1. Hormonal Control of Pregnancy and Lactation

2. Dr. M. Alzaharna (2014) Early Embryonic Development After fertilization, the embryo spends the first four days in the oviduct (fallopian tube) The developing embryo is then transferred to the uterus, and implants in the uterine endometrium By day 6, the trophoblast cells of the embryo begin to produce hCG In a normally developing embryo, hCG levels (in maternal circulation) will double every 3 days, reaching peak at about 2 months of pregnancy 2

3. Dr. M. Alzaharna (2014) Progesterone Levels To maintain the uterine endometrium and inhibit contraction of myometrium, plasma progesterone levels must be maintained during pregnancy Early in pregnancy, this is accomplished by the action of human chorionic gonadotropin (hCG) on the corpus luteum (first 8 weeks of pregnancy) Later in pregnancy, progesterone is produced by the placenta 3

4. Dr. M. Alzaharna (2014) Actions of Human Chorionnic Gonadotropin (hCG) hCG binds to the LH receptor in the corpus luteum, maintaining luteal steroidogenesis during the first 8 weeks of pregnancy In addition, hCG may act to stimulate testosterone production from the developing testes in male embryos 4

5. Dr. M. Alzaharna (2014) Steroid Production by The Placenta Later in pregnancy, the placenta becomes the major steroidogenic organ of pregnancy However, the placenta requires maternal LDL as a source of cholesterol for progesterone production The placenta is dependent upon the maternal and fetal adrenal as a source of androgens for aromatization to produce estrogen Estrogens may be important in increasing uterine blood flow to the fetus, and in the maturation of fetal organ systems 5

6. Dr. M. Alzaharna (2014) Parturition: The Process of Childbirth The mechanisms signaling the onset of labor are not clearly understood, although several theories exist – Potential role of progesterone decreasing progesterone prior to labor would allow uterine contractions to occur however, there is no decline in progesterone before labor in humans some studies suggest there is a decline in uterine progesterone receptors, resulting in decreased progesterone action, leading to labor 6

7. Positive feedback cycles that contribute to initiation of parturition Positive feedback cycles that contribute to initiation of parturition CRH: corticotropin releasing hormone. Green arrows indicate stimulation; red arrows indicate inhibition 7

8. Dr. M. Alzaharna (2014) Potential Role of Oxytocin in Parturition Oxytocin causes uterine contraction However, oxytocin levels do not increase until after labor starts, according to more recent studies Oxytocin may play a role in uterine contraction following labor, resulting in decreased blood loss 8

9. Dr. M. Alzaharna (2014) Potential Role of Relaxin in Parturition Another marker of corpus luteum function is the polypeptide hormone relaxin Relaxin becomes detectable at about the same time as hCG begins to rise, and certain concentrations are maintained for the remainder of the pregnancy until labor Relaxin also decreases uterine contractility during pregnancy 9 Relaxin acts on the cervix, causing dilatation and softening Relaxin does act to soften connective tissues, such as the ligaments connecting the pelvic bones, to allow increase in size of the birth canal

10. Dr. M. Alzaharna (2014) Potential Role of Prostaglandins in Parturition Prostaglandins cause dilation and softening of the cervix Prostaglandins also cause uterine contractions The levels of prostaglandins increase in fetal membranes before the onset of labor 10

11. Dr. M. Alzaharna (2014) Lactation Lactation is the delivery of milk from the mammary gland There are four main stages of lactation, controlled by different hormones: 1.Milk synthesis in alveolar cells 2.Lactogenesis: Secretion of milk from alveolar cells to alveolar lumen 3.Galactopoiesis: Maintenance of milk production and release into alveolar lumen 4.Milk ejection: movement of milk from alveoli into the duct system and out of the breast 11

12. Dr. M. Alzaharna (2014) Lactation 1- Milk Synthesis – Production of breast milk is stimulated by increased levels of prolactin (pituitary) and human placental lactogen (HPL) (from the placenta) during pregnancy – Milk release from alveolar cells is inhibited by the high levels of progesterone and estrogen during pregnancy – Estrogen and progesterone also act with prolactin to increase alveolar duct growth during pregnancy 12

13. Dr. M. Alzaharna (2014)Lactation 2.Lactogenesis – Stimulated by prolactin, and occurs after parturition when estradiol and progesterone levels are decreased 3.Galactopoiesis – The maintenance of established milk production, caused by prolactin 4.Milk Ejection – Movement of milk from alveolar ducts into the main duct system and out of the breast is induced by oxytocin – Oxytocin causes contraction of myoepithelial cells in the breast, causing milk release 13

14. Dr. M. Alzaharna (2014) Regulation of Oxytocin and Prolactin During Lactation There is a positive feedback effect of breastfeeding on the production of oxytocin and prolactin Oxytocin levels increase due to suckling of the breast by the infant In addition, sight, sound, or thought of the infant can also increase oxytocin levels, causing milk ejection Prolactin release is also increased by suckling of the breast by the infant (but not by audiovisual stimuli) 14