Doshas of the body: Except those caused by the external factors, all diseases in the body are caused by the imbalance of The Three Body Humours, The sustaining Forces, Vata, Pitta & Kapha (V, P & K) in the body. These three humours are present all over the body, though there is prominence of Vata in the region below naval area, Pitta is prominent between the naval and heart region and Kapha in the region above heart. Again, the varying composition of the three humours is what is responsible for the formation of the human body.
These humours may be taken as the material substances which make up our body. The three have specific properties, quantity in the body, and specific functions to perform. The imbalance in any one of the three, quantity, quality or functions, which primaily happen as per what we intake, without even bothering to think for a minute, what we are eating. The vitiation primarily takes place in The Dhatus, The Tissues, where The Three Doshas reside. Obviously the effect would be different at different places of the body, depending which Dhatu (The Body Tissue) we are dealing with and which of the Dosha (V, P or K) has got vitiated.
The food that we eat, gets converted to Dhatus (in the form of Rasas – Understand this as Juice or essene), gets assimilated in the body, takes care of formation & balancing of V, P & K in the body, and the excretion of waste products takes place in the form of sweat, urine and faeces, and also, V, P & K.
Now, all the three Doshas (V, P & K) follow the cycle of Accumulation (Sanchaya), Vitiation/Aggravation (Prakopa, Doshas becoming Deranged, fall in quality etc.), and Pacification (Prashama, Decrement or Normalising).
Qualities of Vata: Dry, Mobile, Rough, Subtle, Non-Slippery (Relates to the Nervous System, this is the Nerve Force of the Body).
Qualities of Pitta: Hot, Sharp, Slightly Slippery, Mobile (Relates to the Overall Metabolism System).
Qualities of Kapha: Cold, Heavy, Slippery, Immobile, Sweetness, Provides Firmness and holds the body (Relates to the Immune System, Fills up the Intercellular Spaces of the body).