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GAS EXCHANGE AND SMOKING Chapter. 9 GAS EXCHANGE VIDEO https://www.youtube.com/watch?v=AJpur6XUiq4 GROSS STRUCTURE OF HUMAN GAS EXCHANGE SYSTEM • All organisms take in gases from their environment and release gases to the environment. Animals take in O2 for aerobic respiration and release CO2. Plants also respire, but during daylight hours they photosynthesise at a greater rate than they respire, and so take in CO2 and release O2. • The body surface across which these gases diffuse into and out of the body is called the gas exchange surface. In mammals, including humans, the gas exchange surface is the surface of the alveoli in the lungs. • The gas exchange surface in the lungs is extensive, very thin, well supplied with blood and well ventilated. The trachea and bronchi provide little resistance to the movement of air to and from the alveoli. GROSS STRUCTURE OF HUMAN GAS EXCHANGE SYSTEM 1 2 3 4 5 6 7 8 9 10 11 12 13 PLAN DIAGRAMS OF THE STRUCTURE OF THE WALLS OF THE TRACHEA, BRONCHI, BRONCHIOLES PLAN DIAGRAMS OF AVEOLI AND DISTRIBUTION OF CARTILAGE, CILIATED EPITHELIUM, GOBLET CELLS, SMOOTH MUSCLE, SQUAMOUS EPITHELIUM AND BLOOD VESSELS FUNCTIONS AND WHAT IS… • Cartilage in the walls of the trachea and bronchi provides support and prevents the tubes collapsing when the air pressure inside them is low. • Cillated epithelium is found lining the trachea, bronchi and some bronchioles. It is a single layer of cells whose outer surfaces are covered with many thin extensions (cilia) which are able to move. They sweep mucus upwards towards the mouth, helping to prevent dust particles and bacteria reaching the lungs. • Goblet cells are also found in the ciliated epithelium. They secrete mucus, which traps dust particles and bacteria. • Mucus glands are beneath the epithelium and also makes mucus. • Smooth muscle cells are found in the walls of the trachea, bronchi and bronchioles. This type of muscle can contract slowly but for long periods without tiring. When it contracts, it reduces the diameter of the tubes. During exercise it relaxes, widening the tubes so more air can reach the lungs. • Elastic fibres are found in the walls of all tubes and between the alveoli. When breathing in, these fibres stretch to allow the alveoli and airways to expand. When breathing out, they recoil, helping to reduce the volume of alveoli and expel air out of the lungs. PROCESS OF GAS EXCHANGE BETWEEN AIR IN THE AVIOLI AND THE BLOOD • The air inside an alveolus contains a higher concentration of O2, and a lower concentration of CO2, than the blood in the capillaries. This blood has been brought to the lungs in the pulmonary artery, which carries deoxygenated blood from the heart. O 2 therefore diffuses from the alveolus into the blood capillary, through the thin walls of the alveolus and the capillary. CO 2 diffuses from the capillary into the blood. • The diffusion gradients for these gases are maintained by: • •Breathing movements, which draw air from outside the body into the lungs, and then push it out again; this maintains a relatively high concentration of O2 and low concentration of CO 2 in the alveoli; • Blood flow past the alveolus, which brings deoxygenated blood and carries away oxygenated blood. https://www.youtube.com/watch?v=XTMYSGXhJ4 E SMOKING • Smoking is one of the major avoidable risk factors of chronic, life-threatening diseases of the gas exchange and circulatory systems • The smoke from cigarettes contains several substances that affect the gas exchange system and the cardiovascular system. These include: • tar, a mixture of substances including various chemicals that act as carcinogens. • nicotine, an addictive substance that affects the nervous system by binding to receptors on neurons (nerve cells) in the brain and other parts of the body. It increases the release of a neurotransmitter called dopamine in the brain, which gives feelings of pleasure. It increases the release of adrenaline into the blood, which in turn increases breathing rate and heart rate. There is also some evidence that nicotine increases the likelihood of blood clots forming. • CO, which combines irreversibly with Hb, forming carboxyhaemoglobin. This reduces the amount of Hb available to combine with O2, and so reduces the amount of O2 that is transported to body tissues. LUNG CANCER • Various components of tar can cause changes in the DNA in body cells, including the genes that control cell division, which can cause cancer. These substances are therefore carcinogens. Cancers caused by cigarette smoke are most likely to form in the lungs but may form anywhere in the gas exchange system, and also in other parts of the body. Smoking increases the risk of developing all types of cancer. • Symptoms of lung cancer include shortness of breath, a chronic cough - which may bring up blood - chest pain, fatigue and weight loss. CHRONIC OBSTRUCTIVE PULMONARY DISEASE (COPD) • This is a condition in which a person has chronic bronchitis and emphysema. It can be extremely disabling. CHRONIC BRONCHITIS • Various components of cigarette smoke, including tar, cause goblet cells to increase mucus production and cilia to beat less strongly. This causes mucus to build up, which may partially block alveoli. This makes gas exchange more difficult, as the diffusion distance between the air in the alveoli and the blood in the capillaries is greater. The mucus may become infected with bacteria, causing bronchitis. EMPHYSEMA • Smoking causes inflammation in the lungs. This involves the presence of increased numbers of white blood cells, some of which secrete chemicals that damage elastic fibres. This makes the alveoli less elastic. They may burst, resulting in larger air spaces. This reduces the surface area available for gas exchange. This is called emphysema. A person with emphysema has shortness of breath, meaning they struggle to breathe as deeply as they need to, especially when exercising. SHORT-TERM EFFECTS OF NICOTINE AND CARBON MONOXIDE ON THE CARDIOVASCULAR SYSTEM • The nicotine and CO in tobacco smoke increase the risk of developing atherosclerosis. Atherosclerosis is a thickening and loss of elasticity in the walls of arteries. It is caused by build-up of plaques in the blood vessel wall. The plaques contain cholesterol and fibres. They produce a rough surface lining the artery, which stimulates the formation of blood clots. • A blood clot may break away from the artery wall and get stuck in a narrow vessel elsewhere in the blood system, for example in the lungs or in the brain. This prevents blood passing through so cells are not supplied with O2 and die. If this happens in the brain it is called a stroke. • The loss of elasticity In an artery or arteriole also makes it more likely that the vessel will burst when high-pressure blood pulses through. This is another cause of stroke. • If atherosclerosis happens in the coronary arteries that supply the heart muscle with oxygenated blood, the person has coronary heart disease (CHD). Parts of the muscle may be unable to function properly as they do not have enough O 2 for aerobic respiration. The muscle may die. Eventually, this part of the heart may stop beating, causing a heart attack. SMOKING EFFECTS https://www.youtube.com/watch?v=gwuwrRKI2Y&index=4&list=PLXgIlX9mrPCoCZmX4Gx9AL HEYmYW7INGg • 2:12-3:23 • 3:47-4:30 • 5:30-7:15