PHYSIOLOGY OF LACTATION

ANATOMY

The breast is made of lobes of glandular tissue, with associated ducts for transfer
of milk to the exterior and supportive fibrous and fatty tissue. On average, there
are 15–20 lobes in each breast, arranged roughly in a wheel-spoke pattern
emanating from the nipple area. The distribution of the lobes, however, is not
even.

There   is  a   preponderance   of  glandular   tissue  in  the upper   outer   portion of  the

breast  (responsible    for the tenderness  in  this    region  that    many    women

experience  prior   to  their   menstrual   cycle).

About   80–85%  of  normal  breast  tissue  is  fat during  the reproductive    years.

The 15–20   lobes   are further divided into    lobules containing  alveoli (small

saclike features)   of  secretory   cells   with    smaller ducts   that    conduct milk    to

larger  ducts   and finally to  a   reservoir   that    lies    just    under   the nipple. In  the

nonpregnant,    nonlactating    breast, the alveoli are small.

During  pregnancy,  the alveoli enlarge;    during  lactation,  the cells   secrete milk

substances  (proteins   and lipids).    With    the release of  oxytocin,   the muscular

cells   surrounding the alveoli contract    to  express the milk    during  lactation.

Ligaments   called  Cooper  ligaments,  which   keep    the breasts in  their

characteristic  shape   and position,   support breast  tissue. In  the elderly or

during  pregnancy,  these   ligaments   become  loose   or  stretched,  respectively,

and the breasts sag.

The lymphatic   system  drains  excess  fluid   from    the tissues of  the breast  into

the axillary    nodes.  Lymph   nodes   along   the pathway of  drainage    screen  for