Structure and Function of the Skin
What is skin?
Skin is the soft outer tissue covering vertebrates. It acts as a barrier and protection against water and fluid loss and prevents damage to internal organs and in some animals helps manage body temperatures as well. Other organisms, like arthropods, have other types of tissues that form their exterior, like an exoskeleton, which is made of chitin, or like in turtles and tortoise, an outer shell.
Different classifications of animals have different types of skin, like, fish, amphibians, reptiles and birds.
In mammals, the skin functions as the largest organ and performs various functions.
What is the mammalian skin made of?
The mammalian skin is composed of two primary layers – epidermis and dermis, with a basement membrane in between.
What is epidermis?
The epidermis is composed of the outermost layers of the skin. It forms a protective barrier over the body’s surface, responsible for maintaining fluids in the body and prevents pathogens from entering the body.
The epidermis contains no blood vessels and the cells in the deepest layers are nourished by diffusion from blood capillaries extending to the upper layers of the skin. The melanocytes present in the epidermis are responsible for producing melanin which gives the skin its colour.
What is basement membrane?
The epidermis and the second layer, dermis are separated by the basement membrane, which is a thin sheet of fibres. The basement membrane controls the traffic of cells and molecules between the two layers of the skin, through it’s complex structuring.
What is dermis?
The dermis is the layer of the skin beneath the epidermis and consists of connective tissue, cushioning the body against stress and strain. The dermis provides tensile strength and elasticity to the skin through a complex layering of extracellular matrix of collagen fibrils, microfibrils and elastic fibres embedded in layers of vital cellular fluids and molecules that help maintain the strength of skin.
The dermis is divided into two layers, the Papillary region and Reticular region.
1. Papillary region of dermis
This layer is composed of areolar connective tissue, and is named after the finger like projections called the papillae that extend toward the epidermis. The papillae increase the surface area of the dermis, providing extra strength.
2. Reticular region of dermis
The reticular region lies deep in the papillary region and is usually much thicker. It is composed of dense irregular connective tissue, and receives its name from the dense concentration of collagenous, elastic and reticular fibres that weave through it. These protein fibres give the dermis its properties of strength, extensibility and elasticity. Also located within the reticular region are the roots of the hair, sweat glands, sebaceous glands, receptors, nails and blood vessels.
4 Interesting facts on skin
- The skin renews itself completely in 28 days and sheds 30,000 to 40,000 dead cells per minute while it renews itself. An average human sheds 9 pounds of skin cells in a year.
- The human skin is home to a 1000 species of bacteria.
- The thickest skin in humans is found on the soles of the feet, where as the thinnest is found on the eye lids.
- On a hot day, the sweat glands can produce upto 3 gallons of sweat in a day.
- Goose bumps help retain a layer of warm air over our body.