early human development

Question 1

three periods

Answer 1

pre-embryonic period
embryonic period
fetal period

Question 2

pre-embryonic

Answer 2

first 2 weeks

stages : zygote, morula, blastocyst

Question 3

zygote

Answer 3

a cell 2n

-undergoes rapid mitotic divisions called cleavage divisions

Question 4

morula

Answer 4

72 hours

• a sold ball of 16-32 cells 9cells called blastomeres)
• same size as ovum/zygote

Question 5

blastocyst

Answer 5

5days

• features:
  1. fluid filled cavity develops=blastoceol/blastocyst cavity
  2. Inner cell mass
  3. trophoblast
• blastocyst moves from uterine tube and attached to endometrium of uterine wall= implantation (5-7days after fertilization)

Question 6

inner cell mass

Answer 6

cells will divide and differentiate (undergo changes to become more specialized) to form the embryo

Question 7

trophoblast

Answer 7

made of trophoblast cells

-cells will divide and differentiate to form chorion

Question 8

chorion

Answer 8

provides nutrients to developing embryo
-derived from trophoblast cells
surrounds all embryonic membranes
chorionic villi= projections of the chorion containing the blood vessels that will form fetal part of placenta

Question 9

after implantation

Answer 9

inner cell mass forms a 2 layered (bilayered) embryonic disc composed of

a) epiblast
b) hypoblast

Question 10

epiblast

Answer 10

will undergo mitosis to form:

• amnion-with a fluid filled amniotic cavity
• 3 germ layers of the embryo

Question 11

hypoblast

Answer 11

will undergo mitosis to form the yolk sac

Question 12

embryonic period

Answer 12

3rd to end of 8th week

• 3 germ layers are now present forming the embryo (each layer was formed from mitosis and differentiation of epiblast cells:
  1. ectoderm
  2. mesoderm
  3. endoderm

Question 13

ectoderm

Answer 13

will form the nervous system and the epidermis of the skin

Question 14

mesoderm

Answer 14

will form muscles, cardiovascular system, dermis and most bones

Question 15

endoderm

Answer 15

will form epithelial linings of digestive, respiratory, urinary and reproductive systems and their associated glands

Question 16

during embryonic period

Answer 16

-major organ systems almost completely formed
-heart begins to beat
-limb buds differentiate
-embryonic membranes form:
chorion, amnion, yolk sac, allantois

Question 17

amnion

Answer 17

derived from epiblast

• forms amniotic cavity- surround s embryo/fetus with amniotic fluid
• function of fluid-shock absorption, temperature regulation

Question 18

yolk sac

Answer 18

derived from hypoblast

• forms part of gut (gastrointestinal tract)
• produces earliest blood cells and vessels
• source of primordial germ cells (reproductive cells= primary oocytes and primary spermatocytes)

Question 19

allantois

Answer 19

out-pocket of yolk sac

-forms the umbilical cord and the urinary bladder

Question 20

fetal period

Answer 20

9th week to end of 40th week

-growth and maturation of organs occurs