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1017MSC T6 Respiratory Revision Sheets & Answers 2011

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THE RESPIRATORY SYSEM - EXAMPLE QUESTIONS WITH MODEL ANSWERS A. Multiple-Choice Questions 1) Air and food are routed into the proper channels by the a. trachea b. pharynx c. larynx d. carina e. uvula 2) The loudness of a person's voice depends on a. the thickness of vestibular folds b. the length of the vocal folds c. the strength of the intrinsic laryngeal muscles d. the cross sectional area of the glottis e. the force with which air rushes across the vocal folds 3) The walls of the alveoli are composed of two types of cells, type I and type II. The function of type II is a. to secrete pulmonary surfactant b. to trap dust and other debris c. to replace mucus in the alveoli d. to facilitate movement of macrophages into the alveoli e. to secrete defensins and lysosymes 4) The smallest airways in the conducting zone is (are) the a. primary bronchioles b. terminal bronchioles c. respiratory bronchioles d. alveolar ducts e. alveolar sacs 5) The smallest macroscopic subdivision of the lung is the a. lobe b. segment c. lobule d. primary bronchiole e. terminal bronchiole
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Page 1: 1017MSC T6 Respiratory Revision Sheets & Answers 2011

THE RESPIRATORY SYSEM - EXAMPLE QUESTIONS WITH MODEL ANSWERS A. Multiple-Choice Questions 1) Air and food are routed into the proper channels by the a. trachea b. pharynx c. larynx d. carina e. uvula 2) The loudness of a person's voice depends on a. the thickness of vestibular folds b. the length of the vocal folds c. the strength of the intrinsic laryngeal muscles d. the cross sectional area of the glottis e. the force with which air rushes across the vocal folds 3) The walls of the alveoli are composed of two types of cells, type I and type II.

The function of type II is a. to secrete pulmonary surfactant b. to trap dust and other debris c. to replace mucus in the alveoli d. to facilitate movement of macrophages into the alveoli e. to secrete defensins and lysosymes 4) The smallest airways in the conducting zone is (are) the a. primary bronchioles b. terminal bronchioles c. respiratory bronchioles d. alveolar ducts e. alveolar sacs 5) The smallest macroscopic subdivision of the lung is the a. lobe b. segment c. lobule d. primary bronchiole e. terminal bronchiole

Page 2: 1017MSC T6 Respiratory Revision Sheets & Answers 2011

6) The pleurae are vital to the integrity of the lungs because a. they contain cilia that protect the lungs b. they control the volume of the lungs c. they maintain the proper temperature of the lungs d. they produce a lubricating serous secretion, allowing the lungs to glide

over the thorax wall during breathing e. they secrete lung surfactant 7) Intrapulmonary pressure is the a. pressure within the alveoli of the lungs b. pressure within the pleural cavity c. negative pressure in the intrapleural space d. difference between atmospheric pressure and respiratory pressure e. pressure within the thoracic cavity 8) The relationship between the pressure and volume of gases is given by a. Dalton's law b. Henry's law c. Charles' law d. Boyle's law e. Poiseuille’s law 9) The statement, "in a mixture of gases, the total pressure is the sum of the individual partial pressures of gases in the mixture" paraphrases a. Henry's law b. Boyle's law c. Dalton's law d. Charles' law e. Poiseuille’s law 10) Surfactant helps to prevent the alveoli from collapsing by a. humidifying the air before it enters b. warming the air before it enters c. Increasing the stabilising force of surface tension at the air liquid interface d. interfering with the cohesiveness of water molecules, thereby reducing

the surface tension of alveolar fluid e. protecting the surface of alveoli from dehydration and other environmental

variations

Page 3: 1017MSC T6 Respiratory Revision Sheets & Answers 2011

11) For gas exchange to be efficient, the respiratory membrane must be a. less than 0.1 micrometer thick b. 0.5 to 1 micrometer thick c. at least 3 micrometers thick d. between 5 and 6 micrometers thick e. the thickness of the respiratory membrane is not important in the efficiency of

gas exchange 12) With the Bohr effect, more oxygen is released from haemoglobin at the

tissues because a. a decrease in pH (acidosis) weakens the haemoglobin-oxygen bond b. a decrease in pH (acidosis) strengthens the haemoglobin-oxygen bond c. an increase in pH (alkalosis) strengthens the haemoglobin-oxygen bond d. an increase in pH (alkalosis) weakens the haemoglobin-oxygen bond e. none of the above since the Bohr effect concerns the effect of oxygen

unloading on carbon dioxide loading in the blood 13) The most powerful respiratory stimulus for breathing in a healthy person is a. increase in temperature of arterial blood b. decrease in oxygen partial pressure in arterial blood c. decrease in pH (acidosis) in arterial blood d. increase in pH (alkalosis) in arterial blood e. increase of carbon dioxide partial pressure in arterial blood 14) In the plasma of arterial blood of a healthy person, the quantity of oxygen dissolved in solution a. less than 2 % of the oxygen combined with haemoglobin b. about 7% of the oxygen combined with haemoglobin c. approximately equal to the amount combined with haemoglobin d. much greater than the amount comcined with haemoglobin e. zero because oxygen is insoluble in aqueous solution like plasma 15) Another name for the inflation reflex is a. Bohr-Haldane b. Poiseuille-Laplace c. Fick-Dalton d. Hering-Breuer e. Charles-Henry

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16) Tidal volume is air a. remaining in the lungs after forced expiration b. exchanged during normal breathing c. forcibly inhaled after normal inspiration d. forcibly expelled after normal expiration e. the volume of the conducting airways that has to be cleared during an

inspiration before air reaches the alveoli 17) The vital capacity of an average young male is around a. 1200 ml b. 2400 ml c. 3600 ml d. 4800 ml e. 6000 ml 18) Possible causes of hypoxia include a. too little oxygen in the atmosphere b. breathing compressed air under water c. obstruction of the oesophagus d. taking several rapid deep breaths e. getting very cold 19) The lung volume that represents the maximum volume that can be inspired or

expired is a. tidal volume b. total lung capacity c. vital capacity d. inspiratory capacity e. functional residual capacity 20) Which of the following is not a stimulus for breathing? a. rising carbon dioxide levels b. rising blood pressure c. arterial PO2 below 60 mm Hg d. decreased arterial pH e. increased body temperature

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21) Respiratory groups of neurones that control breathing are located in the a. midbrain and pons b. midbrain and medulla c. midbrain and upper spinal cord d. medulla and pons e. medulla and upper spinal cord 22) The maximal amount of air that can be inspired after a normal (not forced)

inspiration is called a. inspiratory reserve volume b. inspiratory capacity c. functional residual capacity d. vital capacity e. total lung capacity 23) Which statement about CO2 is incorrect? a. its concentration in the blood is decreased by hyperventilation b. its accumulation in the blood is associated with a decrease in pH c. CO2 concentrations are greater in venous blood than arterial blood d. raised CO2 levels in arterial blood stimulates central chemoreceptors e. more CO2 dissolves in the blood plasma than is carried in the red blood

cells 24) Oxygen and carbon dioxide are exchanged in the lungs and through all cell

membranes by a. osmosis b. diffusion c. filtration d. active transport e. reabsorption 25) Select the correct statement about the pharynx a. the adenoids are located in the laryngopharynx b. the auditory tube drains into the nasopharynx c. the laryngopharynx blends posteriorly into the nasopharynx d. the palatine tonsils are embedded in the lateral walls of the nasopharynx e. the oropharynx is lined with pseudostratified columnar ciliated cells

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26) The larynx contains a. the thyroid cartilage b. C-shaped rings of cartilage c. a cricoid cartilage also called the Adam's apple d. an upper pair of avascular mucosal folds called true vocal folds e. lateral cartilage ridges called false vocal folds 27) Which respiratory-associated muscles would contract if you were to blow up a

balloon? a. diaphragm and external intercostals b. diaphragm and internal intercostals c. diaphragm and abdominal muscles d. internal intercostals and abdominal muscles e. external intercostals and abdominal muscles 28) Which of the following is not found on the right lobe of the lung? a. middle lobe b. cardiac notch c. horizontal fissure d. oblique fissure e. segmental bronchi 29) Impairments of oxygen transport do not include a. anaemic hypoxia b. carbon monoxide poisoning c. stagnant hypoxia d. hypoxaemic hypoxia e. histotoxic hypoxia 30) Which of the following correctly describes mechanisms of CO2 transport? a. 20% of CO2 is dissolved directly into the plasma. b. 7-8% of CO2 is carried in the form of carbaminohaemoglobin. c. the majority of CO2 transported in the blood is in the form of carbonic acid d. carbonic anhydrase is responsible for bonding CO2 to haemoglobin. e. the chloride shift mechanism enhances CO2 transport

Page 7: 1017MSC T6 Respiratory Revision Sheets & Answers 2011

31) Which of the following provide the greatest surface area for gas exchange? a. respiratory bronchioles b. alveolar ducts c. alveolar sacs d. alveoli e. alveolar pores 32) The respiratory membrane is a combination of a. alveoli and alveolar sacs b. alveoli, alveolar sacs and alveolar ducts c. alveoli, alveolar sacs, alveolar ducts and respiratory bronchioles d. the area of the alveoli covered by type I cells e. alveolar and capillary walls and their fused basement membranes 33) Inspiratory capacity is a. the total amount of air that can be inspired after a tidal expiration b. the total amount of air that can be inspired after a tidal inspiration c. the total amount of air that can be inspired after a maximal expiration

inspiration d. vital capacity minus functional residual capacity e. total lung capacity minus residual volume 34) Which of the following cells concerned with respiration are not located in the brainstem? a. dorsal respiratory group b. ventral respiratory group c. pontine respiratory group d. carotid bodies e. central chemoreceptors 35) The nose serves all the following functions except a. as a passageway for air movement b. speech production c. as the initiator of the cough reflex d. warming and humidifying the air e. cleansing the air

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36) Which of the following statements is correct? a. H+ acts directly on central chemoreceptors to increase ventilation b. low arterial pH is the most powerful stimulator of respiration. c. arterial blood pH affects central chemoreceptors directly d. arterial blood pH does not affect peripheral chemoreceptors directly e. H+ has little effect on the blood pH. 37) The factors responsible for holding the lungs to the thorax wall are a. the smooth muscles of the lung b. the diaphragm and the intercostal muscles alone c. the visceral pleurae and the changing volume of the lungs d. adhesion forces acting between visceral and parietal pleurae e. the opposing lung and chest wall recoil forces 38) Most inspired particles such as dust fail to reach the lungs because of the a. ciliated mucous lining in the nose b. abundant blood supply to nasal mucosa c. porous structure of turbinate bones d. action of the epiglottis e. powerful cough reflex 39) Which of the following is not the case? a. gas flow equals pressure gradient divided by resistance. b. pressure gradient equals gas flow divided by resistance. c. resistance equals pressure gradient divided by gas flow d. intrapleural pressure is always negative during quiet breathing e. the amount of gas flowing in and out of the alveoli is directly proportional to the

pressure gradient between the external atmosphere and the alveoli. 40) Additional muscle action is required for breathing when a. lung compliance increases b. chest wall compliance increases c. airway resistance decreases d. alveolar surface tension increases e. amount of surfactant in the lungs increases

Page 9: 1017MSC T6 Respiratory Revision Sheets & Answers 2011

41) Select the correct statement about oxygen transport in blood: a. at rest, a molecule of haemoglobin returning to the lungs typically contains one

molecule of O2 b. during conditions of acidosis, haemoglobin will release less of its O2 to the

tissues c. oxyhaemoglobin saturation levels of greater than 95% are only achieved during

exercise when ventilation is increased d. a 50% oxyhaemoglobin saturation level of blood returning to the lungs

might indicate a physical activity level higher than normal e. binding of an O2 molecule to a haemoglobin molecule makes subsequent

binding of O2 molecules more difficult 42) The flow of air into the alveoli is a. trachea - bronchioles - bronchi - alveoli b. trachea - bronchi - bronchioles - alveoli c. bronchi - trachea - bronchioles - alveoli d. bronchioles - trachea - bronchi - alveoli e. bronchi - bronchioles - trachea - alveoli 43) The trachea, bronchi, and bronchioles do all of the following EXCEPT a. warm the air. b. filter the air to remove impurities. c. distribute air to exchange surfaces. d. remove O2 from the air. e. humidify the air. 44) Which one of the following conditions does NOT occur on a large inspiration? a. inspiratory muscles contract b. size of the thoracic cavity increases c. intrapleural pressure becomes more positive d. transpulmonary pressure increases e. lung becomes more inflated 45) During expiration, which of the following does NOT occur? a. respiratory muscles relax b. intrapleural pressure becomes less negative c. transpulmonary pressure decreases d. lung deflates e. alveolar pressure decreases below atmospheric pressure

Page 10: 1017MSC T6 Respiratory Revision Sheets & Answers 2011

46) The pressure that keeps the lungs inflated is a. atmospheric b. alveolar c. transpulmonary d. intratracheal e. partial 47) All of the following can be determined from a spirogram EXCEPT a. expiratory reserve volume b. inspiratory reserve volume c. vital capacity d. functional residual capacity e. inspiratory capacity 48) On a pressure (x axis) volume (y axis) graph, lungs with high compliance

yield a line that a. has a large slope b. has a small slope c. is curved upward d. is curved downward e. is biphasic 49) To overcome the problem of surface tension in the alveoli, specialized

alveolar cells secrete fluid containing a. carbohydrate b. lipid c. acid d. base e. salt 50) Pulmonary surfactants do all of the following EXCEPT a. prevent IRDS b. reduce surface tension c .increase lung compliance d. prevent alveolar collapse e. decrease airway resistance

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51) Low lung compliance tends to make inflation ___, and low airway resistance tends to make rapid breathing ___

a. easy and easy b. easy and difficult c. difficult and easy d. difficult and difficult e. none of the above 52) An arteriole is like a bronchiole in that both a. allow gas exchange b. allow flow in both directions c. are lined with cilia d. contain a layer of smooth muscle e. increase flow rate when constricted 53) Emphysema is a lung disorder leading to the breakdown of alveolar walls and

the formation of larger, but fewer alveoli. Pulmonary oedema leads to an excess of interstitial fluid between the alveoli and pulmonary capillaries. Both disorders reduce the rate of gas exchange, but for different reasons. Those reasons are that emphysema _______; while pulmonary oedema ________

a. decreases diffusion area; increases diffusion distance b. increases diffusion area; increases diffusion distance c. decreases diffusion area; increases gas solubility d. increases diffusion area; decreases diffusion distance e. decreases diffusion area; reduces gas solubility 54) According to gas laws, if the pressure in a closed container doubles, and the

temperature stays the same, then the volume must a. double b. be cut in half c. be cut by three-fourths d. quadruple e. be cut by one fourth 55) Suppose a sealed, rigid container held normal air (21% O2, 78% N2, 1%

Argon) at 760 mmHg pressure. If then more N2 were pumped into the container to raise the total pressure to 800 mmHg, the PO2 would then

a. increase to 160 mmHg b. increase to 168 mmHg c. decrease to 160 mmHg d. decrease to 168 mmHg e. remain the same

Page 12: 1017MSC T6 Respiratory Revision Sheets & Answers 2011

56) Closing the upper airway passage at the end of a lung inflation and contracting abdominal and internal intercostal muscles rapidly produces a marked increase in alveolar pressure. Sudden opening of the airway causes a rapid return of alveolar pressure to normal as air is expelled very quickly. This describes a

a. sniffle b. cough c. gasp d. yawn e. whistle 57) Which of the following gases exerts the greatest partial pressure in venous

blood a. oxygen b. carbon dioxide c. water vapor d. nitrogen e. argon 58) The greatest partial pressure gradient across the alveolar-capillary membrane is found for a. H2O b. CO2 c. N2 d. O2 e. NO 59 The maximum amount of oxygen that can be carried by arterial blood is decreased by a. HCO3- b. H+ c. CO2 d. Biphosphoglyceric acid (BPG) e. anaemia 60) Carbonic anhydrase is a(n) a. carrier of carbon dioxide in the blood b. storage site for carbon dioxide c. enzyme that accelerates the combination of carbon dioxide and water d. enzyme that splits the bicarbonate ion e. enzyme that splits carbonic acid into hydrogen and bicarbonate ions

Page 13: 1017MSC T6 Respiratory Revision Sheets & Answers 2011

61) During the chloride shift in tissue capillary blood, ___the red blood cell a. HCO3- exits b. H2CO3 enters c. CO2 exits d. Cl- exits e. carbonic anhydrase enters 62) Which of the conditions is the most powerful stimulant to alveolar ventilation? a. increased PO2 b. decreased PO2 c. increased H+ concentration d. decreased arterial pH e. increased PCO2 63) Under which condition is alveolar ventilation stimulated via peripheral chemoreceptors? a. PO2 below 60 mmHg b. PO2 above 60 mmHg c. PCO2 below 20 mmHg d. PCO2 between 20 and 40 mmHg e. pH Above 7.5 64) What kind of cell innervates the diaphragm? a. parasympathetic neurone b. interneurone c. preganglionic sympathetic neurone d. postganglionic sympathetic neurone e. alpha motor neurone

Page 14: 1017MSC T6 Respiratory Revision Sheets & Answers 2011

SHORT ANSWER QUESTIONS Q1. Label the identified structures (10 answers, ½ mark each = 5 marks total).

You need only provide the level of detail given for this figure in chapter 22 of Marieb (e.g. answer “nose” is inadequate – and would be incorrect whereas “inferior lobe of left lung” is more detail than required – although this would not be penalised if correct)

Nasal cavity

Nostril

Oral cavity

Larynx

Right lung

Diaphragm

Left main (primary) bronchus

Carina of trachea

Trachea

Pharynx

Page 15: 1017MSC T6 Respiratory Revision Sheets & Answers 2011

Q2. Label the identified structures (10 answers, ½ mark each = 5 marks total). You need only provide the level of detail given for this figure in chapter 22 of Marieb.

(i.e this gas)

Type II (surfactant secreting) cell Red blood cell

Capillary

CO2

Macrophage

Endothelial cell nucleus

Nucleus of type I (squamous epithelial) cell Alveolar

epithelium

Capillary endothelium

Fused basement membranes of alveolar epithelium & capillary endothelium

Page 16: 1017MSC T6 Respiratory Revision Sheets & Answers 2011

Q3. Draw a graph showing the changes in Volume (top line), Intrapulmonary Pressure (middle line) and Intrapleural Pressure (bottom line) during a single inspiration and expiration at rest. Indicate the phases of inspiration and expiration on each line. Label the graph with appropriate scales and units. (5 marks total – 1 mark for each line with correct y axis scale and units; 1 mark for identifying inspiratory and expiratory phases with correct x axis scale and units; 1 mark for correct alignment of the 3 lines)

Intrapulmonary Pressure

Intrapleural Pressure

Page 17: 1017MSC T6 Respiratory Revision Sheets & Answers 2011

Q 4. Name the indicated volumes or capacities on the spirogram below and provide typical values for a healthy young 70 kg adult male (10 answers, ½ mark each = 5 marks total)

Volume/ Capacity

Name Typical value

A

Inspiratory Reserve Volume 3100 ml

D

Residual Volume 1200 ml

C+D

Functional Residual Capacity 2400 ml

A+B+C

Vital Capacity 4800 ml

A+B+C+D

Total Lung Capacity 6000 ml

Page 18: 1017MSC T6 Respiratory Revision Sheets & Answers 2011

Q5. A healthy person exercising at a light load has the following respiratory

measures over a 1 minute period: Mean tidal volume = 1.2 litres Respiratory frequency = 15 breaths/min Mean duration of inspiration = mean duration of expiration Dead space volume = 200 mls Calculate (with units) – (5 marks - 1 mark for each answer) 1. Duration of an average breath Duration of a breath = 60 seconds/respiratory frequency = 60/15 = 4 seconds 2. Minute ventilation Minute ventilation = tidal volume x respiratory frequency = 1.2 litres x 15 breaths/min = 18 litres/min 3. Pulmonary ventilation Pulmonary ventilation = Minute ventilation = 18 litres/min 4. Alveolar ventilation Alveolar ventilation = (tidal volume-dead space volume) x respiratory frequency = (1.2 litres – 0.2 litres) x 15 breaths/min = 15 litres/min 5. Mean inspiratory flow rate of an average breath

Mean inspirartory flow rate = tidal volume/duration of inspiration = 1.2 litres/2 seconds (since duration of inspiration = half of breath duration) = 0.6 litres/second

Page 19: 1017MSC T6 Respiratory Revision Sheets & Answers 2011

Q6. An 18 year male student inhales a small peanut which partially occludes a segmental bronchus in the right lung (this is established later on X-ray). After a severe but unsuccessful coughing fit, the student is able to breathe without much difficulty and heads off to the local Emergency Department. (9 marks total – see below)

Answer the following questions:

1. What would happen to PO2 and PCO2 in the alveoli supplied by this partially occluded airway? (1 mark) The PO2 would fall and the PCO2 would rise

2. How would (a) the pulmonary arterioles and (b) the bronchioles in this

segment of the lung respond? Briefly explain the mechanisms underlying these responses (2 marks) (a) the pulmonary arterioles would constrict in response to low local oxygen levels (hypoxia) and (b) the bronchioles would dilate in response to the raised CO2 levels

3. What benefit would the student get from these autoregulatory responses to

inhaling a peanut? Briefly explain your answer. (2 marks) Vasoconstriction of the pulmonary arterioles would direct blood blow away from the hypoxic region to better ventilated lung regions imoproving gas exchange. Dilation of bronchioles would improve ventilation somewhat in the affected area also helping to improve gas exchange.

4. Would you expect the student’s resting arterial PO2 to change, and if so

how, as a result of this event? Justify your answer (2 marks). Yes a fall in arterial PO2 would be expected. Although autoregulatory mechanisms would compensate for the partially occluded airway, it is unlikely that the coupling of ventilation to perfusion in this region of the lung would be as good as it was before the event. This increase in mismatching of ventilation and perfusion in the lungs as a whole would result in a fall in arterial PO2. (A “No” answer would be acceptable if you argued that the autoregulation could fully compensate for the occlusion to maintain ventilation perfusion coupling at the ideal level)

5. Briefly explain how the autoregulatory mechanism operating in this student

can lead to right heart failure in a patient with chronic obstructive pulmonary disease (COPD) who has had widespread mucous blockage of airways over many years. (2 marks) With widespread blockage of airways the resulting hypoxic pulmonary vasoconstriction would lead to pulmonary hypertension which would result in an increase in right ventricular work to maintain cardiac output. This would lead to right ventricular hypertrophy and ultimately to right heart failure.

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1. On the PO2 (x) axis mark the partial pressures of oxygen that you would expect to find in a healthy individual’s arterial (mark with letter a) and mixed venous (v) blood at rest. (note: mixed venous blood is found in the pulmonary artery and represents the blood returning from all tissues in the body) (1 mark) – see above

2. Using curve A (ODC at normal pH of 7.4) calculate the amount of oxygen delivered to the whole body each minute assuming that fully saturated blood carries 20mls of O2/100mls of blood. Assume that cardiac output is 5 l/min. (you can ignore (a) the small amount of O2 in physical solution and (b) the slight relative acidosis mixed venous compared to arterial blood). (2 marks).

Fall in oxyhaemglobin saturation from arterial to mixed venous blood = 20% (see construction above – anything up to to 25% is ok). 100 mls of blood carrying 20 mls of oxygen yields 0.2 x 20 = 4 mls of oxygen to tissues. Thus 1 litre of blood provides 40 mls O2 and 5 litres (cardiac output = blood flow per minute) delivers 5 x 40 mls = 200mls/min

3. What 4 factors within the blood would cause the normal ODC (curve A) to shift to position C? For each factor you need to indicate whether this curve shift is associated with an increase or a decrease (you do not need to indicate by how much the factors change). (2 marks)

(i) __Increase in PCO2______________________________________

(ii) __Increase in H+ ( or decrease in pH)________________________

(iii) __Increase in temperature_________________________________

(iv) __Increase in BPG (2,3-biphosphoglycerate aka 2,3-DPG)_levels__

A

B

C

Q7. Referring to the oxyhaemglobin dissociation curve (ODC) on the right, answer the questions below (5 marks total – see below):

v a

Page 21: 1017MSC T6 Respiratory Revision Sheets & Answers 2011

Q8. Fill in the Blanks (10 answers, ½ mark each = 5 marks total)

In a healthy individual at rest breathing room air at sea level , the partial

pressure of carbon dioxide (PCO2) in inspired air is approximately

_______0__mmHg. The PCO2 within the alveoli is approximately

_______40___mmHg. Arterial blood has a PCO2 of ______40____mmHg

and this increases to ________45__mmHg in mixed venous blood. At the

tissues, CO2 __diffuses__ down its partial pressure gradient into the capillary

blood. In the blood approximately 70% of CO2 is transported as bicarbonate

(HCO3-), approximately 20% is transported as carbaminohaemoglobin and

the remainder is transported dissolved in plasma. Within the red cell there

is a reversible reaction between CO2 and H2O which is catalysed by the

enzyme carbonic anhydrase. The product of this reaction diffuses out of the

red cell into the plasma down its concentration gradient and chloride (Cl-)

ions move in the opposite direct to maintain ionic balance.

Page 22: 1017MSC T6 Respiratory Revision Sheets & Answers 2011

Q9. Summarise the homeostatic response to an increase in arterial PCO2 (error signal) mediated by the central chemoreceptors. Your answer should indicate: (5 marks total – see below)

(i) the location of receptors that are stimulated by this change (1 mark) (ii) the mechanisms within the central nervous system that leads to a

motor response ( 3 marks) (iii) the effect on breathing and how this brings about homeostasis (1

mark)

(i) Central chemoreceptors located bilaterally in the ventrolateral medulla

(ii) An increase in arterial blood CO2 results in CO2 easily diffusing

from the blood into the cerebrospinal fluid where it is hydrated and forms carbonic acid. As the acid dissociates, H+ is liberated. This (unbuffered) H+ excites the central chemoreceptors which stimulate respiratory groups of neurones close by in the brainstem.

(iii) The depth and rate of breathing increases, increasing alveolar

ventilation. This returns the arterial PCO2 towards normal levels.

Page 23: 1017MSC T6 Respiratory Revision Sheets & Answers 2011

Q10. Fill in the Blanks (10 answers, ½ mark each = 5 marks total)

At rest, spontaneous respiratory rhythm is generated in the brain stem, which

comprises the pons and the medulla. Within this region, the three principal

groups of respiratory neurones are the ventral respiratory group (VRG), the

dorsal respiratory group (DRG) and the pontine respiratory group (PRG).

Periodic bursts of neural activity travel down the _phrenic nerve innervating

the diaphragm causing inspiration. Between bursts of activity, expiration

occurs by passive recoil of the lungs and chest wall Other regions of the brain

that can affect breathing include the hypothalamus and the

(cerebral) motor cortex.


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