Respiratory System II: Breathing and Gas Exchange  Respiratory Volumes and Capacities  Partial Pressure and Gas Exchange  Gas Transport and Hb Cooperativity  Neural Control of Respiration  Respiratory Disorders

Respiratory Volumes and Capacities  Normal breathing moves about 500 ml of air with each breath (tidal volume [TV])  Factors Affecting Respiratory Capacity: Size, Gender, Age, Condition  Expiratory reserve volume (ERV) Amount of air that can be forcibly exhaled Approximately 1200 ml  Inspiratory reserve volume (IRV) Amount of air that can be taken in forcibly beyond the tidal volume Usually ml spirometer

Respiratory Volumes and Capacities  Residual volume Air remaining in lung after expiration About 1200 ml  Respiratory Rate Number of cycles/minute Based on one inspiration and expiration Normally about 15 cycles/min  Minute Ventilation Tidal volume x respiratory rate (breaths/min) Volume of air inhaled/exhaled per minute Normally 5-8 liters

Respiratory System II: Breathing and Gas Exchange  Respiratory Volumes and Capacities  Partial Pressure and Gas Exchange  Gas Transport and Hb Cooperativity  Neural Control of Respiration  Respiratory Disorders

Gas Exchanges Between Blood, Lungs, and Tissues  External respiration (between lungs and outside)  Internal respiration (between bloodstream and tissues)  To understand the above processes, first consider Physical properties of gases Composition of alveolar gas

Basic Properties of Gases: Dalton’s Law of Partial Pressures  Total pressure exerted by a mixture of gases is the sum of the pressures exerted by each gas  (TP = PP N 2 + PP O 2 + PP CO 2 + PP H 2 O )  The partial pressure of each gas is directly proportional to its percentage in the mixture

Basic Properties of Gases: Henry’s Law  When a mixture of gases is in contact with a liquid, each gas will dissolve in the liquid in proportion to its partial pressure  At equilibrium, the partial pressures in the two phases will be equal  The amount of gas that will dissolve in a liquid also depends upon its solubility CO 2 is 20 times more soluble in water than O 2 Very little N 2 dissolves in water

Composition of Alveolar Gas  Alveoli contain more CO 2 and water vapor than atmospheric air, due to Gas exchanges in the lungs Humidification of air Mixing of alveolar gas that occurs with each breath

Table 22.4

External Respiration Defined  Exchange of O 2 and CO 2 across the respiratory membrane in the lungs  Influenced by Partial pressure gradients and gas solubilities Ventilation-perfusion coupling Structural characteristics of the respiratory membrane

Partial Pressure Gradients and Gas Solubilities  Partial pressure gradient for CO 2 in the lungs is less steep: Venous blood Pco 2 = 45 mm Hg Alveolar Pco 2 = 40 mm Hg  CO 2 is 20 times more soluble in plasma than oxygen  Aided also by ventilation-perfusion coupling: where alveolar CO 2 is high, bronchioles dilate; where alveolar CO 2 is low, bronchioles constrict *Perfusion is the ability of blood to flow through tissues.  Partial pressure gradient for O 2 in the lungs is steep Venous blood P O 2 = 40 mm Hg Alveolar P O 2 = 104 mm Hg  O 2 quickly diffuses from alveoli to bloodstream  Aided also by ventilation-perfusion* coupling: Where alveolar O 2 is high, arterioles dilate; where alveolar O 2 is low, arterioles constrict

Respiratory System II: Breathing and Gas Exchange  Respiratory Volumes and Capacities  Partial Pressure and Gas Exchange  Gas Transport and Hb Cooperativity  Neural Control of Respiration  Respiratory Disorders

Gas Transport in the Blood  Oxygen transport in the blood Inside red blood cells attached to hemoglobin (oxyhemoglobin [HbO 2 ]) A small amount (< 2%) is carried dissolved in the plasma  Loading and unloading of O 2 is facilitated by change in shape of Hb As O 2 binds, Hb affinity for O 2 increases As O 2 is released, Hb affinity for O 2 decreases  Change in binding affinity known as positive cooperativity  Fully (100%) saturated if all four heme groups carry O 2  Rate of loading and unloading of O 2 is regulated by many factors  Sigmoidal relationship seen on binding graph Increasingly steeper line (more saturation) as more oxygen present.

Other Factors Influencing Hemoglobin Saturation  Increases in temperature, H +, P CO 2, and BPG (bisphosphoglycerate). They modify the structure of hemoglobin and decrease its affinity for O 2 [  binding with  H + (  pH),  P CO 2,  BPG] Enhanced O 2 unloading in the capillaries where higher CO 2 concentration lowers pH (increases H + )and facilitates more O 2 unloading Decreases in temp, H +, P CO2, and BPG Modify Hb structure and increase O 2 affinity Enhanced loading of O 2 at the lungs [  binding with  H + (  pH),  P CO 2,  BPG]

Figure O2O2 P (mm Hg) Normal body temperature 10°C 20°C 38°C 43°C Normal arterial carbon dioxide (P 40 mm Hg) or H + (pH 7.4) CO 2 Increased carbon dioxide (P 80 mm Hg) or H + (pH 7.2) CO 2 Decreased carbon dioxide (P 20 mm Hg) or H + (pH 7.6) CO 2 (a) (b) Changes in O 2 Binding Curve with Difft Temps and pHs Decreased binding Increased binding Decreased binding Increased binding p O 2 in Hg

Homeostatic Imbalance  Hypoxia (leading to cyanosis) Inadequate O 2 delivery to tissues A variety of causes oToo few RBCs oAbnormal or too little Hb oBlocked circulation oMetabolic poisons oPulmonary disease oCarbon monoxide

Hypoxia, Cyanosis, and CO Poisioning Cyanosis of the face Cyanotic nail beds Cherry red skin from carbon monoxide poisoning

External Vs Internal Respiration In the lungs, plasma HCO 3 - and H + are converted by carbonic anhydrase in the RBC to form carbonic acid which breaks down into CO 2 and H 2 O; CO 2 unloaded into alveoli, blood pH rises as H + removed. Oxygen diffuses from blood into tissue (acidic conditions favor oxygen off-loading known as the Bohr Effect) An opposite reaction to what occurs in the lungs Carbon dioxide diffuses out of tissue into blood plasma as CO 2 and water; tese coverted to carbonic acid (in the RBC) and thence into plasma H + and HCO 3 -, dropping pH External respiration Internal respiration

Respiratory System II: Breathing and Gas Exchange  Respiratory Volumes and Capacities  Partial Pressure and Gas Exchange  Gas Transport and Hb Cooperativity  Neural Control of Respiration  Respiratory Disorders

Neural Regulation of Respiration 1.Respiratory rate and depth is the major regulator of blood pH through retention or loss of CO 2. 2.Phrenic and intercostal nerves enervate intercostals and the diaphragm 3.Neural centers that control rate and depth are located in the medulla, especially the ventral respiratory group (VRG). 4.Suppression of respiratory centers in brain stem (from sleeping pills, morphine, or alcohol) halts respiration, and is fatal 5.Hyperventilation (rapid breathing) drives off CO 2 (hypocapnea)and causes blood pH increase; rebreathing into paper bag acidifies blood; hyperventilation before a dive 6.Hypoventilation (slow, shallow breathing) causes CO 2 retention (hypercapnia), decreasing blood pH, H + triggers faster breathing rate in brain central chemoreceptors 7.Peripheral chemoreceptors in the aortic and carotid arteries are O 2 sensors; low P O2 causes increase in ventilation rate

Respiratory Disorders: Chronic Obstructive Pulmonary Disease (COPD)  Common Features of Bronchitis and Emphysema Patients almost always have a history of smoking Labored breathing (dyspnea) becomes progressively more severe Coughing and frequent pulmonary infections are common Most victims retain carbon dioxide, are hypoxic and have respiratory acidosis Those infected will ultimately develop respiratory failure COPDs are a leading cause of death in the USA