Anatomy Theme 1 - Embryology

Question 1

how many sperm are there per ejaculate?

Answer 1

25 million

Question 2

where does the sperm meet the ovum?

Answer 2

in the ampulla 12-24 hours after ovulation

Question 3

how many sperm will reach the uterine tube and how many will get to where the oocyte is?

Answer 3

1000 sperm reach the uterine tube and 500 get to where the oocyte is

Question 4

what is the layer of cells around the ovum called?

Answer 4

corona radiata

Question 5

what happens when the DNA of the ovum and sperm join?

Answer 5

the second meiotic division

Question 6

what do the acrosomal enzymes do?

Answer 6

make sure the zone pellucid is impermeable to any other sperm

Question 7

what process occurs at day 2-3

Answer 7

cleavage - rapid mitotic divisions

Question 8

how many cells are in the embryo at day 3

Answer 8

16 cells

Question 9

when does the first mitotic division occur

Answer 9

30 hours post fertilisation

Question 10

what is the solid sphere of cells called at day 2-3?

Answer 10

the morula (each cell is a blastomere)

Question 11

how do cells in a morula communicate?

Answer 11

via gap junctions between them

Question 12

at what day does the blastocyst develop from a morula?

Answer 12

day 4-5

Question 13

what is the cavity within a blastocyst called?

Answer 13

blastocele

Question 14

does the blastocyst have the zone pellucida?

Answer 14

no

Question 15

what are the cells at the top and bottom of the blastocyst called?

Answer 15

top - inner cell pass and the bottom is the trophoblast

Question 16

what part of the blastocyst is the whole embryo derived from?

Answer 16

the inner cell mass

Question 17

at what day is the blastocyst in the uterine tube and preparing to implant?

Answer 17

4-5 days

Question 18

what does the inner cell mass do when as is prepares for implantation and at what day does this occur?

Answer 18

starts to differentiate into two layers - the epiblast and hypoblast which occurs at day 6-7

Question 19

which pole of the blastocyst is in contact with the uterine wall

Answer 19

the embryonic pole where the epiblast is

Question 20

what does the hypoblast form?

Answer 20

extra embryonic membranes

Question 21

where does the amniotic cavity form?

Answer 21

within the epiblast

Question 22

at what point does the yolk sac develop and where does this happen?

Answer 22

day 6-8 starts to develop in the hypoblast

Question 23

what is the function of the yolk sac and where is it found?

Answer 23

found in the blastocele cavity and supplies the embryo with nutrients before the placenta develops

Question 24

what does the yolk sac form when the embryo folds?

Answer 24

part of the gut tube

Question 25

what is secreted by the corpus luteum at week two and what is the function of this?

Answer 25

progesterone is secreted to maintain the endometrium and stop it shedding

Question 26

what are the four stages of implantation?

Answer 26

shedding and hatching of the zone pellucida, rotation so the embryonic pole contacts the uterine wall, adhesion via molecular communication and invasion of cytotrophoblasts into the endometrium

Question 27

what does invasion of cytotrophoblasts into the uterine wall trigger in week 2?

Answer 27

a decimal reaction - placenta begins to be made

Question 28

what is a decidua?

Answer 28

a very early placenta

Question 29

what does the syncytiotrophoblast originate from and what does it do?

Answer 29

forms from the trophoblast and burrows into the uterine wall

Question 30

what does the syncytiotrophoblast secrete and what does this do?

Answer 30

secretes HCG and this maintains the endometrium

Question 31

at the start of week three, how many layers does the embryo have?

Answer 31

two - bilaminar disk

Question 32

what process begins at week three and where is it initiated?

Answer 32

gastrulation and is initiated at the primitive streak

Question 33

which cells migrate towards the primitive streak in gastrulation?

Answer 33

epiblast cells

Question 34

what is the first germ cell layer made of epiblast cells dropping down?

Answer 34

endoderm

Question 35

what happens to the hypoblast after gastrulation?

Answer 35

it degenerates and the epiblast forms all three germ layers

Question 36

in what two planes does folding occur from week 4 onwards?

Answer 36

longitudinal and lateral

Question 37

what day does longitudinal folding happen and what does this cause?

Answer 37

starts at day 21 and brings the head and tail closer together

Question 38

what day does lateral folding happen and what does this cause?

Answer 38

starts at day 18 and brings everything inwards and the amniotic cavity down

Question 39

what does lateral folding lead to?

Answer 39

the future gut tube being inside the peritoneal cavity