A common misconception is that women have breasts so that they can feed babies by producing milk. However, the truth is that the mammary glands that secrete the milk in the breasts makes up a pretty small percentage of the overall breast tissue. Most of the average human female breast is actually adipose tissue (fat) and connective tissue. Women with small breasts can nurse a baby just as well as women with large breasts...

The real evolutionary purpose of women having breasts is to attract the male of the species.

Anatomically, the breasts sit over the pectoralis major muscle and usually extend from the level of the 2nd rib to the level of the 6th rib anteriorly. The superior lateral quadrant of the breast extends diagonally upwards in an 'axillary tail'. A thin layer of mammary tissue extends from the clavicle above to the seventh or eight ribs below and from the midline to the edge of the latissimus dorsi posteriorly.

Important parts of the breasts: mammary glands, the axillary tail (tumours most likely to occur here), the lobules, Cooper's ligaments, the areola and the nipple.

The main function of the female breast, or mammary gland, is the production and expression of milk for the nourishment of babies and toddlers. It is also a secondary sexual characteristic in females, and is regarded in many societies as a symbol of femininity, beauty and eroticism. The size, shape and appearance of breasts vary from one woman to another, and can often be a cause of personal anxiety if she feels that hers are too small / too big / too near to her knees.

Structure

The breasts are two large hemispherical eminences situated on the front and sides of the chest. The nipple is the small conical prominence found in the centre of the breast. It is of a pink or brown hue, and is surrounded by a pigmented area of skin called the areola. In a woman who has never been pregnant, the areola is only slightly darker than the surrounding skin, but during pregnancy and lactation, the areola skin darkens considerably. Both the nipple and areola contain muscular fibres that can cause them to become erect when stimulated.

The breast itself is made up of lobules, which are the milk secreting units. Each lobule consists of a variable number of glands that are embedded in loose connective tissue and drain out into an extralobular duct. These extralobular ducts link together to form subsegmental ducts, then segmental ducts, and finally the lactiferous ducts and sinuses. There are 15 - 20 lactiferous ducts, each draining a segment of the breast, and they empty out onto the surface of the nipple through separate orifices.

The lobules of the breast are surrounded by fatty tissue. The breast itself contains no muscle, and its shape is held together by bands of fine ligaments, called Cooper's ligaments. These ligaments attach to the chest wall and skin, and determine the breast's height and shape. They are also the reason that women should wear sports bras during exercise, as they are liable to stretch. Once they have been stretched, they can never retract back; this means that the breast begins to sag.

Development

In the foetus, the nipples develop along what is called 'the milk line', at the level of the fourth rib. The milk line runs from the axilla to the groin, and a common developmental abnormality is accessory nipples. This is the development of an extra nipple/s along the milk line in addition to the two on the chest.

Before puberty, the breast consists of a few rudimentary milk ducts that are connected to the nipple, and there is no glandular tissue. Shortly before menarche, the areola begins to swell and the ducts begin to lengthen and branch. Glandular tissue develops at the end of these branches, and connective tissue and fat begin to fill out the shape of the breast. Eventually, the breast becomes rounded and the areola flattens out. The breast will continue to grow until at least the age of 25, unless accelerated by the intervention of pregnancy. The development of breast tissue requires the co-ordinated action of many hormones, mainly oestrogen, progesterone, and prolactin, but also growth hormone, insulin and glucocorticoids.

Cyclical Variation

The breast undergoes minor changes during each menstrual cycle, unless there is a failure of ovulation or a pregnancy. The breast tissue is sensitive to the changes in the levels of sex hormones during different phases, and women may notice that their breasts feel fuller in the week leading up to their period.

Pregnancy and Lactation

When a pregnancy occurs, the lobules are stimulated to continue developing by the raised levels of oestrogen and progesterone that are being secreted by the ovary and placenta. Another important hormone in this development is prolactin, which is released by the anterior pituitary gland in the brain. The glandular tissue increases in size, and cells become differentiated so that they can synthesise and secrete milk. The nipple also enlarges in preparation for breast-feeding. Lactation itself is stimulated by the combined efforts of prolactin and oxytocin, which are both released on stimulation of the nursing mother's nipple.

For the first few days of nursing, the mother produces a thick, yellowish fluid called colostrum. This fluid is rich in maternal lymphocytes and immunoglobulins, and helps to protect the infant against infection for the first few days of life. After three to five days, the colostrum is gradually replaced by mature breast milk, which has higher levels of fats and sugars.

Involution

As a woman ages, the levels of hormones that she produces start to decrease in line with decreasing ovarian function. The connective tissue in the breast changes from a loose structure to a dense structure, and the milk secreting cells of the glandular tissue are lost. This continues at an uneven rate after a woman experiences menopause, but eventually it will result in fatty tissue being the major component of the breast.

Gynaecomastia

Gynaecomastia is the enlargement of one or both breasts in the male, and is due to an excessive level of circulating oestrogen in the blood. It is quite a common occurrence at puberty, taking the form of a slight swelling of one or both areoles, which also become very tender. This is completely normal, and affected boys are reassured that the vast majority of cases settle down relatively quickly. There is also a temporary gynaecomastia seen after birth, where the male infant has been exposed to high levels of oestrogen from his mother via the placenta.

Adult gynaecomastia is also due to an excess of circulating oestrogen, and investigation is necessary to rule out underlying disease. Examples include liver cirrhosis, where the diseased liver is unable to break down oestrogens, and testicular cancer, which can sometimes result in the release of an excess amount of oestrogen. Other causes include some drug treatments, such as anti-psychotics and digoxin; and hyperthyroidism.

Whilst it is very rare, it is possible for men to get breast cancer. It is for this reason more than any other that a man should seek out a medical opinion if he notices any changes to his nipples or areoles. Mortality rates for male breast cancer are high because so many believe that 'men don't get breast cancer'.

Reference

• Underwood J C E, 2004, General and Systemic Pathology, 4th edition, Churchill Livingstone, 678-679

Breast (?), n. [OE. brest, breost, As. breost; akin to Icel. brjst, Sw. brost, Dan. bryst, Goth. brusts, OS. briost, D. borst, G. brust.]

1.

The fore part of the body, between the neck and the belly; the chest; as, the breast of a man or of a horse.

2.

Either one of the protuberant glands, situated on the front of the chest or thorax in the female of man and of some other mammalia, in which milk is secreted for the nourishment of the young; a mammma; a teat.

My brother, that sucked the breasts of my mother. Cant. viii. 1.

3.

Anything resembling the human breast, or bosom; the front or forward part of anything; as, a chimney breast; a plow breast; the breast of a hill.

Mountains on whose barren breast The laboring clouds do often rest. Milton.

4. Mining (a)

The face of a coal working.

The front of a furnace.

5.

The seat of consciousness; the repository of thought and self-consciousness, or of secrets; the seat of the affections and passions; the heart.

He has a loyal breast. Shak.

6.

The power of singing; a musical voice; -- so called, probably, from the connection of the voice with the lungs, which lie within the breast.

By my troth, the fool has an excellent breast. Shak.

Breast drill, a portable drilling machine, provided with a breastplate, for forcing the drill against the work. -- Breast pang. See Angina pectoris, under Angina. -- To make a clean breast, to disclose the secrets which weigh upon one; to make full confession.

© Webster 1913.

Breast, v. t. [imp. & p. p.Breasted; p. pr. & vb. n. Breasted.]

To meet, with the breast; to struggle with or oppose manfully; as, to breast the storm or waves.

The court breasted the popular current by sustaining the demurrer. Wirt.

To breast up a hedge, to cut the face of it on one side so as to lay bare the principal upright stems of the plants.

© Webster 1913.

Brest, Breast (?), n. Arch.

A torus.

© Webster 1913.