Purpose of of panchakarma is to remove excesss / aggravated doshas, dhatus, malas and toxins to improve metabolic activity of tissue and maintain proper functioning of various systems and organs.

There is natural tendency of the body to remove unwanted substances through GI tract. It takes help of secretion and appearance of moistening agents [kapha], converting agents [pitta] and absorbing and mobilizing agents [vata].

We accumulate many toxins through air, water, food, sounds and even emotions. Those of air accumulate un the lungs and on the skin. Water and food toxins first go to the gastro intestinal tract. Toxins due to bad emotions and sound disturbs the mind as well as body.
Too much toxins are responsible foe ageing. [various free radical theory] they make immune system weak and can cause auto immune diseases. They can also make vital organs like brain, liver, heart and kidney weak. They can also aggravate doshas.

When aggravated doshas attack weak tissue, organs and channels they started the disease process. Many times toxins mask the organ and hence the medicines do not reach the site of the diseases. Hence after panchakarma, the same drug can be used effectively.
Before main panchakarma procedures, oleation and fomentation – internal or external are done. Oleation removes the toxins from the toxins attached to the tissuses. Proper oleation with the fat medium ensures protection to the lumen wall and guards retainable tissues in the body. It ensures maximum secretion of toxins, doshas etc. towards the GI tract.

Sudation liquefies the toxins, doshas which are sticking to the walls of the system/organ making it thin and modable. This makes the centripetal propulsion easy. Also it enhances this by making the pores wide open.

The main purification procedures are responsible for reducing aggravated doshas and toxins from various organs and channels. Many times these are done by direct or remote method. Vamana or medicated emesis removes kledaka kapha directly from the stomach but also reduces avalambaka apha remotely.

Virechan or medicated purgation removes itta and kapha from the intestines but also removes doshas and toxins from the organs like liver, spleen and pancreas.

Basti acts on the distal portion of large intestines. Warm herbal decoctions and fatty substances nourishes all tissues and separates sticky toxins from the wall.

Nasya removes doshas from the region of head and acts on the limbic system of the brain through the cribriform plate at the base of the skull.

Blood letting has to be done by artificial opening in the blood vein. It removes excesss pitta in the blood and purifies the same.