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.
Lower respiratory tract. The major passages and structures of the lower respiratory tract include the windpipe (trachea) and within the lungs, the bronchi, bronchioles, and alveoli. After the inhaled air moves through the larynx, it reaches the trachea. The trachea is a rigid tube about 4.5 inches long and 1 inch wide.