Pi 
, is located in the abdomen under the diaphragm on the left side, radiates a yellow light, and regulates digestion and absorption. Pi and the Stomach, linked by their meridians, are externally–internally related to each other. They are the major viscera of the digestive system. Pi, the source of Qi, Blood, and body fluid for the whole body, maintains vital activity. The body relies on the functions of Pi and the Stomach to digest, transform, and transport the Essence of food and water. TCM says Pi and the Stomach are “the origin of the acquired constitution and the source for generation of Qi and Blood.”
Pi correlates to Earth in the Five Elements Theory. Considering the meridians, it belongs to extreme Yin within Yin, yet it belongs to Yang in function. The Spleen, Pancreas, muscles, lips, and mouth compose the Pi system. Pi’s physiological functions and pathological characteristics are more abstract and invisible, far beyond those of the Spleen and pancreas of CWM’s anatomy.
The physiological and mental functions of Pi ()
(1) Pi regulates transportation and transformation
Pi manages food digestion, the absorption of nutrient essentials from food and water, the transformation and extraction of Qi from ingested food and drink, and the further transportation of the extracts to Fei 
; these extracts then enter the Blood vessels for transportation to Xin 
and onward to the entire body. This is the basis for Qi and Blood production.
Food is first digested and absorbed in the Stomach, then passed on to the Small Intestine. It is Pi’s function to transform food and disperse the Essence throughout the entire body. Pi is the material base which generates vital Essence, Qi, Blood, and body fluid. Leftover water is transported through Fei to be excreted as sweat, and through Shen 
and the Bladder to be excreted as urine. If Pi fails to transform and transport, it will present as abdominal distension, diarrhea, anorexia, lassitude, and emaciation. If Pi fails to digest water, water will stagnate and damp symptoms arise. In this way, the two aspects of the tangible and intangible functions of Pi-Qi are demonstrated.
Pi -Yang or Pi-Qi warms the Pi -viscera, which prefer dryness. Pi -Yang is easily impaired by excessive consumption of cold food and drink. Pi –Qi tends to ascend. The Basic Questions says, “The Pi transports the refined Essence up to the Fei” and “The Pi regulates the activity of elevating the useful lucid Essence” . Elevating Pi –Qi can also lift the viscera to prevent prolapse. Diminished Qi and Blood source of Pi lead to dizziness, vertigo, emaciation, lassitude, and a pale complexion.
(2) Pi commands blood
Pi keeps circulating Blood within the vessels and prevents its outflow. Pi-Qi regulates the Pi viscera, which generate Qi and Blood.
Pi extracts nourishing Qi from food and, assisted by congenital Qi from Shen , forms Blood in Xin . Deficient Pi-Qi cannot properly control Blood, so Blood extrava-sates from the vessels. Pi commanded Blood relies on Pi-Qi and Pi-Yang. “Pi failing to control Blood” leads to hemafecia, hematuria, and metrorrhagia.
(3) Pi regulates the muscles and the four limbs
The limbs depend on the nutritive Essence of food and water, transformed and transported by Pi , to maintain their normal physiological activities. The Basic Questions says, “The Pi regulates the muscles … if the Pi has Heat, there will be thirst, and the muscles will be weak and atrophied” . When the limbs get insufficient nutrients, they will weaken and tire easily. In this case, Pi should always be reinforced.
(4) Pi opens into the mouth
The digestive canal starts at the mouth, where food begins to be prepared for the Stomach to digest and Pi to transform into Essence. The mouth is the orifice of Pi , which regulates the digestive system. The Basic Questions says, “Pi-Qi connects with the mouth. If the Pi is healthy, the mouth can taste the five cereals” . Pi’s 
state can be inferred by observing the mouth and lips. Normal Pi generates a healthy appetite and taste, and maintains moist rosy lips; abnormal Pi causes anorexia and a “flat” or “sticky” taste.
The Basic Questions says, “Saliva comes from the Pi and flows into the Stomach” . Saliva assists digestion, protects the oral mucosa, and moistens the oral cavity. During food intake, saliva helps moisten and dissolve food.
(5) Pi manifests on the lips
Pi’s state can be observed from the lips’ color and shape. The Basic Questions says, “Pi regulates the muscles and manifests on the lips” . Normal Pi –Qi is revealed in moist, rosy lips; abnormal Pi –Qi is revealed in pale, lusterless, dry, or sallow lips.
(6) Pi houses thought and relates to obsessive thinking and anxiety
Pi influences our capacity for thinking, studying, concentrating, and memorizing. Thinking relates to Pi , Xin which houses the Spirit, and also to Shen. Pi is the “residence” of Thought. The Basic Questions says, “Thinking originates from the Pi and develops in the Xin ” . Shen (
, Kidney, with its aura and meridian as one union) also influences thinking, by nourishing the Brain and regulating short-term memory. Normal thinking causes no bodily harm. If Pi-Qi is weak, thinking will be slowed, concentration weak, and memory poor. Excessive studying and mental work weakens Pi’s ability to successfully transform and transport lucid nutrients upward, stagnating Qi in the Middle Jiao, and hindering Pi –Qi flow. This presents as anorexia, epigastric distension and heaviness, dizziness, and vertigo.
Pi relates to emotions, especially obsessive thinking and anxiety. Pathologically, excess anxiety will stagnate Pi-Qi, leading to poor appetite, depression, palpitations, shortness of breath, amnesia, and so on.
For example, Diabetes is a common illness, usually a lifelong (chronic) disease in which there are high levels of sugar in the Blood. High blood sugar levels can produce several symptoms, including Blurred vision, Excessive thirst, Fatigue, and Hunger. Due to its complex syndrome, we suggest that the Spleen-Taiyin meridian–Zang Xiang system be used and a differential treatment be followed. It is to adjust the balance between Lung dryness and Spleen wetness.