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Development of the Respiratory System Lane Block II Unit I


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What is the laryngopharynx?
The inferior 1/3 of the pharynx passage post. to the larynx.
What is the larynx?
An airway supported by hyoid bone, thyroid, cucoid, arteriod and epiglottis cartilages.
What is the upper respiratory tract?
External nose to laryngopharynx.
What is the lower respiratory tract?
Larynx, trachea, bronchi and lungs.
What does the foregut form?
Pharynx, esophagus, stomach, and duodenum
What do pharyngeal arches form?
Form ventral and lateral walls of foregut.
What are pharyngeal pouches?
Pharyngeal pouches are grooves along the inner surface of foregut. It is lined by endoderm.
What is the entire foregut lined by?
What is the respiratory primordium? What does it form?
An invagination of endoderm forms epithelial and glands of the lower Respiratory tract (AKA Laryngotracheal groove)
Which arch is the laryngotracheal groove located on?
Arch 6
When does the development of the lower respiratory tract occur?
During the 4th week of development.
Put these in the proper order and match them with a day.

Laryngotracheal tube, Bronchial buds, Tracheoesphageal fold, Lung bud, Laryngotracheal groove, Tracheoesphageal septum, Laryngotracheal diverticulum
Laryngotracheal groove (day 26-27), Laryngotracheal diverticulum (28), Tracheoesphageal fold (28), Lung bud (31), Tracheoesphageal septum (31), Laryngotracheal tube (35), Bronchial buds (35)
What does the endoderm form in the respiratory tract?
It forms the epithelia and glands of the larynx, trachea, bronchi and lungs.
What does the splanchnic mesoderm form in the respiratory tract?
Forms the smooth muscle and cartilage of tracheal rings.
What does the tracheoesophageal fold become?
The trachea and esophagus.
When does the trachea and esophagus separate?
During the 5th week.
What forms the laryngeal epithelium?
The endoderm of the laryngotracheal tube.
What forms the epiglottis?
The mesenchyme of hypobrachial eminence (ventral ends of the 3rd and 4th pharngeal arches)
What forms the artenoid, cricoid and thyroid cartilages?
The mesenchyme of cranial laryngotracheal tube (4th and 6th pharyngeal arches).
At what week is the larynx closed temporarily?
6th week
When does the larynx reopen?
10th week
How is the larynx formed?
Aritenoid cartilage builds up inferior to the 6th pharyngeal arch. This creates arytenoid swellings and forms the laryngeal inlet from the larngotracheal groove. This then continuous untill they seperate about week 10.
What does the splanchnic mesoderm form?
Cartilage rings and smooth muscle.
What is the transiton of tissues in the trachea?
Cuboidal to PCCE.
What is esophageal atresia?
An an obstruction of the esophagus. The esophagus becomes a dead end pocket.
What is a tracheoesophageal fistula (TEF)? With what other condition are they associated?
An abnormal communication between the trachea and esophagus, 85% occur with esophageal atresia.
What is polyhydramnios?
Excess amnionic fluid in the embryo, occurs when amniotic fluid blocks entrance to the digestive tract.
What occurs during an H-type fistula?
During an H-type fistula there is no esophageal atresia and only TEF.
What are the two kinds of esophageal atresia?
Upper and lower.
What can happen in an infant with TEF?
Gastric juices spill over and the infant will demonstrate pneumatitis (lung inflamation)
What develops from bronchial buds?
Primary bronchi -> Secondary Bronchi -> Tertiary bronchi (conducting bronchioles) -> Respiratory bronchioles.
What arises out fo the pericardioperitoneal canals?
Primordial pleural cavities.
What arises out of splanchnic mesenchyme?
Visceral pleura
What arises out of somatic mesoderm?
parietal pleura (smomatic/intercostal n.)
When do the bronchial buds appear?
4 weeks
When do the left and right primary bronchuses develop?
5 weeks.
When do the secondary bronchi develop?
6 weeks
When do the tertiary bronchi, fissures and lobes develop?
7 weeks
What happens in the pseudoglandular period?
6-16 weeks
conducting airways deveop in lungs
capillaries form in splanchinic mesoderm
What happens in Canalicular period?
16-26 weeks
lumens of bronchi and bronchioles enlarge
respiratory bronchioles and alveolar ducts form by the end of this period
more blood vessels form and gas exchange becomes possible.
What happens in the terminal sac period?
26 weeks to birth
more terminal sacs present
more capillaries contact epithelium
Epithelum (Type I cells) thins over capillaries
Blood air barrier is established (type II cells develop)
Surfactant levels are sufficient by 28-32 weeks
What happens in the alveolar period?
32 weeks - childhood (8 years)
95% of all alveoli form during this period
Mature alveoli appear after birth
Branching produces more respiratory bronchioles, alveolar ducts and alveolar sacs
Cappillaries line up positions near pneumocytes.
What are the changes that occur in the respiratory tract at birth? (3)
1) Replacement of fluid in airways with air
- Expelled during delivery ->(more respiratory problems in infants w/ cesarain)
-Absorbed by pulmonary capillaries
-Absorbed by lymphatics
2) Pulmonary circulation increases as lungs inflate with air
3) Ductus arteriosum and foramen ovale close sending more deoxygenated blood to the lungs.
What are congentical lung cysts?
Caused by blockage of an airway, are air or fluid filled cyst, usually on visceral surface of lung
What is lung agenesis?
Bronchial buds don't grow into mesenchyme of lung, unilateral agenesis is survivable
What is lung hypoplasia? What is it usually associated with and where?
Lung hypoplasia is loops of small intestine are pushed into the thorax which retards development of lungs. It is often associated with congenital diaphromatic hernias. It is usually on the left side and usually fatal.
What is the cause of respiratory distress syndrome (AKA hyaline membrane disease)?
Insufficient surfactant present in lumen of alveoli. This causes atelectasis or the alveoli collapse during expiration.
What are the symptoms of respiratory distress syndrome? (5)
1) Rapid labored breathing shortly after birth
2) Nostral flaring
3) Grunting = difficulty inflating lungs
4) Rib retraction
5) Cyanosis - blue lips and nail beds
What are the treatments for RDS? (3)
Monitor phospholipids in amniotic fluid.
1) Before birth, treat mother with beta methasone and thyroid homone => makes type II pneumocytes
2)After birth, exogenous surfactants
3)After birth, continuous positive airway pressure (don't let alveoli collapse)
What is the frequency of respiratory distress syndrome?
Represents 30% of all neonatal deaths, Occurs in 2% of live newborns, premature babies born before week 32 (1,000 deaths/year)

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