lower respiratory tract

lower respiratory tract,

one of the two divisions of the respiratory system. The lower respiratory tract includes the left and right bronchi and the alveoli where the exchange of oxygen and carbon dioxide occurs during the respiratory cycle. The bronchi divide into smaller bronchioles in the lungs, the bronchioles into alveolar ducts, the ducts into alveolar sacs, and the sacs into alveoli. The alveolar sacs and the alveoli present a total lung surface of about 850 square feet (79 square meters) for the exchange of oxygen and carbon dioxide, which occurs between the most internal alveolar surface and the tiny capillaries surrounding the external alveolar wall. The lower respiratory tract is a continuation of the upper respiratory tract and is a common site of infections, obstructive conditions, and neoplastic disease. Compare upper respiratory tract. See also lung.

---

lower

closer to ground surface.

---

lower airway

the trachea from the entrance to the thorax, bronchi and bronchioles.

lower burner syndrome

acupuncture term meaning chronic accumulation of fluid in the lungs because of failure of the kidneys to excrete the fluid.

lower motor neuron (LMN)

the final common nervous path; the ventral horn cell in the spinal cord and the peripheral motor neuron. A lesion of a sufficient number of these neurons causes atrophy of the muscles supplied by the nerve, weak reflexes and flaccid paralysis.

lower nephron nephrosis

see renal cortical necrosis.

lower respiratory tract

the trachea, bronchial tree, lungs, pulmonary vessels and pleura.

lower urinary tract

includes, ureters, bladder and urethra.