MODULE 5-2 OUTLINE RESPIRATION & GAS EXCHANGE

1. List the main functions of the respiratory system.

• Gas exchange between the atmosphere and the body.

• Homeostatic regulation of blood pH.

• Protection from inhaled pathogens.

• Vocalization.

2. Distinguish between external respiration, ventilation and cellular respiration.

• External respiration involves gas exchange between the atmosphere and the lungs (ventilation), and between the lungs and the blood.

• Ventilation is the exchange of air between the atmosphere and the lungs.

• Cellular respiration involves the use of oxygen to generate ATP from glucose, producing carbon dioxide as a by-product.

3. Describe the structure of the pleural sac and the role of pleural fluid in lung expansion.

• The pleural sac consists of the outer parietal pleural membrane and the inner visceral pleural membrane, separated by pleural fluid. The pleural fluid's cohesive forces hold the pleural membranes together, allowing the lungs to expand against the thorax.  

4. What is a pneumothorax? Why do lungs collapse when the pleural cavity is punctured?

• Pneumothorax is a condition where air enters the pleural cavity. When the pleural cavity is punctured, the seal is broken, and air flows in, causing the lung to collapse to its unstretched size.  

5. Discuss the major components of the upper and lower respiratory tracts and their major functions.

• Upper respiratory tract: Consists of the nasal cavity, pharynx, and larynx. Functions include conducting, warming, humidifying, filtering air, and vocalization.  

• Lower respiratory tract: Includes the trachea, bronchi, and lungs. The trachea branches into two primary bronchi, which further divide into smaller bronchioles, terminating in alveoli. Functions include gas exchange and pH regulation.

6. What are the structural and functional differences between the conducting system and the exchange system?

• Conducting system: Includes the upper and lower respiratory tracts. It is responsible for conducting, warming, humidifying, filtering air, and vocalization.  

• Exchange system: Consists of the alveoli. It is responsible for gas exchange and pH regulation.

Describe the role of the following anatomical features in respiratory function:

a. Cartilage rings in the trachea

b. Smooth muscle surrounding bronchioles

c. Elastic tissue surrounding alveol

• Cartilage rings in the trachea: Provide structural support, preventing the trachea from collapsing.  

• Smooth muscle surrounding bronchioles: Helps regulate airflow by constricting or dilating the bronchioles.  

• Elastic tissue surrounding alveoli: Contributes to the elastic recoil of the lungs, aiding in expiration.

8. Describe the role of the saline and mucus layers covering ciliated epithelium in the upper respiratory tract, and clearly explain how they are produced.

• The airway epithelium has goblet cells that produce mucus and ciliated epithelial cells that produce a saline layer. The saline layer, produced by CFTR channels pumping chloride ions into the lumen, underlies the mucus. Sodium and water follow, hydrating the mucus.  

9. What is the mucociliary escalator and what is its function?

• The mucociliary escalator is a mechanism where cilia on epithelial cells move the mucus layer, trapping pathogens and debris, up and out of the respiratory tract.  

10. Explain why loss of CFTR function results in cystic fibrosis, and describe the main pathological characteristics of CF.

• Loss of CFTR function results in cystic fibrosis. Mutations in CFTR lead to a buildup of thick, sticky mucus and an increased risk of bacterial infections in the respiratory tract.  

11. How does gas exchange occur in the alveoli? Describe the connections between alveolar cells and endothelial cells.

• Gas exchange occurs in the alveoli. The alveolar cell membrane is closely connected to the endothelial cell membrane by a thin basal lamina, facilitating efficient gas exchange between the air in the alveoli and the blood in the capillaries.  

12. Why is there no smooth muscle surrounding alveoli?

• There is no smooth muscle surrounding alveoli because gas exchange occurs here.

13. Why won’t lungs expand by themselves?

• The lungs won't expand by themselves because they lack the musculature to do so. Lung expansion relies on the contraction of thoracic cavity muscles.  

14. Compare and contrast the functions of type I and type II alveolar cells.

• Type I alveolar cells: These are extremely thin and are the majority of alveolar cells. They are primarily responsible for gas exchange.  

• Type II alveolar cells: These cells synthesize surfactants, which are proteins and phospholipids that disrupt cohesion and surface tension, allowing the lungs to expand.

15. Explain the role of surfactants in lung expansion.

• Surfactants, produced by Type II alveolar cells, reduce the surface tension in the alveoli, which is essential for lung expansion.  

16. Broadly describe the importance of the following changes involved in ventilation:

a. pressure/volume changes of the lungs

b. thoracic cavity muscles

• Pressure/volume changes of the lungs: Changes in the volume of the thoracic cavity lead to changes in lung volume, creating pressure gradients that drive air movement (inspiration or expiration).  

• Thoracic cavity muscles: Contraction and relaxation of these muscles cause the volume changes in the thoracic cavity that facilitate ventilation.

17. Describe the role of the following thoracic muscles in ventilation:

a. External intercostals

b. Internal intercostals

c. Diaphragm

d. Scalenes

e. Abdominal muscles

• External intercostals: These muscles contract to pull the ribs up and out, increasing thoracic volume during inspiration.  

• Internal intercostals: These muscles contract during forceful expiration to pull the rib cage inward, decreasing thoracic volume.  

• Diaphragm: This muscle contracts and flattens, increasing the vertical dimension of the thoracic cavity during inspiration.  

• Scalenes: These muscles also contract during inspiration to help elevate the rib cage.  

• Abdominal muscles: These muscles contract during forceful expiration to help decrease thoracic volume.

18. Compare and contrast the mechanisms involved in inspiration and expiration, being sure to point out the pressure/volume differences at each stage and the role of different muscles

• Inspiration:

• Thoracic volume increases.

• The diaphragm and external intercostal muscles contract.

• Alveolar pressure decreases, causing air to flow into the lungs.  

• Expiration:

  • Thoracic volume decreases.

  • Inspiratory muscles relax, and elastic recoil returns lungs to their resting volume (normal expiration).

  • Internal intercostals and abdominal muscles contract during strenuous activity.

  • Alveolar pressure increases, causing air to flow out of the lungs.

19. Compare and contrast compliance and elastance in respiratory physiology.

• Compliance: Measures the ability of the lungs to stretch or expand.  

• Elastance: Measures the ability of the lungs to return to their resting volume when the stretching force is released.

20. Give examples of disease states that arise from changes in compliance and/or elastance.

• Compliance: Pulmonary fibrosis decreases compliance.  

• Elastance: Emphysema decreases elastance.

21. What is partial pressure of a gas? How does partial pressure help us understand how gas exchange works?

• The partial pressure of a gas is the pressure exerted by that gas in a mixture of gases. Partial pressure helps us understand how gas exchange works because individual gases diffuse down their own partial pressure gradients, moving from areas of high partial pressure to areas of low partial pressure.  

22. Compare and contrast alveolar vs. arterial PO2.

• Alveolar PO2 is the partial pressure of oxygen in the alveoli, while arterial PO2 is the partial pressure of oxygen in the arterial blood. A decrease in alveolar PO2 would decrease arterial PO2.  

23. Diagram the pressure gradients at the different sites of gas exchange and show the direction of oxygen and carbon dioxide movement

• Gases diffuse down their own partial pressure gradients.

• Oxygen moves from an area of high PO2 to an area of low PO2.

• Carbon dioxide moves from an area of high PCO2 to an area of low PCO2.

24. Contrast hypoxia and hypercapnia. Why are both dangerous situations for proper gas exchange?

• Hypoxia: Low arterial PO2.

• Hypercapnia: An excess of carbon dioxide in the blood.

• Both are dangerous because they interfere with proper gas exchange, disrupting the delivery of oxygen to tissues and the removal of carbon dioxide from the body.

25. Discuss the anatomical changes and pathological characteristics of the following respiratory diseases:

a. emphysema

b. pulmonary fibrosis (fibrotic lung disease)

c. pulmonary edema

d. Asthma

e. Acute Respiratory Distress Syndrome (ARDS)

• Emphysema: Characterized by the destruction of alveolar elastic fibers.  

• Pulmonary fibrosis (fibrotic lung disease): Characterized by the development of scar tissue around alveoli, which decreases lung compliance.  

• Acute Respiratory Distress Syndrome (ARDS): Caused by viral infection of alveolar epithelia.  

• The document does not explicitly discuss the anatomical changes and pathological characteristics of pulmonary edema and asthma.

26. Clearly explain how SARS Coronavirus causes ARDS.

• SARS Coronavirus causes ARDS by viral infection of alveolar epithelia, leading to lymphocyte activation, cytokine storm/pyroptosis, breach of alveolar epithelia, pulmonary edema & hypoxia.  

27. Compare and contrast the solubility of oxygen and carbon dioxide.

• Carbon dioxide is more soluble in blood than oxygen.  

28. Describe % saturation of hemoglobin, and how it helps improve the transport of oxygen in the blood.

• % saturation of hemoglobin is the percentage of hemoglobin binding sites occupied by oxygen. It improves oxygen transport in the blood because hemoglobin binds to oxygen, significantly increasing the blood's oxygen-carrying capacity.  

29. Draw the oxyhemoglobin dissociation curve (for normal conditions) and explain the physiological significance of the shape of this curve

• The oxyhemoglobin dissociation curve plots the percentage saturation of hemoglobin as a function of PO2. The curve's shape reflects hemoglobin's cooperative binding of oxygen, meaning that as one oxygen molecule binds, it becomes easier for subsequent oxygen molecules to bind. This facilitates efficient oxygen loading in the lungs and unloading in the tissues.  

30. Draw the shifts in the oxygen-hemoglobin dissociation curve that result from changes in:

a. pH

b. temperature

c. CO2 concentration

d. 2,3-BPG concentration

• pH: Decreased pH (acidity) shifts the curve to the right, decreasing hemoglobin's affinity for oxygen and releasing more oxygen to the tissues.  

• Temperature: Increased temperature shifts the curve to the right, decreasing hemoglobin's affinity for oxygen and releasing more oxygen.  

• CO2 concentration: Increased CO2 concentration shifts the curve to the right, decreasing hemoglobin's affinity for oxygen (Bohr effect) and releasing more oxygen.  

• 2,3-BPG concentration: Increased 2,3-BPG concentration shifts the curve to the right, decreasing hemoglobin's affinity for oxygen and releasing more oxygen.

31. Compare and contrast fetal hemoglobin with hemoglobin found in adults, and the difference between their saturation curves. Why is this important for delivery of oxygen to the fetus?

• Fetal hemoglobin (HbF) has a higher affinity for oxygen than adult hemoglobin (HbA). This difference is important for the delivery of oxygen to the fetus, as it allows fetal hemoglobin to more effectively bind oxygen from the maternal circulation in the placenta.  

32. Map the different ways in which oxygen and carbon dioxide are transported in the blood stream, listing specific mechanisms in each case.

• Oxygen transport:

  • Oxygen is transported in the blood bound to hemoglobin (98%) forming oxyhemoglobin.

  • Oxygen is also dissolved in plasma (2%).  

• Carbon dioxide transport:

  • Carbon dioxide is transported dissolved in plasma.

  • Carbon dioxide is converted into bicarbonate by carbonic anhydrase.

  • Carbon dioxide binds to hemoglobin to form carbaminohemoglobin.

33. Discuss the importance of carbonic anhydrase for:

a. CO2 transport

b. bicarbonate production

c. regulation of blood pH

• CO2 transport: Carbonic anhydrase converts CO2 into bicarbonate, which is a major form of CO2 transport in the blood.  

• Bicarbonate production: Carbonic anhydrase is essential for the production of bicarbonate.  

• Regulation of blood pH: Bicarbonate acts as a pH buffer in the blood, helping to regulate blood pH.