102. fetal membranes 103. placenta 104. umbilical cord

Question 1

What are fetal membranes and what are they for

Answer 1

structures that surround the developing foetus
provide for its nutrition, respiration, excretion and protection

Question 2

Name the 4 embryonic membranes

Answer 2

yolk sac, amnion, chorion, allantois

Question 3

Features and function of yolk sac

Answer 3

formed from hypoblast cells
main function (up to week 7-8) is hemopoeisis
source of gonoblasts to form genital ridges
* primary yolk sac week 2
* secondary yolk sac from extraembryonic membrane
*final yolk sac week 4

Question 4

features and function of allantois

Answer 4

a membranous sac
Forms part of the urinary bladder
In the umbilical cord
Main function is to help embryo exchange gases and handle liquid waste

Question 5

features and function of amnion

Answer 5

epiblast derivative

Covers the embryo when it is first formed, filled with amniotic fluid (primarily from maternal blood) then expands to become amniotic sac

Functions of amniotic fluid: absorbs jolts, prevents fetus heat loss, allow for fetal movement

Question 6

feautures and functions of chorion

Answer 6

formed by extraembryonic mesoderm and the two layers of trophoblast=total 2 layers

rapid proliferation forms the chorionic villi which will fuse with uterine wall to form placenta

2 parts: chorion laeve-non placental part
chorion frondosum- placental part

Question 7

What identifies humans as amniotes

Answer 7

allatois, chorion and amnion

Question 8

what is the placenta?

Answer 8

an organ that connects the developing foetus to
the uterine wall

allows nutrient uptake, waste elimination and
gas exchange via the mother’s blood supply

begins to develop at implantation (the trophoblasts)

Question 9

Formation and growth of placenta

3rd week after implantation

Answer 9

lacunae fuse with maternal blood-sinusoids
primary chorionic villi- cytotrophoblast extend into syncytiotrophoblast

secondary chorionic villi- extraembryonic mesoderm extend into the villi

tertiary chorionic villi- blood vessels form in the extraembryonic mesoderm

Question 10

by the 4th month what is the structure of the placenta

Answer 10

foetal portion: Chorion frondosum-bordered by chorionic plate and covered by amnion

maternal portion: Decidua basalis-cotlyedons are seen

discoid shape, 500g, 2-3cm thick, 15-20cm diameter

Question 11

What is the umbilical cord

Answer 11

the connecting cord from the developing embryo to placenta

Question 12

What does the umbilical cord initially form from

Answer 12

develops from yolk sac and allantois
Connecting stalk, primitive cord, definitive cord

Question 13

What is the definitive umbilical cord composed of (5th week)

length – 50-60 cm (10-120 cm)
diameter – 1.5-2.5 cm
weight – 100-150 g

Answer 13

2 arteries
1 vein
Whartons jelly-mucous tissue protects and insulates
Amnion

the umbilical vein supplies the fetus with oxygenated, nutrient-rich blood from the placenta
The umbilical arteries return the deoxygenated, nutrient-depleted blood

Question 14

How is embryonic blood circulation

Answer 14

fetus cannot use lungs so it is network of arteries and veins

main bits: Ductus venosus, Ductus arteriosus, forman ovale

Question 14

brief pathway of fetal circulation

Answer 14

ocygenated blood enters through umbilical vein
Blood from umbilical vein goes through ductus venosus to the inferior vena cava

Blood enters right atrium

Goes through foramen ovale to the left atrium

Blood goes down left ventricle then up though aorta- Ductus arteriousus allows blood to go from pulmonary artery to aorta

Blood will then travel to internal iliac arteries BUT more importantly the umbilical artery that brings blood back to placenta