Chapter 21 the respiratory system

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The check your understanding questions that are throughout the chapter.
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Air moving from the nose to the trachea 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 (with pharyngeal tonsil), oropharynx (with palatine tonsil), laryngopharynx, and larynx (with epiglottis, vestibular fold, and vocal fold).


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.


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


A three-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.


The lungs are perfused by two different circulations. Name the 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.


What is the driving force for ventilation?

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


What causes the intrapulmonary pressure to decrease during inspiration?

The intrapulmonary pressure decreases during inspiration be¬cause of the increase in thoracic cavity volume brought about by the muscles of inspiration.


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.


Resistance in the airways is typically low. Why? (Give at least two reasons.)

Airway resistance is low because (1) the diameters of most airways are relatively large, (2) for smaller air¬ways there are many in parallel, making their combined diameter large, and (3) air has a low viscosity.


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.)


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.


You are given a sealed container of water and air

In a sealed container, the air and water would beat equilibriurn. Therefore, the partial pressures of CO2 and O2 (P C02 and P O2) will be the same in the water as in the air: 100 mm Hg each. More CO2 than 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.


Po2 in the alveoli is about 56 mm Hg lower than in the inspired air. Explain the difference.

The difference in P 02 between inspired air and alveolar air can be explained by (1) the gas exchange occurring in the lungs (02 continu¬ously 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


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 02-enriched alveoli would be dilated. This response allows matching of blocd flow to availability of oxygen.


Rapidly metabolizing tissues generate large amounts of CO2 and H+. How does this affect O2 unloading? What is this affect called?

Both CO2 and H+ increase O2 unloading by binding to Hb. This is called the Bohr effect


List three ways CO2 is transported in blood instate approximate percentages of each.

About 70% of CO2 is transported as bi¬carbonate ion (HC03 -) in plasma. Just over 20% is transported bound to hemoglobin in the RBCs, and 7-10% is dissolved in plasma.


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.)


Which brainstem 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


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

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


An injured soccer player arise 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 hyperpnoea? Explain.

The injured soccer player's PC02 is low. (Recall that normal P CO2 = 40 mm Hg.) The low P cO2 reveals that this is hyperventilation and not hyperpnea (which is not accompanied by changes in blood CO2 levels).


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 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.