Respiration and Gas Exchange

• Oxygen enters the lungs during inspiration (inhalation) and leaves the bloodstream during exhalation (expiration).
• Human cells need energy for contracting muscles, protein synthesis, cell division, active transport, growth, transmitting nerve impulses, and producing heat inside the body.
• In aerobic respiration, chemical reactions take place in the mitochondria and use oxygen to break down glucose and other nutrient molecules to release energy for the cell to use.
• Aerobic respiration equation: glucose+oxygen-->carbon dioxide+water
• Anaerobic respiration is the breakdown of glucose and nutrient molecules without using oxygen.
• Anaerobic respiration happens in the cytoplasm of a cell, not in the mitochondria.
• Anaerobic respiration equation: glucose-->alchohol+carbon dioxide
• Muscle cells in the human body can respire anaerobically for a short time. They make lactic acid instead of alcohol and no carbon dioxide is produced.
• Muscle cells can release some energy from glucose without using oxygen when you do vigorous exercise and your lungs and heart can't supply oxygen to the muscles as quickly as they are using it.
• Gas exchange is the diffusion of oxygen and carbon dioxide into and out of an organism's body.
• The gas exchange surface is a part of the body where gas exchange occurs between the environment and the body.
• Characteristics of gas exchange surfaces:-

  thin to allow gases to diffuse quickly.

  close to an efficient transport system to take gases to and from the exchange surface.

  large surface area so lots of gas can diffuse at the same time.

  have a good supply of oxygen.
• Alveoli are tiny air-filled sacs in the lungs where gas exchange occurs. Because the lungs are so full of air spaces, they feel light and spongy to the touch.
• The trachea is the tube through which air travels to the lungs; it has rings of cartilage in its walls to support it.
• Goblet cells are cells found in the lining (epithelium) of the respiratory passages and digestive system, they secrete mucus. In the nose, they make a liquid containing water and mucus. The water in the liquid evaporates into the air in the nose and moistens it.
• Cilia are tiny projections from some cells in the lining of the respiratory passages; cilia of many adjacent cells beat rhythmically in unison.
• Bacteria or dust particles get trapped in cilia and mucus. Cilia sweep mucus, containing bacteria and dust particles, up to the back of the throat so it doesn't block the lungs.
• Air passes from the nose and mouth into the trachea. Just below the epiglottis is the larynx (voice box), containing vocal cords which can be tightened by muscles when air passes over them.
• While breathing in and out, air pressure in the trachea increases and decreases. The cartilage rings around the trachea prevent it from collapsing when air pressure inside is lower than air pressure outside.
• Thorax is the part of the body from the neck down to the diaphragm. Here, the trachea divides into two branches called right and left bronchi.
• Bronchus (singular for bronchi) is one of the two tubes that takes air from the trachea into the lungs. One bronchus goes to each lung.
• Bronchiole is a small tube that takes air from a bronchus to every part of the lungs. Bronchus branch out into bronchioles.
• Tiny capillaries are closely wrapped around the walls of the alveoli. Oxygen diffuses from the alveoli into the blood and carbon dioxide diffuses the other way.
• The walls of the alveoli are very thin to allow for rapid and easy diffusion of gases. They are one cell thick. Capillary walls are also one cell thick.
• Alveoli have an excellent transport system. Blood is constantly pumped to the lungs along the pulmonary artery. This branches into thousands of capillaries which take blood everywhere around the lungs. Carbon dioxide diffuses out into air spaces of alveoli and oxygen diffuses into blood which is taken back to the heart, in the pulmonary vein, to be pumped around the body.
• Alveoli have a large surface area, total being 100m2. Also, a good supply of oxygen.

  Ventilation is the movement of air into and out of the lungs, by breathing movements.
• Limewater test to compare how much carbon dioxide is present in air you breathe in and air you breathe out:-

  Apparatus- Rubber tubing, 2 test tubes with limewater, glass tube.
• Safety- Limewater is an irritant, don't get into mouth (when blowing into and out of tubing, don't suck too hard).

  Wear safety goggles when breathing into and out of tubing.

  Make sure new tubing is used for each person that does the experiment and make sure it's clean before putting your mouth over it.
• Method- Breathe gently into and out of rubber tubing, you want to create bubbles. Keep doing this until limewater in one test tube becomes cloudy.

  Continue breathing in and out for some time, limewater in other test tube may also become cloudy.
• Inspired air has an oxygen content of around 20-21% and expired air has around 16%. This is because less oxygen is present as the body cells use it in respiration. But it's still a significant amount to breathe out because expired air mixes with normal air in bronchi and trachea so we breathe out a mixture of air in alveoli and atmospheric air.
• Breathing is changing the volume of the thorax so air is drawn into and pushed out of the lungs, using the muscles in the diaphragm and the intercostal muscles.
• Intercostal muscles are between the ribs, which raise and lower the rib cage when they contract and relax. There are internal and external intercostal muscles.
• Diaphragm is a large sheet of muscle and elastic tissue that stretches across your body, underneath the lungs and heart which helps with breathing.
• During inspiration, muscles in the diaphragm contract, making it lower and increasing the volume in the thorax. External intercostal muscles contract, pulling the rib cage upwards and outwards, also increasing the volume of the thorax. Pressure inside thorax falls below atmospheric pressure as its volume increases, air thus flows in along the trachea and bronchi into the lungs.
• During expiration, muscles of the diaphragm relax, decreasing volume of the thorax. External intercostal muscles relax, also decreasing volume of the thorax.
• When forcefully breathing out (coughing for example), internal intercostal muscles contract strongly, making the rib cage drop down even further. Muscles of the abdomen wall also contract, helping to squeeze extra air out of the thorax.
• Oxygen debt is extra oxygen that is needed after anaerobic respiration to break down the lactic acid produced.
• Extra energy can be provided by anaerobic respiration. Muscles continue to respire anaerobically with oxygen they have but also break down some glucose without combining it with oxygen.

  glucose-->lactic acid+energy
• Once activity is done, lot of lactic acid is present in your blood and muscles. This must be broken down by combining it with oxygen in the liver so you continue to breathe faster and deeper to take more oxygen to break down the lactic acid. The faster heart rate helps to transport lactic acid as quick as possible from muscles to liver.
• Brain controls the breathing rate. It constantly monitors pH of the blood that flows through it. If too much carbon dioxide or lactic acid in the blood, the pH falls. When the brain senses this, it sends nerve impulses to diaphragm and intercostal muscles, stimulating them to contract harder and faster resulting in a faster breathing rate and deeper breaths.