What Are Melanocytes?

Melanocytes are dendritic cells that synthesize and secrete melanin. They are located in the epidermal basal cell layer and can also be found in the mucosa. Their function is to produce melanin and transport it to nearby skin cells. The number of melanocytes in normal skin is stable, with a ratio of 4 to 10 basal keratinocytes with one melanocyte. The number of melanocytes in the human body varies from site to site: the neck is the largest, followed by the upper limbs and the back, and the lower limbs and the thorax and abdomen are the least.

Basic Information

Chinese name

Melanocyte

Function

Synthetic secreted melanin absorbs ultraviolet light

Clinical significance

May cause hyperpigmentation or hypopigmentation

Melanocyte action

The melanin in the skin can absorb ultraviolet rays, prevent it from penetrating deep and damage tissue cells, and play a protective role. The number of human melanocytes varies from site to site: the neck is the largest, followed by the upper limbs and the back, and the lower limbs and the thorax and abdomen are the least. This is exactly consistent with the amount of ultraviolet radiation received by various parts of the body, indicating that the difference in the number of melanocytes is related to the degree of ultraviolet radiation. Ultraviolet irradiation can promote the division and proliferation of melanocytes and increase their number; it can also cause the morphology of melanocytes to change, that is, the cells have more branches, deeper staining, and active functions, so they can produce more melanin and cause The surrounding skin cells are transported intracellularly for protection.
The number of melanocytes decreases with age. The blackness of hair depends on the continuous synthesis of melanin by the hair follicle melanocytes. The melanocytes of the hair follicles of the elderly decrease, causing the hair to gradually turn white. The pituitary secretes melanocyte stimulating hormone, estrogen, human prostaglandins E1 and E2, and ultraviolet radiation can promote the increase of pigment. When the melanocytes of the skin abnormally disappear for some reason, it can lead to vitiligo.

Clinical significance of melanocytes

Changes in melanocyte function and number can cause increased pigmentation or decreased pigmentation for the following reasons.
1. The number of melanocytes increases or decreases. For example, melanocytes increase in pigmented moles, but melanocytes disappear at the site of vitiligo lesions.
2. Melanocytes are normal, but the ability to form pigments and transport melanin bodies is enhanced, such as freckles and melasma; abnormal endocrine functions such as melanin increase during Addison disease; thioamino groups in the skin decrease during dermatitis, and tyrosinase inhibition Decreased, causing increased pigmentation.
3. Melanocyte synthesis disorders, such as patients with albinism, although the number of melanocytes is normal, tyrosinase functional defects cannot synthesize pigments, and patients with phenylketonuria lack phenylpropionate hydroxylase and cannot be oxidized to As a result of tyrosine, phenylpropionic acid and its metabolites accumulate in the blood, inhibiting the oxidation of tyrosine to form melanin, which is manifested as hypopigmentation and hair pigmentation. A. ovale produces azelaic acid, which inhibits tyrosinase and interferes with melanin formation, which can cause skin pigmentation in patients with tinea versicolor.
4. Disturbance of melanosomes, due to sponge edema between the epidermis of eczema, the melanocyte granules transported by melanocytes to keratinocytes through dendrites are reduced, resulting in reduced local pigmentation.
5. Melanocytes are damaged or destroyed. Melanin is released to the dermal papilla and is swallowed by tissue cells. Pigmentation and melanosis after inflammation belong to this category.