Lesson 1.1: The Anatomy & Physiology of Lactation

Definition & Explanation
Milk production and release depend on two key hormones: prolactin and oxytocin.

• Prolactin is often called the “milk-making hormone.” It tells the alveoli (milk sacs) to produce milk. Prolactin levels rise when the baby suckles or when milk is removed by pumping or hand expression. The more milk is removed, the more prolactin signals the breast to make more—this is why frequent feeding helps supply.

• Oxytocin is known as the “love hormone.” It triggers the muscle cells around the alveoli to contract, pushing milk down the ducts toward the nipple. This process is called the letdown reflex (covered in Topic 3). Oxytocin release can be influenced by emotions, touch, and relaxation.

Other hormones—like estrogen and progesterone—play major roles during pregnancy but decrease after birth, allowing prolactin and oxytocin to take over.

Example: Imagine a factory. Prolactin is the manager who tells the workers (alveoli) to produce more milk. Oxytocin is the shipping department that moves the product (milk) out of the factory and into the delivery trucks (ducts).

Scenarios & Tips

1. Scenario: A parent says, “I’m worried my milk supply is low because my baby is always nursing.”
   Response: “Frequent nursing actually stimulates prolactin and helps build supply. Babies often cluster-feed to tell your body to make more milk.”
   Tip: Reframe frequent feeding as a normal and healthy sign of hormonal regulation.

2. Scenario: A parent says, “I feel tense, and milk doesn’t come out as easily—why?”
   Response: “Stress can block oxytocin, which controls milk release. Relaxation, deep breathing, and skin-to-skin can help.”
   Tip: Teach quick stress-relief tools that parents can use before or during feeding.

3. Scenario: A parent asks, “Do I need special foods or supplements to increase prolactin?”
   Response: “The most effective way to boost prolactin is frequent milk removal. Foods and teas can support you, but nursing and pumping are the most important drivers.”
   Tip: Keep advice evidence-based—encourage demand-driven feeding over supplements as a first step.

Evidence-Based Insights

1. In a study by Uvnäs-Moberg et al. (2020), researchers conducted a systematic review of how oxytocin and prolactin respond during breastfeeding in human mothers. They found that oxytocin is released in pulsatile bursts in response to infant suckling (with peaks often within minutes), and that a greater number of oxytocin pulses early in lactation was associated with higher milk yield and longer duration of breastfeeding. However, they also observed that stressors (e.g. noise, mental stress) tend to reduce the number of oxytocin pulses during breastfeeding, which could blunt the milk ejection reflex (i.e. the “let-down”) and thereby reduce effective milk transfer (fewer pulses → less efficient ejection). In the same review, the authors noted that prolactin levels also rise during breastfeeding (usually gradually, over tens of minutes) and that oxytocin and prolactin responses are interconnected: oxytocin release seems to help promote physiological states (lower cortisol, calmer autonomic balance) that may support sustained lactation and maternal adaptation. In summary: the “spike after each feeding” claim is partly supported (prolactin does rise in response to feeding), but the relationship is more nuanced (timing, pulsatility of oxytocin matters, and stress can dampen that). (Uvnäs-Moberg et al., 2020) PLOS

2. A more recent empirical study by Nagel et al. (2021) examined how maternal psychological distress (stress, anxiety, depression) relates to lactation outcomes, and they reviewed mechanistic evidence about how stress may interfere with oxytocin and milk ejection. Their summary showed that higher levels of maternal distress are associated with delayed secretory activation (i.e. later onset of full milk “coming in”) and shorter duration of exclusive breastfeeding. One proposed mechanism is that psychological distress interferes with oxytocin release during infant suckling, thereby impairing the milk ejection reflex. If milk ejection is repeatedly weak or delayed, the breast may not be fully emptied, which in turn can lead to reduced milk production over time (since milk removal is a key driver of supply). They also note that maternal distress correlates with elevated cortisol and metabolic shifts (e.g. insulin resistance) which may have downstream effects on lactation physiology. Thus, the original idea that stress “interferes with oxytocin release” is well supported in this more recent review of human lactation data. (Nagel et al., 2021) PMC

   Suggestions for lactation specialists:

   • Recognize that optimal oxytocin pulsatility and timing matter—not just the presence of hormone rise. Encourage feeding environments that reduce disturbance or anxiety (quiet, calm, supportive) to help maintain robust oxytocin release.

   • Monitor for signs that let-down is weak or delayed (baby fussing, long pauses before milk flows), and intervene early (positioning, breast massage, hands-on pumping) to assist the reflex.

   • Screen for maternal psychological distress (stress, anxiety, depression) early in the postpartum period, because elevated distress can impair oxytocin dynamics and thus milk ejection, which over time can affect supply.

   • Use interventions that support maternal mental well-being (emotional support, mindfulness, counseling referrals, peer support) as part of the lactation care plan—not just focusing on mechanical aspects.

   • Emphasize frequent, effective breast emptying especially in the first days, because even if hormonal responses are impaired, mechanical removal is still the key driver of maintaining supply.

Key Terms & Definitions

• Prolactin: Prolactin is the main hormone responsible for stimulating milk production in the breasts. After birth, when the placenta is delivered, prolactin levels rise, signaling the body to begin producing milk. Every time a baby nurses or milk is removed, prolactin levels increase to encourage more milk production. For example, a mother who breastfeeds frequently will naturally produce more prolactin, helping her body maintain a steady milk supply. This is why consistent nursing or pumping is so important for keeping up with the baby’s needs. Prolactin works behind the scenes, ensuring that the milk supply is always ready.

• Oxytocin: Oxytocin is often called the “love hormone” because it is linked with bonding and emotional connection, but it also plays a crucial role in breastfeeding. It is the hormone that triggers the letdown reflex, causing milk stored in the breast to flow out through the ducts. This can happen when the baby latches or even when a parent hears their baby cry. For example, some mothers notice milk leaking at the sound of their baby’s voice—this is oxytocin at work. Beyond milk release, oxytocin also helps the parent feel calmer and more connected to their baby during feeding. This hormone makes breastfeeding both a physical and emotional experience.

• Supply-Demand Cycle: The supply-demand cycle describes how the body makes milk in response to how often and how much milk is removed. The more frequently the baby nurses or milk is pumped, the more milk the body is signaled to produce. For example, a parent who breastfeeds on demand (whenever the baby shows hunger cues) will usually have a stronger milk supply than one who schedules feeds and misses baby’s cues. On the other hand, if milk is not removed often, production naturally slows down. This cycle ensures the body does not waste energy making more milk than the baby actually needs. It’s the body’s built-in system for efficiency and balance.

• Hormonal Regulation: Hormonal regulation refers to the way hormones control important body functions, including milk production and release during breastfeeding. Prolactin and oxytocin are two key hormones in this system, but others—like estrogen and progesterone—also play roles, especially during pregnancy. For instance, during pregnancy, high progesterone prevents full milk production, but after birth, when progesterone drops, prolactin can fully take over to start milk supply. Hormonal regulation makes sure the right processes happen at the right time to support both the parent and baby. For example, when hormones are balanced, the parent can produce enough milk, feel calm during feeding, and recover after birth. This shows how interconnected the whole body is during lactation.