Classical Chinese medicine describes the vital energy (qi) not as one undifferentiated substance but as a family of functional currents, each with its own origin, route and job. Four of these are singled out in the foundational texts: yuan qi (original qi), zong qi (pectoral or ancestral qi), ying qi (nutritive qi) and wei qi (defensive qi).
Yuan qi is the deepest layer. It is described as rooted between the two kidneys, in the region later texts call ming men (the gate of life), and is understood as the primordial endowment a person is born with, drawn from the essence (jing) of both parents. The Huangdi Neijing does not use the term yuan qi as a fixed technical label — that usage was consolidated by later authors such as the Ming physician Zhang Jingyue — but the Neijing already treats the kidney system as the storehouse of prenatal essence. Yuan qi is not spent on daily tasks; it is the baseline that warms and activates all the other qi.
Zong qi assembles in the chest, in the region called shang qi hai, the upper sea of qi. The Lingshu (chapter 4 among others) describes it as formed where the air taken in by the lung meets the food essence raised by the spleen and stomach. Its two documented jobs: it feeds the heart and lung to drive breathing and the beat of the pulse, and it flows down to support the voice and the rhythm of respiration.
Ying qi and wei qi are described together in Lingshu 50 (Ying Wei Sheng Hui) as two halves of one circulation. Both begin from food essence, both run in continuous cycles. Ying qi is the clearer, softer current: it travels inside the vessels alongside the blood, transforming into the nutritive part of the body. Wei qi is the swifter, tougher one: it runs outside the vessels, along the body surface, day and night, and its classical role is warming and guarding — regulating the opening and closing of the pores (couli) and holding the exterior against external pathogens.
The division is functional, not anatomical: one origin (food and air, resting on the prenatal base), several specializations. Later generations summarized it in one line — yuan qi roots, zong qi gathers in the chest, ying nourishes within, wei guards without. The Neijing presents these as descriptions of how the body is observed to work; whether they map onto modern physiological categories is not claimed by the classical sources themselves.
中医基础理论把「气」分成各有来历、各管一段的几股，其中最常引用的是四种：元气、宗气、营气、卫气。
元气是最深一层，后世表述为「根于两肾之间（命门）」，禀受于父母先天之精。《内经》虽未把「元气」固定为术语（这一定型见于明代张景岳等），但已把肾系统当作先天之精的库房。元气不直接干日常的活，它的角色是温煦与推动——其余诸气都靠它打底。
宗气积于胸中（上气海）。《灵枢》多处记载它由肺吸入的清气与脾胃上输的水谷精微「相合」而成，文献明确记载的职责有两条：一是贯心脉、行呼吸——推动肺的呼吸与心的搏动节律；二是下走以支持声音与气息。
营气与卫气在《灵枢·营卫生会》里被作为一对来讲：两者同源（皆出于水谷精微），都在做昼夜不停的循环。营气「清柔」，行于脉中，与血同行，化生身体所需的营养部分；卫气「悍疾」，行于脉外、循体表昼夜运行，经典记载的职能是「温分肉、充皮肤、肥腠理、司开阖」——主管毛孔腠理的开合，抵御外邪，是身体的「卫外」层。
这个分工是功能性的，不是解剖性的：同一个来源（水谷与清气，垫在先天元气之上），几条不同的分工线。后世的概括是一句话——元气根于下，宗气积于胸，营行脉中以濡养，卫行脉外以固表。需要说明：这些是古人对身体运作的观察描述，经典本身并没有主张它们直接对应现代解剖或生理学的某个具体结构。
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