Embryology

Question 1

1. what is the name of the
   a) primitive mouth
   b) primitive gut
2. describe the movements of the primitive heart
3. what is the mesodermal precursor of the diaphragm
4. How does it move?
5. What is the coelom?
6. How does the septum transversum relate to the coelom?
7. What are the openings of the primitive diaphragm called?

Answer 1

1a) oropharyngeal membrane
1b) cloacal membrane
2. initially, heart is more cranial to the oropharyngeal membrane. Inward movements of the oropharyngeal and cloacal membranes (which constrict the yolk sac) tuck it underneath so it is found inferiorly to the oropharyngeal membrane
3. Septum Transversum
4. Moves along with heart due to folding of embryo
5. a fluid filled chamber formed by folding, which generates body walls
6. divides the coelom into peritoneal and pericardial cavities
7. pericardioperitoneal canals

Question 2

1. Describe how the lung buds develop?

2. what is the difference in lung bud development across the two sides?

Answer 2

1. evagination of ventral foregut wall
   then bifurcates into left and right bronchial buds
2. Right side bifucates into 3 secondary bronchial buds and left side bifurcates into 2 secondary bronchial buds. Represents the number of lobes of the lung

Question 3

1. How does the pericardium develop?

2. how do the pleura develop?

Answer 3

1. phrenic nerve and common cardinal veins are covered in a mesothelial lining. As they develop medially, they drag the mesothelial linings with them, and they stick together. This forms the PLEUROPERICARDIAL FOLDS. As they meet in the midline, they fuse to form a double membrane around the heart
2. lungs develop into the remaining mesothelial lining which forms the pleura

Question 4

1. How do the pericardioperitoneal canals close?
2. From which wall do the myoblasts move from?
3. From which cervical level do the myoblasts bring innervation from?
4. How does congenital diaphragmatic herniation occur?
5. how does lung compression hypoplasia occur?

Answer 4

1. development of pleuroperitoneal membranes from the dorsal walls
2. lateral
3. C3,4,5
4. if pericardioperitoneal canals fail to close
5. if myocyte migration is insufficient, and an area of the diaphragm lacks innervation

Question 5

1. what does the primitive heart form from?
2. at what end of the embryo does the primitive heart form?
3. what structure is this initially anterior to?
4. Describe the initial process in heart formation

Answer 5

1. cardiogenic mesoderm
2. anterior
3. oropharyngeal membrane
4. 2 cords develop in the cardiogenic mesoderm. A lumen develops within them, forming the paired heart tubes. The paired heart tubes then bulge towards the midline.

Question 6

1. which veins drain into the tubular heart? (3)
2. what does the arterial system of the heart consist of?
3. what is the outflow of channel of the heart called?
4. What do the vessels of the head and neck develop from?
5. What do the following pharyngeal arches give rise to?
   a) 1
   b) 2
   c) 3
   d) 4
   e) 5
   f) 6

Answer 6

1. common cardinal veins, vitelline veins and umbillical veins
2. dorsal aortae, which fuse to form the descending aorta, and aortic arches
3. aortic sac
4. aortic arches (AKA pharyngeal arch arteries)
   5a) largely disappears but persists as maxillary artery
   5b) largely disappears
   5c) common carotid, plus external and internal carotid
   5d) R subclavian and aortic arch
   5e) disappears
   5f) pulmonary arteries, ductus arteriosus and right subclavian

Question 7

1. what does the fused heart tube form?
2. what structure becomes the right ventricle?
3. what structure becomes the left ventricle?
4. How do the ventricles become separated?
5. How do the atria become separated?

Answer 7

1. cardiac loop
2. bulbus cordis
3. primitive ventricle
4. muscular tissue develops from floor of ventricles towards the endocardial cushions. It does not reach the cushions, leaving the interventricular foramen
   interventricular foramen is filled by growth of the endocardial cushions, which forms the membranous part of the septum that accomodates the AV bundles.
5. ridge from roof of common atrium grows towards the endocardial cushions - septum primium. It leaves a gap called the ostium primum
   a second septum (septum secondum) begins to develop.. It grows over the ostium primum, but does not completely cover it. Leaves an opening - foramen ovale.

Question 8

1. What structure gives rise to the pulmonary trunk and ascending aorta?
2. How do these structures divide?
3. What is tetralogy of fallot?
4. what is transposition of great vessels?

Answer 8

1. trunkus arteriosus
2. a septum develops medially from lateral walls as a spiral structure
3. unequal division of the trunkus arteriosus
4. result of spiral septum twisting in the opposite direction

Question 9

FOETAL CIRCULATION

1. how does oxygenated blood from the placenta travel to the heart? (3 vessels)
2. what happens in the right atrium
3. How can blood travel from RA to LA?
4. How can blood travel from pulmonary artery to aorta?
5. What happens to pressure on both circulatory sides upon lung breathing?
6. What does this do to the foramen ovale?
7. what does the following become?
   a) ductus arteriosus
   b) umbillical vein and ductus venosus
   c) umbilical artery

Answer 9

1. umbillical vein, ductus venosus and IVC
2. oxygenated blood from IVC and deoxygenated blood from SVC mix
3. via foramen ovale
4. via ductus arteriosus
5. pressure in right system decreases and pressure in left system increases
6. presses the septum primum and septim secondum together, closing the foramen, forming the fossa ovale
   7a) ligamentum arteriosum
   7b) round ligament of liver
   7c) medial umbilical ligament