11th Class Biology Breathing and Exchange of gases (Animal Respiration) Respiratory Organs II

Respiratory Organs II

Category : 11th Class

In men the respiratory organ are a pair of lung. Some snakes have unpaired lungs. Respiration by lungs is called pulmonary respiration. Lungs are found in all vertebrates except fishes. In Lung fishes such as protopterus, neoceratodus and lepidosiren air bladder is found, which is modified lung. Respiration in men and rabbit is pulmonary.

Lungs : Lungs lie in thoracic cavity on both side of heart in mediasternum space. Base of lung is attached to diaphragm. Right lung is divided into 3 lobes viz. Superior, Middle, Inferior and left lung is divided into two lobes Superior and Inferior. In rabbit, the left lung is divided into two lobes left anterior and left posterior where as the right lung has four lobes anterior azygous, right anterior, right posterior and posterior azygous. Lungs of reptiles are more complex than those of amphibians. In birds lungs are supplemented by elastic air sacs which increase respiratory efficiency. The narrow superior partion of lung is termed the apex or cupula.



Each lung is enclosed in two membrane called pleura. Pleura are layers of peritonium of thorax. Inner membrane is called the visceral pleuron. It is firmly bound to surface of lungs. The outer membrane is called parietal pleuron. It is attached to chest wall or wall of thoracic cavity. A narrow space exists between the two pleura. It is called pleural cavity. In pleural cavity a watery fluid is found called pleural fluid. Pleural fluid is glycoprotein in nature and secreted by pleura. Pleural fluid lubricate the pleura so that they may slide over each other without friction. This fluids reduces friction bewteen the membrane. When the lungs expand and contract in respiration. Pressure inside pleural cavity is negative - 5 mm Hg. Plurisy is inflamation of pleura and cause collection of fluid in pleural cavity. It results painful breathing (dyspnea). The surface of lung lying against the ribs, known as coastal surface. The mediastinal (medial) surface of each lung contains a region - the hilus, through which bronchi, pulmonary blood vessels, lymphatic vessels and nerve enter and exit.



Pulmonary volumes and capacities

The apparatus commonly used to measure the volume of air exchanged during breathing and the rate of ventilation is a spirometer (spiro=breathe) or respirometer. The record is called a spirogram. There are 4 respiratory volumes and capacity.

Respiratory volumes

(1) Tidal volume (TV) : Volume of air inspired or expired in relaxed or resting position – 500 ml. It consists of 150 ml of dead space volume and 350 ml of alveolar volume.

(2) Inspiratory reserve volume (IRV) : By taking a very deep breath, you can inspire a good deal more than 500 ml. This additional inhaled air, called IRV is about 3000 ml.

(3) Expiratory reserve volume (ERV) : If you inhale normally & then exhale as forcibly as possible, you should be able to push out 1100 ml. of air in addition to 500 ml. of T.V. The extra 1100 ml. is called ERV.

(4) Residual volume (RV) : Even after expiratory reserve volume is expelled, considerable air remains in the lung, this volume, which can not be measured by spirometry, it is called residual volume is about 1200 ml.

(5) Dead space : Portion of tracheobronchial tree where gaseous exchange does not occur called dead space. It is also called conductive zone. Dead space is 150 ml.

(6) Functional residual capacity (FRC) : It is the amount of air that remains in the lungs after a normal expiration. It is about 2300 ml.


                              \[=1100+1200=2300\text{ }ml.\]

(7) Vital capacity (VC) : This is the maximum amount of air that can be expired forcefully from his lungs after first filling these with a maximum deep inspiration. It is about 4600 ml.


\[=3000+500+1100=4600\text{ }ml.\]

(8) Total lung capacity (TLC) : TLC is the sum of vital capacity (VC) and residual volume (RV). It is about 5800 ml.


                                 \[=4600+1200=5800\text{ }ml.\]

(9) Inspiratory capacity (IC) : It is the total amount of air a person can inspire by maximum distension of his lungs.



                           \[=500+3000=3500\text{ }ml.\]


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