Respiration Process and Mechanisms: Pulmonary, External, Internal, and Cellular, Study notes of Physiology

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Physiology of respiartion Chapter 2

PHYSIOLOGY OF RESPIRATION

Introduction : All the living organisms require energy to perform various activities of the life like growth, maintenance and reproduction. The food is the source of energy. The oxygen is essential to release the energy in the form of ATP from the food substances. In lower organisms, exchange of gases takes place through the diffusion mechanism. The respiratory system and Circulatory system plays an important role in supplying the oxygenated blood to the different parts of the body and also to eliminate the C0 2 from the body. i.e. it helps to regulate the pH of blood. The supply of energy in all living organisms is done through the intake of food. During respiration chemical energy trapped in the food is released in the form of ATP. It is utilized by the cells for their metabolic activities. Definition: The process in which an exchange of gases like 0 2 & C0 2 between the body and atmosphere (environment) is called respiration. OR The process of oxidation of food molecules to liberate the energy in the form of ATP molecules called respiration. Respiratory organs : Lower invertebrates like sponges, coelenterates, flat worms etc. exchange 02 and C02 by simple diffusion over their entire body surface. Earthworms use their moist cuticle and insects have tracheal tubes. Gills are used by most of the aquatic arthropods and molluscs where as lungs are used by the terrestrial forms. Among vertebrates fishes use gills where as reptiles, birds and mammals respire through lungs. Amphibians like frogs respire through lungs and also moist skin. Mammals have well developed respiratory system. Types of respiration: Respiration is classified into following three types. 1 Pulmonary respiration: The process in which, an exchange of gases like oxygen and carbon dioxide occurs between the atmosphere and lungs is called pulmonary ventilation. 2 External respiration: The process in which, an exchange of gases like 0 2 and C0 2 occurs between the lungs (alveoli) and blood is called external respiration.

cartilaginous lid called epiglottis. The epiglottis prevents the entry of food into the larynx while swallowing the food. Larynx (Voice Box or Sound Box) : It is a tubular structure connecting the pharynx and the trachea. The larynx is supported by nine cartilages. i.e., thyroid, arytenoid, cricoid, epiglottis etc. Thyroid cartilage is produced into a projection called Adam's apple which is more prominent in males. The larynx is also made up of vocal cords. The vibrations of the vocal cords to produce the sound. Hence the name voice box. The larynx leads to the trachea. Trachea ( wind pipe ) : The trachea is an elongated cylindrical tube, measures about 12cm in length and 2.5cm in diameter. It is located in front of the oesophagus. The wall of the trachea is made up of smooth muscles with elastic connective tissue. It is lined by the ciliated and mucous epithelial cells. The trachea is supported by the 16 to 20 C- shaped cartilaginous rings. The trachea is also involved in trapping the dust particles, bacteria which are removed from the body with the help of mucus and cilia. The trachea divides into two branches called primary bronchi. The right & left primary branchus enters into their respective lungs.

B. Respiratory part: It is meant for exchange of gases. It consists of lungs' primary, secondary, tertiary branchi, respiratory branchioles and alveoli. Bronchial tree : The lungs are enclosed by the numerous tubes from primary bronchi to the alveoli are called bronchial tree. The right primary bronchus on entering the lung divides into three secondary bronchi whereas left primary bronchus divided into two secondary bronchi. Secondary bronchi divide into tertiary bronchi which are supported by cartilaginous rings. The tertiary bronchi divide into bronchioles, terminal bronchiole. Each respiratory bronchiole further divides into 2 to 11 alveolar ducts. Each alveolar duct dilates into atria or infundibulum. Each atrium is made up of cup shaped smaller sacs called alveoli or air sacs. The alveoli are the terminal part of the respiratory passage. Lungs: Pair of lungs are the soft, spongy, elastic, conical structures located in the thoracic cavity on either side of the heart. The lungs are covered by the double layered membrane called pleura. Pleural membrane is made up of outer parietal pleura and inner visceral pleura. In between these two membranes there is a space called pleural cavity filled with pleural fluid. It acts as a lubricant and prevents friction. The right lung is broader than left lung. The right lung is differentiated into three lobes. i.e. anterior superior lobe , middle lobe and posterior inferior lobe, But the left lung is differentiated into two lobes, namely superior lobe & inferior lobe. Each Lung consists of air passages, alveoli, blood vessels, connective tissues and nerves. Diaphragm : The upper thoracic cavity and lower abdominal cavity are separated by the layer of muscle called diaphragm. It is a dome shaped structure present just below the lungs, made up of skeletal muscles. It separates the thoracic cavity from abdominal cavity. It plays an important role in breathing. Alveoli ( Air sacs ) : Each alveolar ducts opens into the sac like structure called alveole. Alveoli are the structural and functional unit of lungs. Alveoli are the sites of actual exchange of gases. Alveoli are lined by the simple squamous epithelium. In Man, both the

Inspiration diaphragm lowered Expiration diaphragm raised

Fig. 2.2 : Mechanism of Breathing

ii. Expiration : The process of exhalation of inhaled air from lungs to the surrounding atmosphere is called Expiration (The process of pushing the C0 2 out of the lungs is called expiration). Expiration is a passive process. Expiration occurs due to the relaxation of phrenic muscles and external intercostal muscles. During expiration diaphragm becomes dome-shape due to the relaxation of phrenic muscles. This decreases vertical dimension. Due to the relaxation of intercostal muscles, the ribs and the chest bone becomes original position. As a result the volume of the thoracic cavity decreases and increase in the intrapulmonary pressure upto 763mmHg. The intra pulmonary pressure is greater than atmospheric pressure. Therefore pushing of inhaled air out of the lungs. On an average a healthy human breaths 12-16 times/min. The volume of air involved in breathing movements can be estimated by using a spirometer. Table : Differences between Inspiration and Expiration

Sl.No Inspiration Sl.No Expiration 1 Process of taking of air into the respiratory system 1 Process of expelling air out of the system 2 Active process, as it involves muscle contraction. Active process since it involves contraction of muscles of thorax and abdomen. 2 Passive process as it involves relaxation of muscles. Passive process since it involves relaxation of thorax and abdomen. 3 Rib cage raised upwards and forwards 3 Rib cage depressed downwards. 4 Diaphragm flattens out or depressed 4 Diaphragm regains its dome shape. 5 Intrapleural pressure drops from 756 to 754 mmHg. 5 Intrapleural pressure restored to 756mmHg. (^6) Intrapulmonary pressure drops from 760 to 758 mmHg. (^6) Intrapulmonary pressure exceeds 760 mm Hg. (^7) Alveoli pulled towards rib cage 7 Alveoli compressed (^8) Atmospheric air rushes into the system. 8 Air expelled out of the system (^9) Inspired air contains about 20% 02 and 0.03 C0 2. (^9) Expired air contains about 16.4% of 0 2 and 4.0% C0 2.

2. External Respiration: It is a second step in the mechanism of respiration. The process of exchange of gases like O 2 and CO 2 between the lungs and blood is called External respiration. The partial pressure of oxygen (PO 2 ) in the alveolar air is 107mm Hg and that in the blood is 40mmHg. Due to this concentration gradient, oxygen diffuses from the alveoli of the lungs into the blood. The partial pressure of carbon dioxide (PCO 2 ) diffuses from the blood into the alveoli of the lings for further elimination.

and from there to heart for supply to various body parts. Partial pressure of oxygen in these blood vessels is 95mm of Hg. The partial pressure of carbon dioxide in alveolar air is about 40mm of Hg. Its partial pressure in capillary blood is 45 mm of Hg. Therefore carbon dioxide diffuses from blood into alveolar air. Blood passing out of the lungs carries PC02 equal to 40 mm of Hg. Gaseous exchange in tissues: Partial pressure of oxygen in blood is 95 mm of Hg that of interstitial fluid is 40 mm of Hg, while in cells it is around 23 mm of Hg. Therefore oxygen from blood first diffuses into interstitial fluid and from there to body cells. About 100 ml of oxygenated blood supplies about 5 ml of oxygen to tissues. PC0 2 at blood in tissue capillaries is 40 mm of Hg, that of interstitial fluid is 45 mm of Hg, while its value is 52 mm of Hg in body cells. Therefore carbon dioxide diffuses from body cells into interstitial fluid and from there to blood.

3. Transport of gases by the blood : The haemoglobin is the respiratory pigment, which is responsible for the transport of oxygen from lungs to the cells and the transport of carbon dioxide from cells to the lungs. When the gases like 02 and C02 enter into the lungs, certain physical & chemical changes occur in the blood. a) Transport of oxygen : The oxygen does not readily dissolve in water. Oxygen is carried in the blood in two ways, as physical solution and oxyhaemoglobin. i. As physical solution by plasma: About 3 - 4 % of oxygen dissolves in blood plasma and is carried as physical solution. ii. As Oxyhaemoglobin by RBC: 96 -97% of oxygen is carried by RBC in a chemical combination with haemoglobin. When oxygen enters into RBC, it combines with haemoglobin and forms oxyhaemoglobin. Each haemoglobin molecule contains four atoms of Iron. Each atom of Iron carries one molecule of oxygen. During the transport of oxygen, each molecule of

haemoglobin combines with 4 molecules of oxygen to form oxyhaemoglobin (Hb0 2 ). Hb + 0 2 Hb0 2 (oxyhaemoglobin) Oxyhaemoglobin is bright reddish in colour. Thus 4 molecules of oxygen is carried by the haemoglobin. Oxygenation: The process of the formation of oxyhaemoglobin by the fusion of oxygen and haemoglobin is called oxygenation. The 100ml of blood contains 15gm of haemoglobin. Thus 100ml of oxygenated blood carries about 20ml of oxygen. By the circulation of blood, the oxyhaemoglobin reaches the tissue cells, oxyhaemoglobin dissociates into oxygen and haemoglobin. Thus the released oxygen is utilized by the body cells for cellular respiration. Then the haemoglobin returns back to the lungs to repeat the process. The partial pressure of oxygen (P02) is very high in alveoli. Therefore lot of 02 binds with haemoglobin in the RBC. HbO 2 Hb + O 2 Oxygen dissociation curve: Oxygen dissociation curve is a graph showing the proportion of oxyhaemoglobin and oxygen pressure. Haemoglobin (Hb) can combine with oxygen (0 2 ) to form Oxyhaemoglobin (Hb0 2 ). Binding of oxygen with haemoglobin is primarily related to partial pressure of oxygen, partial pressure of carbon dioxide, hydrogen ion concentration and temperature. An "S" shaped sigmoid curve is obtained when percentage saturation of haemoglobin with oxygen is plotted against the partial pressure of oxygen. This curve is called Oxygen dissociation curve. In the alveoli where there is high POV low PC0 2 , lesser H+ concentration and lower temperature the factors are all favourable for the formation of Oxyhaemoglobin, where as in the tissue's low pop high PCOV high H + concentration and higher temperature are favourable for the dissociation of oxygen from Oxyhaemoglobin. Every 100ml of oxygenated blood can release 5ml of oxygen to the tissues under normal physiological conditions.

O 2 tension mm of Hg Fig. 2.5 : Dissociation curves showing Bohr effect. b). Transport of Carbon dioxide: The carbon dioxide is continuously produced within the body cells as a waste product of metabolism. It diffuses into the interstitial fluid and from there into blood. The C02 is transported from body cells (tissues) to the lungs by the blood. The carbon dioxide is transported in three forms, namely carbonic acid' carbaminohaemoglobin (carbomino compounds) and bicarbonates. i) Physical solution: About 7% of C0 2 dissolves in the plasma of blood, just as it gets dissolved in the water to from Carbonic acid and is carried to the lungs. On reaching the lungs it dissociates into C0 2 and water. C0 2 thus released diffuses into the alveoli lungs for further elimination. CO 2 + H 2 O H 2 CO 3 ii) As Carbamino compounds by the RBC's : About 20% - 25% of C0 2 combines with amino group of haemoglobin to form carbamino haemoglobin. On reaching the lungs it dissociates into haemoglobin and C0 2. C0 2 thus released diffuses into the alveoli of lungs for further elimination. HbNH 2 + CO 2 HbNHCOOH

iii)As Bicarbonates by the plasma : Remaining 70% of C0 2 from the plasma diffuse into RBCs. RBCs possess a zinc containing enzyme carbonic anhydrase It catalyses the reaction between water and C0 2 to produce carbonic acid. Carbonic acid dissociates to form hydrogen & bicarbonate ions. Carbonic anhydrase C0 2 + HP H 2 C0 3 ( Carbonic acid) H 2 CO 3 H +

• H C0 3 - Bicarbonate ion now passes out from RBCs while chloride ion from plasma passes into RBCs with the help of bicarbonate —chloride carrier protein located in membrane of RBCs. This phenomenon is called Chloride shift or Hamburger's phenomenon. Chloride ion combines with K +^ to form potassium chloride. In plasma, bicarbonate ion gets associated with Na +. K +^ + Cl -^ KCl H 2 CO 3 H +^ + HCO 3 ( bicarbonate) Na +
• HC0 3

- NaHC0 3 (sodium bicarbonate) K +

• HC0 3 - KHC0 3 (Potassium bicarbonate) Chloride shift (Hamberger phenomenon): Defintiton : The diffusion of chloride ions into the RBC form the plasma and back is called chloride shift. OR The outward movement of bicarbonate ions from RBC into the plasma and the inward movement of chloride ions from plasma into RBC is known as chloride shift. From the tissue cells C0 2 diffuses into the RBC via plasma. In the RBC, CO 2 combines with HP to form carbonic acid (H 2 C0 3 ). The H 2 C0 3 immediately ionizes into and bicarbonate ions (HCO 3 - ). Bicarbonate ions are negatively charged and they diffuse into the plasma from

Fig. 2.8 : Scheme of transportation of carbon dioxide (between RBC and alveoli) The C0 2 is carried by the RBC's towards the alveoli for the purification (oxygenation) of blood during that time reversible reaction takes place as shown in the figure.

4. Internal Respiration : The process in which an exchange of gases like O 2 and C0 2 between the blood and tissue cells called internal respiration. Internal respiration is the process in which exchange of gases (0 2 and C0 2 ) occurs between the blood and the tissues of the body. This process also depends on a pressure gradient. At the tissue level, cells have been producing carbon dioxide by oxidation, and have been using oxygen. Hence they have less oxygen (low P0 2 ) and more carbon dioxide (high PC0 2 ). The blood entering tissues has more oxygen (high P0 2 ) and less carbon dioxide (low PC0 2 ). The tissues are

separated from the blood by a thin film of interstitial fluid. Oxygen passes through the fluid and reaches the cells, after diffusing across their membranes.

5. Cellular Respiration (Oxidation) : It includes the various chemical changes takes place inside the cells leads to the production of energy in the form of ATP. Both external and internal respiration is accessory to what is actually occurring at the level of each cell of the body. This is where the oxygen is used to extract energy from the food. The oxygen that diffuses into the tissues is finally utilized in the aerobic breakdown of digested food materials to release energy. For example the glucose molecule in each cell is first metabolized to pyruvic acid and then with help of oxygen pyruvic acid is oxidised to carbon dioxide and water. During this process, hydrogen atoms combine with oxygen liberating most of the energy and it is stored in the form of ATP molecules. C 6 H 12 (^0) 6 oxygen 6C0 2 + + ATP (Energy) Details of aerobic respiration which involves Glycoloysis, Kreb's cycle and ETS have been described in chapter 14-Bioenergetics. Disorders of respiratory system (Respiratory disorders) Following are some of the important disorders of the respiratory system. 1.Rhinitis (Hay fever) : Inflammation of the nose or nasal tract caused by various allergens called hay fever. Causes : It is caused due to the allergic substances like dust, fungal spores, pollen grains etc. Certain weeds like Parthenium and Euphatorium also causes hay fever. Symptoms : Irritation of nose, sneezing, running nose, red watering eyes, nasal blockage, pharyngeal itching, etc. 2.Asthma : The asthma is a respiratory disorder characterized by the person suffering from difficulty in breathing due to the partial blockage of bronchi and bronchioles. It is more common in children than in adults. Causes : Allergies: The common allergens are dandruff pollen, dust, tobacco smoke.

Vital Capacity (VC) : The maximum volume of air a person can breathe in after a forced expiration. This includes ERV,TV and IRV or the maximum volume of air a person can breathe out after a forced inspiration. lt indicates the ability of a person to provide energy to the body for doing strenous work. It is higher in athletes and mountain dwellers. Young persons would possess more vital capacity as compared to children or older persons. Total Lung Capacity : Total volume of air accommodated in the lungs at the end of forced inspiration. This includes RV, ERV, TV, and IRV or vital capacity + residual volume. Atmospheric pressure : The pressure exerted by the surrounding air on the body is called atmospheric pressure. - 760mm Hg. Intra pulmonary pressure : The pressure exerted within the lungs is called intra pulmonic pressure. - [760mm Hg. i.e. Equivalent to the atmospheric pressure]. Intrapleural pressure (intra thoracic pressure) : The pressure exerted within the pleural space is called intra pleural pressure. It is 756mm Hg. and is lesser than intra pulmonary pressure. Two Mark Questions :

1. What is cellular respiration? 2. What is breathing? 3. What is internal respiration? 4. What is external respiration? 5. What are the phases of respiration? 6. Give an account of mechanism of expiration. 7. Distinguish between external and internal respiration. 8. What is Hamburger phenomenon? 9. Define chloride shift. 10. Mention two functions of nasal chambers. 11. Mention two function of larynx.

REVISION QUESTIONS

12. What is Adam's apple? 13. What is epiglotties? 14. What are the parts of the conducting system? 15. Name the parts of respiratory system. 16. What are alveoli? 17. What are pleurae? 18. Define pulmonary ventilation. 19. Define external respiration. 20. Define internal respiration. 21. Name the principal inspiratory muscles. 22. Why inspiration is considered as active and expiration as passive? 23. Define Bohr effect. 24. What is carbonic anhydrase? 25. What is rhinitis? 26. What is asthma? 27. What is bronchiogenic carcinoma? 28. What is name of the partition between thorax and abdomen? 29. Mention any four functions of nasal cavity. 30. What is spirometer? 31. Name the last part of the branchial tree. 32. Name the structural and functional unit of lung. 33. Name the muscles found between the ribs in man which are important in ventilating lungs.

34. How does the diaphragm help in inspiration? Five Mark Questions: 1. Draw a neat labeled diagram of human respiratory system. 2. Give an account of transport of C0 2 in the blood. 3. Write a note on a) Chloride shift b) Respiratory Quotient. 4. What is breathing? Explain the mechanism of breathing in man.