Directions: In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as :
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If the assertion is true but the reason is false.
(d) If the assertion is false but the reason is true.
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Assertion: Vocal cords consist of three pairs of mucous membrane that extend into the lumen of the larynx.
Reason: Sound is produced by only one pair of vocal cords.
(d) Inside the larynx are present two pairs of vocal cords. One pair is of false vocal cords which is least related to sound production and the second inner pair is true vocal cords. When air is forced through the larynx, it causes vibration of the true vocal cords and sound is produced. The pitch of sound is determined by the tension on the vocal cords-greater the tension, higher the pitch.
Assertion: Tracheae, primary, secondary and tertiary bronchi are supported by incomplete cartilaginous rings.
Reason: These rings of cartilage make the wall noncollapsible.
(a) The trachea is the connection between the larynx to that of the bronchi of the lungs. It is also known as the windpipe. The trachea is connected to the primary, secondary as well as tertiary bronchi by incomplete, C shaped like structures which are known as the incomplete rings. They are made up of cartilaginous tissues and are non-collapsible in nature.
Assertion: The lungs are situated in thoracic chamber which is anatomically an air-tight chamber.
Reason: Such an arrangement is essential to avoid any change in pulmonary cavity.
(a) The anatomical setup of lungs in thorax is such that any change in the volume of the thoracic cavity will be reflected in the lung (pulmonary) cavity. Such an arrangement is essential for breathing, as we cannot directly alter the pulmonary volume.
Assertion: The abdominal muscles are primarily involved in generating pressure gradient between the lungs and the atmosphere.
Reason: Abdominal muscles play role in inspiration and expiration.
(d) The diaphragm and a specialised set of muscles-external and internal intercostals between the ribs, help in generating pressure gradient. Besides this, we can increase the strength of inspiration and expiration with the help of additional muscles in the abdomen.
Assertion: If two men, expire the same volume of air after normal inspiration, they have the same expiratory capacity.
Reason: Expiratory capacity includes tidal volume and inspiratory reserve volume.
(c) Expiratory capacity is the total volume of air a person can expire after a normal inspiration. This includes tidal volume and expiratory reserve volume (TV + ERV).
Assertion: Alveoli are the primary sites for exchange of gases.
Reason: All factors in our body are favourable for diffusion of \(\mathrm{O}_2\) from alveoli to tissues and that of \(\mathrm{CO}_2\) from tissues to alveoli.
(b) The solubility of the gases as well as the thickness of the membranes involved in diffusion are important factors that affect the rate of diffusion. A gradient of partial pressure is present for oxygen from alveoli to blood and blood to tissue. Similarly, a gradient of \(\mathrm{CO}_2\) is present in the opposite direction i.e., from tissues to blood and blood to alveoli. It is further dependent on the solubility of the diffusing gases. As the solubility of \(\mathrm{CO}_2\) is \(20-25\) times higher than that of \(\mathrm{O}_2\), the amount of \(\mathrm{CO}_2\) that can diffuse through the diffusion membrane per unit difference in partial pressure is much higher compared to that of \(O_2\). Therefore, all the factors in our body are favourable for diffusion of \(\mathrm{O}_2\) from alveoli to tissues and that of \(\mathrm{CO}_2\) from tissues to alveoli. Alveolus is the primary site of exchange as it has an extensive network of blood capillaries and consists of squamous epithelium. Due to very intimate contact of blood capillaries with the alveoli, the exchange of gases takes place easily.
Assertion: A sigmoid curve is obtained when percentage saturation of haemoglobin with \(\mathrm{O}_2\) is plotted against the \(\mathrm{pO}_2\)
Reason: Every \(100 \mathrm{~mL}\) of oxygenated blood can deliver around \(5 \mathrm{~mL}\) of \(\mathrm{O}_2\) to the tissues under normal physiological conditions.
(b) This clearly indicates that \(\mathrm{O}_2\) gets bound to haemoglobin in the lung surface and gets dissociated at the tissues. Every 100 ml of oxygenated blood can deliver around 5 ml of \(\mathrm{O}_2\) to the tissues under normal physiological conditions.
Assertion: A rise in \(\mathrm{pCO}_2, \mathrm{H}^{+}\)ions and temperature shifts the \(\mathrm{HbO}_2\) dissociation curve to right.
Reason: \(\mathrm{A}\) rise in \(\mathrm{pCO}_2\) or fall in \(\mathrm{pH}\) decreases oxygen affinity for haemoglobin.
(a)Â A shift to the right of oxygen dissociation curve indicates dissociation of oxygen from haemoglobin. In the tissues, low \(\mathrm{pO}_2\), high \(\mathrm{pCO}_2\), high \(\mathrm{H}^{+}\)concentration (low pH or acidity) and higher temperature favour dissociation of oxygen from the oxyhaemoglobin.
Assertion: At the tissue level, 70 percent of \(\mathrm{CO}_2\) formed from catabolism is trapped as bicarbonate in the RBCs.
Reason: At tissue level, carbonic anhydrase in RBCs facilitates the formation of \(\mathrm{CO}_2\) and \(\mathrm{H}_2 \mathrm{O}\) from bicarbonate.
(c) RBCs contain a very high concentration of carbonic anhydrase enzyme which facilitates the following reaction in both directions.
\(
\mathrm{CO}_2+\mathrm{H}_2 \mathrm{O} \stackrel{\begin{array}{l}
\text { carbonic } \\
\text { anhydrase }
\end{array}}{\rightleftarrows} \mathrm{H}_2 \mathrm{CO}_3 \stackrel{\begin{array}{l}
\text { carbonic } \\
\text { anhydrase }
\end{array}}{\rightleftarrows} \mathrm{HCO}_3^{-}+\mathrm{H}^{+}
\)
Assertion: Chloride shift is exchange of \(\mathrm{Cl}\) of plasma and \(\mathrm{HCO}_3^{-}\)of \(\mathrm{RBCS}\).
Reason: Chloride shift maintains an acid-base balance between the RBCs and plasma.
(b) Chloride shift is the movement of chloride ions (CI) into red blood cells. Carbon dioxide reacts with water to form carbonic acid in the red blood cells. The carbonic acid then dissociates into hydrogen carbonate ions \(\left(\mathrm{HCO}_3^{-}\right)\)and hydrogen ions \(\left(\mathrm{H}^{+}\right)\). The plasma membrane is relatively permeable to negative ions. Therefore, the hydrogencarbonate ions diffuse out of the cell into the plasma, leaving the hydrogen ions, which create a net positive charge; this is neutralised by the diffusion of chloride ions from the plasma into the cell.
Assertion: The role of oxygen in the regulation of respiratory rhythm is quite insignificant.
Reason: Increased \(\mathrm{pCO}_2\) and \(\mathrm{H}^{+}\)concentration inputs from chemoreceptors can activate respiratory rhythm centre to make necessary adjustments.
(a) A specialised centre present in the medulla region of the brain called respiratory rhythm centre is primarily responsible for
this regulation. Another centre present in the pons region of the brain called pneumotaxic centre can moderate the functions of the respiratory rhythm centre.
Assertion: Pneumotaxic centre, located in the medulla region of the brain, moderates the respiratory rhythm centre.
Reason: The dorsal respiratory group mainly causes inspiration.
(d) Neural signal from this centre can reduce the duration of inspiration and thereby alter the respiratory rate. A chemosensitive area is situated adjacent to the rhythm centre which is highly sensitive to \(\mathrm{CO}_2\) and hydrogen ions. Increase in these substances can activate this centre, which in turn can signal the rhythm centre to make necessary adjustments in the respiratory process by which these substances can be eliminated. Receptors associated with aortic arch and carotid artery also can recognise changes in \(\mathrm{CO}_2\) and \(\mathrm{H}^{+}\)concentration and send necessary signals to the rhythm centre for remedial actions. The role of oxygen in the regulation of respiratory rhythm is quite insignificant.
Assertion: Emphysema is the permanent abnormal inflation of air space of terminal bronchioles or alveolar sacs.
Reason: Destruction of pulmonary tissues specially alveolar septa and flattening of alveolar ducts occur in emphysema.
(b) Emphysema is a chronic disorder in which alveolar walls are damaged due to which respiratory surface is decreased. One of the major causes of this is cigarette smoking.
Assertion: Inspiration occurs when there is a negative pressure in the lungs with respect to the atmospheric pressure.
Reason: During inspiration, a decrease in pulmonary volume increases the intra-pulmonary pressure than atmospheric pressure which forces the air from outside to move into the lungs.
(c) The movement of air into and out of the lungs is carried out by creating a pressure gradient between the lungs and the atmosphere. Inspiration occurs when the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure, i.e., there is a negative pressure in the lungs with respect to atmospheric pressure.
Assertion: Asthma is a difficulty in breathing causing wheezing.
Reason: Asthma occurs due to inflammation of bronchi and bronchioles.
(a) Asthma is a difficulty in breathing causing wheezing due to inflammation of bronchi and bronchioles.
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