10.4.96 Dr.Richard O.Davies Handout: c:\wpwin\davies\respirat.sys RESPIRATORY SYSTEM: GROSS ANATOMY Dr. Davies is not an anatomist. He says they don't like him to give this lecture. He says they make him say gross anatomy at least five times, and tell us how gross anatomy is extremely important. He showed us this really old picture of himself before taking gross anatomy, and a picture of some toothpaste model/lifeguard was the "after" picture :) Anyway, we'll be talking about the respiratory system, which functions to capture oxygen and secondarily gets rid of CO2. This system is extremely important. "No breathe, no live" -Mr. Miyage, The Karate Kid Must memorize above statement. If animals stop breathing they die. The thing you should know about respiratory system is that there is a valve called the pharynx/larynx/upper respiratory tract, and there is a pump, the lower respiratory tract. Dr. Orsini is an expert on the valve part and maybe we will hear from him later. re: biochem of respiration: combustion of organic compounds. O2 consumed, CO2 produced. There is no O2 consumption in the body w/o CO2 production. bodies don't rust. Bodies have very large O2 need. You have to have a very highly developed structure to capture the oxygen: that's the lung. You also need physiological processes to transfer the O2 from air into the cells. Also need to get the CO2 from the cells to the air. These transport processes operate w/in constrains imposed by gross anatomy of the system. physiology involves transport. So, you pick something up, you move it, and put it somewhere else. these transport processes may be relatively unstressed or can be fully stressed, reaching their maximum, as in excercise or pulmonary or cardiac disease. respiratory transport: O2 picked up from outside air and transported into the body and into the cells. note that a person who's in shape has more mitochondria in the muscles, can use more O2. understanding transport mechanism requires understanding of the gross anatomy of the system. anatomical systems: lung and upper airways. "respiratory system". includes elaborate conducting system of trachea, bronchi, bronchioles, etc. This conducting system is divided into upper: larynx, pharynx, nose, upper trachea; all outside the thorax and surrounded by atmospheric pressure; and lower, intrathoracic part: lower trachea, bronchi, etc, which are surrounded by intrapleural pressure which is less than atmospheric pressure- subatmospheric pressure. Thes airways branch until you get to the respiratory zone, containing alveoli which exchange gas between air and blood. the pump involves the muscles of the thorax/chest wall. muscles of thorax surround the lung, very important. the pump is what transports gas from air to alveolar zone. eg, it gets oxygen into lung and carbon dioxide out of lung. there is also a heart and a circulatory system to be discussed in the future, which transports gas from lung to the tissues of the body and from the tissues to the lung. if you look at the respiratory system as a physiologist, it's basically a large thin membrane organized for the exchange of gas between air and blood. alveolar exchange area in a horse is VERY large, about half the size of a football field. very large surface area. this comes about by internal partitioning. surface area is what is used to exchange oxygen. animal w/high metabolic rate needs large lung surface area. dog lung surface area higher than man's. horse has larger lung surface area than cow, because horse metabolic rate= more than twice that of the cow. so the lung is scaled according to metabolic needs of the animal. shrew: small animal w/huge metabolic rate. HR 1050/min, RR 300/min. shrew has much smaller alveoli, therefore proportionally greater surface area. membrane not only large but extremely thin. much thinner than rbc. less than 1/10 micron. note that only 1/10 micron separates blood from outside air!. And there's lots of blood in there- about 3 quarts blood in horse lung at rest - and that's spread over the area of half a football field. so it's all spread out so thinly, and it is so delicate, it needs protection. So, it's internalized. It's protected by chest wall, bones, muscles. because it's inside the body, far from source of oxygen, far from site of utilization of oxygen, you need pumps to move the oxygen around. again, the pump is powered by muscle contractions. again, from gross anatomical point of view, pump surrounds the lungs. the muscles of the chest, bones, supporting structures, surround the lungs. surrounding structures include ribcage and intercostal muscles, triangularis sternae, transversus thoracis, diaphragm. note that large part of ribcage extends over abdomen. abdominal muscles are also part of the pump. this pump has to change pressures in thorax and size of thorax. anytime this pump acts on lungs, it acts on all the other structures in there as well. if lungs are squeezed all intrathoracic structures are squeezed. degree depends on compliance. heart, large vessels in thorax. if intrathoracic pressure is too high, veins collapse, decrease venous return, affects ability of heart. this happened to Elvis. function of respiratory muscles: * act to change volue of the thorax. lung volume changes secondary to that. change in lung volume = change in thoracic volume * at rest, the predominant active phase is inspiration. to bring gas into the lungs, the thorax must be enlarged. inspiratory muscles are prime movers of the lung at rest. static sequence of respiration: 1. inspiratory muscles contract, thorax expands (diaphragm moves caudally) 2. lung parenchyma is stretched due to the mechanical linkage of the pleural fluid, which has cohesive forces and adhesive forces - passive expansion. intrapleural pressure decreases due to recoil. when you expand thorax, pressure decreases inside thorax even more. So now it's even lower. note that if air gets into intrapleural space, pneumothorax, lungs will collapse, unable to expand, because the cohesive forces are disrupted. 3. alveoli expand in size as lung tissue expands, and 4. the gas inside them expands, and so the pressure decreases (as gas expands) and as pressure decreases, 5 air flows into the lung from the outside. single most important respiratory muscle is the diaphragm.horse w/o a diaphragm is like horse w/2 legs. diaphragm is inserted on sternum, ribs, and vertebral column. it is relatively dome shaped and the fibers, in the human, are directed mostly cranial, parallel to the long axis of the body. in horse, fibers are directed dorsally, parallel to body wall. central part of diaphragm not muscle, but is the tendinous center. the central tendon is tethered to the pericardium. the diaphragm sits on the abdominal contents. diaphragm contracts, and the dome flattens out, pushing back onto abdominal contents. this leads to enlarged thorax, decreased pleural and thoracic pressure. then lungs will expand. that's the usual action of diaphragm remember two things. remember diaphragm sits between closed chamber of thorax and closed chamber of abdomen *consequences of caudal movement of diaphragm* 1. there must occur either - an increase in abdominal pressure or - a displacement of abdominal contents. abdominal movements will be observed if abdominal contents are displaced. 2. the decrease in thoracic presure tends to cause the rib cage to move inward, and expiratory direction. therefore, it is important that the rib cage muscles contract to prevent this, fixing the ribs and preventing distortion. a problem that comes about w/all this is that as diaphragm shortens and you inspire more (more you inspire, shorter diaphragm gets), as you increase volume of inspiration diaphragm gets shorter and shorter and less and less efficient. you want large volumes when you are exercising. but at that time, the diaphragm is getting less efficient, producing less and less tension. this inefficiency has 2 causes. one, has to do w/structure of muscle which we already discussed, eg the optimal interactions of actin and myosin and the decreased tension when muscle overcontracts - cross bridges don't work very well. at normal length, muscle can develop high tension. but if it gets too long or too short, you can't get the same amount of force generated. it gets more and more inefficient. the diaphragm is a bit diff from skeletal muscle in that it reaches max tension when it is somewhat stretched, not when it is at rest. second reason for inefficiency when short has to do w/gross anatomy and geometry of diaphragm. as you inspire, diaphragm gets flatter, flattens curve, gets shorter, and has a larger inward vector, pulling ribcage IN more and more, which is an expiratory maneuver. people get emphysema - what happens is that a large part of lung parenchyma is destroyed, and so lung doesn't recoil and doesn't pull diaphragm, so these patients have a very flat diaphragm and hyperinflated lung, and contraction of diaphragm tends to just pull rib cage together. we make diaphragm more efficient? want it more efficient for excercise and if pulmonary disease exists. accessory muscles: intercostals - external are inspiratory, internals are expiratory, parasternal intercostals are inspiratory, these aid in ventilation. levator somethings. sternomastoid, serratus dorsalis, other neck muscles also aid in ventilation. if accessory muscles are used, diaphragm doesn't have to work as heard. abdominal muscles can also aid ventilation - inspiration and expiration. if abdominal muscles contract at the same time as the diaphragm then the contents of the abdomen can't move out of the way, so you don't have abdominal wall movement, so abdominal pressure will rise, and if abdominal pressure rises, it will hinder the movement of the diaphragm into the abdomen and it will also push the ribcage out laterally. if you cannot flatten diaphragm when it contracts, the muscle shortens, pulling the ribs FORWARD. because of the shape and articulation, they are pulled FORWARD and OUT. think of bucket handle- if you pick it up, it also swings out. this increases the lateral dimension of the thorax, increasing the volume of the thorax. so when diaphragm acts alone, it increases the cranial/caudal distance of thorax. when abd muscles join in, it increases the lateral distance as well. abd muscles also active in expiration. tend to push diaphragm forward and stretch it. when it is stretched, it is at optimum point on tension lenght curve. see handout for points not covered. feel free to go to office rm 211 e. 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