Pulmonary Circulation::
The pulmonary trunk which arises from the right ventricle of the heart supplies the Co2 conataining blood to the lungs for oxygenation the pulmonary trunk divides into two pulmonary arteries These arteries break up into smaller vessels and arterioles Finally they break up into a net work of capillaries which enters in the air sacs in the capillary vessels there are small holes through which the red blood cells are carried in a single file They are moving slowly and interchange of gases take place by diffusion the pulmonary capillaries unite and finally form two pulmonary veins emerging from each lung and take oxygenated blood to the left auricle of the heart the air which undergoes these gaseous exchanges is called the physiological air
The pulmonary vessels have thinner and more permeable walls They are shorter in length and larger in diameter than the vessels of the systemic circulation the systolic and diastolic pressure in pulmonary arteries is 25 and 8 mmHg respectively
The respiratory muscles ::
The diaphragm and intercostal muscles are the skeletal muscles involved in respiratory movements
Diaphragm ::
It is a large dome shaped sheath of muscle which separates the thoracic cavity from the abdominal cavity the contraction of diaphragm brings about a downward movement which decreases the intra thoracic pressure and increases the intra abdominal pressure Diaphragm is innervated by the phrenic nerve on each side This muscle is essential for the maintenance of respiration during anaesthesia because the intercostal muscles become partially inactive during anaesthesia
Intercostal Muscles ::
These are two series of muscles situated in between the ribs (costae) one on the inner side and the other on the outer side The two series (external intercostal and internal intercostal ) muscles causes an increase in the anteroposterior diameter of the thorax due to elevation of the anterior part of the ribs Thus there is pari pasu decrease in intra athoracic pressure when these intercostal muscles are contracted the intercostal muscles are supplied with intercostal nerves
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