topic 8 pt 1

• What is the primary site for gas exchange in the lungs?

  Alveoli

  
• What structural feature do alveoli provide to the lungs?

  They give lungs a "spongey" structure.

  
• What are the key features of alveoli that facilitate gas exchange?

  • Surrounded by a capillary network
  • Close proximity of air to blood
  • Small diffusion distance
• What type of cells make up 95% of the surface area of alveoli?

  Type I alveolar cells (Type I pneumocytes)
• What is the function of Type II alveolar cells?

  They secrete surfactant to decrease surface tension and prevent alveolar collapse.
• What is the role of alveolar macrophages?

  They digest debris.
• What are the components of the respiratory membrane?

  1. Capillary endothelium
  2. Fused basement membranes
  3. Alveolar epithelium
  4. Surfactant surface layer

  
• What is the purpose of small alveolar pores?

  They connect adjacent alveoli to equalize pressure between them.
• What factors influence the gas diffusion rate across respiratory membranes?

  • Gas partial pressure gradient
  • Temperature
  • Surface area
  • Diffusion distance

  
• How does the solubility of gases affect their diffusion rates?

  O2 diffuses quickly due to its small size, while CO2 dissolves 24 times more easily in water, allowing faster outward diffusion.
• What is the pathway of deoxygenated blood during gas exchange?

  It travels in the pulmonary arteries/arterioles to the lungs.

  
• Where does oxygenated blood travel after gas exchange?

  It travels in the pulmonary venules/veins back to the heart.

  
• Describe the process of gas exchange in the lungs.

  • Gases diffuse from high to low partial pressure.
  • O2 saturates venous blood.
  • CO2 diffuses into alveolar air to be exhaled.
  • Converts deoxygenated blood into oxygenated blood.

  
• Describe the process of gas exchange in tissues.

  • O2 enters cells; blood PO2 drops from 95 to 40 mmHg.
  • CO2 diffuses out to be taken away by the blood.
  • Converts oxygenated blood into deoxygenated blood.

  
• What is the normal hemoglobin concentration in blood?

  150 g/L
• How much oxygen can hemoglobin carry at normal cardiac output?

  About 1000 ml O2 min^-1.
• Why is oxygen very insoluble in solution?

  Because normally only 3 mL of O2 per liter of blood is dissolved in plasma (1.5%).
• How is oxygen transported in the blood?

  • Dissolved in plasma (7%)
  • Combined with hemoglobin forming carbaminohemoglobin (23%)
  • As bicarbonate ion in plasma (70%)

  
• What is the role of heme molecules in hemoglobin?

  They act as binding sites for oxygen.

  
• When is hemoglobin fully saturated?

  When carrying its maximum O2 load of 4 molecules of O2.

  
• What happens to oxygen in the lungs?

  • O2 diffuses from alveoli into blood plasma and RBC.
  • Hb combines with O2 to form oxyhemoglobin.
  • PO2 increase favors oxyhemoglobin formation.

  
• What happens to oxygen in the tissues?

  • O2 diffuses from RBC to plasma and then to tissues.
  • PO2 decrease favors the release of O2 from Hb.
• Describe the O2-Hb dissociation curve.

  • Steep slope at low PO2 values (0 - 40 mm Hg).
  • Flat slope at high PO2 values (40 - 104 mm Hg).

  
• What occurs when PO2 is lower than 40 mmHg?

  Small changes in PO2 represent large changes in % saturation of hemoglobin.

  
• What occurs when PO2 is higher than 40 mmHg?

  Large changes in PO2 represent small changes in % saturation of hemoglobin.

  
• How much oxygen does hemoglobin release at PO2: 104 mmHg?

  About 25% O2 (flat part of the curve).

  
• How much oxygen does hemoglobin release at PO2: 40 mmHg during exercise?

  About 40% O2 (steep part of the curve).

  
• What role does hemoglobin play in oxygen transport?

  • Vital for total O2 quantity in blood.
  • If Hb levels are reduced to 50%, O2-carrying capacity is halved.
  • Acts as a storage depot for O2.
• What factors affect the affinity of O2 for hemoglobin?

  • PCO2
  • Acidity (Bohr effect)
  • Temperature
  • 2,3-bisphosphoglycerate (BPG or DPG)

  
• How does increased acidity affect O2 affinity for hemoglobin?

  It decreases O2 affinity, leading to more O2 being released to tissues.

  
• How does increased PCO2 affect O2 affinity for hemoglobin?

  It decreases O2 affinity, leading to more O2 being released to tissues.

  
• How does increased temperature affect O2 affinity for hemoglobin?

  It decreases O2 affinity, leading to more O2 being released to tissues.

  
• What is the role of 2,3-bisphosphoglycerate (BPG) in oxygen release?

  • Intermediate of glycolysis.
  • More BPG in RBC results in more O2 released to tissues.
  • [BPG] depends on RBC activity and hormones (Thyroxine and Growth Hormone).

  
• What happens when the O2-Hb dissociation curve shifts to the right?

  • Decrease in O2 affinity for Hb.
  • % saturation decreases.
  • More O2 is delivered to tissues.

  
• How is carbon dioxide carried in the blood?

  • Dissolved in plasma (7%).
  • Combined with Hb forming carbaminohemoglobin (23%).
  • As bicarbonate ion in plasma (70%).

  
• Describe the process of CO2 transport in tissues.

  • CO2 diffuses from tissues into plasma and enters RBC.
  • Carbonic anhydrase converts CO2 + H2O to H2CO3.
  • HCO3- leaves RBC in exchange for Cl- (Chloride Shift).
  • H+ and CO2 bind to Hb, releasing O2 (Bohr effect).

  
• Describe the process of CO2 transport in the lungs.

  • O2 diffuses into RBC and binds to Hb, promoting H+ release.
  • Cl- leaves RBC in exchange for HCO3- (Chloride Shift).
  • Carbonic anhydrase converts H2CO3 to CO2.
  • CO2 diffuses from RBC and plasma into alveoli.