Mechanics of Breathing Chapter 17 Respiratory System Functions Exchange of gases between the atmosphere and the blood Vocalization Homeostatic regulation of pH Protection from pathogens and inhaled irritants Alveioli are covered in blood vessels allows gas exchange to occur Diaphragm contracts and flattens Increase thoracic volume decrease in pressure Diaphragm relaxes volume down pressure up Single respiratory cycle consists of inspiration followed by expiration Flow p r Air moves in and out due to pressure gradients between atmosphere and When alveolar pressure is lower than atmospheric pressure air moves into According to Boyle s law expansion of lungs causes a decrease in pressure in the lungs thus air pressure rushes into the lungs Ventilation lungs lungs Boyle s Law Pressure of a gas is inversely proportional to its volume Increased thoracic volume causes a decreased intralveolar pressure and inspiration occurs Thoracic volume Exhalation Passive process It s the result of relaxation of the diaphragm and respiratory muscles Lungs thoracic cavity recoil as the result of their elasticity thereby decreasing thoracic volume increasing pressure Pressure is now greater than atmospheric pressure air moves out Air Flow Flow p r Flow from high pressure low pressure Muscular pump creates pressure gradients Resistance to flow o Diameter of tubes Compliance Elastance Compliance the ability to stretch High compliance Stretches easily Low Compliance Requires more force released Law of LaPlace P 2T R 2 x tension radius Elastance ability to return to resting volume when stretching force is them Ventilation dead space Surfactant decreases pressure easier to inflate alveoli Reduces surface tension in lungs making it easier to inflate More concentrated in smaller alveoli Mixture contacting proteins phospholipids Newborn respiratory distress syndrome Total pulmonary ventilation ventilation rate x tidal volume Tidal volume how much air comes out of lungs in one breath Total pulmonary ventilation is greater than alveolar ventilation because of Alveolar ventilation is a better indication of how much fresh air reaches the alveoli Fresh air remaining in the dead space does not get to alveoli Alveolar ventilation ventilation rate x tidal volume dead space volume Normal Ventilation Values Total Pulmonary Ventilation 6 L min Total Alveolar Ventilation 4 2 L min Max Voluntary Ventilation 125 170 L m Respiration rate 12 20 breaths min Gas Exchange Transport Occurs due to diffusion from an area of high concentration to low concentration When dealing with gases in a mixture we talk about differences in partial pressures For our purposes air is made up of Dalton s Law Total pressure of a mixture of gases is the sum of the pressures of the individual gases 20 93 oxygen 0 03 Carbon dioxide 79 04 nitrogen In ambient air PO2 760 0 2093 159 mmHg PCO2 760 0 0003 0 23 mmHg PN2 760 0 7904 600mmHg Diffusion Constants Surface area membrane thickness Diffusion Distance Concentration gradient Primary factor affecting gas exchange Through Partial pressure is the major factor affecting gas exchange Others Length of Diffusion Path Surface area for exchange RBC or hemoglobin concentration Gas exchange Occurs between alveoli capillary Gas must dissolve in blood Gases dissolve in a fluid based on Henry s law Solubility of the gas in the blood Temp of the blood Partial pressure of gas Henry s Law At a constant temp The amount of a given gas dissolves in a given type volume of liquid is proportional to the partial pressure Oxygen diffuses across alveolar epithelial cells and capillary endothelial cels to enter the plasma Gas Diffusion O2 Gas Diffusion CO2 Hypoxia Low O2 in blood supply Region of body deprived of O2 Low arterial pressure of O2 Sensors varialbles CO2 O2 pH Causes of low alveolar PO2 To avoid hypoxia and hypercapnia the body responds to 3 regulated Inspired air has abnormally low O2 content Altitude Alveolar Ventilation is inadequate Decreased lung compliance Increased airway resistance CNS depression Alcohol poisoning Drug overdose Load up at lungs Unload at Cells Oxygen Transport Dissolved in plasma 0 003 ml mmHg PO2 Arterial blood has a PO2 of 100mmHg thus we transport 0 3 ml 100ml of blood Bound to Hemoglobin Hb 1 34ml of 2 g of Hb Can calculate O2 carrying capacity of Hemoglobin if you know Hb concentration Males avg Hb conc 15g 100ml Females avg Hb conc 13 g 100ml Males have larger lungs Have to unload O2 from Hb Protein too big O2 transport in Blood Hemoglobin Saturation Each gram of Hb can transport 1 34 ml of O2 Avg males Hb 15g 100ml Avg females Hb 13g 100ml If Hb is 100 saturated avg male could carry 20 1ml 100ml of bood 15x1 34 If Hb is 100 saturated avg female could carry 17 42 ml 100ml of blood 13x1 34 These values are often called O2 carrying capacities Hb is not normally fully saturated Amount of O2 carried by Hb is dependent on PO2 Effects if Oxyhemoglobin Dissociation Curve on O2 Transport Arterial blood 97 98 saturated O2 carried by Hb in arteries Males 19 7 mlO2 100ml Females 17 07 mlO2 100ml Total O2 transport amount of O2 dissolved in plasma plus amount O2 carried by Hb in veins Males 15 075 mlO2 100ml Females 13 065 mlO2 100ml Total O2 transport transported bound to Hb Arteries Males 0 3 19 7 20 0 ml O2 100ml Females 0 3 17 07 17 37 mlO2 100ml Veins Males 0 12 15 075 15 195 mlO2 100ml Females 0 12 13 065 13 185mlO2 100ml Arteriovenous Oxygen Difference aV O2 difference Males 20 0 15 075 4 805ml O2 100ml Females 17 37 13 185 4 185ml O2 100ml pH goes down curve shifts down to right Unloaded more oxygen Increase oxygen available in tissues Bohr Effect is the shift in the hemoglobin saturation curve resulting from pH change Temperature increases we unload more O2 CO2 transport Dissolved 7 Converted to bicarbonate ion 70 Bound to hemoglobin 23 Hemoglobin also binds H Hb and CO2 carbaminohemoglobin CO2 H2O H2CO3 H HCO3 Carbonic Acid Bicarbonate Unloads more O2 Increase PCO2 Increase Temperature Decrease pH Gas Exchange and Transport CO2 H2O H2CO3 H HCO3 IMPORTANT High leves of H and CO2 breathing increases All areas more metabolically active Produce bicarbonate in RBC but diffuses out of RBC in Choride Shift Study with Large diagram know what is going on each step Regulation of Ventilation Respiratory neurons in the medulla control inspiratory and expiratory muscles Neurons in pons integrate sensory info and interact with medullary neurons to influence ventilation Rhythmic pattern of breathing