Lungs and Gas Exchange

• All of our cells must carry out the process of solar respiration, which requires oxygen.
• The lungs' role is to get the oxygen that we need from the air all around us into our bloodstream where it can be transported to the rest of the body.
• Whenever we breathe in air, it first passes through our mouth or our nose and then down our trachea, also known as the windpipe.
• The trachea divides between our two bronchi and then further divides between successive branch-like structures which we call bronchioles.
• Once the air has made its way through all of these branches, it reaches these small sacks that are arranged like bunches of grapes, these sacks are called alveoli and they're the site of gas exchange.
• Alveoli are made up of just one layer of very thin cells, similar to the blood capillaries that they're next to, creating a really short diffusion pathway which increases the rate that carbon dioxide and oxygen can diffuse across.
• Alveoli have a very large surface area because adults actually have hundreds of millions of alveoli and if they were all spread out flat they would cover half a tennis court.
• The alveolar walls are moist, allowing the gases to dissolve, which increases their rate of diffusion.
• The blood in the capillaries has just returned to the lungs, having passed around the body, meaning that the hemoglobin within the red blood cells has already given up lots of its oxygen to the tissues, resulting in them appearing blue.
• The alveoli are full of fresh oxygen, creating a perfect concentration gradient for the oxygen in the alveoli to diffuse down into the blood.
• Oxygenated blood can then start the cycle all over again.
• Carbon dioxide, being the higher concentration in the blood than in the alveoli, can easily diffuse across and once in the alveoli, can be breathed out.
• Carbon dioxide is not carried by red blood cells like oxygen, it is dissolved in the blood plasma.
• Everything shown in this picture happens continually, all the time, with a constant supply of deoxygenated blood entering the capillaries and oxygenated blood leaving it.
• When you exercise, your breathing rate changes and you can calculate your breathing rate in breaths per minute by dividing the number of breaths taken by the time in minutes that those breaths took.
• If you took 42 breaths in three minutes, your breathing rate would be 14 breaths per minute.