Skin is the body’s tough and fle 서면피부과 xible armor that shields us from heat, chemicals, strong rays of light and physical injury. It also collects sensory information from the environment and regulates internal temperature.
The thin, extensive vascular system of the skin supplies nutrients and helps control temperature by constricting or expanding. The epidermis is divided into layers called stratum basale or stratum germinativum.
The Epidermis
The epidermis is the outermost layer of skin, it is tough and protective. It is made of fibrous proteins, mainly keratin, that form a strong covering. It protects the tissues beneath it from mechanical stress and injury and shields them from sunlight, which is harmful to the cells.
Cells in the epidermis are constantly sloughing and replacing themselves. The epidermis is made up of five layers, which are the stratum basale, the stratum spi 서면피부과 nosum, the stratum granulosum, the stratum corneum, and the stratum lucidum. The basal cells that form the basal layer of the epidermis proliferate and then mature into squamous cells, known as keratinocytes.
As they move upwards through the two thin epidermal layers, these keratinocytes become bigger and flatter and are arranged closer together, forming a thick layer of squamous cells called the stratum granulosum or granule-cell layer. In this layer, keratinocytes secrete a water-soluble protein called keratin. The keratin helps to keep the cells hydrated. The keratinocytes also secrete a protein called cytokines that act as messengers to the immune system. The keratinocytes of the granule-cell layer are also home to lymphocytes that attack and destroy pathogens as they enter the skin.
The cells of the granule-cell layer eventually slough off to form the horny, or cornified, layer of the epidermis. The cornified keratin cells no longer have nuclei, and are therefore referred to as unnucleated squamous cells (also called corneocytes). The cornified keratin provides the waterproof properties of the skin. This layer is also impermeable to water, but allows fat-soluble substances to pass through it.
The Dermis
The dermis is thick and tough connective tissue, rich in collagen and elastic fibers. The dermis also contains fat cells (adipose) for thermal insulation and protection against mechanical stress. The dermis is divided into two regions: the papillary layer, which extends from the epidermis upward, and the reticular layer.
The papillary layer has fingerlike projections called papillae that extend up into the epidermis and contain capillaries. The papillae also contain sensory touch receptors. This layer also has a loose, areolar, or spongy matrix of collagen and elastic fibres.
A thin layer of water and a gel-like substance also lie between the fibrous tissues of the dermis. The gel-like substance helps to give skin its flexibility and resilience.
The dermis is well supplied with blood vessels, which nourish and remove wastes from the epidermis as well as the dermal layers beneath. The dermis is home to hair follicles, sebaceous glands (oil glands), apocrine glands and lymphatic vessels. It also houses nerves, including those that detect pain and temperature changes. It is through these nerves that a portion of the body’s heat is lost by sweating. The dermis has a number of other functions, such as cushioning the subcutaneous tissue, regulating body temperature and sensing the environment. It does this through a complex process of vasodilation or vasoconstriction and through the many tactile sensory touch receptors.
The Subcutaneous Layer
Your skin is a complex network that protects you from the outside environment, regulates your temperature, and controls the fluid flow in and out of your body. The epidermis provides the initial barrier against pathogens, toxins, UV light and chemicals, while the dermis supports your deeper layers and assists in thermoregulation and sensation. The subcutaneous layer contains fat cells and connective tissue, which provides insulation and padding to your organs and muscles.
The dermis is made up of two distinct layers, the papillary dermis and the reticular dermis. Both layers are fibrous and composed of collagen and elastic fibers. The reticular dermis is denser and thicker than the papillary dermis. This layer is highly vascular and contains fibroblasts, mast cells, and adipocytes (fat cells).
In the H&E-stained sample of skin shown above, you can see fingerlike protrusions of dermal connective tissue into the epidermis called dermal papillae. There are also a series of ridges in the tissue called rete ridges. These structures are more apparent in the thick skin on the palms of your hands and feet.
The fat cells found in the subcutaneous layer are known as your body fat. This fat is important for your health. It helps your body store energy in the form of calories, insulates your organs and muscles from shock and changes in the surrounding environment, and cushions your body to prevent injury.
The Basal Layer
The basal layer is a thick and dense area that connects the epidermis to the dermis. It contains many cells that are actively dividing to replace skin cells lost by normal shedding. This layer also contains a lot of melanocytes (cells that make the pigment that gives skin and hair its color).
The cells in this layer have spiny protrusions that help hold them together. The keratinocytes in this layer are constantly undergoing cell division to produce new epidermal cells for the top layers of the skin. This process is called mitosis. The cells in this layer are referred to as basal cells or basal keratinocytes.
As the cells move up through this layer, they become more and more mature (or differentiated) until they reach the stratum spinosum. The keratinocytes in the stratum spinosum start synthesising a substance called keratin and release a water-repellent glycolipid, which helps to keep the body from losing too much water from the skin’s surface. This layer is sometimes referred to as the’spiny layer’.
As the keratinocytes move up through this layer they become flattened and diamond shaped, forming a substance called granules. They also begin to lose their nuclei and cytoplasmic organelles. The granules are then converted to the keratinized squames of the next layer. This layer is sometimes referred to as ‘the granulosum’.