PHYSIOLOGY AND MAINTENANCE OF LACTATION

 PHYSIOLOGY AND MAINTENANCE OF LACTATION

By Jones H.M

Lactation is the process by which milk is synthesized and secreted from the mammary glands of the postpartum female breast in response to an infant sucking at the nipple. Breast milk provides ideal nutrition and passive immunity for the infant, encourages mild uterine contractions to return the uterus to its pre-pregnancy size (i.e., involution), and induces a substantial metabolic increase in the mother, consuming the fat reserves stored during pregnancy.

Structure of the Lactating Breast

Mammary glands are modified sweat glands. The non-pregnant and non-lactating female breast is composed primarily of adipose and collagenous tissue, with mammary glands making up a very minor proportion of breast volume. The mammary gland is composed of milk-transporting lactiferous ducts, which expand and branch extensively during pregnancy in response to estrogen, growth hormone, cortisol, and prolactin. Moreover, in response to progesterone, clusters of breast alveoli bud from the ducts and expand outward toward the chest wall. Breast alveoli are balloon-like structures lined with milk-secreting cuboidal cells, or lactocytes, that are surrounded by a net of contractile myoepithelial cells. Milk is secreted from the lactocytes, fills the alveoli, and is squeezed into the ducts. Clusters of alveoli that drain to a common duct are called lobules; the lactating female has 12–20 lobules organized radially around the nipple. Milk drains from lactiferous ducts into lactiferous sinuses that meet at 4 to 18 perforations in the nipple, called nipple pores. The small bumps of the areola (the darkened skin around the nipple) are called Montgomery glands. They secrete oil to cleanse the nipple opening and prevent chapping and cracking of the nipple during breastfeeding.

The Process of Lactation

The pituitary hormone prolactin is instrumental in the establishment and maintenance of breast milk supply. It also is important for the mobilization of maternal micronutrients for breast milk.

Near the fifth week of pregnancy, the level of circulating prolactin begins to increase, eventually rising to approximately 10–20 times the pre-pregnancy concentration. We noted earlier that, during pregnancy, prolactin and other hormones prepare the breasts anatomically for the secretion of milk. The level of prolactin plateaus in late pregnancy, at a level high enough to initiate milk production. However, estrogen, progesterone, and other placental hormones inhibit prolactin-mediated milk synthesis during pregnancy. It is not until the placenta is expelled that this inhibition is lifted and milk production commences.

After childbirth, the baseline prolactin level drops sharply, but it is restored for a 1-hour spike during each feeding to stimulate the production of milk for the next feeding. With each prolactin spike, estrogen and progesterone also increase slightly.

When the infant suckles, sensory nerve fibers in the areola trigger a neuroendocrine reflex that results in milk secretion from lactocytes into the alveoli. The posterior pituitary releases oxytocin, which stimulates myoepithelial cells to squeeze milk from the alveoli so it can drain into the lactiferous ducts, collect in the lactiferous sinuses, and discharge through the nipple pores. It takes less than 1 minute from the time when an infant begins suckling (the latent period) until milk is secreted (the let-down). 

📌The process of lactation can be considered to take place in Four (4) stages:

4 STAGES

1. Breast preparation 

2. The actual production of milk

3. The flow of milk in the alveoli

4. The withdrawal of milk from the nipple by the baby and maintenance of lactation

I. BREAST PREPARATION 

📌During pregnancy, oestrogens and progesterone induce the alveolar and ductal growth as well as stimulating the secretion of colostrums. 

📌Other hormones such as Human Placental Lactogen (HPL) are also involved and they govern a complex sequence of events, which prepare the breast for lactation. 

📌Although colostrum is present from the 16th week of pregnancy, t6he production of milk is held in abeyance until after delivery, when the levels of placental hormones fall. 

2. PRODUCTION OF MILK 🥛

📌The falling of the levels of placental hormones allows the already high levels of Prolactin to initiate milk production by stimulating the alveolar cells (acini cells/lacteal glands) in the breast. 

📌Prolactin is produced by the anterior pituitary gland. The continued production of Prolactin is caused by the baby sucking at the breast, with concentrations highest during the night.

📌Production of milk starts about the 3rd day after delivery. 

📌Milk is formed as small fatty globules within the cytoplasm cell of the alveoli. The globules arise in the bases of these cells and gradually unite to form small droplets.

📌As new globules are produced the droplets are pushed towards the surface of the cell until finally they burst through the cell membrane and enter the lactiferous tubule, accompanied by a little cytoplasm of the cell substance.

These droplets join with the droplets from other cells and the terminal portions of the tubules within the excreting alveoli become filled with milk.

3. THE FLOW OF MILK

     The flow of milk is influenced by two factors

a. Back pressure

b. Neuro-hormonal reflex

a). Back Pressure

Milk is pushed along the lactiferous tubules towards the nipple by the milk which is continually formed behind it in the alveoli. Some of the milk is stored in the ampullae underneath the areola, until the time the babys next feed.

b). Neuro-hormonal Reflex 

📌 The stimulus of the babys mouth suckling on the sensitive nipple, transmits impulses via spinothalamic tracts, to the hypothalamus and then to the pituitary gland. These impulses cause:

📌The anterior pituitary gland to release the hormone Prolactin into the maternal bloodstream, which is vital for establishment and maintenance of lactation.

📌The posterior pituitary gland to release the hormone Oxytocin into the maternal bloodstream. The Oxytocin reaches the breast and stimulates the myo-epithelial cells to contract forcing more milk towards the nipple, sometimes even causing the milk to spout from the nipple.

📌Oxytocin acts on smooth muscles causing it to contract and while the baby is suckling, the following occurs:

i. Flow of milk towards the nipple

ii. The nipple becomes erect

📌The let-down reflex causes the hindmilk to become available to the baby and may cause the milk to drop from both nipples.  

📌The babys suckling can only remove the foremilk and therefore the reflex is necessary to move the milk from the distal cells, ducts and tubules where it is produced and stored between feeds. If the reflex is inhibited in any way, the baby will only be able to obtain the foremilk and the hindmilk will not become available.

📌The let-down reflex may occur as a result of the baby suckling, but later, hearing the baby cry, or even thinking of feeding the baby, may bring about the let-down

📌Each mother will experience different sensations when the let-down of the milk occurs, such as: a prickling sensation in the periphery of the breasts; an increased feeling of warmth in the breasts; a feeling and fullness in the breasts etc. 

4. THE WITHDRAWAL OF MILK FROM THE NIPPLE BY THE ACTION OF SUCKLING AND MAINTENANCE OF LACTATION

  ✍️ The baby sucks milk from the breasts as follows:

📌The whole nipple and the primary areola are drawn into the babys mouth

The baby closes his/her jaws onto the areola tissue situated over the lactiferous sinuses (ampullae)

📌This expresses the milk from the sinuses into the babys mouth and the milk is then swallowed.

📌A vacuum is created in the babys mouth, which helps to draw more milk from the lactiferous ducts into the lactiferous sinuses.

📌The milk is drawn off from the lactiferous sinuses and lower ducts, more milk flows down from the upper lactiferous ducts, tubules and alveoli.  This continues until the breast is emptied.

📌The stimulus of suckling releases an outflow of Prolactin, which further stimulate the production of milk and the breasts fill again. Therefore, the more the suckling, the greater the amount of Prolactin released and the more milk produced for the next feed.

📌Maintenance of Lactation

 The continued production of breastmilk is a system of supply and demand. Several interdependent factors are responsible for the maintenance of lactation:

📌Suckling- suckling of the baby will provide a stimulus for the Neuro-hormonal reflex

Complete emptying of breasts- this will stimulate the production of Prolactin for production of more milk. If the breasts are not emptied completely, it will lead to engorgement and static milk will result in infection.

📌The mother emotional state- the mother should have a desire to breastfeed her baby. If the mother is over anxious, it will have the negative effect on breastfeeding because the secretion of milk influenced by the hypothalamus. 

📌The emotional status of the mother may affect the release of Oxytocin and let-down reflex. An upset or tense mother may have difficulties with the release of milk. 

📌Adequate rest for the mother- the secretion of Prolactin and milk production takes place during rest and sleep. If the mother is tense, anxious and not sleeping well or rushing around and becoming overtired, less milk will be produced.

📌Adequate and balanced diet this will help in supply of the essential substances needed for milk formulation. The woman is advised to take high protein diet which is essential for milk production. However, the nutritional status of the mother does not affect the quality of milk.