The diaphragm and a specialised set of external and intercostals muscles between the ribs, help in the generation of pressure gradient during normal respiration.

Carbon dioxide is carried by the blood in three forms

(i) In Dissolved State Under normal temperature and pressure, about $7 \%$ of $\mathrm{CO}_2$ is carried by physical solution.

(ii) As Carbamino Compounds $\mathrm{CO}_2$ binds directly with Hb to form an unstable compound carbaminocompounds $\left(\mathrm{CO}_2 \mathrm{Hb}\right)$ About $23 \% \mathrm{CO}_2$ is transported in this form. When $\mathrm{pCO}_2$ is high and $\mathrm{pO}_2$ is low as in the tissues, more binding of carbon-dioxide occurs whereas, when $p \mathrm{CO}_2$ is low and $p \mathrm{O}_2$ is high as in alveol as tissue dissociation of $\mathrm{CO}_2$ from carbamino-haemoglobin takes place.

$$\mathrm{HbO}_2+\mathrm{CO}_2 \rightleftharpoons \mathrm{HbCO}_2+\mathrm{H}^{+}+\mathrm{O}_2$$

(iii) As Bicarbonate Ions $\mathrm{CO}_2$ reacts with water to form carbonic acid $\left(\mathrm{H}_2 \mathrm{CO}_3\right)$ in the presence of carbonic anhydrase in RBC. $\mathrm{H}_2 \mathrm{CO}_3$ dissociates into hydrogen and bicarbonate ions ( $\mathrm{HCO}_3{ }^{-}$).

The whole reaction proceeds as follows

$\mathrm{CO}_2+\mathrm{H}_2 \mathrm{O} \underset{\text { Anhydrase }}{\stackrel{\text { Carbonic }}{\rightleftharpoons}} \underset{\text { Carbonic acid }}{\mathrm{H}_2 \mathrm{CO}_3}$

$\underset{\text { Carbonic acid }}{\mathrm{H}_2 \mathrm{CO}_3} \rightleftharpoons \underset{\substack{\text { Hydrogen } \\ \text { ion }}}{\mathrm{H}^{+}}+\underset{\substack{\text { Bicarbonate } \\ \text { ion }}}{\mathrm{HCO}_3^{-}}$

The carbonic anhydrase reaction mainly occur in RBC as it contain high concentration of enzyme carbonic anhydrase and minute quantity of it is present in plasma too.

As, the solubility rate of $\mathrm{CO}_2$ is 20-25 times higher than that of the $\mathrm{O}_2$, 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 $\mathrm{O}_2$.

(d) Pulmonary ventilation by which atmospheric air is drawn in and $\mathrm{CO}_2$ rich alveolar air is released out.

(a) Diffusion of gases $\left(\mathrm{O}_2\right.$ and $\left.\mathrm{CO}_2\right)$ across alveolar membrane.

(b) Transport of gases by blood.

(c) Diffusion of $\mathrm{O}_2$ and $\mathrm{CO}_2$ between blood and tissues.

(e) Utilisation of $\mathrm{O}_2$ by the cells for catabolic reactions and resultant release of $\mathrm{CO}_2$.

Difference between these are as follows

(a)	Inspiratory Reserve Volume	Expiratory Reserve Volume
	It is the additional volume of air, a person can inspire by a forcible inspiration. It ranges between 2500 mL to 3000 mL .	It is the additional volume of air a person can expire by a forcible expiration. It ranges between 1000 mL to 1100 mL .
(b)	Vital Capacity	Total Lung Capacity
	Vital capacity is the maximum volume of air that 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. i.e., $\mathrm{Vc}=\mathrm{ERV}+\mathrm{IRV}+\mathrm{TV}$	Total using capacity is the total volume of air accommodated in the lungs at the end of a forced inspiration. This includes RV, ERV, TV and IRV or vital capacity + residual volume. i.e., $\mathrm{TLC}=\mathrm{RV}+(\mathrm{ERV}+\mathrm{IRV}+\mathrm{TV})$ or $\mathrm{VC}+\mathrm{RV}$
(c)	Emphysema	Occupational Respiratory Disorder
	Emphysema is a chronic disorder of respiratory system, in which alveolar cells are damaged due to which regulatory respiratory surface is decreased. Cause of emphysema is cigarette smoking.	It is caused due to the long exposure of dust produced by stone grinding or breaking and give rise to inflammation leading to fibrosis and thus causing serious lung damage. Protective masks are provided for the workers in such industries.