Fertilization to Trilaminar

Question 1

What are the steps to fertilization?

Answer 1

1. Sperm binds in a human specific interaction with the zona pellucida glycoprotein
2. Acrosomal enzymes released from sperm head to digest ZP and allow sperm head entry into egg
3. Egg and sperm plasma membranes fuse and sperm contents enter egg
4. Sperm entrance triggers egg compltetion of meiosis 2 and release of cortical granules that harden ZP to prevent further sperm entry

Question 2

What occurs during cleavage?

Answer 2

Zygote undergos mitosis to create many identical daughter cells called blastomeres. Up to cell 8, blastomeres are totipotent.

Question 3

What is compaction?

Answer 3

Cells are confined within ZP and so when they divide the cell mass does not expand

Question 4

What forms when the cells become closer together during compaction?

Answer 4

They begin to form cell junctions. The outer cells which are in contact with the ZP form extensive gap junctions, but fluid can still enter the cell to form the inner cell mass.

Question 5

What is the names of the cells that form extensive gap junctions at the peripheral of the cell?

Answer 5

Trophoblasts

Question 6

What will the trophoblast finally become?

Answer 6

Embryonic part of the placenta

Question 7

What will the inner cell mass become?

Answer 7

Embryo proper (amnion and yolk sac)

Question 8

What will happen when the cell has multiplied to its capacity within the ZP

Answer 8

The blastocyst will hatch

Question 9

Where are the implantation sites

Answer 9

Normal - Middle or upper dorsal uterine wall

Abnormal - ovary, ampulla, uterine tube, lower part of uterus, cervix, peritoneum

Question 10

What drives implantation?

Answer 10

Trophoblast

Question 11

What does the trophoblast divide into?

Answer 11

Cytotrophoblast - made of individulal cells

Syncytiotrophoblast - Single multinucleated cell

Question 12

What are the layers that the embryo divides into?

Answer 12

Epiblast - dorsal surface of embryo
Hypoblast - ventral surface of embryo
Amniotic cavity forms

Question 13

What has begun to form by the end of week 2

Answer 13

The primitive streak

Question 14

Where does the primitive streak form?

Answer 14

Midline at the caudal end of the epiblast. The cranial end of the primitive streak contains the primitive pit and node

Question 15

What can occur after the formation of the primitive streak?

Answer 15

Gastrulation - formtation of endoderm, ectoderm and mesoderm

Question 16

Where will the cells migrate through to form gastrulate?

Answer 16

Primitive streak

Question 17

What will the hypoblast form?

Answer 17

Difinitive endoderm

Question 18

Where is the intraembryonic mesoderm layer formed?

Answer 18

Between the endoderm and epiblast

Question 19

What will the epiblast form?

Answer 19

Ectoderm

Question 20

What will the endoderm form?

Answer 20

Skin and nervous system

Question 21

What will the mesoderm form?

Answer 21

Paraxial - axial skeleton, voluntary muscle and dermis
Intermediate - Urogenital systems
Lateral plate:
Somatic mesoderm - lining of body wall, most of dermis and limbs
Visceral mesoderm - CV system, mesothelial covering of organs, smooth muscle

Question 22

What will the endoderm form?

Answer 22

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