Question

How many nipples are present in a female rat?
A. Two pairs
B. One pair
C. Three pairs
D. Six pairs

Answer 1

Hint: The nipples of a female rat are present in pairs. Half of them are located in the pectoral region and the other half are in the abdominal-inguinal region. The nipples in the female rat become prominent during the third week of pregnancy. A number of mammary glands can be present in one nipple.

Complete answer:
- Six pairs of nipples (12) are present in a female rat. Three pairs are located in the pectoral region and the other three pairs are located in the abdominal-inguinal region.
- The nipples become visible and pronounced during the pregnancy of a rat. Towards the end of the gestational period, the rat sheds its fur in order to expose the nipples.
- The mammary glands in the nipples are made of epithelial cells. They are made up of alveoli and occur in clusters called lobules. The milk or colostrum travels from the lobules to the ducts which lead to the holes of nipples. The mammary tissue contracts, which causes the milk to leave the alveoli. Multiple mammary glands can be present in one nipple of the female rat.
- Almost all female rats possess 12 nipples, however, few rats may have 10 nipples as well.
- Male rats possess rudimentary mammary glands.

Hence, the correct answer is option (D).

Note: The development of mammary glands in the nipples of female rats occurs in several stages. The development of mammary glands and the production of milk and colostrum are influenced by hormones, growth factors, and environmental factors. Some genetic mutations can lead to the development of inverted nipples, which in turn affects milk production.