Fetal Gas Exchange and Circulation
What are the three anatomic structures that constitute fetal shunts?
(1) FORAMEN OVALE, which is the opening between the right atrium and the left atrium, which enables oxygenated blood to flow to the left side of the fetal heart; (2) DUCTUS VENOSUS, which appears continuous with the umbilical vein and shunts 30% to 50% of oxygen-rich blood around the liver to the inferior vena cava; and (3) DUCTUS ARTERIOSUS, which allows most of the pulmonary arterial blood flow to bypass the nonfunctioning fetal lungs and enter the aorta.
During what week of fetal development is the heart rate approximately 95 beats per minute?
16 weeks.
How many weeks gestation does the alveolar type II cells produce surfactant?
22
Fetal survival outside the uterus becomes possible at approximately how many weeks gestation?
24
20% of the ductus arteriosus closes within how many hours of birth?
24 hours.
How long after birth should it take for the ductus arteriosus to close completely?
96 hours.
What are the normal circulatory changes occurring within the transitional stage at birth?
A decrease in pulmonary vascular resistance, a decrease in pulmonary artery pressure, and increase in left ventricular pressure, and an increase in pulmonary blood.
What can occur at any point during gestation?
Abnormal lung development.
What lung development stage formerly thought to be the last stage before birth, and characterized by relatively smooth walled cylindrical structures subdivided by ridges known as secondary crests?
Alveolar phase
What forms the primitive vascular network during the early stages of the embryo?
Angiogenic clusters.
What is the term used to describe the "blood islands" that supply nutrition to the growing embryo?
Angiogenic clusters.
What structures are recognizable during the development of the heart after the heart tubes fuse?
Bulbus cordis, atrial bulge, and ventricular bulge.
What are the 3 identifiable structures of the heart tubes during the 4th week of gestation?
Bulbus cordis, ventricular bulge, and atrial bulge.
What defines the developmental phase of the fetal lung?
Characteristic anatomical growth and maturati
What are the fetal vessels called that are found within intervillous spaces?
Chorionic Villi.
What are the causes of the closure of the ductus venosus?
Clamping of the umbilical cord and closure of the umbilical vein.
After birth what is done that takes away the low-pressure system of the placenta ultimately closing the foramen ovale?
Clamping of the umbilical cord.
What one set of actions causes the systemic circulation to transition from a low-resistance system to a high-resistance system?
Clamping the umbilical cord thus preventing blood flow to the placenta.
What day of gestation are cardiac contractions detectable and bi-directional tidal blood flow begins?
Day 22
At what day of gestation does the heart begin to beat?
Day 22.
When can the fetal heartbeat be detected?
Day 22.
What 3 events happen when the ductus arteriousus closes?
Decreased PVR, increased PaO2 and decreased prostaglandin levels.
How is most of the fetal blood entering the main pulmonary artery shunted to the aort
Ductus Arteriosus.
How is most of the fetal blood entering the umbilical shunted to the inferior vena cava?
Ductus Venosus.
What two shunts normally present in the fetus can result in persistent cyanosis in the newborn?
Ductus arteriousus and foramen ovale.
What shunt allows blood in the pulmonary artery to bypass the lungs and heart?
Ductus arteriousus.
What are the 3 fetal shunts?
Ductus venosus, Foramen Ovale, and Ductus Arteriousus.
What anatomical shunts present in the fetus that allow fetal circulation?
Ductus venosus, foramen ovale, and ductus arteriosus.
What shunt redirects blood away from the liver?
Ductus venosus.
The heart is the first organ to form during fetal development. What gestational week does this occur?
During the third gestational week which is the first organ to form.
What is the name of the three germ layers?
Ectoderm, mesoderm, and endoderm.
What are the phases of human lung development?
Embryonal, canalicular, and saccular.
What is the embryonic germ layer which gives formation to the respiratory system?
Endoderm
What are the minimal developmental features required for an immature human fetus to survive outside the uterus?
Enough alveolar and vascular surface area for gas exchange, 22 - 24 weeks of gestation, and near completion of the canalicular stage of lung development.
What is true when discussing fetal circulation?
Fetal shunts help to shunt the best oxygenated blood to the head, pressure gradients related to blood flow are the opposite of those in an adult, fetal shunts help to bypass the lungs, and the placenta has low vascular resistance.
Most of the fetal blood entering the right atrium is shunted to the left atrium via what?
Foramen ovale.
What shunt is located between the right and left atrium?
Foramen ovale.
Estimates of the exact number of alveoli at birth vary widely, but investigators agree that?
Gas exchange surface area grows proportionally with an increase in O2 consumption and body surface area.
What statement concerning the development of the circulatory system?
Heart development, other than growth is complete when valve formation is complete. Angiogenic clusters supply nutrition in the earliest stages of the growing embryo, and at about 3 weeks, two heart tubes fuse into what will become the basic structure of the four chamber heart.
Why does most of the blood enter the aorta through the ductus arteriosus?
High resistance in the pulmonary vasculature.
A new increase in what closes the foramen ovale which further increases blood flow to the lungs?
Increase in systemic vascular resistance.
Anatomic narrowing of the ductus arteriosus begins in the last trimester by the formation of bulges known as what?
Intimal mounds.
What is the importance of a thorough understanding of each stage of fetal lung development?
It helps identify problems occurring and help to prepare for the delivery and care.
What is the importance of identifying the stages and development of the heart?
It helps in understanding congenital problems that can occur when development doesn't proceed as expected.
What is the pressure difference between adult circulation and fetal circulation?
It is reversed, the right side is high in pressure and the left side is low.
What best describes fetal lung liquid?
It maintains the structure of the airway lumen and developing alveoli preventing complete collapse and with fetal breathing movement. It continuously flows out of the lungs and is swallowed or excreted into the amniotic fluid.
What causes cessation of right to left shunt throughout the foramen ovale after the umbilical cord is clamped?
It removes the low-pressure system. Right-sided heart pressure decreases and left-sided pressure increases.
What structure does the ductus arteriousus transform into after closure?
Ligamentum arteriosus.
How is the ductus arteriosus kept open?
Low PaO2 of the aorta.
Pulmonary hypoplasia is a relatively common abnormality of lung development with a number of clinical associations, including what
Lung tissue compression, oligohydramnios, and maternal diabetes.
What are the three major fetal growth periods?
Ovum, embryo, and fetus.
What are some of the fetus' circulatory systems?
Placental, pulmonary and systemic.
Why are the DA, FO, and DA shunts essential?
Proper nutrients and gas exchange in the fetus and appropriate distribution of blood through fetus along with the pressure gradients induced by circulatory systems.
Which gestational phase of lung development is the bronchial tree formed?
Pseudoglandular.
What increases and decreases when the cord is clamped?
Pulmonary vascular resistance decreases, and systemic vascular resistance increases.
What enters the uterus around the 4th or 5th day and is also known as the fertilized egg?
The Zygote.
What areas of the fetal heart causes the low vasculature of the placenta?
The aorta, left ventricle, left atrium, and entire arterial system.
What will become the fetus?
The blastoderm.
What statement represents Reid's laws of human lung development?
The bronchial tree develops by week 16 of intrauterine life, pre-acinar vasculature develops after the airway has been established and intra-acinar vasculature develops after the alveoli are generated and alveoli increase in number until 8 years of age and grow in size until the chest wall growth is complete.
What allows most of the pulmonary arterial blood flow to bypass the nonfunctioning lungs and enter the aorta?
The ductus arteriosus.
What is continuous with the umbilical vein and shunts 30-50% of oxygen-rich blood around the liver to the inferior vena cava?
The ductus venosus.
Which germ layer is known for the creation of the central nervous system?
The ectoderm.
What week of gestation is the heart fully functional, complete with chambers, valves, and major vessels?
The eighth week.
Which germ layer is known for the creation of the respiratory system?
The endoderm.
What do you call the lining of the uterus?
The endometrium.
Why would a newborn with persistent cyanosis be at risk for refractory hypoxemia?
The foramen ovale and ductus arteriosus are anatomic shunts that allow blood to flow from the right side of the heart to the left side and systemic circulation without passing through the parenchyma of the lung.
Why are the two oximetry readings necessary, and why are the probes placed on the right hand and left foot?
The foramen ovale feeds blood to the head, right arm, and coronary circulation. If this shunt does not close and is not being O2 fed by the umbilical cord it will show by the right-hand oximetry. The left foot would receive blood only if the ductus arteriosus closes begins to close after birth.
What is the opening between the right and left atrium which enables oxygenated blood to flow to the left side of the fetal heart?
The foreman ovale.
Anatomical narrowing of the ductus arteriosus begins in the last trimester by what process?
The formation of bulges known as intimal mounds.
What is the first complete organ to form?
The heart.
Closure of the foramen ovale causes increased pressure where?
The left atrium.
Which germ layer is known for the creation of the cardiovascular system?
The mesoderm
Where does the initial lung bud emerge?
The pharynx.
What two vessels are formed when the truncus arteriosus splits?
The pulmonary artery and the aorta.
During what week of gestation is the heart fully formed?
The third week.
During which week of gestation is the heart fully formed?
The third week.
What will become the placenta?
The trophoblast.
How does oxygenated blood travel from the placenta to the fetus?
The umbilical vein.
Most of the fetal blood entering via the umbilical vein is shunted to the inferior vena cava through the?
Through ductus arteriosus.
Most of the fetal blood entering the umbilical vein is shunted to the inferior vena cava via what?
Through the ductus venosus.
How does oxygenated blood leave the placenta and travel to the fetus?...
Through the umbilical vein.
What four structures are recognizable during the development of the heart after the heart tubes have fused?
Truncus arteriosus, bulbus cordis, ventricular bulge, and sinus venosus.
What describes the pneumocytes when the alveolar epithelial lining undergoes cell division into type I and type II pneumocytes?
Type I pneumocytes account for more than 97% of the alveolar surface areas, surfactant production occurs in the lamellar bodies of type II pneumocytes which release surfactant by exocytosis, and type I pneumocytes are squamous shaped and optimized for gas exchange, type II pneumocytes are cube-shaped and may differentiate into type I cells.
How does oxygenated blood leave the placenta and travel to the fetus?
Umbilical vein.
During what week of fetal growth is the truncus arteriosus divided into two vessels?
Week 6.
What is the gelatinous substance inside of the umbilical cord which helps protect the vessels and keeps the cord from kinking?
Wharton's jelly.
What is the gelatinous substance inside the umbilical cord which helps protect the vessel and prevents the cord from kinking?
Wharton's jelly.
When is heart development fully complete?
When the heart valves have been complete
