Development of the Respiratory System Flashcards
What does fertilisation of a haploid egg by a haploid sperm give rise to?
A single diploid cell
When do cells become pluripotent stem cells?
At 16 cell stage
When is 16 cell stage reached by?
End of day 3
What occurs at day 5?
Hollow ball of cells the blastocyts has outer trophoblast and inner cell mass
What does trophoblast give rise to?
Foetal placenta whereas inner cell mass into embryo
What happens at day 6?
Inner cell mass implanted to uterine endometrium and endrometrial gland enlarges - known as decidua more vascularised
What happens at day 8?
Cell mass differentiates into hypoblast (primitive endoderm) and Epiblast (primitive ectoderm)
What does hypoblast and epiblast together form?
Bilaminer embryonic disc within forms amnion
What happens to amninon?
Extends surrounds full embryo forming embryonic cavity - hypoblast cells migrate and flatten form exocoelomic membrane around inner surface of blastocyst
What happens at day 9?
Hypoblast forms walls of the egg sac and enbryonic position between amniotic cavity and yolk sac
What do cells in york sac develop into?
Gonad and yolk sac in week 4 creates GI tract
What happens in week 3?
Gastrulation
What happens in gastrulation?
Bilaminer disc into trilaminer structure 3 germ layers ectoderm (skin cns) mesoderm (CT and muscle)Endoderm (epithelia of gi and organs)
What day does gastrulation start?
15 with migration of cells from epiblast forming primitive streak - groove on dorsal surface extends from posterior tail to anterior node of bilaminar disc
What happens when primitive disc is formed?
Epiblast cells migrate inwards below primitive streak some displace hypoblast to form endoderm other to form mesoderm
What do epiblast cells form?
Ectoderm
What happens at day 16?
mesoderm cell from node migrate to head of embryo to form notochord
What forms in week 3?
Oropharyngeal membrane on dorsal surface of anterior
Where does cloacal membrane form?
Dorsal surface of posterior
What does oropharyngeal do in week 4?
Breakdown to connect oral cavity to pharynx and gi trict
What does cloacal break to form?
Anal, urinary and reproductive tracts
What happens to embryo in week 4?
Embryonic folding - due to unequal growth rates
What does medial plane form?
Head and tail
What does lateral folds give rise to?
Coalom and pinches off yolk sac giving rise to primitive gut
What does primitive gut have?
3 regions - foregut, midgut and hindgut
What happens at time of folding?
Several pharyngeal arches on either side of head as internal pharyngeal pouches and from ventral wall of foregut
Where does respiratory develop from?
Ventral wall of foregut 4th and 6th pharyngeal arches the respiratory system develops
What grows during week 4?
Lung bud or respiratory diverticulum appear as outgrowths from ventral wall of foregut
What does lung bud have?
Opening common to foregut and extends it seperates from foregut by oesophagotracheal ridges
What do oesophagotracheal ridges form?
Fuse to create oesophagotracheal septum divides the foregut into dorsal oesophagus and ventral trachea - maintained within laryngopharynx
What is lining if larynx and respiratory system?
Endodermal, in origin it is mesodermal from mesenchyme of 4th6th pharyngeal arches
What do mesenchymal cells rapidly divide into?
Laryngeal opening for t shaped opening - differentiates into thyroid cricoid and arytenoid cartilages
What happens as laryngeal cartilages form?
Epithelium proliferates temp blocks lumen of diverticulum - followed by vascularisation and recanalisation resulting in forming laryngeal ventricles for true and false vocal chords
What does diverticulum divide into at week 5?
Seperates from foregut - 2 lateral branches for L and R primary bronchi, R forms 3 secondary bronchi, L 2 secondary bronchi continue to grow till ten tertiary on right and 8 on left
What do bronchi give rise to?
Bronchopulmonary segments of the lungs
Whats formed at month 6?
Bronchioles and upto 17 more divisions, before bronchial tree final occurs 6 more divisions postnatal
What are pericardioperitineal canals?
Narrow either side of foregut - fill as lung bunds sub divide visceral and paritel pleura derived from mesoderm, pleural cavity forms filled with pleural fluid
What happens at month 7?
bronchial subdivisions are narrower and steady vascularisation - respiration possible when cuboid bronchial endothelium flatten to squamous
What extends from respiratory bronchioles?
Primitive alveoli and terminal sacs for type 1 and type 2 alveolar cells
WHt is type 1 and type 2 alveolar associated with?
Type 1 - blood and lymph capillaries
Type 2 - secretes surfactant to prevent collapse of lung
How long does lung grow?
Till 10 of postnatal life
What is oesophageal atreasia?
Oesophagus terminates in a blind ending passag
What is TEF tracheoaphageal fistula?
abnormal opening forms between oesopahgus and trache in 90% together , babies cyanotic and stop breating
What is the vacterl association?
Vertebral, Anal atresia, Cardiac, TEF, Eosophageal atresia, Renal and Limb defects
How do congenital cysts arise?
Abnormal budding of diverticulum resulting in dilated and poorly vascularised terminal or larger bronchioles - in radiographs honeycomb appearece, cysts are air or fluid filled, treated with resp support, antibiotic and surgery
What are other abnormalities of the bronchial tree?
Formation of ectopic lung lobes from trachea or oesophagus , loss of lung lobe or enter lung and formation of blind ending trachea with lung absnece
When does respiratory distress syndrome occur?
insuffiecient quantities of surfactant produce, most common death - collapsed alveoli filled with protein rich fluid and form hyaline membrane filled with CT cells
How to treat RDS?
Resp support with glucocorticoids - enhance surfactant production and synthetic surfactants - signs are rapid and shallow breating, nostrils flare, retraction of chest wall
