Embryology

Question 1

What week doe the primordial heart start forming?

Answer 1

4th week

Question 2

Describe the stages of vasculogenesis

Answer 2

1. Angioblasts are formed from mesenchymal cells (stem cells)
2. Angioblasts go on to form the lining of the endothelium of the vessels
3. Blood islands form which form the lumen of the vessels
4. These blood islands join together to form bigger islands so larger lumen can be formed

Question 3

In what sites do the first blood vessels appear?

Answer 3

• yolk sac
• gallantois
• connecting stalk
• chorion (membrane under which the embryo is buried

Question 4

What are the five chambers of the heart tube?

Answer 4

• trunchus arteriosus
• bulbus cordis
• primitive ventricle
• primitve atrium
• sinous venosus

Question 5

What are the angioblastic cords?

Answer 5

the two tubes which join together to form the heart tube

cord like masses of splanchnic mesenchymal cells ventral to the primordial pericardial celom (a cavity in the mesoderm of an embryo that gives rise in humans to the pericardial cavity) that arrange themselves side-by-side to form the primordia of the endocardial heart tubes.

Question 6

What chambers are responsible for the formation of the cardiac loop?

Answer 6

bulbus cordis
primitive ventricle
these both form the bulboventricular loop

Question 7

What is dextrocardia ?

Answer 7

When the heart tube folds the wrong way so the heart is rotated the opposite way round.

Question 8

What are the two types of heart muscle in the atria and ventricles and where are each found?

Answer 8

• trabeculae carnae: found in ventricles
• pectinate muscles: found in atria and atrial appendages (can remember pect muscles being up high in the chest so therefore at the top of the heart)

Question 9

Form what type of mesoderm is the visceral pericardium derived?

Answer 9

splanchnopleuric mesoderm (splanchnic = at the organ)

so the visceral pericardium lies on top of the organ so is splanchnic

Question 10

Form what type of mesoderm is the serous and fibrous pericardium derived?

Answer 10

somatopleuric mesoderm.

Question 11

Between what days of development do the heart chambers form?

Answer 11

around 27th and 37th days

Question 12

During the formation of heart chambers what two things have to form for this to happen?

Answer 12

septal formation

endocardial cushion formation

Question 13

What occurs during the division of the atria?

• what four septa form?
• why is this done?

Answer 13

Septal Primum forms first which grows from the top of the atria down towards the endocardial cushion in the atrioventricular canal, which creates the foramen primum (ostium foremen) as cells grow up form the endocardial cushion towards the bottom of the septum primum.
Apoptosis (programmed cell death) results in cell death towards the top of the septum primum.
At the same time cells divide and grow up from the endocardial cushion and close over the foramen primum

The septal secondum forms in the left atrium beside the septal primum. As it grows it begins to overlap the foramen primum - this is done to form a valve for the oval foramen to prevent blood from flowing form the right to left atria.

This allows oxygenated blood from the placenta to flow from the left atria to the right atria (by passing the lungs) to be pumped around the embyro.

Question 14

State the four main types of atrial septal defects.

Answer 14

A) Ostium secundum defect
B) Endocardial cushion defect with ostium primum defect
C) Sinus venosus defect
D) Common atrium

Question 15

Are males or females more affected by ASD (atrial septal defects)?

Answer 15

females

Question 16

Are males or females more affected by heart defects?

Answer 16

males

Question 17

What maternal infection acquired during pregnancy can be associated with congenital heart defects?

Answer 17

rubella

Question 18

What are some causes of heart defects?

Answer 18

• maternal alcohol abuse
• drug abuse
• radiation
• genetic (8%)
• chromosomes (2%)

Question 19

Describe the 4 stages of the partitioning of the primitive ventricles.

Answer 19

• Muscular part develops from the proliferation of medial wall
• During the process the IV foramen (interventricular foramen) is formed between the free edge of muscular septum and the fused endocardial cushion
• IV foramen permits communication between left and right ventricles
• IV foramen is closed by the fusion of the right and left bulbar ridges with the endocardial cushion forming membranous part of IV septum.

Question 20

What is the most common form of VSD and who is most affected?

Answer 20

congenital heart disease

males

Question 21

In VSD, is the membraneous or muscular part more usually affected?

Answer 21

membraneous

Question 22

At what stage of development does the bulbus cordis and truncus arteriosus divide?

Answer 22

during the 5th week

Question 23

Why does the bulbus cordis and truncus arteriosus divide?

Answer 23

To form the aorta and the pulmonary trunk.

Question 24

Describe the process of aorta and pulmonary trunk formation.

Answer 24

1. there is active proliferation of the walls of the bulbus cordis and the truncus arteriosus.
2. this forms trunchus and bulbar ridges on the walls
3. They undergo 180 – degree spiralling result in the formation of aorticopulmonary (conotruncal) septum (beginning at the bottom with aorta at the posterior and the pulmonary trunk at the anterior, then in the middle the aorta is on the left as the ridges spiral in a clockwise motion, then the aorta ends up at the anterior of the heart)
4. the cause of spiralling has not been found but it is though to be the turbulent blood flow.
5. the aorticopulmonary septum divides the two ventricles so the aorta is coming out of one ventricle and the pulmonary trunk is coming out of the other ventricle.

Question 25

What two causes can result in abnormal division of BC and TA?

Answer 25

- failure of the ridges to take a spiral course | - defective migration of neural crest cells

Question 26

What is tetralogy of Fallot ?

Answer 26

congenital heart disorder with four abnormalities: - Pulmonary stenosis (obstruction of right ventricular outflow) - Ventricular septal defect (VSD) - Dextroposition of aorta (overriding aorta) - Right ventricular hypertrophy

Question 27

what causes tetralogy of Fallot?

Answer 27

Unequal division of the conus (the upper front part of the right ventricle of the heart) due to anterior displacement of conotruncal (aorticopulmonary) septum

Question 28

From what cells do the semilunar valves proliferate from?

Answer 28

subendocardial tissue

Question 29

From what cells do the tricuspid and bicuspid valves proliferate from?

Answer 29

local tissue around the AV canal

Question 30

During what week does the sinus atrial node develop?

Answer 30

5th week

Question 31

From what heart chamber does the bundle of His develop from?

Answer 31

sinus venosus

Question 32

``` Aortic Arches what forms the: - 3rd arch - 4th arch - 6th arch ```

Answer 32

``` 3rd = the internal carotid arteries 4th = the aorta on the left side and the right subclavian artery on the right 6th = the pulmonary arteries and the ductus arteriosus ```

Question 33

Where does the laryngeal nerve originate from?

Answer 33

a branch off the vagus nerve (10th cranial nerve)

Question 34

Where does the laryngeal nerve go once leaving the vagus nerve?

Answer 34

LEFT - the vagus nerve loops around the left subclavian artery and forms the left recurrent laryngeal nerve RIGHT - the vagus nerve loops under the aortic arch and forms the right recurrent laryngeal nerve

Question 35

what is another name for ductus arteriosus?

Answer 35

ligamentum arteriosum

Question 36

what are the purpose of vitteline arteries and veins?

Answer 36

arteries - supply the yolk sac | veins - drains blood from the yolk sac to the sinus venosus

Question 37

What are the purpose of umbilical arteries and veins?

Answer 37

arteries - Before birth: Paired ventral branches of the dorsal aorta to placenta to allow the blood to be oxygenated. After birth: Proximal portion persists as internal iliac and superior vesical arteries Distal portion degenerates & forms medial umbilical ligaments veins - drain blood from placenta to sinus venosus after being oxygenated

Question 38

What is the purpose of the cardinal veins?

Answer 38

arteries - provides blood from the truncus arteriosus to the body of the embryo veins - drain blood form the body of the embryo to the sinus venosus

Question 39

what are the two sources from which coronary arteries are derived?

Answer 39

1. Migration of proepicardial (angioblasts) cells | 2. Cells of epicardium – epithelial to mesenchymal transition

Question 40

What are some venous system abnormalities which can occur?

Answer 40

SVC is on the wrong side IVC is absent Double IVC Double SVC

Question 41

When do the cardinal veins develop?

Answer 41

5th to 7th week

Question 42

When does the lymphatic system develop?

Answer 42

end of the 6th week

Question 43

how many primary lymph sac develop?

Answer 43

6

Question 44

Name the six primary lymph sacs?

Answer 44

Two jugular lymph sacs, two iliac lymph sacs, one retroperitoneal lymph sac, one chyle cistern

Question 45

Name two abnormalities which can occur with lymphatic system?

Answer 45

- Congenital lymphedema – Dilation of lymphatic vessels | - Cystic hygroma – lump in neck (downs syndrome)

Question 46

what three changes to foetal circulation occurs after birth?

Answer 46

1. Ductus venosus becomes the ligamentum venosum of the liver 2. Oval foramen closes after birth by tissue proliferation and adhesion of septal structures 3. Ductus arteriosus obliterates to form ligamentum arteriosum 1. Ductus venosus - Bypass blood from the umbilical vein to IVC. Regulated by a sphincter (physiological sphincter) 2. Oval foramen - Diverts blood from the right atrium to the left atrium 3. Ductus arteriosus - Diverts blood from the pulmonary trunk into the descending aorta

Question 47

What does PDA stand for?

Answer 47

patent ductus arteriosus (atrial septal defect)

Question 48

What causes PDA?

Answer 48

Cause – when there is a fistula between the aorta and the pulmonary trunk from failure of muscular wall to contract respiratory distress syndrome (Low O2) and lack of surfactant in the lungs

Question 49

Is PDA more common is females or males?

Answer 49

females

Question 50

what infection is PDA sometimes associated with?

Answer 50

Rubella

Question 51

What is coarctation of the aorta?

Answer 51

when the aorta becomes narrowed near or opposite the ductus arteriosus 90% of cases the narrowing is opposite the ductus arteriosus

Question 52

What can be a clinical sign of coarctation?

Answer 52

peripheral pulses; popliteal, dorsal pedis and posterior tibial will be weaker or absent.