* stratum basale * stratum spinosum * stratum granulosum * stratum licidum * stratum corneum. AnswerParty On!
The stratum corneum (Latin for 'horned layer') is the outermost layer of the epidermis, consisting of dead cells (corneocytes).
The purpose of the stratum corneum is to form a barrier to protect underlying tissue from infection, dehydration, chemicals and mechanical stress. Desquamation, the process of cell shedding from the surface of the stratum corneum, balances proliferating keratinocytes that form in the stratum basale. These cells migrate through the epidermis towards the surface in a journey that takes approximately fourteen days.
The stratum spinosum (or spinous layer) is a layer of the epidermis found between the stratum granulosum and stratum basale. This layer is also referred to as the "spinous" or "prickle-cell" layer. This appearance is due to desmosomal connections of adjacent cells. Keratinization begins in the stratum spinosum. This layer is composed of polyhedral keratinocytes, they have large pale staining nuclei as they are active in synthesizing fibrilar proteins, known as cytokeratin, which build up within the cells aggregating together forming tonofibrils. The tonofibrils go on to form the desmosomes allowing strong connections to form between adjacent keratinocytes.
Epidermis and dermis of human skin
The stratum basale (basal layer, sometimes referred to as stratum germinativum) is the deepest layer of the five layers of the epidermis, which is the outer covering of skin in mammals.
The stratum basale is a continuous layer of cells. It is often described as one cell thick, though it may in fact be two to three cells thick in glabrous (hairless) skin and hyperproliferative epidermis (from a skin disease).
The stratum granulosum (or granular layer) is a thin layer of cells in the epidermis. Keratinocytes migrating from the underlying stratum spinosum become known as granular cells in this layer. These cells contain keratohyalin granules, which are filled with proteins that promote hydration and crosslinking of keratin.
At the transition between this layer and the stratum corneum, cells secrete lamellar bodies (containing lipids and proteins) into the extracellular space. This results in the formation of the hydrophobic lipid envelope responsible for the skin's barrier properties. Concomitantly, cells lose their nuclei and organelles causing the granular cells to become non-viable corneocytes in the stratum corneum.
The Malpighian layer of the skin is a term that is generally defined as both the stratum basale and stratum spinosum as a unit, although it is occasionally defined as the stratum basale specifically. Also, the term is occasionally used synonymously as the prickle cell layer (although prickle cell layer generally is defined as the stratum spinosum specifically) or to designate a part of the stratum corneum.
It is named after Marcello Malpighi.
The stratum lucidum (Latin for "clear layer") is a thin, clear layer of dead skin cells in the epidermis named for its translucent appearance under a microscope. It is readily visible by light microscopy only in areas of thick skin, which are found on the palms of the hands and the soles of the feet.
Located between the stratum granulosum and stratum corneum layers, it is composed of three to five layers of dead, flattened keratinocytes. The keratinocytes of the stratum lucidum do not feature distinct boundaries and are filled with eleidin, an intermediate form of keratin.