Internal Organs are called Zang. These are the decision making and balancing centres of the body. They are the Heart,  Liver, Spleen, Lung, Kidney and Pericardium.
Their main functions are manufacturing and storing essential substances including Qi, Blood and Body Fluid.
 External organs, or Fu are the Small Intestine, Gall Bladder, Stomach, Large Intestine, Urinary Bladder and Sanjiao.  They receive and digest food, absorb nutrient substances and transmit and excrete wastes.
 There are also extraordinary organs- the brain and uterus- which have no place in generating Qi but are supplied with nourishment by the body.

 Each of the Zang is internally-externally connected to a Fu, and this pair corresponds to an element in the Sheng = nourishing cycle.

The pairs are as follows:

Internal          External

Heart   Small Intestine.
Liver     Gall Bladder
Spleen    Stomach
Kidney  Urinary Bladder
Pericardium Sanjiao

   ZANG ORGANS

Heart
The channel of the Heart is connected to the Small Intestine.
The Heart also opens into the tongue.
Functions
1. Controlling blood and vessels. Vessels are the site of Blood containment and circulation, the impulse of the Heart sending blood incessantly through the vessels to nourish the whole body. When the Blood supply is sufficient the blood  circulation normal, the complexion will be rosy and lustrous, and vitality full. The tissues and organs are well nourished and function properly.
2. Housing the Spirit. The Heart is considered the main organ is governing mental activities of the brain. Spirit, consciousness, memory, thinking and sleep are all dominated by the function of the Heart. According to Neijing: The Heart controls the vessels and the vessels supply the mind.
 Opening into the tongue. The two functions of the Heart, ie, controlling Blood and vessels and housing the Mind, are closely related to the color, form, vitality and sense of taste of the tongue. This is also expressed as “the tongue is the mirror of the Heart”.

Liver
The channel of the Liver connects with the Gall Bladder.
The Liver opens into the eye. 
 Its problems can manifest on both sides of the ribs, since the channels are bilateral.
Functions
1. Storing Blood. The Liver possesses the function of storing Blood and regulating the volume of circulating Blood. During rest, part of the Blood remains in the Liver, while during vigorous activity Blood is released from the Liver to increase the volume of Blood in Circulation to the  required amount. The Liver, therefore, along with the Heart, supplies the tissues and organs with Blood, and it influences menstruation as well.
2. Maintaining patency for the flow of Qi. This means that the Liver is responsible for harmonious and unobstructed functional activities of the human body, including the following three aspects.
 a. The Liver is related to emotional activities, especially depression and anger. Prolonged mental depression or a fit of anger may weaken the Liver so that is unable to promote the unrestrained and free flow of Qi. Conversely, dysfunction of the Liver is often accompanied by emotional changes such as mental depression and irascibility.
 b. The harmonious and free flowing functional activity of the Liver promotes the functioning of the other Zang-Fu organs, channels and collaterals, especially those of the Spleen and Stomach in digestion and absorption.
 c. This function of the Liver also affects bile secretion, its storage in the Gall Bladder and excretion into the intestines.
3. Controlling the tendons. The Yin and Blood of the Liver nourish the tendons, keeping them in a normal state of contraction and relaxation. When the Liver is supplied with ample Yin and Blood, the tendons are strong and free in extension and flexion.
4. Opening into the eye. Each Zang-Fu organ has a certain influence on the function of the eye. However,  because the Liver stores blood and its channel directly communicates with the eye, it has a closer relation to ocular function, such as vision and movement of the eye, than other Zang-Fu organs.

Spleen
The channel of the spleen connects with the stomach.
It opens into the mouth.
 The main physiological functions of the Spleen are governing transportation and transformation, controlling the blood and domination the muscles.
Functions
1. Governing transportation and transformation. Transportation implies transmission. Transformation implies digestion and absorption. The  spleen has the function of digesting food, absorbing its essential substances with a part of the fluid supplied, and transmitting them to the heart and the lung from where they are sent to nourish the whole body. Normal functioning of the spleen is required for good appetite, normal digestion and absorption, good nourishment and normal transmission of fluid.
2. Controlling blood. The spleen has the function of keeping the blood circulation inside the vessels and preventing it from extravasation.
3. Dominating the muscles. Normal function of the Spleen in transportation and transformation enables the muscles to receive adequate nourishment from the food essentials and thus maintains muscle thickness and strength.
4. Opening into the mouth. The spleen and the mouth co-ordinate functionally in receiving, transporting and transforming food. When the function of the Spleen is normal, the appetite will be good and the lips will be red and lustrous.
 The Qi of the Spleen has the further function of holding and keeping the internal organs in their normal positions.

Lung
The channel of the Lung connects with the Large Intestine.
The Lung opens into the nose.
Functions
1. Dominating Qi and controlling respiration. The Lung is a respiratory organ. Through its function of dispersing and descending, it inhales clean Qi to supply the body’s functions and exhales waste Qi. This is what is known as the function of “getting rid of the stale and taking in the fresh”. As the function of the Lung greatly influences the functional activity of the whole body, the Lung is said to dominate the Qi of the entire body.
2. Regulating water passages. The dispersing and descending function of the Lung regulates water passages, promoting water metabolism. Its dispersing function turns a part of the body fluid into sweat to be excreted, while its descending function continuously sends a part of the body fluid down to the Kidney and on to the Urinary Bladder to be excreted as urine.
3. Dominating the skin and hair. Here the skin and hair signify the entire body surface. The Lung disperses the essentials of food to the body surface, giving lustre to the skin, gloss and luxuriance to the hair, and regulating the opening and closing of the pores.
4. Opening into the nose. The nose is the “gateway” of respiration . Unobstructed breathing and a keen sense of smell depend on good function of the Lung.

Kidney
The Kidney channel connects with the Urinary Bladder.
It opens into the ear.
 Its main physiological functions are: storing essential substances and dominating human reproduction, growth and development, producing marrow which collects in the head forming the brain, dominating the bones and manufacturing blood, dominating body fluid and receiving Qi.
Functions
1. Storing essence and dominating reproduction, growth and development. The essence in the Kidney, also referred to as the Yin of the Kidney, consists of two parts:
Ancestral essence inherited from the parents
Acquired essence transformed from the essential substances of food.
 The vital essence of the Kidney is an important aspect of the Qi (vital functions) of the Kidney, greatly influencing the function of the Kidney in reproduction, growth and development. Neijing:” At the age of 14 for women and 16 for men, the Qi of the Kidney flourishes. Women will have the onset of menstruation, and men mill have seminal emission, both signifying the power of reproduction. When women reach the age of 28 and men around 32, the Qi of the Kidney is at its height, the body grows and develops, reaching the prime of life. When women reach the age of 49 and men around 64, the Qi of the Kidney starts to decline, the body begins to wither and at the same time the function of reproduction gradually fails”.
2. Producing marrow, forming up the brain, dominating the bones and manufacturing blood. The Kidney stores essence which can produce marrow- including spinal cord and bone marrow. The upper part of the spinal cord connects with the brain, while the bone marrow nourishes the bones and manufactures blood. The supply to the brain, the solidity of the bone, and the adequacy of the blood are therefore all closely related to the condition of the essence of the Kidney.
3. Dominating water metabolism. The part of fluid sent down by the descending function of the Lung reaches the Kidney. There is divided by the Yang function of the Kidney into two parts; clear and turbid. The clear = useful fluid it retained, and the turbid = waste fluid flows into the Urinary Bladder to form urine which is excreted.
4. Receiving Qi. Respiration is accomplished mainly by the Lung, but the Kidney helps through its function of controlling reception of Qi. The distribution of the clean Qi inhaled by the Lung to the whole body depends not only on the descending function of the Lung but also on the Kidney’s function of reception and control.
5. Opening into the ear. The auditory function is dependent upon the nourishment from the Qi of the Kidney. Deafness in aged people is mainly due to  deficiency of the Qi of the Kidney.

 Pericardium
 Its channel connects with the Sanjiao. Its main function is to protect the heart. The Pericardium is not generally regarded as an independent organ but as an attachment to the Heart.

FU ORGANS

Small Intestines
 The Small Intestine channel connects with the Heart, with which it is related. Its main function is to receive and temporarily store partially digested food in the stomach. Further digesting the food and absorbing the essential substance and a part of the water in  food, the small intestine transfers the residues with a considerable amount of fluid to the Large Intestine.

Gall Bladder
 The Gall Bladder channel connects with the Liver. Its main function is to store bile and continuously excrete it to the intestines to help digestion. This function of the Gall Bladder is closely related to the function of the Liver in promoting patency of vital energy. It is therefore said that the Liver and Gall Bladder preside over the unrestraint and patency of vital energy.

Stomach
 The Stomach channel is connects with the Spleen.  Its main function is to receive and decompose food. That is to say, the stomach receives and temporarily stores the food mass coming from the mouth through the esophagus while partially digesting it and then sending it downward to the Small Intestine. That is why the function of the stomach is normal when its Qi is descending and abnormal when its Qi is ascending. The Stomach and Spleen act in co-operation and are the main organs carrying on the functions of digestion and absorption. It is said that the Spleen and Stomach are the source of health.

Large Intestine
 The Large Intestine channel connects with the Lung. The main function of the Large Intestine is to receive the waste material sent down from the Small Intestine and, in the process of transporting it to the anus, absorb a part of its fluid content and then turn it into faeces to be excreted by the body.

Urinary Bladder
 The Urinary Bladder channel connects with the Kidney. Its main function is the temporary storage of urine and its discharge from the body when a certain amount has accumulated. This function of the urinary bladder is accomplished with the assistance of the Qi of the Kidney.

Sanjiao
 The channel of Sanjiao connects with the Pericardium.
  Sanjiao  is not a substantial organ, but a generalisation of part of the functions of some of the Zang-Fu organs located in different sections of the body cavity.
Sanjiao is divided into three parts:
(1) Upper jiao (portion) (representing the chest) is a generalisation of the function of the Heart and Lung in transporting Qi and Blood to nourish various parts of the body. It is like an all pervading vapour.
(2) Middle jiao (portion) (representing the epigastrium) is a generalisation of the function of the Spleen and Stomach in digestion and absorption. This may be compared to soaking things in water to cause decomposition and dissolution of substances.
(3) Lower Jiao (portion) (representing the hypogastrium) is a generalisation of functions of the Kidney and Urinary Bladder in controlling water metabolism as well as storage and excretion of urine. It is like an aqueduct, a pathway for the flowing water.

EXTRAORDINARY ORGANS

Brain
 Nei Jing “The Brain is a sea of marrow. Its upper part is under the scalp of the vertex, point Baihui = Du 20 and its lower part reaches point Fengfu = Du 16.
 Yixue Yuanshi  (Origin of Medical Sciences) “The sense organs, i.e., the ears, eyes, mouth and nose, are in the head close to the Brain. Owing to their highest and most obvious position, they may perceive objects, which will impress the Brain directly and remain in the Brain”.
Yilin Gaicuo (Medical Correction) suggested that thinking and memorisation are the main functions of the Brain.
As mentioned previously, the essence of the Kidney produces marrow that forms the Brain. The filling of the “sea” of marrow depends on the essence of the Kidney. Furthermore, the Heart, which houses the mind, and the Liver, which dominates the unrestraint and patency of vital functions, are also related to mental activities.
 A tenet of traditional Chinese medicine, therefore, is that mental activity is dominated by various organs, the Heart being the main one.

Uterus
 The function of the Uterus is to preside over menstruation and nourish the fetus. Internal organs and channels related to the function of the uterus are as follows:
(1) Kidney. The Uterus is connected with the Kidney, and only when the essence of the Kidney is ample can the menstrual period recur regularly, and the impregnation and growth of the fetus be possible.
(2) Liver. The Liver performs the function of storing Blood and regulating the volume of circulating blood, which is also responsible for normal menstruation.
(3) Ren Channel and Chong Channel. Both originate in the Uterus. The Ren Channel regulates the function of all the Yin channels and nourishes the fetus. The Chong Channel has the function of regulating the Qi and Blood of the twelve regular channels. The Qi and Blood of the twelve regular channels pass into the Uterus through the two channels, affecting the amount of menstrual flow and its cycle.