LEC 18: Respiratory System - 08.28.14 Flashcards
1
Q
Upper vs. Lower Respiratory Tract
A
- Upper
- nasal cavities, etc.
- Lower
- larynx
- trachea
- bronchi
- lungs
2
Q
When do the lower respiratory organs begin to form
A
~4 weeks
3
Q
Respiratory primordium
A
- respiratory primordium indicated by median outgrowth from caudal end of ventral wall of primordial pharynx
- elongates to form laryngotracheal tube
4
Q
Laryngotracheal groove
A
- median outgrowth in anterior wall of endodermally-derived foregut
- by end of 4th week the laryngotracheal groove invaginates to form pouch-like respiratory diverticulum (lung bud)
5
Q
Formation of lung bud
A
- by end of 4th week the laryngotracheal groove invaginates to form pouch-like respiratory diverticulum (lung bud)
- as diverticulum elongates, it is invested with splanchnic mesenchyme and its distal end enlarges to form tracheal bud
6
Q
Relationship between respiratory diverticulum and primordial pharynx
A
- respiratory diverticulum separates from primordial pharynx, but maintains communication with it through the primordial laryngeal inlet
7
Q
composition of laryngeal tube
A
endoderm = epithelium and glands of larynx, trachea, bronchi, and pulmonary epithelium
splanchnic mesoderm = connective tissue, cartilage, smooth muscle
8
Q
functions of larynx
A
- swallowing
- respiration
- voice production
upper border = epiglottis
lower border = cricoid cartilage
9
Q
Formation of larynx
A
- forms at cranial end of LT tube
- epithelial lining develops from endoderm of LT tube
- laryngeal cartilages develop from mesenchyme that is derived from neural crest cells
- mesenchyme at cranial end of LT tube proliferates rapidly, forms paired arytenoid swellings
- swellings grow toward tongue, forming T-shaped laryngeal inlet
- Proliferation of epithelium temporarily occludes laryngeal lumen (recanalizes by week 10)
10
Q
recanalization of larynx
A
- T-shaped glottis bounded by lateral arytenoid swellings and cranial epiglottis
- temporarily occludes laryngeal lumen
- recanlized at week 10
11
Q
vocal cords
A
vocal cords form from laryngeal ventricles (recesses)
12
Q
epiglottis
A
- covers larynx
- develops from caudal hypobranchial eminence
- muscles form from myoblasts in 4th-6th arches
13
Q
laryngeal web
A
- incomplete recanalization of larynx in week 10
- partial obstruction of airway in newborn
- not necessarily fatal, may be fixed
14
Q
development of trachea (respiratory diverticulum)
A
- straight portion of respiratory diverticulum is the primordium of the trachea
- bronchial buds develop into bronchial tree
15
Q
What controls the extent of branching within the respiratory tract
A
- mesoderm surrounding endoderm controls the extent of branching within the respiratory tract
- endoderm = epithelium and glands of trachea and pulmonary epithelium
- mesoderm = tracheal cartilage, connective tissue and muscles
16
Q
laryngeal-tracheal diverticulum
A
- by end of week 4, LT groove envaginates to form laryngeal-tracheal diverticulum
- respiratory diverticulum soon separates from the primordial pharynx, however it maintains communication with it through the primordial laryngeal inlet
17
Q
Laryngeal inlet
A
- maintains connection between laryngeotracheal diverticulum and primordial pharynx
18
Q
tracheo-esophageal septum
A
- longitudinal folds develop in laryngeal-tracheal diverticulum
- folds fuse to form tracheo-esophageal septum
- divides laryngealtracheal tube from oro-pharynx and esophagus
19
Q
T-E fistula (tracheoesophageal fistula)
A
- abnormal communication between trachea and esophagus
- most common anomaly of lower respiratory tract
- incomplete fusion of TE folds
- 85% associated with esophageal atresia (poor esophagus development)
20
Q
bronchi and lungs
A
- trachea divides into L/R bronchi
- each bronchus divides again and again, narrowing
- smallest airways end in aveoli (thin air sacs, look like balloons)
- tiny blood vessels surround the 300 million aveoli in lungs
- oxygen picked up from blood vessels
- CO2 dumped (breathed out)
21
Q
primary bronchus vs. secondary bronchi
A
- 5th week, connection of each bronchial bud with the trachea enlarges to form primordium of main bronchus
- R is slightly larger than L bronchus and oriented more vertically (why you get stuff stuck in right side)
22
Q
Describe the differences between R/L bronchi
A
RIGHT
- 3 secondary bronchi
- larger, shorter, more vertical
LEFT
- 2 secondary bronchi
- 2 lobes
23
Q
segmental bronchi
A
- form at 7 weeks
- bronchopulmonary segment = bronchus + mesenchyme
- by 24 weeks, 17 orders of branches
24
Q
Maturation of the lungs (in 4 stages)
A
- pseudoglandular phase (5-17 weeks)
- canalicular period (16-25 weeks)
- terminal sac period (24 weeks until birth)
- alveolar period (birth-8 years)
25
pseudoglandular phase
* 5-17 weeks
* incompatible with life
* formation and growth of duct systems
* bronchopulmonary segments not well developed
26
canalicular phase
* 16-25 weeks
* late canalicular phase may be compatible with life (respiration possible, especially towards end)
* highly vascular
* alveolar sacs not truly differentiated
27
terminal sac phase
* 24 weeks until birth
* capillaries bulge into alveoli
* epithelium very thin
* contact between epithelial and endothelial cells permits gas exchange
* proliferation of capillary network
* Type 1 alveolar cells line terminal saccules
* Type 2 alveolar cells secrete surfactant
* forms monomolecular film over internal walls of terminal saccules
* lowers surface tension
* reaches adequate level in late fetal period
28
alveolar phase
* birth to 8 years
* terminal sacs have very thin epithelial lining
* alveolocapillary membrane allows gas exchange
* terminal saccules = future air ducts
29
surfactant
* Type 2 alveolar cells secrete surfactant
* forms monomolecular film over internal walls of terminal saccules
* lowers surface tension
* reaches adequate level in late fetal period
30
Type 1 vs. Type 2 alvelolar cells
Type 1 alveolar cells = line terminal saccules
Type 2 alveolar cells = secrete surfactant
31
Lungs prior to 26-28 weeks
* respiratory distress
* inadequate surfactant
* insufficient alveolar surface area
* inadequate pulmonary vasculature
32
requirements for autonomous gas exchange
* surfactant
* transformation of lungs to gas exchanging organ
* establishment of parallel pulmonary and systemic circulations
* 95% of alveoli develop post-natally
33
preparation for respiration
* fetal breathing movements
* condition respiratory muscles
* stimulate lung development
* at birth, lungs filled with fluid
* birth
* replacement of intra-alveolar fluid with air
34
normal lung development in-utero depends on...
* adequate thoracic space for lung growth
* fetal breathing movements
* amniotic fluid volume
35
respiratory distress syndrome
* 2% of live newborns
* lack of surfactant production
* lungs are under inflated
* prenatal steroids
* produce exogenous (outside) surfactant
