Chapter 13 BISC306010
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Organizaiton of the Respiratory Stystem 12102014 There are two lungs the right and the left and are divided into lobes They have alveoli which are tiny air containing sacs 0 They are the site of gas exchange with the blood 0 Airways are the tubes hat air ows through from the external environment to the alveoli and back 0 Inspiration or inhalation is the movement of air from the external environment though the airways into the alveoli during breather o Expiration or exhalation is the movement in the opposite direction together expiration and inspiration are known as the respiratory cycle Airways and Blood Vessels air passes through the nose or mouth l pharynx l larynx l trachea l two bronchi l bronchioles l alveoli Conducting zone extends from the top of the trachea to the beginning of the respiratory bronchioles and has no alveoli and does not exchange gases with the blood The respiratory zone extends from the respiratory bronchioles down and contains alveolis therefore that are gas exchanges Oral and nasal cavities trap airborne particles in basal hars and mucus It is an important job of the mucus to latch on to dust and be moved by cilia and be swallowed by the pharynx so that the lungs are clear of any particulate matter and other bacteria 0 Ciliary activity can be decreased by cigarette smoking and which is why smokers cough of mucus Airway epithelium also secretes watery uid upon which the mucus can ride freely o This production of uid is impaired in cystic brosis which is the build up of mucus in lungs and obstructs the airways It is caused by the CFTR CF transmembrane conductance regulator Constriction of bronchioles in response to irritation helps prevent particulate matter and irritants from entering the sites of gas exchange Macrophages also help in infection Because of the low pressure in pulmonary blood vessels there is minimal accumulate of uid in the interstitial spaces of the lungs Site of Gas Exchange Alveoli Alveioli are tiny hollow sacs whose open ends are continuous with the lumens of the airways 0 Air facing surfaces of the alveolar wall are lined by type alveolar cells and interspersed between those cells are type II alveolar cells 0 The walls also contain capillaries and a small interstitial space which had interstitial uid and connective tissue 0 There is a thin wall that separates the alveolar wall capillary and the alveolus therefore which allows for rapid exchange of lare quantities of O and CO by diffusion 0 Some alveolar walls have pores and permit the ow of air between alveoli which is important when the airway leading to the alveolus is occluded by disease Relation of the Lungs to the Thoracic Wall Thorax chest 0 The Wall of the thorax is formed by the spinal column the ribs and breastbone and several groups of muscles that run between the ribs inercostal muscles yet it is completely separated from the abdomen by the diaphragm Each lung is surrounded by the pleural sac o Parietal outermost layer 0 Visceral inner layer parietal and visceral do not touch Ventilation exchange of air between the atmosphere and alveoli Similar to blood it moves by bulk ow from a region of high pressure to low pressure 0 Bulk Flow Change in Pressure Resistance 0 Change in pressure Alveolar Pressure Atmoshpheric Pressure 0 All pressures in the respiratory system are given relative to the atmospheric pressure 760 mmHg 0 During ventilation air moves into and out of the lungs because the alveolar pressure is less than the atmospheric pressure 0 Negative values denote inward pressure gradient Boyles Law P1V P2V2 0 Volume and pressure are inversely proportional Transpulmonary pressure is the difference in pressure between the inside and outside of the lung which is equal to Palv inside Pip outside o It is the transmural pressure that governs the static properties ofthelungs o The transmural pressure of the chest wall Pcw Pip Patm The muscles of the chest wall contract and cause the chest wall to expand during inspiration simultaneously the diaphragm contrats downaard which enlarges the thoracic cavity When the thoracic cavity expands Pip decreases which makes Ptp more positive Palv becomes more negative than Patm and air ows inward due to Boyles law Therefore decreasing the Pip causes the transmural pressure to increase across the lungs and ll with air How is a Stable Balance Achieved Between Breaths o Pneumothorax when atmospheric air enters the intrapleaural space through a wound and the intrapleaural pressure increases 0 this causes the lung to collapse when pleural and airway pressures equalize 0 can also results when a hole is made in the lung such that a signi cation amounts of air leaks from inside the lung to the pleaural space Inspiration Diaphragm and inspiratory intercostal contract I thorax expands I Pip becomes more subatmoshpheric l increase in transpulmonary pressure l lungs expand l Palv becomes more subatmospheric air ows into alveoli By the end of inspiration equilibrium across the lungs is reestablished o The enlargement of lungs causes an increase in the sizes of the alveoli throught the lungs Lung Compliance stretchability the magnitiude of change in lung volume produced by a given change in the transpulmonary pressure 0 The greater the lung compliance the easier it is to expand the lungs at any given change in transpulmonary pressure 0 Low compliance greater than normal transplmonary pressure More energy required to produce given amount of expansion 0 Deterimnants in lung compliance 0 Stretchability of the lung tissues their elastic connective Ussuess Thick lung tissues decrease lung compliances Surface tension the attractive forces between the water molcules n Important for type II alveolar cells to secrete surfactant which reduces the cohesive forces between water molecules on the alveolar surface 0 Therefore lowering the surface tension which increases the lung compliance and easier to expand Mixture of both lipids and proteins but mainly phospholipids 0 When surfactant is de cient respiratory distress syndrome of the newborn can occur where surfactant is too immature to function adequately Lung Volumes and Capacities Tidal volume the volume of air entering the lungs during a single inspiration Vt is equal to the volume leaving the subsequent expiration o Approzimately 500 mL depending on body size 0 The maximum amount of air that can be increasd above this value during deepest inspiration is 3000 mL the insipiratory reserve volume 0 Even after expiration there is still a large volume of air Vital Capacity VC is the maximal volume of air a person can expire after a maximal inspiration 0 Important when measuring pulmonary function Alveolar Ventilation The total ventilation per minute The minute ventilation is equal to the tidal volume X respiratory rate Anatomical Dead Space space within the airways that do not permit gas exchange with the blood 0 Therefore fresh air tidal volume volume of air in dead space 0 Alveolar ventilation the total volume of fresh air ending the alveoli per minute Increased depth of breathing is far more effective in increasing alveolar ventilation than an increase in breathing rate Alveolar dead space is the fresh air that was not used for gas exchange for some reason more common in those with lung disease Anatomical Alveolar physiological dead space or wasted ventilation Partial Pressures of Gases Dalton39s Law in 5 mixture of gases the pressure each gas exerts is independent of the pressure the others exert 0 So total pressure is actually the sum of individual pressures which are termed partial pressures it is directly proportional to tis concentration 0 Henry39s Law the amount of gas dissolved will be directly propotional to the partial pressure of the gas with which the liquid is in equilibrium 0 Net movement is from high to low 0 This occurs between alveolar air and pulmonary capillary blood 0 Does not just deal with concentrations because the concentration of a gas in a liquid is proportional not only to the partial pressure of the gas but also to the solubility of the gas in the liquid Therefore if a liquid is exposed to two different gases having the same partial pressures at equilibrium the partial pressures of the two gases with be identical in the liquid but the concentration of the gases in the liquid will differ depending on their solubility o Alveolar gas pressures set those of systemic artieral blood The Alveolar P02 and PC02 determine the systemic arterial P02 and PC02 Matching of Ventilation and Blood Flow in Alveoli Inadequate oxygen movement between alveoli and pulmonary capillary blood is not a problem with diffusion but instead with mimstaching of the air supply and bloody supply in individual alveoli Alveoli receive CO and supply oxygen to the pulmonary capillary blood 0 At maximum efficiency the correct proportion of alveolar air ow ventilation and capillary blood ow perfusion should be available to each alveolus o Mismatching is named ventilation perfusion inequality This causes a decrease in P02 of ssystemic arterial blood ln diseases lung complicacnce airway resistance and vascular resistance can cause inequalities which can result in extremes n Alveoli with no blood supply at all possibly due to blood clot I There may be blood owing through areas of lung that have no ventilation shunt possibly due to collapsed alveoli Carbon dioxide is impaired by ventilation perfusion inequality but not as much as oxygen In Increase in PC02 lead to increase in alveolar ventilation which prevents further increases in PC02 There are homeostatic responses that help minimize mismatching The most important being the direct effect of low oxygen on pulmonary blood vessels n A decrease in ventilation within a group of alveoli leads to a decrease in alveolar P02 and the areas around it n The decrease leads to vasoconstriction which diverts blood away from the poorly ventilated area Gas Exchange Between Tissues and Blood 0 As blood ows to your systemic capillaries its P02 decreases as its PC02 increases Oxygen is present in two forms Dissolved in the plasma and erythrocyte cytosol 15 o Reversibly combined with hemoglobin materials in the erythrocytes 985 Hemoglobin is broken up into four subunits bound together 0 Each subunit has a heme group poplypeptide attached 0 The 4 polypeptides are known as globin 0 Each contains one iron atom which oxygen binds to 0 There are deoxyhemoglobin Hb and oxyhemoglobin Hb02 o The fraction of Oxyhemoglobin is expressed as percent hemoglobin saturation Blood P02 is one of the most important factors in determining percent hemoglobin saturation Signi cant decrease in hemoglobin is termed anemia Low hemoglobin is also accounted for by a low hematocrit Effect of P02 on Hemoglobin Saturation The Oxygenhemoglobin dissociate curve shows the relationship between the two o The extent to which oxygen combiens with hemoglobin increase very rapidly as the P02 increases from 1060 mmHg steep increase 0 Plateau is a safety factor because even if reduction occurs in the alveolar and lowers P02 only a small decrease happens within the plateau The globin units of deoxyhemoglobin are tightly held by electrostatic bonds in a conformation with a relative low affinity for oxygen 0 Yet when oxygen bings to a heme molecule it breaks some of these bonds between the globin subunits and increase the affinity for the remaining sites Remember that the oxygen bound to the hemoglobin DOES NOT contribute directly to the P02 of the blood only dissolved oxygen does 0 But hemoglobin does play a role in the TOTAL amount of oxygen that will diffuse o Hemoglobin can disturb equilibrium and affects how much oxygen combines with hemoglobin 0 Blood P02 usually remains less that alveolar P02 until hemoglobin is virtually 100 saturated o In tissue capillaries oxygen is continuously diffusing into the cells and causes the interstitial uid P02 to always be less than the P02 of the blood so the ow is always from the plasma to the interstitial uid Effect of Carbone Monoxide on Oxygen Binding to Hemoglobin Carbon Monoxide is a colorless odorless gas that is a product of the incomplete combustion of hydrocarbons like gasoline It has an extremely high affinitiy 210 x oxygen for oxygen binding sides in hemoglobin 0 Therefore it competes with the sites and alteres the hemoglobin molecule so the dissociation curve goes to the left Effects of C02 and Other factors in the Blood different lsoforms An increase in 23 diphosphateglycetrate DPG concentration or temperature or acidity causes the dissociation curve to shift to the right which means less affinity The effects of increases PC02 H concentration and temperature are continuously exerted on the blood in the tissue capillaries because they are greater here than in the blood 0 More metabolically active a tissue is the greater these factors are as well 0 Carbon dioxide and H cause a change in conformation herefore an allosteric effect 0 Fetal hemoglobin is a unqie form of hemoglobin and contains subinuts that are coded for different genes than those postnatal 0 These also alter the shape and results in a shape that has a higher affinity for oxygen and cases an increasein oxygen uptake Therefore although fetal arterial P02 is lower fetal hemoglobin allows for adequate oxygen uptake C02 is a waste product that has toxicity in part because it generates H When arterial blood ows through tissue capillaries the oluem of C02 diffuses from the tissues into the blood 0 C02 is more dissolvable than oxyen so the blood carries more dissolved C02 than oxygen 0 Only 10 of C02 is carried that way 0 2530 react reversibly with amino groups to form carbaminohemoglobin where deoxyhemoglobin has a greater affinity than oxyhemoglobin 0 6065 enters the blood in tissues converted to HCO3 catalyzed by carbonic anhydrase present in RBCs but not plasma also explains why H concentration in tissue caps and systemic venous blood is higher than that in arterial blood and increases as metabolic activity increases 0 add all forms together to get total blood carbon dioxide 0 As blood ows through the tissues a fraction of ozyhemoglobin loses its oxygen to become deoxyhemoglobin while also a large quantitiy of CO enters the blood and undergoes the reactions that generate HCO3 and H Deoxygemoglobin has a much higher af nity for H than oxyhemoglobin o Venous blood is slightly higher than arterial blood for this reason 0 When someone is hypoventilating or has lung disease that prevents normal elimination of C02 0 Arterial PC02 increases as a result as awell as arterial H concentration Increased H Concentration due to carbon dioxide retention ls termed respiratory acidosis Respiratory alkalosis is hyperventilating and decreasing PC02 and H concentration Hemoglobin also has the ability to bind and transport Nitric Oxide Generation of Rhymthic Breathing Breathing relies entirely upon cyclical respiratory muscle excitation of the diaphragm and the intercostal muscles by their motor neurons 0 Disconnection would result in paralysis Control of neural activity resides primarily in the neurons in the medualla oblogonata o Medullary respiratory center is made up of the doral respiratory group res during inspiration and the ventral respiratory group Control of Ventilation by P02 PC02 and H concentration Most important inputs the peripheral Arterial chemocreceptors and central chemoreceptors for automatic control of ventilation initiate re exes Peripheral chemocreceptors are in the neck and thorax and are the carotid and aortic bodies 0 They are close to arterial baroreceptors nd are in intimate contct tiwh the arterial blood 0 Respond to decrease in arterial P02 but no stimulated in paces where moderate P02 tke pace Central Chemoreceptors are in the medulla and provide excitatory synaptic input to the medullary inspiratory neurons they are stimulated by an increase in H Control By P02 0 Ventiliation increases when P02 is decreased to 60 mmHg and this re ex is mediated by peripheral chemoreceptors Control by PC02 o Diseases such as emphysema increase arterial PC02 because of the increase in carbon diozide this stimulates ventilation and the elimination of C02 Largely due to the associated changes in H concentrations Control by changes in Arterial H Concentration 0 Metabolic acidosis H increased 0 Peripheral chemoreceptors play the major role in ventilation o PC02 regulates H concentration at its own expense 0 Hypoxia de ciency of oxygen at the tissue level Hypoxic hypoxia hypoxemia where arterial P02 is reduced Anemic hypoxia or carbon monozide hypoxide ther arterial P05 is normal but the total oxygen content of blood is reduced because of inadequate erythrocytes de cient hemoglobin or competition for hemoglobin brought on by CM lschemic hypoxia also hypoperfusion hypoxia blood ow is too low to tissue Histotoxic hypoxia the quantity og oxygen reaching the tissues is normal but the cell is unable to utliziize the oxygen because a toxic agent has interfered with the cells metabolic machinery cyanide