By: Safana Sadiq

PROCESSES INVOLVED IN LACTATION

Breasts are bilateral glandular structures

Extends from 2nd to 6th rib in the mid-clavicular line.

It lies in the subcutaneous tissue over the fascia covering the pectoralis major or even beyond that to lie over the serratus anterior and external oblique.

ANATOMY OF THE BREASTS

Structures (non lactating breast):

The areola is placed about the center of the breast and is pigmented. It is about 2.5 cm in diameter.

There are numerous sebaceous glands over it.

It contains few involuntary muscles.

The nipple is a muscular projection covered by pigmented skin. It is vascular and surrounded by unstriped muscles which make it erectile.

It accommodates about 15-20 lactiferous ducts and their openings.

Each breast is divided into 15-20 lobes by fibrous septa which radiate from the center.

Each lobe consists mainly of fibro fatty tissue. The glandular tissue consists mainly of duct system in non lactating breast.

One lactiferous duct drains a lobe.

The lobes are divided into lobules, each lobule containing a certain number of alveoli and ducts (10-100).

The alveoli contain acini cells (columnar epithelium), which produce milk and are surrounded by myoepithelial cells

These ducts connect, with larger ones called lactiferous ducts.

There is a dense network of capillaries surrounding the alveoli.

Contraction of myoepithelial cells squeezes the alveoli and ejects the milk into the larger duct.

One large duct leaves each lobe and widens to form a lactiferous sinus or ampulla.

A lactiferous tubule from each sinus opens on the surface of the nipple.

Increase in breast size in early weeks of gestation. This is due to hypertrophy and proliferation of ducts and alveoli which are shown in the peripheral lobules (effects of oestrogen and progesterone).

Vascularity is increased which results in appearance of bluish veins running under the skin.

The axillary tail is enlarged and painful.Presence of striae from stretching.

PHYSIOLOGICAL CHANGES OF THE BREAST IN PREGNANCY

Nipples and areola: The nipples become larger, erectile and deeply pigmented.

Secretion: Secretion can be squeezed from out of the breast (sticky) at about 12th week.

By 16th week, it becomes thick and yellowish. The demonstration of secretion from a breast of the women who has never lactated is an important sign of pregnancy. In latter months, colostrum may be expressed from the nipples.

COMPARISON OF NON-PREGNANT & PREGNANT BREAST

The physiological basis of lactation is divided into four phases:

1. Preparation of breasts (mammogenesis).

2. Synthesis and secretion from the breast alveoli (lactogenesis).

3. Ejection of milk (galactokinesis).

4. Maintenance of lactation (galactopoiesis).

PROCESSES IN LACTATION

Pregnancy is associated with a remarkable growth of both the ductal and lobuloalveolar systems.

Mammogenesis

Milk secretion actually starts on 3rd or 4th postpartum day.

Around this time, the breasts become engorged, tense, tender and feel warmth.

When the progesterone and estrogen are withdrawn following delivery, prolactin begins its milk secretory activity.

Lactogenesis

The secretory activity is enhanced directly or indirectly by growth hormone, thyroxine, glucocorticoids and insulin.

Prolactin stimulates mammary glandular ductal growth and epithelial cell proliferation and induces milk protein synthesis.

Stage 1:Occurs by mid pregnancy.

Mammary gland becomes competent to secrete milk.

Lactose, total protein, and immunoglobulin concentrations increase within the secreted glandular fluid, whereas sodium and chloride concentrations decrease.

High circulating levels of progesterone and estrogen hold the secretion of milk in check.

There are 2 stages of lactogenesis :

Stage 2 (day 2 or 3 to day 8 after birth):

Occurs around the time of delivery.

Onset of copious milk secretion.

Blood flow, oxygen, and glucose uptake increase, and citrate concentration increases sharply.

Progesterone plays a key role.

Removal of the placenta is necessary for the initiation of milk secretion; however, the placenta does not inhibit established lactation control.

Discharge of milk from the mammary glands depends not only on the suction exerted by the baby during suckling but also on the contractile mechanism which expresses the milk from the alveoli into the ducts.

Galactokinesis

Presence of the infant or the infant's cry can induce letdown without suckling.

A sensation of rise of pressure in the breasts by milk experienced by the mother at the beginning of the sucking is called "draught".

The milk ejection reflex is inhibited by factors such as pain, breast engorgement or adverse psychic condition.

Prolactin appears to be the single most important galactopoietic hormone.

Continuous suckling is essential for removal of milk from glands, also release prolactin.

Secretion is the continuous process unless suppressed by congestion or emotional disturbances.

Galactopoiesis

A healthy mother will produce about 500-800 ml of milk/day with about 500 Kcal /day.

This requires 600 Kcal/day for the mother which must be made up from the mother's diet or from her body store.

Inadequate milk production/ lactation failure may be due to infrequent suckling or due to endogenous suppression of prolactin (pyridoxin, diuretics or retained placental bits).

THE END

Fraser DM, Cooper MA.Myles textbook for midwives.15th edition. Philadelphia:churchill livingstone elsevier;2009

Dutta DC.Textbook of obstetrics. 6th edition.Calcutta:New central book agency;2004

Human milk and lactation. [Updated on December 14, 2010, Cited on 5th June 2012]. Available from : http://emedicine.medscape.com/article/1835675-overview

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