Chapter 22 Respiratory System Lecture 8 Part 2: O2 and CO2 Transport Marieb’s Human Anatomy and Physiology Ninth Edition Marieb w Hoehn Chapter 22 Respiratory System Lecture 8 Part 2: O2 and CO2 Transport Slides 1-15; 80 min (with review of syllabus and Web sites) [Lecture 1] Slides 16 – 38; 50 min [Lecture 2] 118 min (38 slides plus review of course Web sites and syllabus)

Just a Quick Review! Atmosphere is composed of several gases, each exerting its own partial pressure, PO2 P  1/V (Boyle’s Law) Inspiration Normal Forced or maximal Expiration The respiratory membrane for gas exchange

Diffusion Across Respiratory Membrane Figure from: Hole’s Human A&P, 12th edition, 2010

Diffusion Through Respiratory Membrane The driving force for the exchange of gases between alveolar air and capillary blood is the difference in partial pressure between the gases. (PP gradients of different gases are independent) Figure from: Hole’s Human A&P, 12th edition, 2010 At a given temperature, the amount of a particular gas in solution is directly proportional to its partial pressure outside the solution (Henry’s Law)

Efficiency of Respiratory Membrane Diffusion Diffusion of gases across the RM of the lung is efficient due to Large partial pressure differences Small distances Lipid solubility of gases Large total surface area Blood flow and air flow are coordinated

Composition of Inspired and Alveolar Air From: Saladin, Anatomy & Physiology, McGraw Hill, 2007

Factors Affecting O2 and CO2 Transport O2 and CO2 have limited solubility in plasma; so a more efficient way to carry these gases is needed... This problem is solved by RBCs Bind O2 to hemoglobin Use CO2 to make soluble compounds Reactions in RBCs are Temporary Completely reversible Less than 2% of O2 is dissolved in plasma; about 5-7% of CO2 is dissolved in plasma

Oxygen Transport Most oxygen binds to hemoglobin to form oxyhemoglobin (HbO2) Oxyhemoglobin releases oxygen in the regions of body cells Much oxygen is still bound to hemoglobin in the venous blood Figure from: Hole’s Human A&P, 12th edition, 2010 PO2 ≈ 100 mm Hg PO2 ≈ 40 mm Hg *PO2 in blood leaving lungs is about 95 mm Hg (not 100) because some of the blood leaving the alveolar capillaries mixes with venous blood returning to the heart from blood vessels serving other structures in the lung (which is not oxygenated) and this reduces the PO2 from 100 mm Hg at the alveoli to about 95 mm Hg in the arterial blood. Tissues Lungs But what special properties of the Hb molecule allow it to reversibly bind O2?

Review of Hemoglobin’s Structure Figure From: Martini, Anatomy & Physiology, Prentice Hall, 2001

The O2-Hb Dissociation Curve Figure from: Hole’s Human A&P, 12th edition, 2010 Recall that Hb can bind up to 4 molecules of O2 = 100% saturation At 75% saturation, Hb binds 3 molecules of O2 on average Sigmoidal (S) shape of curve indicates that the binding of one O2 makes it easier to bind the next O2 This curve tells us what the percent saturation of Hb will be at various partial pressures of O2

Oxygen Release Amount of oxygen released from oxyhemoglobin increases as partial pressure of carbon dioxide increases the blood pH decreases and [H+] increases (Bohr Effect; shown below) blood temperature increases (not shown) concentration of 2,3 bisphosphoglycerate (BPG) increases (not shown) Figure from: Hole’s Human A&P, 12th edition, 2010

Carbon Dioxide Transport in Tissues dissolved in plasma (7%) combined with hemoglobin as carbaminohemoglobin(15-25%) in the form of bicarbonate ions (68-78%) CO2 + H2O ↔ H2CO3 H2CO3 ↔ H+ + HCO3- Figure from: Hole’s Human A&P, 12th edition, 2010 CO2 exchange in TISSUES

Carbon Dioxide Transport in Tissues dissolved in plasma (7%) combined with hemoglobin as carbaminohemoglobin(15-25%) in the form of bicarbonate ions (68-78%) CO2 + H2O ↔ H2CO3 H2CO3 ↔ H+ + HCO3- Figure from: Hole’s Human A&P, 12th edition, 2010 CO2 exchange in TISSUES

Chloride Shift bicarbonate ions diffuse out RBCs chloride ions from plasma diffuse into RBCs electrical balance is maintained Figure from: Hole’s Human A&P, 12th edition, 2010

Carbon Dioxide Transport in Lungs Figure from: Hole’s Human A&P, 12th edition, 2010 CO2 exchange in LUNGS

Review Oxygen travels in the blood bound to Hb Four O2 molecules can be bound to 1 Hb O2 bound to Hb - oxyhemoglobin Uptake and release of O2 is dependent upon PO2 in alveoli and tissues Several factors can increase the release of O2 from Hb Increased PCO2 Increased [H+] (decreased pH) Increased temperature of blood

Review Carbon dioxide can travel in several ways Dissolved in plasma (7%) As carbaminohemoglobin (15-25%) As HCO3- ion (70%) Recall: H2O + CO2 ↔ H2CO3 ↔ H+ + HCO3- Carbonic anhydrase in RBCs accelerates interconversion between CO2 and HCO3- H+ combines with or dissociates from Hb HCO3- diffuses into plasma or into RBCs Cl- diffuses into RBC (chloride shift) as HCO3- exits Diffusion of CO2 is related to PCO2 in alveoli and tissues