Take Home Exam: Respiratory System

Answers must be typed and handed in on 4/27 in class. If you do not bring it in, you will take the exam in class.

I. Multiple Choice

1. Which of the following does not occur during inhalation?a. the ribs are pulled up and outb. air pressure within the chest cavity is reduced

c. the diaphragm is pulled upwardd. the chest cavity becomes larger

2. Hemoglobin transportsa. all of the oxygen and carbon dioxide

b. most of the oxygen and some of the carbon dioxidec. most of the oxygen and none of the carbon dioxided. most of the oxygen and most of the carbon dioxide

3. The Adam’s apple is part of which laryngeal cartilage?a. epiglottis

b. thyroidc. cricoidd. cornicuate

4. Which of the following statements about human lungs is incorrect?a. they are muscular

b. they are elasticc. they are surrounded by pleurad. they are above the diaphragm

5. Which of the following does not occur during exhalation?a. the rib cages muscles relaxb. air pressure within the chest cavity is reducedc. the diaphragm moves upward

d. the diaphragm contracts

6. Since 1 atmosphere of pressure equals 760 mm Hg, which gas has a partial pressure of about 160 mm Hg in inspired air?a. N2

b. O2

c. H2Od. CO2

7. A condition in humans that is characterized by enlargement and degeneration of the alveoli, resulting in decreased lung capacity is known asa. lung cancerb. bronchitis

c. emphysemad. asthma

8. Which of these parts of the brainstem is correctly matched with its main function?a. ventral respiratory groups – stimulate the diaphragmb. dorsal respiratory groups – limit inflation of the lungs

c. pneumtaxic center – inhibits the inspiratory centerd. apneustic center – stimulates the pneumotaxic center

9. The main direct stimulus to pulmonary ventilation is H+ in the cerebrospinal fluid, not the concentration of CO2 in the blood.

a. trueb. false

10. All of the following factors could produce bronchoconstriction excepta. cold airb. histaminec. airborne irritants

d. epinephrine

11. The partial pressure of carbon dioxide in the arterial blood isa. greater than in the tissue spaces

b. less than in the tissue spacesc. less than in the alveolid. greater than in the venous blood

12. The partial pressure of oxygen in the arterial blood isa. greater than in the tissue spaces

b. less than in the tissue spacesc. equal to that in the alveolid. less than in the venous blood

13. One effect of hypoxia isa. pneumothoraxb. atelectasisc. anemia

d. cyanosis

14. Carbon monoxide poisoning causesa. hypoxia

b. apneac. anoxiad. hypocapnia

15. Which of the following is most important in keeping food out of the trachea?a. extrinsic muscles of the larynxb. glottis

c. epiglottisd. vocal cords

16. The trachea possessesa. skeletal muscleb. pleural fluid

c. C-shaped rings of cartilaged. walls with stratified epithelium

17. During an asthma attack, the patient has difficulty breathing because of constriction of thea. trachea

b. bronchic. bronchiolesd. alveoli

18. Lack of surfactant will causea. sudden infant death syndrome

b. respiratory distress syndromec. apnead. atelectasis

19. Fetal hemoglobin has _______ affinity for oxygen than adult hemoglobin.a. greater

b. the samec. lower

20. Because of _____ the lung does not normally collapsea. surfactantb. intrapleural pressurec. elastic recoil

d. all of the above

21, The alveolar ventilation ratea. tidal volume times respiratory rate

b. the minute respiratory volume plus the dead air spacec. the amount of air available for gas exchange in the lungsd. all of the above

22. Which of these values would normally be the highest?a. tidal volumeb. expiratory reserve volumec. vital capacity

d. lung capacity

23. The parietal pleuraa. covers the surface of the lung

b. covers the inner surface of the thoracic cavityc. covers the inner surface of the alveolid. is the respiratory membrane

24. Gas exchange between the air in the lungs and the blood takes place in thea. alveoli

b. bronchic. bronchiolesd. all of the above

25. Expiration requires more energy than inspiration.a. true

b. false

II. Short Answer

Do 5/6 or all 6 for extra credit (5 pt)

1. Explain how the medulla oblongata and pons regulate respiration. Describe 3 stimuli that would modify the respiratory rhythm.

Breathing is fundamentally involuntary due to the medulla oblongata and pons.There are two nerve groupings in the medulla that control breathing, called the respiratory nuclei.

The inspiratory center, or dorsal respiratory group, determines the extent/depth of inhalation proportionally to the frequency of its nerve firings (more motor units of the rib muscles and diaphragm are recruited by these efferent neurons), and also inversely affects respiratory rate by lengthening the duration of consecutive firings. The expiratory center, or ventral respiratory group, has both neurons that control inspiration (these I neurons are in the mid-region) and neurons that control expiration (E neurons, in the posterior and anterior). I’m not sure what significant function the I neurons have (they do not contribute to eupnea i.e. regulated breathing) but the E neurons send inhibitory signals to the inspiratory center in order to maintain adequate expiration, and vice-versa the inspiratory center inhibits the E neurons when inspiration is inadequate.

The pons has two nerve groups as well – the pneumotaxic center and the apneustic center. The pneumotaxic center resides superior to the apneustic center, and continuously inhibits the inspiratory center to control inspiration depth and frequency. The neurons fire faster to cause faster (up to 1 per 1/2s) and shallower breaths, or slower to cause slower (down to 1 per 5s) and deeper inspirations. The apneustic center continuously transmits excitatory signals to the inspiratory center (causing deeper inspiration) but only when the vagus nerve and the connections the pneumotaxic center and apneustic center are cut.

2. Explain the significance of Boyle's Law, Dalton's Law, Charles’ Law and Henry's law to the process of respiration.

Boyle’s law establishes the inverse correlation between volume and pressure of a gas in an adiabatic respiratory environment. Powerful inferences can be made from this law, such as that intrapulmonary/alveolar air pressure must decrease during inspiration since the lungs expand to let in more air, and the vice-versa process occurs during expiration. Boyle’s law also explains why air pressure difference between the alveolar air and the external air is necessary for the lungs to work. Much like a balloon, the lungs can only stay inflated if there is an equilibrium of total internal and external air pressure.

Dalton’s law establishes that gas pressures act associatively and commutatively i.e. the total pressure of a gas mixture is always equal to the sum of its parts. Dalton’s law allows the calculation of gas diffusion rates – interpolating pressures of air leads to discoveries about the individual gases constituting the mixtures. For example, we can tell how much oxygen is absorbed by comparing inspired air with alveolar air, as well as how much nitrogen is absorbed, and how much carbon dioxide and water is released.

Charles’ law describes the thermodynamic connection between temperature and volume of gases. Higher temperature is due to increased kinetic energy of gas particles, which means that more collisions occur and that the particles move faster, filling up a greater amount of space. So, lungs work more efficiently in hot weather than cold.

Henry’s law refers to gas exchange in the alveoli, which are the interface between blood and the air. Assuming constant temperature, the amount of oxygen that is absorbed into the blood is dependent on the amount of pressure applied to the alveoli; the amount of carbon dioxide released into the air is negatively proportional to the partial pressure of the carbon dioxide in the air. Solubility of gas in blood or air matters, so the phenomenon can be understood as diffusion, more or less. The process of releasing carbon dioxide is also called unloading it, and for oxygen “loading” is used. Henry’s law explains why in normal conditions oxygen is absorbed into the blood and carbon dioxide is expelled, processes that are the essence of respiration. Using Henry’s law also allows inferences about the properties of alveolar tissue, since solubility arises from structure.

3. What are hemoglobin saturation and the oxyhemoglobin dissociation curve? Describe 3 factors that can adjust the rate of oxygen unloading to the metabolic rates of different tissues.

A hemoglobin molecule holds four oxygen molecules when saturated. The likelihood of hemoglobin, on average, being saturated depends on the oxygen concentration of the environment. Oxygen concentration is highest where the partial pressure of oxygen is highest, which is in the alveoli (since, after all, the lungs are the source of fresh oxygen). When red blood cells pass through the alveolar capillaries, the hemoglobin molecules become completely saturated with oxygen. Lowest oxygen partial pressure is at the systemic capillaries, but the oxygen saturation is still pretty high – only about a quarter of the hemoglobin molecules are unsaturated.

More oxygen can be unloaded in a more acidic plasma (such as when there is a lot of carbonic acid mixed in) since hydrogen protons cause oxyhemoglobin to change structure and release oxygen. Such a situation can be induced by aerobic exercise, or respiratory arrest, and is called the Bohr effect.

Oxygen unloading can also increase with higher temperature tissues are more active, excreting more carbon dioxide (which leads to more hydrogen protons being present) and also absorbing oxygen from hemoglobin at a better rate.

Yet another way for hemoglobin to unload more oxygen is by the body becoming caught in a stressful situation which elicits a response from the sympathetic nervous system, leading to the release of adrenalin. Adrenalin stimulates the synthesis of bisphosphoglycerate (BPG), a chemical produced through fermentation (the method by which red blood cells get their energy). BPG binds to hemoglobin and reduces its affinity for oxygen.

4. Describe the damage that smoking causes to the respiratory system and describe 2 disorders that can result from long-term smoking.

Cigarette smoke coats the internal lining of the lungs, damaging the surfactant layer, inflaming the mucous lining of the bronchi, impairing the lung’s ability to remove particulates by immobilizing the cilia and increasing presence of sticky mucous producing cells, killing macrophages in the alveoli, and making the lung environment more hospitable to pathogens.

Emphysema is a particular disorder that is characterized by worse lung function because alveolar walls break down, decreasing surface area for gas exchanges. “Thanks” to the destruction of the alveolar membranes, those with emphysema have greater capacity to hold air in lungs which leads to barrel chest from the greater volume of air in the lungs (the fact that less surface area means less surfactant, which in turn means lowered capacity for expiration, doesn’t help either). Also, because of the higher amount of residual or dead air in the lungs and the fact that the lungs can only expand so much (and they’re already somewhat expanded from the higher intrapulmonary pressure), those with emphysema also breathe less usable air per breath. Respiration requires 3-4x as much energy in people with emphysema versus those with healthy lungs.

Chronic bronchitis results from smoke damaging the ciliated columnar epithelial cells that line the bronchi, so that the bronchi are not purged of particulates as efficiently as before. More mucus is produced from the hyperplasic epithelial cells, a problem that is compounded by the deficiency in working cilia to move mucus out of the bronchi. The only way to dislodge the mucus, which is mixed with dead cell fragments and is properly called sputum, is to cough it out. Hence, the “smoker’s cough” is a symptom of a person with chronic bronchitis. The sputum also makes the bronchi more susceptible to bacterial infection, combined with fewer macrophages due to smoke killing many.

5. George Washington went for a walk in the freezing rain on a bleak December day in 1799. The next day, he had trouble breathing and swallowing. A doctor suggested cutting a hole in the president’s throat so he could breathe but other doctors voted him down, instead bleeding the patient, plastering his throat with bran and honey, and placing beetles on his legs to produce blisters. Soon, Washington’s voice became muffled, his breathing was more labored, and he grew restless. For a short time, he seemed euphoric, then he died. Washington had epiglottitis, in which the epiglottis swells to ten times its normal size. How does this diagnosis explain his symptoms? Which suggested treatment might have worked?

The epiglottis blocks food and drink from entering the lungs. It lies between esophagus and trachea, and when swallowing food or drink, nerves are activated which tell the epiglottis to close down on

the trachea. Normally, this brief moment would be the only time in which the epiglottis obstructs the trachea, but if the epiglottis was inflamed, then it would always partially obstruct the trachea, which is why George Washington had trouble breathing. In addition, the swollen epiglottis also partially blocked the esophagus and made swallowing difficult, since due to its swelling the epiglottis cannot completely move back over the trachea during swallowing (this act might cause discomfort also if the epiglottis touched some nerves). Washington’s voice became muffled because talking rests upon movement of air – as a windpipe can’t be played if the openings are blocked, neither can a person talk without adequate air flow. His breathing became more labored as he compensated for less inspiration by breathing deeper. His restlessness is a symptom of hypoxia, and so is his euphoria as his brain became deprived of oxygen. Washington probably would have survived had the lone doctor’s advice (of making a breathing hole in the throat to bypass the obstructed airway due to the epiglottis) been followed – today, this procedure, called a tracheotomy, is considered a viable treatment option and is used when non-surgical treatments fail.

6. Case Study:

A 150 lb. 62-year old man had a chronic productive cough, exertional dyspnea, mild cyanosis, marked slowing of forced expiration and a barrel chest. His pulmonary function and laboratory tests follow:

Frequency (breathing rate) 16 breaths/minAlveolar ventilation rate 4.2 L/minVital capacity 2.2 LFunctional residual capacity (FRC) 4.0LTotal lung capacity 5.2LMaximum inspiratory flow rate 250 L/minMaximum expiratory flow rate 20 L/minPaO2 62 mm HgPaCO2 39 mm Hg

a) What is the disorder of this 62 yr old man?b) How did you reach that diagnosis?c) Is this primarily a restrictive or an obstructive disorder? Why?d) What causes the hypoxia?e) What stimulus increased the breathing rate?

The man has chronic bronchitis and emphysema, both obstructive disorders since airflow is obstructed and pulmonary ventilation reduced. Chronic productive cough is due to sputum buildup, which is made by overactive mucus-producing epithelial cells produced in chronic bronchitis (cyanosis and dyspnea are also symptoms). He must also have emphysema because of the barrel chest, slowed expiration (weak thoracic muscles), lung capacity being at maximum despite dyspnea, high FRC (since his ERV is only 5/4 L per breath, his residual volume must be 2 ¾ L, versus normal 1 L). The partial pressure of oxygen is too low (62mm vs. 104mm) because of the diminished inspiration capacity due to emphysema (the barrel chest and decreased alveolar surface area) and chronic bronchitis (obstructed bronchi) – the man’s hypoxia is caused by these. Predictably, partial pressure of carbon dioxide is also too high (62mm vs. 40mm) for the same reasons. Breathing rate increased because of the man’s hypoxic state, as the increased acidity of the blood and unfulfilled oxygen needs of tissue does set off some alarms such as the hydrogen proton sensitive medulla, which controls breathing rate.