Embryologyyyyy

Question 1

Definition of fertilisation

Answer 1

• Fusion of male and female gametes to give rise to a zygote

- Where? - takes place in the fallopean tube, ampullary-ischemic junction

Question 2

How is sperm movement facilitated?

Answer 2

• Flagella
• Prostaglandins
• Contraction of the uterus.

Question 3

Capacitation

Answer 3

• Sperm interaction of the uterus
• Mucosa secretions of uterus helps to remove proteins and glycoproteins from acrosome head
• Allows sperm to detect and interact with an Oocyte.

Question 4

Acrosomal reaction

Answer 4

• Sperm head binds with ZP3 receptors in ZP

- Releases acrosomal enzymes which help penetration

Question 5

Cortical reaction

Answer 5

• Oocyte depolarises after sperm enters it.
• Secretory vesicles containing Ca2+ are released which bloacks ZP3 receptors.
• Prevents polyspermy.

Question 6

Cleavage

Answer 6

• Zygote undergoes cell division without changing its overall size

Question 7

Different stages of Blastomeres before implantation

Answer 7

• Zygote
• 2- cell stage (day 1)
• 4-cell stage (day 2)
• 8-cell stage (day4) MORULA
• Day 5, Morula enters Uterus and reaches 32-cell stage called Blastocyst.
• -> at this stage blastocyst arrganges Inner Cell mass and Trophoblast with a cavity called Blastocoel

Question 8

What day is IMPLANTATION

Answer 8

• Day 6 into the endometrium

Question 9

What day is Hatching?

Answer 9

• Day 5

Question 10

Week 2:

Trophoblast differentiation (2 different types)

Answer 10

• Cytotrophoblast- Well defined cell layer

- Syncytiotrophoblast= Secretes enzymes so the embryo can borrow further in.

Question 11

Week 2:

ICM different layers

Answer 11

• Epiblast- primitive ectoderm
• -> has a cavity called the Amniotic Cavity which contains amniotic fluid
• Hypoblast= primitive endoderm
• -> hypoblast cells layer the rest of the blastocyst, which forms a new cavity called yolk sac.
• -> cells become squamous and is called the exocoelomic layer. (day 8)

Question 12

Week 2: (day 12)

• hint, migration

Answer 12

• Mesodermal cells migrate from the yolk sac to form a connective tissue layer surrounding the amnion and yolk sac.
• Chorion= Synctiotrophoblast + Cytotoblast + Extraembryonic Mesoderm

Question 13

Week 3:

• GASTRULATION

Answer 13

• Emergence of Primitive streak on Epiblast
• At the head of Primitive streak, primitve node froms
• Invagination of streak and mesenchymal cells from epiblast migrate
• Formation of Trilaminar disc (Ectoderm, Mesoderm, Endoderm)
• Cells from Primitive node form notochord (finishes by day 22-25

Question 14

Neurultion

Answer 14

• Notochord induces cells in ectoderm to thicken forming Neural plate
• Neural plate begins to form, first from primitive node to Oropharyngeal membrane
• Grove forms in the plate
• Folds merge with each other and a tube separates
• Gives rise to Neural crest and tube

Question 15

Somites

Answer 15

• Mesoderm differentiates into 3 regions Paraxial (next to notochord), Intermediate and Lateral regions
• Give rise to different tisses

Question 16

Dermamyotome

Answer 16

Dermis and associated tisue

Question 17

Myotome

Answer 17

Muscles

Question 18

Sclerotome

Answer 18

Cartilages and tendons

Question 19

SRY

Answer 19

• Found on the Y chromosome
• Stimulates testes to develop which as a result means testosterone is produced which causes mesonephric ducts to grow
• Testosterone –> DHT which causes growth of penis etc…
• Sertoli cells secrete Anti-Mullerian hormone which inhibts paramesonephric ducts