Embryology Flashcards
(98 cards)
1
Q
What structures are formed from the 1st aortic/pharyngeal arch?
A
External carotid A., maxillary A.
2
Q
What structures are formed from the 2nd aortic/pharyngeal arch?
A
Stems of stapedial arteries (ears)
3
Q
What structures are formed from the Aortic Sac?
A
Aortic sac is remodeled into the Brachiocephalic A. and the base of the aortic arch
4
Q
What structures are formed from the 3rd aortic/pharyngeal arch?
A
Common Carotid A.
Internal Carotid A.
5
Q
What structures are formed from the 4th aortic/pharyngeal arch?
A
Left: medial portion of aortic arch
Right: proximal right subclavian A.
6
Q
What structures are formed from the 6th aortic/pharyngeal arch?
A
Lungs and Larynx
Pulmonary Arteries:
- left distal Ductus Arteriosus
- Right distal DEGENERATES
7
Q
What structures are formed from the 7th intersegmental Arteries?
A
Right: distal part of right subclavian A.
(4th arch does proximal portion)
Left: entire left subclavian A.
8
Q
What structures are formed from the dorsal aorta?
A
Right: portion of right subclavian
Left: Descending Aorta
9
Q
What is splanchnopleura?
A
Splanchnic mesoderm and endoderm (yolk sac)
10
Q
What is somatopleura?
A
Somatic mesoderm and ectoderm
11
Q
Ectopia cordis
A
Heart trapped outside body cavity
Split sternum (bifed) unable to merge
Can result in dear due to infection if not surgically corrected
12
Q
Somatic mesoderm forms what and originates from where?
A
Parietal Pleura Parietal Pericardium - innermost layer of tissue on pericardial coelom - Fibrous Pericardium - Serous Pericardium Parietal Peritoneum
Lateral Plate mesoderm
13
Q
Splanchnic Mesoderm forms what and originates from where?
A
Visceral Pleura
Visceral Pericardium - outermost tissue layer on heart
Visceral Peritoneum
Lateral plate mesoderm
14
Q
How is the diaphragm formed?
A
Merging of the septum transversum and pleuroperitoneal membrane
15
Q
Where does foregut endoderm come from?
What does it develop into?
A
Comes from 6th pharyngeal arch
Forms the larynx and lungs
16
Q
How are the pericardial cavity and pleural cavity separated?
A
The pleuropericardial membrane with the phrenic nerve
17
Q
Laryngeal Atresia
A
Failure of recanalization at week 10
Results in obstruction of fetal airway
Presents with asphyxia (can’t breathe) at birth
18
Q
Laryngeal Webs
A
Incomplete atresia (blockage) due to incomplete recanalization at week 10
Laryngeal web is tissue between the vocal folds
Patients present in infancy with respiratory distress plus an unusual cry/stridor (high pitch weeze)
19
Q
Laryngomalacia
A
Most common congenital abnormality of the larynx
Collapse of the supraglottic structure during inspiration
Makes it difficult to breathe
20
Q
Endodermal Derivatives of the lung:
A
Pulmonary epithelium
Glands of the trachea
21
Q
Lateral Plate mesoderm derivatives:
A
Splanchnic:
- cartilage
- Connective tissue
- smooth muscle
- visceral pleura
Somatic:
- parietal pleura
22
Q
Tracheoesophageal (TE) Fistula
A
Abnormal passage between trachea and esophagus
Food aspirates into lung - causing cough and infection
Problem with formation of tracheoesophageal folds in WEEK 5
23
Q
What happens at week 4 in lung development?
A
Lung buds
24
Q
What happens at week 5 in lung development?
A
Primary bronchial buds
25
What happens at week 6 in lung development?
Secondary bronchi
3 on the right
2 on the left
(Just like the lobes)
26
What happens at week 7 in lung development?
Tertiary bronchi
10 on right
9 on left
27
What happens at 24 weeks in lung development?
17 orders of branches
Terminal bronchioles are present
Lungs are now a conduction system, but no gas exchange can occur
28
Pseudoglandular Stage of Lung development (Weeks 5-17)
Terminal bronchioles formed; Connective tissue and capillaries present
However, capillaries are NOT in close enough in proximity to terminal bronchioles for gas exchange to occur.
Baby born at this stage will not survive
29
Canalicular Stage of Lung development (Weeks 16-25)
Vascularization (capillaries closer to airway); respiratory bronchioles formed from terminal bronchioles (primordial alveolar ducts)
Terminal sacs present (primitive alveoli)
Baby born at this stage may or may not survive. If born later (closer to 25 weeks) it may be able to survive with medical intervention. Earlier births are less likely.
30
Terminal Sac stage of Lung Development (24 weeks - Birth)
```
Gas exchange occurs
Squamous epithelium (Type I pneumocytes) present
Secretory epithelium (Type II pneumocytes) present - SURFACTANT
Lymphatic capillaries present.
```
Baby born at this stage will survive
31
Alveolar stage of Lung Development (32 weeks - 8 years)
Alveolocapillary membrane (alveoli = endoderm; capillaries = mesoderm) matures over time.
Primitive alveoli become mature alveoli (95% mature after birth)
32
Pulmonary Agenesis
Respiratory bud fails to split resulting in complete absence of lung or lobe
33
Pulmonary Hypoplasia
“Small lung”
| Caused by oligohydramnios (too little amniotic fluid) which retards lung development
34
Respiratory Distress Syndrome
Caused by decreased surfactant production
| Tachypnea, nasal flaring, refractions, grunting, cyanosis
35
Polyhydroamnios
Excess amniotic fluid caused by esophageal atresia or tracheoesophageal fistula
Amniotic fluid can’t be absorbed in stomach or intestines
Amniotic fluid fluid level based on how much is outside the fetus (in womb)
36
Congenital diaphragmatic hernia
GI tract in thorax
Heart sounds in the wrong place due to displaced heart
Barrel chest; scaphoid (indented) abdomen
Failure of septum transversum meeting with pleuroperitoneal membrane
Week 6
37
Congenital lung cysts
Cysts filled with fluid or air
| Honeycomb appearance on X-ray
38
What are the heart fields, where do they come from, and what do they develop into?
Primary Heart Fields:
Splanchnic mesoderm that migrates during Gastrulation from primitive streak.
Develops into left atrium, right atrium, and left ventricle
Secondary Heart Fields:
Come from Pharyngeal arches
Develop into right ventricle, outflow tract, and part of atria (venous pole)
39
What is the Neural Crest contribution to heart development?
Neural crest cells originating from the myelencephalon (medulla) migrate through the 3rd, 4th, and 6th pharyngeal arches.
These cells help with formation of the Truncus Arteriosus (early outflow vessel that later splits into aorta pulmonary trunk) AND the Aorticopulmonary Septum (tissue that splits divides the truncus arteriosus into the aorta and pulmonary trunk)
40
What signals regulate cardiac neural crest migration and differentiation? What happens when there’s too much signaling?
Retinoic Acid (vitamin A), Hox genes, NF-1, and Pax3.
Too much vitamin A will disrupt cardiac development
41
What are the primitive divisions of the fused heart tube?
```
Truncus Arteriosus (blood exits heart tube)
Bulbus Cordis
Ventricle
Atrium
Sinus Venosus (Blood enters heart tube)
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42
Dextrocardia
Heart tube folds to the left (abnormal) instead of to the right (normal)
43
What occurs during Atrioventricular Canal Septation?
Endocardial cushions form from mesoderm and grow together
Results in Right and Left AV canals and separates atria from ventricle
This process is Retinoic Acid (Vitamin A) dependent, thus disruption of retinoids signaling often produces AV canal defects.
44
Changes in the Atria: Right horn of the sinus venosus
Right horn becomes incorporated into the Atrium and becomes the sinus venarum (smooth wall in the Atria)
Crista Terminalis represents the border between the sinus venarum and the pectinate muscle wall
Additionally, the Right horn forms the orifice of the Inferior vena cava, the orifice of the superior vena cava, and the orifice of the coronary sinus
45
What are the pectinate muscles derived from?
They come from the primitive heart tube
46
Changes in the Atria: Left horn of the Sinus Venosus
Remodeled into the Coronary Sinus
47
How does septation of the atria occur?
1) Septum primum forms inferiorly from the top of the atria. As it forms, it contains the Foramen Primum, which disappears as the Septum Primum fuses with the endocardial cushions
2) Foramen Secundum forms in the superior portion of the Septum Primum BEFORE Foramen Primum disappears (ensuring blood can continue to shunt from the right atrium to left atrium)
3) Septum Secundum forms to the right of the Septum Primum and overlaps it. Within the Septum Secundum, the Foramen Ovale forms
48
How does septation of the ventricles occur?
1) Muscular portion of the Interventricular Septum proliferates/migrates up toward the endocardial cushions
2) Muscular portion does not meet with the endocardial cushions, and leaves enough room for the formation of the Interventricular Foramen
49
How doe septation of the bulbus cordis and Truncus arteriosus occur?
1) Neural crest cells associated with Pharyngeal arches 4 and 6 migrate into the Truncus Arteriosus (undivided outflow) and Bulbus Cordis (aka Conus Cordis)
2) neural crest cells form ridges (truncal and bulbar ridges) that spiral 180 degrees to create the aorticopulmonary Septum
3) Ridges fuse and divide the bulbus Cordis and Truncus Arteriosus into Ascending Aorta and Pulmonary Trunk
4) Aorticopulmonary Septum fuses with endocardial cushions
5) The incorporated Bulbus Cordis is now split and made into the newly formed Conus Arteriosus (smooth muscle just before pulmonary valve) and the Aortic Vestibule (smooth muscle just before the aortic valve)
50
Membranous Portion of the Interventricular Septum
The Left and Right Bulbar ridges (from septation of the bulbus Cordis and the Truncus Arteriosus) fuse with the endocardial cushions to close the Interventricular Foramen.
Defects in the Interventricular Septum arise from the membranous portion
51
What are the main cardiac valves called and how are they formed?
```
Aortic Valve and Pulmonary Valve (semilunar valves)
Tricuspid Valve (Between the right atrium and ventricle)
Bicuspid Valve (between the Left atrium and ventricle)
```
1) Valve swellings form from splanchnic mesoderm and neural crest (semilunar valves form between the Truncus arteriosus and bulbus Cordis)
2) valve swellings proliferate as blood flow erodes them into cusps
Disruption of the neural crest that contribute can result in deformations of the valves.
52
Acyanotic Cardiac Anomally
Baby doesn’t turn blue.
Either no shunt or there is a left to right shunt (causes O2-rich blood to mix with O2-depleted blood in the right atrium)
Example: Patent Ductus Arteriosus (ductus arteriosus remains after birth)
53
Cyanotic Cardiac Abnormality
Baby turns blue Because it’s not getting enough O2.
Right to left shunt that causes O2-depleted blood to mix with O2-rich blood in the left ventricle.
54
Atrial Septal Defect: Ostium Secundum
Very common
Includes a patent Foramen ovale
Caused by excessive cell death and resorption of Septum Primum
OR
By inadequate development of Septum Secundum
55
Atrial Septal Defect: Probe Patent Foramen Ovale
Present in 25% of people
| Incomplete adhesion between the Foramen Ovale and the Septum Primum
56
Patent Ductus Arteriosus
Ductus arteriosus remains open after 72 hours after birth (at which point it should be closed)
Acyanotic
Presentation: Loud systolic murmur, trouble breathing
PDA doesn’t close because:
- low o2 content
- Circulating prostaglandin E2 (PGE2) - vasodilator; produced in placenta, mediated by its COX-2 isoform
Treatment:
- COX-2 inhibitors, ibuprofen, indomethacin, physical closure
If it remains untreated, high pressure blood in the aorta will enter the pulmonary trunk and can cause destruction of capillary beds in lungs.
57
Ventricular Septal defect
Acyanotic
Lack of membranous portion of Interventricular Septum (from bulbar ridges - neural crest)
Murmur heard at the left mid to lower sternal border OR left 3rd-4th intercostal space
Louder murmur = smaller hole
58
AV Septal Defect
Acyanotic (Left —>Right shunt)
COMPLETE AV Septal Defect:
- Atrial Septal defects
- Ventricular Septal defects
- Abnormal Valve Leaflets
PARTIAL AV Septal Defect:
- Atrial Septal defects
- Abnormal Valve leaflets
59
“Corrected” Transposition of the Great Vessels
Acyanotic
Interventricular Septum Defect
Right Ventricle and left ventricle grow on opposite sides of the heart than intended.
Caused by improper septation of outflow tract (partial spiraling)
Reversed rotation of heart
60
Transposition of Great Vessels
Cyanotic - aorta carries O2-depleted blood
Aorta and Pulmonary trunk are switched so that right ventricle sends blood through the aorta and the left ventricle sends blood through the pulmonary trunk
Septal defects
Persistent ductus arteriosus
Caused by improper spiraling of the Neural crest cells
61
What early vessels contribute to the formation of the Hepatic Segment of the Inferior Vena Cava?
Right vitelline/hepatic veins and sinuses
62
What early vessels contribute to the formation of the Prerenal Segment of the Inferior Vena Cava?
Right subcardinal V.
63
What early vessels contribute to the formation of the Renal Segment of the Inferior Vena Cava?
Subcardinal-supracardinal anastomosis
64
What early vessels contribute to the formation of the Postrenal Segment of the Inferior Vena Cava?
Right supracardinal V.
65
Double Outlet Right Ventricle
Cyanotic (right to left shunt)
Both Pulmonary trunk and aorta receive blood from the right ventricle due to an Interventricular Septal Defect in most cases
Abnormal migration of bulbar ridges during septation of the ventricles
Misalignment of the Interventricular Septum
66
Truncus Arteriosus
Cyanotic (right to left shunt)
Single great vessel - interventricular Septal Defect
Absence of truncal ridges and bulbar ridges to form and/or migrate to the midline
67
Tetralogy of Fallot
Cyanotic
Very serious, very common
Pulmonary stenosis with Interventricular Septal Defect, over riding aorta, right ventricular hypertrophy.
Deoxygenated blood sent through aorta due to Septal Defect and pulmonary artery stenosis.
Caused by abnormal Septal outflow tract
Treated with increasing pulmonary blood flow
68
Critical pulmonary stenosis
Cyanotic
Cusps of pulmonary valve are fused or thickened
Causes decreased pulmonary blood flow. Decreased perfusion of lungs causes cyanosis, depending on severity.
69
Critical aortic stenosis
Cyanotic due to reduced systemic blood flow
Features: tachypnea (rapid breathing), poor feeding, poor perfusion, may lead to hypoplastic left heart syndrome (left side of heart severely underdeveloped)
70
Hypoplastic left heart syndrome
Cyanotic
Common
Left ventricle is hypoplastic (underdeveloped, small)
Features: bicuspid valve stenosis or atresia, aortic Valve stenosis or atresia, aortic arch also hypoplastic
Dependent on Patent Ductus Arteriosus (PDA) and Atrial Septal Defect (ASD)
- oxygenated blood is directly shunted from the left atrium to the right atrium, mixing with deoxygenated blood.
- mixed blood then enters the right ventricle and is pumped out through the pulmonary trunk where the blood travels to the lungs or the aortic arch via the Ductus Arteriosus.
71
What is vasculogenesis?
Formation of NEW vascular channels by assembly of individual cell precursors called angioblasts (from mesoderm)
Begins at 3rd week of development
72
What is angiogenesis?
Development of blood vessels from pre-existing vessels
73
What is arteriogenesis?
R modeling of existing arteries in response to physiological changes.
74
Describe the process of vasculogenesis:
Process begins in two regions of the embryo:
- Extraembryonic Splanchnic Mesoderm that surrounds the umbilical vessicle/yolk sac
- Region of the aorta called the AGM
1) undifferentiated mesoderm differentiates into angioblasts
2) angioblasts give rise to hematopoietic stem cells and endothelial precursor cells
3) angioblasts aggregate and form Blood Islands (which consist of an outer layer of endothelial precursor cells and and inner mass of hematopoietic stem cells
4) blood island cells proliferate and differentiate into blood vessels and blood cells
75
Angioma
Capillary Hemagioma: excessive growth of small capillary networks (cherry angiomas)
Cavernous hemagioma: proliferation of large dilated vascular channels
Hemagioma of infancy: Benign tumor; up to 10% in Caucasian infants; consist of many endothelial cells
76
What do the ventral segmental arteries develop into/supply?
Ventral segmental arteries develop into abdominal arteries that are seen supplying the GI tract
Splanchnic layer of lateral plate mesoderm
77
What do the lateral segmental arteries develop into/supply?
Lateral segmental arteries develop into the renal and gonadal arteries and supply the gonads and kidneys
Intermediate mesoderm derivatives
78
What do the dorsal segmental arteries develop into/supply?
Dorsal segmental arteries develop into intersegmental arteries in the thorax, which further develop into intercostal arteries, which supply the intercostal muscles.
Derivatives of sorties
79
Describe the formation/degradation timeline of the aortic arches in respect to each other.
Arch 1 develops first
Then the 2nd arch develops
Then the 3rd arch develops and the 1st arch starts to degenerate
Then the 4th arch develops and the 2nd arch starts to degenerate
Then the 6th arch develops and the 3rd arch starts to degenerate
80
How do you explain the difference in position between the left and right recurrent laryngeal nerves?
The left and right recurrent laryngeal nerves originally loop back up around the left and right 6th pharyngeal arch arteries, respectively
However, the distal half of the right 6th pharyngeal artery degenerates, making it so the right recurrent laryngeal now loops around the primitive right subclavian artery.
On the left, the left recurrent laryngeal artery remains looped around the left 6th pharyngeal arch artery, which develops into the Ductus arteriosus, and the further develops into the Ligamentum Arteriosum after birth.
81
Describe the path of fetal circulation, starting at the placenta:
1) O2 rich blood leaves the placenta via the left umbilical vein
2) left umbilical vein carries the blood to a sphincter, which closes in response to high blood pressure and diverts blood toward the developing liver. If blood pressure is normal, blood travels from left umbilical vein to the ductus veinosus (embryonic vessel that bypasses the liver)
3) blood then delivered from the ductus veinosus to the Inferior vena cava
4) Inferior vena cava delivers blood to the right atrium
5) right atrium either sends blood through the Foramen Ovale into the left atrium (most blood does this to bypass the lungs) or it sends the blood to the right ventricle so it can proliferate the lungs or travel to the aorta via the Ductus arteriosus from the pulmonary trunk. Blood returning from the lungs is O2-depleted and mixes with the O2-rich blood in the left atrium.
6) Mostly O2-rich blood then is sent to the left ventricle where it is pumped out through the aorta to proliferate the developing tissues (including the placenta to pick up more O2.
7) O2-deleted blood returns from tissues via the superior vena cava or Inferior vena cava. Whereas O2-rich blood returns from the placenta to the heart via the path described.
82
How does fetal circulation differ from neonatal circulation?
1) within 72 hours after birth, Ductus arteriosus (vessel connecting the pulmonary trunk to the aortic arch) closes and forms into the ligamentum arteriosum in response to decreased prostaglandins and increased bradykinin (which occurs in response to increased arterial O2).
2) aeration of the lungs induces increased pulmonary blood flow, thinning of walls of pulmonary arteries, and decreased pulmonary vascular resistance
3) sphincter in Ductus venosus constricts and forms the Ligamentum venosum
4) occlusion of placental circulation causes decrease in blood pressure in Inferior vena cava and right atrium
5) increased pressure in left atrium + decreased pressure in right atrium causes fusion of Septum Primum with the Foramen Ovale to form the Fossa Ovalis
83
Coarctation of the aorta
Construction of the aorta.
Can be either preductal or postductal (in reference to Ductus arteriosus.
Preductal: blood cannot leave heart via aorta due to construction, so instead blood passes from the pulmonary trunk to the aorta via the Ductus arteriosus, thus bypassing the coarctation.
However, this poses a problem when the Ductus arteriosus disintegrates after birth (blood can no longer perfuse lower structures).
Postductal: No blood is able to travel to lower structures since the vessel is blocked after the Ductus arteriosus. In response, the fetus will develop collateral circulation to get blood to lower structures.
Note: circulation to head and upper extremities are unaffected as blood is able to travel through the brachioceohalic trunk, the right common carotid A., and right subclavian A.
Therefore pulses/blood pressure will be reduced/absent in lower extremities, but normal in upper extremities.
Embryonic mechanism:
Smooth muscle ends up in aorta due to migration error and constricts in response to increased O2 concentration
OR
Remodeling error in aorta development
84
Double aortic arch
Persistence of distal portion of right dorsal aorta
Forms a vascular ring around the trachea and esophagus
Presenting symptoms:
Stridor, respiratory infections, respiratory distress, wheezing, cough, and esophageal complaints including: dysphagia, feeding difficulty, and vomiting
85
Interrupted aortic arch
Both right and left 4th aortic arch arteries are obliterated
Distal right dorsal aorta is retained
Three types (A, B, C). All three types retain the presence of brachioceohalic trunk and its branches (right subclavian and right common carotid). The left subclavian and left common carotid may or may not be present depending on the type.
Many cases are associated with a ventricular Septal Defect and a Patent Ductus arteriosus.
Patients present with weakness, poor feeding, fast heart rate, fatigue, rapid breathing, and low O2 levels (in legs and feet)
Associated with DiGeorge syndrome
Low calcium, immune system abnormalities, and developmental delay
86
Abnormal origin of right subclavian artery
Arises from the distal part of the right dorsal aorta and the 7th intersegmental artery.
Right 4th aortic arch and the proximal part of the right dorsal aorta obliterate
Right subclavian passes behind the esophagus and trachea
87
Right aortic arch
Left 4th aortic arch and left dorsal aorta are obliterated and replaced by the corresponding vessels on the RIGHT side.
This causes the aorta to loop down to the right side instead of the left.
The Ligamentum arteriosum can be either on the right side or the left side. However, if it is on the left side, the right aorta will pass behind the esophagus, which can affect swallowing.
88
What structure develops from the left horn of the sinus venosus?
Coronary sinus
89
What structures develop from the right horn of the sinus venosus?
Orifice of the Inferior Vena Cava, Orifice of the Superior Vena Cava, Orifice of the Coronary Sinus, Sinus Venarum (smooth wall of the atrium), and the Crista Terminalis (border between smooth muscle wall of atrium and the pectinate muscle)
90
What is the fate of the vitelline veins?
Vitelline veins drain blood from the yolk sac
Proximal to heart: The left vitelline vein degenerates, right persist
Within the liver:
- Right forms the hepatic vein (portion of the Inferior vena cava)
- Right and left merge and form the portal vein (from the gut to the liver)
91
What is the fate of the umbilical veins?
Umbilical veins drain blood from the placenta
Right umbilical vein degenerates entirely
Left persists, but the proximal portion degenerates while the distal portion persists and anastomoses with the Ductus venosus providing placental return.
92
What is the fate of the cardinal veins?
Anterior cardinals are responsible for drainage from the cranial territory
- Right Anterior Cardinal V. develops into the Right Jugular V. and the Superior Vena Cava.
- Left Anterior Cardinal V. develops into the Left Brachiocephalic V.
Posterior Cardinals are responsible for drainage from the body wall.
Posterior Cardinal veins almost entirely degenerate except for the Root for the Azygos V. and the Common Iliac V.
- Replaced by Subcardinal V’s and the Supracardinal V’s
93
What structure(s) develop into the hepatic segment of the Inferior Vena Cava?
Right vitelline V.
| Hepatic Veins/sinuses
94
What structure(s) develop into the prerenal segment of the Inferior Vena Cava?
Right subcardinal V.
95
What structure(s) develop into the renal segment of the Inferior Vena Cava?
Subcardinal-supracardinal anastomosis
96
What structure(s) develop into the postrenal segment of the Inferior Vena Cava?
Right supracardinal V.
97
Left superior vena cava
Persistence of left anterior Cardinal vein and obliteration of the right common Cardinal and proximal portion of the right anterior cardinal veins.
Left Superior Vena Cava drains into the right atrium via the coronary sinus
98
Double superior vena cava
Persistence of the left anterior cardinal vein and failure of the left brachioceohalic vein to form.
Left Superior Vena Cava drains blood into the coronary sinus, while the right Superior Vena cava drains blood directly into the right atrium.
