**Question:** Yellowish discoloration of the mucus membrane and teeth is produced by

A. Bilirubin
B. Pigments
C. Carbon monoxide
D. Tobacco and alcohol consumption

**Correct Answer:** A. Bilirubin

**Core Concept:**
Bilirubin is a yellow pigment formed as a waste product during the breakdown of red blood cells and heme proteins. It is primarily cleared from the bloodstream by the liver, where it is conjugated and excreted into the bile. Yellowish discoloration of mucosa and teeth, known as jaundice, occurs when bilirubin levels are elevated due to impaired liver function or hemolysis.

**Why the Correct Answer is Right:**
Bilirubin is the correct answer because it is responsible for the yellow coloration observed in jaundiced individuals. Jaundice is caused by elevated bilirubin levels, which lead to the yellow discoloration of mucous membranes, skin, and sclera. In paediatrics, neonatal jaundice is typically caused by immature liver function, while in adults, it can result from liver diseases, hemolysis, or obstruction of the bile ducts.

**Why Each Wrong Option is Incorrect:**

A. Bilirubin is the correct answer, not C. Carbon monoxide. Carbon monoxide (CO) is a toxic gas produced by the incomplete combustion of carbon-containing fuels, causing methemoglobinemia, a condition characterized by elevated levels of methemoglobin, not bilirubin.

B. Pigments are not the correct answer. Pigments refer to various organic substances that impart color to tissues or fluids, but they do not directly describe the cause of yellow discoloration in jaundiced patients.

D. Tobacco and alcohol consumption can lead to liver damage and impaired bilirubin clearance, contributing to jaundice. However, the primary cause of yellow discoloration in jaundiced individuals is elevated bilirubin levels, which is correct in option A.

**Clinical Pearl:**
In clinical practice, recognizing the cause of jaundice is crucial in determining the appropriate management and prognosis for patients. Jaundice can be a symptom of various liver diseases, hemolysis, or obstructive jaundice, and a thorough clinical evaluation is necessary to identify the underlying cause.