8.1 Reproductive system (embryology) 2

Question 1

where are the villi found in early embryonic development?

Answer 1

ALL along chorion (chorionic membrane)

Question 2

where are villi found in week 12?

Answer 2

final disc shape achieved

chorion looses villi on one side (opposite decidua basalis side) - smooth chorion (chorion laeve)

Question 3

what happens to the chorion and amnion at week 22?

Answer 3

amnion and chorion become a composite membrane
(fuse to form decidua parietalis, decidua basalis still present)
forms: amniochorionic membrane = decidua parietalis

Question 4

what is the desidual basalis?

Answer 4

The area of ENDOMETRIUM between the implanted chorionic vesicle (amniochorionic membrane) and the myometrium, which becomes the MATERNAL part of the placenta

Question 5

what is the degree to which membranes are shared in monozygotic twins?

Answer 5

varies:

1. 2 amnions and 2 chorions (one of each)
2. 2 amnions (inner), but 1 chorion (outer)
3. 1 amnion and chorion (both shared)

Question 6

what is the amnion continuous with?

Answer 6

umbilical cord

Question 7

how do monozygotic twins with 2 amnions and 2 chorions come about?

Answer 7

originally 1 zygote, but during travel along fallopian tube to implantation, the zygote divided into 2 and 2 implantations result

Question 8

how do monozygotic twins with 2 amnions but chorion come about?

Answer 8

1 morula, but the embryoblast (inner cell mass) forms 2 separate bilaminar disks

Question 9

how do monozygotic twins with 1 amnion and chorion come about? (both shared)

Answer 9

1 blastocyst cavity and 1 bilaminar disk

BUT 2 primitive streaks (therefore 2 grooves, 2 notochords etc.)

Question 10

what is the gross morphology of the placenta? (foetal aspect)

Answer 10

shiny outer - covered by amniotic membrane (enclosing foetus and amniotic fluid)
AM over umbilical cord as well
(extremely vascular organ)

Question 11

what is the gross morphology of the placenta? (maternal aspect)

Answer 11

amniochorion membrane surrounding outer

within are cotyledons

Question 12

what are cotyledons?

Answer 12

separations of the decidua basalis of the placenta (implantation side, maternal endometrium), separated by placental septa

(a unit on maternal side separated villus projections from foetal side, villus separated by placental septa on maternal side, which marks the beginning and end of each cotyledon)

Question 13

what does each cotyledon consist of?

Answer 13

a main stem of a chorionic villus as well as its branches and subbranches etc.

Question 14

describe a 1st trimester placenta

Answer 14

placenta established in first trimester
placental ‘barrier’ still relatively thick
cytotrophoblast layer under syncytiotrophoblast

Question 15

what is term placenta?

Answer 15

SA of placenta for exchange INCREASES dramatically
placental ‘barrier’ now THIN
ONLY syncytiotrophoblast layer, cytotrophoblast lost

Question 16

what happens as the placental ‘barrier’ becomes thinner throughout pregnancy?

Answer 16

the diffusion distnce from maternal blood to foetal blood via foetal endothelium and syncytiotrophoblast decreases
(with lost of cytotrophoblast)

Question 17

what do umbilical vein and artery carry?

Answer 17

umbilical vein: oxygenated blood to foetus from placenta

umbilical artery: deoxygenated blood form foetus to placenta

Question 18

where is the maternal blood delivered from?

Answer 18

endometrial spiral arteries and veins

branch to form spiral arteries

Question 19

what does the cytotrophoblast shell contain?

Answer 19

the maternal blood bathing the foetal chorionic villus from spiral arteries, but the maternal blood doesn’t flow freely past the cytotrophoblastic shell

Question 20

what happens to the main stem villus form foetus?

Answer 20

it branches continuous towards maternal direction

the end point (tip) is the anchoring villus, attached to the cytotrophoblastic shell on maternal side

Question 21

how many umbilical arteries and veins do foetus’ have?

Answer 21

2 umbilical arteries: deoxy blood (foetus –> placenta)

1 umbilical vein: oxy blood (placenta –> foetus)

Question 22

what does the placenta synthesise? (metab)

Answer 22

glycogen
cholesterol
fatty acid

Question 23

why is cholesterol synthesised by the placenta?

Answer 23

cholesterol is a pre-cursor for oestrogen and progesterone

both are hormones for supporting pregnancy

Question 24

what are the 2 classes of hormones produced by the placenta? (endocrine)

Answer 24

protein

steroid

Question 25

what are the steroid hormones produced by the placenta?

Answer 25

progesterone | oestrogen

Question 26

what are the protein hormones produced by the placenta?

Answer 26

human chorionic gonadotrophin (hCG) human chorionic somatomammotrophin (hCS) human chorionic thyrotrophin (hCT) human chorionic corticotrophin (hCC)

Question 27

when is hCG produced?

Answer 27

during first 2 months of pregnancy

Question 28

what is the function of hCG?

Answer 28

supports the secretory function of corpus luteum | acts like LH, so CL produce oestrogen and progesterone to support pregnancy - until placenta take over

Question 29

what is hCG produced by specifically?

Answer 29

syncytiotrophoblast layer therefore is pregnancy SPECIFIC (aside from pathological e.g. testicular tumour)

Question 30

where is hCG excreted?

Answer 30

in urine | used as basis for pregnancy testing

Question 31

what are trophoblast diseases?

Answer 31

molar pregnancy | choriocarcinoma - malignant cancer of uterus (womb)

Question 32

what do trophoblast diseases lead to?

Answer 32

massive overgrowth of placenta tissue, there mass over production of hCG (indication of abnormal pregnancy)

Question 33

what is molar pregnancy?

Answer 33

non-viable fertilised egg implants in the uterus and will fail to come to term

Question 34

what are placental steroid hormones responsible for?

Answer 34

(progesterone + oestrogen) | responsible: maintaining pregnant state

Question 35

when does placenta production of steroid hormones take over form CL?

Answer 35

by the 11th week

Question 36

which placental hormones influence maternal metabolism?

Answer 36

progesterone | hCS / hPL

Question 37

how does progesterone influence maternal metabolism?

Answer 37

increases appetite - increase fat store for 2nd half of pregnancy, as baby can only use glucose (BBB), so fat store used by mum to reserve glucose for foetus

Question 38

how does hCS / hPL influence maternal metabolism?

Answer 38

increases glucose availability to foetus

Question 39

what are the different types of transports used in pregnancy?

Answer 39

simple diffusion (gas exchange) facilitated diffusion active transport pino-endocytosis

Question 40

how does simple diffusion work and which molecules utilise this mode of transport?

Answer 40

``` molecules moving down a concentration gradient - water - electrolytes - urea + uric acid - gases (molecules small enough with no charge) ```

Question 41

which molecule uses facilitated diffusion?

Answer 41

glucose (GI: GLUT 1 from intestine, GLUT 2 into blood, GLUT 5 then GLUT 2 for fructose)

Question 42

what limits gas exchange in uteroplacental circulation?

Answer 42

simple diffusion, so FLOW limited, NOT diffusion limited | high flow, low resistance

Question 43

why is it necessary to maintain an adequate uteroplacental circulation flow?

Answer 43

foetal O2 stores are small | rely heavily on HIGH flow gas exchange (via simple diffusion)

Question 44

which molecules undergo active transport?

Answer 44

amino acids iron vitamins

Question 45

how does active transport occur across maternal to foetus?

Answer 45

specific 'transporters' expressed by the SYNcytiotrophoblast

Question 46

describe the foetal immune system

Answer 46

immature

Question 47

how does the foetus gets its immunity?

Answer 47

passive immunity | receptor-mediated process, maturing as pregnancy progresses

Question 48

which immunoglobulins crosses the placenta 'barrier' to be received by the foetus?

Answer 48

IgG only

Question 49

what type of process is passive immunity in foetus? why?

Answer 49

ACTIVE process | as the IgG concentrations in foetal plasma EXCEEDS those in maternal circulation