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Fertilization, Pregnancy And Lactation. Fertilization of the Ovum. Takes place in the fallopian tube. Distally, the last 2cm remains spasmatically contracted – under the influence of estrogen for 3 days after ovulation.
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Fertilization of the Ovum • Takes place in the fallopian tube. • Distally, the last 2cm remains spasmatically contracted – under the influence of estrogen for 3 days after ovulation. • Smooth muscle relaxes under the influence of progeterone – secreted by CL. • This allows the fertilized embryo to enter into the uterus.
Implantation of Zygote • Initially the embryo receives its nutrition from the uterus “milk”. • The trophoblastic cells then secrete proteolytic enzymes which digest the stromal cells of the endometrium. • The trophoblastic cells then forms the placenta. • Blood flows from the 16 day after fertilization • 6 weeks after fertilization – placenta takes over the fertilization of the fetus.
The Placenta • Foods cross the placenta by means of diffusion • Permeability of the placenta increases constantly – reaches a peak in the last month – sharp decrease in permeability. Permeability 0 8 20 40
Diffusion of O2 and CO2 • Gradient: Fetus – 30 mmHg Mother - 50 mmHg • Sufficient O2: ???? • Fetal Hb (increase ability to carry O2) • Fetal [Hb] > maternal [Hb] • Bohr effect: increase affinity for O2 in the fetus – decrease affinity in maternal blood. • CO2 gradient: Fetal CO2 – 48 mmHg • Maternal CO2 – 45 mmHg 20 mmHg gradient
Hormonal Control of Pregnancy • Initially the trophoblast cells secrete Human Chorionic Gonadotrophin (HCG) • Functions of HCG: • Prevents the degeneration of the corpus luteum • Stimulates the growth of the CL. • Increase secretion of both estrogen and progesterone • Prevents mestruation
Hormonal Secretion of the Placenta • Corpus luteum required until the 12th week of pregnancy – placenta secretion of hormones takes over completely. • Corpus luteum degenerates. • During pregnancy the placenta secretes: • HCG • Human chorionic somatomammotrophin (HCS) • Estrogen and progestrogen
Functions of Progesterone • Initially secreted by the Corpus Luteum in moderate quantities • Subsequently, secreted mostly by the placenta. • Action: • Development of the uterine endometrium – essential for the early nutrition of the embryo. • Decrease contractility of the gravid uterus • Contributes to the development of the ovum prior to implantation. • Prepares the breast for lactation.
Fetal Growth • Fetus • At 60 days embryo becomes a fetus • Fetal period • From day 60 to birth is rapid growth • Lanugo • Fine soft hair covering • Vernix caseosa • Waxy coat of protection
Parturition • Labor • First stage • Onset of regular uterine contraction until cervix dilates to fetal head diameter • Second stage • From maximum cervical dilation until baby exits vagina • Third stage • Expulsion of placenta from uterus • Parturition • Process by which a baby is born • In mother • Estrogens overcome inhibitory influence of progesterone • Oxytocin is released • In fetus • Adrenal gland is enlarged prior
Apgar Scores • Assessment of newborn baby • Appearance, pulse, grimace, activity, respiratory effect • Rated on scale of 0-2, 2 denotes normal function • Total Apgar score is sum from five characteristics
Parturition Physiology • Factors which initiate: • Ratio of estrogens/progesterone increase towards the end of pregnancy • Towards the end of term there is an increase responsiveness of the myometrium to oxytocin. • Increase fetal [oxytocin] towards end of term. • Mechanical stretch of the uterus: • Increase movements of the fetus • Increase size of the fetus • Stretch and/or irritation of cervix uterine – uterine reflex
Lactation: • Function of prolactin: prolactin Promotes the secretion of milk Estrogen and progesterone Birth Decrease [estrogen + progesterone Increase lactogenic effect (prolactin) Increase [milk] in the alveoli of the Breast – not the ducts!!!!!
Ejection of Milk: Oxytocin • Ejection of milk: • Neural reflex • Hormonal reflex spinal cord Suckling of breast Afferent conduction of APs Contraction of the myoepithelial cells Ejection of milk Oxytocin secretion hypothalamus Prolactin secretion Increase [milk] in the alveoli of the breast