Sistemụ kpo oku kachasị ewu ewu n'ime ụlọ ọrụ azụmaahịa bụ okporo ụzọ tube nke nwere ọtụtụ ihe eji arụ ọrụ. Karịsịa n'ihe ọkụkụ akwụkwọ nri, a na-eji usoro kpo oku tube rail eme ihe nke ukwuu n'ihi na ọ nwere uru dị ukwuu na nhazi.

Ihe ọzọ a na-ahụkarị n'ime mmiri ọkụ n'ime mmepụta akwụkwọ nri bụ ọkpọkọ osisi. Ọkpọkọ osisi ndị a dị n'akụkụ mkpụrụ osisi niile dị n'ime ụlọ ntu ahụ, nke na-eme ka onye na-akọ ihe nwee ike ijikwa usoro ịcha.