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what happens to the fertilised ovum first and what does it form
when does this happen

divides and differentiates into a blastocysts
as it moves from the site of fertilisation in the upper oviduct to the site of implantation in the uterus


what happens at day 1

fertilisation occurs in the ampulla of the fallopian tube


what happens during days 3-5

transport of blastocyst into the uterus


what happens during days 5-8

what happens to the blastocyte
what happens to the placenta

blastocysts attached to the lining of the uterus

inner cells form embryo and outer cells burrow into uterine wall and become placenta

produces hormones to maintain pregnancy


how is the blastocysts implanted into the uterus

free floating blastocyst attaches to the endometrial lining
cords of the trophoblastic cells begin to penetrate the endometrium and tunnel deeper carving a hole for the blastocyst

boundaries between cells int eh advancing trophoblastic tissue disintegrate


what day is the blastocyst completely buried in the uterine lining

by day 12


what is the placenta derived from

trophoblastic cells (chorion) and decidual tissue


what happens to the trophoblastic cells

they differentiate into multinucleate cells called syncytiotrophoblasts which invade the decide and break down capillaries to form cavities form maternal blood


what does the developing embryo send into the synctiotrophoblast projections

placental villi


what does each villus contain
what does this so

foetal capillaries separated from maternal blood by a thin layer of tissue in the intervillous space

2 way exchange of rep gases, nutrients, metabolites between mother and foetus down a diffusion gradient


when is the placenta and foetal heart functional by

the 5th week of pregnancy


how is the placenta developed

HCG singles the CL to continue secreting prog which stimulates the decidual cells to concentrate glycogen, proteins and lipids


what does the placenta work as

a physiological arteriovenous shunt


what happens as the placenta develops and why

it extends hair like projections (villi) into uterine wall
this increases contact area between the uterus and the placenta and more nutrients and waste materials can be exchanged


blood vessels from the embryo develop where

in the villi


cicrculation within the intervillous space acts as what

partly as a arteriovenous shunt


what role does the placenta play
what does the exchange take place between

fetal lungs

maternal oxygen rich blood and the umbilical blood


what does fatal oxygen saturated blood return to the fetus in and what does the maternal oxygen poor blood flow back in

umbilical vein

uterine veins


supply of the fetus with oxygen facilitated by what

fetal Hb - increased ability to carry oxygen
higher Hb - concentration in fatal blood - 50% more than adults
Bohr effect - fatal Hb can carry more oxygen in low CO2 than in high CO2


what membrane transport mechanisms lead to placental exchange processes

passive transport
simple diffusion
simplified transport
active transport


how does water diffuse into the placenta
does the exchange increase

by osmotic gradient
increases during pregnancy up tot he 35th week - 3.5l/day


electrolytes follow what
and what two things can only go form mother to child

follow water

iron and calcium


how is glucose passed to the child
when is high glucose needed

passes placenta via simplified transport

3rd trimester


fatty acids reach the child how

free diffusion


waste products leave the fetus how

concentration gradient


what drugs can cross placental barrier

thalidomide, carbamazepine, coumarins, tetracycline

alcohol, nicotine, heroin, cocaine, caffeine


What does HCG do

prevent involution of the CL

effect on the tests of the male fetus - development of the sex organs


what does HCS - produced?
what does it do

produced from week 5 of pregnancy

growth hormone like effects - protein tissue formation
decreases insulin sensitivity in mother - more glucose for the fetus
involved in breast development


what does progesterone do

development of decidual cells
decreases uterus contractility
prepares for lactation


what does oestrogen's do

enlargement of uterus
breast development
relaxation of ligaments
estriol level - indicator of vitality of fetus