Breasts Anatomy: Description, Functions & Physiology of Lactation

Description of Breasts

The breasts are the two mammary glands and accessory organs of reproduction.

Shape: They are hemi-spherical in shape but many times the shape depends on the amount of adipose tissue. Circular in nullipara but pendiclous in women who have borne children and lactated.

Situation: They are situated on the superficial fascia of the anterior chest wall, lying over the pectoralis major muscle. They extend from the second rib above to the sixth rib below and from the lateral margin of the sternum to the mid axillary line.

Gross Structure of  Breasts

Areola: Over the centre of each breast is a circular area about 2.5cm in diameter.

The areolar is pink coloured Caucasian, brown for blacks in nullipara and brownish in women who have born respectively.

Nipple: In the centre of the areolar is the nipple. It is a flat shaped protuberance situated about the level of the 4th intercostal space. It is composed of erectile tissue and about 6mm in length. Its surface is perforated by 15-20 minutes opening of the lactiferous ducts.

Montgomery’s tubercle: Within the areolar are situated about 18 sebaceous glands which become enlarged into tubercles during pregnancy.

Axillary Tail of Spence: This is the part of the breast which extends up into the axilla reaching as high as the 3rd rib thus making the circular shape of the breast to be incomplete.

Microscopic structure of the Breasts

The breast is composed of glandular tissue gathered into about 18-20 lobes. These lobes radiate outward from the areolar and are separated from each other by fibrous connective tissue and lies next to but does not communicate with its fellow.

 Each of the 18 lobes is divided by smaller partitions into numerous lobules which are made up of masses of milk secreting units known as alveoli.

 Each alveolus consists of a number of milk forming cells surrounding a small duct in which they pour their secretions. The duct from the alveoli joins together to form larger ducts, these unite with ducts from other lobules until finally a larger duct known as a lactiferous tubule emerges from the entire lobe and runs towards the nipple.

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Ampulla: As it passes beneath the areolar, each lactiferous tubule expands and forms a dilated sac. The ampulla which serves as a reservoir for milk from here the tubule from each lobe enters the nipple and opens independently upon a surface.

Myoepithelial or Breast cells:These are spider shaped contractile cells surrounding the alveoli.

Fatty Tissue: The gland is stabilized in the fat of the chest wall by numerous fibrous processes. The gland tissue is covered by subcutaneous tissue and finally by the skin.

Breasts

Blood, Nerve & Lymphatic Supply to Breasts 

Blood supply: Breasts received blood through internal mammary artery which is a branch of subclavian artery; external mammary artery which is a branch of lateral thoracic artery and the upper intercostal artery which is a branch from the aorta.

Venous Return:The veins form a circular network around the nipple and drain to the internal mammary and axillary veins.

Lymphatic Drainage:The lymph vessels form a plexus beneath the areolar and between the lobes of the breast. The lymphatics of the breasts communicate freely with each other. The lymph drains into the following regional nodes:

  • The axillary glands in both axillary
  • The glands in the mediastinum
  • The gland in the portal tissue of the liver.

Nerve Supply: The functioning of the breast is contributed by hormones as it has poor nerve supply. Some sympathetic fibres pass to it. The skin over the breast is supplied by cutaneous branches of 4th,5th and 6th thoracic nerves.

Functions of Breasts

  • Production and storage of  milk to support growth and development of infants.
  • Cosmetic purpose for female(i.e. it beautifies a woman and distinguish her from a man).

The physiology of the Breast Development

At puberty, the breasts enlarge and assume the adult female size and shape. This is in response to stimulation by oestrogens which mainly promote the growth and development of the lactiferous tubules and ducts and also cause a certain amount of growth of the nipples and the areolar. 

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Further development and enlargement of the breasts occur during pregnancy. The most important feature at this time is the hypertrophy of the alveoli in response to progesterone stimulation, preparatory to the later manufacture of milk

About 3 days after delivery, milk appears in the breast as a result of stimulation by prolactin and the breasts can then be said to have reached their full development.

The physiology of Lactation

The process of lactation can be considered to take place in three stages:

  1. The actual production of milk in the alveoli
  2. The flow of milk along the duct to the nipple
  3. The withdrawal of milk from the nipple by the baby.

The production of milk

Milk is formed as small fatty globules in the base of these cells and gradually unite to form small developments. As new globules are produced, the droplets are pushed towards the surface of the cell until finally they burst through the cell membranes and enter the lactiferous tubules. 

Here, they join with droplets from other cells and eventually the terminal portions of the tubules within the alveoli become filled with milk. 

The manufacturer of milk is under the control of prolactin from anterior pituitary gland. The action of this hormone is suppressed by the progesterone and oestrogen until a few days after the expulsion of the placenta. When the level of these hormones (oestrogen and progesterone) fall to allow prolactin to function. 

Once lactation has been established by prolactin, growth hormone from the anterior pituitary plays some part in its maintenance.

Note: The breasts require a large blood supply for the secretion of milk.

The flow of milk

Milk is pushed along the ducks towards the nipple by the milk which is being continually formed behind it in the alveoli. Some of the milk is stored in the ampullae underneath, the areolar until the time of the baby’s next feed. When milk is drawn off by the infant, the smooth muscle and basket cells in the wall of the duct and alveoli contact and force more milk towards the nipple. This mechanism occurs as a result of a neuro- hormonal reflex. 

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Thus, the stimulus of the baby’s mouth on the sensitive nipple oxytocin is liberated from the posterior pituitary gland. This hormone stimulates the muscle and basket cells to contact and therefore cause more milk to flow to the nipple. 

This makes the mother feel a sensation known as “draught”. Oxytocin may also stimulate the uterus to contract which the mother feels while breastfeeding, resulting in involution.

The withdrawal of milk

The baby sucks the milk by creating a vacuum in its mouth but mainly by performing a clamping action with its jaws. 

Thus, the baby draws the whole areolar not only the nipple, into its jaws, milk is then expressed from the ampullae. More milk flows down the duct until the breast gradually fills in preparation for the next feeding time

Requirements  for successful lactation

  • Adequate intake of food and fluid sufficient to promote 3500 calories per day.
  • Well-developed breasts and nipples.
  • Adequate and frequently repeated sucking stimulus of the nipple for continuous production of milk.
  • Complete emptying of the breasts.
  • Adequate blood supply to the breasts
  • Ducts freed from epithelial debris

The provision of these requirements is part of clinical technique for successful breastfeeding.

Finally, the anatomy and physiology of breasts is really interesting. Breastmilk produced by the breasts is the best gift every child would receive from his or her mother. Therefore, every woman should endeavour to take good care of their breasts as well as improve their overall health.