Study Guide for Exam 4The Respiratory System1) Mechanics of breathing - Breathing consists of two phaseso Inspiration : air flows into the lungs because the pressure outside of the lungs is greater than the pressure inside of the lungs 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 cavityo Expiration : air flows out of the lungs because the pressure inside the lungs is greater than the atmospheric pressure 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 volume2) 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 pressureo Atmospheric pressure ( PATM): pressure exerted by air surrounding the body (760 mm hg at sea level) Negative respiratory pressure is less than PATM and positive pressure is greater than PATMo Intrapleural (intrathoracic) pressure: the pressure between the two pleural layers in thepleural cavity, always lower than atmospheric pressureo Alveolar (intrapulmonic) pressure: the pressure inside the lungs; must be lower than atmospheric pressure for inhalation to occur3) Pulmonary Ventilation- Aka breathing: the inflow and outflow of air, involving the exchange of gases between the atmosphere and alveoli of the lungso Airflow is due to changing pressures inside lungs caused by contraction and relaxation of respiratory muscles4) 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: PRF =o gas flow is inversely proportional to resistance , which is greatest in medium-sized bronchio the pressure gradient between the atmosphere and alveoli (ΔP) is directly proportional to gas flow between the alveoli and atmosphere- as airway resistance rises, breathing becomes more strenuous5) 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 breatho Slow, deep breathing increases AVR, while rapid, shallow breathing decreases AVRAVR = frequency X(Thoracic Vol – dead space)(ml/min)5250 ml/min(breaths/min)15/min(ml/breath)350 ml6) Gas exchange between blood, lungs and tissues- Partial Pressure : the total pressure exerted by a mixture of gases isthe sum of the pressures exerted independently by each gas in themixtureo The partial pressure of each gas is directly proportional toits percentage in the mixture- Solubility is also directly proportional to pressure. An increase inthoracic pressure causes an increase of solubility of gases7) External respiration: Partial pressure gradients- Although carbon dioxide has a lower partial pressure gradient than oxygen, it is 20 times more soluble than O2o It diffuses in equal amounts with oxygenPartial Pressure GradientsVenous Blood Alveolus Arterial BloodPCO245 mm Hg 40 mm Hg 40 mm HgPO240 mm Hg 104 mm Hg 104 mm Hg8) Transport of Respiratory gases by blood- Hemoglobin (hb): oxygen carrying protein in blood containing irono Saturated Hb = when all four hemes of molecule are bound to O2 98% saturated arterial blood contains 20 mL of O2 per 100 mL bloodAtmospheric pressure= 760 mmHg: O2= 20.93%= 160 mm HgCO2= 0.003%= 0.3 mm Hg N2= 79.04%= 600 mm Hg- As it flows through capillaries, 5% is released into tissues- To the right is the Oxygenvs. Hb curveo 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 ionsCO2 + H2O H2CO3 H+ + HCO3-- In red blood cells, carbonic anhydrase catalyzes the reactiono As more carbon dioxide enters the blood, more oxygen dissociates from hb Haldone effect: the lower the PO2 and saturation of hb with O2, the more CO2 can be carried in the blood- 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 Respirationo Respiratory center = the brain stemo Control of respiration : medulla oblongata and Pons both inspiratory and expiratory muscles - inspiratory: diaphragm and external intercostalso during forceful breathing: sternocleidomastoid and scalene- expiratory: internal intercostals and rectus abdominuso higher brain centers in cerebral cortex also have control over voluntary breathingo 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 expirationo 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 fastero This causes a return to normal of PCO2The Urinary System:1) Nephrons- Nephron : functional unit of the kidney. Alters blood composition, regulates blood pH, and affects blood volume and pressureo 85% of nephrons located in renal cortexo Juxtamedullary nephrons: other 15% found at junction of cortex and medulla- Glomerulus : thin capillary beds within nephrons that perform thefirst step of filtering bloodo Its glomerular epithelium is thin, allowing solute rich filtrate to pass from blood into glomeruluso 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 nephron2) Glomerular Filtration- 3 steps in urine formation: Filtration, reabsorption, secretion- The glomerulus is responsible for the 1st step in urine formation, filtration of the bloodo Filtration occurs at the
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