Epidermis vs Dermis
Birds and mammals are endothermic animals. In order to maintain a constant body temperature, these organisms need to have a high metabolic rate and an effective means of controlling heat loss from the body surface. The skin is the organ of the body that is in contact with the environment, and monitor and regulate the changing temperature. The term skin applies to the outer covering of vertebrate animals. The skin is the largest organ of the body and is made up of connective tissue, blood vessels, sweat glands and sense cells. These enable to fulfill numerous functions. The human skin is composed of two main layers, the epidermis and the dermis, that overlay the subcutaneous fat containing adipose tissues.
What is Epidermis?
The epidermis is embryonic ectodermal in origin, and they are separated by the dermis by a basement membrane. The epidermis is composed of many layers of cells forming a stratified epithelium. The cells above the basement membrane are cuboid epithelium and form an actively dividing region known as the Malpighian layer. This lower layer of the epidermis is called the stratum granulosm and the upper layers are called the stratum corneum. The upper layers of cells in the stratum corneum become progressively flatten and start synthesizing Keratin, which is a protein that makes cells water proof. As the keratin content in cells increase they get cornified and die. It is also modified as nails, claws, hooves feathers and hair in animals. The epidermis forms a complete covering to the body perforated only by sweat gland openings and hair follicles. The upper squamous skin cells are constantly shed due to friction.
What is Dermis?
The dermis is mostly mesodermal in origin. It is a dense matrix composed of connective tissue rich in elastin fibers and containing blood capillaries, lymph vessels, muscle fibers, pigment calls, sweat glands and hair follicles. The hair follicles, which are epidermal in origin, invaginates to the dermis to gain nourishment from the blood capillaries in the dermis. Sebaceous glands open into the hair follicle, which secrets sebum. The sebum keeps the skin wet and prevents water loss from the skin. At the base of the hair, follicle is a smooth muscle called erctor pili muscle; this helps in change of position of hair and the amount of air trapped between the hair and skin. Thus, this is used as thermoreglatory function. The sweat glands in the dermis produce sweat and helps in an execratory function as well as a thermoregulatory function. There is both motor and sensory neurons in the dermis. The sensory neurons detect heat, cold, touch, pain and pressure. The blood capillaries present in the dermis supplies nourishment and oxygen to both dermis and the live part of the epidermis through diffusion. Many of the capillaries form loops and have shunts allowing the body to a regulation of heat by blocking blood to the body surface when cold, to help reduce the escaping heat.
What is the difference between Epidermis and Dermis?
• The dermis and epidermis together form the basic body covering; the skin. They together perform the function of protecting internal organs from damage, dehydration, and disease.
• The cornified epidermis prevents damage by friction, and the dermis and the subcutaneous tissues prevent mechanical damage.
• Melanin, the dark pigment in chromatophores of the dermis, protects the body from UV radiation. The sebum and structure of the skin itself prevents the entry of pathogens.
• The dermis and the epidermis together help regulate heat of the body. However, the dermis is of mesodermal in origin and the epidermis is ecteodermal.
• The epidermis modifies to form hair, nails, feathers, antlers, hooves etc. while the dermis does not.
• The epidermis consists of both living and non-living components, but the dermis is entirely alive.
• The dermis is composed to glands capillaries, smooth muscles, pigment cells, and nerves, but the epidermis has none.
• The epidermis is in contact with the external environment, and the dermis is not.
• The epidermal cells are constantly shed, but the dermal cells are not.
These are the significant similarities and differences between dermis and epidermis.