Week 1: fertilization to implantation

Question 1

Name the two divisions of human developmental periods

Answer 1

1.Prenatal development
-Germinal period
-Embryological period
-Foetal period

2.Postnatal period
-Infancy
-Childhood
-Puberty
-Adulthood

Question 2

How long is the germinal period?

Answer 2

It consists of the first 2 weeks

Question 3

How long is the embryonic period?

Answer 3

The embryonic period is 6 weeks, from Week 3-8.
-Most visible development occurs

Question 4

How long is the foetal period?

Answer 4

Week 9 till birth
-Differentiation and growth of tissues and organs occurs
-Rate of body growth increases

Question 5

How many stages of embryologic development?

Answer 5

23 stages
Stage 1: Begins at fertilization
Stage 23: Embryonic development ends

Question 6

When is the most critical stage of development? (Which trimester)

Answer 6

Critical stages of development occur during the first trimester.

Question 7

How long does the process of fertilization take?

Answer 7

24hrs

Question 8

_____________ secreted by the oocyte and follicular cells guide sperm cells to the oocyte for fertilization

Answer 8

Attractant chemical

Question 9

When does the secondary oocyte undergo the second meiotic division?

Answer 9

After the sperm penetrates the oocyte

Question 10

How is variation of the human species achieved

Answer 10

Achieved by the mingling of the maternal and paternal chromosomes

Question 11

What helps the sperm pass through the corona radiata? (3)

Answer 11

-The sperm acrosome releases an enzyme called hyalurodinase, which causes dispersal of follicular cells that make up the corona radiata
-Tubal mucosal enzymes also helps with dispersal of follicular cells
-The tail of the sperm performs propelling movements that help with penetration.

Question 12

What helps the sperm move through the zona pellucida?

Answer 12

-Acrosome releases esterase, acrosin, and neuraminidase
- Cause lysis of zona pellucida, forming a path for the sperm to enter the oocyte

Question 13

What is the zona reaction?

Answer 13

-When the sperm penetrates the zona pellucida, the properties of the zona pellucida changes, thus hindering the other sperm cells from penetrating the oocyte. This is called the zona reaction.

Question 14

What parts of the sperm enters the cytoplasm of the oocyte, and what parts are left behind?

Answer 14

-Sperm head and tail enter oocyte cytoplasm
-Sperm cell membrane and mitochondria remain behind

Question 15

How is the female pronucleus formed?

Answer 15

-After penetration by the sperm, the 2ndary oocyte undergoes meiosis II to form a mature oocyte and a polar body.
The mature oocyte becomes the female pronucleus after the maternal chromosomes have decondensed.

Question 16

How is the male pronucleus formed?

Answer 16

The sperm nucleus enlarges to form the male pronucleus, and the tail of the sperm degenerates.

Question 17

True or false: You can’t distinguish the male pronucleus from the female one

Answer 17

TRUE
Male and female pronuclei are morphologically
indistinguishable

Question 18

Describe zygote cleavage

Answer 18

Repeated mitotic divisions of zygote
* Occurs as zygote passes along uterine tube toward uterus
* Results in rapid increase in cell numbers - Blastomeres
* Blastomeres become smaller with each successive cleavage division
- Lie within zona pellucida
- Eventually change shape and become tightly packed (compaction)

Question 19

When does zygote cleavage start?

Answer 19

• Begins around 30 hours after fertilization

Question 20

How many blastomeres make up the morula? And when does it form?

Answer 20

12-32 blastomeres (compacted)
Forms around day 3 after fertilization, as it enters the uterus

Question 21

When does blastocyst formation occur?

Answer 21

Around 4 days after fertilization

Question 22

Describe blastocyst formation

Answer 22

Begins with formation of blastocystic cavity (fluid-filled space) inside morula
- Fluid passes from uterine cavity through zona pellucida. It separates blastomeres into two parts

Question 23

What are the two parts of the blastocyst? Describe them.

Answer 23

1.Trophoblast
- Thin, outer cell layer (Forms wall of blastocyst)
- Gives rise to embryonic part of placenta.
2. Embryoblast
- Group of centrally located cells
- Gives rise to the embryo

Question 24

How long does the blastocyst float in the uterus?

Answer 24

2 days

Question 25

When does implantation occur?

Answer 25

day 6 post fertilization

Question 26

Explain the process of iimplantation

Answer 26

Blastocyst attaches to endometrial epithelium
- Usually adjacent to embryonic pole
- Trophoblast immediately proliferates rapidly and forms two layers

Question 27

Name the layers of the trophoblast?

Answer 27

Cytotrophoblast (inner layer)
2. Syncytiotrophoblast (outer layer)
- Multinucleated protoplasmic mass (no cell boundaries)
- Lies adjacent to embryoblast/ embryonic pole
- Extends into endometrium to embed blastocyst

Question 28

The _______________ is formed by the blastomeres of the embryoblast, and lies on embryoblast surface facing blastocystic cavity

Answer 28

Hypoblast

Question 29

Phases of fertilization

Answer 29

1. Passage through corona radiata
   2.Passage through zona pellucida
2. Fusion of cell membranes of oocyte and sperm
3. Completion of the 2nd meiotic division
4. Formation of male pronucleus
5. Zygote

Question 30

What does the trophoblast give rise to

Answer 30

Embryonic part of placenta

Question 31

What is the endometrium adjacent to

Answer 31

Embryonic pole