Respiritory Development Flashcards
Explain the role that local mesenchyme tissue plays in lung development
Regional specificity of the mesenchyme determines the differentiation of the developing respiratory tube.
In the developing mammal, the respiratory epithelium responds to local signals from mesenchyme
tissue in two distinct fashions.
In the region of the neck, it grows straight, forming the trachea.
Surrounded by tracheal mesenchyme = straight bronchi
After entering the thorax, it branches, forming the two bronchi and then the lungs.
Retained lung mesenchyme = branching of bronchus
Describe the formation of the trachea and lung buds from the embryonic endoderm
The function of the embryonic endoderm is to
Construct the linings of two tubes within the body.
The first tube, extending throughout the length of the body, is the digestive tube. Buds from
this tube form the liver, gallbladder, and pancreas.
The second tube, the respiratory tube, forms as an outgrowth of the digestive tube, and it
eventually bifurcates into two lungs.
Describe how the formation of lung buds occur
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).
They develop by branching morphogenesis
C) Final septation distinguishes pharynx from larynx and thus trachea from oesophagus
Outline how the lower respiritory structure form
Subsequent divisions generate bronchi, then bronchioles and finally the alveoli
Majority divisions occur in utero (17 of 24)
Further postnatal maturation (7 more divisions)
At birth LUNGS are IMMATURE but functional
Describe the various stages of lung development
Embryonic
Formation of major airways and budding of bronchial branches
Pseudoglandular
Formation of the bronchial trees & portions of the respiritory parenchyma
Acinus is formed
Canalicular
Last generations of lung periphery formed
Epithelial differentiation
Air blood barrier formed
Saccular
Expansion of air spaces
Surfactant is detectible in amniotic fluid
Alveolar
Secondary septations - maturation of the alveolar during the end of fetal development and a
period of time after birth
In all species, lung development continues postnatally (in litter-bearing species this maybe a really long time)
Describe how the timing of the lung development stages varies between different domestic animal species
Stage Man (weeks) Sheep (days) Rat (days)
Embryonic 3-6 (7-15%) 17-40 (11-27%) ?-13 (-61%)
Pseudoglandular 6-16 (15-40%) 40-80 (27-55%) 13-18 (61-85%)
Canalicular 16-26 (40-65%) 80-120 (55-82%) 18-20 (85-95%)
Saccular 26-40 (65-100%) 120-145 (82-100%) 20-21 (95-100%)
Alveolar 32- 2yr (80-270%) 120-0.5y (82-125%) 21- 42 (100-200%)
Define polytocous
litter bearing
Define monotocous
produce single offspring
Define altricial
dependent at birth on each other and the mother
Define precocial
Increased independence and is able to walk within hours of birth
List the 4 factors which influence lung development
Intra-thoracic space
Intra-uterine space
Fetal breathing movements
Lung liquid production
Explain how intra-thoracic space can modulate lung development
Size of space for lungs to develop in
Impaired by conditions like congenital diaphragmatic hernia.
This is a relatively common condition, affecting around 1:4000 births – here the diaphragm fails to close in the fetus and the abdominal contents enter into the thoracic cavity, compressing the lungs and impairing lung growth.
Explain how intra-uterine space can modulate lung development
Size of uterus, amount of amniotic fluid
Fetal lungs need adequate intra-uterine space
Impaired by oligohydramnios which is a lack of amniotic fluid.
A reduction in amniotic fluid volume can lead to uterine compression and changes in fetal posture – and this is quite a common cause of pulmonary hypoplasia.
Too much fluid in the within the fetal lung is known as polyhydramnios
Explain how fetal breathing movements can modulate lung development
Frequency, intensity
The normal, unstressed fetus practices breathing before birth and regular activation of the respiratory muscles is essential for the normal development of the fetal lungs.
During practice breathing, there is relatively little change in lung volume, as it only causes slight movement to the water.
However, the importance of fetal breathing movements can be demonstrated experimentally as abolishing them by denervation of the diaphragm leads to hypoplasia of the lungs (lung hypoplasia)
Explain how lung liquid production can modulate lung development
How much produced…
Lungs need an adequate secretion of fluid to help maintain the appropriate balance of volume and pressure during development.
Lungs secrete liquid into lung cavity which helps to inflate them. This helps lungs grow.
If prevent secretion, lungs or lobes do not develop e.g. right lobes on figure (contrast with left lobe)
Lung liquid is produced from around mid-gestation – it is a secretory product of the pulmonary epithelium and is either swallowed or enters into the amniotic fluid. The secretions are thought to be induced locally (each lung)
