12.6 Fetal Development and Transition Flashcards
What are the five stages of lung development?
- Embyronic
- Pseudoglandular
- Canalicular
- Saccular
- Alveolar
Which layer of the embryo is lung epithelium derived from?
Ectoderm
What is mesenchyme
A loose meshwork of embryonic connective tissue
What germ layer is the surrounding mesenchyme of the lungs during development derived from?
Mesoderm
During what weeks does the embyronic period of lung development occur?
4-7 weeks post conception
During what weeks does the pseudoglandular period of lung development occur?
5-17 weeks post conception
During what weeks does the canalicular period of lung development occur?
16-26 weeks post conception
During what weeks does the Saccular period of lung development occur?
26-36 weeks post conception
During what time does the alveolar stage of lung development occur?
36 weeks PC until 3 years after birth
What occurs during embryonic lung development?
Left and right lung buds appear from the foregut endoderm. Lobular structure in place by end of week 5.
What occurs during pseudoglandular lung development?
- Airway tree is laid down
- Glands, smooth muscle and blood vessels develop
- Lungs fill with fluid
- Cells begin to differentiate, giving rise to epithelium and cartilage
What occurs during canalicular lung development?
- Existing airways widen
- Final rounds of epithelial branching to produce alveoli
- Future alveoli widen, surrounding mesenchyme thins
- Capillary networks come closer to distal epithelium (diagram)
What occurs during saccular lung development?
- Walls of terminal saccules thin, and saccules become completely wrapped in capillaries
- Epithelium differentiation continues, type 2 cells secrete surfactant
What occurs during alveolar lung development?
- Alveoli are formed as septae grow within distal saccules
What are the names of the different shunts in foetal circulation?
- Ductus venosus
- Ductus arteiosis
- Foramen Ovale
Describe the structure and function of the ductus venosus
- Shunts blood into the baby’s inferior vena cava, bypassing the liver
Describe the structure and function of the foramen ovale
- Shunts blood from the right atrium to the left atrium, bypassing the mostly non-functional lungs
REMEMBER: FOSSA OVALIS
Describe the structure and function of the ductus arteriosis
- Shunts blood from the pulmonary artery to the aorta, further bypasing the lungs
What stimulates the respiratory centres in a baby’s brain as it is being born?
- Compression of umbilical blood vessels during labour increases CO2
- Tactile and cold stimuli also stimulate breathing
List three processes that assist in the removal of lung fluid around birth
- Contractions help to expel some fluid
- Sodium is reabsorbed by respiratory epithelium, causing absorption of fluid (stimulated by surges in cortisol and thyroid hormone concentrations)
- Early inspiration creates trans-epithelial pressure gradient that drives fluid into lung tissue and out of airways
What causes closure of the foramen ovale?
- Lungs secrete vasodilators as fluid is removed, decreased right atrial pressure
- Left atrial pressure increased as the baby is disconnected from the low-pressure environment of the placenta
- This pressure gradient causes the flap across the foramen ovale to close
Describe the closure of the ductus arteriosis
- After birth direction of blood flow reverses, diverting blood to the lungs
- As oxygen increases, smooth muscle in the DA contracts, and subsequent remodelling causes DA closure
Describe the loss of function of the of the ductus venosus
- Umbilical cord is clamped/becomes occluded due to swelling of whartons jelly in cold environment
- Umbillical vessels degenrate into ligaments, thus the ductus venosus loses its functions
