Skin protects the body against heat, light, chemical and physical exposure. It regulates the body temperature through a system of blood vessels that constrict or expand as needed.
Cells in the stratum basale/germinativum constantly divide and new cells push older ones toward the surface where they eventually are shed. These cells contain keratin fibers mixed with lipids and secrete defensins, the first line of the immune system.
How it’s made
Despite its appearance, skin is more than just a fleshy surface for pimples and tattoos. It is the largest organ of the body and, along with hair, nails and sweat and oil glands, forms a system called the integumentary system, which provides general protection for the body.
The first layer, the epidermis, is 구월동피부과 a tough covering that protects more delicate layers below. It is made of several’sheets’ of cells that are tightly packed together. At the bottom of the epidermis is where new skin cells form, and as old, dead cells are sloughed off the surface, the newer cells are pushed up to replace them. The epidermis also contains melanocytes, which produce the pigment melanin that gives skin its color.
Under the epidermis is a layer of keratinous tissue, which gives skin its suppleness and strength. It is made of protein fibres such as elastin and collagen, which are held together by glycosaminoglycans. It also contains a layer of fat, which provides warmth and insulation. The dermis also contains blood and lymph vessels, hair follicles and sweat glands.
The dermis is permeated with a tangled, but apparently orderly mass of arteries, veins and capillaries that supply the skin with an enormous amount of blood far in excess of its maximum biologic needs. If the environment is cold and body heat must be conserved, the dermis will react by causing the blood vessels to constrict in quick, successive rhythms.
The epidermi 구월동피부과 s
The epidermis is the outer layer of the skin, a stratified squamous epithelium. It is a thin sheet of flattened cells that overlies a basal layer of round stem cells called keratinocytes. Cells of the epidermis are continuously pushed upward by new cells from below. As they migrate to the surface, the cells become squamous and thickened with a substance called keratin. This is what gives the skin its characteristic texture and color.
The cells of the epidermis are anchored to one another by intercellular bridges known as desmosomes, reinforced by intracytoplasmic structures called tonofilaments. This helps make the epidermis durable. The epidermis also contains pigment-producing cells called melanocytes, which provide the yellow/brown color of hair and skin. Melanin is packaged into little parcels, called melanosomes, and then transferred to keratinocytes. The basal cell layer of the epidermis is home to other immune cells including Langerhans cells, which act as the body’s first line of defence against foreign material.
Between the epidermis and the dermis is a specialised structure called the basement membrane, which consists of proteins that link basal keratinocytes to each other, and to the underlying dermis. This ensures that the epidermis adheres tightly to the dermis. Finally, the epidermis contains blood vessels that supply selected layers of the epidermis with nutrients and control temperature by constricting or expanding in response to the environment.
The dermis
The innermost layer of skin is called the dermis. It contains blood vessels, oil and sweat glands, hair follicles, nerves and other structures. The dermis has two layers – a thin upper layer called the papillary dermis and a thick lower layer called the reticular dermis. These layers merge together without clear demarcation. The dermis provides elasticity to the skin and a sense of touch, as well as thermal protection and protection from chemical and physical injury. It also houses hair, sebaceous glands, adipose lobules and muscle fibres. There are a variety of sensory receptors in the dermis, including skin-sensitive pressure sensors (such as Pacinian corpuscles) and naked dendrites that detect pain.
Cells in the epidermis are tightly attached to the dermis via junctions known as desmosomes. The dermoepithelial junction contains a series of finger-like projections (known as dermal papillae) that increase the area of contact between the epidermis and the dermis. These are more pronounced in thicker skin.
The dermis consists of dense irregular connective tissue, mainly collagen. The papillary dermis is loose and consists of the cells found in the epidermis, while the reticular dermis is much thicker and less cellular than the papillary layer. The reticular dermis is continuous with the hypodermis, which is a thick layer of adipose lobules, nerves and blood vessels.
The hypodermis
The hypodermis, also known as the subcutaneous layer of skin, contains a majority of the body’s fat. It is located beneath the dermis layer of skin and helps connect it to the bones and muscles underneath. It also protects against damage to the epidermis and dermis layers by absorbing shock from bumping into something.
The skin has multiple specialised cell types, including keratinocytes (which form the epidermis), antigen processing Langerhans cells and Merkel cells (tactile receptors). These act as the initial barrier against microorganisms, UV radiation, chemicals and mechanical injury. They release visual and pheromonal signals (blushing, odor, nervous sweating) and can transmit these messages to the brain.
Below the surface of the epidermis lies a thicker papillary layer with small blood vessels and nerves that extend into the dermis. The dermis itself is composed of loose, reticular connective tissue and consists of a network of elastin and collagen fibres. This is what gives the skin its strength and elasticity.
The adipose cells within the hypodermis store most of the body’s fat and can serve as an energy reserve, insulate the body to prevent heat loss and act as a cushion to protect against trauma. These cells are surrounded by a dense matrix of glycosaminoglycans and proteoglycans that has been shown to play a crucial role in fluid distribution homoeostasis 57.
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