CLASS 11TH BIOLOGY CHAPTER- 17 BREATHING AND EXCHANGE OF GASES NCERT QUICK REVISION NOTES FOR NEET AND CBSE EXAM
BREATHING AND EXCHANGEOF GASES
¶ Carbamino haemoglobin: Compound formed in RBCs when CO2 combine with haemoglobin.
¶ Inspiration : Oxygen from fresh air taken by lungs and diffuses into the blood.
¶ Expiration : CO2 given up by venous 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 and water are given off.
¶ Diaphragm : A muscular, membranous partition separating the thoracic cavity from the abdominal cavity.
¶ Hypoxia - Shortage of oxygen in tissues.
¶ Partial Pressure - The pressure contributed by an individual gas in a mixture of gases. It is represented as pO2 for oxygen and pCO2 for carbondioxide.
¶ Pharynx: The tube or cavity which connects the mouth and nasal passages with oesophagus.
It has three parts
(i) Nasopharynx (anterior part)
(ii) Oropharynx (middle part)
(iii) Laryngopharynx (posterior part which continues to larynx)
¶ Adam's Apple: The projection formed by the thyroid cartilage and surrounds the larynx at the front of the neck.
¶ Tidal volume (TV): volume of air during normal respiration (500 ml.)
¶ Inspiratory Reserve Volume (IRV): Additional volume of air inspired by a forcible inspiration. 2500mL to 3000mL.
¶ Expiratory Reserve Volume (ERV): Additional volume of air, a person can expire by a forcible expiration. (RV) volume of air remaining in the lungs even after a forcible expiration (1100 mL to 1200 mL).
PULMONARY CAPACITIES: Use in clinical diagnosis.
¶ Inspiratory capacity - (IC)= (TV+IRV) Total volume of air a person can inspire after a normal expiration.
¶ Expiratory Capacity-Total Volume of air a parson can expire after a normal Inspiration E.C. = TV + ERV ¶ Functional Residual Capacity-Volume of air that will remain 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 Lung Capacity: It includes RV, ERV, TV and IRV or vital capacity + residual volume.
¶ Pulmonary-Anything associated with the lungs is given the prefix 'pulmonary'
steps involved in respiration
(i) Breathing or pulmonary ventilation (intake or atmospheric air and releasing out CO2 rich alveolar air)
(ii) Diffusion of gases (O2 and CO2) across alveolar membrane.
(iii) Transport of gases by the blood.
(iv) Diffusion of O2 and CO2 between blood and tissues.
(v) Utilisation of O2 by the cells for catabolic reactions and resultant release of CO2.
MECHANISM OF BREATHING
Inspiration:
If the pressure within the lungs (intrapulmonary pressure) is less than the atmospheric pressure, i.e., there is negative pressure in the lungs with respect to the atmospheric pressure.
¶ The contraction of diagphragm increases the volume of thoracic chamber in the antero-posterior axis.
¶ The contraction of external intercoastals muscles lifts up the ribs and the sternum causing an increase in the volume of thoracic chamber in the dorso ventral axis.
¶ It causes an increase in pulmonary volume decrease the intra-pulmonary pressure to less than the atmospheric pressure.
¶ If forces the air out side to move in to the lungs, i.e., inspiration.
Expiration :
Relexation of diaphragm and sternum to their normal positions and reduce the thoracic and pulmonary volume.
¶ It increases in intrapulmonary pressure slightly above the atmospheric pressure.
¶ It causes the expulsion of air from the lungs, i.e., expiration.
Mechanism of breathing showing
(a) Inspiration:
Contraction of diaphragm and external intercostal muscles → Increase in the volume of thoracic chamber → Lungs expand → Pressure inside the lungs fall → Air rushes in
(b) Expiration:
Relaxation of diaphragm and sternum → Decrease in the volume of thoracic chamber → Lungs contract → Pressure inside the lings increase → Air rushes out.
RESPIRATORY TRACT:
A pair of external nostrils → nasal chamber through nasal passage → nasopharynx → 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, annelids Frogs-Body surface
(ii) Fishes, tadpole stage of frog and many other aquatic animals-Gills
(iii) Insects and a few other arthropods-Tracheal tubes
(iv) All land vertebrates (amphibians, reptiles, aves and mammal)-Lungs.
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 Hg.
CO2 diffuses from venous blood to alveoli.
potassium (KHCO2).
REGULATION OF RESPIRATION:
A specialised centre in medulla of brain controls the respiratory rhythm. Another region in the pons region of the brain called pneumotaxic centre can moderate the functions of respiratory rhythm centre. Neural signal from pneumotaxic centre can reduce the duration of respiration thereby increasing the respiratory rate. Chemosensitive area present near the rhythm centre, aortic arch can sense the change in CO₂ & Ht concentration, which in turn send signal to rhythm centre to make necessary adjustment so that those substances can be eliminated.
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