What is Dermis.
The Human Dermis. The dermal layer of the skin lies beneath the epidermis and above the subcutaneous tissue (hypodermis). Between the epidermis and the dermis is a membrane called the basement membrane which tightly binds the dermis and epidermis together. The thickness of the skin dermis varies from 0.3 mm on the eyelids to 3 mm on the back. The epidermis and dermis together form the cutaneous tissue.
The Dermis.
The dermis of the skin contains the following:
- Nerve endings which provide the skin with the feeling of touch and heat.
- Sweat glands (eccrine glands which empty on the skin surface).
- Hair follicles.
- Sebaceous glands. ( small glands which secrete an oily substance called sebum to lubricate the skin and the hair. Present all over the skin, more on face and scalp but absent on palms and soles).
- Blood vessels.
- Lymphatic vessels.
- Apocrine glands. ( tiny sweat glands which open into the hair follicles).
As mentioned above, the blood vessels in the skin dermis supply nourishment and remove waste from dermis as well as the epidermis.
Picture of Dermis.
(Click on image to enlarge).
Dermis Tissue.
The dermal tissues spread throughout the dermis and are not spread in layers. They are
- Elastic tissue.
- Collagen tissue.
- Reticular fibers.
Cells of the Dermis.
The cells of the dermis are mainly derived from the somatic mesoderm.
- Fibroblasts which secrete the connective tissue matrix.
- Schwann cells which are responsible for the formation of the perineural structures.
- Endothelial cells which form the blood vessels.
Layer of Dermis.
The layers of the dermis are only two in number and their composition and function are explained below.
1) Papillary Dermis.
This dermis layer consists of loose connective tissue which contains finger like projections called papillae which extend upwards into the epidermis and lock the epidermis to the dermis. Collagen is thinly spread in this layer. The papillary dermis contains a rich network of blood capillaries which also nourish the epidermis. This layer also contains nerve endings.
2) Reticular Dermis.
This layer of the dermis is made up of thick collagen and elastic fibers which run parallel to the skin and is situated deeper below the papillary region. It has more dense connective tissue and gives the dermis its strength, elasticity and extensibility. The roots of hair, the sebaceous glands, blood vessels, sweat glands and receptor nerve endings are situated in the reticular dermis.
Image of dermis layers.
Function of Dermis.
- The main function of the reticular dermis is to give firm support to the skin as a whole.
- The main function of the collagen fibers of the dermis is to support the internal structure of the skin.
- The principal function of the dermal elastic fibers is to give elasticity to the skin in order to facilitate movements. Over extension of these fibers causes stretch marks as seen in post pregnancy period.
- Because of its composition, the dermis also acts as a cementing substance.
- The dermis holds water molecules so as to form an amorphous gel which performs two functions of allowing the oxygen and nutrients to enter down into the deeper tissues and protecting the dermal structure.
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