Written jointly with Dr. Rachana Tiwari
Twak Sharir is a very important part of anatomy in ayurveda. It represents to the skin in modern anatomy. Skin is the biggest organ of body. It makes the integumentory system, comprising hairs nails etc. It constitutes 16% of body weight. Skin has the total surface area is 1.2-2.2 m2. It is a combined product of ectoderm as well as of mesoderm. Akin nervous system epidermis is developed from ectoderm, where as dermis from mesoderm. It is the Updhatu of Mansa Dhatu, which may be because of the common germinal base. The muscles and dermis both are the organs with mesoblastic origin. Dermis is a well vascularised structure, it is very active organ. Epidermis has no blood vessels, only it’s basal layers get nourishment from the source of dermis being next to it. Skin is called as Mansavaha Srotas. MANSAVAHANAM CHA SROTASAM SNAYURMOOLAM TWAK CHA, As per Charaka is suggestive to this fact. Since skin synthesises the vitamin D, and vitamin D is a basic source for calcium. It is assimilated and absorbed from the gut due to assistance of vitamin D. The physiology of action in the muscle is totally calcium dependent. We can appreciate that muscle is big Zero without calcium and calcium is big Zero without vitamin D. As such Charaka has rightly said on the theory of Mansavaha Srotas. Under
Ayurvedic practices Snehan, Swedan, Abhyanga, Avagahana, Alepan, Udvartana etc. are all done based on Twacha, which covers the 75% of Panchkarma discipline. Similarly like for a person aspiring to be a surgeon a perfect knowledge of cadaver anatomy is essential, the perfect knowledge of the structure and function of skin for Panchakarma expert is essential.
FUNCTIONS OF THE SKIN
The basic function of the skin is the physical protection, until the regularity of the skin is not ruptured, nothing can enter from the side of external environment. Skin makes the barrier against bacterias. Open injury is vulnerable to infections. Keratin, protein synthesized by the keratinocytes of the epidermis is one type of structural protein with sulfur as an essential constituent, functions for developing resistance against infections. Protection from UV rays is an important function of the skin. Melanin, a protein synthesized by the melanocytes located in the basal layer of the epidermis, functions to absorb the UV rays, so that the underlying cells are secured. Skin also functions for the removal of wastes from the body, a like kidney. It removes urea, ammonia and CO2 from the body to maintain the homeostasis. Skin also play important role in keeping acid and base in balance, through the excretion of urea CO2 and other acidotic factors it restorates the body with normal pH. Skin is one type of sensory organ, it functions as a touch sensory to identify the physical changes in the external environment e.g., pressure, temperature etc. Skin also functions for the synthesis of vitamin D. Thermoregulation is an important function of skin. During winter and in cold environment, erection of hairs and reduction of surface area are the two changes that are seen in the skin to protect to protect body from cold. By the process of sweating and increase of surface area skin protects body from hot climate. Sweating leads into diffusion of heat from the body keeping us comfortable.
BASIC LAYERS OF THE SKIN
Skin is made from three basic layers.
This is also called epidermis. It is the most outer layer, derived from ectoderm. This provides an over coat type of arrangement to the body, so that the body is physically protected. This is made from various layers of keratinized cells. In all this has two types of cells, keratinized and non- keratinized cells. Keratinised cells synthesize the keratin protein, Keratin is a structural protein which apart from physical protection it deals with many ways to protect the body. Nails, hairs and wool are also products of keratin. Keratinised cells form five layers. From the level of base (inner side) to surface the layers are given as under-
a) Stratum basale: This is basic layer lying at the deepest level in the epidermis. This is made from the single lining of newly formed youngest keratinised cells. The cells are cubidal or columnar epithelial cells. Cells contain the basophilic cytoplasma. Since cells undergo a rapid mitotic cell division, therefore stratum basale layer is also called germinating layer. New skin cannot regenerate if a large area of the stratum basale and it’s stem cells are destroyed. Skin wound of this magnitude requires skin graft to heal. This layer being basic layer functions for mitosis and proliferation, so as to provide stolk of the kertinocytes to next layer which is very active and known as stratum spinosum. Lying within this layer are 10-25 % cells of melanocytes which synthesize melanin protein pigments, as well as the precursor of vitamin D. Langerhan’s cells and occasional merkel’s cells are also located within stratum basale.
b) Stratum spinosum: This layer has many cell sized thickness. Cells are Irregular and spiny in shape and are closely fit together. They are filled with pre-keratin protein filaments. Scattered among cells are melanin protein molecules located at the sunny side (outer side) of the cell nucleus, forming a pigment shield, so as to absorb the UV rays coming from outer side, to protect nucleus from damaging effects of UV rays. Scattered among keratinocytes are Langerhan’s cells which are most abundant in this layer.
c) Stratum granulosum:The thin layer of keratinocytes kake this layer. Cells are limited to five cells and are flattened. Cells accumulate the keratinohyaline granules precursor of keratin for upper layers, and lamellated granules. Lamellated granules contain waterproofing glycolipids that is spewed into extracellular space and is a major factor in checking the water loss across the epidermis. Nuclei and organneles begin to disintegrate at this level. Keratinocytes begin to develop hardening, due to poor blood supply, which is away in the dermis. Cell death is completely a normal sequence of events.
d) Stratum lucidum: This is a clear layer so is called stratum lucidum. It forms thin translucent band just above stratum granulosum. It consists of few rows of clear, flat, dead keratinocytes with indistinct boundaries. Here and in the stratum corneum above, the gummy substance of the keratinohyaline granules clings to the keratin filaments in the cells, causing them to aggregate in parallel arrays. Stratum lucidum is visible only in thick skin.
e) Stratum corneum: It is also called horney layer being hard and toughened in structure. It is made from cornfield cells. Keratinocytes reaching to this level are dead and hardend. They are familiar to every one because of dandruff shedding from scalp. Dead keratinocyte cells make durable over coat for the body. Stratum corneum functions to make skin strong to protect from external injuries. It protects from water loss, biological, chemical and physical assaults. It is amazing that a layer of dead cells also function many roles.
NON-KERATINIZED CELLS: There are three types of non- keratinized cells. These cells do not synthesize keratin instead off the function other important roles, cells are melanocytes, Langerhan’s cell, and Merkel cells. They are spider shaped epithelial cells, located in the basal membrane and are specialized to produce melanin, a dark brown or black pigment. Melanin functions to maintain skin color. It absorbs the UV rays so as to protect deep tissues against injury from UV rays. Skin color is is not only the result of melanin, it is caused by three factors, melanin is one of them, others are hemoglobin and carotene. Red color is from hemoglobin and yellowish color is from carotene, which is the precursor of vitamin A.
Langerhan’s cells: They are dendritic star shaped cells, they arise from bone marrow and migrate to the epidermis. They are antigen presenting macrophage cells, they function to activate the immune system. They multiply and increase in number in allergy.
Merkel cells: They are shaped like a spiky hemisphere, and are present at dermo-epidermal junction. They are specialised sensory cells. They make the merkel disc around sensory nerve ending, and deal with supporting function for touch sensory.
DERMIS: Dermis is composed mainly of connective tissue. It is mesoblastic in origin. Blood vessels, nerves, glands and hair follicles along with some muscle tissues are embedded in dermal tissue. Based on the tissue structure dermis can be divided in two layers, papillary layer and reticular layer.
a) Papillary layer (dense layer)
b) Reticular layer (loose layer)
a) Papillary layer (dense layer): This layer makes up about 1/5 of the thickness of total dermal layer. It consists of areolar connective tissue containing fine elastic fibers. Surface area is increased by small fingerlike structures projecting into epidermis called dermal papillae. Main function of dermal papillae is to make strong junction between epidermis and underlying connective tissue. Papillae are of two types, capillary papillae and nervous papillae (has sensory receptors). Capillary papillae has blood capillaries, this is how basal layer of epidermis is provided nourishment. Nervous papillae has sensory nerve receptors (meissner’s corpuscles) of touch and free nerve endings.
Reticular layer: The deeper portion of the dermis with a thickness of 4/5 of total dermal layer makes the reticular region. This is made from dense irregular connective tissue with bundles of collagen and elastic fibers. Spaces between fibers contain hair follicles, arrector pili, sweat glands, sebaceous glands, nerves and some adipose cells.
HYPODERMIS: Deep to the dermis layer with adipose fat is called hypodermis. Normally it is not considered as a part of skin. It is also called superficial fascia. This layer is made from areolar and adipose tissues. Functions for storage depot for fat as extra energy availability on body needs It also pad the body and keep it warm. This layer contains large blood vessels supplying the skin.
AYURVEDIC SHARIR SIDDHANTA: Acharya Sushruta, the father of surgery has very well elaborated the theory and the anatomy of skin under the heading of Sharir Garbha Vyakarana. Under this presentation he has devised the theory of the development of skin (Twacha) firstly, and then presented the anatomy of skin.
Sushruta says that Twacha (skin) is developed like the milk membrane developed at the surface of boiled milk, in chronological order for the making of layers. Further he has presented that skin has 7 layers, i.e. Avabhasini, Lohita, Sweta, Tamra, Vedini, Rohini, Mansadhara Twacha. These layers of Twacha are analogous with the layers of epidermis, dermis and hypodermis.
Anatomical correlation can be appreciated as under.-
1-Avabhasini- Stratum cornium (1/18 Brihi)
2-Lohita – Stratum lucidum (1/16 Brihi)
3-Sweta- Stratum granulosum (1/12 Brihi)
4-Tamra- Stratum germinosum (1/8 Brihi)
5-Vedini- Papillary layer (1/5 Brihi)
6-Rohini- Reticular layer (1 Brihi)
7-Mansadhara Twacha- Hypodermis (2Brihi)
CLINICAL IMPORTANCE: The functions of skin is not described clearly in Ayurveda. There is no independent description found in this regard. However the functions of skin is reflective in various references scattered in Samhitas. Acharya Charaka has presented the signs of Twaksar Purusha under Viman Sthan, which gives the information about the functions of various properties of Prakrat Twacha-
Acharya Charaka has said that the skin of Twakasar Purusha should be unctuous (Snigdha), smooth (Shlakshna), soft (Mradu), clean/glorious (Prasanna), fine (sukshma), close/not loose (Alpa), thick (Gambhir), soft hairy (Sukumar Loma) and radiant (Saprabha). This type of Twaksarata gives the indication of happiness, prosperity, splendor, pleasure, intelligence, knowledge, health, contentment and longevity.
As such skin is reflective for the internal state of a person. If skin is healthy likely the other systems of the body will be healthy. The symptoms of the sickness of other systems will be reflected on the skin. So that if skin is treated this will benefit to the health of other systems also. This has caused the development of various therapies under Panchakarma system of medicine.
According to Sushruta, skin is the seat of Bhrajak Pitta, accordingly because of Bhrajak Pitta skin functions to catalyze the metabolic process related with the therapies of Abhyanga, Parisheka, Avagah, Alepan, Udvartan etc.
Skin is grossly an organ with ectodermal origin alike nervous system. All the sensory organs have the same type of developmental basis. Because nervous system is evolved to ensure the survival of organism against the changes falling in the internal and external environments. This is why the organs helping any way, for the cause of protection of organism are derived from ectoderm. As such skin is the gate way of person and personality. Ancient Ayurvedic sages were high visionaries, so they could see that if skin is treated and strengthened, with the good health of skin the whole body will be benefited and good health will be ensured. This has given rise to the development of Snehan, Swedan, Udvartan and Avagahan type of therapies.
Acharya Sharangdhar has referred that the healthy skin benefits to the wisdom, knowledge and health in particular, while giving directions on the functions of Pitta, he has given the following direction.-
Tvic kaiNtkr. )ey. lepaWy¥aidpackm\| - xar¥2r pUvR q.D- 5/30
In this reference Kantikaratva of skin holds many meanings, it directly refers to every type of anabolic activities in the body including synthesis of protein lipid and glycogen and hemoglobin. These substances reflect in the skin. As skin synthesize the vitamin D, which is almost an anabolic vitamin. Beneficial role of vitamin D in the treatment of diseases like autoimmune illness, cancer, chronic pain, diabetes, heart disease, hyperparathyroidism, hypertension, mental illness, multiple sclerosis, muscle weakness and coordination, obesity, osteoarthritis is a valuable material in this regard. Functions of vitamin D can not be overlooked at this point. Vita. D is a fat soluble vitamin. Vitamin D is a growth vitamin. It is an anabolic and is also known as anti ageing vitamin. It is much synthesized in white skin because of the higher transparency of white skin people for sun rays. This is why the white skin community is advantageous and physically dominating, globally in comparison with black skin. Vitaamin D helps in the absorption of calcium. It functions in the metabolism of calcium and phosphorus equally. Vita. D functions for assimilation and deposition of calcium in the bones.
This is amazing how Acharya Sharangdhar had foreseen about the role of skin in promotion of knowledge and wisdom. Normally it is not believable, but present studies on vit. D have done such miracles which suggest us to believe on this. Present studies say that vita. D helps in many ways in promoting intellectual health. It helps in the early development of brain. It helps in maintaining and developing cognitive function. It helps in protecting neurons from degeneration and preventing inflammation. It’s deficiency may lead to many diseases e.g., dementia, Alzheimer’s and Parkinsonism. Since Vita. D is synthesized from the skin therefore this is very much truthful to appreciate this.
Skin being an Adhishthan for Abhyangadi therapies, it is referred hat medicines used in such local therapies are absorbed through skin. Skin is also a known route of administration of drugs. Pancha Karma and allied therapies are unique therapies in Ayurveda, credit for the development of such therapies goes to the knowledge of the fuctional importance of skin.
CONCLUSIONS: Twacha (skin) is a very important basic structure of the body. Other than it’s physical values it holds metabolic, behavioral, mental, psychological as well as therapeutic values. Skin is also an important basic component of personality building. As such the due biological knowledge of skin, must be essential for the clinicians dealing with Pancha Karma, physiotherapy, cosmetology. In Ayurveda if it was not the subject of Pancha Karma, half of the value of medicine was lost, alike Shalyavishayardhata of Marma Sharir. People of Ayurveda particularly, should give more emphasis on the study and research in the respective areas of Twaka Sharir to ensure true scientific knowledge about the structure and function of skin.