Physiology of lactation

PHYSIOLOGY OF LACTATION

Presentation by:Prativa DhakalM.Sc. Nursing

Batch 2011

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Objectives Explain the anatomy of breast.

State the physiological changes of breast during pregnancy.

List the components of colostrum

Explain the stages of physiology of lactation.

References

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Anatomy of breast

Breasts are bilateral glandular structures

In female constitute accessory reproductive organs.

The shape of breast varies among the women and also in different periods of life. But the size of base of the breast is fairly constant.

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Anatomy of breast contd…

Development: The parenchyma of the breasts is developed from the ectoderm. The connective tissue stroma is from the mesoderm

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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.

An axillary prolongation (axillary tail), if present, lies in the axillary fossa, sometimes deep to the deep fascia.

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Anatomy of Breast

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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.

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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.

The whole breast is embedded in subcutaneous fat (absent beneath the nipple and areola).

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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.

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The lining epithelium of the duct is cubical, become stratified squamous near the openings.

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.

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These ducts connect, with larger ones called lactiferous ducts.

There is a dense network of capillaries surrounding the alveoli.

These are situated between the basement membrane and epithelial lining.

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

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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.

At places, the fibrofatty connective tissue extends from the skin down to the deep fascia in between the lobes. These bands are called suspensory ligaments of Cooper.

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Blood supply: Arterial supply: Lateral thoracic-branches of the axillary

artery Internal mammary

Inter costal arteries

Veins: The veins follow the courses of arteries.

Lymphatics: a. lateral hemisphere- anterior axillary nodes b. Upper convexity- infra clavicular group c. Medial convexity- mediastinal glands

d. Inferior convexity- mediastinal glands

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Nerve supply: The nerve supply is from fourth, fifth and sixth intercostal nerves.

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Physiological changes of breast during pregnancy

Changes are best evident in primigravida.

In multigravida, the changes are not clearly evident.

Size: Increased size of the breasts becomes evident even in early weeks. This is due to marked hypertrophy and proliferation of ducts (oestrogen) and the alveoli (oestrogen and progesterone) which are marked in the peripheral lobules.

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Physiological changes of breast during pregnancy contd…

There is also hypertrophy of the connective tissue stroma. Myoepithelial cells become prominent.

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

Quite often the "axillary tail" (prolongation of the breast tissue under cover of the pectoralis major) becomes enlarged and painful.

There may be evidence of striation due to stretching of the cutis.

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Contd…

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

Variable number of sebaceous glands (5-15), become hypertrophied and are called Montgomery's tubercles. Those are placed surrounding the nipples. Their secretion keeps the nipple and the areola moist and healthy.

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Contd…

Appearance of secondary areola.

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.

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Comparison of non-pregnant and pregnant breast

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Lactation

For the first two days following delivery, no further anatomic changes in the breasts occur.

The secretion from the breast called colostrum which starts during pregnancy becomes more abundant during the period.

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Lactation

Properties and Components of breastmilk Human milk varies in its composition With the time of day With the stage of lactation In response to maternal nutrition Because of individual variations.

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Components of the colostrum

It is deep yellow serous fluid, alkaline in reaction.

It has got a higher specific gravity; high protein, vitamin A, sodium and chloride content but has got lower carbohydrate, fat and potassium than the breast milk.

It contains antibody (IgA) produced locally.

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Components of the colostrum contd…

Microscopically: fat globules, colostrum corpuscles and acinar epithelial cells.

The colostrum corpuscles are larger polynuclear leucocytes, oval or round in shape containing numerous fat globules.

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Advantages of colostrum

The antibodies (IgA, IgG, IgM) and humoral factors (lactoferrin) provides immunological defence to the new born.

It has laxative action on the baby because of large fat globules.

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Physiology of lactation

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).

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Physiology of lactation contd…

Mammogenesis Pregnancy is associated with a remarkable

growth of both the ductal and lobuloalveolar systems.

An intact nerve supply is not essential for growth of the mammary glands during pregnancy.

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Lactogenesis 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.

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Contd…

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.

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There are 2 stages of lactogenesis :

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.

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Stages of lactogenesis contd…

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 lactationcontrol.

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Stages of lactogenesis contd…

Work by Haslam and Shyamala reveals that progesterone receptors are lost in lactating mammary tissues, thus decreasing the inhibitory effect of circulating progesterone.

In addition, maternal secretion of insulin, growth hormone (GH), cortisol, and parathyroid hormone (PTH) facilitates the mobilization of nutrients and minerals that are required for lactation.

Endocrine control switches to autocrine (supply-demand)

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Galactokinesis 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.

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Ascending impulses from the nipple and areola

thoracic sensory (4, 5 and 6) afferent neural arc

paraventricular and supra optic nuclei of the hypothalamus

Oxytocin from the posterior pituitary produces contraction of

the myoepithelial cells of the alveoli and the ducts containing

milk. ("milk ejection" or "milk let down" reflex)

Milk is forced down into the ampulla of lactiferous ducts,

wherefrom it can be expressed by the mother or sucked by

The baby.

During suckling, a conditioned reflex is set up:

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Neural reflex arc

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Lactation contd…

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.

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Galactopoiesis 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.

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Milk production

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.

For this purpose a store of about 5 kg of fat during pregnancy is essential to make up any nutritional deficit during lactation.

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Stimulation of lactation

Following delivery important steps are:

i. To put baby to the breast at 2-3 hours interval from the first day.

ii. Plenty of fluids to drink

iii. To avoid breast engorgement.

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Inadequate milk production/lactation failure

It may be due to infrequent suckling or due to endogenous suppression of prolactin (ergot preparation, pyridoxin, diuretics or retained placental bits).

Unrestricted feeding at short interval (2-

3hrs.) is helpful.

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Drugs to improve milk production/galactogogues

Metoclopramide (10 mg thrice daily) increases milk volume (60-100%) by increasing prolactin levels.

Sulpuride (dopamine antagonist) has also been found effective.

Intranasal oxytocin contracts myoepithelial cells and causes milk let down reflex.

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Lactation suppression

Bromocriptine (dopamine agonist that inhibits prolactin) 2.5 mg, 1 tab daily for 10-14 days.

Side effects are: hypotension, rebound breast engorgement, secretion, myocardial infarction and puerperal stroke.

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Lactation suppression contd…

Suppression of lactation is necessary if the baby is born dead or dies in the neonatal period or if breast feeding is contradicted.

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References:

Jacob A.A comprehensive textbook of midwifery and gynecological nursing.3rd edition.New Delhi:Jaypee;2012.

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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Physiology of lactation

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