cH-17|Breathing and Exchange of Gases
Chapter-17
Breathing and Exchange of Gases
Points to Remember
Breathing : (External respiration) The process of exchnage of O2 from the atmoshphere with CO2 produced by the cells.
Carbamino haemoglobin : Compound formed in RBCs where CO2 combine with haemoglobin.
Inspiration : Oxygen from fresh air taken in by lungs and diffused into the blood.
Expiration : CO2 given up by venoua blood in the lungs is sent out to exterior.
Respiration : The sum total of physical and chemical processes by which oxygen and carbohydrates (main food nutrient) etc are assimilated into the system and the oxidation products like carbon dioxide anf water are given off.
Diaphragm : A muscular, membranous partition scparating the thoracic cavity from the abdominal cavity.
Hypoxia -- Dhortage oxygen in tissues.
Partial Pressure -- The pressure contibuted by an imdividual gas in a micture of gases. It is represented as pO2 for oxygen pCO2 for carbondioxide.
Pharynx : The tube or cavity which connects the mouth and nasal.passages with oesophagus. It is has three parts (i) Nasopharynx (anterior part) (ii) Oropharynx (moddld part) and (iii) Lafyngopharynx (posterior part which continues to larynx).
Adam's Apple : The projection formed by the thyroid cartilage and surrounds thd larynx at thd front of the neck.
Tidal Volume (TV) : Volume of air taken in/given out during normal respiration (500 mL).
Inspirayory Reserve Volume (IRV) : Additional volume of air, a person can expire by a forecible expiration.
Residual Volume (RV) : Volume of air remaining in the lungs even after aforcible expiration (1100 mL to 1200 mL.)
PULMONARY CAPACITIES : Use in clinical diagnosis.
Inspiratory Capacity (IC) = (TB + IRV) Total volume of air a person can inspire after a normal expiration.
Expiratory Capacity -- Total Volume of air a parson can after a normal inspiration E.C = TV + ERV.
Functional Residual Capacity -- Volume of air that will remaim in lungs after a normal expiration (FRC) = (ERV + RV)
Vital Capacity : (VC) = (ERV + TV + IRV) or the maximum volume of air a person can breath out after a forced inspiration.
Total Long Capacity : It includes RV, ERV, TB and IRV or vital capacity + residual volume.
Pulmonary -- Anything associated with the lungs is given the prefix 'pulmonary'.
Steps involved in respiration -
(i) Breathing ot pulmonary ventilation (intake of atmospheric air and releasing out CO2 rich alveolar air)
(ii) Diffusion of gases (O2 and CO2) across alveolar membrane & blood vessel (capillaries).
(iii) Transport of gases by thd blood.
(iv) Diffusion of O2 and CO2 between bloof and tissues.
(v) Utilisation of O2 by the cells for catabolic reactions and resultant release of CO2
Mechanism of breathing showing (a) Inspiration (b) Expiration.
Respiratory Tract :
A pair of external nostrils → nasal chamber through nasal passage → pharynx → glottis → larynx → trachea → Left and right primary bronchi → secondary and tertiary bronchi → bronchioles → vascularised bag like structures (alveoli) or air-sacs. Each lung is covered with double layered membrane known as pleura with pleural fluid between them.
Respiratory Organs in Animals :
(i) Protozoans, annelid Frogs -- Body Surface
(ii) Fishes, tadpole stage of frog and many other aquatic animals -- Gills (Branchial Respiration)
(iii) Insects and a few other arthopods -- Tracheal tubes
(iv) All land vertebrates (amphibians, reptiles, aves and mammal) -- Lungs, (Pulmonary Respiration)
Conditions required for (cutaneous respiration) :
Skin should be moist and thin. It should be highly vascularised.
Physiology of Respiration :
(a) Exchange of gases -- Diffusion of gases takes place from the region of higher partial pressure to lower (lesser) partial (pressure).
(i) pO2 in alveolar air = 104 mm Hg.
(ii) pO2 in venous blood = 40 mm Hg.
O2 diffuses from alveoli to venous blood.
(iii) pCO2 in venous blood = 45 mm Hg.
pCO2 in alveolar air = 40 mm
pCO2 diffuses from venous blood to alveoli
(b) Transport of O2 by the blood --
(i) About 3% of O2 in dissolved state through plasma.
(ii) As oxyhaemoglobin : 97% of O2 diffuses from plasma into RBCs. Haemoglobin carrt 1-4 molecules of O2.
LUNGS Hb4 O8
-------->
Hb4 + 4O2 Oxyhaemoglobin
<--------
TISSUE
Oxygen dissociation curve
- A Sigmoid curve showing relationship between the % of saturation of haemoglobin with oxygen in blood and pO2 of the blood.
- Fully saturated each of haemoglobin combines with nearly 1.34 ml of oxygen.
- H+ concn..., CO2 tension, temperature affect the curve. Increase in their concentration decreases the affinity of haemoglobin for oxygen.
(c) Transport of Co2
(i) As solution - 7% of CO2 dissolves an carried by the plasma.
(ii) As Bicarbonate - 70% of CO2 in RBCs combines with water form carbonic acid. Carbonic acid dissociates inot bicarbonate ions and H+, Carbonic anhydrase enzymes help in these reactions.
Carbonic Carbonic
--------> -------->
CO2 + H2O H2CO3 <-------- HCO-3 + H+
<-------- anhydrase
anhydrase
(iii) As carbaminohaeoglobin - 23% CO2 combines in RBC with amino group of haemoglobin, from carbaminohaeoglobin.
Regulation of Respiration :
- Respiratory rhythm centre in medulla of brain responsible for this regulation.
- Pneumotaxic center in pons region moderates function of respiratory rhythm centre.
- Chemosensitive area adjacent to rhythm centre is highly sensitive to CO2 and H+ ions.
- Increase in CO2 and H+ ions activates this centre, which in turn signal the rhythm centre to make necessary adjustments and respiratory process by which these substances can be eliminated.
Disorders of Respiratory System :
- Emphysema - chronic disorder in which alveolar walls damaged due to cigarette smoking.
- Asthma - difficulty in breathing due to inflammation of bronchi or bronchioles.
- Occupational disorder - people working in stone grinding or breaking industries, the dust produced damage the defence system of body leading to servere lung damage.
