trigraph. noun. 1  Three letters spelling one consonant, vowel, or diphthong, such as Sch in Schiller or igh in high or thigh. 2  A group of three letters, especially of frequent occurrence in a given language, as the or ing in English or gli in Italian.3  Any combination of three letters of an alphabet. 4  Also called trigram.rigraph. noun. 1  Three letters spelling one consonant, vowel, or diphthong, such as Sch in Schiller or igh in high or thigh. 2  A group of three letters, especially of frequent occurrence in a given language, as the or ing in English or gli in Italian. 3  Any combination of three letters of an alphabet. 4  Also called trigram.
Oxygen-carbon dioxide-The process by which oxygen passes from the air in the LUNGS to the HEMOGLOBIN in the BLOOD, and carbon dioxide from the hemoglobin passes into the air in the lungs.Oxygen-carbon dioxide exchange is fundamental to life and is the primary function of the lungs.Oxygen-carbon dioxide exchange takes place between the alveoli, the tiny bubblelike sacs deep within the lungs, and the capillaries, the tiniest blood vessels of the cardiovascular system.xygen and carbon dioxide molecules (as well as the molecules of other gases such as nitrogen and highly toxic carbon monoxide) can easily pass through the walls of the alveoli and the capillaries, moving in the direction of least resistance. Oxygen molecules move from the alveoli into the capillaries with inhalation.
Cells use the oxygen and produce another gas, called carbon dioxide, as a waste product. It is very dangerous if carbon dioxide builds up in your body, so your blood carries the carbon dioxide to your lungs where it is released into the air when you breathe out or exhale.his module will help you understand how gas exchange occurs in the body and why it is so important. After completing this lesson, each student should be able to: 1  Diagram and label the anatomy of the lungs and the circulatory system. 2  Explain how the processes of gas exchange occurs and what purpose it serves.