Question Corner

Congenital lesions of the skin

Question: Why do moles form on the human body?

B. Murugavel, Kanchipuram, T.N.

Answer 1: The scientific name of mole is Nevus. Medically the moles or nevi are instructive tumours of the skin. The term nevus denotes any congenital lesion of skin. Common acquired nevi are tan-to-brown, uniformly pigmented solid regions of elevated skin with well defined rounded borders. They are usually less than 6mm across.

They are formed when single cells which are normally interspersed among basal Keratinocytes are transferred in to round to oval melanocytes called nevus cells that grow in aggregates or nests along the dermal-epidermal junction. The nuclei of nevi cells are uniform and rounded, contain inconspicuouus nucleoli and show little or no mitotic activity. The early developmental stage in nevi are called junctional nevi. When they grow in to underlying dermis as nests or cords of cells they are called compound nevi. When they are still older the epidermal nests may be lost entirely but dermal nests develop further. Now they are called dermal nevi. Clinically, compound and dermal nevi are often more elevated thqn junctional nevi.

Although nevi are common, their clinical and histological diversity necessitates thorough knowledge of their appearance and natural evolution. Otherwise they become confused with other skin conditions notably malignant melanoma (skin cancer tumour).

There are numerous clinical and histological types of nevi. The following are impotant ones:1. Congenital nevi: These are present at birth and are called acquired nevi.2. Spindle and epitheloid cell nevi: They are red-pink nodules and contain large plump cells with pink blue cytoplasm.3. Blue nevi: These are black blue nodules and are dendritic with heavily pigmented nevus cells.4. Halo nevi: These are identical to ordinary acquired nevi but provided with lymphocytic infiltration sorrounding nevus cells. So they have host immune response.

S. Palaniappan, Pudukkottai, T.N.

Answer 2: Mole consists of cells containing melanin, a dark pigment. Moles may occur at any part of the body and can number as high as forty and may be flat or raised. Colouration could be light brown to blue black. Basically moles are harmless and are just formations on the skin, like say, hair. But these are vital indications of cancer's onset. Any change in size or colour should be taken seriously and medical attention sought.

N. Dharmeshwaran, Chennai


Question: Why does a bird not get electrocuted on sitting on a live wire?

D. Jathin Sai, Naidupeta, A.P.

ANSWER: A bird sitting on a live wire will get electrocuted only if electric current passes through its body. We can compare flow of electricity through a body to flow of water through a pipe or tube. Water will always flow from a higher level to a lower level. Similarly electric current will always flow or pass through from a higher potential or voltage level to a lower potential level. We can take two wires running on poles through a street. One wire which we call live will be at a potential of 230 volts which is called the phase wire and the other one which we call the neutral wire will be at a potential of zero volts. Immediately on sitting on the live wire the bird's potential will also be raised to 230 volts and if by a accident it comes in contact with the neutral wire or touches it, a current will pass through its body from the live wire which is at a higher potential to the neutral wire which is at zero potential.

Birds, animals, and human beings can withstand flow of a certain amount of electric current only through their bodies and excess flow of current will cause immediate death. In the present case the flow of current throngs the bird's body will be enormous and the bird will probably get burnt to death.

If two crows, one sitting on the live wire and the other sitting on the neutral wire, happen to touch each other, both will meet the same fate as the bird mentioned above and will get electrocuted. But if both the sit on the live wire side by side and touch each other nothing will happen as both the crows will be at the same voltage level of 230 volts and there will be no flow of current through their bodies.

A. Albert Rayappa, Pondicherry

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