Pregnancy and Embryonic Development

Question 1

When is pre-embryonic development?

Answer 1

Fertilization to implantation, approximately 2 weeks

Question 2

When is embryonic development?

Answer 2

Implantation to the end of the eight week of pregnancy

Question 3

When is fetal development?

Answer 3

Ninth week of pregnancy to birth

Question 4

What is prenatal development known as?

Answer 4

The gestation period (nine lunar months of 40 weeks)
Prenatal development is divided into three, 3-month trimesters
- First trimester
- Second trimester
- Third trimester

Question 5

What happens during the first trimester?

Answer 5

Rudiments of all organs appear

Question 6

What happens during the second trimester?

Answer 6

Further development of organs and organ systems. The fetus looks like a human.

Question 7

What happens during the third trimester?

Answer 7

Phase of rapid growth. Most organ systems become functional.

Question 8

The First Trimester

Answer 8

Most dangerous period in prenatal life
- Only 40% of conceptions survive
1 to 12 weeks
Four events within the first trimester
1. Cleavage (sequence of cell divisions)
- A blastocyst forms
2. Implantation (implantation into endometrial lining)
3. Placentation (formation of the placenta)
4. Embryogenesis (development of the embryo

Question 9

The First Trimester- Implantation

Answer 9

Gastrulation and Germ Layer Formation
- The ectoderm, mesoderm, and endoderm are collectively known as the germ layers
- Each layer will form specific tissues and organs of the body

Question 10

The First Trimester- Placentation

Answer 10

Placenta develops
Placental circulation
- Blood flows from the fetus to the placenta in paired umbilical arteries
- Blood returns via a single umbilical vein