Breast And Mammary Glands — Structure, Morphology and Functions

1. Difference Between Breast and Mammary Gland

The terms breast and mammary gland are often used interchangeably, but they are not exactly the same.

Breast is the complete anatomical structure. It contains glandular tissue along with adipose tissue, connective tissue, blood vessels, lymphatic vessels, and nerves.

Mammary gland is the specialized glandular tissue present within the breast. Its main function is milk production.

2. External Morphology of the Breast

In an adult female, the breast is a rounded structure located on the anterior chest wall. Its external morphology can be understood through three main features:

• Breast mound
• Areola
• Nipple

2.1 Areola

Areola is the darker circular region surrounding the nipple.

It contains small glands called Montgomery glands. These glands help lubricate and protect the skin of the nipple and areola.

2.2 Nipple

Nipple is the raised structure on the surface of the breast. Mammary ducts open in this region, allowing milk to reach the outside during lactation.

3. Anatomical Position of the Breast

The breast is located on the anterior thoracic wall, with most of its tissue lying over the pectoralis major muscle.

A lateral extension of breast tissue may extend towards the axilla. This is known as the axillary tail of Spence.

4. Composition of the Breast

The breast is made up of several types of tissues and supporting structures.

5. Internal Organization of the Mammary Gland

The mammary gland is a highly organized branching glandular system.

Its basic organization can be understood as:

The mammary gland contains several lobes. Each lobe is further divided into smaller structures called lobules.

6. Lobes and Lobules

Lobes

Mammary gland tissue is organized into several lobes. Each lobe contains glandular tissue and a branching network of ducts.

Lobules

Each lobe is divided into smaller units called lobules.

Lobules are important glandular regions of the mammary gland. Each lobule contains numerous small secretory structures called alveoli.

7. Alveoli — Milk-Secreting Units

Alveoli are the microscopic milk-secreting units of the mammary gland.

They are small sac-like structures lined by secretory epithelial cells.

During pregnancy and lactation, the development and functional activity of the alveoli increase considerably.

8. Myoepithelial Cells

Myoepithelial cells are present around the secretory epithelial cells of the alveoli.

These cells are contractile. During lactation, oxytocin causes the myoepithelial cells to contract, helping push milk from the alveoli into the ducts.

9. Pathway of Milk

Milk produced in the mammary gland passes through progressively larger ducts and eventually reaches the nipple.

In simple terms, alveoli produce milk, while ducts transport milk towards the nipple.

10. Lactiferous Ducts

Lactiferous ducts are larger ducts of the mammary gland that transport milk towards the nipple.

Several smaller ducts join together to form larger ducts, which eventually reach the nipple region.

11. Microscopic Anatomy of the Mammary Gland

Histologically, the mammary gland contains epithelial cells, myoepithelial cells, ducts, lobules, connective tissue, and adipose tissue.

In a non-lactating breast, the glandular structures are relatively less developed, while adipose and connective tissue may be more prominent.

During lactation, the alveoli and secretory epithelial cells become highly active, making the glandular tissue more prominent.

12. Non-Lactating and Lactating Breast

13. Breast Development During Puberty

During puberty, ovarian hormones cause significant development of the female breast.

• Milk ducts become more developed and branched.
• Glandular tissue increases.
• Adipose tissue increases.
• Connective tissue and supporting structures develop.
• The nipple and areola mature.

Role of Estrogen

Estrogen plays an important role in ductal development and overall breast growth.

Role of Progesterone

Progesterone contributes to the development of the lobular and alveolar structures of the mammary gland.

14. Changes in the Mammary Gland During Pregnancy

During pregnancy, the mammary gland undergoes major structural changes to prepare for future lactation.

• Lobular development increases.
• Alveoli become more developed.
• The ductal system develops further.
• Secretory epithelial cells become functionally mature.
• Blood supply increases.

Estrogen, progesterone, and prolactin all contribute to the development and preparation of the mammary gland during pregnancy.

15. Milk Production After Childbirth

During pregnancy, high levels of estrogen and progesterone stimulate mammary gland development but limit full milk secretion.

After childbirth, the placenta is expelled and estrogen and progesterone levels fall rapidly.

This allows prolactin to stimulate the secretory cells of the mammary gland and promote milk synthesis.

16. Prolactin — Milk Production

Prolactin is a hormone secreted by the anterior pituitary gland.

Its main role in lactation is to stimulate the secretory epithelial cells of the mammary gland to produce milk.

17. Oxytocin — Milk Ejection

Oxytocin is synthesized in the hypothalamus and released from the posterior pituitary gland.

When a baby suckles at the nipple, sensory signals are sent to the hypothalamus. This stimulates the release of oxytocin.

Oxytocin causes the myoepithelial cells surrounding the alveoli to contract. This pushes milk from the alveoli into the ducts.

18. Milk Ejection Reflex

19. Breast Milk

Breast milk is a complex biological fluid containing nutrients and immune components that support the growth, development, and early immune protection of the newborn.

Major components include:

• Water
• Lactose
• Proteins
• Fats
• Vitamins
• Minerals
• Antibodies and other immune components

20. Colostrum

Colostrum is the first breast secretion produced during the initial days after childbirth.

It is produced in relatively small amounts but contains important antibodies and other immune components.

It contains immune components such as Immunoglobulin A (IgA), which contributes to early immune protection in the newborn.

21. Cooper’s Ligaments

The breast contains bands of connective tissue that provide structural support. These are called Cooper’s suspensory ligaments.

They help support and maintain the internal structure of the breast tissue.

22. Breast and Pectoralis Major

Pectoralis major is a major skeletal muscle of the anterior chest wall. Most of the breast lies over this muscle.

Therefore, it is important to understand that breast tissue and the pectoralis major muscle are separate structures.

23. Blood Supply of the Breast

The breast receives blood from several arterial sources.

Major sources include:

• Branches of the internal thoracic artery
• Lateral thoracic artery
• Branches of the thoracoacromial artery
• Branches of the posterior intercostal arteries

Blood supply provides breast tissue with oxygen, nutrients, and other substances required for normal tissue function.

24. Lymphatic Drainage of the Breast

Lymphatic drainage of the breast is clinically important.

A large proportion of lymph from the breast drains towards the axillary lymph nodes.

Breast lymphatic drainage is also connected with the parasternal/internal mammary lymph nodes.

25. Male Breast

Both males and females have mammary tissue during embryonic development. In males, the mammary gland normally remains relatively rudimentary.

In females, hormonal changes during puberty, pregnancy, and lactation lead to much greater development of the mammary gland.

26. Stages of Breast Development

27. Relationship Between Morphology, Anatomy, and Function

The breast should not be understood only by its external appearance. Its internal anatomy is closely related to its physiological function.

Each structure has a specific role:

• Lobes and lobules organize the glandular tissue.
• Alveoli produce milk.
• Myoepithelial cells help move milk towards the ducts.
• Ducts transport milk towards the nipple.
• Nipple provides the opening through which milk leaves the breast.

28. Understanding the Mammary Gland as a Tree

The branching organization of the mammary gland can be easily understood by comparing it with a tree.

Just as the branches of a tree divide into smaller branches, the ducts of the mammary gland branch into smaller ducts and ductules that extend into lobules and alveoli.

29. Breast Size and Milk Production

Breast size does not directly determine milk-producing capacity.

Adipose tissue contributes significantly to breast size and volume.

Therefore, a larger breast does not necessarily contain more milk-producing glandular tissue.

30. Breast Changes During the Menstrual Cycle

Changes in ovarian hormone levels during the menstrual cycle can cause some women to experience breast fullness, swelling, or tenderness.

These changes are mainly associated with normal hormonal fluctuations during the cycle.

31. Major Hormones and Their Functions

32. One-Minute Revision

33. Quick Concept Map

34. Important Questions

Question 1. What is the main function of the mammary gland?

The main function of the mammary gland is to produce and secrete milk.

Question 2. Where is milk produced?

Milk is mainly produced by secretory epithelial cells present in the alveoli of the mammary gland.

Question 3. What is the role of prolactin?

Prolactin stimulates milk production in the mammary gland.

Question 4. What is the role of oxytocin?

Oxytocin helps in milk ejection by causing contraction of the myoepithelial cells surrounding the alveoli.

Question 5. What is the areola?

The areola is the pigmented circular region surrounding the nipple.

Question 6. What is the function of Cooper’s ligaments?

Cooper’s ligaments are connective tissue bands that provide structural support to the breast.

Question 7. Where does most breast lymph drain?

A large proportion of breast lymph drains towards the axillary lymph nodes.

35. Final Takeaway

The female breast should not be understood simply as an external structure. It is a highly organized glandular system containing glandular, adipose, connective, vascular, lymphatic, and nervous components.

The mammary gland is organized into lobes and lobules, with alveoli serving as the main milk-secreting units. Milk then passes through the duct system towards the nipple.

During pregnancy, the mammary gland undergoes major developmental changes. After childbirth, prolactin plays the main role in milk production, while oxytocin is responsible for milk ejection.