Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Hypothalamus and Pituitary synthesis TRH CRH GnRH PRH PIH GHRH SS + Blood oxytocin ADH TSH ACTH FSH - + - vessels LH prolactin GH storage and secretion breast kidney adrenal thyroid uterus blood vessels cortex gonads breast many tissues Effects of Oestrogens and Progesterone 1 Parturition • Labour, delivery, birth • Requires – Dilation of cervical canal to accommodate passage of fetus from uterus – Sufficiently strong contractions of uterine myometrium to expel fetus • Exact factors triggering increase in uterine contractility and initiating parturition not fully established • Last weeks of pregnancy – weak contractions that strengthen over time (Braxton-Hicks) • Cervix softens under influence of relaxin 2 Trigger for Parturition – Unknown, but current theory suggests signal is CRH – Placenta: CRH released, acts on fetal pituitary, ACTH • DHEA synthesis • DHEA Oestrogens • Oestrogens enter maternal blood stream – Oestrogen increases number of gap junctions between myometrial cells; increases oxytocin receptors in uterus; increases prostaglandins – Prostaglandins increase uterine contractions – High oestrogen: progesterone ratio parturition – Oxytocin increases uterine contractions • Acts directly on smooth muscle • Increases prostaglandins – Role of inflammation: NFκB Parturition Contractions begin at labour onset, positive-feedback cycle progressively increases force Pressure of fetus against cervix reflexly increases oxytocin secretion Oxytocin causes stronger contractions Positive-feedback cycle progressively increases until cervical dilation and delivery are complete Oxytocin secretion from posterior pituitary uterine contractions strengthen Pressure of fetus against cervix Parturition Initially, weak uterine contractions 3 Stages of labour Cervical dilation (longest stage) Lasts from several hours to 24 hours+ in a first pregnancy Delivery of baby (usually lasts 30 to 90 min) Begins when cervical dilation is complete Delivery of placenta Second series of uterine contractions separates placenta from uterine wall Shortest stage – usually completed within 15 - 30 min after baby is born After delivery, uterus shrinks to pregestational size (involution) 4 Lactation • During gestation – Elevated placental estrogen and progesterone promote development of ducts and alveoli in mammary glands • Prolactin – Stimulates synthesis of enzymes essential for milk production by alveolar epithelial cells – Decrease in placental steroids at parturition initiates lactation • Sustained by suckling – Triggers release of oxytocin and prolactin – Oxytocin • Causes milk ejection by stimulating cells surrounding alveoli to squeeze secreted milk out through ducts – Prolactin • Stimulates secretion of more milk to replace milk ejected as baby nurses Lactation – Much of breast development occurs during first months of pregnancy - mammary glands capable of milk production by mid-pregnancy – Inhibition of lactation during pregnancy • Oestrogen and progesterone during last half of pregnancy block effect of prolactin – Physiological amenorrhoea: possibly due to inhibition of GnRH by prolactin 5 Mammary Gland – Milk produced in alveoli of breasts – Contraction of myoepithelial cells causes milk ejection – Prolactin – milk synthesis – Oxytocin – milk ejection Suckling Reflexes 6