Lecture 18: Embryonic Respiratory System Flashcards
lower respiratory tract consists of
epiglottis, larynx, trachea, left and right lung, pulmonary blood vessels, heart, upper lobes, middle lobe (r), lower lobes
when/where laryngothracheal groove forms
week 4
lower/back part of throat, connects w/ surface ectoderm of mouth
respiratory primordium is
laryngotracheal groove; median outgrowth of ventral wall of pharynx
respiratory diverticulum
bud outpouching of tissue of ventral wall of foregut, will form 2 lungs
laryngotracheal tube tissue layers
endoderm, sphlancnic mesoderm
endoderm of laryngotracheal tube becomes
epithelium and glands of larynx, trachea, bronchi, and pulmonary epithelium
sphlancnic mesoderm of laryngotracheal tube becomes
connective tissue, cartilage, and smooth muscle
larynx functions
communicates with mouth/nasal cavities for swallowing, respiration, voice production
larynx borders
upper: epiglottis
lower: cricoid cartilage
artenoid swellings
cranial end of L-T tube; are 4th and 6th pharyngeal arches mesenchyme that proliferate
laryngeal inlet
T-shaped region of mesenchymal tissue formed by meeting of artenoid swellings; temporarily occludes respiratory tract before recanalizing
vocal cord formation
after recanalization of larynx, laryngeal ventricles/cartilages become vocal cords
epiglottis function
covers the larynx so food doesn’t get into the lungs
epiglottis derivation
caudal hypobranchial eminence 4th-6th arch myloblasts
laryngeal web
non-lethal anomaly, occurs when recanalization of larynx isn’t complete (week 10) and get partial obstruction of newborn’s airway
trachea derivation
lung buds that separate from foregut become trachea and 2 bronchial buds
laryngothracheal (L-T) diverticlum timing
end of week 4
tissue layers of L-T tube
mesoderm, endoderm
where long bud forms
distal end of L-T diverticulum
T-E folds become
T-E septum
number of lobes of each lung
Left: 2; Right:: 3
what T-E septum separates
laryngotrachel tube from oro-pharynx, esophagus
T-E fistula is
when T-E folds don’t completely separate the trachea and esophagus, get abnormal communication between trachea and esophagus
most common anomaly of lower respiratory tract
T-E fistula; 85% associated with esophegeal atresia
incidence of T-E fistula
1/3000-1/4500 live births; male>females; 85% associated w/ esophageal atresia
what surrounds alveoli/why
capillaries; take in oxygen
where lungs form
within pericardioperotneal canals (2)
1st branch off trachea on each side
primary bronchus
branches of primary bronchus
secondary bronchi; 2 on L, 3 on R
characteristics of right secondary bronchi
larger, shorter, more vertically oriented
3 secondary bronchi
more likely to get something stuck in bronchi because of verticality
characteristics of left secondary bronchi
2 secondary bronchi with 2 lobes
more horizontal orientation
number of orders of branching of bronchi by 24 weeks
17 orders
bronchopulmonary segment made of
bronchus + mesenchyme
lung maturation stages
- pseudoglandular pd
- canalicular pd
- terminal sac pd
- alveolar pd
pseoduglandular period
1st period of lung development, 6-16 weeks
formation and growth of duct systems
bronchopulmonary segments not well developed
fetuses can’s surive
inefficient/impossible oxygen exchange
canalicular period
16-25 weeks (2nd pd of lung development)
bronchi and terminal bronchioles enlarge, encompass capillaries
highly vascular
alveolar sacs not truly differentiated
respiration possible
terminal sac period
26 weeks to birth
capillaries bulge into alveoli
epithelium very thin so no intervening mesoderm for oxygen to get across
contact between epithelial and endothelial cells permit gas exchange
type II alveolar cells secrete surfactant
function of surfactant
from type II alveolar cells
form monomolecular fil over internal walls of terminal saccules
lower surface tension
reaches adequate levels in late fetal period
respiratory distress syndrome
babies born prior to 26-8 weeks; due to lack of surfactant, insufficient alveolar surface area, inadequate pulmonary vasculature
alveolar period
gestation/birth to 8 years old
capillaries are immediately adjacent to alveoli- gas exchange easy
terminal saccules will be future alveolar ducts
percentage of alveoli formed after birth
95%
what autonomous gas exchange requires (in alveolar pd)
surfactant
transformation of lungs to a gas exchanging organ
est of parallel pulmonary and systemic circulations
what increases after birth re: lungs
surface area of air-blood barrier, via growth of alveoli and capillaries
number of capillaries from birth to age 8
50 million to 300 million
chest xray of newborn infant vs adult
will be dense
how does fetus prepare for breathing
fetal breathing movements that condition respiratory muscles, stimulate lung development
at birth, what exchanges re: lungs?
intra-alveolar fluid exchanges with air
what in-utero normal lung development depends on
adequate thoracic space for lung growth, fetal breathing movements, amniotic fluid volume
why amniotic fluid matters for lung development
keeps muscles of uterus from collapsing on baby’s lungs/chest
respiratory distress syndrome
caused by lack of surfactant production, so alveoli don’t inflate properly
occurs in 2% live newborns
treat with berthamethasone, a steroid mother takes that causes fetal lung cells to make surfactant
what causes esophageal atresia with a TE fistula
incomplete fusion of T-E folds
