Skin

Skin      

Skin is general covering of the entire surface of the body,including the external auditary meatus and the outer surface of tympanic membrane.

Pigmentation of skin

The colour of skin is determined by atleast by five pigments presentvat different levels and places of the skin 

These are:

1 melanin

2 melanoid

3 carotene

4 heamoglobin

5 oxyhemoglobin

Structures of skin:-

The skin is composed of two distinct layers,epidermis and dermis.

(A) epidermis

It is superficial avascular layer of straited squamous epithelium. It is ectodermal in origion and gives rise to the appendages of the skin,namely hair,sebacious gland,nails.

Structurally ,the epidermis is made up of a superficial cornified zone and a deep germinative zone 

(B) Dermis or corium

Dermis is the deep ,vascular layer of the skin ,derived from mesoderm.

It is made up of connective tissue  mixed with blood vessels , lymphatic and nerves.

The connective tissue is arranged into a superficial papillary layer and a deep reticular layer.

Appandages of skin

1- nail:-

It is hardened keratin  plates on the dorsal surface of the tip of the fingers and toes,acting as a rigid supporter for the distal pads of terminal phalanges.

2- hair:-

Hairs are keratinous filament derived from invagination of the germanitive layer of epidermis in to dermis .

Hair is distributed all over the body,except for the palms , soles, dorsal surface of distal phalanges , labia minora , inner surface of labia majora.

3-sweat glands:-

Sweat glands are distributed all over the skin, except for the lips,glans penis and nail beds.

4-sebaceous glands:-

Sebaceous gland produce an oily secreation, are widely distributed all over the dermis of the skin ,except for the palms and soles. They are specially abundunt in the scalp and face .

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