Neonatal Flashcards
From what part of the neonatal anatomy does the respiratory tract originate from?
Originate as an outpouching from the endodermal tube that gives rise to the GI tract
When is fetal development does alveolar formation begin?
Around 28 weeks gestation
True or false: Alveoli are fully formed at birth
false– will continue to develop for years
What is the stimulus for lung development in the fetus?
Lung fluid in the airway causes a distending force that stimulate growth
What is the effect of oligohydramnios on lung development? Why?
Decreases, since lung development relies on the pressure exerted from the lung fluid for expansion
What inhibits lung from becoming too large in fetal development?
External compression
What are the two major mechanisms that regulate lung development?
- Physical factors
- Transcription factors/regulatory genes
What are the 5 phases of lung development?
- Embryonic
- Pseudoglandular
- Canalicular
- Saccular
- Alveolar
What is the order of airway development? (6)
- Bronchi
- Bronchioles
- Terminal bronchioles
- Respiratory bronchioles
- Alveolar ducts
- Alveolar sacs
What is occurring in the pseudoglandular phase of lung development? (3)
Formation of:
- major airways
- bronchial tree
- portions of the respiratory parenchyma
What is occurring during the canalicular phase of prenatal lung development? (3)
- Last generation of the lung periphery formed
- Epithelial differentiation
- Air-blood barrier formed
What are the two major events that occur in the saccular phase of lung development?
- Expansion of air space
- Surfactant detectable in amniotic fluid
What is the major event that is occurring in the alveolar phase of lung development?
Secondary septation
When in gestation does surfactant develop?
Around week 24
When is the embryonic phase occurring in gestation (weeks gestation)?
0-8 weeks
When do the first segments appear in the five lobes of the lungs?
At the end of the embryonic phase
When have the pulmonary vessels formed in development?
End of the embryonic phase
What controls the first inward breathing movement at the end of the embryonic phase of development? What is different about this movement as compared to regular physiology?
A breathing center in the brain stem.
paradoxical movement, in that when the diaphragm contracts, the thorax moves inwardly and vv
When does the pseudoglandular phase take place in development?
8-17 weeks
What do the lungs look like in the pseudoglandular phase of development? What is significant about the end of this phase?
Resemble a gland
At the end of this phase, precursors of the pneumocytes can be discerned in the respiratory sections as cubic epithelium
When in development does the developing bronchopulmonary epithelium begin to develop amniotic fluid?
Pseudoglandular phase
When does the canalicular phase happen in development?
16-26 weeks
What happens to the pneumocytes in the canalicular phase of development?
Type I pneumocytes differentiate out of the type II
What happens to the capillaries in the canalicular phase of development?
Capillaries approach the walls of the acini
What is the chief characteristic change that occurs during the canalicular phase of development?
Alteration of the epithelium and the surrounding mesenchymal
During what stage of development does the lung epithelium begin to produce a large portion of the amniotic fluid?
Canalicular phase
When can the maturity of the lungs begin to be measured clinically? What is measured for this?
Canalicular phase–based on the activity of the type II cells to produce surfactant
Damage during the canalicular phase of development will produce what complication?
Damage will affect the gas-exchange components and result in structural alterations of the later pulmonary parenchyma
When in development does the saccular phase occur?
24-38 weeks
What are the major morphological changes that occur during the saccular phase of lung development?
Whole clusters of sacs form on the terminal bronchi, which represent the last subdivision of the passages that supply air
What forms at the end of each respiratory tract in the saccular phase?
Smooth walled sacculi form, coated with Type I and II pneumocytes
What are the characteristics of the septa in the saccular phase of development?
Septa contain two networks of capillaries coming from neighboring sacculi
What occurs with the intraductal space and intersaccular space during the saccular phase of development?
Fibroblasts begin to produce extracellular material in the interductal and intersaccular space
At the end of the which phase of lung development, have all generations of the conducting and respiratory branches been generated?
Saccular
What organelle produces surfactant? How is this pacakged to leave the cell?
rER produces it, and packages it into lamellar bodies
What cells produce surfactant?
Type II pneumocytes
What is the major histological evidence that identifies mature type II pneumocytes?
Lamellar bodies
IN the alveolar lumen, the lamellar bodies unravel to form what?
Tubular myelin and ultimately surfactatns
What are the main components of surfactant?
Phosphatidylcholine (lecithin 75%)
What is the best measure of fetal lung maturity? When does this increase?
Ratio of levithin/sphingomyelin concentrations in the amniotic fluid
Increases from the 32nd weeks of gestation
What ratio of lecithin/sphinomyelin is concerning for the development of IFDS?
1.5 or below
What is the function of SP-A (surfactant-specific protein)?
Immune defense function
What is the function of SP-D (surfactant-specific protein)?
Immune defense function
What is the function of SP-B (surfactant-specific protein)?
Critical for surface activity
What is the function of SP-c (surfactant-specific protein)?
Critical for surface activity
What is the major componet of surfactant that is missing from commercial preparations of surfactant?
SP-A and D
What are the stimulants of surfactant synthesis?
Glucocorticoids
Thyroid hormones
cAMP
Epidermal growth factors
What are the two agonists that stimulate surfactant synthesis?
Beta adreergic
Purinoceptors (adenosine)
What maternal disease inhibits the development of surfactant?
DM
What is the effect of a maternal overproduction of thyroid hormone on lung function?
Overbranching of the lungs
What will stimulate cAMP in respiration?
Xanthine
What is the beta agonist that will stimulate surfactant synthesis?
Terbutaline
When in gestation does the alveolar phase take plase?
36-2 weeks postpartum
What fraction of the adult count of 300 million alveoli are formed at birth?
1/3
What happens in the alveolar phase?
Alveoli form from the terminal endings of the alveolar sacculi, and increase in diameter
During the alveolar phase, the alveoli are only present in their beginning form. What lies between them that is not present in their fully mature form?
Between them lies the parenchyma, composed of a double layer of capillaries that forms the primary septa between the alveolar sacculi
What are the three main processes that occur during lung development in late fetal life?
- Increase in the number and size of the alveoli
- Thinning of the CT septa between alveoli
- Alveolar lining cells become flatter
What is the purpose of the thinning of the septa between alveoli during the alveolar phase?
Reduce distance between the alveoli and capillaries, facilitating gas exchange
What is the relative lung compliance in the full term, intrauterine lung? Chest compliance?
Low lung compliance
High chest compliance
What are the breathing movements like in the full term intrauterine lung?
30% of the lungs have shallow breathing movements
Are the vessels in the full term uterine lung dilated or constricted?
Constricted
What are the four major changes the must occur rapidly and concurrently following birth?
- Continuous breathing and ventilation must start
- Functional residual capacity must be established
- Pulmonary vasculature must dilate
- Fetal pulmonary fluid must be absorbed
What are the chemical stimuli that start the breathing process at birth?
Increased pCO2
Decrease pO2
What are the environmental stimuli that occur at the onset of breathing?
Cooling
Light
Sound
Pressure
Is the first breath forceful or weak?
Forceful
Is expiration of the first breath active or passive?
Active
What process allows the air passage to open?
Transpulmonary pressure increases with the adduction of the vocal cords, to establish residual capacity
What happens to the capillaries with the first breath?
Recruitment and distension of the newly oxygenated capillaries
The process of opening alveoli is dependent on what major factor? Why?
Surfactant, which lowers lung surface tension
Initially, there is a high respiratory rate with the first breath. What brings this down?
J receptors are activated by interstitial pressure creased by fetal lung fluid
What hormone surge allows for the resorption of fetal lung fluid? How does this work? What enhances this initial absorption?
NE–stimulates transepithelial Na transport to pull Na and water into the capillaries
Thyroid and steroid hormones, as well as alveolar-capillary pressure gradient increase this
What causes the paradoxical breathing pattern of infants?
Highly compliant chest wall, with low lung compliance
What causes the low dynamic lung compliance after birth?
- Viscous properties of lung tissue
- Distortion of the pliable chest
How do the resistances of the nasal and oral airways compare in infants and adults?
Lower nasal airway resistance in infants compared to oral. vv for adults
True or false: there is a large change in the compliance of the lungs and chest within the first few minutes of life
True
Why are the newborn’s respiratory mechanics not very efficient?
Chest distortion
Round skeletal contour (not optimal resting length for diaphragm and intercostals)
What are the characteristics of the respiratory muscles initially after birth?
Small mass
Few fatigue resistance, slow twitch
What are the three main causes of the in-homogeneous air distribution in the neonatal lungs?
- Pliant airway
- Chest wall distortion
- Immature respiratory muscles
What happens to the pulmonary circulation after birth?
- Decreased pulmonary arteries:alveoli ratio,
- there is less vascular resistance
How does the breathing pattern change as the neonate matures?
Changes from episodic to continuous
Short period of apnea are normal in infants. How can you tell if this is an issue?
Arousal of the infant
Periodic breathing and apnea usually occur when in the neonates early life?
During sleep
Why is hypoxia early in fetal life bad?
Increase***
