Sapta means seven and the word Dhatu refers to various types of tissues the human body is made of.
The word Dhatu in Sanskrit means “that which forms the body”. The root Dha means support and the Dhatus sustain the body.
Modern anatomy describes the structure of human body in different ways. Gross anatomy refers to the structure as seen by the unaided eye. The human body is cut open and the various organs are described as they appear.
This again can be classified as systemic anatomy which describes each system in detail. For example the gastro-intestinal system starts with the mouth which leads to the esophagus, stomach, small intestine and large intestine.
Regional anatomy describes all the structures in a given region and their relation to each other. For example if we dissect the region of elbow we come across fatty tissue, blood vessels, nerves, muscles and the joint.
Microscopic anatomy goes deeper and describes the minute structure of a tissue which cannot be seen by the unaided eye. For example if we take a small piece of the human skin and examine it under a microscope it is found to have several layers. Electron microscope goes even deeper and can reveal what light microscope cannot.
Ayurveda presents a simplified description of the human body. It says human body is made up of seven types of tissues called sapta dhatus. It is worth pointing out that this concept is not entirely against the principles of modern anatomy.
Anatomy describes the different systems in the body like nervous system, musculo-skeletal system, respiratory system, cardio-vascular system etc. But the various organs like lungs, muscles, liver etc have many common features, with some unique features.
The seven dhatus mentioned are Rasa, Raktha, Mamsa, Medho, Asti, Majja and sukra.
Rasa: The food we consume is digested in the stomach and intestine and forms a fluid. This is called Rasa dhatu. In modern science it is called chyle.
This is absorbed into the blood stream and becomes part of the plasma the fluid which can be seen after the cells in the blood settle down at the bottom if blood mixed with an anticoagulant (a substance which prevents blood from clotting) is kept in a tube.
Rakta: Rakta means blood. Blood is responsible for carrying oxygen and nutrients to all the cells of the body.
Mamsa: This refers to muscle tissue. There are three types of muscles in the human body. The skeletal muscles are responsible for movements of joints and are under voluntary control. Smooth muscles are present in internal organs and are not under voluntary control. For example the intestines contain smooth muscles which propel food forward. Cardiac muscle is present only in the heart and is a specialized tissue responsible for pumping of blood.
Meda: This is the adipose tissue which consists mainly of fat. It is responsible for lubrication.
Ashti: This consists of bones and cartilages. Bones give strength to the body.
Majja: This refers to the bone marrow. It is a spongy substance inside the cavity of bones. The cells of the blood are formed in the bone marrow.
Shukra: The shukra dhatu is represented by the semen in the male and the ovum in the female. It is responsible for reproduction. But a part of this dhatu transforms itself into ojas.
The word ojas is a Sanskrit word which literally means vigor. It is somewhat an abstract entity and its equivalent in modern medicine is not known. It is the interface between the spiritual and the material dimension of a human being.
We all know that some people are full of energy, rarely fall sick and have a bright look on their face. On the other hand some people always feel tired, fall sick frequently and look dull. It may not be possible to identify any difference between the two by conducting detailed physiological and biochemical tests.
According to ayurveda the difference is in the level of ojas. Ojas integrates body, mind and spirit together resulting in a unique individual. Ojas is responsible for bala (strength) and vyadhikshamatva (resistance to diseases).
Scriptures describe two types of ojas-Para ojas and Apara ojas. Para ojas is said to be located in the heart and its loss leads to death. Apara ojas is distributed throughout the body.
During the eighth month of pregnancy ojas is unstable and moves between the mother and the fetus. Delivery during this period is risky and the baby may die if ojas has not crossed into the fetus.