Explore topic-wise InterviewSolutions in Current Affairs.

(i) Lungs provide very large surface area for the exchange of gases. Total alveolar surface area is nearly 100 m² whereas total surface area of skin is around 1.6 m² only. 

(ii) Alveoli are lined by thin highly permeable membranous wall. These are surrounded by many blood capillaries. 

(iii) Endothelium of blood capillaries and membranous walls of alveoli are highly permeable to respiratory gases.

Pleuron. It reduces the friction and keeps the two pleura together and the lungs inflated.

The movement is facilitated by the creation of pressure gradient between the lungs and the atmosphere.

Exchange of gases occurs in lung alveoli and tissue cells.

Respiration by lungs is termed as pulmonary respiration.

Cutaneous respiration – Exchange of respiratory gases through the thin, moist, permeable and highly vascularised skin. 

Buccopharyngeal respiration – Exchange of respiratory gases through thin, vascular lining of buccopharyngeal cavity. In frog 

Branchial respiration – Exchange of respiratory gases in gills. 

Pulmonary respiration – Exchange of gases through lungs. 

The answer is: Pleura.

The process of exchange of O₂ from the atmosphere with CO₂ produced by the cells is called breathing.

On mountain-tops about 8000 ft. above from the sea level, one has difficulty in breathing due to considerable decrease in the oxygen in the air. Consequently, the alveolar pO₂ reduces and oxygen cannot be diffused into the blood. Thus, the process of oxygenation of blood progressively gets decreased to such an extent that the person develops mountain sickness. It produces a number of symptoms like breathlessness, headache, dizziness, nausea, vomiting and a bluishness of skin, nails and lips. This is because of lack of adequate oxygen. People suffering from heart ailment or blood pressure should not go to such a height.

Sound is produced by the vocal cords. When expired air is passed through the true vocal cords under pressure from the lungs, the vocal cords are set into vibration which results in the production of sound. 

Factors: The pitch of a sound is determined by the tension on the vocal cords-the greater the tension, the higher the pitch. The quality of voice depends on the resonators above the larynx, namely the pharynx, mouth and paranasal sinuses.

Based on the absence or presence of oxygen, respiration is of two types-anaerobic and aerobic respiration.

Anaerobic respiration also occurs in some tissues of aerobically respiring animals, as they do not get the required supply of oxygen at that time. Skeletal muscles produce lactic acid from glucose during vigorous exercise, because they do not immediately get as much oxygen as it is necessary for their work. This results in muscular pain.

The part of the respiratory system starting with the external nostrils upto the terminal bronchioles constitutes the conducting part.

Respiration is controlled by a respiratory centre located in the floor of the medulla oblongata of the brain. The centre is bilateral and its two halves are connected together by commissural neurons. The sides of this centre are connected with motor respiratory neurons. The nerve cells of the centre are connected with the breathing apparatus forming a reflex arc. These nerve cells are sensitive to chemical composition of blood. Half of the respiratory centre is an inspiratory centre and the other half is an expiratory centre. These two centres control the entire breathing in man with his knowledge about it. Dorsal respiratory group, ventral respiratory group and pneumotaxic groups act as respiratory centres in the brain.

(i) Persons who have stopped breathing may be subjected to artificial respiration. 

(ii) Most common method of artificial respiration is mouth to mouth breathing. 

(iii) In this method, the operator lifts the patients neck by placing a hand below it. The operator then closes the nostrils of the patient with fingers. The operator keeps his own mouth in front of patient's mouth and blows air into the mouth of the patient, then he releases the patients mouth to allow expiration by his lungs. 

(iv) This procedure should be repeated 10-15 times per minute.

CO₂ in the plasma is absorbed by RBC as a physical solution. It is transported as carbonic acid, bicarbonates and carbonic haemoglobin. It is then carried to the heart and from there it is taken to the pulmonary artery and then to the lungs. Dissociation takes place in the alveoli and the CO₂ is finally, exhaled through the nostrils.

(i) The contraction of the external intercostal muscles and diaphragm increases the volume of the thoracic cavity and lowers the pressure in the lungs. 

(ii) To fill up this gap, the fresh air rushes to the lungs resulting in the inspiration. 

(iii) The relaxation of the diaphragm and the intercostal muscles returns the diaphragm and sternum to their normal positions and decreases the volume of the thoracic cavity and subsequently, pressure in the lungs increases. 

(iv) To equalise this pressure, the air from the lungs rushes out through the respiratory passage to bring out expiration.

(a) Inspiratory Reserve volume (IRV) is an additional volume of air a person can inspire by a forcible inspiration. It averages 2500 ml to 3000 ml. Expiratory Reserve volume (ERV) is an additional volume of air that a person can expire by a forcible expiration. This averages 1000 ml to 1100 ml.

(b) Inspiratory capacity (IC) is the total volume of air a person can inspire after a normal expiration. It is the sum of tidal volume and inspiratory reserve volume. Expiratory capacity (EC) is the total volume of air a person can expire after a normal inspiration. It is the sum of tidal volume and expiratory reserve volume.

(c) Vital capacity is the maximum volume of air a person can breathe in after a forced expiration. It is the sum of Tidal volume, expiratory reserve volume and inspiratory reserve volume. It is also the maximum volume of air a person can breathe out after a forced inspiration.

Total lung capacity is the total volume of air accommodated in the lungs at the end of a forced inspiration. It is the sum of Residual volume, expiratory reserve volume, tidal volume and the inspiratory reserve volume.

Functional Residual Capacity (FRC): The volume of air which remains in the lungs after a normal expiration is called Functional Residual Capacity. FRC = ERV + RV.

ERV =1000 to 1100 ml

RV = 1100 to 1200 ml

So, FRC = 2100 to 2300 ml.

The contraction of the external inter costal muscles and diaphragm leads to increase in volume of thoracic cavity. An increase in pulmonary volume decreases the intra-pulmonary pressure to less than atmospheric pressure. Thus forcing air into the lungs from outside. This is inspiration. Relaxation of the diaphragm and the inter-costal muscles returns the diaphragm and the sternum to their normal positions and reduce the thoracic volume and thereby the pulmonary volume. This lead to an increase in intra-pulmonary pressure in comparison to the atmospheric pressure. This causes expiration.

The total volume of air which can be inspired after a normal expiration is called Inspiratory Capacity, while the total volume of air which can be expired after a normal inspiration is called expiratory capacity. IC = TV + IRV, while EC = TV + ERV. 

(a) Inspiratory Reserve volume (IRV): Additional volume of air, a person can inspire by a forcible inspiration.

(b) Expiratory Reserve volume (ERV): Additional volume of air, a person can expire by a forcible expiration.

(c) Total lung capacity: Total volume of air accommodated in the lungs at the end of a forced inspiration. This includes RV, ERV, TV and IRV.

(d) Residual Volume (RV): Volume of air remaining in the lungs even after a forcible expiration.

(e) Functional residual capacity (FRC): Volume of air that will remain in the lungs after a normal expiration. This includes ERV + RV.

3.5 to 4.5 litres.