What is a Promise Ring. A promise ring, sometimes known as a pre-engagement ring, is a simple piece of jewelry that is given as a symbol of a committed, monogamous relationship. In some cases, the promise ring symbolizes purity and a decision to remain celibate until marriage.
Noun. 1. external respiration-the bodily process of inhalation and exhalation; the process of taking in oxygen from inhaled air and releasing carbon dioxide by exhalation. breathing, respiration, ventilation. artificial respiration-an emergency procedure whereby breathing is maintained artificially.
Gas exchange in the lungs is referred to as external respiration as one side of the respiratory membrane - that is, the alveolar air - is actually outside of the body. As blood flows through the pulmonary capillaries, oxygen diffuses into the blood and carbon dioxide diffuses into the alveolar gas.