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Breast Development

The breasts, commonly termed mammary glands are found on the chest wall and extend from the 2nd rib above to the 6th rib below. In females  their primary physiological function is to breastfeed.

Both men and women developed breast from the same embryological tissues.  A milk streak or mammary ridge develops along the trunk on either side from the axilla to the groin and can be seen in a 5-week-old human foetus. 

The mammary glands are paired glands.  In humans, they regressed to the definitive site of the adult nipple.  At the site of a nipple, there is a small mammary pit which at the time of birth everts to form the definitive nipple.  Failure of this evagination process will result in a congenitally inverted nipple which maybe unilateral or bilateral and is reasonably common condition. It can make breast feeding difficult. It is important to differentiate between a ‘life long’ congenitally inverted nipple and new nipple retraction which can be caused by a cancer behind the nipple.

From birth until puberty, the breasts consist of lactiferous ducts with no alveoli.  At puberty, the ducts start to proliferate in women and at the end of the ducts solid masses of cells form and these become the future breast lobules.

During pregnancy, secreting alveoli will develop and in early weeks of pregnancy, proliferation of the ducts and lobules will occur, the there will be  increased pigmentation of the nipple and areola.  The alveoli will display secretory cells.  In the last days of the pregnancy, the breasts secret colostrum, a yellow sticky serous fluid, which is then replaced by the secretion of milk.  When the lactation ceases, the glandular tissue of the breast will return to its resting state. 

After menopause, glandular tissue of the breast atrophies and the connective  tissue becomes less cellular, the amount of collagen decreases, and fatty infiltration will occur in the breast.  The breast may also reduce in size and develop a significant degree of ptosis.

In males, the breasts remain rudimentary in their pre pubertal state.  Occasionally, gynaecomastia or enlargement of the breasts can occur and it  can often be due to hormonal causes. 

The breasts overlie the pectoralis major muscle and cover much of the area over the chest.  Breasts can extend from the collar bone to the middle of the sternum or  (breast bone)  at the sides of the chest, and  can extend into the axilla or armpit and can reach as far back as a latissimus dorsi muscle extending from the lower back to the humerus bone, the longest bone of the upper arm.

The glandular tissue of the breast is supported with oestrogen and thus when a woman reaches menopause and the oestrogen levels decreases, the milk glands will atrophy and disappear resulting in a breast composed of adipose tissue, superficial fascia, suspensory ligaments, and a  skin envelope. 

Breast size varies in women as thus so does the composition ratios of the glandular tissue to the adipose tissue.  This ratio will determine the density or firmness of the breast.  It is important that women who have dense breasts are educated about this as it may impact on the sensitivity of breast screening. 

Dense breasts are more difficult to image with mammography than breasts which contained a significant amount of adipose tissue. Cancers can be camouflaged in mammograms in dense breasts and ultrasound will often be used to assess dense breasts. Increased breast density is an independent risk factor for breast cancer.  One third of all women who have dense breasts will maintain this density in the post menopause.

It is quite common for breasts to be asymmetrical.  About 90% of women’s breasts are asymmetrical to some degree, either in size, volume, or relative position upon the chest. 

From a physiological perspective, the primary function of breasts as mammary glands are  for lactation.  However, many women regard their breasts which are female’s secondary sex characteristics as important as important to their sexual attractiveness as a sign of femineity and important for their sense of self and body image.  Therefore, it is crucial that all of these attributes are considered in the treatment of women with breast cancer.