Embryology

Question 1

What is the relationship/differences between embryology and developmental biology?

Answer 1

Embryology - anatomical description of different stages.
Developmental biology - embryology and the mechanisms involved.

Question 2

Describe the first stage of mammalian embryology.

Answer 2

Fertilised egg undergoes several mitotic divisions producing daughter cells called blastomeres - process known as cleavage as because the cells divide without growing in volume.

Question 3

Describe the second stage in mammalian embryology.

Answer 3

Now called the morula - compaction begins - during compaction the cells become polarised and tight junctions form between them.

Question 4

Explain the net effect of compaction and what it gives rise to.

Answer 4

The net effect of compaction is that cells can now be exposed to two different types of microenvironment depending on their position within the embryo. Cells on the outside are exposed to the medium surrounding the embryo while cells on the inside are not.
Cells on the outside give rise to trophectoderm and those on the inside to inner cell mass (ICM).

Question 5

Describe the third stage in mammalian embryology.

Answer 5

After compaction the future trophectoderm cells begin to secrete fluid, creating a cavity, which will eventually form the blastocoel. Blastocyst will hatch from zona pellucida. ICM cells exposed to this fluid (effectively this forms another different microenvironment) will form the primitive endoderm. The remaining ICM cells form the embryo (epiblast).

Question 6

Describe the fourth stage in mammalian embryology.

Answer 6

As the blastocoel begins to enlarge, the inner cell mass is composed to two types of cells - Adjacent to the blastocoel is a single layer of darkly staining cells, the endoderm, one of the three primary germ layers. The rest of the blastocyst is composed of ectoderm, divided into the ectoderm of the inner cell mass, and the trophectoderm, a single-celled layer bounding the blastocoel ventrally and laterally.

Question 7

What is the role of the trophectoderm?

Answer 7

Nourishment of the young embryo

Question 8

What is gastrulation?

Answer 8

The point in embryogenesis where the basic organization of the organism is established.

Question 9

What are the three germ layers?

Answer 9

Ectoderm, mesoderm and endoderm.

Question 10

What are the derivatives of the endoderm?

Answer 10

• Lung
• Thyroid
• Gut + liver

Question 11

What are the derivatives of the mesoderm?

Answer 11

• Cardiac muscle
• Skeletal muscle
• Kidney + glands
• Blood cells
• Smooth muscle

Question 12

What are the derivatives of the ectoderm?

Answer 12

• Skin
• Nervous system
• Pigment cells