1. The Human Breathing MechanismThe human respiratory system provides an area for gasexchange between the blood and the environment. Itallows oxygen acquisition and the carbon dioxideelimination.The gas exchange in lungs is called breathing (externalrespiration). This exchange involves the taking in andletting out of air.

2. Structure of Human Respiratory SystemAir enters the respiratory system through the nasalcavity.As air passes the nasal cavity, it is warmed andmoistened. Dust is trapped by the hairs.After the air leaves the nasal cavity, it enters thetrachea.The wall of the trachea contains C shaped ringsof cartilage which give it support and prevent itfrom collapsing during inhalation.The trachea branches into two bronchi (singular:bronchus) 3. One bronchus enters the right lung, the others enters theleft lung.Each bronchus branches into smaller tubes calledbronchioles.The bronchioles end in millions of tiny air sacs calledalveoli (singular: alveolus). the lungs are made up of alveoli, bronchioles and bloodcapillaries.The lungs are located in a space called the thoracic cavity.The lungs are protected by the ribcage which consists ofribs and intercostal muscles.The sheet of muscle called the diaphragm separates thethoracic cavity from the abdomen. 4. The human respiratory system 5. Adaptation of the alveoli for efficient gas exchangeLarge surface area the lungs have millions of alveoli toprovide a large surface area for gas exchange.Very thin walls the wall of each alveolus is one cell thick to provide a very short distance for the diffusion ofgases.Moist inner surface the inner surface of each alveolusis moist so that oxygen can dissolve in the moisturebefore diffusing across the alveolar wall.Surrounded by numerous blood capillaries the bloodcapillaries help to transport gases to and from the alveoliquickly. 6. Detailed structure of alveolus 7. Mechanism of human breathingThe breathing mechanism consists of two phases. Thetaking in of air is called inhalation. The letting out of theair is called exhalation.Inhalation 8. during breathing, the lungs expand and return to theirnormal size to pump air into and out of them.The movements of the ribs and the diaphragm bringabout breathing.Exhalation 9. Comparison of the mechanisms ofinhalation and exhalationInhalation ExhalationDiaphragm muscles contract.Diaphragm flattens outDiaphragm muscles relax.Diaphragm arches upwardsIntercostal muscles contract. Intercostal muscles relax.Ribcage moves upwards andoutwards.Ribcage moves downwardsand inwards.Volume of thoracic cavityincreasesVolume of thoracic cavitydecreases.Air pressure surrounding thelungs decreases.Air pressure surrounding thelungs increases.Air flows into the lungs Air is forced out of the lungs. 10. Composition of air in respirationContent Inhaled air Exhaled air Alveolar airOxygen 21 % 16 % 14 %Carbondioxide 0.04 % 4 % 6 %Nitrogen 79 % 79 % 80 %Water vapour Variable Saturated SaturatedTemperature Variable 34 C 37 C 11. The changes in the content of air entering the lungsare due to gas exchange in the alveoli.Common mistake-There is more carbon dioxide than oxygen inexhaled air.The Truth- Exhaled air contains 16 % oxygen, 4 % carbondioxide and 79 % nitrogen. 12. The diffusion of oxygen from the alveoli into theblood capillariesDuring inhalation, air is taken into the lungsthrough the nasal cavity, passing through thetrachea, bronchi, bronchioles and finally alveoli.The air that reaches the alveoli is called alveolarair. It is rich in oxygen and poor in carbon dioxide.The blood that reaches the capillariessurrounding the alveoli is poor in oxygen and richin carbon dioxide. 13. Gas exchange takes place in the lungs bydiffusion.Oxygen diffuses from the alveoli into the redblood cells in the capillaries.At the same time, the red blood cells in thecapillaries release carbon dioxide which diffusesinto the alveoli. 14. Red blood cells contain the oxygen carryingpigment called hemoglobin.Oxygen combines with hemoglobin to formoxyhaemoglobin.The blood cells are transported around thebody. 15. Gas exchange also takes place between thecapillaries and the body cells.Capillaries have a higher concentration ofoxygen than the body cells.Body cells have a higher concentration ofcarbon dioxide than the capillaries.Oxyhaemoglobin releases oxygen whichdiffuses into the body cells.Carbon dioxide diffuses into the blood at thesame time. 16. The importance of a Healthy Respiratory SystemSubstances harmful to the respiratory systemThe quality of the air can have significant effects on ourrespiratory system.As air moves into our lungs, harmful substances in theair may enter too. These harmful substances can causedisease or even death.Air pollutants include smoke of cigarettes, gases fromthe industries, exhaust of engines and haze. 17. Harmful substances in air pollutantsAir pollutant Harmful substancesCigarette Smoke Nicotine, TarGases from FactoriesSulphur dioxide, NitrogenDioxideExhaust Fumes Carbon MonoxideHaze Smoke, Dust 18. Cigarette Smoke Gases from FactoriesExhaust Fumes Haze 19. The effects of harmful substances on therespiratory systemNicotinea. Nicotine is a drug that causes addiction tocigarette smoking.b. Nicotine causes rapid heartbeat, increased bloodpressure and rapid breathing.c. The disease related 20. Tara. Tar contains carcinogens (substances thatcause cancer).b. Tar also irritates the respiratory tract, causingsmokers cough.Sulphur dioxidea. Exposure to sulphur dioxide can cause theirritation of the respiratory system.b. It can cause temporary or permanentdamage to the lungs 21. Carbon monoxidea. Carbon monoxide combines with haemoglobin in theblood faster than oxygen can, hence it is poisonous gaswhich causes suffocation. Low concentration of carbon monoxide can causedizziness, headache and fatigue whereas highconcentrations can fatal. 22. Particular matter (fine particles in the air)a. Continuous exposure to particulate matter causescoughing, nasal congestion, watery nose, constantsneezing and chest pain.b. Those who are very likely to be affected by haze arechildren, the elderly and people with illnesses likeasthma, bronchitis and pneumonia. 23. Diseases of the Respiratory SystemAsthma Heart disease 24. AsthmaThis disease is caused by the narrowing of the fineairways (bronchi and bronchioles) due to the contraction ofmuscles in their walls. This is perhaps because ofsensitivity to air pollutants including smoke.A patient will find it different to breathe, wheezing andfeeling tightness in the chest. 25. Heart diseaseNicotine raises the blood pressure and increase the levelof bad cholesterol in the blood.This makes a smoker more likely to suffer from a strokeor a heart attack. 26. BronchitisChronic bronchitis can be defined as a conditioncharacterized by recurrent or chronic cough every dayover a period of several months.This disease is caused by the inflammation of the liningof the bronchioles. This may be due to infection bybacteria or viruses, or chemicals such as those found intobacco smoke.Smokers cough is an early sign of chronic bronchitis.In severe cases, the patient may turn blue which isspecially noticeable at the lips and fingers due to pooroxygenation of blood. 27. Bronchitis 28. Lung cancerThis disease is caused by a change in the cells inside thelungs such that they divide out of control and producelumps of cells (tumours)Which interfere with the normal functions of the lungs.90% of lung cancer patients have been heavy smokers.The risk of developing this disease is directly related tothe amount of tar that gets into the lungs.Lung cancer may not have any symptoms. When it isdetected, the cancer cells may have spread from thelungs to other organs. 29. Lung cancer 30. Emphysema is a condition in which the structure of thealveoli is broken down by coughing. This reduces thesurface area for gas exchange.Emphysema 31. Ways to improve air qualityImproving indoor air qualityAvoid smoking indoorsMake sure there is a steady supply of fresh air.Minimize air conditioning useKeep carpets and floor dust freeMaintain a low humidity to prevent mould growth. 32. Improving outdoor air qualityAvoid open burning of leaves and trashDo not allow cars or other motor vehicles idle for morethan a minute.Walk, ride a bicycle, car pool or use publictransportation.Keep the motor vehicle well maintained and use a fuel efficient vehicle.Reduce, reuse and recycle waste materials.Implement laws and regulations to control air pollution.