Air Sacs

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Air Sacs


cavities connected to the respiratory pathways or the esophagus that are capable of filling with air but do not function in gas exchange in most vertebrate animals.

In tailless amphibians, air sacs are paired or unpaired processes in the back of the oral cavity called vocal sacs. In reptiles (some turtles and lizards) air sacs are blind processes in the lungs.

Birds have five pairs of air sacs. The abdominal sacs branch off from the main bronchi and are situated between the organs of the abdominal cavity. The other four pairs are extrapulmonary prolongations of secondary bronchi: (1) cervical, lying along the esophagus; (2) clavicular, frequently merging into a single interclavicular sac; (3) anterior thoracic, on the abdominal wall of the thorax; and (4) posterior thoracic, on the dorsal side. The main function of the air sacs in birds is to draw air through the lungs, especially during flight, to regulate heat, and to alter the specific gravity of the birds while swimming and diving. Many skeletal bones in birds (femur, humerus, sternum, and others) have cavities filled with air sac processes. Birds also have air sacs that are not connected to bronchi; the processes of these (pharyngonasal) air sacs in some birds extend to the cranial bones, under the skin, and into the anterior extremities.

Mammals have several kinds of air sacs: (1) some that originated as paired processes on the mucous membrane of the eustachian tubes (in horses, asses, zebras) and are situated on the neck in the region of the atlas; (2) paired and unpaired structures originating in the pharynx and serving to amplify sound (vocal sacs); (3) sacs that branch off from the widened posterior end of the trachea (in male striped seals) or from the esophagus (in male walruses) and serve to alter the specific gravity of the body; and (4) in the sperm whale, a blind air sac about 1 cu m in size that opens into the blow hole, where it collects air before a dive.

Plants have air sacs and cavities filled with air that originated as a result of the layers of the exine of pollen grains diverging. Air sacs are characteristic of the pollen of many gymnosperms, particularly conifers.


References in periodicals archive ?
In subsequent endoscopies, pathologic findings on the left testicle and the air sacs increased.
This prevents the air sacs fulfilling their vital function - taking in oxygen and expelling carbon dioxide - so you become breathless.
By using X-ray movies and CT scans, the group characterized how the skeleton works to move air through the lungs in living animals, and also how to identify the signature traces left on bones that have been invaded by air sacs.
When the smoke and/or particulates travel deeper into the lungs, the aveoli are destroyed, leaving larger air sacs that function less effectively, marking the early stages of emphysema.
The disease causes inflammation and thickening of air sacs in the lungs.
Air sacs bulging from a horse's hearing system may solve the mystery of how such an athletic animal cools its brain during exercise without the standard anatomical gadgetry, argues an international team of researchers.
Preemies face critical breathing problems after their early birth because their lungs are hard to expand and the sticky air sacs within the lungs tend to re-collapse after each breath.
Also, the lungs' air sacs create a mosaic of gas-liquid boundaries that make MRI difficult, if not impossible, with water protons, says Arnold Wishnia, a biophysical chemist at Stony Brook.
Emphysema is an abnormal condition of the lungs in which the walls of the air sacs (alveoli) break down and lead to a decrease in respiratory function and, in severe cases, breathlessness.
Gross lesions identified during necropsy included lesions at renal biopsy sites and adjacent air sacs (attributed to the biopsy procedure) and pectoral muscle hemorrhage and discoloration (at sites of injection).
Researchers had previously suggested that these sounds originate farther down in the head, near a set of nasal air sacs or even in the larynx.