Respiratory and GI Development (Embryo) Flashcards
1
Q
The gut forms from the folding of:
A
Endoderm and splanchnic mesoderm in the ventral direction
2
Q
When does this folding occur?
A
4th week
3
Q
The folding occurs in what directions?
A
Both cephalocaudal and transverse directions
4
Q
What does the gut “pinch off” from?
A
The yolk sac
5
Q
What is the only connection to the yolk sac through?
A
The midgut
6
Q
What does the endoderm form?
A
Epithelial lining of respiratory system and the gut tube EXCEPT for the lower end of the anal canal; Most of the glandular tissue in the respiratory and GI systems
7
Q
The splanchnic mesoderm forms:
A
Muscle, vascular, and connective tissue, and VISCERAL layers of the serous membranes
8
Q
What does the somatic mesoderm form?
A
The parietal layer of pleura, pericardium, peritoneum, and contributes to the body wall
9
Q
What does the ectoderm form?
A
Lower anal canal epithelium and the neural crest cells form support cells of the peripheral nervous system and the enteric plexus
10
Q
Pancreas cells are derived from which germ layer?
A
Endoderm
11
Q
Visceral peritoneum is derived from which layer?
A
Splanchnic mesoderm
12
Q
What is the beginning of the gut tube bounded by?
A
The stomodeum (primitive mouth) and oropharyngeal (Bucoophraryngeal) membrane at the cranial end
13
Q
What is the caudal end of the gut tube bounded by?
A
The cloacal membrane and proctodeum (anal pit). The gut tube is suspended between a dorsal and ventral mesentery
14
Q
The gut develops into 3 sections:
A
Foregut, midgut, and hindgut
15
Q
What does the foregut form?
A
Pharynx and its derivatives, lung epithelium, and gut to the proximal duodenum
16
Q
What does the midgut form?
A
The rest of the duodenum and intestines to about half - 2/3 of the transverse colon
17
Q
What does the hindgut form?
A
The rest of intestines EXCEPT lower anal canal and forms epithelium of bladder and urethra
18
Q
Respiratory system develops as:
A
Diverticulum off of the FOREGUT
19
Q
The endoderm of the diverticulum forms the:
A
Epithelium and glands of the larynx, trachea, bronchi, and lungs
20
Q
Mesoderm around the diverticulum gives rise to the:
A
Smooth muscle, CT, and cartilage EXCEPT for the laryngeal cartilages and muscle
21
Q
What are the laryngeal cartilages and muscle derived from?
A
Mesoderm of the pharyngeal arches
22
Q
What is the laryngotracheal or respiratory diverticulum?
A
In the 4th week, a diverticulum develops in the floor of the pharyngeal endoderm, caudal to the fourth pouches.
23
Q
What is the laryngotracheal (or respiratory diverticulum) surrounded by?
A
Splanchnic mesoderm
24
Q
The diverticulum elongates and its distal end enlarges as:
A
R and L lung buds
25
How do the trachea and esophagus separate?
Tracheoesophageal ridges or folds develop in respiratory diverticulum and these fuse to form a tracheoesophageal septum --> creastes a laryngotracheal tube, separate from the foregut --> develops into the larynx, trachea, bronchi, and lungs
26
Where is communication with the foregut maintained?
At the laryngeal inlet
27
The formation of the septum and the separation of larync and trachea from the foregut requires:
Sonic hedgehog protein
28
Describe the development of the larynx:
Develops at the cephalic end of respiratory diverticulum. The internal lining of larynx develops from endoderm; laryngeal cartilages and muscles develop from the mesoderm of the 4th and 6th pharyngeal arches
29
Two laryngeal swellings develop, the epiglottal and arytenoid swellings which give rise to:
Epiglottis and the laryngeal cartilages
30
What does proliferation of laryngeal epithelium cause?
The lumen to be temporarily occulded
31
What happens in the 9-10th weeks?
There is recanalization and the formation of the ventricles and false and true vocal cords
32
When does the larynx grow rapidly?
In the first 3 years of life after birth
33
Derivatives of the 4th arch are innervated by:
Superior laryngeal nerve
34
Derivatives of the sixth arch are innervated by:
Recurrent laryngeal nerve
35
The respiratory system arises as a diverticulum from where?
Endoderm of floor of pharynx
36
What kind of defect will occur if there is no sonic hedgehog protein?
Defect in the separation of trachea and esophagus
37
What is atresia?
The absence of normal opening or absence of normally patent lumen
38
What is a fistula?
Abnormal passage from an organ to the body surface or between organs
39
What is polyhydramnios?
Excessive amount of amniotic fluid. It may be due to GI abnormalities involving inadequate swallowing of fluid, such as duodenal or esophageal atresia.
40
What is polyhydramnois associated with?
Maternal complications due to abdominal swelling and fetal complications such as impaired uteroplacental perfusion
41
What is oligohydramnios?
Deficient amount of amniotic fluid. There may just be reduced amount or virtually no fluid.
42
What could oligohydramnois be due to?
Faulty development of the urinary system such as renal agenesis or polycystic kidney, resulting in urine not being added to the amniotic fluid. Bilateral renal agenesis leads to severe oligohydramnios.
43
Why is oligohydramnios dangerous to the fetus?
Insufficient amounts of fluid surrounding the fetus allows for compression of the abdomen and thorax --> pulmonary hypoplasia results
44
What is an esophageal atresia and/or tracheoesophageal fistula?
Abnormality in partitioning of the esophagus and trachea by the tracheoesophageal septum.
45
Where is the most common tracheoesophageal variation?
Where the upper part of the esophagus ends in a blind pouch (esophageal atresia) and the lower part opens into the trachea (tracheoesophageal fistula - TEF)
46
What is the most common abnormality in development of the lower respiratory tract?
TEFs - in 1 of 3000-5000 births
47
What are esophageal atresia and TEFs usually accompanied by? And why?
Polyhydramnios because amniotic fluid does not enter the GI tract for absorption
48
Clinical findings for esophageal atresia and TEF:
- Polyhydramnios prenatally
- Copious frothy bubbles of mucus in the mouth
- Difficulty breathing, cyanosis or pneumonia may develop if there is a connection to the trachea
- If there is a fistula, air builds up in abdomen
- Often associated with other abnormalities such as Down's, duodenal atresia, CV defects
49
What is the treatment for TEF?
Surgery. If there are other defects, they are usually corrected first
50
What is recanalization?
When the lumen is occluded by proliferation of cells, vacuoles develop, coalesce, and form a new lumen
51
What is atresia?
Failure to develop a lumen or opening
52
GI abnormalities often result in polyhydramnios or oligohydramnios?
Poly
53
Bronchi and lungs develop from:
Respiratory diverticulum of foregut
54
What is important about the interaction between the endoderm and mesoderm that affects development of bronchi/lungs?
Branching morphogenesis depends on proper interaction of endoderm and splanchnic mesoderm - the epithelium (from endoderm) produces sonic hedgehog protein which acts on the mesoderm --> the mesoderm then produces growth factors that cause the endoderm to develop the airways and air sacs
55
What else is essential to bronchi/lung development?
Adequate vasculature and surfactant
56
When is the embryonic period in lung development?
26 days - 6 weeks
57
What happens during the embryonic period?
- Lung bud develops, branches into main, lobar, and then segmental bronchi
- Bronchopulmonary segments are established
- Branching of bronchila tree will continue until after birth
- There is a pulmonary artery and vein, with an intervening capillary bed
- Primitive pleural cavities develop
58
When is the pseudoglandular period?
5-16 weeks
59
What happens during the pseudoglandular period?
- Continued branching leads to formation of terminal bronchiols
- No respiratory bronchioles, alveoli or contact with blood vessels
60
Is survival likely at pseudoglandular period?
No, it is impossible. The caritlage, glands, and bronchial smooth m are also developing, the diaphragm is forming, and the pulmonary vessels are branching at this time
61
When is the canalicular period?
16-26 weeks
62
What happens in the canalicular period?
- Gas exchange portion of lungs begins to develop
- Each terminal bronchiole divides into several respiratory bronchioles
- Terminal sacs (primitive alveoli) appear toward the latter part of this period
- Type II cells are present
63
When is surfactant formed?
First formed at low levels about the 20-26th week and increases in amount with time
64
Is survival likely at the canalicular period?
It is possible toward the end of the period because vasculature develops close to respiratory bronchioles
65
When is the terminal sac period?
26 weeks - birth
66
What happens in the terminal sac period?
- Terminal sacs (primitive alveoli) increase in number
- Capillaries bulge into the developing alveoli
- Well-developed Type I and Type II cells are present
- Type I cells thin and the rudimentary blood-air barrier is formed The blood-air barrier thins to allow for gas exchange.
67
When is the significant rise in surfactant levels?
Around week 30
68
When is the alveolar period?
30 weeks - 8 years
69
What happens during the alveolar period?
Alveoli mature and increase in number, especially in the first 2 years of postnatal life. Most of the mature alveoli form after birth through age 8
70
How is forensic medicine used to determine if an infant was stillborn or died after birth?
At birth the lungs are half-filled with fluid that is mainly produced by the lungs. The fluid is eliminated through the nose and mouth at delivery and later thru resorption by pulmonary capillaries and lymphatics. Thus, lungs of a stillborn would still have fluid and would SINK in water, whereas the aerated lungs of a newborn would be full of air and would float. Now the lungs, larynx, trachea, and bronchi are removed and placed in water
71
How does forensic medicine use histology to determine stillborn vs. died after birth?
In the newborn, the alveoli are dilated, the bronchi are open, and the capillaries are open and filled with RBCs
72
What is surfactant and what is its purpose?
Complex of lipids, proteins, including phosphotidyl choline and surfactant proteins A, B, C, and D. Surfactant lines the alveoli and reduces surface tension, thus preventing the alveoli from collapsing during respiration. Surfactant is excreted by the fetus into the amniotic fluid. Adequate levels are essential for survival.
73
Describe the assessment of fetal lung maturity using amniotic fluid obtained thru amniocentesis:
The first test dveloped to assess the maturity of fetal lungs was the lecithin to sphingomyelin ration (L/S) ratio. Sphingomyelin is a phospholipid found in cell membranes; lecithin is a phospholipid found in high concentrations in surfactant
74
What level is considered mature?
The L/S ratio gradually increases and is 2 at 35 weeks. 2 is mature, 1.5-2 is borderline and less than 1.5 is immature. At ratios of 1.5-1.9, about 50% will develop respiratory distress syndrome but this test will NOT tell you which mabies will develop RDS
75
What is respiratory distress syndrome (RDS)?
Due to insufficient surfactant and is the leading cause of death in premature babies. The alveoli are partially collapsed and covered by an amorphous material containing fibrin, cellular debris, and macrophages. This material prevents gas exchange (hyaline membrane disease)
76
What is used to treat RDS?
Corticosteroids, assisted ventilation, and administration of artificial surfactant are used to treat the syndrome
77
What is pulmonary hypoplasia?
Underdevelopment of lungs with a reduced number of alveoli and airways. It may be associated with:
- Thoracic compression due to bilateral renal agenesis or urinary outflow obstruction. These result in oligohydramnios, which in turn causes pressure on the fetal thorax
- Decreased intrathoracic space - may be due to a congenital diaphragmatic hernia, which is the most common cause of pulmonary hypoplasia
- Decreased fetal breathing due to CNS damage
78
When placed in water, the lungs of a stillborn infant would:
Sink
79
The capillaries in the lungs of a ________ infant would be open and filled with RBCs:
Newborn
80
An L/S ratio of ______ indicates lung maturity.
2.0
81
When does the body cavity form?
When the lateral mesoderm splits into 2 layers and the embryo undergoes cephalocaudal and lateral folding
82
In the intraembryonic cavity, the somatic mesoderm will give rise to:
The parietal layer of the serous membranes
83
In the intraembryonic cavity, splanchnic mesoderm will form:
The visceral layer.
84
The visceral and parietal layers are continuous with each other at?
The dorsal mesentery
85
At 4 weeks, what does the intraembryonic cavity look like?
A horshoe-shaped cavity, curving around the cranial end of the embryo. The septum transversum has incompletely separated the cranial primitive pericardial cavity from the peritoneal cavity
86
The 3 regions of the intraembryonic cavity at this point are:
1. Pericardial cavity around the heart
2. Two pericardioperitoneal canals which lead into the
3. Peritoneal cavity
87
What are pleuropericardial folds?
Folds that arise from the lateral body wall. Extend medially and the extensions, which enclose the PHRENIC N, are then known as the pleuropericardial membranes.
88
What happens after they become pleuropericardial membranes?
These fuse with each other and the root of the lung, separating the pleural cavities from the pericardial cavity. In the adult, the membranes form the fibrous pericardium
89
What is the course of the phrenic nn in the pleuropericardial membranes?
It starts out in the membranes and becomes located between the fibrous pericardium and the pleura
90
What is the septum transversum?
Thick plate of mesodermal tissue between the thoracic cavity and the stalk of the yolk sac. It partially separates the thoracic and abdominal cavities.
91
The pleuropericardial membranes separate:
The pericardial cavity from the pleural cavities.
92
The pleural cavities still communicate with the peritoneal cavity via the:
Pericardioperitoneal canals
93
The two pleuroperitoneal folds (membranes) grow from the posterolateral walls of the pericardioperitoneal canals and fuse with:
The septum transversum and mesentery of the esophagus, thus separating the pleural and peritoneal cavities.
94
The pericardioperitoneal canals are closed by:
The 7th week
95
The septum transversum becomes:
Central tendon of diaphragm
96
Pleuroperitoneal membranes extend from the posterolateral walls across the pericardioperitoneal canals and fuse with:
Septum transversum to form the posteriolateral portion of the diaphragm
97
As the lungs develop and pleural cavities enlarge, tissue from the _________ is added to the outer margins of the pleuroperitoneal membranes
Body wall
98
Crura of the diaphragm develop from:
Myoblasts in the dorsal mesentery of the esophagus
99
The septum transversum is originally located at the level of somites C 3,4,5 and receives:
Myoblasts from those lebels
100
What accounts for some sensory innervation to th peripheral part of the diaphragm?
The diaphragm descends and carries its nerve supply with it. THe contribution of the body wall to the peripheral part of the diaphragm accounts for some sensory innervation by intercostal nerves
101
The pleuroperitoneal membranes close the:
Pericardioperitoneal canals
102
The septum transversum is derived from which germ layer?
Mesoderm
103
The thoracic cavity is separated from the abdominal cavity by the _____ week.
7th
104
The crura of the diaphragm are derived from:
The dorsal mesentery of the esophagus
105
What is a congenital diaphragmatic hernia?
1 in 2000 babies is diagnosed with this, half of those don't live til 1.
- Hernia is due to posterolateral defect in the diaphragm, usually on the left side
- Due to a defect in the formation of the pleuroperitoneal membrane
- Abdominal structures herniate into the thorax and compress the lung, which becomes hypoplastic
- Heart may be displaced to the R
- Amount of functional lung tissue and the amount of HTN in the pulmonary vessels affect the survival of the infant
106
What is the treatment for this type of hernia?
Surgery may be performed in utero or after the baby is born. The outcome depends on the condition of the lungs and other complications
107
When does the gastrointestinal system develop?
4-12 weeks
108
The GI ssystem is divided into 3 parts, each with its own blood supply:
Foregut, midgut and hindgut
109
What is the foregut?
Pharynx to duodenum at the site of entry of the bile duct. Lower portion supplied by the celiac artery.
110
What is the midgut?
Just distal to the entrance of bile duct into duodenum to right 2/3 of transverse colon. Supplied by the superioer mesenteric artery
111
What is the hindgut?
Left 1/3 of the transverse colon to anal canal above pectinate line. Supplied by the inferior mesenteric artery
112
Blood supply of the foregut:
- Pharyngeal arch sources
- Pulmonary arteries
- Celiac artery
113
Derivatives of the foregut:
- Part of the floor of mouth
- Pharynx and derivatives
- Respiratory system
- Esophagus
- Stomach
- Pancreas
- Liver, gallbladder, and biliary duct system
- Duodenum proximal to bile duct
114
What is the last connection with the yolk sac and umbilical region?
Midgut
115
Blood supply of the midgut:
Superior mesenteri artery
116
Derivatives of the midgut:
- Duodenum distal to bile duct
- Jejunum and ileum
- Cecum and vermiform appendix
- Ascending colon
- Right half-2/3 of transverse colon
117
Blood supply of the hindgut:
Inferior mesenteric artery, except for bladder and urethra
118
Derivatives of hindgut:
- Left 1/3-1/2 of the transverse colon
- Descending colon
- Sigmoid colon
- Rectum
- Superior portion of anal canal
- Derivatives of UG sinus
119
Differentation depends on reciprocal interaction between:
Endoderm and splanchnic mesoderm
120
How does this reciprocal interaction work?
Endoderm secretes Sonic Hedgehog Protein throughout the gut tube --> induces genes in the mseoderm which then --> instruct the endoderm what structures to form (ex: stomach in the foregut region.) Mesoderm then forms appropriate muscle and CT structures for that region
121
Abdominal foregut is initially attached to:
The septum transversum (gut is suspended from body wall by mesenteries)
122
Caudal part of the septum transversum thins to become the:
Ventral mesentery of the stomach
123
The dorsal mesentery is attached to the dorsal border of:
The abdominal foregut, midgut, and hindgut. It attaches the gut to the posterior abdominal wall
124
What is the primitive gut tube a result of?
Body folding, where part of the yolk sac cavity is incorporated into the embryo
125
What is esophageal stenosis?
Rare congenital defect; most is acquired. There is a narrowing of the lumen, due to incomplete recanalization, or to abnormal development of blood vessels in that are leading to ischemia and necrosis of tissue. It may also be due to hypertrophy of muscularis and submucosal layers. Symptoms include vomiting, difficulty swallowing, and failure to thrive.
126
Treatment of esophageal stenosis?
May be dilation with a balloon or surgical resection
127
What is a congenital hiatal hernia?
Esophagus too short and the stomach is pulled up thru esophageal hiatus of diaphragm
128
Initially the ventral border of the stomach is attached to the ventral abdominal wall by a ventral mesentery:
Ventral mesogastrium
129
The dorsal border is attached to the posterior abdominal wall by a dorsal mesentery:
The dorsal mesogastrium
130
What happns to the stomach during the 5th week of development?
The dorsal border elongates to form the greater curvature and the ventral persists as the lesser curvature.
131
As the curvatures form - Lesser curvature to the R and greater curvature to the L. The original L side becomes the ventral surface and is innervated by:
The L vagus n
132
The right side becomes the dorsal surface and is innervated by:
R vagus n
133
As a result of the rotation of the stomach, the dorsal mesogastrium is pulled to the ______ and what forms behind the stomach?
Left; omental bursae (lesser sac)
134
The liver develops within which mesentery?
Ventral
135
Liver develops within the ventral mesentery and divides the mesentery into 2 parts:
Falciform ligament and the lesser omentum
136
The lesser omentum can be subdivided into:
Hepatogastric and hepatoduodenal ligaments
137
What becomes the greater omentum?
The dorsal mesogastrium bulges over the transverse colon and small intestine, due to rotation of the stomach. This double-layered sac becomes the greater omentum and its layers fuse to form one layer hanging from the greater curvature of the stomach
138
The spleen forms in the:
Dorsal mesogastrium, creating the gastroplenic and splenorenal ligaments
139
What is congeintal hypertrophic pyloric stenosis?
A thickening of the muscle of the pylorus, resulting in stenosis of the pyloric canal, which obstructs the passage of food. It is more common in males. I can be congeital condition of sometimes may develop shortly after birth. Symptoms develop within a few weeks after birth and include non-bilious projectile vomiting, constant hunger, dehydration, and abdominal pain. Tx is surgical repair
140
The spleen develops from mesoderm in the:
Dorsal mesogastrium
141
What does the spleen function as?
A hemopoietic center until late fetal life, then it assumes a lymphoid function
142
The dorsal mesogastrium between the stomach and spleen becomes the:
Gastrosplenic ligament
143
The dorsal mesogastrium between the spleen and kidney becomes:
Splenorenal ligament
144
The spleen is retroperitoneal or peritoneal?
Peritoneal
145
The duodenum develops from both the:
Foregut and midgut, with the junction just distal to the entry of the bile duct
146
The duodenum rotates to the ____ with the stomach and becomes fixed in the posterior body wall
R
147
What happens to the duodenum during the 8th week?
The lumen is temporarily obliterated by epithelial proliferation and then is recanalized.
148
What part is the last to recanalize and what occurs here?
The second part of the duodenum and most abnormalities occur here
149
What is duodenal obstruction?
Can range from atresia (where there is no connection with the distal gut) to stenosis (where the lumen is narrowed but some food passes through). It is thought to be due to a failure in the recanalization of the lumen
150
What else can cause duodenal obstruction?
Annular pancreas (but some feel that atresia came first, then the pancreas abnormality)
151
Where does the duodenal obstruction occur?
Just distal to the entry of the bile and pancreatic ducts at the duodenal papilla. Symptoms in atresia and stenosis may be similar but may take longer to develop in the case of stenosis. Atresia is fairly common - 1 in 2500-5000 births. Aldo midgut volvulus
