Tvaca and Dosha: Tvaca is one of the site of vata and pitta.

Vata: Skin has been considered as sparshanemdriya adhishthana which is function of vata.

Pitta: bhrajaka pitta is located on the tvaca for giving luster and colour.

Kapha: snigdhata, shlakshnata, mruduta, sthirata, shitata, prasannata, snigdhavarnata are the attributed to kapha. For ropana karma (self healing process) kapha is responsible factor.

Tvaca and Dhatu:

1. Rasa: In the context of tvaka sara purusha lakshna it has been also said as rasa sara. A 1st layer of tvaca udakadhara also contains rasa (lymph) so it can be easily understood that there is a relation between tvaca and rasa.

2. Rakta: Among its functions varna prasadana: mansa pushti have been mentioned.

3. Mansa: Twak is upadhatu of mansa.

4. Meda: Among its functions snehadharana, svedadharana, drutatva has been mentioned.

5. Aasthi: kesha, roma, and nails are mala of asthi dhatu which areembedded in the skin.

6. Majja: Among its functions to from tvakaasneha, akthisneha.

7. Shukra: It present all over in the body it gives prasannavarnatata skin and help inregeneration of skin.

Tvaca and Mala:

1) Sveda: It is mala of meda which is excreted by tvaca . sveda maintain the luster and humidity of skin.

2) Nails and Hairs: These are mala of asthi dhatu and tvakaagata sneha is mala of majja dhatu.

Modern Review

The skin is the first line of defense against the envioronmental agent and mirror or internal pathology.

Embryological Description:

The skin is developed from the surface ectoderm and its underlying mesenchyme (Mesodermal cells).

1) Surface ectoderm gives rise to the kertinizing general surface epidermis and its appendages, the pilosebaceous units, sudariferous glands and nail units at about 8:10 weeks of gestation.

2) Malacocites, nerves and specialized sensory receptors arise from the neuroectoderm.

3) Dermis and its other elements in the skin that is langerhans cells, macrophages, mass cell, fibroblasts etc originate from the mesoderm.

Macroscopic structures:

The skin is the organ of integumentory system that is covering system of the body. It is formed by about:

       8% of the total body mass.
       2.2 square meter covering area.
       16% of total body weight.

Thickness of the skin is different according to maturation, aging and regional specialization. It may be 0.5 mm on the eyelidand 4 mm on heal. Most of the body skin is average 1:2cm thick. Skin is a fascinating orgain as it forms a self renewing and self repairing interface between the body and its environment. Within limit, it forms an effective barrier against microbial invasion and has properties which can protect against mechanical, chemical, cosmetic, thermal and phototic damage.

Microscopic Structure:

It is characterized by the epidermis, dermis and adenaxa.

1) Epidermis: It is a compound tissue consisting mainly of the continuously self replacing keratinized stratified squamous epithelium. It varies in thickness 0.04 mm on the eyelid and 0.16 mm on palms, 0.1 mm is average thickness. Epidermis contains five layers (Strata).

1) Stratum bascal
2) Stratum spinosum
3) Stratum granulosum
4) Stratum corneum
5) Stratum lucidum

1) Stratum Bascal: It is deepest layer of the epidermis and formed by a single row of columnar kerationcytes. Four types of cells are germinated through these layers which are keratinocytes, melanocytes, langerhans cells and merkels cells.

2) Stratum spinosum: It lies super ficial to bascal and it consists of 5 to 12 layers of polyhedral keratinocytes cells are joined tightly to other cells by bundles of intermediate filaments of the cytoskeleton.This arrangement provides both strength and flexibility.

3) Stratum granulosum: It is 3 to 5 layers of flattened kerationocytes that contains darkly staining granules of proteins called karatophylin. The lipid rich secretion produced by the lamellar granules work as a water repellent sealant that retards loss of body fluid and entry of foreign materials.

4) Stratum lucidum: It is present only in the skin of fingertips, palms and soles. It consists of 3:5 layers of clear, flat, dead kerationocytes.

5) Stratum corneum: This is the most superficial layer consisting of anucleated flattened confirmed 25:30 layers of dead karatinocytes. These cells are continuously shed and replaced by cells from the deeper strata. It serves as an effective water repellant barrier and also protects against injury and microbes.

Adnexa of epidermis: It contains the eccrine glands, apocrine glands and the pilosebaceous apparatus.

1) Eccrine glands: These are distributed all over body except the venillion borders of the lips nailbeds, labia minora, glans penis etc.There density is maximum on the palms, sales and axillae.These glands initiate the sweat formation which dissipate heat by evaporation.

2) Apocrine glands: These are located in the axillar, areolae, periumbilical, perianal, external ear etc areas. These are small and nonfunctional till puberty, after which they enlarge.

3) Hair follicles: They presents all over body except sime parts like palm, sole etc and they protects scalp from injury and sunrays and decrease heat loss.

4) Sebaceous gland: They are lipid producing structures disturbed all over body except palms and soles.

5) Nail unit: The nail unit helps in the appreciation of the fine and tactile stimulation, protect the terminal phalanges from trauma.

Dermis: The dermis rests upon the subcutaneous fat and is 15:40 time thicker than the epidermis. The dermis is composed mainly of noncellular connective tissue containing collagen, elastic tissue and ground substances within which are embedded the nerves, blood vessels, lymphatics, muscles, and pilosebaceous apocrine and eccrine sweat unit. Dermis can be divided into

1) Superficial: Papillary region: It consists of areolar connective tissue containing fine elastic fibers. Elastic fibers play a role in maintaining the elasticity of the skin.

2) Deeper: Reticular region: It consists of dense irregular connective tissue containing bundle of collagen and some elastic fibers. Both these provides strength elasticity to skin.

Pigmentation of Skin: Melanin, carotene and haemoglobin: these three pigmemts give skin a wide variety of colour. Melanin located in epidermis, carotene is mostly in the stratum corneum and dermis and haemoglobin is in red blood cells within capillaries in the dermis.

Physiology of Skin:

1. Thermoregulation
2. Protection
3. Cutaneous Sensation
4. Excretion and absorption
5. Synthesis of vitaminD
6. Immunity
7. Blood reservoir
8. Socio sexual communication
9. Individual identification