Respiratory Physiology II - Gas Exchange & Regulation Lecture Notes PDF

Lecture #12: Respiratory Physiology II – Gas Exchange & Regulation Julia M. Hum, Ph.D. Monday/Wednesday/Friday: 2:00-2:50pm Office Hours: Monday/Wednesday/Friday 11:00am-12:00pm [email protected]  L12: Learning Objectives...

Lecture #12: Respiratory Physiology II – Gas Exchange & Regulation Julia M. Hum, Ph.D. Monday/Wednesday/Friday: 2:00-2:50pm Office Hours: Monday/Wednesday/Friday 11:00am-12:00pm [email protected]  L12: Learning Objectives 1. Describe the physiological importance of Hb to gas exchange and how it facilitates its role in gas exchange 2. Identify the changes on an O2 dissociation curve 3. Diagram CO2 uptake by RBC and recognize how the body handles CO2 transport 4. Compare and contrast active regulation of blood flow in the pulmonary resistance vessels vs. systemic resistance vessels 5. List other active regulators of pulmonary vessels 6. Describe the two types of “limited” gas exchange 7. Define venous admixture and ventilation/perfusion ratio 8. Identify and describe the Va/Q in the context of health and disease states 9. Define the respiratory control pathways 10. Understand the roles of central and peripheral chemoreceptors and predict their response when changes in PO2 and PCO2 occur Unless otherwise noted, figures in today’s lecture are from: Lippincott Illustrated Reviews: Physiology 1e Wilson (Ch. 23,24)  Gas Pressures Gases move between air and blood by passive diffusion The forces driving O2 and CO2 diffusion between blood and air in terms of partial pressure gradients rather than concentration gradients LO1  Hemoglobin To increase O2 content for a given PO2, need O2 carrier Hemoglobin four O2 binding heme groups that combine reversibly with O2 oxyhemoglobin O2 saturation (O2 bound/total that can be bound) O2 associates and dissociates within milliseconds critical, blood in capillaries ~ 1 sec LO1  Hemoglobin Amount of O2 that blood can carry depends on Hb concentration Blood contains: ~150g Hb/L -> 15g/dL Women: 12-16g/dL Men: 13-18g/dL O2 saturation: number of occupied O2 binding sites on a Hb molecule Arterial blood – 100% saturation Venous blood – 75% saturation LO1  Hb binds oxygen with increasing affinity LO1  O2 Dissociation Curve: Dissociation Blood arrives at tissue – Hb must release Heat, CO2, acidic O2 to make available for mitochondria environment Metabolic by-products affect Hb affinity Made possible through allosteric changes that decrease O2 affinity and promote unloading Exposure of binding pocket allowing easier access of O2 LO2  O2 Dissociation Curve: Dissociation Rightward shifts 1. Temperature Exercise – muscle temperature rises Heat, CO2, acidic Causing more O2 to be released to metabolically active environment tissues 2. Carbon Dioxide Aerobic metabolism: increase CO2, causing tissue PCO2 to rise CO2 binds terminal globin amino group Decreases O2 affinity – results in O2 unloading 3. Protonation Metabolic acids increase during metabolism Protonation stabilizes deoxy-form of Hb, decreasing O2 affinity and promoting release LO2,3  O2 Dissociation Curve: Dissociation Leftward Shifts – Decreases in metabolic activity  H+, PCO2 ( pH)  temperature Leftward shift observed in fetus – “fetal hemoglobin” Higher affinity to O2 than Hb Due to weak 2,3 DPG binding Therefore favors O2 at low partial pressures *  affinity of Hb for O2 LO2,3  CO2 Transport CO2 carried to lung and eliminated in expired gas Blood carries 2x the amount of CO2 than O2 Average CO2 produced via metabolism ~ 200 ml/min ~288,000 ml/day Body handles CO2 much differently than O2 1. CO2 highly water soluble – no transport protein needed 2. CO2 generates large amounts of acid in solution – buffer system needed Mechanisms of Transport 1. Dissolved in blood 2. HCO3- in plasma and RBC - main mechanism 3. Carbaminohemoglobin LO3  CO2 Transport: Uptake by RBCs LO3  Gas Exchange Diffusion-limited gas exchange – amount of gas transported across alveolar-capillary limited by diffusion process Perfusion-limited gas exchange – amount of gas transported across the alveolar-capillary limited by blood flow LO6  Diffusion-limited Exchange CO