[BIO] Chapter 8 - Respiration

© Hee Xin Wei (Copyrighted) Topic 8: Respiration in Humans

Chapter Analysis FOCUS EXAM WEIGHTAGE •Constitute to around 9% in Paper 2 in the past 5 years •commonly tested in MCQ and structured questions •tested once in section B in the past 5 years •straightforward chapter •linked to transport in humans chapter

human respiratory system alveoli gaseous exchange Key Concept

Respiratory System Nasal passages Passages leading from the nostrils lined with a moist mucous membrane Pharynx Common passage for the opening to oesophagus and trachea Larynx Voice box containing vocal cords Trachea •Breathing tube supported by C-shaped cartilage which prevents the trachea from collapsing as the air pressure in the lungs changes. •branches into two bronchi, one to each lung. Bronchi •Branches repeatedly within the lungs to produce numerous finer tubes called bronchioles. •The bronchioles at the end of the branching terminate in clusters of air sacs called alveoli. Cilia (not pictured) Hair-like structures that cover the epithelial lining of the trachea and bronchi. The mucus traps dust, pollen and other particles and the cilia sweeps it upwards into the pharynx

Alveoli -Sites of gaseous exchange in the lungs. -Blood entering the lungs from the heart has a lower concentration of oxygen and a higher concentration of carbon dioxide than the atmospheric air entering the alveoli in the lungs. -Oxygen diffuses from the alveolar air into the blood capillaries -Carbon dioxide diffuses from blood capillaries to the alveoli -Oxygen and carbon dioxide concentration gradients are maintained by: •Continuous flow of blood through the blood capillaries. •Movement of air in and out of the alveoli, caused by breathing. ADAPTATION OF LUNG FOR GASEOUS EXCHANGE 1.The numerous alveoli in the lungs provide a large surface area to volume ratio for gaseous exchange. 2.The wall of the alveolus is only one cell thick. This provides a short diffusion distance for gases, ensuring a faster rate of diffusion. 3.A thin film of moisture covers the surface of the alveolus. This allows oxygen to dissolve in it. 4.The walls of the alveoli are richly supplied with blood capillaries. The flow of blood maintains the steep concentration gradient of gases.

absorption of oxygen 1.The alveolar air contains a higher concentration of oxygen than the blood, oxygen dissolves in the moisture lining the alveolar walls and then diffuses into the blood capillaries. 2.Oxygen combines with the haemoglobin in red blood cells to form oxyhaemoglobin. 3.This reaction is reversible depending on the amount of oxygen in the surroundings. 4.When the blood passes through oxygen-poor tissues, the oxyhaemoglobin releases oxygen, which will then diffuse through the walls of the blood capillaries into the cells of the tissues. oxygen + haemoglobin —> oxyhaemoglobin oxyhaemoglobin —> oxygen + haemoglobin (surrounding has low oxygen)

removal of carbon dioxide AT TISSUE CELLS (a)Carbon dioxide produced by tissue cells due to respiration diffuses into blood plasma and then enters into red blood cells. (b)In RBC, carbon dioxide reacts with water to give carbonic acid, catalysed by carbonic anhydrase. (c)Carbonic acid then dissociates into hydrogen carbonate ions/bicarbonate ions and hydrogen ions. (d)The hydrogen carbonate ions diffuse out of red blood cells, into the plasma •Carbon dioxide is mainly transported in the blood plasma •A small amount of carbon dioxide is also carried and dissolved in the red blood cells. IN THE LUNGS (e)Hydrogen carbonate ions diffuse back into red blood cells where they combine with hydrogen ions to form carbonic acid, then into water and carbon dioxide. (f)The carbon dioxide diffuses out of the blood into the alveolar space where it is expelled during exhalation. CO2 + H2O —> H2CO3 —> HCO3- + H+ HCO3- HCO3- + H+ —> H2CO3 —> CO2 + H2O

Inhalation and Exhalation Smoking Key Concept

Breathing Inhalation/Inspiration 1.During inhalation, the diaphragm contracts, flattens and moves downwards. 2.The external intercostal muscles contract while the internal intercostal muscles relax, causing the ribs to move upwards and outwards. 3.Sternum moves up and forward. 4.The thoracic cavity increases in volume, causing the air pressure of the lungs to fall below that of the atmosphere. 5.Air rushes into the lungs. Exhalation/Expiration 1.During exhalation, the diaphragm relaxes and arches upwards. 2.The internal intercostal muscles contract while the external intercostal muscles relax, moving the ribs downwards and inwards 3.Sternum returns to its original position. 4.The thoracic cavity decreases in volume, causing the air pressure in the lungs to be higher than that of the atmosphere. 5.Air flows out of the lungs

pathway of air Pathway that the air travels during inhalation Nostrils → Nasal Passages → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli Exhalation is the reverse