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The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. [1] The epidermal layer provides a barrier to infection from environmental pathogens [ 2 ] and regulates the amount of water released from the body into the atmosphere through transepidermal water loss .
The stratum corneum (Latin for 'horned layer') is the outermost layer of the epidermis. Consisting of dead tissue, it protects underlying tissue from infection, dehydration, chemicals and mechanical stress. It is composed of 15–20 layers of flattened cells with no nuclei and cell organelles.
In the epidermis of skin in mammals, reptiles, and birds, the layer of keratin in the outer layer of the stratified squamous epithelial surface is named the stratum corneum. Stratum corneum is made up of squamous cells which are keratinized and dead. These are shed periodically.
The epidermis itself is devoid of blood supply and draws its nutrition from its underlying dermis. [5] Its main functions are protection, absorption of nutrients, and homeostasis. In structure, it consists of a keratinized stratified squamous epithelium; four types of cells: keratinocytes, melanocytes, Merkel cells, and Langerhans cells.
Histologic image showing a section of epidermis. Stratum basale labeled near bottom. The stratum basale (basal layer, sometimes referred to as stratum germinativum) is the deepest layer of the five layers of the epidermis, the external covering of skin in mammals. The stratum basale is a single layer of columnar or cuboidal basal cells.
The epidermis is the outermost cell layer of the primary plant body. In some older works the cells of the leaf epidermis have been regarded as specialized parenchyma cells, [1] but the established modern preference has long been to classify the epidermis as dermal tissue, [2] whereas parenchyma is classified as ground tissue. [3]
from ectoderm (e.g., the epidermis); from endoderm (e.g., the lining of the gastrointestinal tract); from mesoderm (e.g., the inner linings of body cavities). However, pathologists do not consider endothelium and mesothelium (both derived from mesoderm) to be true epithelium. This is because such tissues present very different pathology.
Histologic image showing a section of epidermis. Stratum spinosum labeled slightly below center. The stratum spinosum (or spinous layer/prickle cell layer) [1] is a layer of the epidermis found between the stratum granulosum and stratum basale. [2] This layer is composed of polyhedral keratinocytes. [3] [4] These are joined with desmosomes. [3]