According to Ayurveda our body have many channels through which all the material either nutritive or waste material move either way is called srotras. The literal meaning of the word srota is body passages or body channels. These channels are present throughout the visible and invisible body of the cells, molecules and atoms.

The body channels carry solids, liquids, gases, nerve impulses, nutrients, waste products and secretions in and out of the human body physiologies. According to some physicians human body is a network of appropriate nutrients and energies through the channels results in healthy mind and body. Any kind of blockage, deficiency or excess in the channels can result in various diseases.

The body channels are classified in two categories :
Internal channels
External channels

There are thirteen srotas in the internal channels. Among thirteen srotas, three srotas connect the individual to the external environment by inhaling and exhaling air, food and water. These three srotas are :
Prana vaha srotas – carries the breath to all parts of the body
Anna vaha srotas – transports solid and liquid foods
Udaka vaha srotas – transports water

The other seven srotas are associated with the seven dhatus or tissues. These are :
Rasa vaha srotas – carries plasma and lymph
Rakta vaha srotas – carries blood cells specially haemoglobin
Masma vaha srotas – carries muscle nutrients and wastes
Meda vaha srotas – supplies adipose tissues
Asthi vaha srotas – carries nutrients to bones and transports wastes
Majja vaha srotas – supplies bone marrow and nerves including the brain
Shukra vaha srotas – carries the sperm and ova and supply nutrient to them

The other three srotas eliminates the metabolic waste from the body. These are :
Purisha vaha srotas – carries faeces
Mutra vaha srotas – carries urine
Sweda vaha srotas – carries sweat

The external channels have their natural openings on the surface of the body. The pair of ears, eyes and nostrils, the mouth, anus and the urethra is the nine openings of the channels opening externally.

According to some ancient authorities there are three more srotas related to lactation, menstruation and the flow of thoughts to the mind. These three srotas are :

Artava vaha srotas – carries the menstrum.
Stanya vaha srotas – carries the breast milk during lactation.
Mana vaha srotas – carries thoughts, ideas, emotions and impressions.

The food and activity that promotes the morbid tendencies of the three humors and are harmful to the body elements results in blockage of the body channels.

Ayurveda helps in diagnosing the affected srotas, its nature and extent of blockage and ultimately helps in knowing the process of disease. Ayurveda also takes the help of doshic imbalances, dhatus and Agni in the assessment of disease.