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The respiratory system Structures Organs of the respiratory system Larynx Trachea Rib cage Bronchus Mediastinum Lung Right or Left Lung? Diaphragm • Passage for air from nasal cavity to trachea • Trachea • Carries air to & from lungs. Lined with mucous membrane and cilia • Rib Cage • Forms the framework of the chest. Providing protection to organs inside • Mediastinum • Area where heart fits between lungs • Covered by a pleural membrane that • Lungs lines lungs and the inside of the chest wall (two layers – visceral & parietal). Pleural fluid fills in between layers to hold in place. • Muscle contracts and relaxes to change • Diaphragm the chest volume during breathing • Larynx The head (LS) Nasal cavity Soft palate Pharynx Epiglottis Larynx Trachea Section through the head Nasal cavity Palate Teeth Tongue Pharynx Epiglottis Hyoid bone Vocal cords Larynx Esophagus The Miles Kelly Art library, Wellcome Images The nose (nasal cavity) • Air enters and leaves the body through the nose • Here it is cleaned (filtered), warmed and moistened before entering the body • The nasal secretions contain an anti-bacterial enzyme - lysozyme More functions • Epiglottis - Flap of tissue which, when swallowing, closes off the trachea to prevent food and liquid from entering the lungs • Larynx – the organ of voice. Air going to and from the lungs passes through the larynx. It contains vocal cords which vibrate to make sound. Vocal cords can change the pitch and volume. The mucous lining • The nasal cavity and upper airways have a mucous lining • The epithelial lining contains goblet cells which secrete a clear, sticky mucus • The function of mucus is to trap dirt particles and microbes before they enter the lungs Cilia • Cilia – microscopic hair-like structures that beat back and forth to help move mucus along and trap the particles. The bronchial tree Larynx Trachea Bronchus Bronchiole The Sourcebook of Medical Illustration (The Parthenon Publishing Group, P. Cull, ed., 1989) Trachea & bronchi • The trachea & bronchi are reinforced with C-shaped rings of cartilage. These prevent the tubes collapsing during inhalation. The bronchi Cartilage rings Muscular wall Mucous lining The Miles Kelly Art library, Wellcome Images • The upper airways are lined with a ciliated mucous membrane –The sticky mucus traps dirt & microbes –The cilia sweep the dirty mucus up the trachea and into the throat The ciliated lining tissue Mucussecreting goblet cells Cilia G. Meyer, ANHB-UWA, Alveoli Alveoli • The bronchioles terminate in microscopic clusters of air sacs called the alveoli. These make up most of the lung • Gas exchange takes place in the alveoli The alveoli (air sacs) Alveoli are wellsupplied with blood capillaries = increasing efficiency of Gas exchange (taking in O2 around the body, and removing CO2) Section through a lung showing alveoli and blood supply M I Walker, Wellcome Images Muscles • Diaphragm and Intercostals (rib muscles) • These muscles are involved in contracting and relaxing during inspiration and expiration to change the volume of the thoracic cavity, and therefore changing the volume of lungs. Pleura • Double layered – 2 layers: Visceral and Parietal • These linings lubricate chest movements, and help to keep lungs in position. Contains a pleural cavity between layers filled of pleural fluid which lubricates the surfaces and allows the layers to slide against each other easily during respiration. The respiratory system Gas exchange Exchange surfaces • Like all exchange surfaces, the alveoli are well suited because they: – are very thin (only 1 layer of cells) – have a large surface area – due to the millions of alveoli – have a rich blood supply – network of capillaries so close – are moist – because only gases can diffuse into & out of the blood only when they are dissolved in fluid. Terms You need to understand the difference between the terms BREATHING (aka VENTILATION) and RESPIRATION Breathing • Breathing (sometimes referred to as ventilation) is the process of moving air into and out of the lungs. • The purpose of breathing is to exchanged oxygen and carbon dioxide between the lungs and the air . Respiration • Respiration is the transport of oxygen from the air to the tissues and the transport of carbon dioxide in the opposite direction. [not to be confused with the process of cellular respiration discussed earlier] External respiration vs. Internal respiration • External respiration is the movement of O2 and CO2 between the lungs and the bloodstream. • Internal respiration is the exchange of O2 and CO2 between the blood and the tissues that need it. Thoracic volume Rib cage relaxes Diaphragm domed Rib cage raised Diaphragm flattens Inspiration vs. Expiration • Air flows from areas of higher pressure to areas of lower pressure. • INSPIRATION – taking air into the lungs • EXPIRATION – breathing out. Opposite to inspiration INSPIRATION • Pressure of air in the lungs is less than outside. • Low pressure inside is achieved by increasing the volume of the lungs. • Diaphragm and external intercostals muscles contract – becomes flatter and rib cage moves outwards • Air flows in until the pressure becomes equal. • During normal breathing mainly diaphragm involved. Heavier inspiration, movements of the rib cage become more important. Expiration • Diaphragm and external intercostals relax. • Diaphragm moves back up into the chest cavity and rib cage moves downwards. • Lung volume reduces and air is greater inside = thus air flows out until pressures are equal. • At rest, expiration is a passive process. During forceful expiration, the intercostals muscles contract to actively lower the rib cage Gas Exchange • Concentration gradients again! • The blood in the capillaries around the alveoli has a low oxygen concentration (as it has already delivered all the oxygen to the cells and returning to the lungs) • the air outside (in the alveoli) is high in oxygen concentration. • Oxygen will move from high to low concentration = from the alveoli to the blood capillaries. • Oxygen dissolves in the moisture on the inside of the alveolus and diffuses through the membrane, through the walls of the capillaries and into the blood. • The blood in capillaries around the alveoli are high in Carbon Dioxide (has come from the cells and picked up the wastes) • Carbon dioxide diffuses out of the blood and into the air in the alveolus. • Thus the expired air contains less oxygen, and more carbon dioxide, than inspired air. External respiration Partial pressure (mmHg) Alveolar air Deoxygenated blood Oxygenated blood Oxygen 100 40 100 Carbon Dioxide 40 44 40 Breathing maintains the correct concentration of gases in the lungs Concentration gradient Transport of Oxygen and Carbon Dioxide % of Gases • Inspired Air: 20.95% Oxygen 0.04% Carbon dioxide • Expired Air 15.8% Oxygen 4.3% Carbon dioxide • The other 79% is mainly made up of nitrogen, with varying amounts of water vapour Concentration gradients • The concentration gradient for oxygen and carbon dioxide is maintained by: – Constant flow of blood through the capillaries. Always replaced by more blood pumping around the body. The new blood is low in O2 and high in CO2. – The continual movement of air in and out of the alveoli as we breathe in and out. ‘New’ air is low in CO2 and high in O2. • Blood is the major transport medium for oxygen and carbon dioxide • Both oxygen and carbon dioxide gases are transported in the blood – but in different ways Oxygen • Is carried by: – 3% carried in solution in the blood plasma (as not very soluble in water) – 97% carried in combination with haemoglobin (found in Red Blood Cells) Oxygen transport • Oxygen combines with haemoglobin in RBCs to form oxyhaemoglobin Hb + O2 = HbO2 Hb + O2 = HbO2 • Oxygen combines with haemoglobin where the oxygen concentration is high (capillaries in the lungs). Oxyhaemoglobin breaks down into O2 and Hb where oxygen concentrations are low (at the cells which need the oxygen) • Oxygenated blood is blood with a high proportion of oxyhaemoglobin. • Oxyhaemoglobin is bright red in colour, so the blood in the arteries (except pulmonary arteries) is bright red. Haemoglobin is dark red or purplish in colour. The deoxygenated blood in the veins (except pulmonary veins) is therefore dark red. Carbon Dioxide • Is carried by: – 7-8% carried in solution in the blood plasma – 22% combines with the globin part of the haemoglobin molecule to form a compound called carbaminohaemoglobin – 70% carried in plasma as bicarbonate ions, HCO3- Carbon dioxide transport - • Most CO2 is transported in the plasma as dissolved bicarbonate ions Carbon Dioxide • Blood in the capillaries – most CO2 reacts with water to form carbonic acid (H2CO3). • Carbonic Acid then dissolves into hydrogen ions and bicarbonate ions CO2 + H2O = H2CO3 = H+ + HCO3- Gas Percentages OYXGEN CARBON DIOXIDE 3% dissolved in plasma 8% dissolved in plasma 97% as oxyhaemoglobin 22% as carbaminohaemoglobin 70% as bicarbonate ions Oxygen saturation Disorders of the Respiratory System Disorders / Complications • • • • • • • Asthma Emphysema Lung Cancer Laryngitis Bronchitis Pneumonia High Altitudes – tissues do not get enough O2 Diseased lung tissue B A CDC C Photo by Pöllö A. healthy lung tissue B. Smoker’s lung C. Emphysema Some Respiratory Disorders Asthma: • an allergic response to foreign substances that enter the body (dust, pollen, animal fur). These trigger an ‘attack’ where the muscles surrounding the bronchioles spasm – causing a narrowing o the air passages making it difficult to breath Asthma Emphysema • Caused by long term exposure to irritating particles in the air. E.g. Smokers inhale tobacco smoke, those who work in situations where a lot o dust or asbestos • The irritating particles cause damage to the alveoli. They lose their elasticity and may break down – reducing the internal surface area of the lungs. • Due to loss of elasticity – lungs are constantly inflated and expiration requires voluntary effort. • Inadequate S.A. for gas exchange. Smoking Effects The effects of tobacco smoke on the respiratory system include: • Irritation of the trachea and larynx • Reduced lung function and breathlessness due to swelling and narrowing of the lung airways and excess mucus in the lung passages • Impairment of the lungs’ clearance system, leading to the build-up of poisonous substances, which results in lung irritation and damage • Increased risk of lung infection and symptoms such as coughing and wheezing • Permanent damage to the alveoli of the lungs. Smoking