Melanin functions

Melanin is the brown black, non-haemoglobin-derived pigment
normally present in the hair, skin choroid of the eye, meninges and adrenal
medulla. It is synthesized in the melanocytes and dendritic cells, both of which
are present in the basal cells of the epidermis.

Melanin is stored in the form of cytoplasmic granules in the phagocytic cells called the melanophore, present in the under lying dermis. Melanocytes possess the enzyme tyrosinase necessary for the synthesis of melanin from the amino acid called tyrosine Tyrosine tyrosinase Melanin

Various disorders of melanin pigmentation cause generalized and
localized hyperpigmentation and hypopigmentation.

Generalized hyperpigmentation

a) In Addison’s disease, there is generalized hyperpigmentation of the skin,
especially in areas exposed to light and buccal mucosa.
b) Hyper pigmentation on skin of face, nipples and genitalia during pregnancy
under the influence of oestrogen.
c) In chronic arsenical poisoning, there is characteristic rain-drop pigmentation
of the skin.

Generalized hypopigmentation

Albinism is an extreme degree of generalized hypo pigmentation in
which tyrosinase activity of the melanocytes is genetically defective and no
melanin is formed. Albinoes have blonde hair, poor vision and severe
photophobia. They are highly sensitive to sunlight. Chronic sun exposure
may lead to pre-cancerous lesions, squamous and basal cell cancers of the
skin.

Localised hypopigmentation

a) Leucoderma is a form of partial albinism and is an inherited disorder.
b) Vitiligo is local hypopigmentation in the skin.
c) Acquired local hypopigmentation can result from various causes such as
leprosy, healing of wounds, radiation dermatitis, etc.

Melanin functions

Generalized hyperpigmentation

Generalized hypopigmentation

Localised hypopigmentation

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