lung development

Question 1

what is the embryonic phase of branching morphogenesis?

Answer 1

• shows development of the lungs in increments of 7 days, 7 days and then 14 days
• the left lung develops 2 lobes
• the right lung develops 3 lobes
• induvidual lobes might be affected and show up on x rays
• things like oedemas might be found

Question 2

what is the pseudoglandular phase of branching morphogenesis?

Answer 2

• it is characterised by branching morphogenesis of airways into mesenchyme
• Pre-acinar airways are then all present by 17 weeks
• Middle lobe of right lung is most often affected by aspirations as objects naturally fall into it.
• Development of cartilage, gland and smooth muscle tissue begins and continues into Canalicular phase.
• the bronchial cartilage displays incomplete rings

Question 3

what factors drive branching morphogenesis?

Answer 3

• lung buds - have a consistent appearance during airway formation
  (there are epithelial cells at the tips which are highly proliferative and therefore can differentiate as needed)
• genetics and transcription factors are also involved

Question 4

what is vasculogenesis and angiogenesis?

Answer 4

• the pulmonary vessels develop along side the airways

- a circulation is present by 5 weeks gestation

Question 5

what is the canalicular phase ?

what happens in this phase?

Answer 5

• happens between 16 -27 weeks
• the airspaces at the peripheries enlarge
• the epithelium thins allowing efficient gas exchange
• epithelial cells differentiate into type 1 and type 2 cells
• at 24 weeks surfactant is available
• babies are viable at 24 weeks

Question 6

what is the the saccular/ alveolar phase?

what happens in it?

Answer 6

28 -40 weeks

• the alveolar walls are formed
• Alveoli appear from 29/40 weeks and multiply up to the age of 3 while 1/3rd of adult alveoli number are formed by term

Question 7

what happens at the 29th week, 34th week and 38th week of formation of alveolar walls?

Answer 7

♣ 29th week – Saccule wall is formed; epithelium on both sides with a double capillary network.
♣ 34th week – Secondary septa develop from the wall led by elastin produced by myofibroblasts.
♣ 38th week – Capillaries have coalesced to form ONE sheet alveolar wall, thinner and longer with less matrix. Muscle and elastin form at the tip.
♣ At 40 weeks, there is about 150 x 106 alveoli.

Question 8

*** show a diagram of an alveoli:

Answer 8

*** insert

Question 9

what is the lungs at birth in man?

Answer 9

• the volume is small and related to body weight
• all airways are present and differentiated
• there is a blood gas barrier as in an adult
• 33- 55% of alveoli allow normal gas exchange
• most of the arteries and veins are present

Question 10

what possible mechanisms are there to increase flow after birth?

Answer 10

• expansion of alveoli dilates the arteries
• Expansion stimulates release of vasodilator agents
• Inhibition of vasoconstrictors present during fetal life
• Direct effect of oxygen on smooth muscle cells

Question 11

how do the blood vessels change at birth?

Answer 11

• decrease in pulmonary vascular resistance
• there is a 10 fold increase in pulmonary blood flow
• arterial lumen increases and the wall thins rapidly
• Change in cell shape and
  cytoskeletal organisation not loss of cells
• Once thinning has occurred, arteries grow and maintain a relatively thin wall

in the end there is a low pressure low resistance pulmonary vascular system

Question 12

how does the alveoli grow during childhood and adolescence?

Answer 12

• Alveoli increase in number up to 9-13 years
• Adult alveolar number (300-600 million)
• Alveoli increase in size and complexity to increase surface area until body growth complete after adolescence(x20)
• Arteries, veins and capillaries increase alongside the alveoli (cap volume x35)

Question 13

what is the normal bronchial cartilage like?

Answer 13

• normally there are incomplete rings that form posteriorly
• irregular plates
• they calcify with age

Question 14

what happens with Congenital bronchial cartilage defects

Answer 14

• Generalised – laryngotracheomalcia

- Localised – malacic segment which may occur due to external compression

Question 15

what are lung growth anomalies?

Answer 15

• Agenesis – complete absence of lung and vessel
• Aplasia – blind ending bronchus, no lung or vessel
• Hypolasia – bronchus and rudimentary lung are present, all elements are reduced in size and number

Question 16

info about agenesis?

Answer 16

Abnormal flow in 4th week
Commonly associated with other pathology
Mediastinal shift towards an opaque hemithorax

Question 17

what is under development of the lungs?

Answer 17

• hypolasia
• common usually secondary
• lack of space
• can be intrathoracic or extrathoracic
• Lack of growth
  Congenital Thoracic
  Malformation CTM

Question 18

what is cystic pulmonary airway malformation?

Answer 18

• this is a defect in the pulmonary mesenchyma
• this is due to abnormal differentiation in the 5th to 7th week
• there is normal blood supply
• happens for 1 in 8300 - 35000

Question 19

what is type 2 CCAM?

Answer 19

• Multiple small cysts
• May be associated with renal agenesis, cardiovascular defects, diaphragmatic hernia and syryngomyelia
• Histologically bronchiolar epithelium with overgrowth, separated by alveolar tissue which was underdeveloped

Question 20

what is Congenital Lobar Emphysema?

Answer 20

• Progressive lobar overexpansion

- Underlying cause
Weak cartilage
Extrinsic compression
One way valve effect
Alveoli expand (not disrupted)

• Males > females
  CHD association

Question 21

what is intralobar Sequestration?

Answer 21

• 75% of pulmonary sequestrations
• Abnormal segment share visceral pleural covering of normal lung
• No communication to tracheobronchial tree
• Lower lobe predominance
  L > R