11 Gas Exchange in Humans 1. List the features of gas exchange surfaces in humans, limited to large surface area, thin surface, good blood supply and good ventilation with air 2. Name and identify the lungs, diaphragm, ribs, intercostal muscles, larynx, trachea, bronchi, bronchioles, alveoli and associated capillaries 3. Name and identify the internal and external intercostal muscles 4. State the functions of the cartilage in the trachea 5. Explain the role of the ribs, the internal and external intercostal muscles and the diaphragm in producing volume and pressure changes in the thorax leading to the ventilation of the lungs. GAS EXCHANGE = swapping carbon dioxide for oxygen occurs through diffusion of gas occurs on the gas exchange surface / respiratory surface which is the wall lining of the alveolus Below are the properties that are important to enable efficient gas exchange and maximum absorption of O 2: Properties of Surface Reason Large surface area For maximum absorption as more gas molecules can diffuse across at the same time Thin (one cell thick) Gases only need to diffuse across a short distance Moist Enable gases to dissolve easily and cells die if not kept moist Covered by a dense network of blood capillaries (good blood supply) For gases to be carried to and from the lungs to other cells. Constantly flowing to maintain concentration gradient. Good ventilation with air High concentration gradient for O2 & CO2 are maintained by regular supplies of air 1. C- shaped ring cartilage in trachea: prevent it from being compressed or collapsing under pressure and allows expansion during inhalation 2. Ciliated epithelial cells: have cilia (fine hair) that beats in a coordinated way to carry mucus away from lung surface up the throat 3. Goblet cells produce mucus to trap pathogens and dust particles 4. Basement membrane: holds the cell in place Cells like these form the mucous membrane which lines the whole trachea & bronchiole tree. Breathing to provide a constant supply of fresh air Pleural membrane = ‘stick’ the outside of lungs to the inside of chest cavity, so that the lungs will follow movement of chest wall. So if chest cavity expand, lungs will expand too & vice versa. Concept: Large volume = low air pressure Air flows from high pressure to low pressure Action of Inhalation 1) External intercostal contract pull ribcage upwards and outwards (internal intercostal muscle relax) 2) Diaphragm muscles contract and flatten (move downwards) 3) Volume of chest cavity increases less air but bigger lung volume pressure decrease 4) Higher atmospheric pressure causes air to flow into lungs and fill it up Action of Exhalation 1) External intercostal relax pull ribcage downwards and inwards (internal intercostal muscle contracts) 2) Diaphragm muscles relax and curve inwards (move upwards) 3) Volume of chest cavity decreases more air but smaller lung volume pressure increases 4) Higher lung pressure causes air to flow out from lungs Internal intercostal muscles is only used during active expiration, for eg: coughing & sneezing 11 Gas Exchange in Humans (Part 2) 1. State the differences in composition between inspired and expired air, limited to oxygen, carbon dioxide and water vapour. 2. Explain the differences in composition between inspired and expired air 3. Use limewater as a test for carbon dioxide to investigate the differences in composition between inspired and expired air 4. Investigate and describe the effects of physical activity on rate and depth of breathing 5. Explain the link between physical activity and rate and depth of breathing in terms of the increased carbon dioxide concentration in the blood, detected by the brain, causing an increased rate of breathing 6. Explain the role of goblet cells, mucus and ciliated cells in protecting the gas exchange system from pathogens and particles The composition of inspired and expired air Testing for CO2 To investigate the differences in composition between inspired and expired air, we use limewater because it changes colour when the gas is bubbled through, from colourless to milky. If hydrogen carbonate (red yellow-orange) There is more CO2 present in expired air ---> it makes limewater change colour more quickly (than inspired air). Effects of physical activity on breathing During exercise, more oxygen is needed for respiration to produce more energy: Increase in breathing rate = more breaths per minute Increase in tidal volume = more amount of air per breath These two factors can increase the amount of air breathed in and out from 8 dm3/min to ~50 dm3/min Note: Vital capacity = max of air inhaled in one breath The total lung volume is greater than vital capacity (some air always remains in the lungs). If not, alveoli walls would stick together, the lung would collapse. Explanation: Link between physical activity and rate & depth of breathing 1. When you run, muscles in your legs use up a lot of energy & need a lot of O2 very quickly. 2. They combine O2 + glucose as fast as they can, to release more energy for muscle contraction 3. Some extra energy (not much) is produced by anaerobic respiration: some glucose is broken down without combining with O2: Glucose ---> lactic acid + energy. 4. More CO2 is also being produced (CO2 acidic in blood) and lactic acid concentration in tissue and in the blood ↑(increase) ---> blood pH ↓(decrease – more acidic) 5. Breathing control centre in brain sense the drop in pH ---> nerve impulses sent to the diaphragm and the intercostal muscles, stimulating them to contract harder and more often ---> faster and deeper breathing. 6. You breath deeper and faster to get more O2 into your blood. (more CO2 lost from lungs) 7. Your heart beast faster to get O2 to the leg muscles as quickly as possible. (more blood pumped to tissue to carry CO2 away) 8. So that CO2 concentration and blood pH are kept at a safe level. Adapted from: http://biology-igcse.weebly.com/inspired-expired-air.html Practice Questions: 1. Which of the following is correct: When we inhale, (a) our intercostal muscles contract and our ribs move down (b) our diaphragm muscles contract and the ribs move up (c) our diaphragm muscles contract and the ribs move down (d) our intercostal muscles contract and the diaphragm muscles relax. 2. Which of the terms (i) vital capacity, (ii) tidal volume, (iii) residual air, could reasonably apply to each of the volumes given below? (a) 500 cm3, (b) 5000 cm3, (c) 1000 cm3. 11 Gas Exchange in Humans 1. List the features of gas exchange surfaces in humans, limited to large surface area, thin surface, good blood supply and good ventilation with air 2. Name and identify the lungs, diaphragm, ribs, intercostal muscles, larynx, trachea, bronchi, bronchioles, alveoli and associated capillaries 3. Name and identify the internal and external intercostal muscles 4. State the functions of the cartilage in the trachea 5. Explain the role of the ribs, the internal and external intercostal muscles and the diaphragm in producing volume and pressure changes in the thorax leading to the ventilation of the lungs. _________________________ = swapping carbon dioxide for oxygen occurs through diffusion of gas occurs on the gas exchange surface / respiratory surface which is the wall lining of the _________________ Below are the properties that are important to enable efficient gas exchange and maximum absorption of O2: Properties of Surface Reason Large (one cell thick) Covered by a dense network of blood capillaries (good blood supply) Good ventilation with air Constantly flowing to maintain concentration gradient. C-shaped ring cartilage in trachea: ______________________________ __________________________________________________________ Ciliated epithelial cells: ______________________________________ Goblet cells produce mucus to ______________________________ __________________________________________________________ Basement membrane: _______________________________________ Cells like these form the mucous membrane which lines the whole trachea & bronchiole tree. Breathing to provide a constant supply of fresh air ________________________ = ‘stick’ the outside of lungs to the inside of chest cavity, so that the lungs will follow movement of chest wall. So if chest cavity expand, lungs will expand too & vice versa. Concept: Large volume = low air pressure Air flows from high pressure to low pressure Action of Inhalation 1) External intercostal ________________ pull ribcage _____________ and _____________ (internal intercostal muscle relax) 2) Diaphragm muscles _______________and _______________ (move downwards) 3) Volume of chest cavity _________________ less air but bigger lung volume pressure __________ 4) __________________ atmospheric pressure causes air to flow into lungs and fill it up Action of Exhalation 1) External intercostal ______________ ______________________________________________ (internal intercostal muscle relax) 2) Diaphragm muscles ______________ and ___________________________ (move upwards) 3) _____________________ ___________________________ more air but smaller lung volume pressure inside the lungs _____________________ 4) __________________ air pressure in lungs causes air to flow out from lungs Internal intercostal muscles is only used during active expiration, for eg: coughing & sneezing 11 Gas Exchange in Humans (Part 2) 1. State the differences in composition between inspired and expired air, limited to oxygen, carbon dioxide and water vapour. 2. Explain the differences in composition between inspired and expired air 3. Use limewater as a test for carbon dioxide to investigate the differences in composition between inspired and expired air 4. Investigate and describe the effects of physical activity on rate and depth of breathing 5. Explain the link between physical activity and rate and depth of breathing in terms of the increased carbon dioxide concentration in the blood, detected by the brain, causing an increased rate of breathing 6. Explain the role of goblet cells, mucus and ciliated cells in protecting the gas exchange system from pathogens and particles The composition of inspired and expired air Testing for CO2 To investigate the differences in composition between inspired and expired air, we use ___________________ because it changes colour when the gas is bubbled through, from colourless to __________________. If hydrogen carbonate (red yellow-orange) There is more ________________ present in expired air ---> it makes limewater change colour more ___________ (than inspired air). Effects of physical activity on breathing During exercise, more oxygen is needed for respiration to produce more energy: Increase in ___________________ = more breaths per minute Increase in ___________________ = more amount of air per breath These two factors can increase the amount of air breathed in and out from 8 dm3/min to ~50 dm3/min Note: _______________ = max of air inhaled in one breath The total lung volume is greater than vital capacity (some air always remains in the lungs). If not, alveoli walls would stick together, the lung would collapse. 1. 2. 3. 4. 5. 6. 7. 8. Explanation: Link between physical activity and rate & depth of breathing When you run, muscles in your legs use up a lot of energy & need a lot of O2 very quickly. They combine O2 + glucose as fast as they can, to release more energy for _______________________. Some extra energy (not much) is produced by ________________ respiration: some glucose is broken down ______________________________________: Glucose ---> ____________________ + energy. More CO2 is also being produced (CO2 ____________ in blood) and ____________________________ in tissue and in the blood ↑(increase) causing ______________________________ (more acidic) The breathing control centre in brain sense the drop in pH ---> nerve impulses sent to the _______________ and the ________________, stimulating them to contract harder and more often --> faster and deeper breathing. You breathe deeper and faster to __________________ into your blood. (more CO 2 lost from lungs) Your heart beast faster to ______________________________________ as possible. (also more blood pumped to tissue to carry CO2 away) So that ____________________________ and __________________ are kept at a safe level. Practice Questions: 1. Which of the following is correct: When we inhale, (a) our intercostal muscles contract and our ribs move down (b) our diaphragm muscles contract and the ribs move up (c) our diaphragm muscles contract and the ribs move down (d) our intercostal muscles contract and the diaphragm muscles relax. 2. The percentage of oxygen absorbed from the air in the lungs is always about the same, so how can the oxygen supply to the blood be increased during vigorous activity? ____________________________________________________________________________________ ____________________________________________________________________________________ 3. Which of the terms (i) vital capacity, (ii) tidal volume, (iii) residual air, could reasonably apply to each of the volumes given below? (a) 500 cm3, (b) 5000 cm3, (c) 1000 cm3.
