Early Embryology 1

Question 1

Fertilization

Answer 1

Day 0

1) Capacitation- seminal proteins pass corona radiata (outside egg)
2) Acrosomal reaction- release acrosome enzymes/pass zona pellucida (2nd layer)
3) Fusion of plasma membrane of sperm and oocyte (Sperm inside released, inactivating sperm receptors=prevents multiple pregnancies)

Question 2

Week 1: Fertilization

Answer 2

Location: Ampulla of fallopian tube

1) female pronucleus
2) Male pronucleus
3) Chromosomes condense
4) Mitotic division = zygot

Question 3

Week 1: Cleavage and Morula Formation

Answer 3

Repeased cell division

Form more blastomeres (16-32=morulas)

Question 4

Week 1: Blastocysts Formation

Answer 4

Location: Uterus fluid-filled blastocystic cavity

-Morula enters blastocystic cavity

Two layers formed:

1) Embryoblast: Embryo
2) Trophoblast: Placenta

Question 5

Week 1-2: Implantation

Answer 5

Location: Posterior wall of body of uterus close to the fundus

• 6-10 days
• Blastocyte enters endometrium
• Trophoblast divides in two parts
  1) Cytotrophoblast (inner)- makes cells/mitotically active
  2) Syncytiotrophoblast (outer)- Contains human chorionic gonadotrophin (HCG), allows blastocyst to burrow into the endometrium

Question 6

Week 2: Bilaminar Disc

Answer 6

-Embryo implantated results in embryonic disc

Embryonic Disc:

1) Epiblast = forms germ layers
2) Hypoblast= Hypoblast = yolk sac (lubrication)

Question 7

Week 3: Gastrulation

Answer 7

-Germ layers form

Question 8

Mesoderm

Answer 8

Paraxial

• Muscle
• Skin
• Bone

Intermediate
-Urogential organs and ducts

Lateral

• Heart
• Spleen
• Adrenals

Question 9

Endoderm

Answer 9

-Lining of epithelium of gut, organs, thryroid glands, lining of bladder

Question 10

Ectoderm

Answer 10

• Nails
• Sweat glands
• Epidermis
• Sensory cells

Neuralectoderm:
1) Neural tube- CNS, retina, pineal body, posterior pituitary

2) Neural crest cells- PNS, melanocytes, cranal nerves, glial and schwann cells, connective tissue/bones, adrenal medula