Source: http://www.yoga.net.au/benefits2  

Identification of area of body that is affected by Salamba Sirsasana (Supported Headstand)

The entire body is reconditioned by the regular practice of Salamba Sirsasana.    But in particular, there are four major systems in the body that the practice of inversions positively influences: circulation/cardiovascular, lymphatic, nervous, and endocrine (Iyengar, 1991; Werner, 2004; Raman, 2004). 

Hatha Yoga Pradipika on Inversions.  The third chapter of Svatmarama's Hatha Yoga Pradipika is named mridavidhanam mentions about the inverted yoga postures. Hatha Yoga Pradioka deals with asanas in the first chapter, pranayama in the second chapter, mudras as well as bandhas in the third chapter and samadhi in the fourth. Mudra means a seal while bandhas means bondage. Mudra seals the energy and bandha regulates the energy. Svatmarama devotes six stanzas (slokas) to explain vipadta kami in the third chapter.

The detailed descriiption of the effects of Salamba Sirsasana (Supported Headstand)

Inverted poses refresh the system as the glandular and circulatory systems get rest from the strain of gravity (Raman, 2004).    The "nourishing" effects of Salamba Sirsasana will be described for the major systems that Sirsasana benefits, including:

Endocrine System

The headstand a favorable reconditioning effect on endocrine gland secretion (Copeland, 1975), to enable it to withstand greater stress and strain (Kuvalyananda & Vinekar, 1963).     All the other inverted postures come under viparita kami. Inversions done accurately are always relaxing and reduce stress and strain. The blood circulation to the brain is improved in Sirsasana; the sluggish cells are rejuvenated and the brain being the seat of intelligence is stimulated. It also stimulates the pituitary and pineal glands on which the growth, health and vital strength of a person depends.

Nourishes and stimulates the pituitary and pineal glands.   In particular, Headstand provides refreshed blood and bathes and nourishes the hypothalamus, pineal gland and the pituitary gland.   These glands play an important role in the endocrine system.  The endocrine system uses hormones to regulate the metabolism of the cells.   Our growth, health and vitality depend on the proper functioning of these two glands that control the chemical balance of the body.  The secretions of the pituitary regulate sexual characteristics and growth of the reproductive organs. It also regulates the function of adrenal, thyroid and the ovaries. It is the hormone which stimulates the production of milk in nursing mothers. Thus, pituitary is the master gland which plays a very important role in regulating menstruation and pregnancy. The inverted postures in turn regulate the functioning of this master gland.

Circulatory System

Inversion exercises the heart and encourages venous return.  Inversions do much the same for the body that aerobic exercise does. According to author Elaine N. Marieb, "The important factor stretching cardiac muscle is the amount of blood returning to the heart (venous return) and distending its ventricles"(Human Anatomy & Physiology 4th edition, Benjamin/Cummings Science Publishing, 1998 p 679.) Inversions use gravity to bring more blood to the heart - turning yourself upside down encourages venous return (Iyengar, 1991; Werner, 2004; Raman, 2004).     .

Reduces heart strain. Normally, your heart works against gravity; inverting your entire body in the headstand lessens the strain on your heart.  The heart works persistently to ensure that freshly oxygenated blood makes its way up to the brain and its sensory organs. When inverting, the pressure differential across the body is reversed, and blood floods to the brain with little work from the heart (Iyengar, 1991; Werner, 2004; Raman, 2004).    

Minimise fatigue and brain tissue degeneration.   Headstand allows a plentiful supply of oxygen-rich blood to reach your head and brain (Sivananda, 2004) - Increasing the blood flow through the brain cells increases your thinking power, clarity, memory, concentration, and the sensory faculties (Iyengar, 1991, pg 190) and moreover minimises brain tissues do not degeneration (Raman, 2004).     Fatigue of the brain cells which occurs as part of everyday life will not occur with regular daily practice of Head stand.  This is due to the rejuvenation of the brain cells with fresh blood and O2 (Raman, 2004).    

Minimise risk of stroke and Parkinson's disease.  According to Dr Raman (Raman, 2004):

“An ischemic stroke never results for those who practice this regularly as the blood supply is kept up par excellence.  …… It can also prevent the occurrence of atherosclerotic Parkinson's disease.

Lymphatic System

The headstand also importantly increases circulation and drainage of lymphatic fluid.   

Fluid build up reduced. Lymph, like the blood returning to your heart via the veins, is dependent upon muscular movement and gravity to facilitate its return.  Thus, in the headstand, lymph fluid is relieved from the legs and ankles and with regular practice prevents the buildup of fluid in the legs and feet.

Strengthening the immune system. Because the lymphatic system is a closed pressure system and has one-way valves that keep lymph moving towards the heart, when one turns upside down, the entire lymphatic system is stimulated, thus strengthening your immune system.

Nervous System

Headstand stimulates the nervous system.

Increases mental alertness and clarity.    The immediate change felt after performing this pose is an enhanced alertness which lasts through the day.  

Soak brain fresh blood.  The most important aspect of inverted poses is to soak the brain with blood for a fixed period of time which never happens in other systems of exercises. According to Dr Raman (Raman, 2004):

“This rejuvenates the brain cells and prevents age related cerebral atrophy. Senile changes in brain are prevented. And as mentioned before ischemic strokes can be completely prevented as the blood supply is enhanced without pressure.”

Calms the brain and helps relieve stress and mild depression.  It is a centering, calming and soothing pose.  A cooling effect is felt on the face in the pose. 

Respiratory System

Healthier lung issue. Inversions also ensure healthier and more effective lung tissue. When standing or sitting upright, gravity pulls our fluids earthward, and blood "perfuses" or saturates the lower lungs more thoroughly. The lower lung tissue is thus more compressed than the upper lungs. As a result, the air we inhale moves naturally into the open alveoli of the upper lungs. Unless we take a good, deep breath, we do not raise the ration of air to blood in the lower lungs. When we invert, blood perfuses the well-ventilated upper lobes of the lungs, thus ensuring more efficient oxygen-to-blood exchange and healthier lung tissue, oxygen consumption and blood flow (Jevning et al, 1983).

Strengthens the lungs.  When done properly, headstand helps the spine become properly aligned, improving posture, facilitating good breathing and reducing muscular stress.  The inversion rests the lungs which feel refreshed. The vital capacity increases as the lungs learn to breathe against the strain of the body organs resting on it in the posture (Raman, 2004).

Digestive System

Increase heat and improves digestion.  Headstand increases gastric fire and produces heat in the body.

Tones and cleans digestive organs. The weight of the abdominal organs on the diaphragm encourages deep breathing, which gently massages the internal organs.  By reversing the pull of gravity on the organs, especially the intestines, it helps to cleanse them by releasing congested blood in the jejunum and colon. Fresh warm blood invigorates the cells and overcome problems of the liver, kidneys, stomach, intestines and reproductive system (Raman, 2004).

Constipation eliminated.  The change in posture enhances peristaltic contractions and aids good elimination. Constipation is eliminated provided the water and fiber content of the diet are normal (Raman, 2004).

Musculo skeletal system.     Headstand strengthens the spine, neck, shoulders and arms. The muscular system of the abdomen and legs are toned.

Other Inversions and there effects

Iyengar has rightly said that one must practice asanas regularly and in case, one does not have enough time then one should at least do the inversions. If Sirsgsana is the father of asanas, then Sarvangsana is the mother of isanas. The health of the body and mind is dependent on the practice of these two isanas as the health and happiness of the children is dependent on their parents.

Viparita karni is a mudra where the head is down and legs are up, palate is down and the navel is up, moon or soma chakra which lies in the centre of the brain is down and sun or surya chakra which lies in between the navel and diaphragm is up. It has to be learnt under the guidance of a Guru and practices everyday gradually increasing the duration of stay in the posture. In the upright position the sun (navel) swallows the nectar which is dropped down by the moon but in viparita karni the sun absorbs the nectar. The practice of viparita karni increases gastric fire and improves the digestion and keeps the person younger preventing him from getting wrinkles or grey hair and postpones death.

Sarvangasana works effectively on the thyroid and parathyroid by increasing the blood supply. Halasana is effective on adrenals