Qi is the constantly moving subtle substance that constitutes the human body and maintains its vital activities.

There are three main sources of Qi in the human body: the innate essence inherited from parents, the essence of water and grain in food, and the pure Qi existing in nature.

Qi has many important physiological effects on the human body. The normal functioning of the internal organs, meridians, limbs, bones, five senses and nine orifices all depends on the physiological effects of Qi.

Generally speaking, the physiological effects of Qi include five aspects: promotion, warming, defense, consolidation, and qi transformation.

Yuan Qi is the most original Qi in the human body.

Yuan Qi is mainly composed of the essence of the kidneys and is generated from the essence of the kidneys.

The distribution of primordial energy is throughout the body, reaching everywhere. The internal organs, meridians, body parts, five senses and nine orifices are all places where primordial energy rises, falls, enters and exits.

The main physiological functions of Yuan Qi are twofold: one is to promote and stimulate the growth, development and reproduction of the human body. The other is to promote and stimulate the physiological activities of the internal organs and meridians.

If the kidneys are deficient in essence and energy due to congenital deficiency, postnatal malnutrition, or long-term illness, and the kidneys lack the source of vital energy, various diseases may occur.

Zong Qi is the Qi that accumulates in the chest. The place where Zong Qi accumulates is called "Tan Zhong" (between the two breasts). Because it is the place where Zong Qi is most concentrated, it is also called "Qi Hai".

Zong Qi is mainly composed of the fresh air from nature inhaled by the lungs and the essence of water and grain produced by the spleen and stomach from food.

The main functions of Zong Qi are twofold:

1. It is to walk the Xi Dao to control breathing. All breathing, speech, and voice are related to the Zong Qi. When the Zong Qi is abundant, the breathing is slow and the rhythm is even, the speech is clear and the voice is loud; otherwise, the breathing is short and the voice is low.

Second, it is to circulate Qi and blood through the heart meridians. All the beating of the heart and the circulation of Qi and blood are related to Zong Qi. If the pulse is gentle, the rhythm is consistent, and there is spirit and root, it is a manifestation of abundant Zong Qi. On the contrary, if the pulse is agitated, scattered, weak, or irregular, it means that the Zong Qi is insufficient or even weak.

Zhongqi refers to the Qi of the middle burner. Because the spleen and stomach are located in the middle burner, the Qi of the spleen and stomach is generally called "Zhongqi".

It is generally believed that the formation of Zhong Qi is formed by the combination of the Yuan Qi distributed in the Zhongjiao and the water and grain essence produced by the spleen and stomach.

The middle qi is mainly distributed in the middle burner, spreading between the spleen, stomach, and intestines, and it rises and falls, constantly mediating.

The main functions of Zhongqi include three aspects:

1. It controls the rise and fall of Qi. The middle burner is the hub of the rise and fall of Qi. When the middle Qi is abundant and harmonious, the Qi of the liver and spleen will rise healthily, and the Qi of the lungs and stomach will descend smoothly. When the rise and fall are smooth, all organs will be at peace.

Second, it stimulates the spleen and stomach to absorb and transport. When the middle qi is abundant, the spleen rises and the stomach descends normally, the water and grain are received and transported normally, and the essence of water and grain is continuously produced to generate qi and blood, nourishing the whole body.

Third, it maintains the position of the internal organs. The reason why the internal organs maintain their relatively constant position depends on the rise and fall of the qi of the middle jiao spleen and stomach.

Ying Qi, also known as "Rong Qi", is the Qi that flows in the veins.

The distribution and movement of Ying Qi are clearly discussed in Suwen Bi Lun, which points out that Ying Qi "harmonizes the five internal organs, flows through the six bowels, and then enters the meridians."

It explains that the nutrient energy enters the meridians, circulates throughout the body, flows into the internal organs, and reaches the limbs, repeating the cycle over and over again.

The main functions of Ying Qi:

1. It is the transformation of blood.

Second, it nourishes the whole body. The nourishing qi enters the blood vessels and causes the body fluids to penetrate into the blood vessels. The two combine to form blood.

The so-called Qi can produce blood, mainly refers to: Ying Qi transforms into blood. Ying Qi is produced by the refined part of the essence of grains, and is a nutrient necessary for physiological activities such as viscera and meridians, and plays an important role in maintaining human life activities.

The Inner Canon of Medicine states that the Nutritive Qi "harmonises the five internal organs, and spreads throughout the six bowels", "nourishes the four extremities", etc., which emphasizes that the Nutritive Qi has a nourishing effect.

Wei Qi is the Qi that circulates outside the veins. It is so called because it protects the skin and resists external pathogens.

The distribution of Wei Qi is fast, smooth and agile, and is not restricted by blood vessels, so it can "flow through the skin, between the flesh, fumigate the peritoneum, and spread to the chest and abdomen" (Suwen Bi Lun). This shows that Wei Qi spreads throughout the body, externally between the skin and muscles, and internally to the peritoneum of the chest and abdomen - the area inside the diaphragm of the chest cavity.

The main physiological functions of Wei Qi are three-fold:

First, it protects the skin and prevents the invasion of external pathogens. In clinical practice, if a patient is prone to colds and fever, the treatment is usually based on the theory that the Wei surface is not solid. The theoretical basis is here. Second, it warms the internal organs, muscles, fur, etc. Wei Qi has a strong warming effect. If Wei Yang is deficient, the warming power is weakened, and cold symptoms such as cold body, cold limbs and low body temperature may appear. If Wei Qi is stagnant and turns into heat, hot symptoms such as fever and malignant fever may appear.

Third, it regulates the opening and closing of pores and controls sweat excretion, which is what Lingshu Benzang says about the Wei Qi having the function of “controlling opening and closing”.