BIO271H1 2014 SECTION 2 NOTES (Lectures 7-10).pdf

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Christopher Garside

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Lecture 7 Respiratory SystemsALL respiratory organs HAVE to be thin and moistTwo Major Animal Lineages have Colonized Terrestrial Habitats 1 Arthropods Crustaceans Chelicerates Insects 2 Vertebrates Fish Amphibians Reptiles Birds MammalsBirdsparabronchial lungs are stiff and change little in volume o lungs themselves do not change in volume o lungs are parabronchilungs between a series of flexible air sacs that act as bellows o increase in suction to decrease pressuresacs change volume in birds not in the lungs o posterior and anterior air sacs o no alveolialmost unidirectional flowbirds have high metabolic rates have higher body temperature compared to oursincreases requirement for energymaking this an energetically efficient systemgas exchange occurs as air flows through parabronchi in lungs o air flow through parabronchi is unidirectionalair goes into posterior air sacsparabronchianterior air sacsair moves outair diffuses into air capillarieswhere actual diffusion of gases occuracross air capillariesair capillaries are surrounded with blood in capillariesmassive increase in surface area very thin wall o bird lungs do not change in volume parabronchiblood flow is cross currentdetermined by a change of direction of air flowair will be crossing over the capillaries from a different direction o cross current partial pressure of oxygen in the blood exiting the respiratory surface can be higher than the partial pressure of oxygen in the medium exciting the respiratory surfaceopposite concurrent o birds are cross currentgas exchange occurs in air capillaries o passive gas exchange o very thin wallsBird Ventilationbird lungs are stiff and do not change in volume air sacs do 1 expansion of the chest using muscles in the chestincreases the sacsdecreased pressureallows fresh air to flow through the bronchi to the posterior air sacsfresh air does NOT flow directly through the lungs flows into the posterior air sacs 2 compression of the chest mostly elastic recoil some muscular action pushes fresh air from the posterior air sacs into the parabronchifresh air diffuses into the air capillarieswhere diffusion of gases occur 3 expansion of the chest pulls air from the parabronchi into the anterior air sacs 4 compression of the chest takes the air from the anterior air sacs and releases it to the environmentrequires 2 cycles of inhalation and exhalation o steps 1 and 3 occurs at the same time steps 2 and 4 occurs at the same time o when you have inhalation fresh air to the posterior air sacs the air which has been used in the parabronchi go into anterior air sacs o exhalation air moves from the posterior air sacs into the parabronchi AND the old air in the anterior air sacs move out o not exactly 2 cycles of inhalation and exhalation for ventilation but for a single breath it is air does mix a little bitfresh air as its moving to the posterior air sacs does mix a little with the parabronchiair flow is unidirectionalallows cross current andor counter current flowair moving into the parabronchi do not change in volume stiffair capillaries are covered in blood vesselsvery efficient exchangePO2 if blood leaving is higher than PO2 of exhaled aircross current partial pressure of O2 leaving the blood is higher than the partial pressure of O2 in the exhaled mediumMammalstwo main parts to respiratory system 1 conduction zone mouth nasal cavity pharynx larynx trachea bronchi bronchiolesallows fresh air to get into the lungsNOT involved in gas exchangetends to be large in diameterlow resistancedont have to develop a big pressure difference to move air2 respiratory zone respiratory bronchioles alveolar ducts alveoligas exchange zone90 of gas exchange occurs across the alveolirespiratory sacs on respiratory bronchioles and alveolar ductssome gas exchange alveoli are the primary site of gas exchange o type I alveolar cells thin walledprimary alveolar cellswhere gas exchange occurs o type II alveolar cells relatively thick wallednot efficient in allowing diffusionnot involved in diffusionmonitors fluid balance across the walls of the alveolisurfactant secretion o outer surface of alveoli are covered in capillaries8090 of surfacevery thin wall capillaries very thin wall alveoli very closely togetherreducing diffusion distanceefficient systemPleural SacLung Environmentthoracic cavity houses the lungseach lung is surrounded by a pleural sac o two membranes with small space between themvisceral membrane directly surrounds lungs themselvesparietal membrane directly attached to the thoracic wall itselfin between visceral and parietal membranes pleural cavity a small amount of liquid here pleuralas the chest expands the lungs follow there needs to be a connectionno fluid in the pleural sac Lungs would collapse o pleural cavity contains a small volume of pleural fluidhas cohesive forcesresist in external forcelung has elastic recoilpulls on visceral membrane of the pleural sac when chest expands o chest wants to go out lung wants to go innegative intrapleural pressureo transpulmonary gradienttranspulmonary pressureatmospheric pressure alveolar pressureintrapleural pressurewill always be positivekeeps the lungs openalveolis and bronchioles do no collapse o if you puncture lungsallows intrapleural pressure to equalize to atmospheric pressurelung collapses do not have positive transpulmonary gradient anymorekeeps lung opened o intrapleural pressure is subatmospherickeeps lung expandedany change in thoracic cavity will be transferred to change in the lungschanges of pressure in the lungs Boyles Lawhow air gets into the lungsalso reduces friction between the visceral without the fluid between the 2 membranes pressure differences cannot be transferred o as chest expands lung followsneed to be a connection between the lungslungs would collapse without the fluidswater is very cohesiveresistant in external forceMammalian Tidal VentilationInspirationInhalation o Somatic motor neuron firing stimulates inspiratory muscles2 primary sets of inspiratory muscles diaphragm separates thoracic and abdominal cavity and external intercostals between ribs 1 Contraction of the external intercostals and the diaphragm 2 Ribs move outwards and up and the diaphragm moves downVolume of the thorax increasesIntrathoracic pressure decreasesBoyles lawvolume increases pressure must decreaseIntrathoracic pressureintrapleural pressureIntrapleural pressure decreases at rest its already subatmospheric but now its even lowerTranspulmonary pressure gradient Pincreases TBecause intrapleural has been decreasedLungs expandBecause of a greater transpulmonary pressureAir is pulled in because of the pressure gradientMammalian Tidal VentilationExpiration Exhalation usually passiveno muscles involved but elastic recoil of the chest wall o Dont need muscles to expire just elastic recoil o Nerve stimulation of inspiratory muscles stops o Somatic motor neurons stops firingMuscle relax ribs and diaphragm return to original positions o Volume of the thorax decreases Intrathoracic pressure increases intrapleural pressure increases o Passive recoil of the lungs pushes air outduring rapid and heavy breathing exhalation is active via contraction of the internal intercostal muscles abdominal muscles also involved o need rapid air exchange during exercise o motor neurons stimulated during exercise o energy required will depend on elastic properties and resistance for both inhalation and exhalation during exercisecompliancehow easy to stretchhow much pressure to cause the expansionthe more compliant less pressure gradient needed the more easy to stretch
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