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Parakeratinized epithelium is sometimes found in the oral mucosa and in the upper regions of the oesophagus. [12] Transitional: Transitional epithelia are found in tissues that stretch, and it can appear to be stratified cuboidal when the tissue is relaxed, or stratified squamous when the organ is distended and the tissue stretches.
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.
Only one layer is in contact with the basement membrane; the other layers adhere to one another to maintain structural integrity. Although this epithelium is referred to as squamous, many cells within the layers may not be flattened; this is due to the convention of naming epithelia according to the cell type at the surface.
The nucleus is large, ovoid and occupies most of the cell. Some basal cells can act like stem cells with the ability to divide and produce new cells, and these are sometimes called basal keratinocyte stem cells. Others serve to anchor the epidermis glabrous skin (hairless), and hyper-proliferative epidermis (from a skin disease). [1]
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.
Almost all of the mass of an atom is located in the nucleus, with a very small contribution from the electron cloud. Protons and neutrons are bound together to form a nucleus by the nuclear force. The diameter of the nucleus is in the range of 1.70 fm (1.70 × 10 −15 m [7]) for hydrogen (the diameter of a single proton) to about 11.7 fm for ...
For example, the expression of N-cadherin is crucial to maintaining separation of precursor neural cells from precursor epithelial cells. [2] Likewise, while the surface ectoderm becomes the epidermis , [ 6 ] the neuroectoderm is induced along the neural pathway by the notochord , which is typically positioned above it.
Merkel cells are found in the skin and some parts of the mucosa of all vertebrates. In mammalian skin, they are clear cells found in the stratum basale [2] [3] (at the bottom of sweat duct ridges) of the epidermis approximately 10 μm in diameter. They are oval-shaped mechanoreceptors essential for light touch sensation and found in the skin of ...