A noncovalent bond between an electronegative atom (commonly oxygen or nitrogen) and a hydrogen atom covalently bonded to another electronegative atom. Particularly important in stabilizing the three-dimensional structure of proteins and formation of base pair s in nucleic acids.
Introduction[edit] The respiratory system serves three principal purposes in the human body: gaseous exchange; sound production; and assistance in compression of the abdomen. It can be divided into two structural divisions, upper and lower, as well as two functional divisions, conducting and respiratory.
Functionally, these structures make up the system's conducting portion, which consists of the nasal cavities, nasopharynx, larynx, trachea, bronchi (Gr. bronchos, windpipe), bronchioles, and terminal bronchioles; and a respiratory portion (where gas exchange takes place), consisting of respiratory bronchioles, alveolar ducts, and alveoli.