PT3 Science Chapter 18: Respiration 18.1 The Human Breathing Mechanism 1. What is “Respiration”（呼吸作用）? The chemical process whereby energy is released from glucose or other simple substances is known as Respiration. 2. In cellular respiration, glucose is combined with oxygen in the cells to release energy. 3. The process which our body takes in oxygen from oxygen from atmosphere and release carbon dioxide is dioxide is known as Breathing (Exchange Breathing (Exchange of gases). 4. The structure of the human respiratory system.
a. Nasal Cavity 鼻腔 b. Throat / Pharnyx 咽喉 c. Trachea 气管 d. Lungs 肺 e. Bronchi 支气管 f.
Bronchioles 细支气管
g. Diaphragm 横隔膜 h. Intercostal Muscles 肋间肌 i.
Ribs 胸骨
j.
Alveoli 肺泡
5. Flow from air from the atmosphere to the lungs. a. The air enters the nose through both Nostrils（鼻孔）. i. The walls of nostrils are lined with hairs to trap dust particles in particles in the air. b. From the Nostrils, air enters the Nasal Cavity. Cavity. i. The Nasal Cavity secretes Mucus 黏液, which is a slimy substance that traps bacteria and other foreign particles in particles in the inhaled air. c. From Nasal Cavity, air enters the Trachea . i. C-shaped Cartilages keep Cartilages keep trachea open therefore it does not collapse. d. The Trachea branches into left and right bronchus. Each Bronchus goes Bronchus goes into a lung. Then each bronchus branches into smaller tubes called Bronchioles. Bronchioles. e. The bronchioles end in many tiny air sacs called Alveoli ( Alveoli ( Alveolus ). Alveolus in plural plural ). i. The Alveoli is surrounded by blood by blood capillaries. capillaries. ii. Gas exchange takes place in the lungs by Diffusion. Diffusion. f. The passage of air in the human respiratory system can be summarized as follows:
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PT3 Science Chapter 18: Respiration
Nostril
Nasal Cavity
Thachea
Bronchus
Bronchiole
Alveolus
6. An alveolus has the following adaptations to allow it to exchange gases effectively. a. It has a very large surface area when compared to its volume. b. It has walls which are very thin and elastic. c. It is surrounded by a network of blood capillaries. d. It is moist. 7. The Intercostal Muscles move the ribs up and down during breathing. 8. The Diaphragm lies at the base of the thoracic cavity 胸腔, and also separates the thoracic cavity from the abdomen 腹部. 9. Structure of lungs.
a. The lungs are made up of bronchioles, alveoli and blood capillaries. b. The lungs are protected by a bony structure called the Rib Cage. i. A human being has 12 pairs of ribs. c. The Thoracic Cavity houses the lungs. 10. The breathing Mechanism a. Inhalation – the process of taking air into the lungs; Exhalation – the process of expelling carbon dioxide from the lungs into atmosphere.
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PT3 Science Chapter 18: Respiration Inhalation The external intercostal muscles contract. The rib cage moves upward and outward. The diaphragm contracts and flattens. The volume of the thoracic cavity increases. The air pressure in the thoracic cavity decreases. Air from the surroundings enters the lungs.
Exhalation The external intercostals muscles relax. The rib cage moves downward and inward. The diaphragm relaxes and curves upward. The volume of the thoracic cavity decreases. The air pressure in the thoracic cavity increases. Air is forced out of the lungs.
18.2 Transport of Oxygen in the Human Body 1. The transport of oxygen involves the following processes. a. The Diffusion of Oxygen from alveoli into the blood capillaries. b. The transport of oxygen by red blood cells. c. The diffusion of oxygen from the blood capillaries into the cells. 2. The heart, blood vessels (Veins or Arteries) and blood capillaries make up the Blood Circulatory System. 3. Blood vessels from lungs carry blood rich in oxygen to th e rest of the body for respiration. 4. Blood vessels also carry blood in low in oxygen from the rest of the body back to the lungs after respiration. 5. The concentration of oxygen in alveoli is higher than the concentration of oxygen in the capillaries. It is reverse for the concentration of carbon dioxide. Parts Oxygen Content Carbon Dioxide Content High Low Alveoli Low High Capillaries a. The difference in oxygen concentration in these two parts causes a diffusion of the gas through the thin, moist walls of the alveoli and capillaries. b. Once the capillaries are rich with oxygen, they pass the oxygen to the cells in the various parts of the body.
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PT3 Science Chapter 18: Respiration °
6. Oxygen is not soluble in blood or even less soluble at body temperature (37 C). 7. Oxygen combines easily with Haemoglobin which is a special respiratory pigment in the red blood cells, to form Oxyhaemoglobin. 18.3 The Importance of a Healthy Respiratory System 1. Smoking is very harmful to the respiratory system. a. Three most hazardous chemicals – Tar , Nicotine and Carbon Monoxide. b. High temperature of the smoke may harm body cells. c. Smoking is the most preventable single cause of death in the world. d. Tobacco smoke is the most important risk factor for diseases shown as below: i. Emphysema 肺气肿 ii. Heart Diseases iii. Asthma iv. Bronchitis 支气管炎 v. Pneumonia 肺炎 vi. Lung cancer e. Tar is a mixture of many toxic chemicals. It contains of i. Carcinogens 致癌物质 – they cause cancer. f. Nicotine in the tobacco causes an addiction to smoking. g. Carbon Monoxide – highly poisonous gas, reduce the amount of oxygen in the blood. h. Sulphur Dioxide – acidic and damages lung tissues. 2. Industrial Wastes – other harmful substances that may enter our respiratory system. a. Cement dust, coal dust, sulphur dioxide and asbestos 石棉 dust. 3. Pollutants from motor vehicles (carbon monoxide, oxides of nitrogen and hydrocarbons) are also harmful. 4. Pollutants such as oxides of nitrogen can directly or indirectly cause Haze. a. Haze can cause throat irritation and inflammation of the upper respiratory tract which, in turn, cause breathing difficulties. 5. Asbestos dust is also a carcinogen which causes lung cancer. 6. Bacteria, viruses and other microorganisms which produces toxins to cause infections that affect respiratory system. 7. Improving the quality of air a. Education to inculcate good practices. b. Publicity through mass media. c. Campaigns and contests to increase awareness. d. Forums and seminars to inform the public, and exchange ideas and information. e. Law and enforcement to catch the culprits 罪犯.
