respiratory development

Question 1

how are lung buds formed? what other tissues grow in this manner?

Answer 1

by the process of branching morphogenesis
lay down respiratory tracts then add the surface area- many genes involved, the kidneys and mammary glands also grow like this.

Question 2

describe the formation of the respiratory system

Answer 2

Highly influenced by surrounding mesenchymal tissue.

A. Formation of laryngotracheal groove- this buds into two main bronchi.

B. Further budding may be unequal- e.g. 3x on right (3 right lobes) 2x on left (2 left lobes)- fixed in the genetic blueprint.

C. Final separation distinguishes pharynx from larynx and thus trachea from oesophagus. Branching is highly influenced by positional information. Signals are from surrounding mesenchymal cells. (Pharyngeal mesodermal cells contribute to heart development).

Question 3

Describe the role of local mesenchyme in the formation of the lungs

Answer 3

Prevents lungs from developing in the neck- extends down into the chest.

Left lobe- surrounded by
tracheal mesenchyme= straight bronchi- didn’t start branching.

Right lobe- retained lung
mesenchyme= branching of bronchus.

Lung-branching or tracheal-straight- is enabled by local signals from the mesenchymal tissue, such as local growth factors.

Question 4

Describe the further development of the lungs after the formation of the trachea

Answer 4

• subsequent divisions generate bronchi, then bronchioles and finally the alveoli
• majority of divisions occur in utero (17 of 24) and rest further postnatal maturation
• at birth, lungs are immature (dont work super well) but functional => need to be able to get rid of fluid and start exchanging air within minutes

Question 5

what is the trachea developed from

Answer 5

the foregut at the respiratory diverticulum

Question 6

describe the 5 different stages of lung development

Answer 6

1. embryonic
2. pseudoglandular
3. canalicular
4. saccular
5. alveolar

in all species lung development will contine post natally (in litter baring species, this may be a relatively long time

Question 7

what 4 factors influence lung development

Answer 7

• intra-thoracic space (size of space for the lungs to develop in)
• intra uterine space (size of uterus, amount of amniotic fluid)
• fetal breathing movements (fetus prepares for first breath by practicing breathing movements to strengthen muscles)
• lung liquid production

if there is an issue with any of the above = underdeveloped lungs and neonatal support needed. if only mild, manifests in exercise intolerance

Question 8

why is intra-thoracic space important for lung development

Answer 8

the lungs need sufficient intra-thoracic space in which to grow
- can be impraied by conditions like congenital diaphragmatic hernias (abdominal contents invade thoracic space if diaphragm doesnt close)

Question 9

why is sufficient intra-uterine space important for lung development

Answer 9

fetal lungs need adequate intra-uterine space in order to develop
- too little amniotic fluid causes uterine compression, too much compresses fetus

Question 10

why are fetal breathing movements important for lung development

Answer 10

in late gestation, the fetus develops respiratory muscles and matures alveoli by mimicing breathing movements. this only moves fluid around in the lungs but is hard work and helps muscles to develop in preparation for first breath

Question 11

why is lung liquid production important for lung development

Answer 11

• lungs secrete liquid into the lung cavity which helps inflate them and helps them grow.
• if secretion is prevented, lungs or lobes do not develop

Question 12

describe the role of glucocorticoids in lung maturation in utero

Answer 12

Glucocorticoids mature lung (steroid hormones from the cortex of the adrenal glands which effect glucose metabolism, enables development of all organs):
in order to reduce work of breathing
- increase elastin content
- thinning of alveolar wall and interstitial tissue
- differentiation of type 2 pneumocytes

in order to help lung inflation and prevent lung collapse
- increase in surfactant production
- increase in enzymes responsible for phospholipid synthesis

in order to produce more lung liquid
- increase in pulmonary beta adrenoceptors
- increase in expression of epithelial sodium channels and sodium potassium ATPase

in order to prepare for new gaseous environment
- increase antioxidant enzymes

Question 13

what is surfactant

Answer 13

• enables alveolar cells to touch one another without sticking
• 90% phospholipid, 10% protein
• made by type 2 pneumocytes in the lung
• fluid filled lungs have very low compliance (cant open) as water has high surface tension
• air filled lungs are very compliant due to surfactant reducing surface tension
• no surfactant = respiratory distress syndrome