Body Cavities and Respiratory Development Flashcards
what are the primordium of the intraembryonic coelom, and where do they appear?
they are isolated coelomic spaces in the lateral plate and the cardiogenic mesoderm
what does the intraembryonic coelom dive the lateral plate mesoderm into?
a somatic layer of lateral mesoderm and a splanchnic layer of lateral mesoderm
what is the somatic layer of lateral mesoderm continuous with?
the extraembryonic mesoderm covering the amnion
what is the splanchnic layer of the lateral mesoderm continuous with?
the extraembryonic mesoderm covering the umbilical vesicle
what is somatopleure?
the somatic mesoderm + the overlying ectoderm- forms the body wall
what is the splanchnopleure?
splanchnic mesoderm+ underlying endoderm–> forms the embryonic gut
how will the intraembryonic coelom be divided?
into a pericardial cavity, pleural cavities, and a peritoneal cavity
what are the cavities lined with?
mesothelium
what is the parietal wall derived from?
somatic mesoderm
what is the visceral wall derived from?
splanchnic mesoderm
what does the pericardial cavity open into?
2 pericardioperitoneal canals
head fold movements reshape the intraembryonic coelom; how is the pericardial cavity now positioned?
it is relocated to be ventral and anterior to the foregut
what are the end points of the pericardioperitoneal canals continuous with?
the IE ad EE coeloms- this will be where the peritoneal cavity is positioned
bolding folding occurs in what aspects?
cranial, caudal, and the lateral aspects simultaneously
which folding occurs first and on what day does it occur?
head folding; the embryo elongates cranially starting 4th week/ day 22
what occurs due to the embryo’s elongation cranially?
the neural folds project dorsally and overgrow the oropharyngeal membrane
what is moved inferiorly to the developing forgut due to head folding?
the septum transversum, primordial heart, pericardial cavity, and the oropharyngeal membrane
what is the folding of the caudal end of the embryo due to?
growth of the distal neuro tube
before folding, the primitive streak lies cranial to the cloacal membrane. After caudal folding, where does it lie?
it lies caudal
what produces the lateral folds?
rapid growth of the spinal cord and somites
How does laterally folding happen?
the lateral folds will grow out and downward (ventrally) and then eventually meet along the midline
what happens when the lateral folds fuse together?
the connection between the umbilical vesicle and the midgut is reduced, and it forms the vitelline duct
what is the gut tube covered with?
splanchnic mesoderm
what are body wall malformations and what are two examples?
they result from a failure of the lateral body folds to fuse completely when the anterior abdominal wall forms (4th week); gastroschisis and congenital epigastric hernia
where is the site of the abdominal defect in cases of gastroschisis?
to the right of the umbilical cord rather than midline
where is the site of a congenital epigastric hernia?
it is midline
in order to get the different cavities that are derived from the intraembryonic coelom, what must occur?
we must close off the canals/connections to separate and form the body cavities
partitions form in the top and bottom ends of the pericardioperitoneal canals due to what?
growth of the lungs
what are the more cranial/superior pair of folds that form on the pericardioperitoneal canals?
the pleuropericardial folds
what is the role of the pleuropericardial folds?
they will separate the pericardial cavity and the pleural cavities (heart and lungs)
what are the more caudal/inferior pair of folds that form on the pericardioperitoneal canals?
the pleuroperitoneal folds
what is the role of the pleuroperitoneal folds?
they will separate the pleural cavities from the peritoneal cavity (lungs and gut)
what do the pleuropericardial folds become once they enlarge?
they become the pleuropericardial membranes
what do the pleuropericardial membranes fuse with and when?
they fuse with the ventral mesenchyme around week 7
when are the pericardial and pleural cavities separate?
week 7 with the fusion of the pleuropericardial membranes
what is going to push the pleurocardial membrane/ pericardial cavity down?
the outgrowth of the bronchial buds (lungs)- they grow ventrally into the pericardioperitoneal canals which causes the pleural cavity to expand
the extension of the lungs within the pericardioperitoneal canals will form what?
it splits the mesenchyme to form an outer layer (the thoracic wall) and an inner layer (the fibrous pericardium)
what do the pleuroperitoneal folds become as they enlarge?
they will form pleuroperitoneal membranes
what do the pleuroperitoneal membranes fuse with and when?
they fuse with the dorsal mesentery of the esophagus and septum transversum (week 6)
what other feature also contributes to the pleuroperitoneal membranes to complete closure?
myoblasts
which pleuroperitoneal opening closes slightly before the other?
the opening on the right- thought to be due to the development of the liver (so therefore the left is prone to congenital malformations
what do the pleuroperitoneal membranes ultimately contribute to?
the primordial diaphragm
what are the 4 different components that help form the thoracic diaphragm?
the septum transversum, the pleuroperitoneal membranes, the dorsal mesentery, and the myoblasts
what does the septum transversum go on to form in the diaphragm?
the central tendon of the diaphragm
what do the myoblasts form in the diaphragm?
the crura of the diaphragm
what do the pleuropericardial membranes contain within them?
cardinal veins and myoblasts migrating through en route to the diaphragm
when the myoblasts are migrating to the diaphragm, what do they do?
they pull the ventral rami C3-C5 with them (aka the phrenic nerve)
where does the phrenic nerve lie?
on the fibrous pericardium
what is congenital diaphragmatic hernia (CDH)?
it is a posterolateral defect that is caused by a lack of myoblasts populating the pleuroperitoneal membranes
what are the effects of congenital diaphragmatic hernia?
there is an area of weakness and subsequent herniation of viscera bulge into the pleural cavity (left side typically impacted)
how does the respiratory system start its development?
as a median outgrowth known as the laryngotracheal groove
where is the laryngotracheal groove found?
in the floor of the foregut/primordial pharynx
what forms when the laryngotracheal groove evaginates?
the laryngotracheal diverticulum (endoderm)
what is the laryngotracheal diverticulum the primordia of?
it is a primordium of the tracheobronchial tree
what is derived from the endoderm of the laryngotracheal groove?
pulmonary epithelium and glands of the larynx, trachea, and bronchi
what is the endoderm of the laryngotracheal diverticulum surrounded by and invested in? And what is derived from this structure?
splanchnic mesoderm (from the lateral plate); will give rise to the connective tissue, cartilage, and smooth muscle in these structures
what does the distal end of the laryngotracheal diverticulum enlarge to form?
a globular respiratory bud, which is the origin of the respiratory tree
how is the tracheoesophageal septum formed and when does this occur?
tracheoesophageal folds develop from the endoderm; at the end of week 5
what is the purpose of the fusion of the tracheoesophogeal folds?
it divides the cranial portion of the foregut: the ventral part is the laryngeotracheal tube; dorsal part is the primordium of the oropharynx and the esophagus
what does the upper portion of the laryngeotracheal tube form first?
the larynx
what is the epithelial lining of the larynx?
endoderm of the laryngeotracheal tube
what is the cartilage of the larynx derived from?
the mesenchyme of the 4th and 6th pairs of pharyngeal arches (NCC derived)
what does the mesenchyme of the 4th and 6th pharyngeal arches produce?
paired arytenoid swellings
what do the arytenoid swellings create?
they convert the primordial glottis into a T-shaped laryngeal inlet (the passageway for air)
what initially happens to the laryngeal inlet?
the laryngeal epithelium proliferate and occludes the laryngeal lumen/ inlet
when does recanalization of the laryngeal inlet occur?
by the 10th week
what occurs with the recanalization and erosion to create the final laryngeal inlet?
we get the proper positioning and shaping of the vocal and vestibular folds
what is laryngeal atresia?
a rare birth defect resulting from the failure of recanalization of the larynx
what does laryngeal atresia result in?
obstruction of the fetal airway or congenital high airway obstruction syndrome (CHAOS syndrome)
what happens to the airways in patients with laryngeal atresia?
the airways become dilated and the lungs enlarged and filled with fluid; the diaphragm becomes flattened or inverted and there is fetal ascites
what does the epiglottis develop from?
the hypopharyngeal eminence
what is the hypopharyngeal eminence produced from?
mesenchyme of the 3rd and 4th pharyngeal arches
what does laryngeal muscle develop from?
myoblasts of the 4th and 6th pharyngeal arches
in the neonate, where is the larynx found?
it is in a high position in the neck and is in contact with the soft palate; allows the neonate to have completely functionally separate respiratory and digestive systems (this is why infants are obligatory nose breathers)
after the larynx develops from the laryngotracheal diverticulum, what develops next?
the trachea and 2 primary bronchial buds
what does the endoderm differentiate into when the trachea forms?
the endoderm from the laryngotracheal diverticulum differentiates into the tracheal epithelium and glands
what does the splanchnic mesenchyme differentiate into when the trachea forms?
the tracheal cartilage, connective tissue, and muscle
what are tracheoesophageal fistulas?
there is an abnormal connection between the trachea and the esophagus; failure of the foregut endoderm to proliferate rapidly enough in relation to the rest of the body
what is the most common congenital anomaly of the lower respiratory tract?
tracheoesophageal fistulas
what are 85% of cases of tracheoesophageal fistulas associated with?
esophageal atresia (blind esophagus)
what is the presentation of a tracheoesophageal fistula?
pt cannot swallow, they frequently drool saliva, and immediate regurgitation when fed
what can the fetus develop with tracheoesophageal fistula?
polyhydramnios- because the fluid cannot enter the stomach/intestines for absorption
when does the distal end of the laryngotracheal diverticulum enlarge to form the respiratory bud?
4th week
what happens to the respiratory bud?
it grows ventrocaudally and bifurcates- forms the primary bronchial buds
where do the primary bronchial buds grow?
laterally into the pericardioperitoneal canals
what does the outgrowth of the primary bronchial buds require?
requires inductive interactions between the endoderm and splanchnic mesoderm (goes both directions in the lungs)
what is the branching of the primary bronchial buds partially regulated by?
FGF family members from the endoderm that tell the mesoderm to branch
when do the primary bronchial buds begin to branch?
5th week
what is the branching pattern of the lung endoderm regulated by?
the splanchnic mesenchyme
when are bronchopulmonary segments established?
by the 7th week
what are bronchopulmonary segments?
segmental bronchi +mesenchyme
how many stages are there for lung maturation? and what are they?
4; pseudoglandular, canalicular, terminal sac, and alveolar
when do you have the pseudoglandular stage of lung maturation?
5-17 weeks
what is a key characteristic of the pseudoglandular stage of lung maturation?
all major elements of the lung have formed, except those involved with gas exchange; fetus cannot survive
when do you have the canalicular stage of lung maturation?
16-25 weeks
what is a key characteristic of the canalicular stage of lung maturation?
it overlaps the pseudoglandular stage; there is vascularization occuring; there are now respiratory bronchioles, and the primordial alveolar and sacs are present; +/- survival
when do you have the terminal sac stage?
24 weeks-birth
what is a key characteristic of the terminal sac stage?
numerous alveoli are forming; surfactant is now produced
when do we have the alveolar stage of lung maturation?
32 weeks- 8 years
how do we get more air structures once we are born?
the primitive alveoli are still able to form additional primitive alveoli; once they go to the mature alveoli, they can no longer divide out to keep adding alveoli
what is lung growth dependent on?
the increase in number of alveoli not the size of the respiratory bronchioles and primordial alveoli
what are fetal breathing movements essential for and why?
essential for normal lung development; it is an intermittent pattern that conditions the respiratory muscles
at birth, aeration of the lungs requires rapid replacement of the intra-alveolar fluid with air; how does this occur?
- released from the mouth/nose by pressure on the fetal thorax during vaginal delivery; 2. pulmonary capillaries, arteries, and veins; 3. lymphatics
what is pulmonary agenesis?
complete absence of a lung or a lobe and accompanying bronchi
what causes pulmonary agenesis?
the respiratory bud fails to split into r/l bronchial buds
what is pulmonary hypoplasia?
you still have both buds of the lung that form, but due to pressure that is on one side, you actually get a smaller lung tissue that forms; negatively impacts lung development
what could cause pulmonary hypoplasia?
it occurs with severe and chronic oligohydraminos
what is oligohydramnios (potters) sequence?
we have renal agenesis, which causes oligohydramnios; the secondary malformation is pulmonary hypoplasia; and fetal compression
what is respiratory distress syndrome(RDS)?
rapid, labored breathing that develops shortly after birth
what is a major cause of RDS?
surfactant deficiency
what effect does a surfactant deficiency have on the fetus?
lungs are underinflated, alveoli contain a fluid that resembles a glassy membrane(hyaline membrane disease), irreversible changes in the type II alveolar cells make them incapable of producing surfactant
