🌬💨 Flashcards
5 stages of lung development
- Embryonic
- Pseudoglandular
- Canalicular
- Saccular
- Alveolar
about embryonic stage of lung development [brief]
establishes basic lung structure (symetric, some lobes on R side, some on L side) as a template for further growth
about psudoglandular stage of lung development [brief]
pseudoglandular because…
establishes the branched network of gas conducting airway
lung develops almost the same way as glands
about canalicular stage of lung development [brief]
formation of the blood-gas barrier
about saccular stage of lung development [brief]
formation of the respiratory acinus – the zone of gas exchange
about alveolar stage of lung development [brief]
formation of the alveolus and high surface area for gas exchange 5x increase in surface area for 2x increase in lung volume
STAGE 1: EMBRYONIC
gestation: ________
the primordial lungs develop as an outgrowth of _________
note that many women don’t know at this point that they’re pregnant => _________
week 4: ___________
week 6: ___________
26 days - 6 weeks the foetal foregut (oesophagus) bad lifestyle/habits can have a massive impact on the template of the cardiovascular system and the lungs trachea develops formation of basic lung template
STAGE 2: PSEUDOGLANDULAR
gestation weeks: _______
branching of the airway and vascular duct system for up to __ further generations beyond Embryonic stage
fluid secretion into the airways creates a ________ which gives _______ for the growth of the airway in 3D
end of this stage: the airways and vasculature have developed to ________
developmental outcome: formation of the conducting airways of the lung and accompanying blood vessels, together known as _________
Airway growth follows a _________: allows airways to fill spaces of varied dimension
Key advantages:
- Achieves ________ among terminal airway branches. Mechanical force dispersed evenly among units
- ________ in the number of airways at each branch disperses air flow resistance which would otherwise increase with distance into the lung
- Each branch comes at _________
- _______(🔽/🔼) in resistance as we go deeper
Foetuses exchange _________ in the womb by a breathing like movement, movement of that fluid allows for ___________
purpose: __________
6-16 21 distending pressure, mechanical support completely fill the space available in the chest cavity the respiratory tree
programme of Irregular Dichotomous Branching
even dispersal of gas
Regulated increase
different stage
🔽
amniotic fluid
branching of the lungs
to generate concentration gradient
STAGE 3: CANALICULAR
gestation weeks: ______
onset marked by _______________ within the mesenchyme that surrounds the more distal reaches of the embryonic respiratory system to form ______________
diameter of the airways _______(🔽/🔼) with a consequent _______(🔽/🔼) in epithelial thickness to a more cuboidal structure; epithelial cell differentiation begins
terminal bronchioles branch to form _________ around which the alveoli will develop
differentiation of the mesenchyme progresses down the developing respiratory tree, giving rise to ________, _______, and ________
earliest stage of lung development at which premature infants can survive (youngest infant delivered at ____ weeks of pregnancy)
16-24 extensive angiogenesis a dense capillary network 🔼 🔽 the respiratory acini chondrocytes, fibroblasts and myoblasts 24
STAGE 4: SACCULAR
_______ [gas exchange zone] is defined
gestation weeks: ______
branching and growth of the ________ or _________
continued thinning of the stroma brings the capillaries into apposition with the prospective alveoli
Completion of pneumocyte differentiation. Type I pneumonocytes differentiate from cells with a type-II like phenotype. These cells then flatten, increasing the epithelial surface area by dilation of the saccules, giving rise to __________. Surfactant production is fully operational.
By 26 weeks, a rudimentary though _____________ has formed. Maturation of the alveoli continues by further enlargement of the terminal sacs, deposition of elastin foci and development of vascularised septae around these foci. The stroma continues to thin until the capillaries protrude into the alveolar spaces.
thin-walled airways are maintained patent by ____ driven fluid secretion into the luminal space
the Respiratory Acinus
24-36
terminal sacs or primitive alveolar ducts
immature alveoli
functional blood/gas barrier
Cl-
STAGE 5: ALVEOLAR
gestation weeks: _____________
maturation of the lung indicated by the ______________ begins at 36 weeks, though new alveoli will continue to form for up to 6 years
_______(🔽/🔼) in the relative proportion of parenchyma to total lung volume still contributes significantly to growth for 1 to 2 years after birth, thereafter all components grow proportionately until adulthood
_____ driven fluid absorption from the lung lumen clears the lung of fluid and maintains a thin film of liquid on the surface of the airways throughout adult life
pulmonary circulation becomes fully established as ________ [action]
enlargement of the gas exchange surface occurs by pocketing on the wall of the saccular lung
a single capillary network occupies the septal walls between each alveolus
the membranes over which gas exchange occurs (the blood gas barrier) thin to ______nm
invaginations change direction of formation by __ degrees from previous stage
lungs SA increases x____ for x___ lung volume increase
36 weeks to ~ 6 years postnatal age
appearance of fully mature alveoli
🔽
Na+
the umbilical blood supply is cut off
200nm
90 degrees
x5
x2
what is ENaC?
maternal hormones which affect ENaC?
Epithelial Na+ Channel
a Na+ selective ion channel found in all secretory epithelia (e.g. lung, kidney, gut, salivary duct, sweat duct)
maternal cortisol increases in last trimester & crosses into fetal circulation and induces ENaC subunit gene expression and membrane insertion in epithelial cells lining the fetal airways
during labour, a rise in maternal Adrenaline crosses into fetal circulation and activates the channel fluid is rapidly cleared from the fetal lung in preparation for the first breath
some fluid is coughed up during the first breath
structure + dangers of mutations of ENaC
- no of subunits + names
- effects of knockout of one of the subunits
- effect of mutations
3 subunits: α, β, ɣ
knockout of α is lethal at brith, because lungs are flooded with fluid
may result in problems during infant & adult life, e.g. high altitude pulmonary edema (HAPE)
ENaC-driven fluid clearance from the lung at birth is rapid
*what are the details (time vs. lung aeration)?
1 min (after birth) –> ~55%
100 min –> 80%
2 days –> 100%
advantage of fractal design of airway and vasculature?
colossal proportions in a small space
