Study Guide for Exam 4 The Respiratory System 1 Mechanics of breathing Breathing consists of two phases o Inspiration than the pressure inside of the lungs air flows into the lungs because the pressure outside of the lungs is greater For this to occur the lungs must expand increasing lung volume which decreases its pressure allowing air to flow in The diaphragm contracts causing it to flatten This allows the lungs thoracic cavity to expand The external intercostals also contract elevating the ribs and widening thoracic cavity o Expiration than the atmospheric pressure air flows out of the lungs because the pressure inside the lungs is greater During quiet breathing exhalation is passive resulting from elastic recoil of the chest wall lungs During forceful breathing the rectus abdominus and internal intercostals contract increasing abdominal pressure and forcing the diaphragm upwards decrasing volume 2 Pressure Relationships in the thoracic cavity Pressure in the thoracic cavity can be controlled by the diaphragm Respiratory pressure is always described relative to atmospheric pressure o Atmospheric pressure PATM pressure exerted by air surrounding the body 760 mm hg at sea level than PATM Negative respiratory pressure is less than PATM and positive pressure is greater o Intrapleural intrathoracic pressure pleural cavity always lower than atmospheric pressure atmospheric pressure for inhalation to occur o Alveolar intrapulmonic pressure the pressure between the two pleural layers in the the pressure inside the lungs must be lower than 3 Pulmonary Ventilation Aka breathing the inflow and outflow of air involving the exchange of gases between the atmosphere and alveoli of the lungs o Airflow is due to changing pressures inside lungs caused by contraction and relaxation of respiratory muscles 4 Physical Factors affecting pulmonary ventilation Airway resistance friction is the major source of resistance to airflow o the relationship between flow F pressure P and resistance R is F P R o gas flow is inversely proportional to resistance which is greatest in medium sized bronchi o the pressure gradient between the atmosphere and alveoli P is directly proportional to gas flow between the alveoli and atmosphere as airway resistance rises breathing becomes more strenuous 5 Dead space and alveolar ventilation Anatomical dead space volume of the conducting respiratory passages 150 mL o Conducting zone is composed of the bronchioles Alveolar Ventilation Rate AVR how much air is reaching alveoli in one breath o Slow deep breathing increases AVR while rapid shallow breathing decreases AVR AVR frequency X Thoracic Vol dead space ml min breaths min 5250 ml min 15 min ml breath 350 ml 6 Gas exchange between blood lungs and tissues Atmospheric pressure Partial Pressure the total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture o The partial pressure of each gas is directly proportional to its percentage in the mixture is also directly proportional to pressure An increase in Solubility thoracic pressure causes an increase of solubility of gases 760 mmHg O2 20 93 160 mm Hg CO2 0 003 0 3 mm Hg N2 79 04 600 mm Hg 7 External respiration Partial pressure gradients Although carbon dioxide has a lower partial pressure gradient than oxygen it is 20 times more soluble than O2 o It diffuses in equal amounts with oxygen Partial Pressure Gradients PCO2 PO2 Venous Blood 45 mm Hg 40 mm Hg Alveolus 40 mm Hg 104 mm Hg Arterial Blood 40 mm Hg 104 mm Hg 8 Transport of Respiratory gases by blood Hemoglobin hb oxygen carrying protein in blood containing iron o Saturated Hb when all four hemes of molecule are bound to O2 98 saturated arterial blood contains 20 mL of O2 per 100 mL blood As it flows through capillaries 5 is released into tissues To the right is the Oxygen vs Hb curve o Plots the saturation of Hb vs Pressure of O2 98 sat 20 mL 75 sat 15 mL CO2 diffuses quickly into red blood cells and joins with H2O to form Carbonic acid which quickly dissociates into ions CO2 H2O H2CO3 H HCO3 In red blood cells carbonic anhydrase catalyzes the reaction o As more carbon dioxide enters the blood more oxygen dissociates from hb Haldone effect can be carried in the blood the lower the PO2 and saturation of hb with O2 the more CO2 The H2CO3 HCO3 buffer system o If concentration of H begins to rise excess H is removed by combining it with HCO3 o if concentration of H starts to decline carbonic acid dissociates releasing H 9 Control of Respiration o Respiratory center the brain stem o Control of respiration medulla oblongata and Pons both inspiratory and expiratory muscles inspiratory diaphragm and external intercostals o during forceful breathing sternocleidomastoid and scalene expiratory internal intercostals and rectus abdominus o higher brain centers in cerebral cortex also have control over voluntary breathing o central chemoreceptors located in medulla 70 response o peripheral chemoreceptors located in aortic and carotid bodies 30 response both of these affect the rate of inspiration and expiration o When these receptors detect an increase of CO2 they both work together to mediate a response o They send an impulse to the respiratory center in the brain which sends an impulse to respiratory muscles causing them to contract faster o This causes a return to normal of PCO2 The Urinary System 1 Nephrons Nephron affects blood volume and pressure functional unit of the kidney Alters blood composition regulates blood pH and o 85 of nephrons located in renal cortex o Juxtamedullary nephrons other 15 found at junction of cortex and medulla Glomerulus thin capillary beds within nephrons that perform the first step of filtering blood o Its glomerular epithelium is thin allowing solute rich filtrate to pass from blood into glomerulus o The blood pressure in the glomerulus is high forcing solutes and fluids out of the blood Juxtaglomerular JG apparatus microscopic structure in kidney that regulates function of each nephron 2 Glomerular Filtration 3 steps in urine formation Filtration reabsorption secretion The glomerulus is responsible for the 1st step in urine formation filtration of the blood o Filtration occurs at the renal corpuscle of the glomerulus o Blood pressure moves fluid across filtration membrane The actual filtering structure is the membrane of the glomerular capillaries The filtration membrane keeps larger molecules in the blood stream o The resulting
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