Development of the Respiratory System Flashcards
Describe the development of the layers of the trilaminar embryo
- ectoderm develops a neural groove with the tips of the walls of the groove forming a neural crest
- lateral plate mesoderm divides into parietal (somatic) and visceral (splanchnic) mesoderm which becomes serous membranes
- parietal layer forms body walls
- visceral layer surrounds organs
Describe the process of lateral folding of the trilaminar embryo
- parietal layer of lateral plate mesoderm merges with ectoderm
at same time:
- pinching of the primitive yolk sac which becomes the gut tube
- visceral layer of lateral plate mesoderm envelopes gut tube
- leading edge of ectoderm and parietal layer of lateral plate mesoderm moves antero-medially to come together and fuse in midline
What are the results of lateral folding of the trilaminar embryo?
- a cavity which becomes thoracic, abdominal and pelvic cavity (continuous by pericardio-peritoneal canals until diaphragm forms)
- thoracic body wall from surface ectoderm and parietal layer of lateral plate mesoderm deep to it
- gut tube suspended by visceral layer of lateral plate mesoderm
- parietal layer of lateral plate mesoderm becomes parietal pleura
As lateral folding of the embryo occurs what other process is taking place?
- cranio-caudal folding also takes place
- head and tail folds meet 2 lateral folds at umbilicus
Describe the development of the lung buds
- in cervical portion of gut tube in ventral midline respiratory diverticulum appears
- respiratory diverticulum expands ventrally and towards the chest in front of the gut tube
- meanwhile tracheo-oesophageal ridges grow towards each other to separate respiratory diverticulum from gut tube
- diverticulum bifurcates into 2 branches which can later expand/dilate
- terminal ends of dilatations are lung buds that will become lungs
Describe the development of the pharyngeal arches
- 4-5 weeks of development pharyngeal arches appear separated from one another by pharyngeal clefts
- 5 pharyngeal arches (1,2,3,4,6) have a cartilaginous element (aortic arch), an artery and a nerve (cranial nerve)
Describe the position of the laryngeal opening and what the sections of the diverticulum develop into
- laryngeal orifice is between the epiglottal and laryngeal swellings
- upper end of diverticulum becomes larynx
- middle section of larynx becomes trachea
- lower end becomes tertiary bronchi, bronchioles and alveoli
What is the epithelium of the respiratory system derived from?
endoderm
What are the 4 overlapping stages of lung development?
- pseudoglandular
- canalicular
- terminal saccular
- alveolar
Why are the first 2 overlapping stages of development of the lungs not compatible with life?
As the sections involved in gas exchange has not been developed yet
When is surfactant secreted and what cells secrete them?
- from 20 weeks
- type 2 pneumocytes
From when can the foetus survive?
28 weeks
What are the 4 sources of origin of the diaphragm?
- pleura-peritoneal folds
- septum transversum
- mesentery of the oesophagus
- muscular in-growth from the body wall
Describe the development of the diaphragm
- pleura-peritoneal folds fuse with the septum transversum
- septum transversum forms central tendon of diaphragm
- contains myoblasts from somites in C 3,4,5 (phrenic nerve)
- crura develops from mesentery of oesophagus
- muscular in-growth occurs from the body wall
What causes diaphragmatic hernias?
failure in the normal development of one of the sources of origin of the diaphragm or fusion of them
