Embryology Flashcards
What are the 5 stages of respiratory system development?
1) Embryonic (wk 0-5)
- initial budding and branching
2) Pseudoglandular (wk 6-16)
- branching completes (till terminal bronchioles)
3) Canalicular (wk 17-24)
- Respiratory bronchioles
- formation & widening of canals
4) Saccular (wk 25-birth)
- terminal sacs and capillaries
5) Alveolar (8mths in utero-)
- alveoli development
What occurs during the embryonic stage of respiratory development (1st 5 weeks)?
1) Lung bud forms → tracheoesophageal septum/separation
2) Budding and branching of primary, secondary, tertiary bronchi
Where does the lung bud/respiratory diverticulum arise from?
outpouching of developing foregut
How do the trachea and oesophagus separate during fetal development?
Embryonic phase:
Tracheoesophageal folds emerge and fuse in the midline
→ Tracheoesophageal septum
→ separation
How are the bronchi formed during fetal development?
During 2nd half of embryonic phase:
1) Respiratory diverticulum bifurcates into left and right bronchial buds → primary bronchi
2) Primary bronchi bud and branch into secondary bronchi:
- 2 for left lung / 3 for right (supply each lobe)
3) Secondary bronchi bud and branch into tertiary bronchi (supply each bronchopulmonary segment)
What occurs during the pseudoglandular stage of respiratory development (wk 6-16)?
Tertiary bronchi bud and branch into bronchioles and terminal bronchioles within bronchopulmonary segments
When do bronchioles start to develop in a fetus?
6-16 weeks
What occurs during the canalicular stage of respiratory development (wk 17-24)?
1) Bronchioles bud and branch into respiratory bronchioles → alveolar ducts
2) Formation and widening of canals
When does canalisation of the respiratory mesenchyme occur in a fetus?
17-24 weeks
What occurs during the saccular stage of respiratory development (wk 25-birth)?
Alveolar ducts → alveolar sacs
(production of pneumocytes + surfactant)
When do fetuses start producing surfactant?
from 25wks (saccular stage)
What occurs during the alveolar stage of respiratory development (8mths in utero-childhood)?
1) Proliferation of alveoli
2) Maturation of alveoli
3) ↑Vascularisation (pulmonary capillaries)
During fetal life, the lungs are _______ as the alveoli are ________. Hence, pulmonary resistance is (high/low).
Lungs are filled with fluid, alveoli are collapsed.
- pulmonary resistance is high
During fetal life, the fetus receives oxygen from __________. Thus, the heart has _____ to ________.
Fetus receives oxygenation form placenta
Heart has valves to bypass lungs
At birth, the baby takes a breath, causing the lungs to _____ and pulmonary resistance to (increase/decrease). Hence, the cardiac shunts (open/close).
Inflate with air
- pulmonary resistance decreases
- cardiac shunts close
What are the formative components of the diaphragm?
1) Somites (muscle progenitors)
2) Septum transversum
3) Pleuroperitoneal folds
Where is the septum transversum located in a fetus and when does it develop?
22 days in:
- in region of developing cervical vertebrae
- caudal/posterior to the heart
During fetal development, the developing diaphragm moves from (up/down) to its final position.
Down from cervical to thoracic region
What is a fistula?
An abnormal connection between two body parts, such as an organ or blood vessel and another structure
What is the pathogenesis of a tracheoesophageal fistula?
Failure of Tracheoesophageal folds to fuse in the midline
What are 3 clinical features of a baby with a tracheoesophageal fistula?
1) Polyhydramnios (fetal failure to absorb amniotic fluid → accumulation in womb) esp in atresia
2) Failure to thrive
3) Aspiration/↑risk of lung infection
How many types of tracheoesophageal fistulas are there?
5
A: atresia w/o fistula
B: atresia w proximal fistula
C: atresia w distal fistula
D: atresia w proximal & distal fistula
E: fistula w/o atresia
Which form of tracheoesophageal fistula is most common?
Type C
(Atresia w distal fistula)
How are tracheoesophageal fistula diagnoses confirmed?
1) Imaging (Xray)
- feeding tube unable to enter GIT
- GIT distended w air
2) Scope (endoscopy)
How is a tracheoesophageal fistula treated?
Surgical repair/closure
What is Newborn Respiratory Distress Syndrome (Hyaline Membrane Disease)?
Alveoli collapse due to insufficient surfactant production in immature lung of premature infants
On average, how preterm do babies have to be to be at risk of Newborn Respiratory Distress Syndrome?
Before 35 weeks (sufficient surfactant levels)
↑risk the more preterm it is
What are 2 clinical features of a baby with Newborn Respiratory Distress Syndrome?
1) Cyanosis
2) Respiratory distress (rapid & laboured breathing)
- Clinical sign: indrawing of ribcage ← use of accessory muscles
How does Newborn Respiratory Distress Syndrome appear on a chest X ray?
Ground glass appearance/opacification
- ↑ patchiness
- ↓ lung vol.
What are 3 ways babies with Newborn Respiratory Distress Syndrome are treated?
1) Antenatal corticosteroids
- accelerate lung development and surfactant production
2) Surfactant therapy
- artificial injected through airways
3) Continuous Positive Airway Pressure (CPAP)
- keep airways and alveoli open
What is the pathogenesis of a Congenital Diaphragmatic Hernia?
Failure of normal closure of the pleuroperitoneal membrane during fetal development
On which side do Congenital Diaphragmatic Hernia usually occur?
Left posterolateral diaphragm
What are some structures that are affected in a Congenital Diaphragmatic Hernia?
1) Heart
2) Lungs
3) Intestines
4) Liver
5) Diaphragm
What are 3 clinical features in a baby with a Congenital Diaphragmatic Hernia?
1) Scaphoid abdomen
(herniated of abdominal contents into chest)
2) Mediastinal shift
- Lung displacement → respiratory distress + pulmonary hypertension
- Cardiac displacement → change in location of apex beat
3) Absent breath sounds
(over area of herniation)
How is a Congenital Diaphragmatic Hernia treated?
Surgical repair
