Gas Exchange in Humans PDF

Unit 11 - Gas Exchange in Humans 11.1 Features of Gas Exchange Surfaces Features of Gas Exchange Surfaces The surfaces where gas exchange occurs in an organism are very different and different organisms have evolved different mechanisms for getting the gases to the gas excha...

Unit 11 - Gas Exchange in Humans 11.1 Features of Gas Exchange Surfaces Features of Gas Exchange Surfaces The surfaces where gas exchange occurs in an organism are very different and different organisms have evolved different mechanisms for getting the gases to the gas exchange surface depending on size, where they live etc. All gas exchange surfaces have features in common These features allow the maximum amount of gases to be exchanged across the surface in the smallest amount of time They include: Large surface area to allow faster diffusion of gases across the surface Thin walls to ensure diffusion distances remain short Good ventilation with air so that diffusion gradients can be maintained Good blood supply to maintain a high concentration gradient so diffusion occurs faster 11.2 The Breathing System The Breathing System 11.3 Investigating the Differences in Inspired & Expired Air Investigating the Differences in Inspired & Expired Air A simple experimental setup can be used to investigate the differences between inspired and expired air When we breathe in, the air is drawn through boiling tube A When we breathe out, the air is blown into boiling tube B Lime water is clear but becomes cloudy (or milky) when carbon dioxide is bubbled through it The lime water in boiling tube A will remain clear, but the limewater in boiling tube B will become cloudy This shows us that the percentage of carbon dioxide in exhaled air is higher than in inhaled air 11.4 Differences in Inspired & Expired Air Composition of inhaled & exhaled air Air that is inhaled, or breathed in, differs in its gas composition to air that is exhaled, or breathed out; this is due to the process of gas exchange that takes place in the alveoli Inhaled air can also be referred to as inspired air Exhaled air is also known as expired air Inhaled air is drawn from the surrounding atmosphere, and so its gas composition matches atmospheric levels During gas exchange in the alveoli oxygen enters the blood from the alveoli, and carbon dioxide and water vapour leave the blood and enter the alveoli This gas exchange process means that the gas composition of exhaled air differs to that of the air that was previously inhaled Inhaled air contains around 21 % oxygen and exhaled air contains around 16 % oxygen  Inhaled air contains around 0.04 % carbon dioxide and exhaled air contains around 4 % carbon dioxide Inhaled air contains less water vapour than exhaled air 11.5 Investigating the Effects of Physical Activity on Breathing Investigating the Effects of Physical Activity on Breathing Exercise increases the frequency and depth of breathing This can be investigated by counting the breaths taken during one minute at rest and measuring average chest expansion over 5 breaths using a tape measure held around the chest Exercise for a set time (at least 3 minutes) Immediately after exercising, count the breaths taken in one minute and measure the average chest expansion over 5 breaths Following exercise, the number of breaths per minute will have increased and the chest expansion will also have increased Explaining the Link Between Physical Activity & Breathing (Extended) Frequency and depth of breathing increase when exercising This is because muscles are working harder and aerobically respiring more and they need more oxygen to be delivered to them (and carbon dioxide removed) to keep up with the energy demand If they cannot meet the energy demand they will also respire anaerobically, producing lactic acid After exercise has finished, the lactic acid that has built up in muscles needs to be removed as it lowers the pH of cells and can denature enzymes catalysing cell reactions It can only be removed by combining it with oxygen - this is known as ‘repaying the oxygen debt’ This can be tested by seeing how long it takes after exercise for the breathing rate and depth to return to normal - the longer it takes, the more lactic acid produced during exercise and the greater the oxygen debt that needs to be repaid Mechanism for increasing breathing during exercise The rate of respiration increases in muscle cells when exercising heavily CO is a product of aerobic respiration, so CO levels increase in the muscle cells This CO diffuses out of the cells into the blood plasma CO in solution causes a slight drop in pH so the blood becomes slightly more acidic The blood flows around the circulatory system and passes to the brain where the increased carbon dioxide levels are detected by chemoreceptors in the brain Chemoreceptors are cells that detect chemical changes in the body They can detect changes in blood gas levels, as well as changes in pH  The chemoreceptors are located in the medulla oblongata of the brain The brain sends nerve impulses to the diaphragm and the intercostal muscles to increase the rate and depth of muscle contraction The rate of inspiration increases, along with the the volume of air moved in and out with each breath The result is greater absorption of oxygen and removal rate of carbon dioxide This supports the increased rate of respiration in the exercising muscle cells 11.6 Identifying Intercostal Muscles Identifying Intercostal Muscles (Extended) Muscles are only able to pull on bones, not push on them This means that there must be two sets of intercostal muscles; one to pull the ribcage up and another set to pull it down One set of intercostal muscles is found on the outside of the ribcage (the external intercostal muscles) The other set is found on the inside of the ribcage (the internal intercostal muscles) 11.7 Function of Cartilage in the Trachea Function of Cartilage in the Trachea (Extended) Rings of cartilage surround the trachea (andbronchi) The function of the cartilage is to support the airways and keep them open during breathing If they were not present then the sides could collapse inwards when the air pressure inside the tubes drops 11.8 Volume & Pressure Changes in the Lungs Volume & Pressure Changes in the Lungs (Extended) The diaphragm is a thin sheet of muscle that separates the chest cavity from the abdomen; it is ultimately responsible for controlling ventilation in the lungs When the diaphragm contracts it flattens and this increases the volume of the chest cavity (thorax), which consequently leads to a decrease in air pressure inside the lungs relative to outside the body, drawing air in. When the diaphragm relaxes it moves upwards back into its domed shape and this decreases the volume of the chest cavity (thorax), which consequently leads  to an increase in air pressure inside the lungs relative to outside the body, forcing air out The external and internal intercostal muscles work as antagonistic pairs (meaning they work in different directions to each other) During inhalation the external set of intercostal muscles contract to pull the ribs up and out: This also increases the volume of the chest cavity (thorax), decreasing air pressure, drawing air in During exhalation, the external set of intercostal muscles relax so the ribs drop down and in: This decreases the volume of the chest cavity (thorax) increasing air pressure, forcing air out When we need to increase the rate of gas exchange (for example during strenuous activity) the internal intercostal muscles will also work to pull the ribs down and in to decrease the volume of the thorax more, forcing air out more forcefully and quickly – this is called forced exhalation There is actually a greater need to rid the body of increased levels of carbon dioxide produced during strenuous activity! This allows a greater volume of gases to be exchanged 11.9 Protecting the Breathing System Protecting the Breathing System (Extended) The passages down to the lungs are lined with ciliated epithelial cells Cilia comes from the Latin for eyelash, so unsurprisingly these cells have tiny hairs on the end of them that beat and push mucus up the passages towards the nose and throat where it can be removed  The mucus is made by special mucus-producing cells called goblet cells because they are shaped like a goblet, or cup The mucus traps particles, pathogens like bacteria or viruses, and dust and prevents them getting into the lungs and damaging the cells there The function of cilia and mucus 1. The mucus is produced by goblet cells and traps bacteria, dust, particles 2. The cilia beat 3. And push the mucus away from the lungs towards the throat