lecture 1 week 8

Question 1

where and when does fertilisation occur?

Answer 1

in the ampulla of the uterine tube within 12 hours of ovulation

Question 2

how many chromosomes do the sperm and ovum consist of and what is this called?

Answer 2

the sperm and ovum consist of 23 chromosomes each. (haploid) The reduction of 2 chromosomes to single chromatids is completed in the oocyte on fertilisation.

Question 3

what is the zona pellucida?

Answer 3

outer, protective shell of ovum composed mainly of glycoproteins.

Question 4

when does cleavage begin within the ovum?

Answer 4

within 36 hours of fertilisation

Question 5

what is the polar body in the ovum?

Answer 5

the other half of genetic material which the oocyte has ‘discarded’ to form 23 chromosomes composed of single chromatids. lies in the perivitelline space.

Question 6

what is the sperm tail composed of?

Answer 6

essentially it is a flagella with microtubules.

Question 7

what is the acrosome?

Answer 7

specialised lysosome in the sperm head, dissolves the bona pellucid to allow the sperm to enter the ovum.

Question 8

what happens between fertilisation and the cleavage stage?

Answer 8

the male and female pro nuclei fuse, the nuclear envelope dissipates and normal mitosis takes place. The zona pellucida remains intact.

Question 9

what is the cytoplasm composed of at this early stage?

Answer 9

the maternal cytoplasm is shared at this stage so there is maternal mitochondrial DNA.

Question 10

what is the morula?

Answer 10

the ball of cells which is 16+ cells. Moves from the uterine tube into the uterus (approx. 30-40 cells) about 3-4 days after fertilisation. The bona pellucida begins to disintegrate. An outer and inner layer of cells becomes defined.

Question 11

what is the outer layer of cells called in the morula?

Answer 11

trophectoderm

Question 12

what is the inner layer of cells called?

Answer 12

inner cell mass

Question 13

what is the blastocyst composed of and after how many days does this develop?

Answer 13

after 4.5+ days. The blastocyst consists of an outer layer of cells called the trophectoderm and a cavity forms in the middle - celled a blastocoel. the trophoblast consists of the outer cells closest to the inner cell mass.

Question 14

what is a blastocoel?

Answer 14

the inner cavity in a blastocyst.

Question 15

what is the difference between the trophectoderm and the trophoblast?

Answer 15

the trophectoderm is the outer cells of the blastocyst which surround the blastocoel and the trophoblast is the outer cells which are nearest to the inner cell mass.

Question 16

up to what stage are the embryo cells described as totipotent?

Answer 16

up to the blastocyst stage.

Question 17

at 5-6 days which cells are usually preferred for genetic testing?

Answer 17

the trophectoderm cells.

Question 18

at what stage does the embryo attach to the uterus wall?

Answer 18

at 5.5-6 days

Question 19

at which side does the embryo attach to the uterus wall?

Answer 19

at the embryonic pole (side with the inner cell mass)

Question 20

how does the embryo attach to the uterus wall?

Answer 20

by the down regulation of anti-adhesion molecule - MUC-1 - in the epithelial cells of the uterus wall. The embryo uses integrins laminin and fibronectin to attach to glycol-components on the epithelial cells of the uterus wall.

Question 21

how many days after fertilisation does implantation begin?

Answer 21

after 6-7 days

Question 22

which part of the embryo ‘invades’ the uterus wall and how?

Answer 22

the trophoblast via metalloproteases and immunosuppression of host/graft and graft/host reactions

Question 23

what are the invading parts of the trophoblast called?

Answer 23

the syncytiotrophoblast and cytotrophoblast

Question 24

what happens 8 days after fertilisation?

Answer 24

the trophoblast divides to form two layers: the ‘invasive’ syncytiotrophoblast and the cytotrophoblast. The inner cell mass divides to form two layers- the epiblast and the hypoblast. The amniotic cavity begins to form as a space within the epiblast.

Question 25

What has happened at day 9?

Answer 25

the hypoblast cells have extended from the inner cell mass to coat the blastocyst cavity which is now the primitive yolk sac. spaces begin to develop in the syncytiotrophoblast. The amniotic cavity has formed a significant space within the epiblast.

Question 26

what are the trophoblastic lacunae?

Answer 26

spaces which have developed in the syncytiotrophoblast at day 9.

Question 27

what is the embryonic disc?

Answer 27

at days 11 and 12 the area at the embryonic pole, cells which used to be the inner cell mass. consists of a bilayer (0.1-0.2 mm long)

Question 28

what has happened to the blastocyst at day 11 and 12

Answer 28

The embryonic disc is bilayered. The blastocyst has become completely embedded in the endometrium. The syncytiotrophoblast cells erode the walls of large maternal capillaries which bleed into the spaces and provide primitive placental circulation (breakthrough bleeding may occur). A new layer has developed between the yolk sac and cytotrophoblast called the extra embryonic mesoderm.

Question 29

what has happened to the developing embryo by the end of week 2 (at the time the woman expects her next period)

Answer 29

Two layers have formed in the trophoblast which completely surround the blastocyst: the syncytiotrophoblast (outer) and cytotrophoblast (inner). Two layers have formed in the inner cell mass: the epiblast (upper cells; ectoderm) and hypoblast (lower cells; endoderm). Two cavities have formed: the amniotic cavity and the chorionic cavity.

Question 30

what has the chronic cavity developed from?

Answer 30

the spaces in the extra embryonic mesoderm fuse to form the chronic cavity which essentially replaces the primary yolk sac (although there is a small remnant of the primary yolk sac)

Question 31

how does preeclampsia and how does it develop?

Answer 31

Develops after about 20 weeks. the cytotrophoblast invasion of the uterus is defective. The spiral arteries retain their muscular walls and act as high resistance vessels which increase blood pressure in the mother. Can cause kidney problems which result in protein in the urine (proteinuria).

Question 32

what is the most common site of ectopic pregnancy?

Answer 32

in the ampulla. (Risk of ectopic pregnancy is higher with inflammation of the pelvis) Ectopic pregnancy can cause rupture and blood loss.

Question 33

what are some key characteristics of foetal alcohol spectrum disorder?

Answer 33

growth retardation, CNS damage, effects on facial development.

Question 34

what are the effects of alcohol on the developing embryo in the first 2 weeks?

Answer 34

in the first two weeks stemness of cells protects against alcohol damage.

Question 35

what are some effects of alcohol on the developing fetes at 3-6 weeks?

Answer 35

implantation failure, neurological defects, minor developmental defects in face related to neural crest cells.

Question 36

what are the effects of alcohol on the developing fetus at 6-7 weeks?

Answer 36

defects in the corpus callous (major hemisphere connection) can develop.

Question 37

when is the dorsal/ventral axis established?

Answer 37

in the oocyte.

Question 38

what determines the left/right axes?

Answer 38

cilia movement