Lactation

1. Lactation

2. Mammary gland development • Cyclic changes in ovarian steroid hormones • Essential for mammary development • Estradiol • Development of mammary alveoli (secretory unit) • Progesterone • Development of mammary ducts

3. Final stage of mammary gland development • Pregnancy • Ovarian/placental steroid hormones • Periparturient period • GH and prolactin • Placental lactogen? • Glucocorticoids

5. Lactation • Parturition • Metabolic shift • Fetal growth to synthesis and secretion of milk • Mobilization of nutrients • Storage within the body • Fats • Triggered by changes in hormones

6. Lactation and re-initiation of reproductive cycle • Lactating women • High prolactin • Low LH and estradiol • No ovulation • Lactation-induced anovulation/amenorrhea (infertility) • Women remain anovulatory as long as they breast-feed their babies • Increased survivability of the infants

7. Lactational anestrus in the domestic species • Divert nutrients for lactation • Ensure the survival of offspring • Lactation stimuli/physical contact between mother and offspring • Animals remain in anestrus (absence of estrus) until nutrient intake exceeds nutrient demand

8. Lactation • Critical for survival of newborn • Nutrients • Immune system • Passive immunity

9. Milk composition

10. Milk composition • Varies greatly among species • Frequency of nursing • Increased frequency, lesser the concentrations of fats • Derived via synthesis or filtration • Alveolar epithelial cells • Components of blood

11. Changes in milk composition during lactation • Colostrum • First week of lactation • High concentrations of proteins • Immunoglobulins • Low in fats and water-soluble vitamins • Concentrations of proteins • Decrease as lactation progresses • Increased fat and lactose content

12. Milk fat • Major source of energy • Highly digestible • Carrier of fat-soluble vitamins • Synthesized by the smooth ER of alveolar epithelium

13. Lactose • Promotion of bacterial growth in intestine • Provides component for myelin sheath in neurons • Synthesized by the Golgi apparatus

14. Milk ejection • Process • Transport of milk from alveoli to ducts • Nipple or teats • Milk ejection reflex • Central nervous system • Regulation of prolactin and oxytocin release

16. Function of oxytocin • Lactation • Critical for milk let-down • Oxytocin receptors • Grandular cells in the mammary alveoli • Myoepithelial layers in the mammary ducts • Contraction of myoepithelial layer • Secretion stimulated by suckling • Tactile response • Regulated by the CNS

17. Suckling stimuli • Increased release of oxytocin • Increased synthesis • Release of oxytocin • Conditioned • Response to factors other than actual suckling stimuli

18. Inhibition of milk ejection reflex • Stress • Physical • Psychological • Cause • Inhibition of oxytocin release • Release of catecholamines • Constriction of mammary gland blood supply

19. Ejection of milk • Combination of factors • Pressure within the nipple/teat from accumulating milk • Contraction of alveoli by oxytocin • Expression of milk by the infant • Stripping of milk from teat/nipple • Aided by suckling

20. Inhibition of lactation • Medical reason • Transmission of infectious agent • HIV • Unnecessary • Stillbirth • Abortion after the first trimester • Social issues • Returning to the workforce

21. Inhibition of lactation • Inhibition of periparturient prolactin surge • Dopamine receptor agonists

22. Termination of lactation • Loss of suckling stimuli • Distension of alveoli and ducts • Mechanical atrophy • Physical destruction of alveolar epithelium • Loss of blood supply • Compression of vessels • Hypoxia and ischemia • Loss of alveolar epithelium • reduction of alveolar size

23. Termination of lactation • Loss of suckling stimuli • Distension of alveoli and ducts • Loss of alveolar epithelium • Reduction of duct size • Reduced lumen diameter • Involution of mammary gland • 3 months after cessation of lactation