17A/B: Respiratory System

Question 1

external vs. internal respiration

Answer 1

• external respiration: exchange of O2/CO2 between lungs and external environment
• internal respiration: exchange of O2/CO2 between blood and tissues

Question 2

pulmonary ventilation

Answer 2

the physical movement of air into and out of the lungs (aka breathing)

Question 3

structures and functions of the upper vs. lower respiratory systems

Answer 3

• upper [nasal cavity, pharynx]: filters, warms and humidifies incoming air to protect lower respiratory system, reabsorbs heat and water from outgoing air
• lower [larynx, trachea, bronchus, bronchioles, alveoli] conducts air to and from gas exchange surfaces

Question 4

Explain the membrane that lines the conducting portion of the respiratory tract.

Answer 4

• respiratory mucosa lines the conducting portion of the respiratory tract
• contains ciliated columnar epithelial cells with mucous cells
• beating of cilia sweeps out mucus trapped with particles = mucociliary escalator

Question 5

What structures do the following types of respiratory epithelial cells line?: stratified squamous epithelium, cuboidal epithelium, simple squamous epithelium

Answer 5

• stratified squamous epithelium lines inferior pharynx
• cuboidal epithelium lines narrow bronchioles
• simple squamous epithelium lines gas exchange surfaces (alveoli)

Question 6

epiglottis

Answer 6

• forms lid over glottis

- folds over during swallowing to prevent solids/liquids from entering respiratory tract

Question 7

Explain the glottis and its vocal folds and vestibular folds.

Answer 7

• glottis: passageway of air through larynx
• vocal folds vibrate to produce sound waves
• vestibular folds protect against foreign objects entering glottis

Question 8

What is intrapulmonary pressure? What happens during periods of negative intrapulmonary pressure and positive intrapulmonary pressure?

Answer 8

• intrapulmonary pressure: pressure inside respiratory tract, inside alveoli
• negative intrapulmonary pressure (Poutside > Pinside): inhalation occurs, thoracic cavity increases volume, air flows in
• positive intrapulmonary pressure (Pinside > Poutside): exhalation occurs, thoracic cavity decreases volume, air flows out
  [negative and positive refers to pressure difference between atmospheric and intrapulmonary pressure]

Question 9

Explain what happens to O2 and CO2 levels during external respiration with respect to partial pressure.

Answer 9

• blood arrives at respiratory membrane (alveolus) via pulmonary artery [PO2=40, PCO2=45]
• diffusion occurs between pulmonary capillaries and alveolus [PO2=100, PCO2=40]
• blood departs in pulmonary venules [PO2=100, PCO2=40]

Question 10

Explain what happens to O2 and CO2 levels during internal respiration with respect to partial pressure.

Answer 10

• blood arrives via peripheral capillaries [PO2=95, PCO2=40]
• diffusion occurs between capillaries and interstitial fluid/tissues [PO2=40, PCO2=45]
• blood leaves and returns to heart via systemic vessels [PO2=40, PCO2=45]

Question 11

Describe how oxygen transport occurs (pickup vs delivery)

Answer 11

• O2 pickup: O2 diffuses from alveolus to RBC; binds to Hb to form Hb•O2
• O2 delivery: Hb•O2 dissociate and O2 diffuses into peripheral tissues

Question 12

Describe how carbon dioxide transport occurs (pickup vs. delivery)

Answer 12

• CO2 pickup: CO2 diffuses from tissue into RBC; may either bind to Hb as Hb•CO2 or be converted into H2CO3 by carbonic anhydrase, which will dissociate into H+ and HCO3-. H+ binds to Hb and HCO3- exchanges with Cl- (chloride shift)
• CO2 delivery: CO2 diffuses from RBC to alveolus; Hb•CO2 dissociates; Hb•H+ dissociates; chloride shift brings back in HCO3-; produces CO2 again so it can be transported out

Question 13

Discuss the inhalation reflex

Answer 13

• inhalation reflex prevents overexpansion of the lungs
  1. lung expansion stimulates stretch receptors in smooth muscle around bronchioles
  2. respiratory muscles inhibited by respiratory rhythmicity centers (DRG); inhalation stops
  3. expiratory centers of VRG stimulated; forced exhalation begins

Question 14

Discuss the deflation reflex

Answer 14

• deflation reflex inhibits expiratory centers and stimulates inspiratory centres when lungs are deflating
  1. stretch receptors stimulated when elastic fibers recoil and alveolar volume reduced
  2. expiratory centres of VRG inhibited
  3. DRG activated and inspiratory centers of VRG activated to start forced inhalation

Question 15

What is hypercapnia and what happens to counteract it?

Answer 15

• hypercapnia: increased arterial PCO2

- homeostasis restored by increasing respiratory rate, which increases CO2 elimination

Question 16

What is hypocapnia and what happens to counteract it?

Answer 16

• hypocapnia: decreased arterial PCO2

- homeostasis restored by decreasing respiratory rate, which decreases CO2 elimination