Breast


Image Caption : Breast Anatomy : Structures of the healthy breast are visible in a Breast MRI: Nipple, Breast Tissue, Fat, Suspensory Ligaments, Ducts, Chest Wall Muscle, Ribs

BREAST ANATOMY

The breasts of an adult woman are milk-producing, tear-shaped glands. They are supported by and attached to the front of the chest wall on either side of the breast bone or sternum by ligaments. They rest on the major chest muscle, the pectoralis major.

The breast has no muscle tissue. A layer of fat surrounds the glands and extends throughout the breast.

Illustration of the components of the breast

The breast is responsive to a complex interplay of hormones that cause the tissue to develop, enlarge and produce milk. The three major hormones affecting the breast are estrogen, progesterone and prolactin, which cause glandular tissue in the breast and the uterus to change during the menstrual cycle.

Each breast contains 15 to 20 lobes arranged in a circular fashion. The fat (subcutaneous adipose tissue) that covers the lobes gives the breast its size and shape. Each lobe is comprised of many lobules, at the end of which are tiny bulb like glands, or sacs, where milk is produced in response to hormonal signals.

Ducts connect the lobes, lobules, and glands in nursing mothers. These ducts deliver milk to openings in the nipple. The areola is the darker-pigmented area
around the nipple.

REVIEW: BREAST ANATOMY

Here is what we have learned from
Breast Anatomy:

  • The breasts of an adult woman are milk-producing, tear-shaped glands.
  • A layer of fatty tissue surrounds the breast glands and extends throughout the breast, which gives the breast a soft consistency and gentle, flowing contour.
  • The breast is responsive to a complex interplay of hormones that cause the breast tissue to develop, enlarge and produce milk.
  • Each breast contains 15 to 20 lobes arranged in a circular fashion.
  • Each lobe is comprised of many lobules, at the end of which are tiny bulblike glands, or sacs, where milk is produced in response to hormonal signals.
  • Ducts connect the lobes, lobules, and glands; in nursing mothers, these ducts deliver milk to openings in the nipple.
  • Breast tissue is drained by lymphatic vessels that lead to axillary nodes (which lie in the axilla) and internal mammary nodes (which lie along each side of the sternum).

National Cancer Institute / NIH

The Breasts

Whereas the breasts are located far from the other female reproductive organs, they are considered accessory organs of the female reproductive system. The function of the breasts is to supply milk to an infant in a process called lactation. The external features of the breast include a nipple surrounded by a pigmented areola (Figure), whose coloration may deepen during pregnancy. The areola is typically circular and can vary in size from 25 to 100 mm in diameter. The areolar region is characterized by small, raised areolar glands that secrete lubricating fluid during lactation to protect the nipple from chafing. When a baby nurses, or draws milk from the breast, the entire areolar region is taken into the mouth.

Breast milk is produced by the mammary glands, which are modified sweat glands. The milk itself exits the breast through the nipple via 15 to 20 lactiferous ducts that open on the surface of the nipple. These lactiferous ducts each extend to a lactiferous sinus that connects to a glandular lobe within the breast itself that contains groups of milk-secreting cells in clusters called alveoli (see Figure). The clusters can change in size depending on the amount of milk in the alveolar lumen. Once milk is made in the alveoli, stimulated myoepithelial cells that surround the alveoli contract to push the milk to the lactiferous sinuses. From here, the baby can draw milk through the lactiferous ducts by suckling. The lobes themselves are surrounded by fat tissue, which determines the size of the breast; breast size differs between individuals and does not affect the amount of milk produced. Supporting the breasts are multiple bands of connective tissue called suspensory ligaments that connect the breast tissue to the dermis of the overlying skin.

Anatomy of the Breast

This figure shows the anatomy of the breast. The left panel shows the front view and the right panel shows the side view. The main parts are labeled.

During lactation, milk moves from the alveoli through the lactiferous ducts to the nipple.

During the normal hormonal fluctuations in the menstrual cycle, breast tissue responds to changing levels of estrogen and progesterone, which can lead to swelling and breast tenderness in some individuals, especially during the secretory phase. If pregnancy occurs, the increase in hormones leads to further development of the mammary tissue and enlargement of the breasts.

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