Structurally the lungs are two organs, while functionally they work as a single organ. By contrast, structurally the heart is one organ, while functionally the right heart and the left heart work as two discrete organs. The lungs flank the heart, each weighing 300 to 400 grams. The right lung is larger and heavier than the left lung. The surfaces of the lungs are covered with pleura—a strong membranous structure lined by smooth mesothelial cellsa—except in the hilar regions where the main stem bronchi and pulmonary arteries enter the lungs and pulmonary veins leave it. The pleura gives lungs a smooth, shiny surface, marked out into polyhedral spaces respresnting lobular divisions of the lungs. The color of the lung at birth is pink-white. The adult lungs show varying degrees of dark slate-colored complexion, with or without heavy black anthracotic (carbonaceous) pigment. The substance of the lung parenchyma is of light porous texture.

The right lung contains three lobes while the left has two. The lower lobes on the two sides form almost the entire surface of the lungs. The upper and the middle lobe on the right side make the anterior surface of the lungs. The right main stem bronchus is more direct in line with the trachea—the musculocartilaginous tube that connects larynx (sound box) to lungs—being more vertical than the left main stem bronchus. Not unexpectedly, aspirated matrials —foreign bodies, vomitus, and blood from nasopharynx and oropharynx—more often lodge in the right lung.

The main stem bronchi branch into major bronchi which, in turn, divide progressively and bipinnately throughout the organ, eventually producing terminal bronchioles that measure about 1 mm. in diameter and lack cartigenous tissue in their walls. Next, the terminal bronchioles divide progressively to form respiratory bronchioles that open into alveoli—the air spaces that impart to the lungs a porous texture. All bronchial tubes are lined by mucosa which contains a rich supply of mucous glands and is covered over with ciliated tall columnar epithelium.

The lungs receive venous, deoxygenated blood from the right ventricle of the heart via the pulmonary arteries and send oxygenated blood to the left ventricle via the pulmonary veins. That contrasts with veins elsewhere which carry deoxygenated blood and arteries in tissues which carry oxygenated blood. The pulmonary arteries subdivide progressively to form smaller pulmonary arteries and eventually pulmonary venules and pulmonary capillaries. The capillaries form plexuses in the mucosa. In the septae between alveoli, such the capillary network forms a single layer, providing an intimate contact between air in the air sacs and deoxygenated blood in pulmonary capillaries for efficient gaseous exchange—oxygen diffusing into the blood and carbon dioxide moving out into the air sacs. The lungs also receive arterial blood from bronchial arteries that arise from the aorta.

The nerve supply of the lungs is derived from the sympathetic and pneumogastric nerves. Those nerves form anterior and posterior pulmonary plexuses. The lymphatics of the lung comprise superficial and deep sets that terminate into bronchial lymph nodes located in the hilum (root) of the lung.

List of Related Articles

* Lungs

* Classification of Lung Diseases

*  Limbic Breathing for Healing

*  Limbic Breathing for Blood Pressure 

*  Limbic Breathing for Chemical Sensitvity

*  Limbic Breathing for Children

*  The Pleura

* Asthma - Simplified

* Sinuses: Anatomy and Physiology

* Lung Cancer Stats

* Sinsusitis and Sinus Polyps

* The Nose

* The Bowel-Nose Connection