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NARAYANA GROUP 53 NEET ZOOLOGY VOL-I BREATHING AND EXCHANGE OF GASES CO N T E N TS NEET SYLLABUS Breathing and Exchange of Gases * Introduction * Respiratory organs * Human Respiratory System * Mechanism of Breathing * Respiratory Volumes and Capacities * Exchange of Gases * Transport of Gases * Regulation of Respiration * Disorders of Respiratory System  Respiratory organs in animals  Respiratory system in humans  Mechanism of breathing and its regulations in humans  Exchange of gases  Transport of gases  Regulation of respiration  Respiratory volumes  Disorders related to Respiration Asthma, Emphysema, Occupational respiratory disorders 17
NEET ZOOLOGY VOL-I 54 NARAYANA GROUP BREATHING AND EXCHANGE OF GASES INTRODUCTION * Oxygen (O2 ) is utilised by the organisms to indirectly break down nutrient molecules like glucose, amino acids, fatty acids etc., to derive energy for performing various activities. * Carbon dioxide (CO2 ) which is harmful is also released during the above catabolic reactions. It is, therefore, evident that O2 has to be continuously provided to the cells and CO2 produced by the cells have to be released out. * All physical and chemical reactions in which atmospheric air oxidises food in the body cells resulting in the production of energy and liberation of CO2 are included in respiration. * Process of exchange of oxygen from the atmosphere with carbon dioxide produced by the cells is called breathing commonly known as respiration. * Respiration is a catabolic process( energy releasing process). * Respiration is a physico-chemical process. Types of Respiration  Anaerobic respiration and Aerobic respiration. 1) Anaerobic respiration :  It occurs when nutrients are incompletely oxidised without using O2 .  Anaerobic respiration is low energy yielding process. eg: 1) Lower organisms like bacteria, yeast etc., end product is ethyl alcohol. 2) Skeletal muscles (under certain conditions), end product is lactic acid. 3) Some endoparasites Entamoeba histolytica (obligatory anaerobe) due to lack of mitochondria. 4) Mature RBC due to lack of mitochondria. 2) Aerobic respiration  Cells utilize O2 for completely oxidising the nutrients.  O2 is used either from atmospheric air or from water. It involves A) External respiration (breathing/ventilation)  It is purely a physical process.  It is the exchange of O2 present in surrounding gaseous or liquid medium and CO2 in blood through a liquid medium by diffusion across the body surface or respiratory surface. B) Internal respiration  It is the exchange of O2 present in blood and CO2 in the body cells through tissue fluid at cellular level. C) Cellular respiration  It is the utilization of O2 by cells for energy production and resultant release of CO2 . RESPIRATORY ORGANS * Mechanisms of breathing vary among different groups of animals depending mainly on their habitats and levels of organisation. * Respiratory organs are not well developed in sponges, coelenterates and flatworms. In these animals exchange of gases (O2 & CO2 ) take place by simple diffusion over their entire body surface.
NARAYANA GROUP 55 NEET ZOOLOGY VOL-I BREATHING AND EXCHANGE OF GASES  Table : Respiratory organs in different animals Respiratory structures/organs for exchange of gases in different animal groups Animal Groups Protozoans (e.g., Amoeba, Paramecium) Sponges (e.g., Sycon) Cnidarians (e.g., Hydra) Ctenophora / Comb Jellies. (e.g., Hormiphora) Platyhelminthes (i) Free living (e.g., Planaria) (ii) Parasites (e.g., Liver ?uke, Tapeworm) Nematihelminthes (Nematoda) (i)Free living (e.g., Rhabditis) (ii) Parasites (e.g., Ascaris) Annelids (e.g., Nereis, Earthworm, Leech Arenicola, Amphitrite, Terebella Arthropods (a) Crayf ish, Prawn (b) Insects, Centipedes, Millipedes, Ticks, Peripatus (c) Scorpions, Spiders (d) Mites (e) Limulus (King crab) Mollusca (e.g., Unio, Pila) Echinoderms (e.g., Starf ish) Hemichordata (e.g., Balanoglossus) Chordata (i)Urochordata (e.g., Herdmania) (ii) Cephalochordata (e.g., Branchiostoma) (iii) Vertebrata (a) Cyclostomes, Fishes (b) Amphibians (e.g., Frog) (c) Reptiles, Birds, Mammals Respiratory Structures/Organs Plasmalemma, Pellicle. Plasma membrane of each cell Body wall Body wall Body surface Anaerobic respiration (No exchange of gases) Body surface Anaerobic respiation (No exchange of gases) Body wall (Cutaneous respiration), gills (Branchial respiration) Gills (Branchial respiration) Tracheae (Tracheal Respiration) Book lungs Cutaneous respiration Book gills Two ctenidia (gills) in Unio, one ctenidium (gill) and one pulmonary sac (lung) in Pila Dermal branchae, Tube feet Pharyngeal wall Pharyngeal wall Gills (Branchial respiration) Skin, Buccopharygeal cavity & lungs Lungs Pharyngeal wall 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. S. NO. HUMAN RESPIRATORY SYSTEM * The respiratory system consists of the external nostrils, nasal chambers, pharynx, larynx, trachea, bronchi, bronchioles and lungs. * Human have a pair of external nostrils opening out above the upper lip. * It leads to a nasal chamber through the nasal passage. The nasal chamber opens into pharynx.  Nasal passage is functionally divided into 3 regions : (i) Vestibular region : Skin, hair, sebaceous glands are present
NEET ZOOLOGY VOL-I 56 NARAYANA GROUP BREATHING AND EXCHANGE OF GASES (ii) Respiratory region : It is lined by pseudo stratified columnar ciliated glandular epithelium (Natural air conditioner). It has three twisted bony plates are called conchae or turbinals (superior, middle, inferior) (iii) Olfactory region : Neuro sensory epithelium (Olfactory epithelium/Schneidarian membrane) Pharyngeal tonsil Opening of pharyngotympanic (Eustachian) tube Uvula Oropharynx(strat.squ.) Palatine tonsil Laryngopharynx (strat.squ.) Esophagus Trachea Nasal cavity Nasal conchae (superior, middle and inferior) Nasal meatuses (superior, middle, and inferior) Nostril Hard palate (palatine & maxillary) Soft palate (muscle) Tongue Lingual tonsil Hyoid bone Larynx Epiglottis Vestibular fold Thyroid cartilage Vocal fold Cricoid cartilage Thyroid gland Bronchus Diaphragm Cut end of rib Lung heart Epiglottis Larynx Trachea Pleural membranes Alveoli Pleural fluid Bronchiole Figure. Diagrammatic view of human respiratory system (Sectional view of the left lung is also shown)