Respiratory Physiology II: Guyton Chapter 42 - 45

Question 1

[16-minute video]: Guyton and Hall Medical Physiology (Chapter 26) - Respiratory Insufficiency - Pathophysiology, Diagnosis, Oxygen Therapy

Answer 1

💨

Question 2

Discuss the organisation of the respiratory centre in the brainstem.

Answer 2

The respiratory center is composed of several groups of neurons located bilaterally in the medulla oblongata and pons of the brain stem. It is divided into three major collections of neurons:
(1) a dorsal respiratory group, located in the dorsal portion of the medulla, which mainly causes inspiration
(2) a ventral respiratory group, located in the ventrolateral part of the medulla, which mainly causes expiration
(3) the pneumotaxic center, located dorsally in the superior portion of the pons, which mainly controls rate and depth of breathing.
[Diagram 1] [Diagram 2]

Question 3

Where are most neurons of the dorsal respiratory group located?

Answer 3

Most neurons are located in the nucleus of the tractus solitarius (NTS).

Question 4

Besides the NTS, where else are neurons involved in respiratory control located?

Answer 4

Additional neurons are located in the adjacent reticular substance of the medulla.

Question 5

Explain the inspiratory ramp signal.

Answer 5

💨 The signal originates from the dorsal respiratory group (DRG) in the medulla oblongata.
💨 It generates a rhythmic, ramp-like discharge of nerve signals. This signal starts weakly and increases steadily over about 2 seconds during normal inspiration.
💨 The signal is transmitted to the inspiratory muscles, primarily the diaphragm.
💨 As the signal ramps up, it causes the inspiratory muscles to contract, leading to the expansion of the lungs.
💨 The signal ceases abruptly, allowing the inspiratory muscles to relax and the lungs to recoil, leading to expiration.
[Diagram]

Question 6

What are two qualities of the inspiratory ramp that are controlled?

Answer 6

(1) The rate of increase of the magnitude of the ramp signal [so that during heavy inspiration, the ramp increases rapidly and therefore fills the lungs rapidly]
(2) The point at which the ramp suddenly ceases [That is, the earlier the ramp ceases, the shorter the duration of inspiration. This method also shortens the duration of expiration. Thus, the frequency of respiration is increased.]

Question 7

(a) In which nucleus is the pneumotaxic center located?
(b) What is the function of the pneumotaxic centre?

Answer 7

(a) nucleus parabrachialis
(b) It transmits signals to the inspiratory center, controlling the “switch-off” point of the inspiratory ramp, thereby controlling the duration of inspiration. [This will have the secondary effect of controlling the breathing rate because limitation of inspiration also shortens expiration and the entire period of each respiration.]

Question 8

In which nuclei are the ventral respiratory group of neurons found?

Answer 8

nucleus ambiguus rostrally
nucleus retroambiguus caudally

Question 9

Discuss the activity and function of the ventral respiratory group.

Answer 9

💨 The neurons of the ventral respiratory group remain almost totally inactive during normal quiet respiration. Therefore, normal quiet breathing is caused only by repetitive inspiratory signals from the dorsal respiratory group transmitted mainly to the diaphragm, and expiration results from elastic recoil of the lungs and thoracic cage.

💨 The ventral respiratory neurons do not appear to participate in the basic rhythmical oscillation that controls respiration.

💨 When the respiratory drive for increased pulmonary ventilation becomes greater than normal, respiratory signals spill over into the ventral respiratory neurons from the basic oscillating mechanism of the dorsal respiratory area. As a consequence, the ventral respiratory area also contributes extra respiratory drive.

💨 Electrical stimulation of a few of the neurons in the ventral group causes inspiration, whereas stimulation of others causes expiration. Therefore, these neurons contribute to both inspiration and expiration. They are especially important in providing the powerful expiratory signals to the abdominal muscles during very heavy expiration.

💨 Thus, this area operates more or less as an overdrive mechanism when high levels of pulmonary ventilation are required, especially during heavy exercise.,

Question 10

Explain the Hering-Breuer inflation reflex.

Answer 10

(1) Stretch receptors located in the walls of the bronchi and bronchioles detect excessive stretching of the lungs during deep inhalation.

(2) When these receptors are activated, they send nerve impulses via the vagus nerve to the brainstem, specifically to the medulla and the apneustic center in the pons.

(3) The brainstem responds by inhibiting the inspiratory neurons, which stops further inhalation and initiates exhalation.

Question 11

What is the function of the Hering-Breuer reflex?

Answer 11

It acts as a protective mechanism to prevent over-inflation, thus protecting the lungs from potential damage due to over expansion.

Question 12

Discuss the mechanism of direct control of the respiratory center activity by CO₂ and H⁺.

Answer 12

💨 Within the medulla oblongata is a neuronal area known as the chemosensitive area. This area is highly sensitive to changes in either blood PCO₂ or H⁺ concentration, and it in turn excites the other portions of the respiratory center.
💨 CO₂ from the blood diffuses into the CSF because it is lipid soluble.
💨 In the CSF, CO₂ reacts with water to form carbonic acid, which dissociates into bicarbonate and hydrogen ions (H⁺). This reaction is catalyzed by the enzyme carbonic anhydrase.
💨 The increase in H⁺ concentration lowers the pH of the CSF. The chemosensitive area detects this change in pH.
💨 The chemosensitive area sends signals to the dorsal and ventral respiratory groups to increase the rate and depth of breathing.

Question 13

Briefly discuss the attenuated stimulatory effect of CO₂ on the respiratory centers after 1-2 days.

Answer 13

💨 This decline is partly as a result of renal readjustment of the H⁺ concentration in the circulating blood back toward normal after the CO₂ first increases the H⁺ concentration. The kidneys achieve this readjustment by increasing the blood HCO₃⁻, which binds with H⁺ in the blood and cerebrospinal fluid to reduce their concentrations.
💨 But, even more importantly, over a period of hours, the HCO₃⁻ also slowly diffuses through the blood–brain and blood–cerebrospinal fluid barriers and combine directly with H⁺ adjacent to the respiratory neurons as well, thus reducing the H⁺ back to near normal.

Question 14

What is the peripheral chemoreceptor system important for?

Answer 14

It detects changes in blood PO₂, to a lesser extent, changes in CO₂ and H⁺ concentrations.

Question 15

Where are most chemoreceptors located?

Answer 15

In the carotid bodies

Question 16

Where are the carotid bodies located?

Answer 16

Bilaterally in the bifurcations of the common carotid arteries.
[Diagram]

Question 17

Through which nerves do the afferent fibers from the carotid bodies pass?

Answer 17

Through Hering’s nerves to the glossopharyngeal nerves and then to the dorsal respiratory area of the medulla. [Diagram]

Question 18

Where are the aortic bodies located?

Answer 18

along the arch of the aorta
[Image]

Question 19

What are glomus cells and where are they found?

Answer 19

Glomus cells are chemoreceptor cells that detect changes in blood oxygen levels and are found in the carotid and aortic bodies. They synapse directly or indirectly with nerve endings.

Question 20

How do glomus cells respond to low PO₂ levels?

Answer 20

💨 Glomus cells have O₂-sensitive potassium channels that inactivate when blood PO₂ decreases markedly. This inactivation causes the cell to depolarize, opening voltage-gated calcium channels and increasing intracellular calcium ion concentration.

💨 The increased calcium ion concentration stimulates the release of a neurotransmitter that activates afferent neurons, sending signals to the central nervous system and stimulating respiration.

[Diagram 1] [Diagram 2]

Question 21

How do increased CO₂ and H⁺ concentrations affect respiratory activity, and what is the difference between their direct effects on the respiratory center and their effects through chemoreceptors?

Answer 21

Increased CO₂ and H⁺ concentrations stimulate respiratory activity, with their direct effects on the respiratory center being significantly stronger (about seven times) than their effects through chemoreceptors. However, peripheral chemoreceptors respond much faster, making them crucial for the rapid respiratory response to CO₂, especially at the onset of exercise.

Question 22

How does low arterial oxygen pressure (PO₂) affect alveolar ventilation, and what primarily regulates ventilation in healthy humans at sea level?

Answer 22

Low arterial oxygen pressure significantly increases alveolar ventilation when PO₂ drops below 100 mmHg, with a dramatic increase at very low PO₂ levels [60 mmHg and lower]. However, in healthy humans at sea level, the regulation of ventilation is primarily driven by carbon dioxide (PCO₂) and hydrogen ion (H⁺) concentrations rather than oxygen levels.

Question 23

What is acclimatization?

Answer 23

Acclimatization is the process by which the body adjusts to low atmospheric oxygen concentrations over a period of days to weeks.

Question 24

During strenuous exercise, O₂ consumption and CO₂ formation can increase as much as 20-fold. Yet, in the healthy athlete, alveolar ventilation ordinarily increases almost exactly in step with the increased level of oxygen metabolism. The arterial PO₂, PCO₂, and pH remain almost exactly normal. Therefore, what causes intense ventilation during exercise?

Answer 24

The brain, on transmitting motor impulses to the exercising muscles, is believed to transmit collateral impulses into the brainstem at the same time to excite the respiratory centre.

Question 25

What is maximum expiratory flow?

Answer 25

Maximum expiratory flow is the highest flow rate achieved during forced expiration, beyond which the flow cannot be increased even with additional force due to dynamic compression of the airways.

Question 26

How does increased pressure applied to the outsides of the alveoli and bronchioles affect maximum expiratory flow?

Answer 26

◾ Increased pressure applied to the outsides of the alveoli and bronchioles **compresses these structures**, **reducing their diameter** and **increasing resistance to airflow**. ◾ This compression **limits the maximum respiratory flow**, as the narrowed airways restrict the amount of air that can be expelled from the lungs. *Further notes:* Maximum respiratory flow curve: [**[Diagram](https://www.researchgate.net/profile/Mohsen-Kazemi-3/publication/311972317/figure/fig1/AS:444968046206976@1483100057487/A-Collapse-of-the-respiratory-passageway-during-maximum-expiratory-effort-an-effect.png)**]

Question 27

Why does maximum expiratory flow rate decrease as lung volume becomes smaller?

Answer 27

✔ As lung volume decreases, the airways become narrower, increasing resistance to airflow. This makes it harder to expel air quickly. At lower lung volumes, the pressure outside the airways may become lower than the pressure outside, causing them to collapse. ✔ The elastic recoil of the lungs, which helps push air out, is reduced at lower lung volumes. *Further notes:* Maximum respiratory flow curve: [**[Diagram](https://www.researchgate.net/profile/Mohsen-Kazemi-3/publication/311972317/figure/fig1/AS:444968046206976@1483100057487/A-Collapse-of-the-respiratory-passageway-during-maximum-expiratory-effort-an-effect.png)**]

Question 28

What are the characteristics of constricted lungs in the maximum expiratory flow-volume curve?

Answer 28

Constricted lungs have **reduced total lung capacity (TLC)** and **reduced residual volume (RV)**. The lung cannot expand to a normal maximum volume, resulting in a **lower maximal expiratory flow** compared to the normal curve. [**[Diagram 1](https://ketaminenightmares.com/pex/saqs/other/clinical_measurement/2017A11_respiratory_flow_volume_curves_files/image001.jpg)**] [**[Diagram 2](https://www.researchgate.net/publication/325559051/figure/fig2/AS:634061244596225@1528183389569/Flow-Volume-loop-output-of-the-spirometry-showing-FVC-manoeuvre-for-healthy-and.png)**] *Further notes:* Constricted lung diseases include **fibrotic diseases like tuberculosis** and **silicosis**, and conditions that constrict the chest cage such as **kyphosis**, **scoliosis**, and **fibrotic pleurisy**.

Question 29

Why is it more difficult to expire than to inspire in diseases with airway obstruction?

Answer 29

💨 In airway obstruction diseases, **the closing tendency of the airways is increased by the extra positive pressure required for expiration**. 💨 During inspiration, the negative pleural pressure pulls the airways open, allowing air to enter easily but trapping it in the lungs. 💨 This effect increases both the total lung capacity (TLC) and residual volume (RV) over time, and the maximum expiratory flow rate is greatly reduced.

Question 30

Name one fairly common disease that causes severe airway obstruction and affects the maximum expiratory flow rate.

Answer 30

Asthma

Question 31

What is the FVC test and how is it performed?

Answer 31

✔ The Forced Expiratory Vital Capacity (FVC) test is a clinical pulmonary test that **records the forced expiratory vital capacity on a spirometer**. ✔ The person **inspires maximally** to the total lung capacity (TLC) and then **exhales into the spirometer with maximum expiratory effort** as rapidly and completely as possible.

Question 32

Distinguish between Vital Capacity and Forced Vital Capacity.

Answer 32

◾ Vital Capacity is the maximum amount of air a person can exhale after a maximum inhalation, whereas the Forced Vital Capacity is the maximum amount of air a person can exhale forcefully and rapidly after a maximum inhalation. ◾ Vital capacity is measured without any time constraint, meaning that the person can exhale slowly and completely. Forced Vital Capacity is measured with a time constraint, requiring the person to exhale as quickly and forcefully as possible.

Question 33

What is FEV1?

Answer 33

The Forced Expiratory Volume in 1 second is the volume of air that a person can forcefully exhale in the first second of a forced breath. [It is usually expressed as a percentage of the total Forced Vital Capacity.]

Question 34

What is the FEV1/FVC% in a normal person?

Answer 34

In a normal person, 80% of the FVC is expired in the first second (FEV1/FVC%).

Question 35

Explain how the FEV1/FVC ratio is affected by lung fibrosis.

Answer 35

◾ In lung fibrosis, the compliance of the lung is reduced, making the lungs stiffer and less able to expand. ◾ This results in a decrease in lung volumes, including both FVC and FEV1. ◾ However, while FVC and FEV1 are reduced, FEV1 is not reduced as much as FVC, hence the FEV1/FVC ratio can actually be higher than normal or remain relatively unchanged. ◾ This is because the stiff lungs of a person with lung fibrosis can expel air quickly due to the high elastic recoil.

Question 36

What is pulmonary emphysema?

Answer 36

This is a condition characterized by permanent enlargement of air spaces in the lungs as a result of damage to the alveoli.

Question 37

Discuss the major pathophysiological changes in the lungs due to pulmonary emphysema.

Answer 37

💨 **Chronic infection** caused by **inhaling smoke or other irritants** leads to deranged protective mechanisms of the airways, **partial paralysis of the cilia**, **excess mucus secretion** and **inhibition of alveolar macrophages**. 💨 This then results in **chronic obstruction of many smaller airways** due to excess mucus and inflammatory edema of the bronchiolar epithelium. 💨 One will therefore experience **difficulty in expiring air**, causing **entrapment of air in the alveoli**, overstretching them, and **marked destruction of alveolar walls** [50 - 80%]. 💨 [**[Diagram](https://media.springernature.com/full/springer-static/image/art%3A10.1038%2Fnrdp.2015.76/MediaObjects/41572_2015_Article_BFnrdp201576_Fig1_HTML.jpg)**] 💨 Gallery: [**[Image 1](https://www.shutterstock.com/image-photo/normal-healthy-lung-left-emphysema-260nw-121998454.jpg)**] [**[Image 2](https://upload.wikimedia.org/wikipedia/commons/thumb/1/1d/Histopathology_of_emphysema.jpg/746px-Histopathology_of_emphysema.jpg)**] [**[Image 3](https://journal.chestnet.org/cms/10.1378/chest.117.5_suppl_1.251S/asset/ec9b65af-e421-4e1a-a98b-31e55cb2a48d/main.assets/gr8.jpg)**]

Question 38

What are the physiological effects of chronic emphysema?

Answer 38

💨 **Increased airway resistance** due to bronchiolar obstruction, resulting in increased work of breathing, especially during expiration. 💨 **Decreased diffusing capacity of the lung** due to the **marked loss of alveolar walls**, reducing the ability to oxygenate blood and remove CO2. 💨 **Abnormal ventilation-perfusion ratios**, with some parts of the lungs being well ventilated and others poorly ventilated, causing **physiological shunt and dead space**. 💨 **Decreased number of pulmonary capillaries** due to the loss of alveolar walls, leading to **increased pulmonary vascular resistance**, **pulmonary hypertension**, and **right-sided heart failure**.

Question 39

What are the long term effects of chronic emphysema?

Answer 39

Both **hypoxia** and **hypercapnia** develop due to **hypoventilation of many alveoli and loss of alveolar walls**. The net result is severe, prolonged, and devastating air hunger [aka. dyspnea] that can last for years until hypoxia and hypercapnia cause death.

Question 40

Define "pneumonia".

Answer 40

The term "pneumonia" includes any inflammatory condiiton of the lung in which some or all of the alveoli are filled with fluid and blood cells.

Question 41

How does bacterial pneumonia affect the alveoli and spread in the lungs?

Answer 41

Bacterial pneumonia begins with infection in the alveoli, causing the **pulmonary membrane to become inflamed** and **highly porous**, leading to **fluid and blood cells leaking into the alveoli**. The infected alveoli become filled with fluid and cells, and the infection spreads from alveolus to alveolus, eventually consolidating large areas of the lungs.

Question 42

What are the two major pulmonary abnormalities caused by pneumonia, and what are their effects?

Answer 42

(1) **reduction in the total available surface area** of the respiratory membrane, and (2) a **decreased ventilation-perfusion ratio**. These effects cause hypoxemia (low blood O2) and hypercapnia (high blood CO2).

Question 43

Explain why pulmonary vasoconstriction occurs at high altitudes.

Answer 43

◾ Pulmonary vasoconstriction at high altitudes occurs as a response to low oxygen levels in the air. ◾ This process is known as hypoxin pulmonary vasoconstriction (HPV). ◾ When the oxygen levels in the alveoli decrease, the blood vessels in the lungs constrict to redirect blood flow to areas of the lung that are better ventilated.

Question 44

What does FEV1/FVC measure and why will the ratio increase with lung fibrosis? (a) the forced expiratory volume in one second in relation to the total forced vital capacity; lung fibrosis causes the lungs to become less pliable (b) the functional expiratory volume in one second in relation to the total functional vital capacity; lung fibrosis causes the lungs to become less pliable (c) the functional expiratory volume in one second in relation to the total functional vital capacity; lung fibrosis causes the lungs to decrease in size (d) the forced expiratory volume in one second in relation to the total forced vital capacity; lung fibrosis causes the lungs to decrease in size (e) none of the above

Answer 44

(a) the forced expiratory volume in one second in relation to the total forced vital capacity; lung fibrosis causes the lungs to become less pliable

Question 45

An anesthetized male is breathing with no assistance. He is then artificially ventilated for 10 min at his normal tidal volume but at twice his normal frequency. He is ventilated with a gas mixture of 60% O₂ and 40% N₂. The artificial ventilation is stopped and he fails to breathe for several minutes. This apneic episode is due to which of the following? (a) Low arterial PCO₂ suppressing the activity of the peripheral chemoreceptors (b) Low arterial PCO₂ suppressing the activity of the medullary chemoreceptors (c) High arterial PCO₂ suppressing the activity of the peripheral chemoreceptors (d) Decrease in arterial pH suppressing the activity of the peripheral chemoreceptors (e) High arterial PCO₂ suppressing the activity of the medullary chemoreceptors

Answer 45

(b) Low arterial PCO₂ suppressing the activity of the medullary chemoreceptors *Explanation:* While peripheral chemoreceptors, located in the carotid and aortic bodies, also respond to changes in blood gases, including CO₂, their response to PCO₂ is less significant compared to medullary chemoreceptors.

Question 46

The peripheral chemoreceptors are most active when (a) PaO₂ levels are greater than 90 mmHg (b) pH of arterial blood rises (c) pH of arterial blood falls (d) PaO₂ levels are below 60 mmHg (e) PaCO₂ levels are below 40 mmHg

Answer 46

(d) PaO₂ levels are below 60 mmHg

Question 47

The effect of a fall in arterial pH on the central chemoreceptors: (a) occurs indirectly through CO₂ entry across the blood brain barrier (b) results in hypoventilation (c) occurs directly as H⁺ passes through the blood brain barrier (d) results in respiratory alkalosis (e) has a negligible effect on ventilation

Answer 47

(a) occurs indirectly through CO₂ entry across the blood brain barrier

Question 48

What conditions of the lungs would cause a an increase in FEV1/FVC? What about a decrease FEV1/FVC? (a) This ratio increases as the lungs become stiff and less pliable, decreasing when there is increased resistance in the lung. (b) This ratio decreases as the lungs become stiff and less pliable, decreasing further when there is increased resistance in the lung. (c) This ratio increases as the lungs become stiff and less pliable, increasing further when there is increased resistance in the lung. (d) This ratio decreases as the lungs become stiff and less pliable, increasing when there is increased resistance in the lung. (e) All of the above

Answer 48

(a) This ratio increases as the lungs become stiff and less pliable, decreasing when there is increased resistance in the lung.

Question 49

The basic rhythm of respiration is generated by neurons located in the medulla. Which of the following limits the duration of inspiration and increases respiratory rate? (a) dorsal respiratory group (b) pneumotaxic centre (c) nucleus of tractus solitarius (d) apneustic centre (e) ventral respiratory group

Answer 49

(b) pneumotaxic centre

Question 50

The following lung function tests remain unchanged in mild to moderate obesity except ________. (a) work of breathing (b) Forced Expiratory Volume in 1s (FEV1) (c) Total Lung Capacity (TLC) (d) Forced Vital Capacity (FVC) (e) Forced Expiratory Volume in 1s/Forced vital capacity ratio [FEV1/FVC]

Answer 50

(a) work of breathing

Question 51

Alveolar ventilation increases several-fold during strenuous exercise. Which of the following factors is most likely to stimulate ventilation during strenous exercise? (a) decreased mean arterial pH (b) increased mean arterial PCO₂ (c) decreased mean venous PO₂ (d) collateral impulses from higher brain centers (e) decreased mean arterial PO₂

Answer 51

(d) collateral impulses from higher brain centers

Question 52

Hypoventilation ________. (a) results in respiratory acidosis (b) results in metabolic alkalosis (c) results in respiratory alkalosis (d) results in a mixed acid base disorder (e) none of the above

Answer 52

(a) results in respiratory acidosis

Question 53

Regarding control of ventilation (a) Peripheral chemoreceptors respond to decreases in arterial PO₂ (b) The most important factor in control of ventilation under normal conditions is the PO₂ of the arterial blood (c) The central chemoreceptors respond to changes in oxygen concentrations (d) The apneustic centre lies in the medulla (e) The chemoreceptors in the aortic bodies respond to a fall in arterial pH

Answer 53

(a) Peripheral chemoreceptors respond to decreases in arterial PO₂ *Further notes:* The apneustic centre is located in the lower pons. [**[Diagram](https://storage.googleapis.com/dl.dentistrykey.com/clinical/RegulationofRespiration/0_3s20B9780323597128000424.jpg)**]

Question 54

When respiratory drive for increased pulmonary ventilation becomes greater than normal, a special set of respiratory neurons that are inactive during normal quiet breathing then becomes active, contributing to the respiratory drive. These neurons are located in which of the following structures? (a) Ventral respiratory group (b) Dorsal respiratory group (c) Apneustic center (d) Nucleus of the tractus solitarius (e) Pneumotaxic center

Answer 54

(a) Ventral respiratory group

Question 55

Which of the following statements is **false**? (a) Dorsal respiratory group in upper pons is responsible for inspiration. (b) Apneustic centre can inhibit the inspiratory centre. (c) Pneumotaxic centre is responsible for prolonged inspiratory gasp interrupted by transient expiratory efforts. (d) Intrinsic periodic firing of the inspiratory phase comes from the medulla but can be voluntarily over-ridden by the cortex. (e) None of the above.

Answer 55

(a) Dorsal respiratory group in upper pons is responsible for inspiration.

Question 56

In the medulla oblongata, the nucleus of tractus solitarius contains the ________ neurons. (a) pontine respiratory group (b) ventral respiratory group (c) dorsal respiratory group (d) pre-Botzinger complex (e) medullary respiratory group

Answer 56

(c) dorsal respiratory group

Question 57

The lung pathology most likely to result from certain kinds of heart disease is ________. (a) emphysema (b) asthma (c) pulmonary edema (d) fibrotic lung disease (e) lung cancer

Answer 57

(c) pulmonary edema

Question 58

At high altitudes all of the following things occur in an effort to acclimatise except ________. (a) hypoventilation (b) pulmonary vasoconctriction (c) O₂ dissociation curve shifts to the right (d) increased numbers of capillaries per unit volume in peripheral tissues (e) polycythemia

Answer 58

(a) hypoventilation

Question 59

What is sickle cell anaemia and how does it affect the perfusion of oxygen in the blood? (a) It is a genetic disease in which red blood cells are sickle-shaped, increasing oxygen perfusion into the blood. (b) It is a genetic disease in which red blood cells are sickle-shaped, reducing oxygen perfusion into the blood. (c) It is a deficiency disease in which red blood cells are sickle-shaped, reducing oxygen perfusion into the blood. (d) It is a deficiency disease in which red blood cells are sickle-shaped, increasing oxygen perfusion into the blood. (e) None of the above.

Answer 59

(b) It is a genetic disease in which red blood cells are sickle-shaped, reducing oxygen perfusion into the blood.

Question 60

Which of the following statements is true? (a) Central chemoreceptors respond directly to changes in blood pH. (b) Peripheral chemoreceptors are 100% responsible for the ventilatory response to hypoxia. (c) Central chemoreceptors are responsible for 80% of ventilatory responses to hypercapnia. (d) Aortic bodies do not respond to acidosis. (e) All of the above.

Answer 60

(c) Central chemoreceptors are responsible for 80% of ventilatory responses to hypercapnia.

Question 61

The lung volume that would be increased with obstructive lung disease is ________. (a) tidal volume (b) inspiratory reserve volume (c) functional residual volume (d) vital capacity (e) residual volume

Answer 61

(e) residual volume

Question 62

Upon breath-holding, the breaking point is reached due to ________. (a) hypoxia (b) hypercapnea (c) acidosis (d) both (a) and (b) (e) (a), (b) and (c)

Answer 62

(e) (a), (b) and (c)

Question 63

**Respiratory drive** (a) Under resting conditions, the drive that is responsible for maintaining the respiratory rhythm is the hypoxic ventilatory drive. (b) If there is hypercapnea, the carbon dioxide indirectly stimulates the central chemoreceptors. (c) Hypoxia of 90 mmHg has a large excitatory effect on the peripheral chemoreceptors. (d) The peripheral chemoreceptors are stimulated by a rise in H+, resulting in hypoventilation. (e) Chronic airway obstruction may cause the hypercapnoiec drive to be more effective.

Answer 63

(b) If there is hypercapnea, the carbon dioxide indirectly stimulates the central chemoreceptors.