Essence, Ki, Spirit and Blood are the core constituents of the human body. They are made by the metabolism of the Eum and Yang in the nutrition we take in. Essence(精) is the house of Spirit(神), so when Essence is harmed Spirit loses a place to stay and is unable to guard the body. According to the Neijing "what comes with birth is Essence, and the parents' Essence combined becomes Spirit." "The parents' Spirit united forms body, therefore what is there before the formation of body is Essence." Wherever Essence is, Spirit exists, and by storing Essence, Spirit becomes whole.

        Original Ki is rooted in Essence. Essence is Eum and Ki is Yang, and Yang has its root in Eum. In this sense, Essence is the mother of Ki. When Essence is deficient Ki cannot exist, and if this state is continued a living creature dies.

        If Spirit is made into Ki and forms Bodily Fluid, a life begins. So, if Spirit does not dwell in a body it is not living, and if the creature loses Spiriti it dies.

        In concentrated words, Essence is the unit of the formation of human body, and Spirit is expressed as the state of mind and manifested through one's mentality. Ki is the energy of life or life force. The representative of the material constituent of the body is Blood and it circulates.

        Here are some quotes from Dong Eui Bo Gam, which puts chapters on Essence, Spirit, Ki, and Blood in the very front of the book.

Essence

● Essence is the fundament of life.

l ● Essence is the ultimate treasure.

l ● The five organs each contain Essence

l ● Taste supports Essence.

        The concept of Essence is the basic element that makes up body and maintains life. There are two major forms of Essence, one of which is inherent, that is stored in the Kidney, and is related to growth and development. It is called the Essence of reproduction. Another, acquired Essence is transformed from grain (food) and water.

Ki

l● Ki is the root of Essece and Spirit.

l● Grain makes Ki.

l● Ki protects the exterior of the body by becoming the defensive Ki.

l● Ki is the base of respiration.

l● Lung masters Ki.

        There are many names to a Ki. Genuine Ki(眞氣) is also known as original Ki. This is the ultimate Ki of all, that is the sum of inherent Ki, acquired Ki and the heavenly Ki inhaled by the Lung. The five organs distribute and operate Ki. Genuine Ki flows into collaterals an meridians to become the 'Ki of the colaterals and meridians.' There are nutritious Ki and defensive Ki. Nutritious Ki flows into the vessels, along with Blood. It is what makes Blood and delivers nutritions. Defensive Ki is fast and brave, flowing the exterior of the body along with the vessels. Inside the body, it is scattered around the Stomach to warm the Intestines. Outside, this Ki flows between the skin and the inner organs to protect them. Chief Ki provides the source of energy for the Heart, by flowing between the mouth and the abdomen. It regulates respiration and the heart rate.

        The five effects of Ki are activation of movement(推動), warming the body(溫煦), defending it(防禦), vaporizing(氣化) and retaining(固攝). Ki makes possible growth, development, metabolism and activities; sustains body temperature to a certain level; protects the exterior; disperses Blood and Bodily Fluid--they become sweat and urine; and it keeps blood in the blood vessels.

Spirit

l● Spirit is the master of the body.

l● The five tastes produce Spirit.

l● Heart contains Spirit.

l● The five organs contain the seven Spirits.

        The concept of Spirit is the homeostasis of everything between the Heaven and the Earth. It is the most critical element of every living creatures' reproduction. The ultimate normal state of the body is Spirit. It also means the mental activities of people. It is first given by parents and later supplemented by consumption of food, etc. The effect of Spirit is related to the five organs, and each Spirit becomes concretized in them. They make possible all the emotional expressions.

Blood

l● Water and grain makes Blood, which is Eum compared to Ki.

l● Blood becomes nutrition.

l● Blood is the partner of Ki.

        Water and grain from the Stomach and Spleen become Ki, Bodily Fluid and chyme. Among the three of them, Bodily Fluid and Nutritious Ki meet and get influenced by Heart to turn red and become Blood. The Heart masters Blood, and Blood circulates the body under the command of the Heart. Liver sores Blood. When a body mobilized, Blood circulates through the meridians and the collaterals.  When it stops, Blood returns to the Liver. Spleen is in charge of the regulation of Blood and holds it inside the vessels while circulation.

        Ki is the mentor of Blood. It means that the three relations of Blood and the organs mention above are made possible by the function of Ki in the organs. Furthermore, nutritious Ki makes Blood. In some texts, confusing though it is, Blood is cited as the mother of Ki, for Blood gives Ki the power to enable the body movements.