2017 Embryology Revision

Question 1

Embryology week 1

Explain what happens during days 3, 5 and 6

Answer 1

Day 3: morula is formed

Day 5: blastocyst is formed, via a cavity and cell layer being formed

Day 6: implantation into the uterine lining

Question 2

Embryology week 2

1. What 3 things happen on day 8?
2. What forms on day 9?
3. On day 13, what is there cavitation of and what does this form?

Answer 2

1. Syncytiotrophoblast invades the endometrium
   Bilaminar disc is formed (epiblast and hypoblast)
   Amniotic cavity is formed
2. Primary yolk sac
3. Cavitation of extraembryonic mesoderm
   Forms chorionic cavity

Question 3

Embryology week 3
Day 15

1. What happens?
2. What does this form?
3. Where does it extend from and to?

Answer 3

1. Indentation of ectoderm
2. Forms primitive streak
3. From primitive node to cloacal membrane

Question 4

Embryology week 3 - days 14-19

What process occurs?

Answer 4

Gastrulation

Question 5

Embryology week 3 - days 14-19 - gastrulation

1. Where do cells migrate from?
2. Where do they go?
3. What is formed?

Answer 5

1. Primitive streak
2. Between the epiblast and the hypoblast
3. Intraembryonic mesoderm

Question 6

Embryology week 3 - days 14-19 - gastrulation

1. What does ectoderm become?
2. What does endoderm become?
3. What does mesoderm become?

Answer 6

1. Ectoderm: skin and neural tissue
2. Endoderm: epithelial lining of gut, respiratory and urinary systems
3. Mesoderm: muscle, bone, connective tissue, some organs and lining of body cavities

Question 7

Embryology - somites

1. Days?
2. How do they appear?
3. Nervous supply spread?

Answer 7

1. Days 20-30
2. Appear sequentially
3. Each supplied by a single spinal nerve

Question 8

Embryology- Neurulation

1. Days?
2. The notochord forms from what?
3. What does the notochord form within?
4. What does the notochord induce the formation of?
5. What does the notochord become?

Answer 8

1. Days 19-25
2. Primitive node cells
3. Mesoderm
4. Neural plate
5. Nucleus pulposus of IV discs

Question 9

Embryology- neurulation

1. What is neurulation?
2. What is the simple 3 step process?
3. What closes on day 25?
4. What closes on day 27?

Answer 9

1. Formation of neural tube
2. Neural plate forms
   Folds to form neural groove
   Then neural tube forms
3. Cranial neuropore
4. Caudal neuropore

Question 10

Embryology - neural crest cell migration

1. What happens to these cells?
2. Name 4 things that these cells are involved in
3. Name 3 things that can go wrong with defective migration

Answer 10

1. Re-differentiate into other cell types
2. Heart septation, face and skull connective tissues, GI tract ganglia and melanocytes
3. Malformed face, nervous system absences and cardiac/gut defects

Question 11

Embryology - neural tube defects

What is spina bifida?

Answer 11

Defective neural tube closure and anomalies of the covering tissues

Question 12

Embryology- limbs

1. Between which weeks?
2. Which appear first and how long before the other?
3. How are the digits formed?

Answer 12

1. Weeks 4-8
2. Upper limb buds 36 hours before lower
3. Programmed cell death

Question 13

Embryology- folding

1. What are the 2 types of folding?
2. What causes the head to fold?
3. When does folding occur?

Answer 13

1. Lateral folding and cephalo-caudal folding
2. Rapid growth of brain and limited space available
3. Weeks 3-4

Question 14

Embryology - lateral folding

What is drawn around the entire disc?

Answer 14

Amniotic cavity

Question 15

Embryology

What is the intraembryonic coelom and what does it become?

Answer 15

Cavity within mesoderm

Becomes body cavity

Question 16

Embryology- teratogenesis

1. Define teratogenesis
2. When is the embryo at risk of a structural abnormality and why?
3. When is the embryo at risk of a functional abnormality?
4. What happens before week 3?

Answer 16

1. Abnormality induced in developing embryo by harmful, foreign substances
2. Weeks 3-8 because this is when cell division, organogenesis and midline union takes place
3. Week 8 onwards
4. Embryo will self-abort

Question 17

Embryology- teratogens

Name 5 common teratogens and give 1 outcome for each

Answer 17

1. Alcohol: fetal alcohol syndrome
2. Vitamin A: cleft palate
3. Maternal diabetes: heart and neural tube defects
4. Rubella: deafness
5. X-rays: spina bifida

Question 18

Embryology - teratogens

Name 5 basic mechanisms of teratogens

Answer 18

1. Mutations in DNA
2. Interruption of DNA/RNA synthesis
3. Failure of normal cell to cell interactions
4. Interfering with cell differentiation
5. Chromosomal abnormalities

Question 19

Embryology- lungs

1. When does the respiratory diverticulum first develop and what is it an outgrowth of?
2. Its an out pouching of what?
3. What does the trachea, bud grow into at 4-5 weeks?
4. Which septum forms next?
5. How many bronchial buds form on the right and how many form on the left?

Answer 19

1. 4 weeks: outgrowth of foregut
2. Outpouching of endoderm
3. Splachnopleuric mesoderm
4. Tracheo-oesophageal septum
5. Right = 3
   Left = 2

Question 20

Embryology- lung bud division

1. What are the 4 main divisions of the lung bud and what does each one produce?
2. What happens at 6 months that allows the air spaces to inflate?

Answer 20

1. Primary - main bronchi
Secondary - lobar bronchi
Segmental bronchi
Intrasegmental bronchi
2. Surfactant produced

Question 21

Embryology- What are the steps of heart development and when does it start?

Answer 21

Mid week 3
Cardiogenic mesoderm develops
Cords of angioblastic cells
Forms 2 primitive heart tubes on either side 
When the embryo folds, the tubes fuse

Question 22

Embryology- heart

1. What turns the heart tube 180 degrees?
2. When does the heart grow into (and get completely surrounded by) pericardium?
3. What are the 2 pericardial sinus’s?
4. With regards to the heart tubes, what happens at 20 days, 21 days and 23 days?

Answer 22

1. Longitudinal folding
2. Week 4
3. Transverse pericardial sinus and oblique pericardial sinus
4. 20 days: paired heart tubes
   21 days: fusion
   23 days: large single heart tube

Question 23

Embryology- Primitive heart tube

1. What 2 things are at the venous end?
2. What 1 thing is at the arterial end?
3. Name the 5 sections of the primitive heart tube from the venous end to the arterial end

Answer 23

1. Right horn and left horn
2. Aortic sac
3. Sinus venosus
   Atrium
   Ventricle
   Bulbis cordis
   Truncus arteriosus

Question 24

Embryology- primitive heart tube
What do the following things become:
1. Sinus venosus?
2. Atrium?
3. Ventricle?
4. Bulbis cordis?
5. Truncus arteriosus?

Answer 24

1. Sinus venosus = smooth wall of RA
2. Atrium = rough wall of RA and LA
3. Ventricle = rough part of LV
4. Bulbus cordis = rough part of RV and outflow tracts for RV and LV
5. Truncus arteriosus = roots of aorta and pulmonary trunk

Question 25

``` Embryology- septum in heart tube Explain what the following changes into once the septum separates the heart tube: Right horn and left horn Sinus venosus Atrium Ventricle Bulbus cordis Truncus arteriosus ```

Answer 25

``` Vena cavae and coronary sinus Sinus venosus RA and LA RV and LV R outflow tract and L outflow tract Pulmonary trunk and aorta ```

Question 26

Embryology- folding heart tube 1. At 22 days how does the growing bulbis cordis move? 2. At 24 days how does the heart shift?

Answer 26

1. Infero-anteriorly | 2. Postero-superiorly

Question 27

Embryology - AV canal | Explain how the AV canal is partially seperated

Answer 27

AV canal enlarges Swelling in endocardial cushions grow ventrally and dorsally Meet in the middle to partially separate the AV canal

Question 28

Embryology- atrial septation Explain the 4 stages of atrial septation and give the time frame they occur within

Answer 28

Weeks 4-5 1. Septum primum forms with ostium primum at the bottom 2. Ostium secondum forms on a part at the top 3. Spetum secondum is formed 4. Causes a foramen ovale to be formed (R-L shunt in utero)

Question 29

Embryology- ventricular septation 1. When does it occur? 2. What 3 things is the septum made of? 3. Which direction does the muscle section go in and where is it incomplete? 4. What completes this region?

Answer 29

1. Week 5-7 2. Muscle, membrane and endocardial cushion 3. Muscle goes towards endocardial cushion and is incomplete in the cranial region 4. Bulbar ridges growing down

Question 30

Embryology- Tetralogy of Fallot 1. What are the 4 things involved in the tetralogy of fallot? 2. What do they cause?

Answer 30

``` 1. Pulmonary stenosis RV hypertrophy Over-riding aorta VSD 2. Cyanosis (deoxygenated blood entering arterial circulation) and Tet spell ```

Question 31

Embryology - Aortic arches 1. What does the 3rd arch become? 2. What does the 4th arch become? 3. What does the 6th arch become?

Answer 31

1. Common and internal proximal carotid arteries 2. Right: part of right subclavian artery Left: part of aortic arch 3. Pulmonary arteries and ductus arteriosus