissues? [Hint: Ask yourself which curve allows Hb to "let go" of more O2 (hold less O2).] Name three conditions in the tissues that would cause the curve to shift this way.

The shift shown in graph (b) would allow more oxygen delivery to the tissues. Conditions that would cause the curve to shift this way are increased temperature, increased PCO2, decreased pH, or an increase in BPG levels.

Air moving from the nose to the larynx passes by a number of structures. List (in order) as many of these structures as you can.

The structures that air passes by are the nasal cavity (nares, nasal vestibule, nasal conchae), nasopharynx, oropharynx, and laryngopharynx.

The lungs are perfused by two different circulations. Name these circulations and indicate their roles in the lungs.

The two circulations of the lungs are the pulmonary circulation, which delivers deoxygenated blood to the lungs for oxygenation and returns oxygenated blood to the heart, and the bronchial circulation, which provides systemic (oxygenated) blood to lung tissue.

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

The ventral respiratory group of the medulla (VRG) is thought to be the rhythm-generating area.