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