7. Coitus & Conception: from ovulation

Question 1

by the time of ovulation, what has happened to the ovum?

Answer 1

ovum (primary oocyte) in the ovulatory follicle has completed its first meiotic division to form a secondary oocyte

Question 2

what does a secondary oocyte contain?

Answer 2

contains haploid number of chromosomes and the bulk of the cytoplasm of the primary oocyte

Question 3

where are the remaining haploid chromosomes contained?

Answer 3

in a structure called the first polar body

Question 4

what is the secondary oocyte surrounded by?

Answer 4

follicular cells

Question 5

what are the follicular cells surrounding the secondary oocyte called?

Answer 5

cumulus

Question 6

where are the secondary oocytes surrounded by follicular cells (cumulus) embedded within?

Answer 6

embedded in a gelatinous matrix

Question 7

where is the secondary oocyte released from and picked up by?

Answer 7

released from an ovulatory follicle and picked up by the fimbria of the uterine tube

Question 8

what happens to the secondary oocytes after they have been picked up by the fimbria of the uterine tubes?

Answer 8

it is then guided into its lumen by the ciliary movements of the lining cells towards the ampulla

Question 9

what is significant about the ampulla of the fallopian tube?

Answer 9

the site of fertilisation

where the oocyte and the sperms come together

Question 10

what is fertilisation?

Answer 10

the sperm and ovum come together in the act of fusion

Question 11

how does the sperm fuse with the ovum during fertilisation?

Answer 11

only 1 sperm penetrates the cytoplasm of the ovum and the sperm’s nucleus fuses with the ovum’s nucleus

Question 12

what makes up the bulk of the sperm head?

Answer 12

its nucleus

Question 13

what is the product of fertilisation?

Answer 13

zygote

Question 14

what does the entry of the sperm into the ovum set off?

Answer 14

a series of events in the ovum that prevent other sperms from entering the ovum

Question 15

why is it important to prevent other sperms from entering the ovum?

Answer 15

ensures that the zygote contains diploid chromosomes for the normal development to proceed

Question 16

within a few hours of fertilisation, what happens to the zygote?

Answer 16

the zygote begins to divide by a series of mitotic cell divisions - known as cleavage

Question 17

what does cleavage form?

Answer 17

a ball of cells called the morula

Question 18

what forms after morula?

Answer 18

a hollow structure - the blastocyst

Question 19

during the transformation of the zygote –> morula –> blastocyst, what happens to the zygote?

Answer 19

it is gradually transported along the uterine tube towards the uterus

Question 20

what does the blastocyst comprise of?

Answer 20

the earliest rudiments of both the embryo itself (inner cell mass) and the placenta

Question 21

which cells form the placenta?

Answer 21

trophoblast cells

Question 22

when does the blastocyst enter the uterine cavity?

Answer 22

4-5 days after fertilisation

Question 23

by the time the blastocyst enters the uterine cavity, what is significant about the endometrium?

Answer 23

the endometrium is ready to receive the blastocyst for pregnancy to be established

Question 24

after a day or so in the uterine cavity, what happens to the blastocyst?

Answer 24

the blastocyst attaches itself to the uterine endometrium

Question 25

what is implantation?

Answer 25

when the blastocyst attaches to the uterine endometrium

Question 26

what does implantation involve?

Answer 26

involves an interaction between the trophoblast cells and the lining epithelium of the uterus

Question 27

what is further embedding of the blastocyst into the endometrium dependent upon?

Answer 27

the invasive property of the trophoblast

Question 28

what happens to the blastocyst by the end of implantation?

Answer 28

it now has an outer syncytium called the syncytiotrophoblast

Question 29

what is different about syncytiotrophoblast?

Answer 29

differentiated from the underlying cellular cytotrophoblast

Question 30

when is the blastocyst fully embedded within the endometrium?

Answer 30

by the 10th day after fertilisation

Question 31

what leads to the establishment of the early placenta?

Answer 31

cellular interactions of the blastocyst and the endometrium and
establishment of relationship between embryonic and maternal tissues