Unit 5 - Early Human Development

Question 1

Zygote

Answer 1

• 1 diploid cell

Question 2

Where are zygotes formed

Answer 2

In uterine tube

Question 3

How is the morula formed

Answer 3

The zygote undergoes 4-5 mitotic divisions called cleavage divisions that will form the morula

Question 4

Morula

Answer 4

• solid ball of 16-32 cells
• same size as ovum/zygote

Question 5

How is the blastocyst formed

Answer 5

The morula cells continue to divide and begin to differentiate into different cell types with specific form and function

Question 6

Blastocyst features

Answer 6

1. Fluid filled cavity
   - blastocyst cavity
2. Embryoblast (inner cell mass)
   - cells with later divide and differentiate to form the embryo
   - embryos can’t grow by themselves
3. Trophoblast (made of trophoblast cells)
   - cells will divide and differentiate to form chorion (provides nutrients to developing embryo)

Question 7

Implantation

Answer 7

Blastocyst moves from uterine tube and attaches to endometrium of uterine wall

Question 8

Stages of cell during the first 2 weeks of early human development

Answer 8

1. Zygote
2. Morula
3. Blastocyst
4. Implantation
5. Extra-embryonic membranes start to form

Question 9

What happens after implantation

Answer 9

The embryoblast (inner cell mass) differentiates into a bilayered (2 cell layers) embryonic disc made up of
1. Epiblast
2. Hypoblast

• the extraembryonic membranes start to form

Question 10

When in the embryonic period

Answer 10

3rd week to end of the 8th week

Question 11

Parts of the embryonic period

Answer 11

• 3 germ layers are now present forming the embryo
  1. Ectoderm
  2. Mesoderm
  3. Endoderm

Question 12

Ectoderm

Answer 12

• germ layer
• will form the nervous system and the epidermis of the skin

Question 13

Mesoderm

Answer 13

• germ layer
• will form the cardiovascular system, dermis, and most bones

Question 14

Endoderm

Answer 14

• germ layer
• will form epithelial linings of digestive, respiratory, urinary and reproductive systems and their associated glands
• forms organ linings for some (most) organs

Question 15

During the embryonic period

Answer 15

• major organ systems are almost completely formed
• heart begins to beat (4 weeks, no fingers or toes yet)
• limb buds differentiate
• extraembryonic membranes continue forming
  1. Chorion
  2. Amnion
  3. Yolk sac
  4. Allantois

Question 16

Chorion

Answer 16

• derived from trophoblast cells
• surrounds all embryonic membranes
• contain chorionic villi

Question 17

Chorionic villi

Answer 17

• projections of the chorion containing the blood vessels that will form fetal part of placenta

Question 18

Placenta

Answer 18

Where nutrients, wastes, oxygen/carbon dioxide move between fetal and maternal blood

Question 19

Amnion

Answer 19

• derived from epiblast
• forms amniotic cavity (surrounds embryo/fetus with amniotic fluid)

Question 20

Function of amniotic fluid

Answer 20

• shock absorption
• temperature regulation

Question 21

Yolk sac

Answer 21

• derived from hypo last
• forms part of digestive tract
• source of reproductive germ cells and embryonic blood cells

Question 22

Allantois

Answer 22

• projections off of the yolk sac
• forms the umbilical cord and the urinary bladder

Question 23

When is the fetal period

Answer 23

9th week to end of 40th week

Question 24

What happens during the fetal period

Answer 24

• growth and maturation of organs occur