Lactation

Development of the breast Breast development begins at puberty Estrogen and progesterone produced in each ovarian cycle affect the breast tissue Stromal tissue Adipose tissue Glandular tissue

Hormones in pregnancy

Growth of ductile tissue Function of estrogen Ductile system laid down even in non gravid female due to estrogen from ovaries starting at puberty Very high level of estrogen in pregnancy Further growth of the ductile system Branching of the ductile system Stromal cell proliferation Deposition of fats GH, Prolactin, Cortisol & insulin are also required for proper growth of the breast

Growth of lobule-alveolar system Function of progesterone Further proliferation Budding of alveoli from the ducts Formation of lobules Development of secretory characteristics Secretory changes comparable to effects of progesterone on endometrium

Mammary gland

Mammary gland

Initiation of lactation Functions of Prolactin Prolactin causes milk secretion Prolactin production starts at 5th week of pregnancy and continues to increase for rest of the pregnancy Human chorionic somatomammotrophic hormone also has lactogenic effects

Initiation of lactation But estrogen and progesterone inhibit actual milk secretion Only a few ml/day secretion in pregnancy This secretion is free of fats and concentrated with proteins and lactose Colostrum Colostrum is very rich in antibodies and imparts passive immunity against many organisms

Initiation of lactation After parturition estrogen and progesterone levels fall Prolactin now causes copious milk secretion in next 1-7 days Other maternal hormones like GH, Parathyroid hormone, Cortisol, and insulin etc are also required for milk secretion Within a few weeks Prolactin level will return to basal level Breast feeding → stimulation of Prolactin secretion

Initiation of lactation Suckling by the baby → signals to hypothalamus → inhibition of PIH → ↑ Prolactin 10 – 20 fold This prolactin will produce milk for subsequent nursing period Without breast feeding breast stop producing milk within 1-2 weeks Continued breast feeding is capable of causing milk secretion even for years

Prolactin secretion after parturition

Hypothalamic control Prolactin secretion is controlled by hypothalamus Prolactin inhibitory hormone (PIH) which is constantly being produced Prolactin releasing hormone (PRH) Suckling stimulation → ↓PIH and ↑ PRH → milk secretion PIH is most probably dopamine

Suppression of ovarian cycle 50 % of the nursing mother have lactational amenorrhea No ovulation No pregnancy Suckling signals → suppression of GnRH Prolactin → ↓ GnRH Absence of gonadotrophic hormones (FSH & LH) No ovarian cycle No menstrual cycle Adaptation after a few months Natural WAQFA

Ejection of milk Function of Oxytocin

Posterior Pituitary Gland Neurohypophysis Develops as an outgrowth of Hypothalamus Glial cells or Pituicytes- do not secrete hormones Support terminal nerve endings of neurons in Hypothalamus Supraoptic Nuclei Paraventricular Nuclei Nerve fiber pass through Hypophyseal stalk Two Hormones ADH or vasopressin Oxytocin

Hypothalamic control of posterior pituitary

Posterior Pituitary Gland Cutting of Hypophyseal Stalk Transient fall in both hormones Normal secretion from cut nerve endings after a few days Hormones synthesized in nerve cell bodies in hypothalamus Transported in combination with carrier protein “Neurophysins” along the nerve fibers in axoplasm Stored in bulbous nerve endings Released by exocytosis due to nervous impulses from the hypothalamus

Chemical structure Both Oxytocin and ADH are polypeptides having Nine amino acids ADH Cys-Tyr-Phe-Gln-Asn-Cys-Pro-Arg-gly Oxytocin Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-gly Only two amino acids differ Functions also overlap

Functions of Oxytocin Produced mainly in Paraventricular nuclei Milk ejection or milk let down Milk expressed out of alveoli into the ducts Suckling stimuli → signals through sensory nerves to cortex → signals to Paraventricular nuclei →signals to posterior pituitary →release of Oxytocin into the blood →contraction of myoepithelial cells around the alveoli → expression of milk into the ducts

Stimulation & Inhibition of Oxytocin and milk ejection Stimuli for Oxytocin release Sucking sensation from areola and nipple Crying of the baby Fondling of the baby by the mother (Uterine cervical stretch or irritation) Oxytocin release may be inhibited by Many psychogenic factors Anxiety Tension Other conditions of generalized sympathetic stimulation

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