Sapta Dhatus:

The dhatus are the basic varieties of tissues which compose the human body. The word “dhatu” comes from a Sanskrit word which means “that which enters into the formation of the body”

The primary Dhatus are:

Rasa dhatu (Chyle, Lymph, Plasma)
Rakta dhatu (Haemoglobin fraction in blood)
Mamsa dhatu (Muscle tissue)
Medas dhatu (Fat or Adipose tissue)
Asthi dhatu (Bone-tissue including cartilage)
Majja dhatu (Bone Marrow)
Sukra dhatu (Semen, Sperm, Ovum).

Together the dhatus and upadhatus make up the physical bulk of the body.
The upadhatus include hair, nails, ligaments, etc; they are important structurally but usually are not implicated in disease conditions of the body.

Each dhatu consists of countless infinitesimal paramanus (cells) which are units of structure and function. Each paramanu contains innumerable suksma srotas (channels, pores) through which it receives nutrients and subtle energies and eliminates waste materials. The srotas of each dhatu are unique in their structure and function and in the materials which move through them. All the seven dhatus are well connected to each other - damage or malformation of one dhatu can in turn affect all other dhatus.

According to Ayurveda, diseases are due to Tridosha (Vata, Pitta and Kapha) but actual pathology took place in Sapta Dhatu (Rasa, Rakta, Mamsa, Medas, Asthi, Majja, Sukra) whichever is weak.

To Sum Up:

The Sapta (seven) Dhatus (tissues) elements form the pillars of the body that form the means of nourishment and growth while providing support to the body as well as the mind.

Rasa (fluid) dhatu –Derived from the digested food, it nourishes each and every tissue and cell of the body and is analogous to the plasma.

Rakta (blood) dhatu – Regarded as the basic of life, it is analogous to the circulating blood cells. It not only nourishes the body tissues, but provides physical strength and colour to the body.

Mamsa (muscle) dhatu – The muscle tissue, its main function is to provide physical strength and support for the medas dhatu.

Medas (fat) dhatu – Consists of adipose tissue providing support to ashti dhatu. It also lubricates the body.

Ashti (bone) dhatu – Comprising of bone tissues, including cartilages, its main function is to give support to the majja dhatu and provide support to the masma dhatu.

Majja (marrow) dhatu – Denoting the yellow and red bone marrow tissue, its main function is to fill up the ashti and to oleate the body.

Sukra (semen) dhatu – The main aim of this reproductive tissue is to help reproduction and strengthen the body.

Since the dhatus support and derive energy from each other, affecting one can influence others. For instance, interference in the manufacture of the plasma affects the quality of the blood, which in turn effects the muscle. Each tissue type has its own agni, which determines metabolic changes in the tissues. And forms by-products, which are either used in the body or excreted. The tissues are also governed by the three doshas, and any imbalance in them also causes imbalances in dhatus.

Vedic Astrology is able to pinpoint inherent and/or transient weaknesses in specific Dhatus.