In Traditional Chinese Medicine (TCM), it is well known that the liver (Gan 肝) and gallbladder (Dan 胆) are interrelated, as are the heart (Xin 心) and small intestine (Xiao Chang 小肠), the spleen (Pi 脾) and stomach (Wei 胃), the lungs (Fei 肺) and large intestine (Da Chang 大肠), and the kidneys (Shen 肾) and bladder (Pang Guang 膀胱). Beginners in TCM may find it confusing—how can the heart relate to the small intestine, or the lungs to the large intestine? Understanding the biochemical pathways of the human body from a TCM perspective clarifies these interrelationships.
1. The Liver and Gallbladder. The liver is responsible for detoxifying blood. It is common knowledge that detoxification and filtration produce residues. After detoxification, the residues enter the gallbladder and become bile. Bile, besides aiding digestion, also serves as a channel for the liver to clear residues. The gallbladder is merely a container for storing bile. The liver continuously secretes bile, especially during the peak detoxification period from 1:00 AM to 3:00 AM. Bile is stored in the gallbladder until food enters the stomach, at which point it is rapidly released into the duodenum to facilitate digestion. This process is automatically controlled by the body, and the liver’s detoxification process represents the rising and dispersing of Yang energy. This biochemical process can be expressed as: the metabolic pathway for detoxification from the liver to the gallbladder is from interior to exterior, corresponding to the Wood element.
2. The Heart and Small Intestine. The heartbeat generates a continuous supply of energy and heat, which is why TCM refers to it as “fire”. For the heart fire to be utilized by various organs, it must first descend to the small intestine, which is considered the body’s second heart. This fire raises the temperature and peristaltic force of the small intestine, which then transmits energy to other organs. This biochemical process is what the “Nei Jing” describes as the heart transferring heat to the small intestine, reflecting the function of fire’s transmission. It can be expressed as: the energy transmission pathway from the heart to the small intestine is from interior to exterior, corresponding to the Fire element.
3. The Spleen and Stomach. After food enters the stomach, it is transformed into absorbable nutrients, which is the function of the stomach. In TCM, the stomach refers not only to the stomach itself but also to the entire gastrointestinal system. However, for the nutrients in the gastrointestinal system to become part of the body, the spleen must distribute and transform the five colors of nutrients. This is akin to a factory producing products in the stomach, which must then be distributed by the spleen’s logistics system to their respective destinations: green nutrients to the liver, red to the heart, yellow retained by the spleen, white to the lungs, and black to the kidneys. Furthermore, the metabolism of fluids also relies on the spleen and stomach, as stated in the “Nei Jing”: “The fluids enter the stomach, overflow into the essence, ascend to the spleen, the spleen qi disperses the essence, and ascends to the lungs, regulating the water pathways, and descends to the bladder.” Thus, the digestion of the stomach combined with the absorption of the spleen represents the transformation function of the Earth energy. This biochemical process can be expressed as: the nutrient transformation pathway from the stomach to the spleen is from exterior to interior, corresponding to the Earth element.
4. The Lungs and Large Intestine. At first glance, this may seem confusing, but understanding the primary biochemical function of the large intestine clarifies it. The large intestine absorbs moisture from food residues, and this moisture ascends to the lungs. The lungs, having received this moisture, can then regulate the downward flow of heart fire and exert the function of metal energy to consolidate and descend. Therefore, the “Nei Jing” states that “the lungs are the upper source of water”; their relationship is indeed close. This biochemical process can be expressed as: the material transmission pathway for moisture from the large intestine to the lungs is from exterior to interior, corresponding to the Metal element.
5. The Kidneys and Bladder. This relationship is easier to understand. The kidneys collect the water produced by the body’s metabolism, ensuring that no drop of water is wasted. Before this water enters the bladder, it is filtered by the kidneys once more, allowing only good water to be reused while the bad water is sent to the bladder, which filters it again before expelling it from the body. This biochemical process represents the hidden function of water energy and can be expressed as: the material transformation pathway for moisture from the kidneys to the bladder is from interior to exterior, corresponding to the Water element. Thus, even without defining the concepts of “Fu as exterior and Zang as interior”, we can discern their interrelationships by observing their biochemical processes and directions.
