Development of the Respiratory System Flashcards
This deck will only have exam-format questions on this topic. However, the first card is a lecture on this topic.
Outline the five stages of lung development in order beginning from the earliest.
(1) Embryonic
(2) Pseudoglandular
(3) Canalicular
(4) Saccular
(5) Alveolar
[Diagram]
Outline the events that occur in the embryonic stage of lung development.
(a) Formation of the respiratory diverticulum and septation of the foregut.
(b) Formation of the right and left bronchial buds. [Bronchial buds correspond to the principal bronchi (1st generation).]
(c) Main pulmonary vessels form.
Note: week 4-7
Outline the events that occur in the pseudoglandular stage of lung development.
(a) Branching of the airways to the terminal bronchiole (generation 16) [aka. formation of the remaining components of the conducting zone].
(b) Accompanying vasculature also forms.
Further notes:
[week 7:17]
Growth and expansion occurs into the intraembryonic coelom.
Intraembryonic coelom is the future pleural cavity.
Outline the events that occur in the canalicular stage of lung development.
(a) This is the phase of airway canalization.
(b) formation of the respiratory bronchioles [generation 17-19] and alveolar ducts
(c) formation of accompanying vasculature
(d) [Note that the epithelial lining of the airways is cuboidal.]
Note: week 17-26
Outline the events that occur in the saccular/terminal sac stage of lung development.
(a) ballooning of terminal ends of the airways [alt. formation of saccules]
(b) Type I cells appear, hence establish a primitive respiratory membrane.
Further notes:
[week 27-36]
Sufficient number of alveolar sacs and capillaries are present to enable infant survival.
Surfactant secretion occurs but it is still inadequate.
Outline the events that occur in the alveolar stage of lung development.
(a) expansion and thinning of the alveoli
(b) further surfactant secretion
(c) increased capillary network
(d) Note: week 36 - 2 years - it extends postnatally
Click on Answer to view notes on foetal lung fluid.
➤ The fetal lung is filled with fluid during gestation, producesd largely by pulmonary epithelial cells.
➤ The fluid is under higher pressure than the amniotic fluid - hence its efflux occurs - forming the basis of amniotic fluid analysis for surfactant to determine fetal pulmonary maturity.
➤Its removal begins shortly before delivery and continues for several hours after delivery - primarily via the pulmonary circulation and lymphatics.
➤ Delayed clearance of fetal lung fluid results in transient tachypnea of the newborn.
choanal atresia
Further notes:
Choanal atresia is a congenital disorder in which the nasal choanae, (i.e., paired openings that connect the nasal cavity with the nasopharynx), are occluded by soft tissue (membranous), bone, or a combination of both, due to failed recanalization of the nasal fossae during fetal development.
Identify the congenital anomaly: [Image].
Congenital High Airway Obstruction Syndrome (CHAOS)
Further notes:
This is caused by atresia and other conditions that cause obstruction of the trachea or larynx. This stunts the development of the lungs by preventing the flow of fluid into and out of the lungs, which is very important for expansion of the lung alveoli.
Name A to E: [Image].
A: esophageal atresia without tracheoesophageal fistula
B: esophageal atresia with proximal tracheoesophageal fistula
C: esophageal atresia with distal tracheoesophageal fistula
D: esophageal tresia with proximal and distal tracheoesophageal fistula
E: tracheoesophageal fistula without esophageal atresia
Further notes:
📝 Clinical presentations of A: 1. frothing at the mouth, 2. vomiting of breast milk, 3. inability to advance a nasogastric tube
📝 Type B presents similarly to A with choking.
📝 Type C presents similarly to A with distension of the abdomen due to entry of gases.
📝 Type E is diagnosed late.
Identify the congenital anomaly: [Image].
tracheomalacia
Further notes:
➤ tracheal wall “softening” due to an abnormality in the cartilaginous ring
➤ congenital immaturity of the tracheal cartilage resulting in partial collapse of the tracheal walls during increased airflow
Identify the congenital anomaly: [Image].
bronchial atresia
➤ focal obliteration of a bronchus
➤ the bronchus has no communication with the central airways
➤ the segment distal to the atresia becomes filled with mucus
➤ upper lobe bronchi are more frequently affected
Identify the congenital anomaly: [Image].
pulmonary agenesis
➤ unilateral absence of the mainstem bronchus (and its corresponding lung)
➤ caused by failed induction, arrest, unequal growth or destruction of the lung bud
