Each of the twelve organs has its own function in TCM theory, often quite distinct from our western physiological understanding.

Lung: The Lungs are the most superficial of the Yin organs and are almost always the first organs affected by attacks of the external evils, especially Wind and Dryness. The Lungs like to be moist and hate to be dry. An overly dry Lung is evidenced by a cough without phlegm or with scanty-sticky phlegm, plus dryness in the throat, nose, and mouth, and thirst. The Lungs are responsible for spreading moisture to the surface of the skin and to the lower parts of the body. They govern Qi and respiration, and, along with the Spleen, manage the body's defensive Qi (Wei Qi). The Qi of the Lungs has a descending and dispersing action.

Large Intestine: The Large Intestine, a Yang organ, is paired with the Lungs. As in western medicine, its function is understood to be receiving food and drink from the Small Intestine, absorbing water from them, and excreting stool as a waste product. Diseases of the Large Intestine include all manner of digestive upsets, as well as more serious disorders such as Crohn's disease, ulcerative colitis, and dysentery.

Stomach: The Stomach, paired with the Spleen, is the most important of the Yang organs. It is in charge of "rotting and ripening" our food and drink before passing them to the Spleen, which extracts the refined essence of the mix, turns it into Food Qi, and transports it to all parts of the body. Without the action of the Stomach, the Spleen cannot effectively do its job and our overall Qi is weakened. For this reason, the Stomach is said to be the "origin of Qi." Zhang Jie Bin put it this way: "Stomach Qi is the nourishment of life itself. If the Stomach is strong, life will be healthy; if the Stomach is weak, life will be unhealthy." The Stomach is very closely related to the tongue's coating, and a thin white coat indicates healthy Stomach Qi. The major causes of Stomach deficiency (aside from the poor quality of the food we eat) are eating late at night and eating on the run. Unlike the Spleen, the Stomach likes dampness and dislikes dryness. A dry Stomach leads to Heat, to which the Stomach is very susceptible. This may show up in chronic bad breath, mouth and gum sores, and strong thirst. The Qi of the Stomach has a descending action, and "rebellious" (i.e., moving in the wrong direction) Stomach Qi can lead to vomiting, acid reflux, belching, and hiccups.

Spleen: Similar to the pancreas in western medicine, the Spleen's main function is transforming food and water into food essence and transporting these nutrients to all corners of the body. It is said to like dryness and dislike dampness, and when the Spleen Qi is deficient, pathogenic Dampness occurs. Pathogenic Dampness is seen in obesity, edema, copious sputum (if it rises to the Lungs), and most commonly in poor digestion (loose stools, diarrhea). The Spleen is also in charge of maintaining our muscles, promoting clear thinking and good memory, and keeping our Blood flowing within the veins. Fatigue is the most common symptom of deficient Spleen Qi, while excessive menstrual bleeding, easy bruising, and blood in the urine can all be due to "Spleen failing to control the Blood." The Qi of the Spleen has an ascending action, and its deficiency is thus associated with prolapse of the organs and "sinking" sensations in the body.

Heart: As in western physiology, the Heart in TCM is said to control Blood circulation. Thus, a deficiency of Heart Qi and Blood can result in symptoms of both vessel and organ deficiency, including paleness, a weak pulse, and serious symptoms such as angina pectoris and irregular heartbeat. The Heart is also said to control mental and emotional activities, predominantly as they relate to consciousness and thought. Dysfunction of the Heart can thus lead to insomnia, excessive dreaming, mental restlessness, and even delirium. It also controls our speech, and thus a person who stutters or talks excessively may be thought to have an imbalance (usually Heat) in the Heart organ or channel.

Small Intestine: The Small Intestine, a Yang organ, is paired with the Heart and is in charge of separating clear, useable substances from turbid waste in the food and liquid passed to it from the Stomach. The clear substance is distributed by the Spleen (as Food Qi) to all corners of the body, while the turbid is sent to the Urinary Bladder and Large Intestine for further processing and excretion. If there is dysfunction of the Small Intestine, poor digestion will result. Heart Fire can also sometimes transfer to the Small Intestine, in turn causing the symptoms of an acute urinary-tract infection due to the Small Intestine's close relationship with the Urinary Bladder.

Urinary Bladder: Paired with the Kidney, the Urinary Bladder is a Yang organ in charge of storing and excreting urine, much as we understand it in western medicine. It also has some transformative power, receiving "turbid" fluids from the Small Intestine and transforming them into urine. Bladder problems commonly lead to urinary incontinence or frequent urination.

Kidney: The Kidneys are often referred to as the "Root of Life," as they store the Essence (known as Jing) we inherit from our parents (prenatal Essence) as well as the Essence we get from the food we eat and air we breath (postnatal Essence). Essence is the source of nourishment for a fetus and later controls our growth, development, sexual maturation, and fertility. Infertility and impotence can be due to a lack of Kidney Essence, as can retarded growth in children and premature senility in adults. Although we can be born with a congenital deficiency of Essence, it is more frequently lost through improper lifestyle habits, especially excessive and premature sexual activity. The Kidneys are also the root of the body's Yin and Yang, as well as that of our bones and bone marrow, brain, and hearing. The Kidneys govern water and Body Fluids, and any problems with the urinary system or other aspects of processing and controlling fluids (edema, bedwetting, frequent UTIs) is likely related to the Kidneys. The Kidneys are said to house "willpower" and their deficiency can lead to indecisiveness and aimlessness. They are also the source of Fire for the whole body; this is housed in the Gate of Vitality (Ming Men), situated between the two Kidneys, and a decline in this Fire can lead to tiredness, lack of vitality, mental depression, and feelings of cold. Sexual function and libido are predominantly a function of Kidney Yang and Ming Men Fire. Kidney Qi also aids in "grasping Qi," which helps the Lungs to allow us to take deep breaths. Asthmatic patients tend to show Kidney deficiencies.

Pericardium: The Pericardium, a muscular layer surrounding the Heart, is charged with protecting the Heart, the "emperor" of the organs. As such, it is referred to as the "palace of the emperor" and is the affected first when the Heart is attacked. Symptoms such as coma and delirium are commonly due to Heat attacking the Pericardium. The Pericardium is considered a Yin organ and is paired with the San Jiao, its Yang counterpart.

San Jiao: The San Jiao, or Triple Warmer, is not actually an organ but rather a set of functions related to the three divisions of the torso, known as the three jiaos. The upper jiao refers to the area above the diaphragm (Lung and Heart), the middle jiao refers to the area between the diaphragm and the umbilicus (Spleen and Stomach), and the lower jiao refers to the area between the umbilicus and the genitals (Kidney, Liver, Gall Bladder, Intestines, and Urinary Bladder). Together, these three areas are known as the San Jiao, and points along the San Jiao meridian are used to treat disorders of all three areas. The main physiological functions of the San Jiao are controlling the activities of the body's Qi, by serving as the passageways through which Qi flows, and regulating the transportation of fluids through the body. Basically, it functions like a series of locks in a canal, alternately restraining and releasing Qi and fluids as needed.

Gall Bladder: The Gall Bladder is a Yang organ paired with the Liver, which belongs to Yin. As in western medicine, the Gall Bladder stores and excretes bile, while the Liver produces and secretes it. Unique to TCM, the Gall Bladder is also said to control courage in decision-making, and thus someone who is indecisive can often be treated successfully by treating the Gall Bladder meridian. It also has some effect on the quality and length of sleep, and someone who lacks Gall Bladder Qi may wake early and have trouble falling back asleep.

Liver: The Liver is said to regulate the smooth flow of Qi and thus affects the Qi of all the other organs and channels. Stagnant Qi (that which is not flowing smoothly) is the cause of many diseases and discomforts and is most commonly seen in those whose emotions are easily upset. In these situations, stagnant Liver Qi often "attacks" the Spleen, causing digestive upset that's worse in times of stress. Anger is especially damaging to the flow of Liver Qi, causing it to rise and often bringing with it Heat. This is why a red face and volatile emotions are associated with the Liver and why we speak of "rising frustration." The Liver's second major job is storing the Blood, which allows it to regulate Blood volume throughout the body. The soul is said to be anchored by Liver Blood, the deficiency of which can lead to a "lost" or ungrounded feeling, especially at night, when Blood is meant to return to the Liver. Menstruation is closely tied to Liver function, and menstrual disorders are not uncommon in those with Liver Qi and Blood problems. Finally, the Liver controls the sinews and tendons, causing tremors and seizures when in disorder, and is also in charge of the nails and partially responsible for our vision.