Embryology

Question 1

When is meiosis II of oogenesis complete?

Answer 1

On fertilisation

Question 2

Where does fertilisation usually occur?

Answer 2

In the ampullary region of the Fallopian tube

Question 3

How long are sperm viable for?

Answer 3

Five days

Question 4

True or false: sperm are initially incapable of fertilisation

Answer 4

TRUE

Question 5

What do sperm require to become capable of fertilisation?

Answer 5

Capacitation-tail of sperm moves faster, causing plasma membrane to alter

Question 6

Define embryonic age

Answer 6

Time since fertilisation

Question 7

Define gestational age

Answer 7

Time since last menstruation, so embryonic age plus 2 weeks

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 to end of eighth week

Question 10

What is the foetal period?

Answer 10

Time from beginning of ninth week to birth at 38 weeks (gestational age)

Question 11

Complete the sentences:

Before the blastocyst can implant, it has to lose the _____ _________. This is thought to prevent the morula/blastocyst adhering to the oviduct. The process of losing this structure is called __________.

Answer 11

Zona pellucida

Hatching

Question 12

What does the zona pellucida stop?

Answer 12

Morula enlarging

Question 13

What does the trophoblast become?

Answer 13

Yolk sac and placenta

Question 14

What is the difference between histiotrophic and haemotrophic nutrition?

Answer 14

Histiotrophic-nutrition provided to embryo not from maternal blood, important up to 12th week

Haemotrophic-nutrition provided by mother’s blood, important from 12th week on

Question 15

What is the normal site of implantation?

Answer 15

Upper part of the body of uterus, most often on the posterior wall

Question 16

What is an ectopic pregnancy?

Answer 16

Embryo attaches outside uterus (eg ovaries, in Fallopian tube, interstitial, abdomen etc)

Question 17

What is a syncytiotrophoblast?

Answer 17

Epithelial covering of embryonic placental villi which invades wall of uterus for nutrient circulation between embryo and mother

Question 18

What is a cytotrophoblast?

Answer 18

Inner layer of trophoblast

Question 19

How does the yolk sac deliver nutrient to the developing embryo?

Answer 19

Attaches outside the embryo and delivers via primitive aorta

Question 20

Which layers does the trophoblast differentiate into in the second week?

Answer 20

1) cytotrophoblast

2) syncytiotrophoblast

Question 21

Which two layers does the embryoblast form in the second week?

Answer 21

1) epiblast

2) hypoblast

Question 22

Which two cavities does the hypoblast contribute to in the second week?

Answer 22

1) yolk sac

2) chorionic cavity

Question 23

What is a conceptus?

Answer 23

Product of conception but unsure whether it is an embryo or foetus

Question 24

True or false: the embryonic period is when all the major structures and systems are formed

Answer 24

TRUE

Question 25

Give examples of teratogenic agents which interfere with development

Answer 25

Thalidomide Rubella Warfarin

Question 26

What are the key events and processes in early development? (5)

Answer 26

1) fertilisation and implantation 2) gastrulation 3) neurulation 4) segmentation 5) folding

Question 27

What is gastrulation?

Answer 27

Bilaminar disk is converted to trilaminar disk with three germ layers

Question 28

Which layers make up the bilaminar embryonic disk?

Answer 28

Epiblast | Hypoblast

Question 29

Which layers make up the trilaminar disk?

Answer 29

Ectoderm Mesoderm Endoderm

Question 30

What does the ectoderm develop into?

Answer 30

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

Question 31

What does the mesoderm develop into?

Answer 31

Supporting tissues eg muscle, cartilage, bone, vascular system

Question 32

What does the endoderm develop into?

Answer 32

Internal structures eg epithelial lining of GI tract, respiratory tract, parenchyma of glands

Question 33

What is situs inversus?

Answer 33

Complete mirror-image viscera, commonly resulting from immotile cilia

Question 34

How many lobes does the left lung have?

Answer 34

Two

Question 35

How many lobes does the right lung have?

Answer 35

Three

Question 36

What marks the start of the embryonic period?

Answer 36

Gastrulation

Question 37

How does gastrulation occur?

Answer 37

Primitive streak forms in the caudal epiblast, leading to migration and invagination of epiblast cells

Question 38

Why does gastrulation occur?

Answer 38

To ensure the correct placement of precursor tissues to allow subsequent morphogenetic to take place

Question 39

What is the notochord?

Answer 39

Structure that runs down the midline

Question 40

By which process does CNS development begin?

Answer 40

Neurulation

Question 41

What is the role of the notochord in neurulation?

Answer 41

Important signalling role-signals overlying ectoderm to thicken and directs its conversion to neurectoderm

Question 42

What are somites?

Answer 42

Organisation of paraxial mesoderm into body segments

Question 43

Where and when do the first pair of somites appear?

Answer 43

At day 20 in the occipital region (skull)

Question 44

How many somites are left in total at the end?

Answer 44

31

Question 45

What forms when the ventral wall of the somites breaks down?

Answer 45

Sclerotome

Question 46

What forms when the dorsal portion of the somites is organised?

Answer 46

Dermomyotome

Question 47

What are the somite derivatives? (3)

Answer 47

1) dermatome 2) myotome 3) sclerotome

Question 48

True or false: organisation of mesoderm into somites gives rise to non-repeating structures

Answer 48

FALSE - repeating structures such as vertebrae, ribs, intercostal muscles and spinal cord segments

Question 49

What is cephalocaudal folding driven by?

Answer 49

Growth of neural tube

Question 50

What is lateral folding driven by?

Answer 50

Growth of somites

Question 51

What does folding achieve? (3)

Answer 51

1) Draws together the margins of the disk, creating a ventral body wall. 2) Pulls amniotic membrane around the disk so that the embryo is suspended within the amniotic sac 3) Pulls connecting stalk centrally

Question 52

What occurs at the end of the fourth week of development?

Answer 52

Nervous system started to form Segments appeared Embryo folded