THE LARGEST ORGAN OF THE BODY _SKIN

Skin is developed from the surface ectoderm and its on, its underlying mesenchyme. Surface ectoderm gives rise to the cornifying general surface & its appendages. The interface between ectoderm & mesenchyma, is known as

the Basement membrane zone (BMZ). The skin covers the entire external surface of the body. Skin forms 8% of the total body mass and  its surface area varies with height and weight. It is a major site of intercommunication between the body and its environment.

                                                     There are two main layers;

 Epidermis

Dermis

Between the skin and underlying structures there is a layer of subcutaneous fat.

Epidermis

          The epidermis is the most superficial layer of the skin and is composed of stratified keratinized squamous epithelium.

there are no blood vessels or nerve endings in it.

The Epidermis also includes -Melanocytes (Pigment forming cells), Langerhans cells (Antigen presenting cells ) Merkel cells (Sensory mechanoreceptor)

Dermis

The Dermis is the tough, elastic & innermost layer of the’skin. It is formed from connective tissue and the  matrix contains collagen fibers interlaced with elastic fibres. 
         Two layers of Dermis are as follows;

                      Papillary layer
                       Reticular layer

          In Dermis other structures are Blood vessels, lymph vessels, sensory nerve endings, Sweat glands &

their ducts, hairs, arrector pili muscels & sebaceous glands.

Functions 

•          Protection
•          Regulation of body temperature
•          Formation of vitamin-D
•          Sensation 
•          Absorption
•          Excretion