Showing posts with label keratinocytes. Show all posts
Showing posts with label keratinocytes. Show all posts
D. Merkel's cells
D. Merkel's cells: Scattered in the stratum basale, these cells are most numerous in thick skin. They resemble basal keratinocytes but have a clearer cytoplasm containing many small dense granules. Free nerve endings form a disklike expansion (Merkel's disk) that covers the basal surface of each Merkel's cell. This arrangement suggest that the cells function as sensory mechanoreceptors, but other evidence suggests that they may have DNES-related functions
B. Pigmentation System
B. Pigmentation System: Skin color is conferred mainly by the pigments melanin and carotene, the thickness of the epidermis, the number of dermal blood vessels, and the color of the blood in those vessels.
1. Melanins contribute to skin, eye, and hair color. Synthesized by melanocytes, they include the dark brown pigment eumelanin, found in the epidermis, iris, and brown and black hair; and the cysteine-rich pigment pheomelanin, found in red hair. 2. Melanocytes derive from the neural crest and migrate into the epidermis during em bryogenesis. Although they are scattered among the keratinocytes of the stratum basale, they are not attached to them by desmosomes. They have round cell bodies, central nuclei, and long cytoplasmic processes that pass between the cells of the strata basale and spinosum and terminate in small indentations on the keratinocyte surfaces. Melanocytes make up 10-25% of this layer's cells but do not participate in keratinization.
1. Melanins contribute to skin, eye, and hair color. Synthesized by melanocytes, they include the dark brown pigment eumelanin, found in the epidermis, iris, and brown and black hair; and the cysteine-rich pigment pheomelanin, found in red hair. 2. Melanocytes derive from the neural crest and migrate into the epidermis during em bryogenesis. Although they are scattered among the keratinocytes of the stratum basale, they are not attached to them by desmosomes. They have round cell bodies, central nuclei, and long cytoplasmic processes that pass between the cells of the strata basale and spinosum and terminate in small indentations on the keratinocyte surfaces. Melanocytes make up 10-25% of this layer's cells but do not participate in keratinization.
EPIDERMIS
The epidermis contains 2 major and 2 minor cell populations specialized for specific functions. Major populations include the keratinocytes and melanocytes. Minor populations include Langerhans' and Merkel's cells.
A. Keratinizing System: The keratinocytes make up most of the epidermis. They participate in the continuous turnover (renewal) of the skin surface by passing through 4 overlapping processes: cell renewal, or mitosis; differentiation, or keratinization; cell death; and exfoliation (the sloughing of dead cells from the skin surface). The entire process takes 15-30 days and occurs in waves. A cell layer produced by a mitotic wave in the basal layer undergoes keratinization in synchrony. Each wave pushes the cell layers produced in earlier waves toward the surface. The layers from several waves, each at a different depth and step in the process, give a stratified appearance to vertical sections of the epidermis. The 5 layers of the epidermis are distinguished by the shape, staining properties, contents, and orientation of the keratinocytes they contain.
A. Keratinizing System: The keratinocytes make up most of the epidermis. They participate in the continuous turnover (renewal) of the skin surface by passing through 4 overlapping processes: cell renewal, or mitosis; differentiation, or keratinization; cell death; and exfoliation (the sloughing of dead cells from the skin surface). The entire process takes 15-30 days and occurs in waves. A cell layer produced by a mitotic wave in the basal layer undergoes keratinization in synchrony. Each wave pushes the cell layers produced in earlier waves toward the surface. The layers from several waves, each at a different depth and step in the process, give a stratified appearance to vertical sections of the epidermis. The 5 layers of the epidermis are distinguished by the shape, staining properties, contents, and orientation of the keratinocytes they contain.
Subscribe to:
Posts (Atom)