L8 Embryology

Question 1

Prior to gastrulation, embryonic cells are __?__

Answer 1

Pluripotent

Question 2

Where does fertilisation take place?

Answer 2

Ampulla region of the oviduct

Question 3

What is a ‘morula’?

Answer 3

The classic ball of 16 cells that forms as the fertilised zygote divides repeatedly.

Question 4

What distinguishes a blastocyst from a morula?

Answer 4

Blastocyst contains a fluid sac of nutrients

Question 5

The zygote divides into two __1__. Whilst the __2__ splits equally, the other contents of the cell do not - meaning one daughter cell will get more of certain factors than the other.

Answer 5

1. blastomeres

2. nucleus

Question 6

When the zygote contains 8 cells, the blastomeres undergo compaction. What is this process?

Answer 6

Compaction: flattening of blastomeres, maximising cell-cell contacts and forming tight junctions.

Question 7

How does rotational cleavage occur in the zygote?

Answer 7

Each time the blastomeres divide they form a new cleavage plane

Question 8

Why does the zygote need to form tight junctions?

Answer 8

To create a closed environment

Question 9

Around day 5 the morula becomes a __?__

Answer 9

blastocyst

Question 10

The outside of the blastocyst is made up of [1. polar/non-polar] cells (called __2__) and is called the __3__

Answer 10

1. polar
2. trophioblasts
3. trophectoderm

Question 11

The inside of the blastocyst is made up of [1. polar/non-polar] cells and is called the __2__. These internal cells form two layers: the __3__ and the __4__.

Answer 11

1. non-polar
2. inner cell mass (ICM)
3. epiblast
4. hypoblast

Question 12

The __?__ is a fluid filled sac that develops within the blastocyst.

Answer 12

blastocoel

Question 13

Around day __?__, the blastocoel begins to invades the uterine epithelium.

Answer 13

seven

Question 14

At 8 days (when the blastocyst pentrates the uterine tissue), the trophoblasts of the trophectoderm differentiate into __1__ and __2__.

Answer 14

1. cytotrophoblasts

2. syncytiotrophoblasts

Question 15

Syncytiotrophoblasts do what?

Answer 15

Proliferate in uterine tissue as the blastocyst penetrates the wall of the uterus.

Question 16

Around day 9 of gestation, a new cavity opens up adjacent to the epiblast. What is this cavity?

Answer 16

The amnionic cavity

Question 17

What does the ectoderm give rise to?

Answer 17

• Epidermis
• Nervous system
• Pigment cells

Question 18

What does the mesoderm give rise to?

Answer 18

• Gonads
• Bones
• Muscle
• Kidneys
• Heart
• Blood cells
• Most internal organs

Question 19

What does the endoderm give rise to?

Answer 19

• Lining of gut

- Respiratory system

Question 20

What is ‘pattern formation’?

embryology

Answer 20

The process by which a spatial and temporal pattern of cell activities is organised within the embryo.

Involves coordinated mechanisms of cellular communication.

e.g. axis specification, formation of germ layers

Question 21

What is ‘induction’?

embryology

Answer 21

The process by which the presence of one tissue influences the development of others.

Certain tissues, especially in very young embryos, have the potential to direct the differentiation of adjacent cells.

Question 22

What is ‘morphogenesis’?

embryology

Answer 22

The achievement of developmental diversity by formation of different structures from the same initial structure.

E.g. Gastrulation, neurulation, limb formation etc.

Juxtacrine (adjacent cells) or paracrine (nearby cells, but not touching) signalling leads to yes/no response. However, can also be variable as a result of modulation by interplay with other signals.

Question 23

What is a morphogen?

Answer 23

A signalling molecule that forms an extracellular concentration gradient.

e.g. hedgehog, wingless, activin

Cells nearer the source of secretion are exposed to a higher concentration than those further away, affecting the way they develop and allowing differentiation/specialisation

Question 24

In order for morphogenesis to occur, what characteristics must responding cells posses?

Answer 24

• competency to respond
• ability to detect inducing agent
• ability to quantify levels of inducing agent