Melanin

1. Overview

Mammary glands are highly specialized exocrine glands within the integumentary system responsible for producing and secreting milk to nourish newborns. Present in both sexes but functionally developed in females, they are modified sweat glands derived from the ectoderm. The activity of mammary glands is tightly regulated by hormonal signals, particularly during puberty, pregnancy, and lactation. In addition to their reproductive role, they are also important in clinical medicine due to their association with various benign and malignant diseases.

2. Location

Mammary glands are located in the anterior thoracic wall, overlying the pectoralis major muscle. Specific features include:

• Spanning from the second to the sixth ribs, extending from the lateral border of the sternum to the midaxillary line.

• The glandular tissue is embedded in subcutaneous fat and supported by suspensory ligaments (Cooper's ligaments).

• Each breast contains 15–20 lobes radiating from the nipple, with the nipple surrounded by a pigmented area called the areola.

In males, mammary glands remain rudimentary due to the lack of estrogenic stimulation.

3. Structure

The mammary gland is composed of several structural components:

• Lobes and lobules:

  • Each breast contains 15–20 lobes, each subdivided into lobules, which are clusters of alveoli (milk-producing units).

• Alveoli:

  • Rounded clusters of secretory epithelial cells surrounded by myoepithelial cells and connective tissue.

• Ductal system:

  • Milk from alveoli drains into intralobular ducts, then into lactiferous ducts, which open onto the nipple via lactiferous sinuses.

• Areola and nipple:

  • Areola contains sebaceous glands (Montgomery glands), while the nipple is the terminal conduit for milk ejection.

• Supportive tissue:

  • Includes adipose tissue and fibrous connective tissue that shape and suspend the gland.

4. Function

The primary function of mammary glands is to produce, secrete, and deliver milk to the newborn. Key functional activities include:

• Milk synthesis: Alveolar epithelial cells produce milk components—proteins (casein), lipids, lactose, water, and antibodies.

• Milk secretion: Stimulated by prolactin; secretory products are exocytosed into the lumen of alveoli.

• Milk ejection (let-down reflex): Triggered by oxytocin-induced contraction of myoepithelial cells, expelling milk through the ducts to the nipple.

5. Physiological role(s)

Mammary glands contribute to several essential physiological and reproductive processes:

• Neonatal nutrition: Milk provides balanced nutrition, including essential macronutrients, vitamins, and minerals.

• Passive immunity: Breast milk contains IgA antibodies, lysozymes, and lactoferrin to protect the infant from pathogens.

• Hormonal interaction: Respond to prolactin (milk production), oxytocin (milk ejection), estrogen, and progesterone (development and maintenance).

• Maternal bonding: Breastfeeding fosters emotional attachment between mother and infant through tactile and hormonal cues.

• Reproductive cycle modulation: Lactation suppresses ovulation temporarily by reducing GnRH secretion (lactational amenorrhea).

6. Clinical Significance

Mammary glands are of major clinical importance due to their susceptibility to hormonal changes, infection, and neoplasia:

• Mastitis:

  • Bacterial infection (usually Staphylococcus aureus) of lactating breasts causing pain, redness, swelling, and fever.

• Fibrocystic breast changes:

  • Common benign condition characterized by painful, lumpy breasts due to hormonal fluctuations during the menstrual cycle.

• Gynecomastia:

  • Benign enlargement of male breast tissue due to hormonal imbalance or medication side effects.

• Breast cancer:

  • The most common cancer in women worldwide; often arises from the ductal epithelium (ductal carcinoma) or lobules (lobular carcinoma).

  • Early detection via mammography and self-exams is crucial for favorable outcomes.

• Galactorrhea:

  • Inappropriate or excessive milk secretion not related to childbirth or nursing, often linked to hyperprolactinemia.

• Surgical and cosmetic relevance:

  • Breast reduction, augmentation, and reconstructive surgery require detailed anatomical knowledge of the mammary gland.