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BASIC INFORMATION
BACKGROUND NEEDED
THE BREASTFEEDING ANSWER BOOK
The breast—or mammary gland—is a complex and efficient organ. Development of the
breast begins before birth during the early weeks of gestation, but the mammary gland doesn’t
become fully functional until the onset of lactation. The breast continues to change under
the influence of normal physical processes—such as menstrual cycles, pregnancies, birth, and
weaning—through menopause, when the gland begins to atrophy. Knowledge of breast
anatomy and function will be helpful in understanding how normal bodily functions and environmental influences affect breastfeeding.
BREAST ANATOMY
Composition of the breast
The breast is a secretory gland composed of the following parts:
• glandular tissue, which makes and transports milk,
• connective tissue, which supports the breast,
• blood, which nourishes breast tissue and provides the nutrients needed to make milk,
• lymph, which removes waste,
• nerves, which make the breast sensitive to touch and allow the baby’s suck to stimulate the release of hormones that trigger the let-down, or milk-ejection, reflex and the
production of milk,
• adipose (fatty) tissue, which offers protection from injury.
The size of the breasts is determined to a great extent by the amount of fatty tissue present,
which has no effect on milk production or the quality of the milk produced.
The enlargement of the breasts during pregnancy and lactation normally indicates that
the mammary gland is becoming functional, although breast growth continues for the first
month after birth.
Alveoli
Alveoli are grape-like clusters of glandular tissue in which milk is synthesized from blood.
Alveoli cells secrete milk. They are surrounded by a network of band-like myoepithelial
cells, which cause the alveoli to contract when stimulated by the oxytocin released during
the let-down, or milk-ejection, reflex. This action expels the milk into the ductules and down
into the ducts.
Ductules and milk ducts
Ductules are branch-like tubules extending from clusters of alveoli. It was once thought that
each ductule emptied into larger ducts, called lactiferous or mammary ducts. Current research,
however, is changing our understanding of the structure of the breast and seems to indicate
that the largest ducts may be located near the periphery or outer area of the breast (Hartmann
2002).
Milk or lactiferous sinuses
Until recently, it was believed that wider milk ducts, called milk or lactiferous sinuses, exist
under the nipple and areola and that milk collects there. It was thought that these wider milk
sinuses were responsible for rewarding the baby with more milk when he latched farther onto
the breast.
Ultrasound examination of the breast during breastfeeding by Peter Hartmann’s research
team in Perth, Australia, however, has revealed that these wider milk sinuses do not exist (Kent
2002). The diameter of the ducts near the nipple and areola are the same as the ducts closer
to the nipple and farther back in the breast (average size is about 1.2 ml). It still appears tobe
true, however, that a bigger mouthful of breast enhances the milk flow received by the baby,
but the reasons for this are not yet fully understood.
Manually locating what we thought were milk sinuses has been an important aspect of
successful hand-expression. Mothers were told to find these “milk sinuses” with their fingers