Physiology: Pregnancy and such Flashcards
Fertilization
process by which sperm and egg fuse to form a zygote
Process of Fertilization
400 million sperm deposited in cervix, 50-200 reach ampullary-isthmus junction
sperm undergo capacitation in uterus
fertilization occurs in ampulla
zygote - divides to from a blastocyst - inner cell mass (fetal zone) and outer trophectoderm (placental zone)
Blastocyst divisions - Trophectoderm
placental zone
Blastocyst division - Inner Cell Mass
fetal zone
Implantation
process by which blastocyst attaches itself on the endometrial surface and invades the uterine decidua
Process of Implantation
takes 6-7 days
uterine endometrium at site differentiates into decidual cells
embryo development and uterus must be synchornized
Trohpectoderm Differentiation
6-7 days after fertilization
outer: Syncticotrophoblast
inner: Cytotrophoblast
Syncticotrophoblast secrete
Chorionic Gonadotropin (hCG) hCG stimulates corpus luteum to secrete progesterone until placenta is fully mature
Placenta Functions
supply nutrients and oxygen
remove metabolic by-products and CO2
provide endocrine support to maintain pregnancy and for fetal development
Placenta is composed of:
chorionic villi and uterine endometrium
Functions of Synctiotrophoblast layer in placenta
separates maternal blood form fetal blood
hormones secreted: hCG, placental lactogen (hPL), chorionic somatotropin (hCS), progesterone (P), estrogens and prostaglandins
Human Chorionic Gonadotropin
functionally similar to: LH, longer half-life
urinary, B-fragment serves as diagnostic tool for onset and progression of pregnancy
Functions of hCG
induces progesterone synthesis and secretion by syncytiotrophoblast cells
7th week “Luteal-Placental Shift” - placenta takes over steroid functions of corpus luteum
Placental Synthesis of Estrogen - Feto-Placental Unit
+: hcG on placenta cause cholesterol to be converted to progesterone
+: ACTH on fetal adrenal, causes CYP 17 to convert progesterone to DHEA-Sulfate and DHEA
DHEA in adrenal gland is converted to estrone (E1) by aromatase in the placenta
estrone (E1) can be converted to estradiol (E2)
Fetal liver: DHEA-Sulfate is converted to 16a-DHEA-Sulfate which in the placenta is converted to estriol (E3)
Placental membrane is permeable to:
glucose oxygen amino acids fatty acids Na, K, Cl ketone bodies vitamins viruses lipid soluble narcotics