LEC 18: Respiratory System - 08.28.14 Flashcards Preview

STRUCTURES - WEEK 2 > LEC 18: Respiratory System - 08.28.14 > Flashcards

Flashcards in LEC 18: Respiratory System - 08.28.14 Deck (35):
1

Upper vs. Lower Respiratory Tract

  • Upper
    • nasal cavities, etc.
  • Lower
    • larynx
    • trachea
    • bronchi
    • lungs

 

2

When do the lower respiratory organs begin to form

~4 weeks

3

Respiratory primordium

  • respiratory primordium indicated by median outgrowth from caudal end of ventral wall of primordial pharynx
  • elongates to form laryngotracheal tube

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4

Laryngotracheal groove

  • 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)

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5

Formation of lung bud

  • 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

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6

Relationship between respiratory diverticulum and primordial pharynx

  • respiratory diverticulum separates from primordial pharynx, but maintains communication with it through the primordial laryngeal inlet

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7

composition of laryngeal tube

endoderm = epithelium and glands of larynx, trachea, bronchi, and pulmonary epithelium

splanchnic mesoderm = connective tissue, cartilage, smooth muscle

8

functions of larynx

  • swallowing
  • respiration
  • voice production

upper border = epiglottis

lower border = cricoid cartilage

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9

Formation of larynx

  • 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)

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10

recanalization of larynx

  • T-shaped glottis bounded by lateral arytenoid swellings and cranial epiglottis
  • temporarily occludes laryngeal lumen
  • recanlized at week 10

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11

vocal cords

vocal cords form from laryngeal ventricles (recesses)

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12

epiglottis

  • covers larynx
  • develops from caudal hypobranchial eminence
  • muscles form from myoblasts in 4th-6th arches

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13

laryngeal web

  • incomplete recanalization of larynx in week 10
  • partial obstruction of airway in newborn
  • not necessarily fatal, may be fixed

 

14

development of trachea (respiratory diverticulum)

  • straight portion of respiratory diverticulum is the primordium of the trachea
  • bronchial buds develop into bronchial tree

 

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15

What controls the extent of branching within the respiratory tract

  • 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

 

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16

laryngeal-tracheal diverticulum

  • 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

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17

Laryngeal inlet

  • maintains connection between laryngeotracheal diverticulum and primordial pharynx

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18

tracheo-esophageal septum

  • longitudinal folds develop in laryngeal-tracheal diverticulum
  • folds fuse to form tracheo-esophageal septum
  • divides laryngealtracheal tube from oro-pharynx and esophagus

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19

T-E fistula (tracheoesophageal fistula)

  • 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)

 

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20

bronchi and lungs

  • 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)

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21

primary bronchus vs. secondary bronchi

  • 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)

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22

Describe the differences between R/L bronchi

RIGHT

  • 3 secondary bronchi
  • larger, shorter, more vertical

 

LEFT

  • 2 secondary bronchi
  • 2 lobes

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23

segmental bronchi

  • form at 7 weeks
  • bronchopulmonary segment = bronchus + mesenchyme
  • by 24 weeks, 17 orders of branches

 

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24

Maturation of the lungs (in 4 stages)

1. pseudoglandular phase (5-17 weeks)

2. canalicular period (16-25 weeks)

3. terminal sac period (24 weeks until birth)

4. 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

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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

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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

 

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28

alveolar phase

  • birth to 8 years
  • terminal sacs have very thin epithelial lining
  • alveolocapillary membrane allows gas exchange
  • terminal saccules = future air ducts

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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