How are the lungs designed in human beings to maximise the area for exchange of gases?

How are the lungs designed in human beings to maximise the area for exchange of gases? Answer • The respiratory system starts from the nostrils , extending into a trachea (windpipe). • As the trachea extends, it divides into two tubes called the bronchi which are connected to each lung. • These bronchi further branch into numerous bronchioles , which end in small balloon shaped structures called alveoli . • These alveoli provide a maximum area for the exchange of gases to occur. Being surrounded by thin walls and blood capillaries, the exchange of gases is most effective here.

Lungs contain millions of alveoli which provide a surface for the exchange of gases. An extensive network of blood vessels is present in the wall of the alveoli. By lifting our ribs and flatten the diaphragm, the chest cavity becomes spacious. Air is sucked into the lungs and alveoli. The oxygen from the breath, diffuses into the blood and CO 2from the blood brought from the body, diffuses out into the air.

Exchange of gases in tissues occurs through diffusion. Oxygen is carried as oxyhaemoglobin from lungs to tissues. It dissociates and carbon dioxide diffuses out into blood from tissues. It is transported in dissolved form and reaches lungs where again it diffuses to alveoli. Lungs have a tree like branching pattern of bronchi and bronchioles. The terminal part of bronchiole ends into sac like structures called alveoli which are present in groups. Alveoli have curved wall to increase surface area for exchange of gases. The wall of alveoli is extremely thin and is lined by blood capillaries.

In the lungs, the air passage (wind pipe) divide into smaller tubes, called bronchi which in turn form bronchioles. The bronchioles which terminate in ballon-like structures, called alveoli. The alveoli present in the lungs provide maximum surface for exchange of gases. The alveoli have very thin walls and contain an extensive network of blood vessels to falicitate exchange of gases. Fig. Alveoli in the lungs. First step of break down of glucose (6 carbon molecule) takes place in the cytoplasm of cells of all organisms. This process yield a three carbon molecule compound called Pyruvate. Further break down of pyruvate takes place in different manners in different organisms. (i) Anaerobic respiration: This process takes place in absence of oxygen e.g., in yeast during fermentation. In this case pyruvate is converted into ethanol and carbon dioxide. (ii) Aerobic respiration: In aerobic respiration break down of pyruvate takes place in presence of oxygen to give rise 3 molecules of carbon dioxide and water. The release of energy in aerobic respiration is much more than anaerobic respiration. (iii) Lack of oxygen: Sometimes, when there is lack of oxygen, especially during vigorous activity, in our muscles, pyruvate is converted into lactic acid (3 carbon molecule compound). Formation of lactic acid in muscles causes cramp. Fig. 6.19. Break down of glucose by various pathways during cellular respiration. The transport system (called circulatory system) in human beings mainly co...

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Answer: • Each lung has a highly branched respiratory tract called a respiratory tree. • A primary bronchus divides into secondary bronchi, secondary into segmental bronchi, segmental bronchus into bronchioles which divides into terminal bronchioles, respiratory bronchioles, alveolar sacs and alveoli. • The alveoli are thin-walled and richly supplied with a network of blood vessels to facilitate the exchange of gases between blood and the air-filled in alveoli. • These alveoli have a balloon-like structure that provides maximum surface area for the exchange of gases.

Solution Correct answer is option A. Explanation for correct option • The exchange of gases can take place on the surfacewhich is provided by the alveoli. • The walls of the alveoli are supplied with anextensive network of blood vessels. • Thus, lungs maximize the area for a gaseous exchangethrough the presence of large numbers of alveoli which are richly supplied withblood. Read the given statements and choose correct answer :- (i) Initial bronchioles are supported by incomplete cartilagenous rings. (ii) In human lungs are solid and spongy. (iii) Alveoli wall contains simple squamous epithelium and white fibrous connective tissue (iv) Lungs are covered by a single layered pleura Which among the following statement is correct? A. Normal breathing rate of a person is 15 to 18 times per minute. B. Total area of gas exchange seen in the whole alveoli in two lungs is 36 to 72 square metre. C. The total volume of air breathed in an out in the cycle of inhalation and exhalation is 500 ml. D. Wind pipe is supported by rings of cartilage in order to avoid its collapse when there is lesser air in it.