Wk 8 early embryology development

Question 1

The first cleavage - 2 cell stage **

Answer 1

• 24 hours post fertilisation, the first cleavage occurs
  Forms 2 cell embryo (2 daughter cells)

Question 2

What is a blastomere?

Answer 2

Each daughter cell is called a blastomere

Question 3

The blastocyst: what undergoes formation between blastometers?

Answer 3

• The tight and gap junctions undergo formation between the blastometers in the morula to create 2 differentiated cell populations:
  
  • Inner cell mass = future embryo
    Trophoblast = future placenta

Question 4

How is a blastocoele created?

Answer 4

• Tight junctions and sodium pump activation cause water to diffuse into the embryo, creating a blastocoele in the early blastocyst (5-12 days post fertilisation)

Question 5

Hatching blastocyst

Answer 5

• Where their is pulsing of the blast, causing a break in the zona pellucida (ZP)

Question 6

Timing of embryonic stages in different species

Answer 6

Question 7

What hormone drives uterine histotroph (aka uterine milk) production?

Answer 7

• Progesterone (pregnancy hormone)

Question 8

What is role of uterine histotroph and where is it produced?

Answer 8

• To support embryo development (aka uterine milk)
  Produced by the uterine glands

Question 9

MCQ:
You want to collect blastocysts from super ovulated inseminated ewes for an embryo transfer program. How long after ovulation (fertilisation) would you flush, and where would you find embryos

Answer 9

• 5 days, and in the uterus

If we collect at 24 hours, we will have a 2 cell embryo most likely. If we collect too late at 15 days, we will have elongated embryo by this time and not the blastocysts.

Question 10

Myometrial contractions: what is the role of this and what inhibits it?

Answer 10

• Help to space embryos apart, and stop under P4 (progesterone) influence.

Question 11

Gastrulation forming the three germ layers (NOT germ cells) are:

Answer 11

• Gastrulation = early developmental process which embryo transforms into multidimensional structure.
• Ectoderm: nervous system, hair, skin
• Mesoderm: muscle, bone, CV system, reproductive organs
  Endoderm: digestive system, respiratory system, glands

Question 12

Cell potency: 3 types of cell potency

Answer 12

• Totipotent cells = whole
• Pluripotent cells = many
  Multipotent cells = several

Question 13

Embryos implant via trophectoderm into endometrium: What species is embryo implantation non invasive in

Answer 13

• Cow, ewe, sow and mare

Question 14

What species is implantation invasive in

Answer 14

Bitch, queen, rodents and primates

Question 15

Window of receptivity: explain this concept in relation to implantation

Answer 15

• Requires the developing embryo and the endometrium to be in synch
• The endometrium is only receptive to implantation for a short period - the window of receptivity (implantation)
  Varies considerably and can be up to 3-4weeks post fertilisation.