Lactation Physiology

This entry details the physiological processes governing the synthesis and secretion of milk from the mammary glands, covering hormonal influences, anatomical considerations, and galactagogue substances.

Mammary Gland Development and Structure

• Alveoli: The primary milk-producing structures within the mammary gland. Their development and function are crucial for lactogenesis.
• Ducts: The network of tubes that transport milk from the alveoli to the nipple.
• Myoepithelial Cells: Cells surrounding the alveoli that contract in response to oxytocin, facilitating milk ejection.
• Blood Supply: Extensive vascularization supporting the metabolic demands of milk synthesis.

Hormonal Regulation of Lactation

• Prolactin: The primary hormone responsible for stimulating milk synthesis by the alveolar cells. Its release from the anterior pituitary is influenced by various factors, including nipple stimulation.
• Oxytocin: Released from the posterior pituitary in response to nipple stimulation, causing contraction of myoepithelial cells and the "milk ejection reflex" (let-down).
• Human Placental Lactogen (hPL): During pregnancy, hPL prepares the mammary glands for lactation.
• Estrogen and Progesterone: High levels during pregnancy inhibit milk production; their decline after parturition allows lactation to proceed.
• Insulin and Cortisol: These hormones play permissive roles, contributing to optimal mammary gland function.

The Lactation Process

• Lactogenesis I: Differentiation of alveolar cells during pregnancy, increasing in size and complexity.
• Lactogenesis II: Begins with the expulsion of the placenta, characterized by copious milk production and a shift in hormonal milieu.
• Galactopoiesis: Maintenance of established milk production, dependent on frequent and effective milk removal.

Factors Affecting Milk Supply

• Frequency and Effectiveness of Milk Removal: Regular nursing or pumping is essential to maintain milk production through autocrine control mechanisms.
• Maternal Nutrition: Adequate caloric intake and essential nutrients are necessary for sufficient milk synthesis.
• Maternal Hydration: Maintaining sufficient fluid intake is important for overall health and may impact milk volume.
• Maternal Rest and Stress Management: Stress and sleep deprivation can negatively impact hormone levels and milk supply.
• Certain Medications and Medical Conditions: Some medications and medical conditions can interfere with lactation.

Galactagogues: Substances and Practices Believed to Enhance Milk Production

• Herbal Galactagogues: Fenugreek, blessed thistle, fennel, and milk thistle are commonly used, although scientific evidence supporting their efficacy is limited and individual responses vary.
• Prescription Galactagogues: Domperidone and metoclopramide, although used off-label in some regions, have potential side effects and require medical supervision.
• Foods: Oatmeal, brewer's yeast, and other foods are sometimes cited as galactagogues, but scientific evidence is lacking. Their perceived benefits may be related to their nutritional content.
• Frequent Nursing/Pumping: The most effective strategy involves maximizing milk removal to signal increased demand to the mammary glands.