Topic 4 - Embryology

Question 1

Where is the oocyte fertilised by the sperm?

Answer 1

• in the ampulla of the Fallopian tube

Question 2

What name is given to a fertilised oocyte?

Answer 2

• Zygote

Question 3

Which site is ideal for implantation?

Answer 3

• Posterior uterine wall

Question 4

Explain cleavage.

Answer 4

• the splitting by first mitotic division of the zygote into 2 blastomeres of equal size

Question 5

What is the name of the glycoprotein shell that surrounds the pre-embryo before hatching occurs and how is it involved in fertilisation?

Answer 5

• Zona pellucida

- A Sperm cell must break through it using enzymes to fertilise the egg

Question 6

In the morula, pre compaction, each cell could be said to be…?

Answer 6

• Totipotent (they could become any cell in the body), embryonic stem cells

Question 7

Compaction leads to the formation of the first cavity, what names are given to the inner and outer cell masses in this blastocyst?

Answer 7

Outer - trophoblast

Inner - embryoblast

Question 8

Briefly describe hatching.

Answer 8

• the blastocyst breaks free from the zona pellucida cell, its no longer constrained and can enlarge freely and interact with uterine surface for implantation.

Question 9

What are the jobs of the tropho and embryoblasts?

Answer 9

Trophoblast - gives supporting tissue

Embryoblast - forms embryonic tissue

Question 10

The epiblast and hypoblast form a structure called the…?

Answer 10

• bilaminar disc

Question 11

Why is implantation interstitial?

Answer 11

• To get close to the mothers tissues to receive support

Question 12

What is ectopic pregnancy?

Answer 12

• implantation in the Fallopian tube instead of the uterine body (wrong place)

Question 13

What is placenta praevia?

Answer 13

• implantation in the lower uterine segment (wrong place), can cause large haemorrhaging at birth as placenta is highly vascular and can form a block across the gap

Question 14

Why is Caesarean section indicated for placenta praevia?

Answer 14

• to bypass the placenta covering the opening, avoiding massive haemorrhaging (placenta is highly vascular)

Question 15

Totipotent week 1 embryonic stem cells can be removed from the…?

Answer 15

• Morula

Question 16

Explain the process of compaction.

Answer 16

• the cells become two distinct groups, inner cell mass and outer cell mass and a cavity forms as a result.
• inner cell mass = embryoblast, outer cell mass = trophoblast
• the structure is now a blastocyst instead of a morula

Question 17

In week 2, what are the two types of cells that come from the outer cell mass (trophoblasts)?

Answer 17

• syncytiotrophoblasts and cytotrophoblasts

Question 18

Which cells, in week 2, are formed from the inner cell mass (embryoblasts)?

Answer 18

• epiblasts (give the embryo itself!)
• hypoblasts
• together they form the bilaminar disc

Question 19

What is the name of the breakaway yolk sac from the primitive one of the embryo?

Answer 19

• Secondary/definitive

Question 20

List, in order, the 5 main processes that occur within the first 4 weeks.

Answer 20

• fertilisation and implantation
• gastrulation
• neurulation
• segmentation
• folding

Question 21

Pre - gastrulation, what forms on the dorsal surface of the epiblast?

Answer 21

• the primitive streak and node

Question 22

Explain what occurs during gastrulation.

Answer 22

• epiblast cells pile up at the primitive streak, and burrow down into the bilaminar disc
• bilaminar disc becomes the trilaminar disc, endoderm, mesoderm and ectoderm, these are all formed from the epiblast layer, the hypoblast layer degenerates as it is no longer needed.

Question 23

What are the derivatives of the layers of the trilaminar disc?

Answer 23

Endoderm - internal structures e.g. epithelial lining of GI tract, respiratory tract
Mesoderm - supporting tissues e.g. muscle, cartilage, bone, vascular system
Ectoderm - structures to make contact with the outside e.g. nervous system, epidermis.

Question 24

How is the necessary asymmetry of the body achieved in an embryo?

Answer 24

• by action of ciliated cells at the primitive node that “waft” molecules where they need to be
• an example of a pathology is situs inversus where the viscera are reversed due to defective cilia

Question 25

In which layer of the trilaminar disc is the notochord located?

Answer 25

• midline of the mesoderm

Question 26

What does the neurochord do in neurulation?

Answer 26

• directs the conversion of overlying ectoderm into Neurectoderm tissue
• signals the ectoderm to thicken and edges elevate out of the disc before curling towards each other to form the neural tube

Question 27

What are somites?

Answer 27

• paraxial (close to axis/notochord) mesoderm (mid layer) segments (chopped up bits)

Question 28

What are three somite derivatives?

Answer 28

• deratome becomes skin section (dermis)
• myotome becomes muscle section (muscle)
• sclerotome becomes hard tissue section (bones)

Question 29

What does the segmentation of mesoderm into somites give rise to?

Answer 29

• repeating structures

- e.g. vertebrae, ribs, intercostal muscles, spinal cord segments

Question 30

Where is a woman most likely to get pain in an ectopic pregnancy?

Answer 30

• Iliac fossa (that’s where the Fallopian tube is)