Lección 1: La fisiología de la lactancia

The major constituents are lactose, triglycerides composed of a variety of fatty acids, proteins, cellular components as well as ions and water. Quantitatively minor components, such as the myriad bioactive factors present in breast milk, also play a central role in the health and well-being of infants and are of paramount significance. Lesson two provides more in depth information on the various components of breast milk and their roles in growth and development.

The synthesis of human milk takes place in the lactocytes, which are secretory alveolar cells, by one of two methods. Components such as protein, fat and lactose are synthesized directly in the cells while vitamins and minerals are extracted by lactocytes from the maternal plasma. Milk components are then transported into the alveolar lumen via exocytosis or apocrine secretion where the constitution of the final milk takes place. The milk then remains in the alveolar lumen until it is removed by suckling, which stimulates further active milk synthesis (Blackburn 2013).

Milk synthesis is dependent on five cellular pathways:

Four transcellular pathways which are responsible for:

• Fat synthesis and secretion (I): lipids are transported into the alveolar lumen by the milk fat globule (MFG). The MFG consists of a triglyceride core surrounded by a phospholipid membrane to prevent globule coagulation and improve secretion effectiveness.
• Exocytosis of milk protein and lactose (II): Protein, lactose and calcium are exocytosed in Golgi secretory vesicles.
• Secretion of ions and water (III): water and small ions such as Na+, K+, Cl- as well as monosaccharides are secreted via direct transport.
• Transcytosis of substances such as immunoglobulins (IV): macromolecules such as immunoglobulins, proteins, hormones and growth factors are transported in vesicles from the maternal plasma into the alveolar lumen. (Blackburn 2013)

and one paracellular pathway which is responsible for the passage of plasma components and leukocytes between epithelial cells (V).

Figure 4: Secretory pathways involved in milk synthesis.
One paracellular and four transcellular pathways are responsible for transporting milk components from lactocytes and maternal plasma into the alveolar lumen when final milk composition occurs.
Source: ENeA own