Early Embryonic Development

Question 1

What is the basic overview of human development?

Answer 1

Fertilization

Single cell

Ball of cells

Cavities + two layered disc

Three layered disc with middle layer

Segments in middle layer

Question 2

Where does fertilization occur?

Answer 2

In the ampulla of the uterine tube within two hours of ovulation

Question 3

What is the hard shell that surrounds the egg?

Answer 3

Zona pellucida

Question 4

How does the sperm break down the zone pellucida?

Answer 4

By releasing hyaluronic acid from its acrosome

Question 5

How does the egg push away other sperm during fertilization?

Answer 5

Changing its polarity

Question 6

What happens to the genetic material once fertilization has occurred?

Answer 6

The nuclear membrane breaks down to form pro nucleuses

All the sperms mitochondria and flagella also broken down through proteolysis

Question 7

What happens in the first week of development?

Answer 7

The DNA replicates and undergoes normal somatic mitosis

Question 8

What stages are repeated during the first week of development?

Answer 8

M and S phase because there is no cell growth ie G1 and G2

Question 9

When is the initial cleavage of the first cell?

Answer 9

36 hours

Question 10

What happens at the 8 cell stage?

Answer 10

Compaction- central cells are linked by gap junctions

Question 11

What is 16 cells called?

Answer 11

Morula

Question 12

Where does the morula travel?

Answer 12

Transported along the uterine tube and arrives at the uterus within 3-4 days after fertilisation

Approx 30-40 cells

Question 13

After 4 days what happens to the morula?

Answer 13

Loses its zona pellucida and becomes a blastocyst

Question 14

What are the different layers of the blastocyst?

Answer 14

Trophoblast

Blastocoel- cavity

Trophectoderm

Question 15

What has to occur to allow the blastocyst to bind the epithelium wall?

Answer 15

Has to be a decrease of MUC-1 (ant-adhesion molecule)

Binding via selectins to glycol-components

Integrins, laminin and fibronectin have to initially penetrate

Question 16

What are the main events that occur once the blastocyst has been implanted into the uterine wall?

Answer 16

Some of the invading trophoblast cells group together to form syncytiotrophoblasts

These invade via metalloproteases

Question 17

What happens on day 8?

Answer 17

Trophoblasts become invasive through syncytiotrophoblasts and cytotrophoblasts

Two layers formed- epiblast and hypoblast

Amniotic cavity begins to forms as a space within the epiblast

Question 18

What happens on day 9?

Answer 18

The hypoblast cells will migrate and coat the blastocyst cavity and once it has done this, it will be renamed to the primary yolk sac

Spaces develop within the syncytiotrophoblasts

Extraembryonic mesoderm will from deep to the trophoblasts

Question 19

What happens on days 11 and 12?

Answer 19

The embryonic disk has two layers now

The blastocysts has fully buried into the endometrium

Syncytiotrophoblast cells erode through the walls of large maternal capillaries

Question 20

What happens to the spaces developed in the syncytiotrophoblasts?

Answer 20

Invaded by capillaries which now provide the blastocyst with blood

Question 21

What is the end result of 2 week development?

Answer 21

Trophoblast has two layers:; Syncytiotrophoblast and cytotrophoblast

Inner cell mass has the epiblast and hypoblast

2 cavities from the amniotic and chorionic cavity

Question 22

What are the two layers of the inner mass cell going to develop to?

Answer 22

Epiblast- ectoderm

Hypoblast- endoderm

Question 23

What is ectopic pregnancy?

Answer 23

The blastocyst doesn’t bury into the uterine wall

Most common in the ampulla

Question 24

What are some examples of environmental causes of malformations?

Answer 24

Drugs or chemicals

Infectious agents

Ionizing radiation

Question 25

What effect does alcohol have on foetal development?

Answer 25

Growth retardation

CNS damage

Effects on facial development