RESPIRATION IN ANIMALS -

Respiration is the process of oxidation of food within the cells and tissues to form CO2, water and ATP (energy). Energy is stored in the bonds formed between ADP and iP. When respiration occurs in presence of oxygen, it is called as Aerobic Respiration. When respiration occurs in absence of oxygen, it is called Anaerobic Respiration Animals take in oxygen and release CO2. 6.1 GASEOUS EXCHANGE IN ANIMALS :-   Main objective of respiration is to provide O2 tissues and remove CO2 from them. It occurs in different ways in different organisms like. 1 - Protozoans, Proiferans, Cnidarians respire through body surface. They take oxygen dissolved in water. 2 - Higher aquatic vertebrates like fishhave gilesfor exchange of gases. 3 - Terrestrial animals like amphibians, reptiles, birds, mammals have well developed lungsfor exchanging gases 4 - In Earthworms, respiration occurs by skin (body wall). Body wall surface is moist due to gland cells secretions and coelomic fluid. Body wall is richly supplied by blood which has respiratory pigment haemoglobin dissolved in it. Atmospheric O2 differs into blood and gets circulated in tissues. CO2 also diffuses out through body wall. 5 -   In Cockroach, respiratory organs are highly branched air tubes called Trancheaewhich cover the entire body cavity (Haemocoel). Each tracheae opens outside by an opening called ‘Spiracle’ or stigmata. Cockroach has 10 pairs of stigmata (2 pairs are thoracic and 8 pairs are abdominal). There are 3 longitudinal tracheal trunks which are interconnected by transverse tracheae. Main tracheae branches repeatedly into smaller tracheae - (Tracheoles). Each spiracle is surrounded by Scleritewhich extends inwords and opens into atrium(Tracheal chanber). Abdominal segment have tergo - sternal muscles which contract and relax rhythmically. This results in expansion and contraction of abdominal cavity. When it expands, air rushes in. when it contracts, air goes out. Gaseous exchange occurs between tissues and air present in the tracheses. 6.2- RESPIRATION IN HUMANS : Respiratory system in humans is formed of two parts : Respiratory Tract and B Respiratory organs. (A) Respiratory Tract : It is the passage way for fresh air to flow from outside into lungs. It consists of: 1 - External Nares (Nostrils) :- It is a pair of opening at the end of nosc just above the mouth. It opens into naslal chamber. 2 - Nasal Cavity :- It is divided into 2 nasal chambers. It helps in warming, filtering and moistening the air. 3 - Internal Naras :- Nasal chambers open into nasopharynx by internal nares. 4 - Pharynx :- It is short tube behind the buccal cavity. It has three parts - nasopharynx (upper part), oropharynx (middle part) and laryngopharynx (lower part). 5 -Larynx : (voice box) :- A small tybular part present in the neck. Serves as connection between pharynx and Trachea. Glottis guards the opening of larynx. 6 -Trachea :- (Wind pipe) :- It is tubular structure, 12 cms long and 2.5 cms in diameter. It goes downwards and divides into right and left primary bronchi in the middle of thoracic cavity. Primary bronchi enters into lungs, divide and redivide to form secondary and tertiary bronchi, bronchioles. Bronchioles subdivide into many alveolar ducts which lead into alveoli or air sac. (B) Respiratory Organs :- These are a pair of lungs lying in thoracic / pleural cavity. A double layered pleural membrane protects the lungs. Pleural fluid is filled in the space between the two pleural membranes. MACHANISM OF RESPIRATION :- It occurs in these steps :- 1. Breathing                          2. Exchange of O2 & CO2                 3. Transport of gases in the blood 1 - Breathing :- Breathing is Inspiration (intake of fresh air) and Expiration (expelling of foul air). The diaphragm, intercostals muscles and abdominal muscles play a role in this. When diapmagm muscles and  intercostals muscles contract sumuttareously, the volume of thoracic cavity increases. Thus pressure of air in the lungs decreases. The greater air pressure outside the body causes the air to flow in (Inspiration). When lungs contract, their volume decreases. So air pressure in the lungs increases. Hence air is exhaled from the lungs (Expiration).During exercise, breathing rate increases as more O2is required. TIDAL VOLUME (TV) :- It is the volume of air inspired and expired with every normal breath. It is about 500 ml in an adult person. INSPIRATORY RESERVE VOLUME (IRV) :- It is the extra amount of air that can be inspired forcibly after a normal inspiration. It is about 2500 - 3000 ml. EXPIRATORY RESERVE VOLUME (ERV) :-It is the extra amount of air that can be expired forcibly after a normal expiration. It is about 1000 ml of air. RESIDUAL VOLUME (RV) :- It is the volume of air which remains still in the lungs after the most forceful expiration. It is about 1500 ml. PULMONARY CAPACITIES :- When two or more above mentioned pulmonary volumes are considered together, such combinations are called Pulmonary capacities. INSPIRATORY CAPACITY (IC) :- It is the total volume of air that can be inhaled after a normal expiration. IC = TV + IRV IC is about 3000 - 3500 ml of air. FUNCTIONAL RESIDUAL CAPACITY (FRC) :- Amount of air that remains in the lung after normal expiration is called Functional Residual Capacity. It is about 2500 ml of air. FRC = ERV +RV VITAL CAPACITY (VC):- It is the maximum amount of air that can be expelled from the lungs by forced exhalation after a forced inhalation. VC ranges from 3400 - 4800 depending upon the age, sex and height of the individual. 2.Exchange of Gases :- 2and CO2 occurs in alveoli of lungs. O2 in alveoli has higher partial pressure than in blood flowing in lungs. So O2 diffuses from & alveoli into the blood. It passes into blood plasma and then combines with Haemoglobin of RBC to form Oxyhaemoglobin. CO2 in lung capillaries have higher partial pressure than alveoli. So CO2 diffuses from blood into alveoli after which it has to be expelled. Alveolar mambrane is also called ‘Respiratory Membrane’as it is very then and contains rich network of blood capillaries which remain in contact with inspired air. DIFFUSING CAPACITY :- The volume of gas that diffuses through respiratory membrane per minute for a pressure difference of 1 mm Hg. 3. Transport of Gases in blood :- Blood is the medium of transportation of O2 from lungs to tissues and CO2 from tissues to lungs. (a)Transport of Oxygen :- (i) As dissolved gas :- 3% of O2 in blood is dissolved in plasma which then carries it to body cells. (ii) As Oxy haemoglobin :- About 97% of O2 is carried in combination with Hb of RBC. 1 molecule of Hb can combine with 4 molecules of O2. Under high partial pressure, O2 binds with Hb in pulmonary capillaries. When this oxygenated blood reaches different tissues, the partial pressure of O2 declines, bonds between O2 and HB become unstable and O2 is released. Under normal conditions, opproximately 5 ml of O2 is transported by 100 ml of blood. The amount of O2 that can bind with Hb is determined by Oxygen tension, which is expressed as partial pressure (Po2).  At lower Po2, Oxygen is released from Hb. Haemoglobin would be completely free from O2 at zero Po2. this relationship is expressed by plotting the oxygen saturation of blood against Po2of oxygen. A S - shaped curve called ‘Oxygen - dissociation curve’ is obtained. It is dependent on Po2, Pco2, temperature and pH. (b)Transport of CO2 :- (i) As dissolved gas :- About 7% Co2 gets dissolved in blood plasma and is carried to the lungs. 0.3 ml of Co2 is transported per 100 ml of blood. (ii) As bicarbonate ions :- 70% Co2 reacts with H2O form carbonic acid in RBCs in presence of enzyme carbonic anhydrase. H 2CO3dissociates to form bicarbonate ions and H+ ions. Most of the HCo3- diffuse into blood plasma to be carried by it. (iii) As carbaminohaemoglobin :- About 23% of Co2 entering RBCs combine with - NH2 (amino) group of Hb to form carbamino - haemoglobin (HbCo2). Oxyhaemoglobin of RBC (HbO2) is acidic and remains associated with K+ ions. Thus forming KHbO2. H+ ions formed from dissociates from K+. Haemoglobinic acid (HHb) is formed. CHLORIDE SHIFT  /HAMBURGER SHIFT :- Exit of Hco3-  ionic balance between plasma and RBC. To maintain this ionic balance, chloride ions diffuse from plasma into RBC. This movement of Cl - ions is called as ‘Chloride Shift’ or ‘Hamburger Shift’. It was reported by Hamburger in 1918. RELEASE OF CO2 IN ALVEOLI OF LUNGS :- Deoxygenated blood reaches alveoli of lungs. It contains Co2 dissolved in plasma, as carbaninohaemoglobin and as Hco3- ions. Co2 is to be released in the lungs from these. - Co2 dissolved in plasma diffuses into alveoli. - Carbaminohaemoglobin splits into Co2 and Hb. - Oxyhaemoglobin donates H+ which joins with Hco3- to form H2Co3. H2Co3 then splits into H2O and CO2 in presence of enzyme carbonic anhydrase Co2 is released. 6.3 REGULATION OF RESPIRATION :-  Respiration is under dual control :- Nervous and chemical. (a)Nervous Control :- ‘Respiratory Centres’(group of neurons located in medulla oblongata of brain) control respiration. There are 3 respiratory centres :- 1 - Dorsal respiratory group :- located in dorsal portion of medulla oblongata. Signals from here are transmitted to diaphragm which helps in inspiration. 2 - Ventral respiratory group :- located in ventral portion o medulla oblogata. Remain inactive during normal respiration and become active only in enhanced respiration requirement. Signals from here control inspiration & expiration, both. 3 - Pneumotaxic centre :- located dorsally in upper pone. Controls the swithching off of inspiration. When this signal is strong, inspiration occurs for only 0.5 seconds and lungs are filled partially. When this signal is strong, inspiration occurs for only 0.5 seconds and lungs are filled partially. When this signal is weak, inspiration lasts for 5 seconds and lungs get fully filled. (b)Chemical control :- 1 - Co2 concentration :- Increase in Co2 conc. in blood increases the respiration rate. Co2 stimulates inspiratory as well as expiratory centres. 2 - O2 concentration :- Conc. of O2 doesn’t effect respiration directly. 6.4 RESPIRATORY DISORDERS :-1. BRONCHITIS :- It is the inflammation of bronchi which results in regular coughing and thick greenish yellow sputum. It occurs due to smoking or exposure to air pollutants like carbon monoxide. 2. BRONCHIAL ASTHMA :- It is caused by allergic reaction to foreign substances that effect respiratory tract. There are spasms of smooth muscles present in bronchiole wall. There is coughing and breathlessness. Exhaling is more difficult than inhaling. 3. EMPHYSEMA :- It is inflation / abnormal distension of bronchiole or alveolar sac which results in loss of elasticity of these parts. Lungs (Alveolar sac) remains filled with air even after expiration and so lung size increases. It occurs due to uigarette smoking or chronic bronchitis. 4. PNEUMONIA :-  In this, alveoli become acutely inflamed. Fluid and dead WBC accumulate in lung tissues. It occurs mainly due to infection of bacteria Streptococcus pneumonial 5. OCCUPATIONAL LUNG DISEASES :- It is caused due to exposure of potentially harmful gases, fumes or dust present in the environment where a person works. eg. Silicosis (exposure to silica), Asbestosis (exposure to asbestos dust in mining). In it, inflammation occurs due to fibrosis of upper part of lung.