Congenital Abnormalities

Question 1

Describe the development of the lungs.

Answer 1

5 stages:

1. Embryonic stage:
   - Laryngo-tracheal groove (caudal to pharynx, on floor of foregut) extends caudally into splanchnic mesoderm (SM later forms CT of lung)-> lined with endodermal cells which later become bronchial tree.
   - Tracheo-oesophageal septum separates trachea from oesophagus.
   - Tracheal outgrowth bifurcates to form 2 lung buds caudally.
2. Pseudoglandular development (no gas exchange):
   - Bronchial tree develops to level of terminal bronchioles
   - Lung resembles exocrine gland
   - Blood vessels start forming
3. Canalicular stage (early foetal; some gas exchange possible)
   - Bronchi and bronchiole lumens enlarge
   - Respiratory bronchioles form
   - Highly vascularised
4. Terminal sac stage
   - Terminal sacs form (clusters of enlarged air spaces)
   - Terminal sac epithelium thins as more P2 (surfactant) differentiates into P1 (gas exchange).
5. Alveolar stage
   - Alveoli form with capillaries bulging into their lumens
   - Surfactant production continues.

Question 2

Name a congenital abnormality of the lung.

Answer 2

Hypoplasia

Question 3

Describe the formation of the diaphragm.

Answer 3

1. Septum transversum (tendinous component) partially separates thoracic and abdominal cavity.
2. Pleural peritoneal folds (muscular component) fuse with dorsal mesentery of oesophagus and septum transversum, completing the partition between thoracic and abdominal cavity

=> primitive diaphragm

Question 4

What congenital defects can you get in diaphragm?

Answer 4

Diaphragmatic hernia (abdominal organs displaced into thoracic cavity)

• pleural peritoneal hernia
• hiatal
• retrosternal/parasternal (weakness in costal diaphragm)
• pericardiac

Question 5

Name a congenital pericardial defect.

Answer 5

Defective formation of pleuropericardial membranes (usually L side). In rare cases part of atrium herniates into pleural cavity with each heartbeat.

Question 6

Describe the development of the foramen ovale.

Answer 6

1. In L atria, septum primum grows from dorsal atrial wall to endocardial cushions - foramen primum (disappears eventually)
2. Same time foramen secundum appears IN septum primum
3. Septum secundum grows on R of septum primum and partially covers foramen secundum
4. This complex valve opening = foramen ovale

Question 7

Name some congenital atrial septal defects.

Answer 7

Persistent foramen ovale
Ostium primum defect (cats)
Ventral atrial septum

Question 8

Describe the development/fates of the aortic arches.

Answer 8

1st & 2nd: degenerate/may contribute to minor vessels in the head.

3rd –> common & internal carotid arteries –> buds into external carotid arteries

4th:

• L –> definitive aortic arch
• R –> contributes to R subclavian artery

6th:
- buds from arches –> pulmonary arteries
- Proximally contributes to pulmonary trunk
- L distal arch–> ductus arteriosus (channel between pulmonary trunk & aorta)
- R arch distally disintegrates

Question 9

What is a vascular ring abnormality?

Answer 9

A persistent aortic arch.
2 possibilites:
- humans: trachea constricted
- Dogs/cats: double aortic arch around trachea AND oesophagus

Question 10

Describe the linkage of vascular network of foetus & extraembryonic membranes.

Answer 10

Yolk sac

• vitelline vessels (sac wall)
• form simultaneosly with intraembryonic network and link
• 1st nucleated RBC form from cells of vascular cords
• Allantois extends from hindgut as a vascular membrane; its blood vessels are continuous with umbilical arteries/veins