first 4 weeks of human embryonic development

Question 1

gametogenesis

Answer 1

• process of the production of male and female gametes or sex cells from the primordial germ cells via meiotic cell division
• genetic variability
• chromosome number goes from diploid-haploid

Question 2

fertilisation

Answer 2

-gametes form zygotes
1-penetration of the corona radiate
2-penetration of the zona pellucida
3-fusion of the oocyte and sperm cell membranes

Question 3

acromosome reaction

Answer 3

induced by the zona proteins following binding of the acrosomal region of the sperm with the Mona pellucida of the oocyte
leads to the release of enzymes needed to penetrate the zona pellucida

Question 4

cortical and zona reactions

Answer 4

sperm’s contact with the plasma membrane of the oocyte leads to the release of the lysosomal enzymes from cortical granules in the plasma membrane which becomes impenetrable to other spermatozoa.

Question 5

cleavage

Answer 5

first week
repeated series of rapid mitotic cell divisions of the large zygote to produce an increasing number of small daughter cells called blastomeres
morula: a solid ball of 12-16 cells following cleavage
compaction: a process of blastomeres reorganisation and segregation into inner cell mass and outer cell mass

Question 6

blastocyst

Answer 6

morula develops a fluid-filled cavity with a compact inner cell mass at one side of the cavity enclosed by a thin, single-layered epithelium of trophoblast

Question 7

parthenogenesis

Answer 7

process where an unfertilised egg goes on to develop into a new individual

Question 8

the bilaminar embryonic germ disc

Answer 8

the embryo blast differentiates into two layers - an outer layer called epiblast and an inner layer called hypoblast (primitive endoderm)
the formation of the bilaminar embryonic germ disc establishes and defines the primitive dorsal-ventral axis of the embryo-epiblast is dorsal and hypoblast is ventral

Question 9

the primitive streak

Answer 9

marks the start of gastrulation

defines all the major body axes of the developing embryo

Question 10

gastrulation

Answer 10

process of epiblastic cells movement through the primitive streak that leads to the trilaminar germ disc
gastrulation commences with the formation of the primitive streak on the 15th day