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.
1 Respiration includes gas exchange in the lungs, circulation of gases through the blood stream, and transfer of gases at the cellular level. 2  Air is drawn into the air sacs of the lungs, where oxygen from the air can enter the blood. 3  Carbon dioxide exits from the blood into the alveolar air. Oxygen then diffuses into the cells, and carbon dioxide enters the blood. 2  The blood then circulates back to the lung, where the process begins again. 3  Definition of Ventilation Ventilation is the process of moving gases through the respiratory tract.