Topic 9: Lactation Flashcards
What are the essential requirements for successful lactation?
- the infant’s ability to suck with sufficient strength
- breast structure allowing sucking to occur,
the release of pituitary hormones in the mother (stimulated by the sucking process) - that emotional responses in the mother do not inhibit this process.
What are the four stages of lactation?
- initiation and maintenance of milk secretion
- milk production
- milk ejection
- ingestion of milk
Explain the initiation and maintenance of the milk phase
Lactogenesis begins in the last trimester of pregnancy and results in small amounts of colostrum being produced. Full lactation, however, does not occur immediately and over the first two to three days after birth only a small amount of colostrum is secreted. Lactation is reasonably well established within 10 days, however for first-time mothers it may take up to 3 weeks or even longer.
What is lactogenesis?
Initiation of milk secretion
What does the maintenance of lactation require from the infant?
To continually suck, which stimulates the production of prolactin. The newborn infant’s rooting and sucking reflexes are strongest 20–30 minutes after birth.
What secretory processes are involved in lactation?
- exocytosis,
- fat synthesis and secretion,
- secretion of ions and water and
immunoglobulin transfer from the extracellular space.
Explain exocytosis
Proteins, lactose and some ions are secreted by exocytosis. Most of the proteins in human milk are specific to human milk and not found elsewhere. Inclusion of proteins derived from maternal plasma occurs mainly in colostrum. The three main milk proteins: casein, a-lactalbumin and b-lactalbumin are all synthesised within the mammary gland from amino acids. Lactose, which is the predominant carbohydrate in milk, is synthesised from glucose and galactose.
Explain fat synthesis and secretion involved in lactation
Short-chain fatty acids are synthesised by the alveolar cells predominantly from acetate, while long-chain fatty acids and triglycerides are derived from maternal plasma. Some triglyceride is also synthesised from intracellular carbohydrate. The triglycerides, synthesised in the alveolar cells, coalesce into large droplets which then make their way to the top of the alveolar cell and are enveloped by the apical membrane before separating from the cell.
Explain the secretory process of secretion of ions and water
Sodium, potassium and water move freely across the apical membrane. Water moves across the membrane in response to the osmotic gradient set up by the secretion of lactose and the electrolytes follow in response to the movement of water across the cell membrane.
Explain the immunoglobulin transfer from the extracellular space
Immunoglobulin A (and possibly other proteins) attach to receptors on the basal membrane of the cell from where they enter (by endocytosis) and are transported to the apical membrane for subsequent release into milk. Under normal circumstances, substances do not pass directly from the maternal capillaries into the milk.
During mastitis and involution of the glands, however, the junctions between the alveolar cells become ‘leaky’ and allow plasma constituents to pass directly into the milk. When this happens the milk tends to be high in sodium and chloride and lower in lactose and potassium.
Explain demand feeding
Since prolactin is produced in response to nipple stimulation, the importance of ‘demand feeding’ rather than 3-hourly to 4-hourly scheduled feeding is clear from a biological perspective. A baby sucks most vigorously when it is hungry. Therefore a baby fed on demand will provide optimal nipple stimulation.
Demand feeding results in more frequent, intense nipple stimulation and an increased prolactin production which assures an adequate milk supply. An additional advantage of demand feeding throughout the day and night is that it stimulates prolactin secretion, which acts as a natural contraceptive.
Explain the let-down reflex
The ‘let-down’ of milk occurs in response to the infant’s cry or simply thoughts about feeding the infant.
What factors influence milk ejection?
- Negative emotions such as anxiety and uncertainty, or just lack of interest can, however, inhibit the reflex. A poor ‘let-down’ reflex sets up the cycle whereby the hungry baby sucks harder, causing pain and cracked nipples, which may become infected.
- Nipple infection leads to greater discomfort for the mother, further reducing the likelihood of satisfactory milk ejection. This can result in mastitis or a breast abscess, which may make breastfeeding more difficult.
- Importantly, the Australian Breastfeeding Association states that when mastitis occurs, it is important not to wean. In particular, this is because breasts should be kept as empty as possible, and breastfeeding is the best way to do this [4].
- Complimentary bottle feeds can also impact lactation, not only because demand is reduced but also because the baby tends to suck less strongly as bottle teats require less active sucking.
What are the four factors required for correct milk ingestion?
Milk ingestion requires both an adequate let down reflex and functional rooting, suckling and swallowing reflexes in the baby.
Explain the composition of colostrum
Colustrum is very high in protein (4–5%) but contains less fat and lactose than mature milk. It is slightly lower in energy than mature milk ~240KJ v 280 KJ/100 mL. Some of the extra protein comes from the anti-infective agents that are particularly high in colostrum, such as the immunoglobulins. Colostrum is lower in most of the B vitamins than mature milk, but higher in the fat-soluble vitamins A, D and E, and in minerals.
