chapter 6 The Respiratory System and Its Regulation

Learning Objectives Find out how the respiratory system brings oxygen to muscles and tissues and rids the body of carbon dioxide Learn the steps involved in respiration and gas exchange Discover how your respiratory system regulates your breathing and gas exchange

Anatomy of the Respiratory System

Transportation of Oxygen and Carbon Dioxide Pulmonary ventilation (breathing): movement of air into and out of the lungs Pulmonary diffusion: the exchange of O2 and CO2 between the lungs and the blood Transport of O2 and CO2 via the blood Capillary diffusion: the exchange of O2 and CO2 between the capillary blood and the metabolically active tissue

Pressure1 x Volume1 = Pressure2 x Volume2 Boyle’s Law If temperature is constant: Pressure1 x Volume1 = Pressure2 x Volume2

Pulmonary Ventilation Inspiration: active process involving the diaphragm and the external intercostal muscles Pressure in the lung is less than the air pressure outside the body, air following the pressure gradient coming into the lung Expiration: usually a passive process involving relaxation of the inspiratory muscles; pressure increases in the lungs and air is forced out Active process during forced breathing

Process of Inspiration and Expiration

Lung Volumes Measured by Spirometry Reprinted, by permission, from J. West, 2000, Respiratory physiology: The essentials (Baltimore, MD: Lippincott, Williams, and Wilkins), 14.

Pulmonary Ventilation Key Points Pulmonary ventilation is the process by which air is moved into and out of the lung (inspiration, expiration) Inspiration is an active process in which the diaphragm and intercostal muscles contract, increasing dimensions and volume of the thoracic cage Expiration at rest is normally passive; the inspiratory muscles relax, decreasing the thoracic cage Forced inspiration and expiration are active processes involving accessory muscles Lung volumes and capacities are measured by spirometry

Pulmonary Diffusion Replenishes blood's oxygen supply that has been depleted for oxidative energy production Removes carbon dioxide from returning venous blood

Blood Flow to the Lungs at Rest: Pulmonary Hemodynamics Low pressure and resistance circulation compared to the systemic circulation Lungs receive 4-6 L/min of blood flow Pulmonary artery mean pressure = 15 mmHg (aortic pressure = 95 mmHg) Left atrial pressure = 5 mmHg Pulmonary vessels are thin walled

Pressures in the Pulmonary and Systemic Circulations Reprinted, by permission, from J. West, 2000, Respiratory physiology: The essentials (Baltimore, MD: Lippincott, Williams, and Wilkins), 36.

Respiratory Membrane: Gas Exchange Alveolar wall Capillary wall Basement membranes (0.5-4.0 mm) Gases will move along a concentration gradient based on partial pressures

Anatomy of the Respiratory Membrane

Partial Pressures of Air Standard atmospheric pressure (at sea level) = 760 mmHg Gas Percent of Air Partial Pressure N2 79.04% 600.7 mmHg O2 20.93% 159.1 mmHg CO2 0.03% 0.2 mmHg

Partial Pressures and Gas Exchange in the Lung and Tissues

Fick’s Law of Diffusion Reprinted, by permission, from J. West, 2000, Respiratory physiology: The essentials (Baltimore, MD: Lippincott, Williams, and Wilkins), 26.

Uneven Distribution of Blood Flow in the Lung Reprinted, by permission, from J. West, 2000, Respiratory physiology: The essentials (Baltimore, MD: Lippincott, Williams, and Wilkins), 44.

Pulmonary Diffusion Key Points Pulmonary diffusion is the process by which gases are exchanged across the respiratory membrane in the alveoli The amount and rate of gas exchange depends on the partial pressure of each gas Gases diffuse along a pressure gradient, moving from an area of higher pressure to lower pressure Vgas A / T x D x (P1 - P2) (continued) .

Pulmonary Diffusion (continued) Key Points Oxygen diffusion rate increases as you move from rest to exercise Exercising muscle requires more oxygen for metabolism; when venous oxygen is depleted, oxygen exchange at the alveoli is facilitated due to an increased pressure gradient The pressure gradient for carbon dioxide exchange is less than for oxygen exchange, but carbon dioxide’s membrane solubility is 20 times greater than oxygen, so CO2 crosses the membrane readily

Oxygen Transport Oxygen is transported bound to hemoglobin (>98%) or dissolved in plasma (<2%) Hemoglobin concentration largely determines the oxygen-carrying capacity of blood Increased H+ (acidity) and temperature of a muscle favors oxygen unloading in the muscle Oxygen carrying capacity seldom limits performance in healthy individuals

Oxyhemoglobin Dissociation Curve Reprinted, by permission, from S.K. Powers and E.T. Howley, 2004, Exercise physiology: Theory and application to fitness and performance, 5th ed. (New York: McGraw-Hill Companies), 205. With permission from The McGraw-Hill Companies.

Effects of pH and Temperature on the Oxyhemoglobin Dissociation Curve Reprinted, by permission, from S.K. Powers and E.T. Howley, 2004, Exercise physiology: Theory and application to fitness and performance, 5th ed. (New York: McGraw-Hill Companies), 206. With permission from The McGraw-Hill Companies.

Carbon Dioxide Transport Bicarbonate ions Muscle: CO2 + H2O → H2CO3 → H+ + HCO3- Lung: H+ + HCO3- → H2CO3 → CO2 + H2O Dissolved in blood plasma Bound to hemoglobin (carbaminohemoglobin)

Gas Exchange Key Points O2 is transported in the blood primarily bound to hemoglobin Hemoglobin unloading of O2 in tissues is enhanced by: Decreased PO2 Decreased pH Increased temperature Hemoglobin is ~98% saturated with oxygen, and O2 carrying capacity typically does not limit performance CO2 is primarily transported as bicarbonate ion in the blood

Gas Exchange at the Muscles: Arterial–Venous Oxygen Difference

Oxygen Transport in the Muscle: Myoglobin Reprinted, by permission, from S.K. Powers and E.T. Howley, 2004, Exercise physiology: Theory and application to fitness and performance, 5th ed. (New York: McGraw-Hill Companies), 207. With permission from The McGraw-Hill Companies.

Factors Affecting Oxygen Uptake and Delivery 1. Oxygen content of blood 2. Amount of blood flow 3. Local conditions within the muscle

Gas Exchange at the Muscle Key Points (a-v)O2 difference is the difference in the oxygen content of the arterial and mixed venous blood throughout the body O2 delivery to the tissues depends on the O2 content in the blood, blood flow to the tissues, and local conditions CO2 exchange at the tissues is similar to O2 exchange except CO2 leaves the muscle to be transported to the lungs -

Regulation of Pulmonary Ventilation Higher brain centers Expiratory centers Inspiratory centers Chemoreceptors Mechanoreceptors in the active muscles and the lung muscles Hypothalamic input Conscious control

Central and Peripheral Regulators of Respiration