Respiratory Physiology

1. Function of hemoglobin in respiration:

• Oxygen transport: Hemoglobin (Hb) is a protein found in red blood cells that has the ability to bind with oxygen (O2) to form oxyhemoglobin (HbO2). HbO2 transports oxygen from the lungs to the tissues in the body to provide energy for cellular activity.
• Carbon dioxide transport: Hemoglobin also has the ability to bind with carbon dioxide (CO2) to form carbaminohemoglobin (HbCO2). However, the capacity of Hb to transport CO2 is lower than that of oxygen.
• Note: Besides Hb, CO2 is also transported in the blood as bicarbonate (HCO3-) and dissolved in plasma.

2. Four respiratory processes of the lungs:

• Ventilation: This is the process of exchanging air between the lungs and the external environment.
  • Inspiration: Air from the environment enters the lungs due to the contraction of the diaphragm and intercostal muscles.
  • Expiration: Air from the lungs escapes to the outside due to the relaxation of the diaphragm and intercostal muscles.
• Diffusion: This is the process of gas exchange between the alveoli and the pulmonary capillaries.
  • Oxygen: Oxygen from the alveoli diffuses into the blood in the capillaries because the partial pressure of oxygen in the alveoli is higher than the partial pressure of oxygen in the blood.
  • Carbon dioxide: Carbon dioxide from the blood in the capillaries diffuses into the alveoli because the partial pressure of carbon dioxide in the blood is higher than the partial pressure of carbon dioxide in the alveoli.
• Transportation: Oxygen and carbon dioxide are transported in the blood by hemoglobin, transporting oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs.
• Cellular respiration: This is the process of using oxygen to generate energy for cellular activity.

3. Pulmonary circulation:

• Blood from the right ventricle is pumped into the pulmonary artery, branching to the alveoli and forming a network of capillaries surrounding the alveoli.
• Here, gas exchange takes place between the alveoli and the blood in the pulmonary capillaries.
• Then, oxygen-rich blood travels through the pulmonary vein back to the left atrium.

4. Characteristics of blood from the right ventricle and after passing through the capillaries to the left atrium:

Characteristic	Right ventricle	Left atrium
Color	Dark red	Bright red
CO2 concentration	High	Low
O2 concentration	Low	High

5. Muscles involved in the respiratory process:

• Diaphragm: This is the main muscle involved in inspiration.
• External intercostal muscles: These muscles help lift the rib cage, creating negative pressure in the pleural cavity, aiding in inspiration.
• Internal intercostal muscles: These muscles participate in expiration.

6. Inspiration and expiration:

• Inspiration: The diaphragm contracts, moves down, increasing the size of the chest cavity in the vertical direction; The external intercostal muscles contract, raising the rib cage, increasing the size of the chest cavity in the anteroposterior direction. The pressure in the pleural cavity decreases, the alveoli expand, and air enters the lungs.
• Expiration: The diaphragm relaxes, the external intercostal muscles relax, the chest cavity decreases in size, the pressure in the pleural cavity increases, the alveoli contract, and air exits the lungs.

7. How does the alveolar pressure change relative to the environment during inspiration and expiration?:

• Inspiration: Alveolar pressure decreases below atmospheric pressure (about -1 cm water) due to the expansion of the alveoli.
• Expiration: Alveolar pressure increases above atmospheric pressure (about +1 cm water) due to the contraction of the alveoli.

8. Pleural cavity pressure:

• The pleural cavity is the space between the parietal and visceral pleura, a closed cavity.
• Inspiration: The pressure in the pleural cavity decreases (usually -7 cm water) due to the expansion of the chest cavity, creating negative pressure that helps the alveoli expand.
• Expiration: The pressure in the pleural cavity increases (usually -5 cm water) due to the contraction of the chest cavity.

9. Factors that initiate respiration:

• The respiratory center in the medulla oblongata controls the breathing rate, regulated by the following factors:
  • CO2 concentration in the blood: Increased CO2 concentration in the blood stimulates the respiratory center to increase breathing rate.
  • O2 concentration in the blood: Decreased O2 concentration in the blood stimulates the respiratory center to increase breathing rate.
  • Blood pH: Decreased blood pH (increased acidity) stimulates the respiratory center to increase breathing rate.

10. Function of surfactant:

• Surfactant is a surface-active substance secreted by alveolar cells that reduces the surface tension of water in the alveoli.
• It helps prevent alveolar collapse, keeping the alveoli expanded and facilitating gas exchange.

11. Explaining the indicators in the graph:

• Tidal volume (Vt): Volume of air inhaled or exhaled in a single breath (without exertion ~ 500 ml).
• Inspiratory reserve volume (IRV): Volume of air that can be forcefully inhaled after a normal inspiration.
• Expiratory reserve volume (ERV): Volume of air that can be forcefully exhaled after a normal expiration.
• Residual volume (RV): Volume of air remaining in the lungs after a forceful expiration.
• Vital capacity (VC): VC = IRV + Vt + ERV
• Total lung capacity (TLC): TLC = VC + RV

12. What are the Tiffeneau ratio and Gaensler ratio?

• Tiffeneau ratio: This is the ratio of the forced expiratory volume in 1 second (FEV1) to the vital capacity (VC), used to assess respiratory function.
• Gaensler ratio: This is the ratio of FEV1 to the forced vital capacity (FVC), also used to assess respiratory function.
• Note: Both of these ratios are used to diagnose chronic obstructive pulmonary disease (COPD) and restrictive lung disease.

13. Which indicators increase (decrease) when suffering from obstructive and restrictive syndromes?

• Obstructive syndrome:
  • FEV1 decreases due to airway obstruction.
  • The Tiffeneau ratio and Gaensler ratio decrease due to a decrease in FEV1.
  • VC decreases due to airway obstruction, preventing full inhalation.
• Restrictive syndrome:
  • VC decreases due to restriction of lung expansion.
  • FEV1 decreases due to a decrease in VC.
  • The Tiffeneau ratio and Gaensler ratio decrease due to the decrease in both FEV1 and VC.

14. What is dead space?

• Dead space is the volume of air in the conducting airways (larynx, trachea, bronchi) that does not participate in gas exchange.
• Dead space is constant, about 150 ml in adults.

15. When does the Barcroft curve shift to the right, and by what factors?

• The Barcroft curve is a graph that shows the relationship between the partial pressure of oxygen in the blood (PO2) and the oxygen saturation of hemoglobin (SpO2).
• The Barcroft curve shifts to the right when the oxygen-binding capacity of hemoglobin decreases.
• Factors that cause the Barcroft curve to shift to the right:
  • Increased CO2 concentration in the blood: Increased CO2 makes the blood acidic, reducing the oxygen-binding capacity of hemoglobin.
  • Increased H+ concentration in the blood: Increased H+ concentration (decreased blood pH) reduces the oxygen-binding capacity of hemoglobin.
  • Increased temperature: Increased temperature reduces the affinity of hemoglobin for oxygen.
  • Increased 2,3-DPG (2,3-diphosphoglycerate): 2,3-DPG is an organic compound produced in red blood cells that reduces the affinity of hemoglobin for oxygen.

16. How many ways are there to transport O2 in the blood? What is the process of O2 exchange?

• There are 2 ways to transport O2 in the blood:
  • Free oxygen: A small portion of oxygen dissolves in plasma.
  • Oxygen bound to hemoglobin: Most oxygen is transported by hemoglobin in red blood cells, in the form of oxyhemoglobin (HbO2).
• Process of O2 exchange:
  • At the alveoli: Oxygen from the alveoli diffuses into the blood in the pulmonary capillaries because PO2 in the alveoli is higher than PO2 in the blood. Hemoglobin in red blood cells binds with oxygen, forming HbO2, making the blood oxygen-rich.
  • At the tissues: HbO2 in the blood comes in contact with tissue cells; because PO2 in the blood is higher than PO2 in the tissue, oxygen diffuses from the blood into the tissue cells to supply energy. Hemoglobin releases oxygen, making the blood oxygen-poor.

17. How many ways are there to transport CO2 in the blood?

• There are 3 ways to transport CO2 in the blood:
  • Free CO2: A small portion of CO2 dissolves in plasma.
  • CO2 bound to hemoglobin: CO2 binds to hemoglobin to form carbaminohemoglobin (HbCO2).
  • CO2 in the form of HCO3-: Most CO2 is transported in the blood as bicarbonate (HCO3-).

18. How many mechanisms are there to regulate the respiratory process?

• There are 2 mechanisms for regulating respiration:
  • Neural mechanism: Controlled by the respiratory center in the medulla oblongata, including:
    • Inspiratory center: Stimulates the contraction of the diaphragm and external intercostal muscles, aiding in inspiration.
    • Expiratory center: Stimulates the relaxation of the diaphragm and external intercostal muscles, aiding in expiration.
    • Respiratory rhythm center: Regulates the breathing rate, ensuring regular breathing.
  • Humoral mechanism: Regulated by chemical factors in the blood:
    • CO2 concentration in the blood: Increased CO2 in the blood stimulates the respiratory center to increase breathing rate.
    • O2 concentration in the blood: Decreased O2 in the blood stimulates the respiratory center to increase breathing rate.
    • Blood pH: Decreased blood pH (increased acidity) stimulates the respiratory center to increase breathing rate.

19. Special parameters:

• In 100 ml of blood, there are ~ 14-16 g of hemoglobin.
• 1 g of hemoglobin binds ~ 1.34 ml of oxygen.
• Under normal conditions, 100 ml of blood releases ~ 5 ml of oxygen to the tissues.
• Under exertion, 100 ml of blood releases ~ 15 ml of oxygen to the tissues.
• In 1 inspiration-expiration cycle, it lasts 5 seconds.
• In 1 minute, a normal person breathes ~ 12 times.

20. What does the autonomic nervous system control?

• The autonomic nervous system controls the activity of the smooth muscles of the bronchioles, lung parenchyma.
• Sympathetic nervous system: Relaxes the smooth muscles of the bronchioles, helping the airways dilate.
• Parasympathetic nervous system: Contracts the smooth muscles of the bronchioles, helping the airways constrict.

21. Where is the respiratory control center located?

• The respiratory control center is located in the pons and medulla oblongata.

22. How does the pleural cavity pressure change during inspiration?

• During inspiration, the pleural cavity pressure decreases from -5 cm water to -7 cm water.
• The pleural cavity volume increases by 0.5 liters.

23. How does the alveolar pressure change during inspiration?

• During inspiration, the alveolar pressure decreases from 0 to -1 cm water.
• The alveolar volume increases by 0.5 liters.

24. Physiological characteristics of the pleura:

• The pleura is a thin membrane, consisting of two layers: the parietal and visceral layers.
• The parietal layer attaches to the chest wall, while the visceral layer covers the lung surface.
• The space between the two layers is called the pleural cavity.
• The pleura serves to connect the lungs to the chest wall, helping the lungs expand and contract during respiration.

25. Factors that reduce lung collapse:

• Surfactant secreted by alveolar cells reduces the surface tension of water in the alveoli, helping to prevent alveolar collapse.

26. Structure of the exchange membrane:

• The gas exchange membrane consists of 4 layers:
  • Alveolar cell membrane
  • Alveolar basement membrane
  • Capillary basement membrane
  • Endothelial cell membrane of the capillaries

27. Good gas exchange efficiency depends on:

• Good gas exchange efficiency depends on the matching of alveolar ventilation and pulmonary capillary circulation.
• Good alveolar ventilation ensures an adequate oxygen supply to the alveoli.
• Good pulmonary capillary circulation ensures good blood flow for transporting oxygen to the tissues.

28. Hering-Breuer reflex:

• The Hering-Breuer reflex is an automatic reflex that helps regulate breathing rate.
• When the alveoli are excessively expanded, the receptors in the alveoli send signals to the respiratory center, stimulating expiration.
• Conversely, when the alveoli are excessively contracted, the receptors in the alveoli send signals to the respiratory center, stimulating inspiration.

Note:

• Respiratory physiology is a complex process, involving numerous factors, mechanisms, and reflexes.
• This article is just a brief introduction to respiratory physiology. Further research is needed for a deeper understanding.
• If you have any respiratory problems, consult a doctor for advice and treatment.