Gas Exchange and Smoking AICE Biology Topic H
Learning Outcomes • 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. • Describe the distribution of cartilage, ciliated epithelium, goblet cells and smooth muscle in the trachea, bronchi and bronchioles. • Describe the functions of cartilage, ciliated epithelium, goblet cells, mucous glands, smooth muscle and elastic fibers in the gas exchange system.
The Gas Exchange System • Structures • Lungs • Have a HUGE surface area to increase efficiency of gas exchange • Found in the thoracic cavity, surrounded by pleural membranes • Trachea • Tube from the pharynx to the bronchi • Contains c-shaped cartilage rings to prevent collapse and rupture • Lined with pseudostratified columnar epithelium with ciliated cells and goblet cells
SEM image of trachea epithelium, including both ciliated and non-ciliated epithelial cells (called goblet cells) • Goblet cells secrete mucous to trap dust and pathogens, and the cilia sweep it up the trachea so it can be swallowed
Structures cont’d • Bronchi • Two main branches from the trachea • Found in the lungs • Lead to bronchioles • Also contain cartilage • Bronchioles • Smaller branches off of the bronchi • Surrounded by smooth muscle to help control diameter (no cartilage)
Alveoli • Air sacs at the end of bronchioles • Simple squamous epithelial lining – single, thin cell layer allows for efficient gas exchange • Surrounded by capillaries • Gases are exchanged according to partial pressure gradients • Alveoli have elastic fibers to help them to withstand changes in pressure
Learning Outcome (d) Describe the process of gas exchange between air in the alveoli and the blood
Learning Outcomes (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 system.
(h) Explain how tobacco smoking contributes to atherosclerosis and coronary heart disease (CHD) • Evaluate the epidemiological and experimental evidence linking cigarette smoking to disease and early death. (j) Discuss the difficulties in achieving a balance between preventions and cure with reference to coronary heart disease, coronary by-pass surgery, and heart transplant surgery.
Tar and Carcinogens • Cigarette tar is the residue that is deposited in the airways when the chemical particulates in tobacco smoke condense. • It can coat the cilia on the epithelial tissue, preventing them from functioning properly & decreasing gas exchange • The tar also contains carcinogens, which are toxins that cause cancer
Lung Cancer • Smoking is the leading cause (86%) of lung cancer (second-hand smoke causes 3% of cases) • Signs & Symptoms: • Persistent & intense coughing • Chest, shoulder, & back pain • Change in color & amount of sputum • Shortness of breath • Coughing blood • Recurrent bronchitis or pneumonia • Lung tissue biopsy is used to confirm diagnosis & determine the type & stage
Chronic Obstructive Pulmonary Disease (COPD) • Smoking is the leading cause of COPD, and is reponsible for 85-90% of COPD deaths • Signs & Symptoms: • Couging • Increased sputum production • Shortness of breath & wheezing • Chest tightness • Fatigue
COPD continued • 2 Main Forms: • Chronic bronchitis • Inflammation of the bronchial tubes • Persistent mucus-producing cough, which can lead to damage and scar-tissue formation in the lungs • Emphysema • Linings of the alveoli become damaged, turning them into large irregularly shaped air pockets • Also destroys elastic fibers in the bronchioles, causing them to collapse
Carbon Monoxide • One of the 4,000+ chemicals that enters the body as a result of smoking • CO binds irreversibly to hemoglobin (forming carboxyhemoglobin), thus preventing the binding of O2 • Hemoglobin’s affinity for CO is approximately 200x its affinity for O2 • Since the blood is carrying less oxygen, the heart has to work harder, increasing chances of cardiovascular disease
Nicotine • Addictive chemical in cigarette smoke • Stimulates the nervous system • Release of adrenaline • Arterioles constrict (diameter decreases) • Leads to an increase in heart rate and blood pressure • Also causes platelets to be stickier, increasing the risk of blood clots
Atherosclerosis • Caused by a build up plaque called an atheroma in the arteries, narrowing and hardening them • Atheroma is composed of cholesterol, dead muscle cells, platelets, and fibers • Smoking increases risk of atherosclerosis • Chemicals in cigarette smoke can damage the endothelium in the arteries, increasing the formation of atheromas • High blood pressure (caused by nicotine & CO) can contribute to plaque formation • Smoking can interact with other risk factors that increase cholesterol level
Coronary Heart Disease (CHD) • Caused by atherosclerosis in the coronary arteries, which supply oxygen to the heart • Blood pressure increases as the heart has to work harder in order to receive enough oxygen • Because smoking increases the risk of atherosclerosis, it increases the risk of CHD
CHD Prevention & Treatment • CHD Preventative measures include: • Diet low in saturated fat • Regular exercise • Not smoking • Treatment options include: • Lifestyle changes • Surgical procedures such as angioplasty & coronary bypass • Can treat CHD, but it will only be a temporary fix unless lifestyle is changed
Epidemiological Evidence • Shows correlation but not causation • 90% of COPD deaths occur in smokers, and COPD is very rare in non-smokers • 98% of people with emphysema are smokers and 20% of all smokers suffer from emphysema • Lung cancer is 18x more likely in smokers than in non-smokers
Experimental Evidence • Animals exposed to smoke (or forced to smoke) have developed both tumors and COPD • Cigarette tar was painted on the skins of mice & cancerous growths formed