Embryology

Question 1

Describe the development of IV septum

Answer 1

1. Common ventricle formed by: primitive ventricle, bulbous cordis & conus cordis
2. Separated into left & right by formation of IV septum
3. IV septum developed from: muscular septum, membranous septum, conus septum, spiral septum
4. Muscular septum → forms the main bulk; formed from floor of primitive ventricle
5. Membranous septum → arises from wall of ventricle in the adsorbed bulbous cordis area
6. Conus septum → arises from wall of ventricle in the adsorbed conus cordis area
7. Lower part of spiral septum → forms within the truncus arteriosus
8. These 4 embryonic structures fuse together to form the IV septum

Question 2

Explain the embryological basis of a tracheoesophageal fistula

Answer 2

1. Trachea is formed by resp. diverticulum which pouches out of ventral aspect of upper gut tube
2. Process begins @ 4th week of IUL
3. First, there is only a ridge separating the developing resp. diverticulum from the foregut (the tracheoesophageal septum)
4. After, the foregut & lung bud get separated maintaining communication only via the laryngeal orifice
5. Abnormalities of the partitioning of tracheoesophageal septum can occur (tracheoesophageal fistula)

*In babies, they can choke when feeding due to the obstruction and they tend to regurgitate

Question 3

Congenital abnormalities of GIT

Answer 3

→ Vitelline fistula:
1. Vitelline duct connects primary mid gut loop to yolk sack through the umbilicus (in foetus)
2. In adults, this connection atrophies
3. Duct may be persistent (in some cases) causing a potent vitelline fistula
4. Causes SI to be connected to outer environment & faecal matter may be seen at umbilicus

→ Vitelline cyst :
1. Some instances, vitelline duct becomes ligamentous of its extremities causing a cyst in the middle
2. May cause volvulus of the SI leading to strangulation & atresia

Question 4

Pancreatic anomalies

Answer 4

1. Agenesis (failure to develop)
2. Congenital cysts
3. Annular pancreas

Question 5

Diverticulosis

Answer 5

1. Condition where bulbous pouches of peritoneum that are distended with fat (appendices epiploicae) project in places from the serous coat
2. Blood vessels perforate the muscle wall & through these vascular perforations, mucous membrane can herniate
3. Inflammation of these mucosal hernia is known as diverticulosis

Question 6

What has fenestrated capillaries?

Answer 6

1. Kidneys
2. Exocrine glands
3. Choroid plexus
4. SI

Question 7

Mixing of blood in the foetus

Answer 7

1. LIVER: left umbilical vein → portal vein
2. RA: IVC → SVC
3. LA: RA → pulmonary veins
4. ARCH OF AORTA: LV → pulmonary trunk

• oxygenated → deoxygenated

Question 8

List the cardiac defects

Answer 8

1. Atrial septal defect (ASD)
2. Ventricular septal defect (VSD)
3. Persistent truncus arteriosus
4. Tetralogy of Fallot
5. Dextrocardia

Question 9

State the embryological basis of Tetralogy of Fallot

Answer 9

1. Due to unequal division of the conus; results from ANT displacement of conotruncal septum
2. Leads to:
   → Pulmonary infundibular stenosis
   → Overriding of the aorta
   → Ventricular hypertrophy
   → } VSD