Why does a jaundiced person’s eyes and skin look yellow


… asks JANANI from Chennai

PROF DR V NAGARAAJAN, Madurai, Tamil Nadu, answers…

There are two types of bile pigments, both are yellow in colour, one being Bilirubin, and the other, Biliverdin. These two pigments impart colour to the bile salts, which are called glycocholate, and taurocholate.

These are by-products of haemoglobin, which are present in the red blood cells of the body, and owing to wear and tear of the red blood cells, they break, and liberate haemogloin and its derivatives, which are ultimately converted to these bile pigments by the liver cells. They conjugate later with the bile salts.

The bile is necessary for digestion, as it reduces the surface tension of the fat molecules, and disintegrates them to finer particles, as emulsion of the fat. The digestive enzymes for fat then act on them converting them to basic fatty acids, and lipoproteins.

These bile pigments have affinity to the some areas of the body, viz subcutaneous tissue, sclera of the eye. But to get them to combine with these tissues they should be lyophillic (otherwise called affinity to attach themselves to water molecules). There are two types of bile pigments, direct and indirect. The former is lyophillic, soluble in water and other is insoluble called lyophobic. The soluble bilirubin gets deposited under the skin in the subcutaneous region, and sclera, the white portion of the eye ball.

In jaundice, in new born ( physiological and pathological ), these salts which are in the skin are converted to soluble, dissembled products by a treatment called phototherapy ( photooxidation). A person looks yellow due to coloration of the eye, and skin owing to the deposit of the soluble bilirubin under the skin and sclera due to deposits of these soluble bile pigments. Hence in jaundice a person appears yellow.

This week’s questions:

* Why do we have difficulty writing in a straight horizontal line with our eyes closed?

… asks Sapna Prasad, Chennai

* Why do we feel a spinning sensation after un-mounting from a merry-go-round?