The Anatomy of Human Lungs
The lungs are pink spongy organs to the left and right of the heart that provide the means to get oxygen from the air into your red blood cells. Each lung has an apex at the superior end that rises above the level of the 1st rib and into the root of the neck. Each lung also has three surfaces:
Costal surface: Next to the sternum, ribs, and costal cartilage
Mediastinal surface: The hilum and the medial (middle) surfaces of the lung
Diaphragmatic surface: The underside of the lungs, just above the diaphragm
Before the lungs can oxygenate the blood, they need air, which is provided by the airways, starting with the trachea. The trachea is a tube made up of incomplete cartilaginous rings that connects the larynx with the lungs. It terminates in a bifurcation, creating the right and left primary (main) bronchi.
Two primary bronchi run from the bifurcation of the trachea to the hila of the lungs. The bronchi, arteries, and veins are referred to collectively as the root of the lung and reside in the hilar spaces.
The right primary bronchus is wider and shorter than the left primary bronchus. It also runs more vertically. The left primary bronchus passes underneath the arch of the aorta and anterior to the esophagus.
The primary bronchi enter the hila of the lungs and form the bronchial trees by first dividing into the secondary bronchi (one for each lobe of each lung) and then into tertiary bronchi.
In each bronchopulmonary segment, the bronchi form more branches that eventually end in terminal bronchioles. Each terminal bronchiole divides into many respiratory bronchioles that lead to outpouchings for the exchange of gases. Each respiratory bronchiole has up to 11 alveolar ducts. Each duct has up to six outpouchings called alveolar sacs surrounded with capillaries. Each alveolar sac contains alveoli where gas exchange between the air and the blood takes place.
Asthma is a disease of the lungs that causes the walls of the bronchi and bronchioles to swell and become too narrow as a result of inflammatory responses.
The right lung is just a little bit larger than the left lung, and it has three sections, called lobes. They’re referred to as the upper, middle, and lower lobes. They’re marked by two fissures, or deep grooves: the oblique fissure and the horizontal fissure. The horizontal fissure divides the upper and middle lobes, and the oblique fissure divides the middle and lower lobes.
The left lung is a bit smaller, and it has the cardiac notch, an indentation that makes room for the heart. The left lung has only two lobes, the upper lobe and the lower lobe, which are separated by the oblique fissure.
The lungs need nerves to keep you breathing, and they also need blood supply and lymph drainage to perform their vital functions. And don’t forget they also need to resupply the blood that comes to the lungs for gas exchange.
The nerves that serve the lungs come from the pulmonary plexuses that are located anterior and posterior to the roots. They contain sympathetic fibers from the sympathetic trunks and parasympathetic fibers from the vagus nerve.
The blood vessels that supply the lungs with blood for gas exchange include the pulmonary arteries that leave the heart with oxygen-poor blood (unlike other arteries in the body) and the pulmonary veins that return oxygen-rich blood to the heart:
Pulmonary trunk: Leaves the right ventricle of the heart and splits into the right and left pulmonary arteries, each of which go to the respective lung
Pulmonary arteries: Branch off into lobar and segmental arteries within the lungs
Pulmonary capillaries: Surround the alveolar sacs
Lobar and segmental veins: Form from the merger of capillaries and drain into four pulmonary veins (two for each lung), which empty into the left atrium of the heart
Venous blood is returned from the lung structures by bronchial veins and by the pulmonary veins. The right bronchial vein drains into the azygos vein. The left bronchial vein drains into the accessory hemiazygos vein or the superior intercostal vein.
Two lymphatic plexuses drain lymph from the lungs:
Superficial lymphatic plexus: Lying under the visceral pleura, this plexus drains lymph from the lung tissue and the visceral pleura. The plexus drains into the bronchopulmonary lymph nodes.
Deep lymphatic plexus: This plexus is in the mucosal layers and connective tissue of the bronchi. It drains the roots of the lung and passes that lymph into the pulmonary lymph nodes.
All lymph from the lungs drains into the tracheobronchial lymph nodes, which are located near the bifurcation of the trachea. From there the lymph drains to the right and left bronchomediastinal lymph trunks, which end near the junction of the subclavian and internal jugular veins.
The right bronchomediastinal lymph trunk merges with other trunks to form the right lymphatic duct.
The left bronchomediastinal lymph trunk ends at the thoracic duct.
The right lymphatic duct and thoracic duct return lymph to the blood.