 structure of lungs themselves how the lungs look like lungs are in pair one right and one left these are present inside the chest cavity these are supported and protected by rib cage because lungs are spongy they are delicate they are and the heart you know that between the lungs heart exists so rib cage actually protects these two vital organs heart and lungs lungs are also protected by another structure called pleural cavity lungs are present inside a membranous structure we call this membrane structure pleural cavity the membrane which is covering this pleural cavity are called pleura the area between the lung and the pleural cavity is filled with a fluid so that when lungs expand and contract during inhalation and exhalation resistance should not be there so this pleural cavity actually helps the lungs to reduce resistance while expanding and collapsing below lungs because lungs are present in the chest cavity below the lungs a muscular floor of the chest is present this muscular floor is called diaphragm let us look at a diagram you can see on the left side of the diagram that lungs are present on both sides of the chest cavity and there is a surrounding membrane around them pinkish in color this membrane is the this membrane actually makes the pleural cavity down there you can see a muscular part will just below the lungs this is the diaphragm and there is another more close look at the alveoli now present inside the lungs one alveolus if you look at the diagram B one alveolus is one air sac with its most of the alveoli is shown from the surface and the other one is shown as a cross section which is showing by arrows direction of movement of air through these alveoli in the diagram C you can see the surf the two respiratory surfaces through which the exchange of gases actually occur you can see a blood vessel capillary with the two RBCs moving through it and the surface of the alveolus you can see that these are two close these are very close to each other and simply by diffusion the takes place of materials the materials the gases oxygen and carbon dioxide they are exchanged because these surfaces are too close to each other that the exchange could take place simply by diffusion have another look on the lungs the diagram this is both cross sections now breathing for inhalation of air and exhalation of getting air inside the body and removing air from the body this process is called breathing the breathing is inhalation and exhalation activity of the lung of the human being lungs are spongy in nature and these cannot pull or push air inside or outside which means that lungs on themselves cannot pull air in or cannot push air out these needs these lungs needs help there are two structures which help them now we recall that lungs are surrounded by the ribs and on the lower side on the posterior side of the body lungs have a diaphragm a floor of the chest these two structures actually help the lungs in inhalation and exhalation look at the diagram which explains the process of inhalation and exhalation in the first part you can see breathing in and breathing out during breathing in the muscles of the ribs contract when the muscles of the ribs contract then the chest cavity there which have which have ribs moves outwards and upwards that is it is expanded at the same time the muscles of the diaphragm you know diaphragm is a muscular structure diaphragm contract when it contracts it has become less gnome shaped that is it actually goes down move towards posterior side the result is that pressure in the chest cavity because it is expanded is reduced and when this pressure is reduced then the pressure on the lungs is also reduced the result is that lungs are expanded when they are expanded air is pulled in that is from nasal cavity to trachea to bronchi and to lungs we call this process inhalation saas lena that is a vaa ko andar lekar jaan so these two process actually help the inhalation after that when air is filled in the lungs exchange occur then the process of exhalation exhalation saas ko vaa lekar what happen in exhalation the muscles of the ribs relax when muscles of the ribs relax then as you can see in the second diagram when the muscles of the ribs relax then the chest cavity the ribs actually the rib cage moves downwards then the diaphragm muscles they also relax at the same time muscles of the diaphragm they also relax when they relax they move the position of the diaphragm moves towards changes towards anterior side the diaphragm become more dome like the result is increase in pressure inside the chest cavity when the pressure increases the result is increase in the increase in pressure upon the lungs because lungs are present in the chest cavity and lungs then goes back to their previous position the result is exhalation air goes out from the lungs towards bronchi to trachea and we call this process exhalation so inhalation and exhalation are actually help by the intercostal muscles of the ribs and then the muscles the muscular diaphragm we call overall this process as we call overall process as breathing or ventilation when the air enters inside the lungs then the gas exchange should take place and the alveoli are the actual surface for gas exchange guests are exchanged against a partial pressure that is the difference in partial pressure results in the exchange of gases by diffusion the blood is distributed around alveoli in very thin layers blood cells and alveolar air they are in very close contact for exchange of gases as we know that red blood cells have hemoglobin inside and hemoglobin have a capacity to bind with oxygen to make an oxy hemoglobin oxygen diffuses into the blood capillaries and then makes a oxy hemoglobin then carbon dioxide this is exchange in the form of this oxy hemoglobin and tissues have to release their carbon dioxide inside the blood which is the product of their metabolism carbon dioxide is a more dissolved more easily carbon dioxide is a gas which is more easily dissolvable so this is present in the tissue fluids from here it enters into the blood capillaries this is transported in blood as about 20 percent as carboxy hemoglobin because hemoglobin have a capacity to absorb the carbon dioxide 5 percent by some plasma proteins that is 5 percent is bound to some plasma proteins and about 70 percent as bicarbonate ion combined with the sodium so there is a reaction that takes place a carbon dioxide plus water there is an enzyme called carbonic anhydrase which help in production of bicarbonate ions and the bicarbonate molecule and bicarbonate molecule is readily converted into its ionic forms hydrogen and bicarbonate look at a diagram this diagram shows a very close picture of an alveolus with blood capillary as you can see in the diagram first of all an alveolus is shown then in second the second part the B part an alveolus is shown in a cross section you can see that many capillaries are surrounding one if we count them these are five five capillaries are surrounding one alveolus and every capillary from every capillary one blood cell is passing if we enlarge it even a more we can see that the blood cells are in a very close contact with the respiratory surface the surface of the alveolus so diffusion of oxygen and diffusion of carbon dioxide takes place simply against the gradient