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Respiratory System > 16. Lung Development > Flashcards

16. Lung Development Flashcards

1
Q

What are the 4 phases of intrauterine lung development?

A 
• Embryonic (0-7 weeks)
- tracheal bud forms from the foregut (week 4-5)
- main bronchi
• Pseudoglandular (5-17 weeks)
- conducting airways
- bronchi and bronchiole
- morphogenesis into mesenchyme
- development of cartilage, glands and smooth muscle
• Canalicular (16-27 weeks)
- respiratory airways
- blood gas barrier starts to develop (thinning epithelium)
- epithelial differentiation (Type I and II)
• Saccular/Alveolar (28-40 weeks)
- alveoli appear
- surfactant detectable
- infant becomes viable
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2
Q

What happens to the lungs postnatally?

A
  • Alveoli multiply and enlarge in size with chest cavity

* Development into adolescence

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3
Q

How do the lungs heal from pneumonia in children compared to adults?

A
  • Children - reversible effect, should return to normal due to continuous development
  • Adults - tend to scar
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4
Q

What is vasculogenesis and how does it occur?

A
  • Forming of the blood vessels
  • Occurs along the frame that the airways create
  • Develop in the canalicular phase
  • Pulmonary artery branching follows bronchial branching (week 16)
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5
Q

What is a hypoplastic lung and how can it be seen?

A
  • Interruption to bronchial branching
  • Development of a small lung with little branching
  • Isotope ventilation scan - poor air supply to the lung
  • Isotope perfusion scan - poor artery development
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6
Q

How many lungs have after 56 days of development?

A
  • 3 lobes on the right

* 1 lobe on the left

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7
Q

Describe the mechanism of formation of alveolar walls

A

• Saccule Wall
- epithelium on both sides with double capillary network
- myofibroblasts and elastin fibres at intervals in the wall
• Secondary septa develop from the wall led by elastin produced by the myofibroblast
- capillary lines both sides with matrix between
• Capillaries have coalesced to form one sheet alveolar wall
- thinner and longer with less matrix
- muscle and elastin at the tip
• Process continues into the 3rd trimester - larger SA
• Continues into life

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8
Q

What is primary ciliary dyskinesia?

A
  • aka Kartagener’s syndrome
  • Malfunction in movement
  • Right lower lobe collapse
  • Dextrocardia
  • Possible total situs inversus
  • Absence of outer and inner dynein in cilia
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9
Q

What is laryngomalacia?

A
  • Incomplete rings posteriorly in larynx
  • Irregular plates
  • Calcify with age
  • Malacia - softening of the airway so its prone to collapse ( => occlusion)
  • Malcic segment - localised
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10
Q

What is agenesis and what causes it?

A
  • Complete absence of the lung and vessel
  • Very rare
  • Interrupted blood flow in first month of development
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11
Q

What is aplasia?

A

Blind ending of bronchus (no lung or vessel associated with it)

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12
Q

What is hypoplasia and what causes it?

A

• Bronchus and rudimentary lung are present
• Reduced in size and number
• Usually secondary and caused by a lack of space
• Intrathoracic or extrathoracic
- caused by hernia of diaphragm, chest wall pathology, oligohydramnios, lymphatic/cardiac mass
• Lack of growth, caused by:
- congenital thoracic malformation
- Cystic Pulmonary Airway Malformation (CPAM/CCAM) (defect in pulmonary mesenchyma, normal blood supply)
- Type 2 CCAM - multiple cysts
• Congenital Large Hyperlucent Lobe
- progressive lobar expansion
- cartilage fails and results in a one-way valve like effect
- extrinsic compression, alveoli expand
• Intralobar sequestration
- abnormal segment share of visceral pleura
- abnormal blood supply
- lower lobe is more common

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13
Q

What can “insults” to the dividing bronchus lead to?

A
  • Agenesis (early malfunction)
  • Local lesion
  • Malformation of systemic supply
  • Malformation in the lung
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14
Q

How does a pregnant mother smoking affect the development of a child’s lung?

A
  • Increased respiratory movements and changes in thoracic pressures
  • Removed soft tissue support and interstitial tissue development
  • Reduced elasticity of alveoli
  • Reduced airway diameter
  • Reduced support - wheezy infant
  • COPD at old age
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15
Q

What is special about the cells at the tips of the buds in lung development?

A

• Epithelial cells at tips
- highly proliferative multipotent progenitor cells
- differentiate into a wide range of cells
- depending on different growth factors
• Cells behind the tip divide and differentiate into the various cell types

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16
Q

What are the different growth factors involved in lung development?

A

Inductive
• FGF - branching morphogenesis
• EFG - epithelial proliferation and differentiation
- e.g. VEGF - surrounds the lung bud, induces differentiation in the mesenchyme, coalesce to form capillaries, airways act as a structural guide

Inhibitory
• TGF-beta - matrix synthesis and surfactant production, inhibits the proliferation of epithelium & blood vessels
• Retinoic acid - inhibits branching

17
Q

What is primary and terminal apnoea and how is it dealt with?

A
  • Failure of attempted breathing at birth (could be umbilical strangulation)
  • Terminal apnoea - 2nd attempt with failure - decreased blood pressure, maintained heart rate
  • Resuscitation - if delivery of oxygen fails following terminal apnoea. Results in an increase in heart rate and BP.
  • Apgar score - determines severity of apnoea and need for resuscitation
18
Q

How does the lung develop following birth?

A

• Loss of alveolar elasticity - reduced compliance
• Similar elasticity in infants and elderly (increased susceptibility to problems)
• Lung function increases to a point, then decreases with age
• Respiratory diseases increase the reduced function later in life
• Increased birth weight - increased lung function in adult life
- premature babies - increased risk of reduced lung functio

19
Q

What are the lungs like at birth?

A
  • Small volume relative to body weight
  • All airways differentiated
  • 33-50% of the alveoli present
  • Most arteries and veins present
20
Q

What are the mechanisms to increase flow after birth?

A

• Expansion of alveoli causes dilation of arteries
- stimulates release of NO
- NO and PGI2 can also be used as synthetic dilators
• Vasoconstrictor inhibitors present from foetal life
• Oxygen is the final stimuli - relaxes the smooth muscle
• Airway resistance falls
• Lung compliance rise takes 24 hours
• Lymphatic system removes fluid filling lungs - lungs remain stiff until this is done

21
Q

How do the blood vessels change at birth?

A
  • Decrease in pulmonary vascular resistance
  • 10-fold rise in pulmonary blood flow
  • Rapid increase in arterial lumen diameter and wall thins (maintained through artery growth)
  • Chemo-receptors and respiratory centre reset
  • Change in cell shape and cytoskeletal organisation
22
Q

Describe the circulation in a foetus

A
  • Mostly bypasses the lungs
  • Placenta => right atrium => right ventricle or left atrium (through foramen ovale)
  • Some goes from the right ventricle to the lung (via pulmonary trunk)
  • Most goes from the right ventricle to the aorta (via the ductus arteriosus) as pulmonary artery pressure > systemic artery pressure
23
Q

How does circulation change at birth?

A
  • Massive CNS stimulation due to change in environement
  • Low pressure placental circulation cut => rise in systemic arterial pressure
  • Lung aeration => fall in pulmonary arterial pressure (as lungs stretch)
  • Increased PO2 and decreased PCO2
  • Ductus arteriosus closes due to changes in prostaglandings
  • Foramen ovale closes due to increase in left atrial pressure (due to rise in systemic arterial pressure)
24
Q

What happens to the surfactant in a foetus?

A

• Once secreted by the lamellar bodies, these bodies create a force resulting in distension, keeping the airways open at lower pressures
• Generated in late 2nd/early 3rd trimester - premature babies at risk of alveolar collapse
• Idiopathic respiratory distress syndrome: alveolar collapse => hypoventilation and hypoxic acidosis => pulmonary vasoconstriction
- baby grunts to try and raise pressure
- continuous ventilation required but surfactant can be replaced

25
Q

How can lung function be measured?

A
  • Forced expiratory measurements made using a pneumotachograph
  • Change in flow-volume loop

Respiratory System (18 decks)

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