When do mammary glands primarily develop within the breasts? a. During the last weeks of fetal...


When do mammary glands primarily develop within the breasts?

a. During the last weeks of fetal development

b. At birth

c. During infancy

d. During puberty

e. During pregnancy

Mammary Glands

Mammary glands are the defining anatomical features of mammals. They are basically modified sweat glands that can produce milk. These exocrine glands are present inside the breast. In humans, these glands are present on the pectoralis major muscle in the thorax region. They are generally functional in females and non-functional in males.

Answer and Explanation: 1

Mammary glands primarily develop within the breasts during puberty.

High levels of estrogen and progesterone production during puberty stimulate the development of secondary sexual organs, including the mammary glands in females.

Progesterone helps in the development of the ductal system in the mammary glands, whereas estrogen triggers the growth of the mammary glands. Estrogen also stimulates the development of alveolar tissue of mammary glands - the tissues involved in milk production.

The correct answer, therefore, is choice (d).


  • Since puberty is a human biological stage considered to be completely separate from birth and infancy, choices b and c are considered incorrect.
  • Pregnancy, including the last weeks of fetal development, only triggers the active state of the mammary glands but does not necessarily trigger the development per se of those glands. Choices a and e, therefore, are incorrect.

Learn more about this topic:

Physical Growth in Adolescence


Chapter 13 / Lesson 1

Learn all about physical development in adolescence. Learn what puberty is, identify the physical changes in adolescence, and see the sex differences in this stage.

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