When you feel the pinch hard on your hand, it is the skin that you refer to as getting hurt. Never do most of us really wonder on what lies beneath, and the term that science has used to define skin. For the wise heads and eager minds, that want to know more about the skin, we will narrow down to giving you a complete view, right from the basics. The cutaneous membrane is also known as the skin. It is a soft covering that shields the underlying organs. The term is derived from, 'cutaneous' meaning 'of the skin' and 'membrane' that means a thin layer that covers a cavity, space, or organ. Integument membrane is also another name. This membrane is a type of tissue that belongs to the stratified squamous epithelium. The skin is a major part of the integumentary system, which is an organ system, taking care of maintaining the body functions internally. The integumentary system has several accessory organs like hair, nails, etc., and the skin which is a major part.
The simplicity of the outer look of the skin, actually has complex layers right beneath it, that carry most of the processing of the major functions. The cutaneous membrane has two major layers. Mainly, epidermis and dermis.
Epidermis: This forms the outer layer of the skin, and is a structure made up of keratinized stratified squamous epithelial cells. It has no blood vessels and contains 4 types of cells, 5 layers of cells forming a tissue. The cells that make the epidermis are - Keratinocytes, Melanocytes, Langerhans, and Merkel. Keratinocytes are the most abundantly found cells and basically undergo keratinization (a process where keratin is deposited in epithelial cells). Melanocytes are responsible for the production of melanin. Merkel cells are associated with sensory neurons, while Langerhans are responsible for regulating the immune reactions. Apart from the cells the epidermis has sub layers, they are:
|➊||Stratum corneum||This is the outermost layer of the epidermis, this consists of keratin filled dead cells that slough off and are replaced by new cells. The main function is hydration and maintaining the elasticity of the skin|
|➋||Stratum lucidum||This forms the next layer beneath stratum corneum. It is a thin layer of cells separating the corneum and the granulosum that lies beneath it. This is found only in the thick areas like palms and sole of the feet.|
|➌||Stratum granulosum||This forms the third layer that contains flattened granular cells containing keratin granules. These cells accumulate basophilic keratohyalin granules that are responsible for the waterproofing properties of the skin.|
|➍||Stratum spinosum||This consists of cells that can be described like spiky, this is also known as 'prickle cell' layer. The main function of this layer is keratinization, that begins in this layer.|
|➎||Stratum basale||This is the bottom layer of the epidermis, and contains cylindrical cells or cubodial cells. They mainly function for cell division to produce new keratinocytes, to replace the sloughed cells in the epidermis.|
Dermis: This is the inner layer of the skin, and connects to the epidermis by a basement membrane and also protects the body from stress and strain. It consists of blood vessels, sweat glands and Meissner's Corpuscles, that are receptors for light, heat and touch. It consists of 3 types of tissues and 2 layers. The two regions that make the dermis are:
|➊||Papillary layer||This is made of loose areolar connective tissue. These tissues extend to the epidermis and give the projections of fingerprints on the skin.|
|➋||Reticular layer||This is thicker than the papillary layer, that contains dense connective tissue, collagen and elastic fibers. This makes an important layer as it is made of blood vessels, hair follicles, sebaceous glands. It also consists of Pacinian corpuscles, which function as receptors for pressure and touch. This is the layer that gives the skin its elasticity, strength and resiliency. An interesting fact is that, what we know as stretch marks is due to the excess stretching that causes tearing of the dermis. The tattoos that are inked permanently are because of the ink injected in the dermis.|
After a detailed explanation of the term and its physical structure, let's learn some of its important functions.
- The most important function is protection. This can be in many ways like physical protection from injury, water loss and from other microorganisms. Maintaining the pH and also preventing microorganism growth is one of the vital functions of this membrane. The cutaneous membrane is also responsible for the immunity of the body (langerhan cells in the epidermis).
- The other vital function is to get rid of the waste in the body in the form of sweat, and get rid of the dead cells of the skin. It is also responsible for maintaining the body temperature.
- Sensation is yet another important function of the skin. The dermis is made up of certain cells that are specially responsible for sensations of touch and pressure.
- The skin is responsible for synthesis of Vitamin D in the body. It also helps in absorbing essential elements like oxygen, nitrogen, carbon dioxide, etc.
- The skin helps storage of water and prevents fluid loss. It also houses almost 10% of the body's total blood vessels, and uses only 2% of these for its functioning.