Mechanisms of Disease During Embryogenesis

Question 1

How do we inherit traits from our parents?

Answer 1

Phenotypic differences are coded into our genes

Question 2

What are the 2 periods in human development

Answer 2

Embryonic period:
Up to the end of week 8
Most of the organogenesis occurs in these first 8 weeks

Fetal period:
The remaining time in utero
Involves growth and modelling

Question 3

What are the steps in embryogenesis

Answer 3

fertilisation
cleavage
gastrulation
neurulation and somitogenesis
organogenesis

Question 4

Where does fertilisation occur

Answer 4

The Ampulla region

Question 5

Describe the journey of the egg from fertilisation to implantation

Answer 5

It takes 10 days to travel down the uterine tube.
The zygote undergoes cleavages to form a morula and then a blastocyst.

Question 6

What is defined as a morula?

Answer 6

A morello is a zygote consisting of 12-16 cells

Question 7

Explain the process of compaction and formation of the blastocysts

Answer 7

The outside cells are polar, moving to the edge and becoming the trophectoderm.
The cells pump fluid inside, asymmetrically pushing the cells, and more cells accumulate on one side.
The inner cell mass becomes 2 different cell types. The blastocyst is formed, 32-64 cells.

Question 8

Describe the formation of the amniotic cavity

Answer 8

Epiblast cells from the bilaminar disk organise to form this cavity

Question 9

Explain the process of gastrulation

Answer 9

Formation of 3 layers from 2 layers.

Hypoblast (primitive endoderm) is displaced by involuting cells that become definitive endoderm, and mesoderm

Question 10

What are the first steps in neurulation

Answer 10

Gastrulation occurs bottom-up,
When the primitive streak reaches the top it regresses leaving a rod-like structure behind.

The notochordal process secretes molecules which instruct the ectoderm to become neural tissue.

The neural plate folds to form the neural tube inside the embryo

Question 11

Explain what happens during day 20 of embryo development

Answer 11

Neural folds rise out of the plane of the disk.
The neural folds meet and fuse to create the neural tube.

The mesoderm cells reorganise. They segment to form somites which are the precursors too bone and tissue

Question 12

Explain the “silk purse” model aka folding

Answer 12

The whole embryo folds over itself to protect the endoderm and mesoderm using the ectoderm.

The septum and heart move from the Margin to the centre.

The yolk sac, allantois and stalk make the umbilical cord.

Prochordal and cloacal plates delimit the gut tube

Question 13

Explain Organogenesis

Answer 13

• Differentiation of somitic derivatives
• Development of sensory organs
• Limb formation
• Formation of face structures
• Formation of genital structures