Embryology Of Respiratory/Cardiac Flashcards
Development of the respiratory tract begins in week 4 with the formation of what? What gene controls this process?
- laaryngeotracheal/respiratory diverticulum
- Tbx4 gene in the endoderm of the foregut -> outgrowth of foregut into the surrounding splanchnic mesoderm (future esophagus)
How does the septum that divides the trachea and esophagus form?
-the diverticulum grows distally and separated from the esophagus by the tracheoesophageal septum (distally)
What is a tracheoesophageal fistula?
- most common malformation
- abnormal communication between trachea and esophagus
- caused by improper formation of tracheoesophageal septum
- can sometimes result in an esophageal atresia (esophagus ends in pocket)
How can polyhydramnios be an indicator of TEF?
- in utero babies normally swallow amniotic fluid, reducing fluid volume
- this can be associated with CNS anomalies and esophageal atresia
What are the symptoms of esophageal atresia and TEF?
- infant drools excessively and is accompanied by frequent choking, coughing, and sneezing
- when fed, these infants swallow normally but begin to cough and struggle as the fluid is regurgitated
- the infant may become cyan otic and may stop breathing as the overflow of fluid from the pouch is aspirated into the trachea and lungs
How is TEF treated?
-close the fistula and rejoin the two winds together to make a complete esophagus
How are the bronchi formed?
- left and right lung buds
- in week 5, they divide into 2 bronchial buds
- these will become the primary bronchi
- the secondary bronchi are formed when the primary buds undergo a series of branching a to form the respiratory bronchioles
What tissue type differentiates into the smooth muscle, nerves, and blood vessels of the lungs?
-splanchnic mesoderm
What are the stages of lung development? When do these typically occur?
- embryonic (weeks 4-7)
- pseudoglandular (weeks 8-16)
- canalicular(weeks 17-26)
- terminal sac(weeks 26- birth)
- postnatal/alveolar
What stage is it a little more safe for a premie to be born? Why?
-after week 24/canalicular because there is enough pulmonary tissue to potentially survive breathing
What occurs during the embryonic stage?
- initial formation of respiratory diverticulum to formation of bronchiopulmonary segments
- lungs grow into pleural cavities
- differentiation of pleura
What happens during the pseudoglandular stage?
- major formation and growth of duct systems within bronchiopulmonary segments
- no respiratory components or gas exchange
- resembles a gland
WHat occurs during the canalicular stage?
- formation of respiratory bronchioles and terminal sacs
- vascularization increases
- capillaries found in walls
What happens during the saccular stage?
- alveoli develop from respiratory bronchioles
- epithelium lining alveoli differentiates into two types
What are the two different types of cells found in the alveoli and what are their function(s)?
Type I pneumocyte
-form part of blood-air barrier
Type II pneumocyte
- secretory cells that produce surfactant
- reduces surface tension
- facilitates alveolar expansion
When are up to 90% of alveoli formed? How does this happen?
-formed after birth due to septae ion of preexisting alveoli
What is infant respiratory distress syndrome?
- occurs primarily in the immature lung
- 60% of cases occur in infants born at less than 28 weeks
- 5% of cases occur in infants born at less than 37 weeks
- labored breathing
- deficiency/absence of surfactant
- coats alveoli and maintains alveolar potency
- results in incomplete expansion or collapse of parts of or a whole lung
What is pulmonary agenesis?
- complete absence of lungs, bronchi, and vasculature
- bilateral or unilateral
- bronchial buds do not form
What is pulmonary hypoplasia? What other condition. May cause this?
-poorly developed bronchial tree
-partial or total
-can be caused by congenital diaphragmatic hernia
+abdominal contents herniated into thoracic cavity
+caused by failure of pleuroperitoneal membranes to fuse. With other components
+most common in posterolateral side
+clinical signs: unusually flat abdomen, breathlessness, and cyanosis
When does the cardiovascular system begin developing? Why does it develop so early?
- primitive system present by week 4 (first functioning system)
- necessary because of rapid growth
- embryo can no longer meet nutritional or oxygen needs by diffusion
- requires both pump, tubing, and delivery system
What are the general trends in the development of the heart?
- 2 chambered to 4 chambered structure
- the vascular system separates into systemic and pulmonary portions
- systemic arterial outflow -> left
- systemic venous return -> right
Generally, how is the cardiovascular system created?
-left and right endocardial tubes begin fusing together and finally turn into a single structure
What are the embryonic circuits?
- series of aortic arches that connect to dorsal aortae
- D. Aortae subdivide into smaller vessels to supply embryo
- blood drained by anterior and posterior Cardinal veins
- common Cardinal vein
What are the nutritional circuits?
- vitelline: supply and drain yolk sac “nursery for blood cells”
- umbilical/placental
- umbilical vein carries oxygenated blood from the placenta
What are the adult structures for the following:
- Truncus arteriosus
- Bulbus cordis
- Primitive ventricle
- Primitive atrium
- Sinus venosus
- Aorta, pulmonary trunk
- Smooth part of right ventricle (conus cordis), smooth part of left ventricle (aortic vestibule)
- Trabeculated part of the right and left ventricles
- Trabeculated part of right and left atria (auricles)
- Smooth part of right atrium (sinus venarum), coronary sinus, oblique vein or left atrium
What is dextrocardia?
-heart bends to the. Left inside of the right -> most common positional abnormality
What happens after the primitive heart folds in terms of partitions?
- atrium and ventricles are separated by narrow AV canal
- dorsal and ventral blocks of tissue grow together (endocardial cushions)
- divide single AV canal into separate right and left AV canals
- canals and their valves regulate blood flow from atria to ventricles
What is the atrioventricular communis?
- the formation and fusion of endocardial cushions is the critical first step in the development of the 4 chambered heart
- large communication between chambers that occurs when the cushions fail to fuse
How does the interventricular septum form?
- two parts
- muscular portion develops in the midline on the floor of the primitive ventricle
- grows upward towards endocardial cushions and down growing bulbar ridges
- closed by membranous portion, divides AV canals
What are 25% of all heart defects?
- ventricular septal defects: opening between the L and R ventricles, associated with shunting of the blood
- require surgical correction in the membranous portion
- possible that there are more trabecular defects that spontaneously close
What is the foramen ovale a remnant of?
- the closing of the atrial septum, there was a shunt
- there are two foramen (secundum and primum) that fuse together
Atrial septal defects
- presen in 10-15% of patients with congenital cardiac anomalies
- ostium (foramen) primum defects: similar to endocardial cushion defects
- secundum type: involve foramen ovale and septum primum
- sinus venosus: usually near opening of SVC
- common atrium
Changes in sinus venosus
- L & R horns are equal in size
- right horn enlarges as blood is shunted from L -> R
- shunts involve “nutritional” vascular circuits and embryonic circuits
- move. All systemic inflow to the right side
- these are the nutritional circuits: vitelline and. Umbilical
- embryonic circuit: Cardinal vein
What are the two shunts and what are they responsible for?
Vitelline veins:
- liver develops in septum transversum
- veins become incorporated into liver as hepatic sinusoids, hepatic veins, part of IVC and some of the veins that drain the GI tract
Umbilical veins:
- loses direct connection with heart (ligamentum teres)
- joins large venous shunt -> ductus venosus
- connects umbilical vein with IVC
- bypasses the liver and diverts oxygenated blood into the heart
What does the ductus venosus do?
- connects umbilical vein with IVC
- bypasses the liver and diverts oxygenated blood into the heart
What happens to the sinus venosus?
- loss of vitelline veins, reused as part of GI system
- reroute get of umbilical vein to utilize the ductus venosus to bypass the liver yet not have a direct connection to the right atrium
How does shunt 2 anastomose?
- anterior cardinal veins become connected
- anastomosis becomes left brachiocephalic vein
- right anterior cardinal and common cardinal become SVC
Shunting of blood meaning ________ horn becomes much larger.
Right
What does the partitioning of the AV canal and TA form?
-valves -> TA (semilunar valves), AV (bicuspid and tricuspid)
Neural crest cells invade ridges that form in the _______ ________ and ________ __________.
- bulbus cordis
- truncus arteriosus
What is the tetralogy of Fallot?
- congenital heart defect that involves four anatomical abnormalities
- pulmonary stenosis
- VSD
- overriding aorta
- right ventricular hypertrophy
How is the arterial system developed?
- 6 pairs of aortic arches
- connect aortic sac/TA to dorsal aortae
- pharyngeal arches (organize development of head and neck)
What is a patent ductus arteriosus?
-an abnormal connection between the aorta and pulmonary artery in the heart.
What occurs during the early and late phases of lung development?
- early: positioning of lung primordium and primary lung bud formation
- late: mechanism od bronchial branching and cytodifferentiation
