RESPIRATION SYSTEM IN HUMAN GASEOUS EXCHANGE – RESPIRATORY SYSTEM HUMAN RESPIRATION SYSTEM A. Respiration organs. B. Breathing mechanism. C. Internal respiration. GASEOUS EXCHANGE IN HUMAN A. Respiration organs. B. Breathing mechanism. C. Internal respiration. GASEOUS EXCHANGE OCCURS IN THE RESPIRATORY SYSTEM The most important are the two lungs. Each lung is filled with many tiny air spaces called air sacs or alveoli. It is here that the oxygen diffuses into the blood. Because they are so full of spaces, lungs feel very light and spongy to touch. The lungs are supplied with air through the windpipe or trachea. AIR IS TAKEN DOWN INTO THE LUNGS 1. The NOSE and MOUTH Air can enter the body through either the nose or mouth. The nose and the mouth are separated by the palate, so you can breathe through your nose even when you are eating. Is is better to breathe through your nose, because the structure of the nose allows the air to become warm, moist, and filtered before it gets to the lungs. Inside the nose are some thin bones called turbinal bones which are covered with a thin layer of cells. Some of these cells make a liquid containing water and mucus which evaporates into the air in the nose and moistens it. Other cells have very tiny hair-like projections called cilia. The cilia are always moving, and bacteria or particles of dust get trapped in them and in the mucus. Cilia are found all along the trachea and bronchi, too. They waft the mucus, containing bacteria & dust, up to the back of the throat, so that it doesn’t not block up the lungs. 2. The TRACHEA The air then passes into the windpipe or trachea. At the top of the trachea, is a piece of cartilage called epiglottis. This closes the trachea and stops food going down the trachea when you swallow. This is a reflex action, which happens automatically when a bolus of food touches the soft palate. The air then passes into the windpipe or trachea. At the top of the trachea, is a piece of cartilage called epiglottis. This closes the trachea and stops food going down the trachea when you swallow. This is a reflex action, which happens automatically when a bolus of food touches the soft palate. Just below the epiglottis is the voice box or larynx. This contains the vocal cords. The vocal cords can be tightened by muscles so that they make sounds when air passes over them. The trachea has rings of cartilage around it, which keep it open. 3. The BRONCHI The trachea goes down through the neck and into the thorax. The thorax is the upper part of your body from the neck down to the bottom of the ribs and diaphragm. In the thorax, the trachea divides into two. The two branches are called the right and the left bronchi. One bronchus goes to each lung and then branches out into many smaller tubes called bronchioles. 4. The ALVEOLI At the end of each bronchiole are tiny air sacs or alveoli. This is where gaseous exchange takes place. ALVEOLAR WALLS FROM THE RESPIRATORY SURFACE The walls of the alveoli are respiratory surface. Tiny blood vessels, called capillaries, are closely wrapped around the outside of the alveoli. Oxygen diffuses across the walls of the alveoli into the blood. Carbon dioxide diffuses the other way. The walls of the alveoli have several features which make them an efficient gaseous exchange surface. They are very Thin Alveolar walls are only one cell thick. The capillary walls also only one cell thick. An oxygen molecule only has to diffuse across this small thickness to get into the blood. They have an excellent transport system Blood is constantly pumped to the lung along the pulmonary artery. This branches into thousands of capillaries, which take blood to all parts of the lungs. Carbon dioxide in the blood can diffuse out into the air spaces in the alveoli, and oxygen can diffuse into the blood. The blood is then taken back to the heart in the pulmonary vein, ready to be pumped to the rest of the body. They have a large surface area They have a good supply of O2 In fact, the surface area is Your breathing movements enormous! The total keep your lung well surface area of all the supplied with Oxygen. alveoli in your lungs is over 100 m2. THE RIBS & DIAPHRAGM MOVE DURING BREATHING To make air move in and out of the lungs, you must keep changing the volume of your thorax. First, you make it large so that air is sucked in. then, you make it smaller again so that air is squeezed out. This is called breathing or ventilation. There are 2 sets of muscles which help you to breathe. One set is in between the ribs. This set is called intercostal muscles made up of the external and internal intercostal muscles. The other set is in the diaphragm. The diaphragm is a large sheet of muscle and elastic tissue which stretches across your body, underneath the lung and hearth. BREATHING IN IS CALLED INSPIRATION When breathing in, the muscles of the diaphragm contract. This pulls the diaphragm downwards, which increases the volume in the thorax. At the same time, the external intercostal muscles contact. This pulls the ribs cage upwards and outwards. Together, these movements increase the volume of the thorax. As the volume of the thorax increases, the pressure inside it falls below atmospheric pressure. Extra space has been made and something must come in to fill it up. Air therefore rushes in along the trachea and bronchi into the lungs. BREATHING OUT IS CALLED EXPIRATION When breathing out, the muscles of the diaphragm relax. The diaphragm springs back up onto its domed space because it is made of elastic tissue. This decreases the volume in the thorax. The external intercostal muscles also relax. The rib cage drops down again into its normal position. This also decreases the volume of the thorax. As the volume of the thorax decreases, the pressure inside it increases. Air is squeezed out through the trachea into the nose and mouth, and on out of the body. INTERNAL INTERCOSTAL MUSCLES CAN FORCE AIR OUT Usually, you breathe out by relaxing the external intercostal muscles and the muscles of the diaphragm. Sometimes, you breathe out more forcefully – when coughing, for example. Then the internal intercostal muscles contract strongly, making the rib cage drop down even further. The muscles of the abdomen walls also contract, helping to squeeze extra air out of the thorax. EXERCISE CAN CREATE AN OXYGEN DEBT All the cells in your body need oxygen for respiration and all of this oxygen is supplied by the lungs. The oxygen is carried by the blood to every part of the body. Sometimes, cells may need a lot of oxygen very quickly. Imagine, you are running in a race. The muscles in your legs are using up a lot of energy. To produce this energy, the mitochondria in the muscles will be combining oxygen with glucose as fast as they can, to provide the energy for the muscles. A lot of oxygen is needed to work as hard as this. You breathe deeper and faster to get more oxygen into your blood. Your heart beats faster to get the oxygen to the leg muscles as quickly as possible. Eventually a limit is reached. The heart and lungs cannot supply oxygen to the muscles any faster. But more energy is still needed for the race. How can that extra energy be found? Extra energy can be produced by anaerobic respiration. Some glucose is broken down without combining it with oxygen : Glucose lactic acid + energy It doesn’t release very much energy, but a little extra might make all the difference. When you stop running, you will have quite a lot of lactic acid in your muscles and your blood. This lactic acid must be broken down by combining it with oxygen. So, even though you do not need the energy anymore, you go on breathing hard. You are taking in extra oxygen to break down the lactic acid. While your are running, you built up an oxygen debt. You ‘borrowed’ some extra energy without ‘paying’ for it with oxygen. Now, as the lactic acid is combined with oxygen, you are paying off the debt. Not until all the lactic acid has been used up, does your breathing rate and rate of heart beat return to normal?