Theory of meridians and collaterals are whole theory of existence of human life that people have researched and summarized during existence since thousands years ago. Life activity of human body is completed under coordination of meridians and collaterals system. Function of meridians and collaterals is unifying function of human body.

Function study of human system in modern medicine exceeds to formation of meridians and collaterals theory, such as nervous system, blood circulation system, respiratory system, urinary system, alimentary system, metabolism system, endocrine system, genital system and immune function. Comprehensive function study of human system has been reconstructed recently, such as development of frontier branches of science. Though meridians and collaterals theory is a general theory, it is on the foundation of comprehensive function. Theory of qi and blood, viscera and bowels, yin and yang, five elements, qi transformation and five movements and six dlimates is on the foundation of meridians and collaterals theory. Meridians and collaterals can not stand certain function, it can reflect summation of these function, such as qi and blood are transferred by energy of meridians and collaterals, function of viscera and bowels are regulated by meridians and collaterals. Function of viscera and bowels are called qi transformation process, "meridians and collaterals regulate asthenia and sthenia", meridians and collaterals regulate content of qi of viscera and bowels and keep normal qi transformation, luxus of qi and weakness of qi are disease.

Roles of engendering and restraining of five elements are realized by meridians and collaterals. Role of engendering and restraining is restricted function between viscera and bowels, it must realize by association of meridians and collaterals between viscera and bowels, if no association of meridians and collaterals, there is not transferred route of engendering and restraining between viscera and bowels and roles of engendering and restraining are not existence. Proportion of yin and yang is balanced by meridians and collaterals. Function of human body has different proportions of yin and yang, unbalance of proportion will cause disease and the proportion is regulated by meridians and collaterals. Process of qi transformation is completed by meridians and collaterals. Food, water and oxygen which people ingest become excretion of energy and waste, this process is done by coordination of viscera and bowels and this coordination is completed by meridians and collaterals between viscera and bowels. Five movements and six dlimates impact human body only on meridians and collaterals. Five movements and six dlimates are changes of nature which is outside of human body and has important affection on human body; it plays roles by tertiary collateral vessel which is distributed over surface of human. Whole concept of TCM also includes which is called brain higher nervous activity at present, brain is called extraordinary organs.

Twelve meridians connect brain and Spirit of five viscera and six bowels pertain to brain, these essential qi are transferred by meridians and vessels that brain can educe normal function. Brain is hidden pathogen of spirit and hidden pathogen is where spirit exists. Spirit is function of hidden pathogen. TCM relegate function of hidden pathogen to viscera and thinks that higher nervous activity of ethereal soul, corporeal soul, ideation and will originate from these viscera, such as liver storing soul, lung storing soul, spleen storing will, kidney controlling aspiration, if brain departs these viscera it will lose function of thought such as "liver storing soul", soul is yang qi, if liver is damaged and loses function of liver in human body, on condition of no extrinsic factor brain is not damaged but human is coma and no ethereal soul. "Lung storing soul", normal hearing and eyesight is corporeal soul, if lung is damaged, function of lung will be damaged, on condition of no extrinsic factor brain is not damaged but ears can not distinguish meaning and eyes can not see objects. "Spleen storing will", will is idea, if spleen is damaged; function of pancreas will be lost totally, on condition of no extrinsic factor brain is not damaged but loses idea. "Kidney controlling aspiration", aspiration is directed thinking, if kidney is damaged, function of kidney will be damaged totally, on condition of no extrinsic factor brain is not damaged but aspiration is not existed. These whole function are reflected by meridians and collaterals system, otherwise viscera are storing but not coming out.

The above area basic concepts of meridians and collaterals function, it is difficult to show complicated function of meridians and collaterals on diagram. In order to have a general understanding, except illustration of function in each diagram, diagrams of this chapter will only illustrate on transferring materials of meridians and collaterals, general circulation of meridians and collaterals, spigot role in circulation, meridian qi changes of life period, regulation relation of meridian qi of five viscera, meridians and collaterals function of five sense organs and routes of evil qi starting disease for reference.