Pregnancy & Placentation - Lecture (1).pdf

MD1020 Reproduction – Week 7 Assoc. Prof. Damien Paris ([email protected])  Placentation:  maturation & function  Maternal adaptations to pregnancy:  anatomical, metabolic & physiological  Sexual differentiation of the reproductive tract:  determination of sex  development of the re...

MD1020 Reproduction – Week 7 Assoc. Prof. Damien Paris ([email protected])  Placentation:  maturation & function  Maternal adaptations to pregnancy:  anatomical, metabolic & physiological  Sexual differentiation of the reproductive tract:  determination of sex  development of the reproductive tract  Explain the basic development, structure & function of the placenta  Describe the impact of pregnancy & placental hormones on the maternal anatomy, metabolism & physiology of major body systems  Apply principles of sexual differentiation to the development of the reproductive tract  Pre-implantation (up to blastocyst-stage):  nutrients derived from uterine secretion (histiotrophic nutrition)  Post-implantation (up to 3.2kg foetus):  nutrients derived from maternal blood (haemotrophic nutrition)  achieved via haemochorial placenta in humans  development starts from beginning of Week 2  fully functional by end of Week 12 after fertilization (nutritive, respiratory, excretory, immunological & endocrine functions established)  Transports nutrients from maternal circulation to foetus  Exchanges gases between foetus & mother  Excretes foetal waste into maternal compartment  Immunomodulatory role in maternal acceptance of foetus  Delivery of maternal antibodies to foetus (passive immunity)  Produces hormones that regulate maternal & foetal organs Marieb & Hoehn 2010 Maternal bloodfilled Lacuna Decidua basalis Maternal blood Chorionic villus Chorion Chorionic villus Umbilical cord & blood vessels Cytotrophoblast Extraembryonic mesoderm Day 16 Week 4½  extra-embryonic mesoderm lines cytotrophoblast & with syncytiotrophoblast collectively form chorion & chorionic villi  chorion & villi of the embryo combine with maternal decidua basalis (stratum functionalis of endometrium) to form the true placenta  Primary stem villi (11-13 days after fert): cytotrophoblast expands into syncytiotrophoblast projections  Secondary stem villi (16 days): extraembryonic mesoderm proliferates into projection  Tertiary stem villi (21 days): mesoderm differentiates into connective tissue & blood vessels Placenta Chorionic villi Maternal arteries Decidua basalis Umbilical cord Uterus Decidua capsularis Week 13 Chorionic villus containing fetal capillaries Maternal blood-filled lacuna Fetal arteriole Fetal venule Maternal veins Marieb & Hoehn 2010 Myometrium Stratum basalis of endometrium Maternal portion of placenta (decidua basalis) Fetal portion of placenta (chorion) Umbilical arteries Umbilical vein Umbilical cord  villi become highly vascularised & project into maternal blood supply  maternal & foetal blood separated by syncytiotrophoblast, cytotrophoblast, villus connective tissue, & foetal capillary endothelium  chorion in decidua capsularis compressed → discoidal haemochorial placenta  placenta is fully functional by the end of week 12 after fertilization Senger 2005 Most invasive: O2, CO2, nutrients & waste, etc. must diffuse across 3-4 tissue layers that separate foetal & maternal blood progesterone oestrogen hCG CRH relaxin hCS/hPL hCT Marieb & Hoehn 2010  hCG: maintains CL, suppresses maternal immune system  oestrogen: enlarges uterus, develops breasts & later relaxes pelvic      ligaments & pubic symphysis relaxin: later relaxes pelvic ligaments & pubic symphysis progesterone: maintains functional endometrium, quietens uterus, develops breasts, ↑respiratory tidal volume hCS/hPL: ↓glucose & ↑fatty acid metabolism in mother, develops breasts hCT: ↑maternal metabolism CRH: stimulates cortisol production via foetal H-P-adrenal axis  changes in anatomy, metabolism & physiology  influenced by placental hormones  ↑ vascularisation of reproductive organs  breast development & finally milk synthesis (progesterone, oestrogen, human chorionic somatomammotrophin/ human placental lactogen - hCS/hPL, prolactin)  dramatic uterine enlargement (oestrogen)  fist-size to filling abdominal cavity  pressure on internal organs  alters centre of gravity → lordosis & backache  later, pelvis & ligaments relax & widen (relaxin, oestrogen)  waddling gate  considerable weight gain ~13 kg Marieb & Hoehn 2010 (a) Before conception (b) 4 months (c) 7 months (d) 9 months foetus requires proteins, calcium, iron & energy for development  ↑ appetite (cortisol)  elevated fat storage & blood glucose levels  ↑ fatty acid consumption & ↓ glucose metabolism in mother (hCS/hPL)  free-up glucose in blood for foetal metabolism → 10% risk gestational diabetes  ↑ rate of maternal metabolism hCS (human chorionic thyrotrophin - hCT)  elevated calcium for foetal bone development Wikipedia 2012 Marieb & Hoehn 2010  gastrointestinal system:  initial nausea (elevated progesterone, oestrogen)  reflux & constipation  urinary/renal system:  ↑ frequency & volume of urine  Na+ & water retention (renin, angiotensin II, aldosterone)  respiratory system:  ↑ tidal volume: greater need of O2 (progesterone)  cardiovascular system:  ↑ blood volume 25-40%, & periodic ↑ cardiac output 20-40% (thyroxine, triiodothyronine) Name the two chromosomes that determine sex in humans. Which one contains the gene responsible? Does anyone know the name of the gene?  sex of offspring depends on sex chromosomes (X & Y):  females have XX  males have XY  a single gene on Y chromosome, sex determining region on the Y (SRY), controls ‘maleness’ genetic sex (XY or XX) determines gonadal sex (testis or ovary) determines phenotypic sex (internal & external genitalia) Meiotic events Spermatogonium XY Type A daughter cell XY Mitosis Before birth XY Growth Meiosis I X Meiosis II X X Y Y Late spermatids X X Infancy and childhood (ovary inactive) Each month from puberty to menopause Secondary spermatocytes Early spermatids Y Y sex determined by sperm Spindle X X Y Y Primary oocyte XX Primary oocyte XX Primary oocyte 1 X-bearing 2 X-bearing 2 Y-bearing XX Meiosis I X X First polar body Spermatozoa XX Growth Primary spermatocyte Y Oogonium Mitosis Type B daughter cell XY XX Meiosis II of Polar body Polar bodies (all polar bodies degenerate) X X X X Secondary oocyte Ovulation Sperm Meiosis II X Second Ovum polar body  during week 5 of embryo development gonadal tissue (gonadal ridge) develops → future ovaries or testes  primordial germ cells migrate into gonadal ridge → future oogonia or spermatogonia  testis or ovary development regulated by the presence (XY) or absence (XX) of the SRY gene:  SRY produces testis determining factor (TDF) → testis & Sertoli cells  Sertoli cell produces müllerian inhibitory factor/anti-müllerian hormone (MIF/AMH) → Leydig cells  Leydig cells produce testosterone → male genitalia TDF MIF (AMH) testosterone testosterone no TDF no MIF (AMH) no testosterone no testosterone genetic sex gonadal sex phenotypic sex Senger 2005 genetic sex (XY or XX) determines gonadal sex (testis or ovary) determines phenotypic sex (internal & external genitalia)