Early Development

Question 1

What is the embryo dependent on until 4-8 cell stage and why?

Answer 1

Maternal mRNAs and proteins

—> genes of embryo not transcribed

Question 2

What is the Zona Pellucida?

Answer 2

Hard protein shell inhibiting polyspermy and protects early embryo

Question 3

What type of cells are in the inner cell mass?

Answer 3

Pluripotent embryonic cells —> contribute to final organism

Question 4

What type of cells are in the trophoectoderm?

Answer 4

Extra-embryonic cells —> contribute to extraembryonic structures that support development

Question 5

How is the blastocoel formed?

Answer 5

Trophoblast pumping Na+ ions into cavity

Question 6

What must happen for the blastocyst to implant?

Answer 6

Needs to escape the zona pellucida

Question 7

How does the blastocyst escape the zona pellucida?

Answer 7

Enzymatic degradation

Cellular contractions

Question 8

Trophoblast cells fuse to form…

Answer 8

Syncitiotrophoblast

Question 9

What do syncititiotrophoblast do?

Answer 9

Destroy local maternal cells in the endometrium and create interface between embryo and maternal blood supply

Question 10

What to syncitiotrophoblasts secrete?

Answer 10

hCG —> detection of beta subunit in blood or urine is bases of pregnancy testing

Question 11

What is the bi-laminar embryonic disc made of?

Answer 11

Epiblast

Hypoblast

Question 12

When the bilaminar disc is formed, what to cavities are there?

Answer 12

Amniotic cavity

Blastocoel

Question 13

At around 15 days post fertilisation what is the name of the structure that form along the midline of the epiblast?

Answer 13

Primitive streak

Question 14

What is gastrulation?

Answer 14

Conversion of a bilaminer embryonic disc into a trilaminer

Question 15

What is the notochord?

Answer 15

Rod-like structure formed of cartilage-like cells

Key organising centre for neurulation and mesoderm development

Question 16

What are somites?

Answer 16

Blocks of mesoderm

One of each pair either side of the neural tube

Question 17

What two types of tissue do somites initially form?

Answer 17

Sclerotome —> vertebrate and rib cartilage

Dermomyotome

Question 18

What does dermomyotome divide into?

Answer 18

Dermatome —> dermis of skin, some fat and connective tissue of neck and trunk

Myotome —> muscle do the embryo

Question 19

Through what types of folding does the primitive gut arise from?

Answer 19

Ventral folding —> head and tail ends curl together

Lateral folding —> two sides of the embryo roll

Question 20

The presence of what gene in the Y chromosome directs gonaodal cells to become sertoli cells?

Answer 20

SRY

Question 21

What does an absence SRY lead to?

And what does it require reinforcement from?

Answer 21

Gonadal cells adopt a granulosa cell fate and ovary development

Requires reinforcement by FOXL2