BL - Embryology

Question 1

What are the tubes called that connect the ovaries with the uterus?

Answer 1

Fallopian tubes

Question 2

Briefly explain the process of oogenesis.

Answer 2

• oogonium splits into another oogonium and a primary oocyte
• primary oocyte splits into 1st polar body and secondary oocyte
• 1st polar body splits to form two more polar bodies (polar body still undergoes mitosis despite having no role)
• secondary oocyte splits to form secondary polar body and ovum

Question 3

Where does fertilisation take place usually?

Answer 3

The ampullary region of the Fallopian tube

Question 4

True or false - sperm must be introduced into the female reproductive tract within five days before ovulation?

Answer 4

True. Sperm are viable for five days, but secondary oocytes are only viable for 12-24 hours.

Question 5

What is capacitation?

Answer 5

When the tail of the sperm moves faster causing the plasma membrane to alter.

Question 6

Why is semen not rejected by the body?

Answer 6

The body only develops antigens for semen if it is exposed to the blood supply. This means that there are no antibodies for its antigens.

Question 7

What is the difference between embryonic age and gestational age?

Answer 7

Embryonic age is time since fertilisation, while gestational age is time since last menstruation.

Question 8

What is the “germinal stage”?

Answer 8

Time from fertilisation to the end of the second week.

Question 9

What is the “embryonic period”?

Answer 9

Time from third week to end of eighth week

Question 10

What is the “foetal period”?

Answer 10

Beginning of ninth week to birth at 38 weeks.

Question 11

What is the zona pellucida?

Answer 11

A ‘shell’ that surrounds the egg, preventing it from adhering to the oviduct. It must be lost before the blastocyst can implant.

Question 12

What does the fertilised egg form when it reaches the 16-celled stage?

Answer 12

A morula

Question 13

What forms after the morula?

Answer 13

Blastocyst

Question 14

Where does implantation usually occur?

Answer 14

The posterior wall of the upper part of the body of the uterus.

Question 15

What is an ectopic pregnancy?

Answer 15

This occurs when the blastocyst implants in the wrong place, eg the fallopian tube.

Question 16

What is placenta praevia?

Answer 16

This occurs when the placenta forms very close to (or even occluding) the vaginal opening.

Question 17

Why is the second week of development known as the “week of twos”?

Answer 17

• the trophoblast differentiates into two layers
• the embryoblast forms two layers
• the hypoblast contributes to the formation of two cavities

Question 18

During which stage of development is the foetus at greatest risk of congenital malformation due to environmental exposure?

Answer 18

The embryonic period

Question 19

What appears in the dorsal surface of the epiblast at three weeks?

Answer 19

The primitive streak

Question 20

What are the two layers of the “bilaminar disk”?

Answer 20

• epiblast

- hypoblast

Question 21

What are the three layers of the “trilaminar disk”?

Answer 21

• ectoderm
• mesoderm
• endoderm

Question 22

What do the two holes in the mesoderm go on to form?

Answer 22

The mouth and anus

Question 23

What does the ectoderm form?

Answer 23

Organs and structures that maintain contact with outside world, eg nervous system, epidermis

Question 24

What does the mesoderm go on to form?

Answer 24

Supporting tissues, eg muscle, cartilage, bone

Question 25

What does the endoderm go on to form?

Answer 25

Internal structures eg epithelial lining of GI tract

Question 26

What is situs inversus?

Answer 26

Complete mirror image viscera

Question 27

How does the embryonic disk signal which side is left and which is right?

Answer 27

Action of ciliated cells at the node results in left-ward flow of signalling molecules. This causes side-specific signalling cascades to be initiated.

Question 28

What is gastrulation?

Answer 28

The process of the bilaminar disk being converted to a trilaminar disk. Occurs in third week of development.

Question 29

What is the notochord?

Answer 29

A solid rod of cells that runs down the midline, which directs conversion of overlying ectoderm to neurectoderm (beginning of central nervous system).

Question 30

How does the ectoderm over the notochord form the neural tube?

Answer 30

• notochord signals cause overlying ectoderm to thicken
• neural plate edges elevate out of the plane of the disk and curl towards each other
• this creates neural tube

Question 31

What are the four different sections of the mesoderm?

Answer 31

Paraxial, intermediate, somatic, splanchnic

Question 32

What are somites?

Answer 32

Organisation of the parasail mesoderm into segments. The first pair appear at day 20 in the occipital region. There will be 31 in total

Question 33

How do somites form myoterm?

Answer 33

• somites appear as regular block of mesoderm cells around small cavity
• followed by organised degeneration where ventral wall of somite breaks down and forms sclerotome
• organisation of dorsal portion forms combined dermomyotome
• myotome proliferates and migrates, dermatome disperses

Question 34

What are the three somite derivatives?

Answer 34

• DERMATOME (“skin section”, dermis)
• MYOTOME (“muscle section”, muscles)
• SCLEROTOME (“hard tissue section”, bones)

Question 35

What are the functions of segmentation?

Answer 35

• Organisation of mesoderm into somites forms repeating structures:
  Vertebrae, ribs, intercostal muscles, spinal cord segments
• It also guides innervation

Question 36

What is achieved by folding of the trilaminar disk?

Answer 36

• creates a ventral body wall
• pulls amniotic membrane around the disk (leading to embryo being suspended within amniotic sac)
• pulls connecting stalk ventrally