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. Smooth muscle relaxes under the influence of progeterone – secreted by CL. This allows the fertilized embryo to enter into the uterus.

FERTILIZATION

EARLY STAGES OF DEVELOPMENT

BLASTOCYST

FORMATION OF PLACENTA

MATURE PLACENTA AND FETUS

THE “PLACENTAL BARRIER” Sugars, fats and oxygen diffuse from mother’s blood to fetus Urea and CO2 diffuse from fetus to mother Maternal antibodies actively transported across placenta  Some resistance to disease (passive immunity) Most bacteria are blocked Many viruses can pass including rubella, chickenpox, mono, sometimes HIV Many drugs and toxins pass including alcohol, heroin, mercury Placental secretion of hormones  Progesterone and HCG (human chorionic gonadotropin, the hormone tested for pregnancy): maintain the uterus  Estrogens and CRH (corticotropin releasing hormone): promote labor 8

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

DIFFUSION OF O 2 AND CO 2 Gradient: Fetus – 30 mmHg Mother - 50 mmHg Sufficient O 2 : ???? 1.Fetal Hb (increase ability to carry O 2 ) 2.Fetal [Hb] > maternal [Hb] 3.Bohr effect: increase affinity for O 2 in the fetus – decrease affinity in maternal blood. CO 2 gradient: Fetal CO 2 – 48 mmHg  Maternal CO 2 – 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 12 th 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

CHANGES IN HORMONES DURING PREGNANCY

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  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 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

FACTORS INFLUENCING PARTURITION

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 Suckling of breastAfferent conduction of APs spinal cord hypothalamus Prolactin secretion Oxytocin secretion Increase [milk] in the alveoli of the breast Contraction of the myoepithelial cells Ejection of milk