From a combination of the rajas aspect of the five subtle elements, is produced
praaNa, or vital air. This has five divisions, according to the function performed.
These are described in the Bhaashya on Pras'na Upanishad.3.5, thus:--- He (praaNa) places apaana, a division of himself, in the two lower apertures, as engaged in the
work of ejecting the excreta . praaNa himself, who occupies the position of the
sovereign, resides in the eyes and the ears and issues out through the mouth and
nostrils. In the navel is samaana, which is so called because it assimilates all that
is eaten or drunk, distributes them equally in all parts of the body and effects
digestion. udaana, another division of praaNa, moves throughout the body and
functions upwards. It leads the soul out of the body at the time of death and takes
it to other worlds according to one's puNya and paapa. vyaana regulates praaNa
and apaana and is the cause of actions requiring strength. (See also Br.up.1.5.3.S.B).

    Br.up.3.9.26.S.B. : The force called praaNa would go out (through the mouth and
nostrils) if it were not held back by apaana. The force called apaana would also
depart (through the lower orifice) if it were not held back by vyaana. All these three
forces would go out in all directions, if they were not fixed to udaana. All these four
forces rest on samaana. taitt.up.2.2.S.B. -praaNa is that aspect which goes out
through the mouth and nostrils. Vedaantasaara-Paras 84 and 85---According to
Saankhya, there are five more vital forces known as naaga, kuurma, kr.kala,
devadatta and dhananjaya. Their functions are, respectively, causing vomiting,
winking, creating hunger, producing yawning and nourishing the body