Body Cavities and Respiratory Embryo Flashcards
1
Q
What produces the lateral folds?
A
rapid growth of SC and somites
2
Q
How does head folding occur?
A
- embryo elongates cranially and caudally week 4
- neural folds project dorsally and overgrow oropharyngeal mem
- endoderm is incorporated as foregut
- Septum transversum, primordial heart, pericardial coelom and oropharyngeal form
3
Q
What three things happen after head folding?
A
- Pericardial cavity is ventral
- Pericardioperitoneal canals run dorsally on sides of foregut
- Intraembryonic and extraembryonic coeloms are in communication
4
Q
What is Gastroschisis?
A
- protrustion of viscera usually is to right of umbilical cord rather than midline
- Bowel is not covered and floating in amniotic fluid
- Results from failure of lateral body folds to fuse at week four
5
Q
What is congenital epigastric hernia?
A
- Midline bulge of abdominal wall located between the xiphoid process and umbilicus
- The bowel is covered by skin and subcutaneous tissues
6
Q
What is the significance of intraembryonic coelom with body wall formation?
A
- Divides the lateral mesoderm into somatic layers of mesoderm and splanchnic layer of lateral mesoderm
- Somatic (parietal) continuous with extraembryonic mesoderm covering amnion
- Splanchnic (visceral) layer of lat mesoderm is continuous with extraembryonic mesoderm covering umbilical vesicle
7
Q
What three divisions does the intraembryonic coelom consist of?
A
- Pericardial cavity
- Pericardioperitoneal canals (2)
- Peritoneal cavity
8
Q
What is the more superior fold that divides the pericardial caivity from pleural cavity?
A
Pleuropericardial folds
9
Q
What fold separates the pleural cavities from peritoneal cavity?
A
Pleuroperitoneal folds
10
Q
How do pleuropericardial membranes form?
A
- Pleuropericardial folds form as outgrowths of lateral body wall and grow ventrally
- They enlarge as the pleuropericardial membranes and project across upper limit of pericardioperitoneal canals
11
Q
What causes the pleural cavity to expand and what results from this expansion?
A
- Bronchial bud outgrowths (lungs) are growing ventrally and shapes the cavity
- It splits mesenchyme into an outer layer and inner layer
- Thoracic wall (outer)
- Fibrous pericardium (inner layer of mesenchyme, but outer layer of the pericardial sac)
12
Q
How do pleuroperitoneal membranes form?
A
- Pleuroperitoneal folds form as outgrowths of lateral body wall and project into the pericardioperitoneal canals forming the pleuroperitoneal membranes
- Myoblasts contribute to pleuroperitoneal membranes to complete closure
- right closes before left
13
Q
When do the pleuroperitoneal membranes fuse with dorsal mesentery of esophagus and septum transversum?
A
6th week
14
Q
What are the four components of the diaphragm?
A
- Septum transversum:
- Expands and fuses with dorsal mesentery of esophagus and pleuroperitoneal membranes
- central tendon
- Pleuroperitoneal mem:
- fuses wit hdorsal mesentery of esophagus and septum transversum
- Primordial diaphragm
- Dorsal mesentery:
- Median portion of diaphragm
- Myoblasts:
- grows into dorsal mesentery
- Crura of diaphragm
15
Q
What do myoblasts form that is part of the adult diaphragm?
A
Crura
16
Q
What forms from the septum transversum?
A
Central tendon of the diaphragm
17
Q
A
18
Q
How does the diaphragm get innervation?
A
- Myoblasts will pull C3,4,5 ventral rami with them as they pass through the pleuropericardial membranes
- Eventually phrenic will lie on the fibrous pericardium
19
Q
What is a congenital diaphragmatic hernia?
A
- Lack of myoblasts populating pleuroperitoneal membranes and results in weakness and herniation of abdominal viscera into pleural cavity
- Lung maturation can be delayed and polyhydramnios may also be present
- Left side is usually impacted
- Can be corrected at brith
20
Q
How does the respiratory system start and where is this structure located?
A
- As a median outgrowth called the laryngotracheal groove
- Which is located in the floor of the foregut/primordial pharynx
21
Q
What does the laryngotracheal groove evaginate into?
A
Laryngotracheal diverticulum, the primordium of the traccheobronchial tree
22
Q
What does the endoderm of the laryngotracheal groove form?
A
- Pulmonary epithelium and glands of larynx trachea and bronchi
23
Q
What does the splanchinic mesoderm of the respiratory system form?
A
- CT
- Cartilage
- Smooth mm
24
Q
How does the laryngotracheal diverticulum and splanchnic mesoderm relate?
A
The diverticulum elongates and becomes invested with the splanchnic mesoderm. The distal end elarges to form respiratory bud
25
When do tracheoesophageal folds develop?
Fuse to form the trachoesophageal septum at end of week 5
26
Where does the cartilage of the larynx come from?
Mesenchyme of the fourth and sixth pharyngeal arches
(NCC derivative)
27
when do vestibular and vocal folds form?
* Forms during recanalization around week 10
28
What is laryngeal atresia, what causes it, what happens to lungs and dipahrgam and what is the treatment?
* Rare, results from failure of recanalizstion of larynx
* Obstruction of the upper fetal airway or Congeniatal high ariway obstruction syndrom (CHAOS)
* Airways become dilated and lungs enlarged and filled with fluid
* Diaphragm is flattened or inverted and fetal ascites or hydrops is present
* Treatment is by endoscopic dilation of laryngeal web
29
Where does the epiglottis develop from?
* Hypopharyngeal eminence produced from the mesenchyme of 3 &4 PA
30
What PA's do laryngeal muscles develop from?
Myoblasts of 4th and 6th arch
31
Describe position of larynx an epiglottis in neonates?
* High position in the neck of the neonate
* Epiglottis is in contact with the soft palate and separates respiratory and digestive tracts
32
What does the endoderm contribute to the trachea?
* Differentiates into the tracheal epithelium and glands
33
What does the splanchnic mesoderm contribute to the trachea?
* CT
* Muscle
* tracheal cartilages
34
What is a tracheoesophageal fistula and what is associated with it?
* Most common anomaly of lower respiratory tract
* Abnormal conection btw trachea and esophagus
* Failure of th eforegut endodemr to proliferate quick enough in relation to the rest of the body
* 85% of cases associated with esophageal atresia (blind esophagus)
35
How do patients with tracheoesophageal fistula present?
* Can't swallow
* Frequently drool
* Immediate regurgitation after feeding
* Gastric and intestinal contents may reflux through fistula into trachea and lungs
* Can develop **polyhydramnios** as fluid can't enter stomach/intestines for absorption
36
In week 4, the laryngotracheal diverticulum enlarges to form \_\_\_\_.
In week 4, the laryngotracheal diverticulum enlarges to form **respiratory bud**
37
How does the respiratory bud grow, what induces this, and what does it form?
* Ventrocaudally and bifurcates forming the **primary bronchial buds**
* Requires FGF and inductive interactions btw endoderm and splanchinc mesoderm
38
Describe the order of bronchi.
* Main bronchi
* Secondary bronchi
* Lobar
* Segmental
* Intrasegmental branches
39
What are bronchopulmonary segments?
* Form during week 7
* Made of segmental bronchi and mesenchyme
40
Describe psuedoglandular lung maturation.
* Weeks 5-17
* All major elements formed **except** those involved with gas exchange
* Fetus cannot live
41
What happens in the canalicular lung maturation stage?
* Overlaps with the psuedoglandular
* Vascularization
* Respiratory bronchioles present
* Primordial alveolar and sacs present
* may or may not survive
* weeks 16-25
42
What is the terminal sac maturation stage?
* Numerous alveoli form
* Thin epithelium with increased vascularization such as:
* Type 1 pneumocytes
* Type 2 pneumocytes (surfactant!)
* Lymphatic capillaries
* Gas exchange can occur
* Survivable with appropriate care
* 24 wks to birth
43
What is the alveolar stage of maturation?
* 32 wks-8 yrs
* Alveolocapillary membrane
* Primitive alveoli form more primitive alveoli
* Mature alveoli
## Footnote
*Primitive alveoli are key to adding more alveoli, once they turn mature they can't add more*
44
When do 95% of mature alveoli develop?
Postnatally
45
What is lung growth dependent on?
* Increase in **number** of respiratory bronchioles and primordial alveoli
46
How long are new alveoli added?
Until 8 years of age as the CT septa divide immature/promordial alveoli
47
What is the significance of fetal breathing movemnts?
* Essential for normal lung maturation exercising the respiratory muscles
* Forceful enough to cause aspiration of amniotic fluid and helps stimulate lung dev
* At birth aeration of lungs reuires rapid replacecment of intralveolar fluid with air
48
How is the intra-alveolar fluid cleared?
* Released from mouth and nose by pressure on thorax duirng vaginal delivery
* Pulmonary capillaries rteries and veins
* Lymphatics
49
What is unilateral agenesis?
* Compelte absence of a lung or lobe accompanying bronchi
* Respiratory bud fails to split into L and R
50
What is pulmonary hypoplasia?
* Results from restriction of fetal thorax due to uterine pressure
* Decreased hydrostatic pressure on the lungs affects stretch receptors and lung growth
* It occurs wit hsevere and chronic oligohydramnios
* Risk increases significantly with oligohydramnions at less than 26 weeks
51
what is RDS?
* Rapid labored breathing developing after birth
* Surfactant deficiency is major cause as lungs are underinflated
* Accounts for 5-7-% of deaths in premature infants
* Alveoli contain glassy membrane fluid and it is an irreversible change in type 2 alveolar cells
52
Signs and Symptoms of RDS?
* Tachypnea
* Nasal flaring
* Suprasternal intercostal or subcostal retractions
* Grunting and cyanosis
* Opacification on x ray
53
How does head folding movements reshape the intraembryonic coelom?
* Pericardial cavity is relocated ventrally anterior to foregut
* Pericardial cavity opens into pericardioperitoneal canals located dorsal to foregut
* Caudal periotneal cavity is positoned where IE and EE coelomes are continuous
