Chapter 1 Respiration
- 1. 1 FORM 3 SCIENCE NOTES CHAPTER 1 RESPIRATION 1.1 The Human Breathing Mechanism Human respiratory system provides area for gas exchange between blood and environment. Allows O2 acquisition 获得 and CO2 elimination 排斥. Structure of the human respiratory system Air enters the respiratory system from nostrils and passes through nasal cavity 鼻腔. Nasal cavity warm and moisten the air. Hairs in it trap dust. Air enters the trachea 气管. Wall of trachea contains C-shaped rings of cartilage which give support and prevent from collapsing during inhalation. The trachea branches into two bronchi 支气管 (singular: bronchus) and each bronchus branches into smaller tubes called bronchioles 细支气管. Bronchioles end in millions of tiny air sacs 气囊 called alveoli 肺泡 (singular: alveolus). Lungs are located in a space called thoracic cavity 胸腔 and are made up of alveoli, bronchioles and blood capillaries 微血管. Lungs are protected by rib cage which consists of ribs 肋骨 and intercostal muscles 肋间肌肉. A sheet of muscle called the diaphragm 横隔膜 separates the thoracic cavity from the abdomen 腹部. Pathway of air during inhalation in the human respiratory system: Nostrils Nasal cavity Trachea Bronchus Bronchioles Alveolus Blood capillaries Human breathing mechanism
- 2. 2 Adaptation of the alveoli for efficient gas exchange Large surface area - Lungs have millions of alveoli to provide large surface area for gas exchange. Very thin walls - Wall of each alveolus is one-cell thick to provide short distance for diffusion of gases. Moist inner surface - Let O2 dissolve in the moisture before diffusing across alveolar wall. Surrounded by numerous blood capillaries - Help to transport gases to and from alveoli quickly. Mechanism of human breathing Breathing consists of 2 phases 阶段: - Inhalation 吸气 – Taking in of air - Exhalation 呼气 – Letting out of air Muscles involved in breathing: Intercostal muscles, Diaphragm Inhalation Exhalation Gas exchange in alveolus
- 3. 3 Inhalation Exhalation Diaphragm Contract and flattens out Relax and arches upwards Intercostal muscles Contract Relax Rib cage Move upwards and outwards Move downwards and inwards Volume of thoracic cavity Increases Decreases Air pressure in lungs Decreases Increases Movement of air Flows into the lungs Forced out of the lungs Comparison of the mechanisms of inhalation and exhalation Content Inhaled air Exhaled air Alveolar air 肺泡内的空气 O2 21% 16% 14% CO2 0.04% 4% 6% N2 79% 79% 80% Water vapour Variable Saturated Saturated Temperature Variable 34 C 37 C Composition of air in respiration Changes in contents of air after entering lungs are due to gas exchange in alveoli. 1.2 The Transport of Oxygen in the Human Body The diffusion of oxygen from the alveoli into the blood capillaries Alveolar air is rich in O2 and poor in CO2. Blood that reaches capillaries surrounding alveoli is poor in O2 and rich in CO2. Gas exchange takes place in the lungs by diffusion. O2 diffuses from alveoli into red blood cells in the capillaries. At the same time, red blood cells in capillaries release CO2 which diffuses into the alveoli. The transport of oxygen by blood Red blood cells contain the O2-carrying pigment called haemoglobin 血红蛋白. O2 combines with haemoglobin to form oxyhaemoglobin 含氧血红蛋白. The diffusion of oxygen from the blood capillaries into the body cells O2 has a higher concentration 浓度 in the capillaries that in the body cells. CO2 has a higher concentration in the body cells than in the capillaries. Oxyhaemoglobin releases O2 which diffuses into the body cells. At the same time, CO2 diffuses into the blood. Oxygen + Haemoglobin Oxyhaemoglobin
- 4. 4 1.3 The Importance of a Healthy Respiratory System Substances harmful to the respiratory system Air pollutant Harmful substances Cigarette smoke Nicotine, tar Gases from factories Sulphur dioxide, nitrogen dioxide Exhaust Carbon monoxide Haze Smoke, dust Harmful substances in air pollutants Effects of harmful substances on the respiratory system Nicotine 尼古丁 - Drug that cause addiction to cigarette. - Causes rapid heartbeat, increased blood pressure and rapid breathing. - Causes Emphysema 气肿, Heart disease, Stroke 中风, Lung cancer 肺癌 Tar 焦油 - Contains carcinogens 致癌物. - Irritates 刺激 respiratory tract 呼吸道, causing “smoker‟s cough”. Nitrogen dioxide 二氧化氮 (NO2) - Dissolves in the mucus layer on walls of trachea and alveolus. - Forms acid which destroy lung tissues. - Motor vehicles, electrical power stations and industries burn fuels which release NO2. - In big towns, reddish-brown layer in atmosphere is due to presence of NO2. Sulphur dioxide 二氧化硫 (SO2) - Cause irritation of respiratory system. - Cause both temporary and permanent damage to lungs. Carbon monoxide 一氧化碳 (CO) - Combines with haemoglobin in blood faster than O2, hence it is a poisonous gas which cause suffocation 窒息. Particulate matter (fine particles in the air) - Continuous exposure to particulate matter cause coughing, nasal congestion 鼻塞, watery nose, constant sneezing and chest pain. - Those who are very likely to be affected by haze are children, elderly and people with illnesses like asthma 哮喘, bronchitis 支气管炎 and pneumonia 肺炎.
- 5. 5 Diseases of the respiratory system Asthma - Caused by the narrowing of fine airways (bronchi and bronchioles) due to contraction of muscles in their wall. This is because of sensitivity to air pollutants including smoke. - Difficult to breath, experienced wheezing 气喘 and fell tightness in the chest. Bronchitis - Chronic bronchitis 慢性支气管炎 can be defined as a condition characterized by recurrent or chronic cough every over a period or several months. - Caused by inflammation 发炎 of the lining of the bronchioles. This may be due to infection by bacteria or viruses, or chemicals in tobacco smoke. - „Smoker‟s cough‟ is an early sign of chronic bronchitis. - Patient may turn blue, especially noticeable at lips and finger due to poor oxygenation of blood in severe cases. Lung cancer - Caused by change in the cells inside lungs such that they divide out of control and produce lumps of cells (tumours 肿瘤) which interfere with the normal functions of the lungs. - 90% of lung cancer patients are heavy smokers. - Risk of developing lung cancer is directly related to the amount of tar that gets into lungs. - Lung cancer may not have symptoms. When it is detected, the cancer cells may have spread form the lungs to other organs. Emphysema - Condition which structure of alveoli is broken down by coughing. This reduces surface area for gas exchange. - Patient cannot take in enough O2 and becomes very short of breath. Heart diseases 心脏疾病 - Nicotine raises blood pressure and increases level of „bad‟ cholesterol 胆固醇 in the blood. - Makes smoker more likely to suffer from a stroke or heart attack 心脏病. Influenza 流感 - Caused by viruses which attack the mucus membranes in respiratory system. - Spreads through tiny droplets in air. - Blocked nose, teary eyes, giddiness, headaches, aches in limbs, cough and fever are some symptoms. Pneumonia - Cause by bacteria, viruses and chemical substances in polluted air. - Trachea and alveolus are attacked by bacteria and viruses. - Lungs are filled with pus 脓 and fluid and patient will suffer from chest pains, fever and coughs. Tuberculosis 肺结核 - Caused by bacterial infection (Mycobacterium tuberculosis) which are carried by water droplets and dust in air. - Infection occurs when water droplets and dust are inhaled. - Patient suffers prolonged cough and spits out blood in end stages.
- 6. 6 Ways to improve air quality Improving indoor air quality - Minimize usage of air conditioner - Maintain low humidity to prevent mould growth 发霉 - Keep carpets and floor dust-free Improving outdoor air quality - Walk, ride, car pool or use public transportation - Keep motor vehicle well maintained - Use fuel-efficient vehicles - Reduce, reuse and recycle waste materials (3R)