Embryology 2

Question 1

Capacitation

Answer 1

Glycoproteins coat added to the sperm is removed by proteases in the uterine/cervical fluid —> this allows the cell membrane of the sperm to become permeable not calcium ions —> activating strong tail lashing and allowing the acrosome reaction to occur later

Question 2

Fertilisation occurs

Answer 2

High up in the fallopian tube

Question 3

Sperm can wait for hours to days

Answer 3

Bound to epithelial tissues lower down in the Fallopian tube if it is the wrong time in the menstrual cycle for fertilisation

Question 4

Acrosome reaction

Answer 4

Occurs when the sperm reach the zona pellucida of the egg

The acrosome membrane and plasma membrane of the zona pellucida fit together in a lock and key mechanism —> acrosomal contents spill out and digest the zona pellucida

Question 5

The sperm which have a reacted acrosome

Answer 5

Burrow down into the secondary oocyte —> one sperm reaches the egg and another reaction occurs causing the sperm to fuse with the egg —-> the nucleus of the sperm then enters the cytoplasm of the oocyte

Question 6

Fusion of sperm with oocyte causes

Answer 6

Activation of calcium channels in the oocyte which

1. Releases cortical granules
2. Resumes meiosis of the oocyte

Question 7

Releasing of cortical granules

Answer 7

Alter the zona pellucida making it more impenetrable to any more sperm

Any further binding of the sperm would result in the embryo being unsuccessful

Question 8

Meiosis of the oocyte resumes

Answer 8

So the chromosomes decondense and form male and female pronuclei

No diploid cell is formed -> both haploid cells enter straight into the first cell division of the embryo

Question 9

Reasons for assisted fertilisation

Answer 9

Blocked/absent oviducts -> due to pelvic inflammatory disease such as chlamydia or gonorrhoea

Blocked vans differentia/ efferentia-> due to impotence or low male fertility

Female age

Question 10

Superovulation

Answer 10

Encouraging ovaries to make more oocytes

Question 11

Stages of assisted fertilisation

Answer 11

Superovulation-> oocyte harvesting -> sperm harvesting -> mixing of sperm and oocyte in liquids which mimic those in the female reproductive tract -> observation of early development -> embryo transfer

Question 12

Oocyte harvesting

Answer 12

Follicular aspiration usually using a laparoscope from would be pregnant or donor

Question 13

Sperm harvesting

Answer 13

Usually masturbation, but can be by aspiration of the epididymis if there is a blockage or by intra-cytoplasmic sperm injection

Question 14

Intracellular-cytoplasmic sperm injection - ICSI

Answer 14

Sperm nuclei injected directly into the oocyte of the female

Can be controversial as sperm used haven’t matured -> should sperm which have defects be used for fertilisation

Question 15

Cleavage

Answer 15

The first cell divisions an embryo undergo

No growth just more cells

Question 16

At the 4 cell stage

Answer 16

The genes of the embryo are switched on -> maternal mRNA is broken down and mRNA synthesis from embryos own DNA begins

Question 17

Cells on outside of embryo

Answer 17

become epithelial cells and begin pumping fluid inwards

Question 18

Cells on the inside of the embryo

Answer 18

Become the inner cell mass

Question 19

Trophectoderm

Answer 19

Made of trophoblasts -> will make the placenta and some other extra-embryonic membranes

Question 20

The inner cell mass makes

Answer 20

The body itself plus some extra-embryonic membranes

Question 21

hCG hormone

Answer 21

Made by the trophoblast cells

Prevents the menstrual cycle from continuing when there is an embryo

Question 22

The blastocyst digests its way out of the

Answer 22

zona pellucida - when this occurs the embryo should have travelled down the Fallopian tube into the uterus

Question 23

When trophoblasts touch the uterine lining

Answer 23

It implants itself into the epithelium via finger like projections

This allows the exchange of nutrients between the two tissues