BISC 307L 2nd Edition Lecture 34 Current LectureFunctions of the Respiratory System1. Gas Exchange -O2 and Co2 (respiratory gases) between blood and atmosphere2. Regulation of Body pH-H+ + HCO3- D H2CO3 D CO2 + H2O -this is the way that the respiratory system regulates body pH because it can get rid of variable amounts of Co2 and push the reaction to the right, lowering H ion concentration. This isthe second line of defense against changes in blood pH. Buffers in the blood and the kidneys have a powerful ability to secrete acid or not. The capacity of the respiratory system to regulate pH is slower to act than the buffers, but it has a greater capacity. So buffers are faster but limited capacity – respiratory system is slower but it has a much greater capacity. The slowest, but most powerful, are the kidneys ability to secrete or not secrete acid.3. Protection from Inhaled Pathogens/Irritants-viruses, spores, other particles 4. Vocalization -air blowingover the vocal folds willcause them to vibratein order for speech andcommunication tooccur. Lungs and ThoracicCavityThe main body cavity isdivided into an upperthoracic and lowerabdominal cavity. Inthe thoracic, there are three cavities: a right and left pleural cavity, along with a pericardial cavity. The pleural cavity is the cavity in which the lung sits, and the whole cavity is lined with the pleural membranes, which covers the lungs and also covers the inside of the pleural cavity. So there are two layers, and between them, there is an intrapleural space. Most of the actual pleural space is a very small volume – a few mm on each side of the chest, because the lung occupies most of that cavity. In the intrapleural space, is a small volume of pleural fluid, which isslippery mucus. It is slippery because in breathing movements, the lung has to move relative to the wall, so the pleura will rub against each other, and the lubricating fluid prevents there from being any friction during those movements.The muscles involved in the inspiration/expiration – inspiratory muscles are the diaphragm, the external intercostal muscles (between the ribs), and the two sets of neck muscles which attach at the top of the rib cage – the scalenes and sternocleiomastoids. The expiratory muscles are the abdominal muscles and the internal intercostal muscles. Lung Lobules and AlveoliFigure on the right shows the microscopic anatomy of the lungs. The airways – the larynx through trachea through the bronchi are all rigid tubes of rough cartilage. When you get down to the bronchioles, you can see a terminal bronchiole, which aren’t reinforced by cartilage, have smooth muscle, and are collapsible. The smooth muscle around the bronchioles are capable of contraction causing bronchoconstriction or relaxing to cause bronchodilation. These airways lead to the alveoli, where gas exchange occurs. Bottom left – here is the inside of the alveoli. There are two types of epithelial cells – type I alveolar (flat, and responsible for gas exchange) and the yellow cells, which are thicker but fewer in number - the type II alveolar cells that secrete mucus containing surfactant, which coats the inside of the alveolus. The inside of the alveolus has to be wet all the time. The alveoli are surrounded by capillaries. Can see how its orientation on the very bottom right. The purple is the type I alveolar cell, the gray is the basement membrane, the next cell is the endothelium of the capillary, then plasma, and the RBC.Because these cells are so thin, the whole capillary is .1-1.5 micrometers from the alveolar end to the plasma. That thinness is important for gas exchange.Properties of GasesGases are also fluids – everything we’ve learned about movement of fluids is applicable to gases. Dalton’s Law: The total P of a gas mixture (like air) equals the sum of the P’s that each gas in the mixture would exert independently.i.e., Phumid air = PN2 + PO2 + PCO2 + PH2O = 760 mm Hg (at sea level)Shown on the graph is total atmospheric pressure as a function of altitude. At 0 altitude we have pressure of 760, and 21% of that total pressure is due to oxygen. So the partial pressure ofO2 would be 21% of 760. As you go up in altitude, the total pressure drops down so the total weight of the column of air pushing down gets less and less. The dot on the very right demonstrates the pressure on mount everest, which is about 30% of sea level. Boyle’s Law: The P of a given amount of gas is inversely proportional to its volume. This predicts that as you change the volume in your lung, you change the pressure. A pressure gradient can cause air to come into and out of the lungs. Pressure Changes in QuietBreathingGraph time scale of 8seconds. There are twoinspirations and twoexpirations. We are measuring thealveolar pressure, which isimportant because thedifference betweenalveolar and atmosphericpressure is what createsthe gradient for air tocome in or out. We are also looking at intrapleural pressure in blue. Start at time 0. We have just expired/breathed out. No air is going into or out of the respiratory system because there is no pressure. Pressure in the alveoli is 0. Pressure in the intrapleural space is not 0, it is closer to -3 mmHg. There is a negative pressure in there, it is lower than atmospheric pressure. If outside is 760, then here it is 757 in. The air outside the body is pushing the chest in. At this moment, the inside of the alveoli is also 0, so there is a force of 3 mm pushing the lung out against the chest wall. The outside of the lung is stuck, or pressed upagainst the inside of the chest wall- it keeps the lungs inflated. Intrapleural pressure is also below atmospheric pressure, and below alveolar pressure, because if it wasn’t the lung would collapse. Why is intrapleural pressure negative? It is due to differential growth during fetal life of the chest and the lungs. The thoracic cavity grows more than the lungs such that when the lungs arefully inflated with air, their natural volume is slightly less than the pleural cavity they occupy. The lungs are very elastic. It wants to pull away from the inside of the chest wall, creating the negative pressure in there. It doesn’t actually pull away because this space is completely filled with pleural fluid, which is mostly incompressible water, and even though it can show pressure changes, it cannot change its volume. That’Inspiration – diaphragm contracts and pulls downward,