Embryology: Fertilisation To Trilaminar

Question 1

What is fertilisation

Answer 1

union of gametes - fusion of sperm and oocyte to form a zygote

Question 2

Where does fertilisation take place

Answer 2

ampulla of the uterine tube

Question 3

Fertilisation (1/4)

Answer 3

Sperm binds to zona pellucida glycoprotein

Question 4

Fertilisation (2/4)

Answer 4

Acrosomal enzymes released from sperm head; sperm digests its way into egg

Question 5

Fertilisation (3/4)

Answer 5

Egg and sperm plasma membranes fuse and sperm contents enters the egg

Question 6

Fertilisation (4/4)

Answer 6

Sperm entry triggers completion of meiosis 2 and release of cortical granules by oocyte (make ZP impenetrable to other sperm)

Question 7

What is cleavage

Answer 7

Zygote undergoes series of mitotic divisions that divide fertilised egg into blastomeres

Question 8

What is a blastomere

Answer 8

one of the cells that are produced during cleavage of a zygote and that form the morula

Question 9

Up to what stage are blastomeres thought to be totipotent

Answer 9

8 cell stage

Question 10

What is a totipotent cell

Answer 10

Cells that can differentiate into any cell type including embryonic and placental cells

Question 11

Mosaicism

Answer 11

Individuals with 2 or more cell line with different chromosome complements

Question 12

When can mitotic nondisjunction occur

Answer 12

Early division of zygote

Question 13

mitotic nondisjunction

Answer 13

The failure in mitosis for the two members of a chromosome pair to separate (to disjoin) normally, which causes both chromosomes to go to one daughter cell while none go to the other daughter cell

Question 14

How many blastomeres in morula

Answer 14

16+

Question 15

What does the inner cell mass of a blastocyst form

Answer 15

Embryo

Question 16

What does the trophoblast of a blastocyst form

Answer 16

Feral placenta

Question 17

Blastocyst hatching

Answer 17

developing embryo (at around five days after fertilization) that is hatching out of the zona pellucida (ZP(Protective coating))

Question 18

On what day (number) does implantation typically occur

Answer 18

Day 6

Question 19

Where does implantation occur

Answer 19

Posterior or anterior uterine wall

Question 20

Ectopic pregnancy

Answer 20

implantation outside the uterus

Question 21

Placenta previa

Answer 21

placenta lies low in uterus and partially/completely covers cervix

Question 22

Development of the bilaminar embryo - day 7.5

Answer 22

Trophoblast divides into cytotrophoblast (individual cells) and syncytioblast (single multinucleated cell which produces hCG)

Embryobast divides into epiblast (dorsal surface) and hypoblast (ventral surface)

Amniotic cavity begins to form

Question 23

Development of the bilaminar embryo - day 9

Answer 23

amniotic cavity (epiblast) and primitive yolk sac (hypoblast) are formed

-Implantation complete

Question 24

Development of the bilaminar embryo - day 12

Answer 24

Uteroplacental circulation established

chorionic cavity is formed (Extraembryonic mesoderm develops then degenerates)

Question 25

Development of the bilaminar embryo - day 13

Answer 25

- Further development of chorionic cavity - Presence of existing stalk (later umbilical cord) - Second wave of hypoblast cells migrate to form definitive yolk sac

Question 26

Development of the bilaminar embryo - Implanted embryo

Answer 26

Uteroplacental circulation forms Amniotic cavity present above embryonic disc Chorionic cavity developed and encircles embryo

Question 27

Implantation + location

Answer 27

Embryo implants into endometrial lining on posterior or anterior uterine wall

Question 28

Primitive streak features

Answer 28

-Primitive streak appears in midline at caudal end of epiblast - Cranial end of Primitive streak = Primitive Pit and Node

Question 29

Gastrulation

Answer 29

Invagination of the epiblast cells through the primitive stream to form the 3 primary germ layers

Question 30

What layers is the trilaminar embryo composed of

Answer 30

ectoderm, mesoderm, endoderm

Question 31

Fate of Epidermis

Answer 31

- Epidermis of skin, hair, nails - Nervous system

Question 32

Fate of mesoderm

Answer 32

Paraxial mesoderm: axial skeleton, skeletal muscle - Intermediate mesoderm: urogenital systems - Lateral plate mesoderm - Somatic layer: dermis, lining of body wall, parts of limbs - Visceral layer: cardiovascular system, mesothelial covering of organs, smooth muscle

Question 33

Fate of endoderm

Answer 33

- Lining of gut tube - Lining of respiratory tract - Lining of bladder and urethra