Vascular System and Innervation of the Lungs
The lungs make up the terminal portion of the respiratory apparatus and the largest portion of respiratory tissue. They are a pair of organs situated within the thoracic cavity and they are supplied with inhaled air that comes from the upper segments of the tract including the nasal cavity, the pharynx, the larynx, the trachea, the bronchi and the bronchioles. Their main function is breathing so that oxygen and carbon dioxide can be exchanged, with oxygen being inhaled and sent to the tissues and carbon dioxide being released via exhalation. This articles will focus upon the blood supply, venous drainage, innervation and lymphatics drainage of the pulmonary tissues. It will also mention some a pathological disorder that can affect the lung tissues.
Blood Supply and Venous DrainageA pulmonary artery is assigned to each lung and it functions by carrying deoxygenated blood from the right ventricle of the heart to the lung. Lobar and then segmental arteries are the radiating divisional branches of the pulmonary arteries and supply the entire pulmonary organ as a whole. The pulmonary veins carry oxygenated blood into the left atrium of the heart. The bronchial arteries originate from the thoracic aorta and carry oxygenated blood to the pulmonary tissues, by travelling along the posterior surface of the bronchi. The thoracic aorta gives rise to the left bronchial arteries, while the single right bronchial artery stems from either the superior posterior intercostal artery or the left superior bronchial artery. These branches anastomose with the branches of the pulmonary arteries, forming an arterial network throughout the lung tissue. The pulmonary veins govern the venous drainage of the lungs by collecting the blood that flows into the bronchial veins. They empty into the azygos and hemiazygos veins.
The innervation of the lungs occurs via the pulmonary plexuses which runs both anteriorly and posteriorly along the lung roots. The nervous structures within the plexuses contain postganglionic sympathetic fibers that originate from the sympathetic trunks which happen to innervate the bronchial tree, the pulmonary vessels and the glands of the bronchial tree. The characteristics of the sympathetic fibers include bronchodilation, vasoconstriction and inhibition of glandular secretion. Other fibers that run in the pulmonary plexuses include the preganglionic parasympathetic fibers which are contributed by the vagus nerve (CN X) as well as small parasympathetic ganglia and postganglionic parasympathetic nerves which innervate the smooth muscle of the bronchial tree, the pulmonary vessels and the bronchial glands. The characteristics of parasympathetic fibers include bronchoconstriction, vasodilation and glandular secretomotor stimulation. Finally, the visceral afferent fibers present function by transmitting information that is needed in the coughing reflex, stretch reception, blood pressure, chemoreception and nociception.
The lungs have a large complex of freely connecting lymphatic vessels. The lymph formed within the lungs drains into the pulmonary lymph nodes which are found along the lobar bronchi. Also, the bronchopulmonary lymph nodes which sit on the left and right major bronchi. Finally the superior and inferior tracheobronchial lymph nodes which conjugate around the superior and inferior aspects of the bifurcation of the trachea.
Coughing is a natural reflex that plays a very important role in the maintenance of healthy lung tissue. The ability to cough allows the body to remove dust, mucus, saliva and other debris from the lungs. If a patient is unable to cough, the likelihood of contracting an infection or an inflammation greatly increases. Another way to keep lung matter healthy and free from particulates is to breathe deeply in a rhythmic manner and there are various techniques and exercises that help on to do so.