Embryology

Question 1

What is the term for the fertilised egg?

Answer 1

Oocyte

Question 2

What does the morula turn into?

Answer 2

The cells of the morula reorganise to form a cavity, known as the blastocyst cavity (blastocoel).

From this point, the morula is known as the blastocyst.

Question 3

Development of a human

Answer 3

 Pre-embryonic phase 0-3 weeks
 Embryonic phase 4-8 weeks
 Foetal phase 9-40 weeks
 Postnatal, childhood and adolescence

Question 4

What are gametes and where are they formed?

Answer 4

Sperm (formed in the testis) and ovum (formed in the ovaries)

Question 5

What can be found in the testis and what is their role?

Answer 5

Little cells called spermatogonia which are going to divide to form the sperms

Question 6

What can be found in the ovaries

Answer 6

In the ovaries, there are follicles and within these follicles, you have the oogonia which is the parent cell going to divide to form the ovum.

Question 7

When does the morula transform into a zygote?

Answer 7

End of day 5

Question 8

What does the morula form?

Answer 8

Blastocyte

At 7 days, the blastocyst begins to burrow into the uterine wall (endometrium)

Question 9

What hormone is used to detect pregnancy?

Answer 9

HCG

Question 10

What does the inner cell mass flatten and form?

Answer 10

Two layers (bilaminar disc)

The top is called the epiblast and the bottom is called the hypoblast.

Question 11

What does the bilaminar disc divide?

Answer 11

Divide the cavity with the cavity above the epiblast, the amniotic cavity and the cavity below the hypoblast, the yolk sac.

Question 12

What does the bilaminar disc form?

Answer 12

Embryo

Question 13

How does the embryo fold?

Answer 13

The embryo folds such that the amniotic cavity now covers the entire embryo

The yolk sac becomes smaller and smaller

Question 14

What does the hypoblast become?

Answer 14

Yolk sac

Question 15

What does the epiblast become?

Answer 15

Ectoderm, definitive endoderm, and mesoderm

Question 16

What is the placenta formed from?

Answer 16

Chorionic villi

Question 17

What type of twins always have 2 different placentas?

Answer 17

Non-identical twins (dizygotic)

Question 18

What type of twins can have either one or two placentas?

Answer 18

Identical twins (monozygotic)

Question 19

Where does the primitive streak form and what happens when it is formed?

Answer 19

In the midline of the epiblast by the dipping in of cells (invagination).

Once the primitive streak is formed, the axis of the embryo is formed.

Question 20

What is gastrulation?

Answer 20

Formation of 3 germ layers

Question 21

What are the three germ layers and what do they each form?

Answer 21

Ectoderm – forms skin, nervous system, sympathetic trunk, dorsal root ganglia

Mesoderm – forms muscle tissue, skeletal tissue, urinary and reproductive system

Endoderm – forms gut tube, respiratory tube

So, the bilaminar disk has become a trilaminar disk and the cells have become specialised.

Question 22

What layers form the skin, muscles, spinal cord and nucleus pulposus of the vertebrae?

Answer 22

The skin is formed from the ectoderm
The muscles, the vertebrae and the vertebral arches are formed from the mesoderm
The neural tube forms the spinal cord
The notochord mostly disintegrates but some of it remains as the nucleus pulposus of the vertebrae

Question 23

What forms the pleura and gut tube?

Answer 23

The lateral plate mesoderm will form the coverings of the respiratory tube (pleura) and the gut tube (peritoneum).

Question 24

What buds out of the ventral wall of the primitive foregut in week 4?

Answer 24

Trachea and lung buds

Question 25

What seprates the trachea and lung bunds from the oesophagus?

Answer 25

Oesophagotracheal septum at 6-7 weeks

Question 26

What four structures form the diaphragm?

Answer 26

Septum transversum
Pleuroperitoneal folds
Skeletal muscle ingrowth from the peripheral body wall
Dorsal mesentery of the oesophagus

Question 27

What part of the diaphragm does the septum transversum form?

Answer 27

Central tendon of the diaphragm

Question 28

What part of the diaphragm does the pleuroperitoneal folds form?

Answer 28

Somatic mesodermal folds grow in from the periphery to fuse with septum transversum

Question 29

What part of the diaphragm does the skeletal muscle ingrowth from the peripheral body wall form?

Answer 29

Muscular part of the diaphragm