A REVIEW LITERATURE OF TWAK SHARIR - W.R.T. RACHANA AND KRIYA SHARIR

Ayurveda is an ancient & holistic system of medicine. Sushruta Samhita an oldest one Samhita of Ayurved. Acharya Sushruta in sharrer sthan has mentioned five Gyanendriyas (sense organs). skin, which is largest covering organ of body, in Ayurveda it comes under the term Sparshanendriya and adhishthana is Twacha (skin). Skin performs many functions like touch sensation, cold, temperature, pain, pressure, etc. skin serve to be first line of defense whatever we get into from environment the first response is from skin. Functions of all three dosha are well elaborated in the twak . Vata is responsible for carrying sensory input from twak to murdha by vyaan vayu , Piita in form of bhrajak pitta controls all the types of metabolic activities, and Kapaha regulates functions of sweat gland and sebaceous glands and maintains moisture. Being largest organ in the body it is also site of mana and rasa dhatu. Rasa dhatu kshaya is firstly and well elaborated in twak . Aging is the process that is well depicted in twak . Ayurveda advocates preventive and curative measure to control aging of twak . This article has been comprehended with all details about skin ( twak ) including Utpatti , synonyms, kriya, Rachna sharir of Twacha , types (layers) etc. skin is one of rog marg variety of diseases are observed on skin which are very unpredictable. Skin is not only rogmarg but also it is part of treatment modality. understanding twak an account with anatomy & physiology will help in various ways for diagnosis, prognosis, treatment etc.


INTRODUCTION
Skin is uppermost or outer part of body, which is more exposed than any other, so it becomes easy to examine, inspect or observe. Though the chances of exposure to sun light, microbes, pollutants, damage may increase, skin is quite capable to protect from all such. skin is protective in nature, so it heals easily from such damages. Skin can reflect one's emotions, psychology, behaviours, moods, interpretation. sweating, blushing are reactions observed on skin. Skin Colour change is very much helpful for diagnosis, or examination of patient. it has a great role in medical diagnosis process. In anaemia colour changes to pale, in jaundice -yellowish, bluish skin is indicative of less oxygen supply. Skin patches or rases are indicative of diseases such as chickenpox, measles, food allergy, cosmetic allergy. Some other conditions like moles, hyperpigmentation, warts, age spots, pimples are due to involvement pathology of skin. people are so mad for beauty of skin they invest much more time and money for the same. Everyone wishes for youthful and young appearance of skin.
dosha -dhatu & mala are the main components of sharir. twacha is updhatu of mamsa dhatu as well as moolsthan of mamsa. twacha covers mamsa dhatu. twacha has several views regarding uttapti, layers, diseases. acharya charka and sushruta has elaborated twacha in different way. skin maintains normal physiological conditions. Acharya yogratanakar has included twak pariksha in ashthvidh pariksha. to study skin with respect to Rachana & kriya is important to deal with all such factors helpful for diseases and its management. Twacha is the seat for various twakrogas. Almost each rogahas its one or many lakshanas having vyaktisthanas twacha. Twacha is a seat of sparshanendriya. To know the vikruti first one should know the prakruti. Skin is the vital body part and sensory organ too. In modern times, the physicians are challenged with many novel diseases, as well as with novel forms of old diseases, that mark the medical practice more challenging and interesting too.

MATERIAL AND METHODOLOGY
Available literature regarding Twak (twacha) in Ayurvedic text such as Bruhartryi, Laghutrayi, Ghanekartika etc. and modern text such as Cunningham's manual of practical anatomy, Human anatomy by B.D. Chaurasia. Materials from electronic media and journals related to the skin.

REVIEW OF TWAK WRT RACHANA AND KRIYA SHARIR
In ayurved Samhitas Twak is explained in detail with layers, types, and diseases. It is described as outer protective layer and sensory organ. Acharya Sushrut and Charak has explained very clearly different layer, its breadth, functions, and diseases for that particular layer. Ayurveda explains seven layers of the skin in detailed. each layer provides support to other layers so in whole all together perform functions better. In Ayurveda, skin is considered a manifestation of inner health. Position of twak is very crucial as it is the site of Vyaan Vayu, Bhrajak Pitta, Rasa dhatu and Mana also. It functions as bridge between body and mind. It should not be considered merely a covering of the body. It is in fact the mirror of the body which reflect the healthy or diseased state.

UTPATTI (FORMATION OF TWAK)
Formation of Twak (Utpatti) According to Sushruta and Vaghbhata, after Shukra, Shonita sanyoga, pachyamanawastha occurs and seven layers of Twak are formed like cream over milk. Twak is matruja organ and still it is generated as the sparshanendriya from Atmaja bhava. As per charaka, Twak is also generated during third month as it is Dnyanendriya. Twak is considered as an updhatu of mamsa dhatu along with vasa that are produced by matrija bhava itself. Acharya Vagbhata says that Twak is derived by the action of rakta dhatvagni from rakta.
Synonym: Twak, Twacha, Charma, Sparshan, Sparshanendriya etc. Acharya Sushruta has described seven layers of Twak in Samhita along with specific name. Acharya Sushruta has clearly mentioned the thickness of each layer of twak but we are not able to find it applicable all over body uniformly. Twak width is having great anatomical variations i.e., different at different places e.g., it is quite thick over chest, abdomen and thin over forehead and fingers. We should consider the twak width of abdomen as reference as Sushruta has mentioned that during surgery thickness of incision in abdomen should be of thumb width.

MODERN ASPECT OF SKIN
Skin outermost cutaneous membrane which covers the external surface area. Skin is the largest organ of the body in accordance with weight and body surface area. Adult skin area is about 2 square meter (22 square feet) and weight about 4.5 kg (10 -11 lb) i.e 16 % of total body weight. Thickness of skin ranges between 0.5 mm (0.02in,.) to 4.0 mm (0.16in.). almost over body it is 1mm (0.04 -0.08 in) thick. skin is composed of two parts. Bhishagratna (1911) • Epidermis: outer superficial thin portion made up of epithelial tissue.
• Dermis: deep thick portion of connective tissue. Another one layer is attached deep to dermis is subcutaneous layer, it is not part of skin. It consists of areolar & adipose tissue which is also known as hypodermis. fibres from dermis anchor the skin to subcutaneous layer and again it attaches to underlying organ and tissues.
This deep layer (subcutaneous layer) works as storage for fat, blood vessels which supply skin. It contains nerve endings called as lamellated corpuscles which are sensitive to pressure. The subcutaneous layer serves as a storage depot for fat and contains large blood vessels. Garde (1999)
irregular, polyhedral cells with cytoplasmic processes. they extend outward and contact to another cell by desmosomes.

DERMIS
Dermis is connected to epidermis at basement membrane level. dermises consist of two layers. 1) Papillary layer: it is upper layer, thin consists of loose connective tissue and contacts epidermis. 2) Reticular layer: it is deep layer, thick less cellular in nature. It contains dense connective tissue, collagen fibres. Dermis has hairs, hair follicles, muscles, sensory neurons, sweat gland and blood vessels.

HYPODERMIS
Hypodermis also known as subcutaneous fascia is deeply situated to dermis. This deep layer consists of hair follicles, sensory neurons, blood vessels and adipose lobules. Table 2 Table 2

RELATION WITH TRIDOSHA
Vat: Touch sensation (Sparsh) and circulation is related to Vyan Vayu. Excess vayu represented by darkness of skin Pitta: Bhrajak pitta related for giving lustre and colour. Excess pitta by yellowness of skin Kapha: related to moisture or snigdhata and represented whiteness of skin.

RELATION WITH TRIMALA
Sweda: Sweat (Sweda) among trimala excreted by skin which helps to maintain body temperature.

TWAK SARA: TWAK SARA IS ALSO KNOWN AS RASA SARA
Acharya kashyapa has clearly mentioned that as rasa dhatu nourishes twak, twak sara lakshanas are same as rasa sara. Skin of twak sara person is characterized by glossy, smooth, soft, clear, fine, less numerous, deep rooted, and tender hairs and such individual is endowed with happiness, good fortunes, power, enjoyment, intellect, knowledge, health, excitement, and longevity.

PHYSIOLOGICAL ASPECT OF VATA (VYAAN & PRAAN) IN TWAK
When we consider the panchgyanendriya, sparshgyanendriya dwells the twak. It is vata that is key factor in any type of sparsh gyan (sensory knowledge). It is vyaan vata that is specially located in the twak and is responsible for carrying information from twak to mana and same is carried to soul by prana vata.
If we consider things in terms of contemporary medicine, we find that a variety of sensory receptors are found in skin e.g., free nerve endings for pain, Ruffini end organ and Krause end bulb for warmth and cold respectively, Meissner corpuscle and Merkel disc for touch and Pacinian corpuscle for pressure sensation. Basically, all these receptors act like transducers that convert various form of energy (stimuli) into action potentials in nerve fibres. Different level of neurons carry these sensory information form sensory receptor to spinal cord, spinal cord to thalamus and finally from thalamus to cerebral cortex.

PHYSIOLOGICAL ASPECT OF PITTA (BHRAJAK) IN TWAK
Twak is considered as seat of pitta dosha also, specially Bhrajak pitta. Bhrajak pitta is responsible for digestion and absorption of substances used in the form of abhyanga (oil massage therapy), parisheka (bathing), avagaha (washing), lepana(poulticing) etc. It is responsible for glow of one's natural complexion. Achary charka has clearly mentioned that temperature and skin colour is controlled by pitta dosha. Variations in temperature and colour is duet to pitta Prakopa. further commentor Chakrapani Datta, in his commentary on this has stated that regulation of the heat and variations in the colour of the body are function of bhrajak pitta.
As per modern physiology melanin, carotene, haemoglobin is responsible for variations in skin colour. Melanocyte is responsible for colour of skin. it is present in the germinal layer of epidermis the cells which synthesize melanin by enzyme tyrosinase, which is in avabhasini layer of skin. Melanocytes are almost same in all people's; skin colour difference is due to the amount of pigment produced by melanocytes. All these phenomena are attributed to function of Bhrajaka pitta but same cannot be only limited to this. Mode of function of absorption of medicaments applied on twak is one of the important tasks to be understood. Prabha or chhaya is correlated to circulatory events that takes place in the Asrigdhara layer of the skin which corresponds to the vascular bed of the skin. The hue and intensity of the skin depends upon the rate of flow of rakta. Again, Udakadhara layer, which is first layer of twak as per Charak, is layer that regulates water homeostasis in the body.

PHYSIOLOGICAL ASPECT OF KAPHA IN TWAK
A prominent layer of fatty tissue is found below twak(skin). This adipose tissue is nothing else but meda dhatu only. Meda dhatu is considered as one of sites where kapha resides. Twak itself is updhatu of vasa or fatty element. Ultimately, we can interpret that kapha and meda (adipose) are found below twak. Sweda(sweat) is considered as mala of meda that is excreted or expelled from body with help of Roma Koopa (sweat gland). Sweat by evaporation not only removes excessive amount of salt from body but other harmful chemicals also. It also regulates body temperature e.g., after exercise or in fever it decreases temperature. In condition of kapha kshaya there is dryness in the skin. This raskshaya is nothing but decrease/absence of Jala mahabhoota. Secretions by sebaceous glands may be attributed to meda (adipose tissue) dhatu underlying twak.

TWAK ACCORDING TO DIFFERENT PRAKRITI
According to Physiological point of view skin is reflection of healthy state, as each constitutional type has its own skin colour.

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Kapha prakriti individuals has shweta complexion, which is corelated with arishtak, kanak, Kamal. kapha people have beautiful skin without a single patch owing to its Snigdh, accha properties. Healthy twak also reflects a good status of Ojas, as varna bheda is one of the important features of Ojas vyapad.

TWAK AGING YOGIC EXERCISES AND MEDITATION
Aging is the process of degeneration which occurs in any living organism with time passage. Which includes various changes, decreased ability of senses, immunity, skin tone etc. though aging is common it depends upon several factors. skin undergoes various changes like dryness, wrinkles, scales, patches, loosing elasticity. It can be attributed to genetic defects, environmental effect, disease, and an apoptosis. According to ayurveda aging is known as Jara means becoming old. Charak and Sushruta consider that Jara starts when an individual attains the age of 60 and 70 respectively. At this age some traits are seen in body elements, sense organs strength etc.
Beautiful healthy skin contributes variety of factors like dosha balance, percentage of dosha, age, prakriti, nutrition etc. moisture, supply of nutrition, metabolic activities, blood circulation and many more factors contribute to healthy skin. Ayurved has a wide variety to maintain healthy skin like ojavardhan, vyadhishaman, Rasayan, yoga practice, balanced diet. lifestyle, seasonal regimen, mental health are some factors which controls aging.

DISCUSSION
Though the skin is an independent organ at the same time it is in contact with all the organs and systems of human body the skin communicates with the organisms by means of the nervous system, circulation, and endocrine glands. Though difference of opinion is observed in texts (ayurved and modern), but both have potential. ayurved and modern science described types, functions, thickness, diseases etc. ayurved samhitas described diseases in different layers. Brainstorming deep study has been done in above project. This explains various opinions of classical and modern text as well about skin. Its function, its formation, and its structure.

CONCLUSION
Skin is most precious part or organ of body which have crucial role in one's personality. To keep balance or to maintain healthy skin everyone must go through skins anatomy and physiology. Physiologically Dosha, dhatu, mala together form the basis of the body. All the three dosha are present in the skin and perform the various physiological functions i.e., sensory, metabolic transformations and sweat secretion etc. Different prakriti types also are having different features of skin. Aging of skin is one of most early signs of oldness. Ayurved explains well to maintain skin health with different modalities for healthy aging. in above literary research functional, structural, physiological aspects of skin according to classical text and modern texts were studied.