Avain lungs

The lung is the essential organ of respiration in air-breathing vertebrates. Its principal function is to transport oxygen from the atmosphere into the bloodstream, and excrete carbon dioxide from the into the atmosphere. This it accomplishes with its mosaic of specialized cells that form millions of tiny, exceptionally thin-walled air sacs where gas exchange takes place. Lungs also have nonrespiratory functions.Medical terms related to the lung often begin with pulmo-, from the Latin pulmonarius "of the lungs, cognate with the Greek pleumon "lung".

The respiratory function of the lung
Nonrespiratory functions of the lung
Mammalian lungs
Anatomy
Avian lungs
Reptilian lungs
Arachnid lungs
Crustacean lungs
Evolutionary origins

The respiratory function of the lung
Energy production in living organisms often uses oxygen and produces carbon dioxide. Hence, life necessitates an efficient means of oxygen delivery to cells and carbon dioxide excren smaller organisms, such as single-celled bacteria, this process of gas exchange can take place entirely by simple diffusion. In larger organisms this is not possible; only a small proportion of cells are situated close enough to the for oxygen from the atmosphere to enter them through diffusion. Two major evolutionary adaptations made it possible for organisms to attain great multicellularity: an efficient circulatory system that conveyed gases to and from the deepest tissues in the and a large respiratory system that centralized the task of obtaining oxygen from the atmosphere and bringing it into the body, whence it could rapidly be distributed to all tissues via the circulatory system.

In air-breathing vertebrates, respiration occurs in a series of steps. Air is brought into the animal via thes, birds and mammals this often consists of the nose, the pharynx, the larynx, the trachea, the bronchi and bronchioles, and the terminal branches of the repiratory tree. The lungs of these animals are a rich lattice of alveoli, which provide an enormous surface area for gas exchange. A network of fine capillaries transports blood over the surface of alveoli. Oxygen from the air inside the alveoli diffuses into the blood across the exceptionally thin alveolar membranes, and carbon dioxide moves from the blood to the alveoli via the same process. drawing and expulsion of air is driven by muscular action; ietrapods, air was driven into the lungs by the pharyngeal muscles, whereas in reptiles, birds and mammals a more complicated musculo-skeletal system is used. In the mammal, a large muscle, the diaphragm, drives ventilation by periodically altering the intra-thoracic volumd pressure; by increasing volume and decreasing pressure, air is sucked into the airways, and by reducing volume and increasing pressure, the reverse occurs.
Nonrespiratory functions of the lung
In addition to respiratory functions such asexchange and regulation of hydrogen ion concentration, the lungsnfluence the concentration of biologically active substances and drugs used in medicine in arterial blood
filter out small blood clots formed in the systemic veins
serve as a physical layer of soft, shock-absorbent protection for the heart, which the lungs flank and nearly enclose.

Mammalian lungs
The lungs of mammals have a spongy and are honeycombed with epithelium having a much larger surface area in total than the outer surface area of the lung itself. The lungs of humans are typical of this type of lung. The environment of the lung is very moist, which makes them a hospitable environment for bacteria. Many respiratory illnesses are the result of bacterial or viral infection of the lungs.Breathing is largely driven by the diaphragm below, a muscle that by contracting expands the in which the lung is enclosed. The rib cage itself is also able to expand and contract to some degree.As a result, air is sucked into and pushed out of the lungs through the and the bronchial tubes or bronchi; these branch out and end in alveoli which are tiny sacs surrounded by capillaries filled with blood. Here oxygen from the air diffuses into the where it is carried by hemoglobin.The deoxygenated blood from the heart reaches the lungs via the pulmonary artery and, after having been oxygenated, returns via the pulmonary veins.