Biology Notes 2024-2025 PDF (M.E.S Indian School)

M.E.S INDIAN SCHOOL, DOHA - QATAR NOTES 2024- 2025 Section: BOYS’ AND GIRLS’ Date :18:06:2024 Class & Div.: XI (ALL DIVISIONS) Subject :BIOLOGY Lesson: CH.17:...

M.E.S INDIAN SCHOOL, DOHA - QATAR NOTES 2024- 2025 Section: BOYS’ AND GIRLS’ Date :18:06:2024 Class & Div.: XI (ALL DIVISIONS) Subject :BIOLOGY Lesson: CH.17: BREATHING AND EXCHANGE OF GASES xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx BREATHING AND EXCHANGE OF GASES The process of exchange of O2 from the atmosphere with CO2 produced by the cells is called breathing, commonly known as respiration. Respiratory organs in different animals Invertebrates like sponges, coelenterates, earthworms by simple diffusion through body surface. (Cutaneous respiration) Insects - Tracheal tubes Aquatic mollusks and fishes - Gills Aquatic mollusks and arthropods - book Lungs Amphibians - Skin , Lungs Reptiles, Birds, and mammals - Lungs HUMAN RESPIRATORY SYSTEM External nostrils Nasal cavity Nasopharynx Larynx Conducting part Trachea Bronchi Bronchioles F 061, Rev 01, dtd 10th March 2020 1  Terminal bronchioles Alveolar duct Exchange part Alveoli  Nasopharynx - a portion of pharynx. Larynx- (sound box) - a cartilaginous box which helps in sound production Glottis - Opening of the larynx Epiglottis - the lid which guards the opening of larynx (glottis).It prevent the entry of food into the larynx. Trachea – a straight tube Bronchus-divides into right and left primary bronchi and then branches out into bronchioles. The tracheae, primary, secondary and tertiary bronchi, are supported by C shaped cartilaginous rings Alveoli- thin bag like structures into which terminal bronchiole ends. bronchi, bronchioles and alveoli comprise the lungs. Conducting part-transports the atmospheric air to the alveoli, Exchange part- alveoli and their ducts-Here diffusion of O2 and CO2 takes place. The lungs Pleura- A double layered covering of lungs- a fluid in between -called pleural fluid. It reduces friction on the lung surface. Situated in the thoracic chamber an air-tight chamber. The thoracic chamber is formed dorsally by the vertebral column, ventrally by the sternum, laterally by the ribs and on the lower side by the dome- shaped diaphragm. Any change in the volume of the thoracic cavity will be reflected in the lung (pulmonary) cavity. F 061, Rev 01, dtd 10th March 2020 2  Steps of respiration 1. Breathing by which atmospheric air is drawn in and CO2 rich alveolar air is released out. 2. Diffusion of gases (O2 and CO2) across alveolar membrane. 3. Transport of gases by the blood. 4. Diffusion of O2 and CO2 between blood and tissues 5. Utilization of O2 by the cells and resultant release of CO2 (cellular respiration). MECHANISM OF BREATHING Inspiration- Atmospheric air is drawn in Occurs passively when intra pulmonary pressure is less than atmospheric pressure. 1. Intercostal muscles contract. 2. Lift up the ribs and sternum. 3. Diaphragm contracts and flattens. 4. Volume of thoracic cavity increases. 5. As the volume increases, air pressure decreases. EXPIRATION (Breathing out) Occurs when intra pulmonary pressure is higher than atmospheric pressure. 1. Intercostal muscles relax. 2. Ribs move downwards. 3. Diaphragm relaxes and arches upward. 4. Volume of thorax decreases. 5. Air pressure in thorax increases.  On an average, a healthy human breathes 12-16 times/minute.  The volume of air involved in breathing movements can be estimated by using a spirometer. 3 F 061, Rev 01, dtd 10th March 2020  RESPIRATORY VOLUMES 1. TIDAL VOLUME (TV) Volume of air inspired or expired during a normal respiration. It is approx. 500 ml. i.e., a healthy man can inspire or expire approximately 6000 to 8000 ml of air per minute. 2. INSPIRATORY RESERVE VOLUME (IRV) Additional volume of air, a person can inspire by a forcible inspiration. This averages 2500 ml to 3000 ml. 3. EXPIRATORY RESERVE VOLUME (ERV) Additional volume of air, a person can expire by a forcible expiration. This averages 1000 ml to 1100 ml. 4. RESIDUAL VOLUME (RV) Volume of air remaining in the lungs even after a forcible expiration. This averages 1100 ml to 1200 ml. PULMONARY CAPACITIES 5. INSPIRATORY CAPACITY (IC) Total volume of air a person can inspire after a normal expiration. This includes tidal volume & inspiratory reserve volume (TV+IRV). 6. EXPIRATORY CAPACITY (EC) Total volume of air a person can expire after a normal inspiration. This includes tidal volume and expiratory reserve volume (TV+ERV). 7. FUNCTIONAL RESIDUAL CAPACITY (FRC) Volume of air that will remain in the lungs after a normal expiration. This includes ERV+RV. 4 F 061, Rev 01, dtd 10th March 2020  8. VITAL CAPACITY (VC) The maximum volume of air a person can breathe in after a forced expiration. V C includes ERV, TV and IRV or the maximum volume of air a person can breathe out after a forced inspiration.(ERV+TV+IRV) 9. TOTAL LUNG CAPACITY Total volume of air accommodated in the lungs at the end of a forced inspiration. This includes RV, ERV, TV and IRV or vital capacity + residual volume. (RV+ERV+TV+IRV+RV) or (VC + RV) EXCHANGE OF GASES Occurs in Alveoli and also between blood and tissues. Mechanism Simple Diffusion based on pressure gradient Factors that can affect the rate of diffusion of gases 1. Partial pressure of gases 2. Solubility of the gases 3. Thickness of the membranes involved in diffusion. 4. Surface area of respiratory membrane (lungs). Partial pressure- Pressure of an individual gas in a mixture of gases is called partial pressure. Partial pressure of oxygen is represented as pO2 and of carbon dioxide as pCO2.The diffusion membrane is made up of three major layers. 1. Squamous epithelium of alveoli, 2. The endothelium of alveolar capillaries 3. The basement substance in between them. Its total thickness is much less than a millimeter. 5 F 061, Rev 01, dtd 10th March 2020  TRANSPORT OF GASES Transport of oxygen 3 % is carried in a dissolved state through the plasma. 97 % of O2 is transported by RBC (binding with Hb) O2 can bind with hemoglobin to form oxyhemoglobin. Each Hb molecule can carry a maximum of 4 molecules of O2. Factors affecting the binding of oxygen with Hb 1. Partial pressure of O2. 2. Partial pressure of CO2, 3. Hydrogen ion concentration 4. Temperature OXYGEN DISSOCIATION CURVE A sigmoid curve is obtained when percentage saturation of hemoglobin with O2 is plotted against the pO2. This curve is called the Oxygen dissociation curve. It is highly useful in studying the effect of factors like pCO2, H+ concentration, etc., on binding of O2 with hemoglobin. In the alveoli - High pO2 low pCO2 lesser H+ concentration and lower temperature. This leads to the formation of oxyhemoglobin. In the tissues - low pO2, high pCO2 , high H+ concentration and higher temperature. This leads to the dissociation of oxygen from the oxyhemoglobin O2 gets bound to hemoglobin in the lung surface and gets dissociated at the tissues. Every 100 ml of oxygenated blood can deliver around 5 ml of O2 to the tissues under normal physiological conditions. TRANSPORT OF CARBON DIOXIDE 1. 25 % by RBCs. as carbamino hemoglobin 2. 70 % of it is carried as bicarbonate. 6 F 061, Rev 01, dtd 10th March 2020  3. 7 % in a dissolved state through plasma.(As carbonic acid) 1. As carbamino hemoglobin (25%) Depends on the partial pressure of CO2. pCO2 is high and pO2 is low as in the tissues --binding of carbon dioxide occurs pCO2 is low and pO2 is high as in the alveoli--dissociation of CO2 from carbamino- hemoglobin, i.e., CO2 bound to hemoglobin from the tissues is delivered at the alveoli. 2. As bicarbonate RBCs contain an enzyme, carbonic anhydrase. At tissue site ,it facilitates the following reaction. 𝑪𝒂𝒓𝒃𝒐𝒏𝒊𝒄 𝒂𝒏𝒉𝒚𝒅𝒓𝒂𝒔𝒆 𝑪𝒂𝒓𝒃𝒐𝒏𝒊𝒄 𝒂𝒏𝒉𝒚𝒅𝒓𝒂𝒔𝒆 CO2 + H2O ⇔ H2CO3 ⇔ HCO3- +H+ In tissue pCO2 is high, CO2 diffuses into RBC and dissociates into HCO3 – & H+. In alveoli where pCO2 is low, the reaction proceeds in the opposite direction leading to the formation of CO2 and H2O. Thus, CO2 trapped as bicarbonate at the tissue level and transported to the alveoli is released out as CO2. 3. As Carbonic acid About 7 per cent of CO2 is carried in a dissolved state through plasma. CO2 + H2O → H2CO3 Every 100 ml of deoxygenated blood delivers approximately 4 ml of CO2 to the alveoli. REGULATION OF RESPIRATION respiratory rhythm centre –present in medulla of the brain-controls respiration pneumotaxic centre -present in the pons of the brain - moderate the functions of the respiratory rhythm centre. Reduces the duration of inspiration and thereby alter the respiratory rate. A chemosensitive area is situated adjacent to the rhythm centre which is highly sensitive Increase in CO2 activates this centre- signal the rhythm centre to start expiration in the process by which these substances can be eliminated. Receptors associated with aortic arch and carotid artery also can recognize changes in CO2 and H+ 7 F 061, Rev 01, dtd 10th March 2020  concentration and send necessary signals to the rhythm centre for remedial actions. DISORDERS OF RESPIRATORY SYSTEM 1. ASTHMA-Difficulty in breathing ,wheezing due to inflammation of bronchi &bronchioles 2. EMPHYSEMA-Chronic disorder in which alveolar walls are damaged due to which respiratory surface is decreased. Major cause of this is cigarette smoking. 3. OCCUPATIONAL RESPIRATORY DISORDERS In certain industries, like involving grinding or stone-breaking, so much dust is produced that the defence mechanism of the body cannot fully cope with the situation. Long exposure leads to inflammation and fibrosis (proliferation of fibrous tissues) Workers in such industries should wear protective masks. Eg :- Silicosis, Asbetosis -------------THE END------------- 8 F 061, Rev 01, dtd 10th March 2020