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The cells of these two layers, together called the Malpighian layer(s) after Marcello Malpighi, divide to form the superficial granular layer (Stratum granulosum) of the epidermis. [20] The cells in the stratum granulosum do not divide, but instead form skin cells called keratinocytes from the granules of keratin.
In humans, they constitute 90% of epidermal skin cells. [1] Basal cells in the basal layer (stratum basale) of the skin are sometimes referred to as basal keratinocytes. [2] Keratinocytes form a barrier against environmental damage by heat, UV radiation, water loss, pathogenic bacteria, fungi, parasites, and viruses.
Melanin is produced within the skin in cells called melanocytes and it is the main determinant of the skin colour of darker-skinned humans. The skin colour of people with light skin is determined mainly by the bluish-white connective tissue under the dermis and by the haemoglobin circulating in the veins of the
These stem cells develop into both keratinocyte precursors and melanoblasts - and these melanoblasts supply both hair and skin (moving into the basal layer of the epidermis). There is additionally evidence that melanocyte stem cells are present in cutaneous nerves, with nerve signals causing these cells to differentiate into melanocytes for the ...
It emerges and originates from the outer layer of germ cells. The word ectoderm comes from the Greek ektos meaning "outside", and derma meaning "skin". [2] Generally speaking, the ectoderm differentiates to form epithelial and neural tissues (spinal cord, nerves and brain).
Freckles and moles are formed where there is a localized concentration of melanin in the skin. They are highly associated with pale skin. They are highly associated with pale skin. Nicotine has an affinity for melanin-containing tissues because of its precursor function in melanin synthesis or its irreversible binding of melanin.
The dermis is composed of three major types of cells: [3] fibroblasts, macrophages, and mast cells.. Apart from these cells, the dermis is also composed of matrix components such as collagen (which provides strength), elastin (which provides elasticity), and extrafibrillar matrix, an extracellular gel-like substance primarily composed of glycosaminoglycans (most notably hyaluronan ...
Biologically, calluses are formed by the accumulation of terminally differentiated keratinocytes in the outermost layer of skin. Though the cells of calluses are dead, they are quite resistant to mechanical and chemical damage due to extensive networks of cross-linked proteins and hydrophobic keratin intermediate filaments containing many ...