biology4alevel600

9.1    The gas exchange system 9.2    Smoking The gas exchange system is responsible for the uptake of oxygen  into the blood and excreting carbon dioxide. An understanding of this system shows how cells, tissues and organs function  together to exchange these gases between the blood and the environment. The health  of this system and of the cardiovascular system is put at risk by smoking. Learning outcomes Candidates should  be able to: 9.1    The gas exchange system 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. a)   describe the gross structure of the human gas exchange system b)   observe and draw plan diagrams of the structure of the walls of the trachea, bronchi,  bronchioles and alveoli indicating  the distribution of cartilage,  ciliated epithelium, goblet  cells, smooth muscle, squamous epithelium and blood vessels c)

• The gas exchange system • Smoking and smoking-related diseases Learning Outcomes Candidates should be able to: (a) [PA] describe the structure of the human gas exchange system, including the microscopic structure of  the walls of the trachea, bronchioles and alveoli with their associated blood vessels; (b) [PA] describe the distribution of cartilage, ciliated epithelium, goblet cells and smooth muscle in the  trachea, bronchi and bronchioles; (c) describe the functions of cartilage, cilia, goblet cells, mucous glands, smooth muscle and elastic fibres in  the gas exchange system; (d) describe the process of gas exchange between air in the alveoli and the blood; (e) describe the effects of tar and carcinogens in tobacco smoke on the gas exchange system; (f) describe the signs and symptoms that enable diagnosis of lung cancer and chronic obstructive pulmonary disease (COPD) (emphysema and chronic bronchitis); (g) describe the effects of nicotine and carbon monoxide on the cardiovascular

 1 The human heart, like that of all mammals, has two atria and two ventricles. Blood enters the heart by the atria and leaves from the ventricles. A septum separates the right side of the heart, which contains deoxygenated blood, from the left side, which contains oxygenated blood.  2 Semilunar valves at the entrances to the blood vessels that leave the heart (aorta and pulmonary artery) prevent back flow of blood into the heart, and atrioventricular valves prevent backflow of blood from ventricles into the atria.  3 The heart is made of cardiac muscle and is myogenic (the muscle is self-stimulating). 4 The sinoatrial node (SAN) sets the pace of contraction for the muscle in the heart. Excitation waves spread from the SAN across the atria, causing their walls to contract. A non-conducting barrier prevents these excitation waves from spreading directly into the ventricles, thus delaying their contraction. Th e excitation wave travels to the ventricles via the atrioventricular node (AVN

 1. Blood is carried away from the heart in arteries, passes through tissues in capillaries, and is returned to the heart in veins. Blood pressure drops gradually as it passes along this system. 2. Arteries have thick, elastic walls, to allow them to withstand high blood pressures and to smooth out the pulsed blood flow. Capillaries are only just wide enough to allow the passage of red blood cells, and have very thin walls to allow effi cient and rapid transfer of materials between blood and cells. Veins have thinner walls than arteries and possess valves to help blood at low pressure flow back to the heart.  3. Blood plasma leaks from capillaries to form tissue fluid. This is collected into lymphatics as lymph, and returned to the blood in the subclavian veins. Tissue fluid and lymph are almost identical in composition; both of them contain fewer plasma protein molecules than blood plasma, as these are too large to pass through the pores in the capillary walls.  4. Red blood cells are