Embryogenesis

Question 1

Gametogenesis

Answer 1

Process of formation of germ cells (gametes) from primordial germ cells

Question 2

Spermatogenesis

Answer 2

Spermatogonia (diploid, mitotic division)–> Primary spermatocyte (diploid, 1st meiotic division)–>secondary spermatocytes (haploid, 2nd meiotic division) –> spermatids (4 x haploids) which undergoes spermeogenesis to produce sperm cells which then stores in epididymis. Sertoli cells also support spermatogenesis process found in seminiferous tubule

Question 3

Oogenesis

Answer 3

Oogonia (diploid, mitotic division, pre-natal) –> primary oocytes (diploid, 1st meiotic division) –>secondary oocyte (haploid, but gets arrested into prophase I until puberty and at puberty complete the 1st meiotic division) –> secondary oocyte (haploid, also produces 1st polar body, 2nd meiotic division but arrested in metaphase) –> it completes when sperm enters secondary oocyte and produces fertilized oocyte and second polar body.

Question 4

Meiosis

Answer 4

formation of haploid daughter cells from diploid cells
Chromosomes duplicates in interphase before entering prophase I
Prophase I – Chiasma formation, crossing over of non sister chromatids for exchange for genetic information.
Metaphase I – Independent assortment, homologous pair of chromosomes assigned to daughter cells randomly
Anaphase I – homologous pair of chromosomes pulled over by mitotic spindle to opposite poles, centromere still attached to sister chromatids. produces two haploid cells.
Telophase I - cytokinesis, uncoiling of chromosomes and nucleus reappear
Prophase II - centrosome moving to opposite pole, nucleus disappear, mitotic spindle appears. No crossing over
Metaphase II – chromosomes aligned to spindle equator
Anaphase II – chromatids separate by pulling over of centromere by mitotic spindle and chromatids move to opposite poles
Telophase II – cytokinesis, chromatids uncoiling and nucleus reappear.

Question 5

Testosterone secreted from which cell

Answer 5

Leydig cell

Question 6

Steps of fertilization

Answer 6

1. Sperm penetrates chorona radiata - release of hyaluronidase enzyme creates passage for sperm
2. Penetration into zone pellucida - again acrosin - proteolytic enzyme is important
3. Zona reaction - zona pellucida becomes impermeable to other sperms
4. Fusion of membrane of sperm and oocyte - Sperm head and tail enters oocyte and plasma membrane stays behind
5. completion of meiotic cell division in oocyte to produce haploid chromosomes and formation of female pronuclei
6. formation of male pronuclei and degeneration of tail
7. Fusion of male and female pro-nuclei to form diploid chromosome
8. Oocyte containing two pro-nuclei is called ootid which is called zygote after fusion of pro-nuclei

Question 7

Zygote cleavage

Answer 7

After fertilization occurs in ampula –> forms zygote
1. Zygote starts diving rapidly by mitotic division –> increase number of blastomere
2. two-stage, four-stage, eight-stage division occurs and when it reaches to nine stage division it starts organizing into a compact ball shape structure called conceptus
3. it leads to cell differentiation to produce embryoblast (inner cell mass) and trophoblast (outer layer)
4. blastomere consisting of 12-32 cells is called morula - produces in 3 days and come out in uterus in 4 days
5. After 2 days in uterine cavity zona pellucida disintegrates and morula converts into blastocyst
6. blastocyst starts hatching into the epithelial lining of endometrium after 6 days

Question 8

Development of embryonic disc, umbilical vesicle and amniotic cavity

Answer 8

1. cell differentiation in embryoblast leads to formation of bilaminar disc consisting of
   a. epiblast: columnar cells forming base of amniotic cavity
   b. hypoblast: cuboidal cells forming roof of exocoelomic cavity and exocoelomic membrane
2. hypoblast with exocoelomic membrane produces - umbilical cavity
3. Bilaminar disc, amniotic cavity and umbilical cavity - produces lacunae in syncytiotropoblast region for access of nutrition and oxygen from endometrial capillary network
4. Chorionic cavity forms from extraembryonic mesoderm
5. Hypoblast thickening forms prechordal plate - future cranial region and future site of mouth and organizer of head region of embryo