Fetal Circulation Flashcards
The fetal portion of the placenta is known as the ____________, the maternal portion is the __________.
villous chorion; decidua basalis
The _________ (materal/fetal) side of the placenta is divided into lobes or cotyledons and shreds of the decidua basalis.
Maternal
Where does the umbilical cord attach?
- The umbilical cord attached to the fetal surface and the amniotic covering of the cord is continuous with the amnion
The placenta begins to develop at the implantation of the _________.
Blastocyst
*This happens around day 7- 13
In the trophoblast, two distinct layers are formed. The outer layer is called the __________ and the inner later is called the _________.
Synctiotrophoblast; cytotrophoblast
Decidual reaction
Stromal cells accumulate glycogen and lipid, now called decidual cells.
NOTE: Stromal cells are large, round epithelial like cells secrete nutrients and regulatory substances.
Which trophoblast layer is being described below?
Actively invades the uterine wall, rupturing maternal capillaries and thus establishing an interface between maternal blood and embryonic extracellular fluid, facilitating passive exchange of material between the mother and the embryo.
Syncytiotrophoblast
The syncytiotrophoblast lacks proliferative capacity and instead is maintained by fusion of underlying cytotrophoblast cells. True or false.
True
Contents of secondary villi
Trophoblast and mesoderm
- Extraembryonic mesoderm grows into core of villi
Contents of primary stem villi
Trophoblast only
- Developed days 11-13
- Projections into cytotrophoblasts and syncytiotrophoblast
Contents of tertiary villi
Trophoblast, mesoderm, and blood vessels
- Day 21
- Blood vessels appear in the mesoderm core
One main stem villus forms a unit of the placenta known as the __________, they are separated from each other by septa.
Cotyledon
NOTE: Chorionic villi may be either free or anchored to the decidua basalis (the mainstem villi)
Maternal blood supply to the intervillous space via _________.
Spiral arteries
At around ______ weeks the cytotrophoblast disappears, while the syncytiotrophoblast is retained to the end.
20
The barrier that separates the fetal and maternal blood is composed of:
Syncytium
Endothelium
Connective tissue
REMEMBER: The cytotrophoblast disappears at week 20
True or False. A placental mmal fetus has fetal hemoglobin with lower affinity for oxygen than the mother’s hemoglobin in the placenta.
False
*Fetal hemoglobin can carry up to 30% more oxygen
By the 5th week the umblical cord replaces the _____ as a source of nutrients for the embryo/ fetus.
Yolk sac
Allantois is part of and forms an axis for the development of the __________
Umbilical cord
Allantois is an outpocketing of the ______.
Yolk sac
The allantois invades the ________that suspends the embryo in the chorionic cavity during the third week.
connecting stalk
*Also known as the body-stalk and is a band of mesoderm that connects the caudal end of the embryo to the chorionin development.
The umbilical cord is a composite structure formed by contributions from the ____________, ________, and ______.
Fetal conencting stalk
Yolk sac
Amnion
How is the final umbilical structure formed?
Between days 28-40 the amniotic cavity presses the stalk and its contents into a thin tube like structure that is covered by the amniotic epithelium forming the final umbilical cord structure.
The unbilical arteries develop early in the fourth week and initially arise from the paired _________.
Dorsal aorta
Explain the development of the umbilical arteries.
- Week four, unblicial arteies arise from the paired dorsal aorta
- Week 5, these connections are obliterated
- Arteries form a new connection with the 5th lumber intersegmental artery
NOTE: The 5th lumbar intersegmental artery forms the internal iliac artery
_______________ (deoxygenated/oxygenated) blood passes form left and right umbilical arteries to the placenta.
Deoxygenated
In most placentas the umbilical arteries are connected in the area of the cord’s insertion to the placental surface called the ___________.
Hyrtl anastomosis
What are branches of the umbilical artery?
Chorionic arteries
Intraplacental arteries
Wharton’s jelly is a gelainous substance mainly composed of ___________.
Mucopolysaccharides
What is the function of Wharton’s jelly?
- Helps protect vessels
- Contains a large quantity of water which aids in the prevention of umbilical blood vessel compression
- Prevents kinking of the cord
Only one umbilical artery is present in approximately 1 in 200 infants. Which artery is most commonly absent?
Left umbilical absent
NOTE: Presence of a single umbilical artery may indicate cardiovascular abnormalities
The ____ veins bring oxygenated blood from the chorion. The ___ veins return deoxygenated blood from the yolk sac. The ________ veins return deoxygenated blood from the wall of the embryo.
Umbilical; vitelline; common cardinal
NOTE: All of these veins drain into the sinus venosus
From week 5 which veins are obliterated?
The right umbilical vein.
The left vitelline vein.
The left common cardinal vein.
A persistent right umbilical vein can be associated with what other anomalies?
- Single umbilical artery
- Dextrocardia ( heart points toward the right side of your chest instead of the left side)
- Cardiac anomalies
What are causes of persistent right umbilical vein?
- First trimester folic acid deficiency
- Specific tetragons such as retinoic acid
- Early obstruction of left umbilical vein
- Trisomy 18
What are the three major shunts found in the circulatory system of the fetus? Where do these shunts divert blood?
- Foramen ovale- Diverts from pulmonary to the systemic circuit
- Ductus arteriosus- Diverts from pulmonary to the systemic circuit
- Ductus venosus- Connects the umbilical vein to the inferior vena cava
The distal part of the left umbilical vein becomes the main channel through the _______.
Liver
REMEMBER: The right umbilical vein obliterates by the 5th week
What is teh course of the left umbilical vein?
- Passes towards the transverse fissure of the liver, where it splits into two
- One joins the left branch of the portal vein
- Second branch becomes the ductus venosus
The _____ connects the intra-abdominal umbilical vein to the IVC.
Ductus venosus
NOTE: Blood bypasses the liver through the ductus venosus
A sphincter mechanism close to the entrance of the umbilical vein regulates flow of umbilical blood through the liver __________.
sinusoids
The blood that flows to the liver passes through the sinusoids of the liver and enters the IVC via the ___________.
hepatic veins
The fetal cardiovascular system is adapted so that the most highly oxygenated blood is delivered to the _______ and the ______.
Myocardium; brain
The narrow diameter of the ductus venosus __________ (accelerates/ decclerates) blood through the IVC.
Accelerates
Blood from the placenta is ______
During various points in fetal circulation, the oxygenated blood of the placenta is mixed with less oxygenated blood. What are these areas?
Liver, right and left atrium, ductus arterious
*This reduces oxygen content
Th valve of the inferior vena cava is known as the _________.
Eustachian valve
*The valve is continuous witht he limbus of the fossa ovalis
What is the function of the eustachian valve?
During prenatal life it directs the more oxygenated blood from the inferior vena cava towards and through the foramen ovale
Function of the foramen ovale
The foramen ovale serves as a one way valve for right to left shunting of oxygenated blood in utero
The crista dividens plays a role in separating oxygenated blood from the ____________ and deoxygenated blood from the ____________draining the caudal portion of the fetus into the left and right atria.
ductus venosus; inferior vena cava (IVC)
NOTE: It deflects the highly oxygenated blood to the left atrium
The crista divedens becomes the ___________ int he interatrial septum after birth.
Limbus of the fossa ovalis
What is the flow of blood in the fetus beginning with the superior vena cava?
- Blood coming from the superior vena cava is directed primarily through the tricupsid valve into the right ventricle (50% saturated with oxygen
- The blood from the right ventricle flows through the pulmonary trunk (a small quantity of this blood flows to the fetal lungs)
- Most of the blood from the pulmonary trunk enters the descending arota through the ductus arteriosus
- Blood in the aorta provides lower levels of oxygen to the caudal part of the body and then enters umbilical arteries to be reoxygenated in the placenta.
From where does the ductus arteriosus arise?
Arises from the distal part of the left sixth aortic arch passing to the dorsal aorta
*After further development in utero it connects to the aorta below the left subclavian artery
At birth the umbilical cord is clamped. What happens to some of the fetal structures?
- Umblical vessels are obliterated
- Circulation of the fetal blood through the placenta ceases, acute changes in the pulmonary and systemic vascular resistance occur and the lungs begin to function
- Foramen ovale, ductus arteriosus and umbilical vessels close and transform into corresponding ligaments
How is fetal lung fluid expelled?
- Contraction through the birth canal- squeezes lungs
- Absorption via lymphatic system
- Clearance via pulmonary capillaries
First breath
-
Lungs inflate with first breaths
- The resistance in the pulmonary vessels is reduced; blood pressure in the pulmonary circuit falls. Blood from the pulmonary trunk follows the path of least resistance into the pulmonary arteries and travels to the lungs to be oxygenated
-
Foramen ovale and ductus arteriosus close
- The increased volume of blood entering the left atrium from the lungs effectively raises the pressure in the atrium, causing the closure of the flaplike valve of the foramen ovale. This structure is now called the fossa ovalis. The ductus arteriosus constricts, closing the shunt to the aorta. The remaining structure is called the ligamentum arteriosum.
Mechanism of closure of the foramen ovale
Postnatal lung expansion and initiation of the pulmonary circulation reverses the atrial pressure gradient, causing functional closure of the foramen ovale.
- Increase in pulmonary blood flow
- Increase in oulmonary venous return to the left atrium
- Left atrial pressure exceeds right atrial pressure
- This reversal of the pressure gradient allows the flap of the foramen ovale to push against the atrial septum and the shunt is closed
True of false. Patent foramen ovale is mro common in females than males.
True
Ration 3:1
Closure of the ductus venous. Mechanism.
- Loss of the umbilical blood supply causes the sphinter in the ductus venosus to constrict thereby diverting blood to the hepatic sinusoids
NOTE: Closure of the ductus venosus becomes permanent after two to three weeks. The remnants of the ductus venosus form the lifamentum venosum
The intra abdominal portion of the umbilical vein becomes the ______.
Ligamentum teres
NOTE: The lumen of the umblical vein does not disappear completely and can be cannulated in adults for the injection of contrast medium or chemotherapeutic drugs.
Closure of the ductus arteriosus. Mechanism.
- Ductus arteriosus closes as a result of increased oxygen saturation which produces ductal constriction.
- Reduced ductal blood flow caused by increased pulmonary flow and decreased levels of prostagladins
Failure of the ductus arteriosus to close can lead to a __ to __ shunting of blood.
Left; right
*Persistent ductus arteriosus is more common in girls more often than boys
Which substance facilitate closure of the ductus arteriosus?
- Prostagladin inhibitors
- Acetylcholine
- Histamine
- Catecholamines
Persistent ductus arteriosus is more common in infants with what conditions?
Premature
Neonatal respiratory distress syndrome
Down syndrome
Mothers who had rubella
Congenital heart problems, such as hypoplastic left heart syndrome, transposition of the great vessels, and pulmonary stenosis.
Under which circumstances would a newborn revert back to a fetal type circulation?
Can be caused by stimuli which cause the pulmonary arterioles to constrict and elad to an icnrease in pulmonary vascular resistance.
REMEMBER: Persistent fetal circulation favors right to left shunting through the foramen ovale and ductus arteriosus. However, there is no placenta to provide oxygenation
What conditions can result from persistent fetal circulation?
- Hypoxia
- Hypercarbia
- Acidosis
- Cold
Aorta and other major arteries are assembled from varied precursors. Variations and anomalies are common due to this complicated ontogeny.
What is the key to diagnosis of coartication of the aorta?
Blood prssure discrepancies between the upper and lower extremeties
*Rare but much more common with Turner’s syndrome or neural crest development disorders
In cases of aorta coarctation, collateral circulation develops to compensate for postductal circulation, usaully by way of the _________ arteries.
Internal thoracic and intercostal arteries
Vascular ring
An unusual congenital condition in which the anomalous configuration of the arch, associated vessels, or both surrounds the trachea and esophagus, forming a complete or incomplete ring around them.
