Early Embryonic Development III

Question 1

What are the two types of twinning?

Answer 1

Dizygotic

Monozygotic

Question 2

What are dizygotic twins?

Answer 2

Twins arising form two ova, produced from two separate ovarian follicles and each is fertilzed by a single sperm

Question 3

What are monozygotic twins?

Answer 3

Twins arising from single ovum fertilized by single sperm

Question 4

3 ways that monozygotic twins can occur

Answer 4

1. Two cell stage pre-implantation of embryo splits with each blastomere going on to produce an embryo with its own fetal membranes - can occur in cattle
2. Duplication of the ICM. Twins develop with shared yolk sac and chorion but separate amnions - can occur in sheep
3. Trhough formation of two primitive streaks giving rise to two offspring. Share common amnion, yolk sac and chorio. If streaks dont separate can get conjoined twins

Question 5

5 consequences of twin pregnancies?

Answer 5

High rate of abortion

Poor neonatal viabiliyt

Growth retarded fetuses

Reduced fertility after twin abortions

Dystocia

Question 6

How can twin pregnancie be dealt with in horses?

Answer 6

Before 40 days of gastration : manual trauma

After 40 days

• Manual trauma
• Ultrasound guided puncture of conceptus
• Surgical removal of fetus (high risk to remaining fetus and mare)

Ultrasound guided injection of the fetus

Question 7

What is gastrulation?

Answer 7

Stage in the epiblast of cell proliferation, migration and differentiation that results in the formation of 3 germ layers

• ectoderm
• mesoderm
• endoderm

Question 8

What are the 3 germ layers formed during gastrulation?

Answer 8

Ectoderm

Mesoderm

Endoderm

Question 9

Explain the ectoderm>

Answer 9

Epidermis of the skin, epithelium of oral and nasal cavities, nervous system and sense organs

Question 10

What does the mesoderm become?

Answer 10

Muscle, connective tissue including bone, components of circulatory, urinary and genital systems

Question 11

What does the endoderm become?

Answer 11

Mucosal epithelium and glands of respiratory and digestive systems

Question 12

What is the morphologicial beginning of gastrulation?

Answer 12

Formation of the primitive streak along the midline

Question 13

What is ingression?

Answer 13

movement of epiblast cells inward between epiblast and hypoblast

Question 14

What are ingressing cells known as?

Answer 14

Mesoendodermal cells and are described as mesenchymal

Question 15

What are cells that inegrate and then displace the hypoblast become?

Answer 15

Endoderm

Question 16

What is located under the endoderm and hypoblast?

Answer 16

Primitive yolk sac

Question 17

What becomes intra-embryonic mesoderm?

Answer 17

Mesenchymal cells that move cranially and laterally but stay between endoderm and epiblast

Question 18

What becomes the extra-embryonic mesoderm?

Answer 18

Cells migrating further laterally between hypoblast and trophectoderm

Question 19

What does the extra-embryonic mesoderm split into?

Answer 19

Two sheets

1. Somatic or parietal mesoderm
2. Visceral of splanchnic mesoderm

Question 20

What does the somatic or parietal mesdorm sheet associate with?

Answer 20

Trophectoderm

Question 21

What does the visceral of splanchnic mesoderm sheet associate with?

Answer 21

Hypoblast

Question 22

What is the cavity that forms between somatic and visceral mesoderm call?

Answer 22

Embryonic coelom

Question 23

Where does primitive node move towards as grastrualtion progresses?

Answer 23

Towards tail

Question 24

What is important for brain development?

Answer 24

Prechordal mesoderm

Question 25

4 things to notice at the end of gastrulation?

Answer 25

1. Pear shaped embryo
2. Embryo with three germ layers
3. Embryo with a column of mesoderm - the notochord established a cranial to caudal axis
4. Relative to the notochord, the embryo has a right and left side

Question 26

What are tissues do neural crest cells form?

Answer 26

Melanocytes - pigment cells of the skin

Neurons for central, sympathetic and enteric nervous system

Parts of craniofacial mesenchymal derivatives

• Otic capsul
• Palate