Embryology: Development of the Placenta and Fetal Circulation, Animation
Summary
TLDRThe video script delves into prenatal nutrition, highlighting two key phases: the trophoblastic phase, where the trophoblast digests endometrial tissue for nutrition from weeks 2 to 8, and the placental phase from week 9 onward. It explains the development of the placenta, the exchange of nutrients and waste between maternal and fetal blood, and the unique fetal circulation with its shunts. The script also discusses the transition at birth, where the lungs' function and systemic resistance changes lead to the closure of fetal shunts and adaptation to extrauterine life.
Takeaways
- 🌱 Prenatal nutrition is divided into two phases: the trophoblastic phase from week 2 to 8 and the placental phase starting from week 9.
- 🌀 The placenta is a hybrid organ that takes over the role of feeding the embryo gradually from week 4 to 12.
- 🔍 The syncytiotrophoblast, a layer of the trophoblast, digests endometrial tissue while maternal capillaries dilate to form sinusoids.
- 🌿 The cytotrophoblast invades the syncytiotrophoblast to form primary chorionic villi, which are essential for the development of the placenta.
- 🚀 Extraembryonic mesoderm cells fill the villi in week 3, differentiating into fetal blood vessels, including the umbilical vessels.
- 🔄 Fetal blood travels to the placenta via umbilical arteries and exchanges substances with maternal blood within the chorionic villi.
- 🚫 The placenta is permeable to certain substances but prevents the mixing of maternal and fetal blood to protect the fetus from the maternal immune system.
- 🛡️ Fetal circulation is distinct, featuring a placental-umbilical circuit and three fetal shunts that bypass the liver and lungs.
- 🔄 The umbilical vein carries oxygen-rich blood to the liver, which is bypassed via the ductus venosus due to the liver's immature filtering function.
- 💓 Fetal blood bypasses the lungs through the foramen ovale and ductus arteriosus, adapting to the non-functional fetal lungs.
- 🌟 Post-birth, lung expansion and umbilical cord clamping lead to the closure of fetal shunts and adaptation to neonatal circulation.
Q & A
What are the two major phases of prenatal nutrition mentioned in the script?
-The two major phases of prenatal nutrition are the trophoblastic phase and the placental phase.
What is the duration of the trophoblastic phase of prenatal nutrition?
-The trophoblastic phase lasts from week 2 to week 8 of pregnancy.
What is the role of the trophoblast during the trophoblastic phase?
-During the trophoblastic phase, the trophoblast digests and derives nutrition from the endometrial tissue.
How does the placenta gradually take over the role of feeding the embryo?
-The placenta gradually takes over the role of feeding the embryo through a transition period from week 4 to 12.
What is unique about the composition of the placenta?
-The placenta is unique as it is a hybrid organ containing both maternal and fetal components.
What is the function of the syncytiotrophoblast during week 2 of pregnancy?
-In week 2, the syncytiotrophoblast invades and digests the nearby endometrial tissue, facilitating the digestion of nutrients for the embryo.
What are the three umbilical vessels that connect the embryo to the placenta?
-The three umbilical vessels are the two umbilical arteries and the single umbilical vein.
How does the exchange of nutrients and waste occur between the maternal and fetal blood?
-The exchange occurs in the capillaries within the chorionic villi, where fetal waste like carbon dioxide moves into maternal blood, and nutrients and oxygen move into fetal blood.
Why do maternal and fetal blood not mix in the placenta?
-Maternal and fetal blood do not mix because blood cells cannot move across the placenta, which protects the fetus from being attacked by the maternal immune system.
What are the three fetal shunts mentioned in the script, and what is their purpose?
-The three fetal shunts are the ductus venosus, the foramen ovale, and the ductus arteriosus. They allow blood to bypass the liver and lungs, adapting fetal circulation to the placental-umbilical circuit.
How do the changes at birth affect the fetal circulation and the closure of the fetal shunts?
-At birth, the expansion of the lungs with air reduces pulmonary vascular resistance, and the clamping of the umbilical cord increases systemic vascular resistance, leading to the closure of the fetal shunts as they become unnecessary and transform into ligaments.
Outlines
🍼 Prenatal Nutrition Phases and Placenta Development
The script discusses prenatal nutrition, which is divided into two phases: the trophoblastic phase from week 2 to 8, where the trophoblast digests endometrial tissue for nutrition, and the placental phase starting from week 9. The transition period from week 4 to 12 is critical as the placenta takes over nourishment duties. The placenta, a hybrid organ of maternal and fetal components, develops from the endometrium and the embryo's trophoblast. The script details the process of maternal blood vessel dilation, formation of chorionic villi, and the establishment of fetal blood circulation through the umbilical vessels. It also explains the placental permeability to certain substances and the separation of maternal and fetal blood to protect the fetus from the maternal immune system.
Mindmap
Keywords
💡Prenatal nutrition
💡Trophoblastic phase
💡Placental phase
💡Placenta
💡Syncytiotrophoblast
💡Cytotrophoblast
💡Chorionic villi
💡Umbilical vessels
💡Fetal circulation
💡Fetal shunts
💡Foramen ovale
💡Ductus arteriosus
Highlights
Prenatal nutrition involves two phases: the trophoblastic phase and the placental phase.
The trophoblastic phase occurs from week 2 to week 8, where the trophoblast digests endometrial tissue for nutrition.
The placental phase begins from week 9, with a transition period from week 4 to 12.
The placenta is a hybrid organ with both maternal and fetal components, developing from the endometrium and the trophoblast.
Syncytiotrophoblast invades and digests nearby endometrial tissue while maternal capillaries form sinusoids.
Cytotrophoblast invades syncytiotrophoblast to form primary chorionic villi.
Extraembryonic mesoderm cells fill the villi and differentiate into fetal blood vessels, including umbilical vessels.
Fetal blood travels to the placenta via two umbilical arteries, and waste moves into maternal blood.
The placenta is permeable to lipid-soluble fetotoxic substances, which can harm fetal development if consumed by the mother.
Maternal and fetal blood do not mix due to the separation provided by the placenta, protecting the fetus from maternal immune system attack.
Fetal circulation differs from neonatal circulation due to the placental-umbilical circuit and presence of three fetal shunts.
The umbilical vein carries nutrient-rich blood from the placenta to the liver, bypassing it via the ductus venosus.
Fetal blood bypasses the pulmonary circuit through the foramen ovale and the ductus arteriosus.
After birth, the lungs expand, pulmonary vascular resistance drops, and the foramen ovale closes.
Systemic vascular resistance increases post-birth, causing fetal shunts to close and become ligaments.
The fetal shunts play a crucial role in directing blood flow to the fetus's vital organs before birth.
At birth, changes in vascular resistance and lung function lead to the closure of fetal shunts.
Transcripts
Prenatal nutrition consists of 2 major phases: - the trophoblastic phase, where the
trophoblast digests and derives nutrition from
endometrial tissue, from week 2 to week 8, - and the placental phase from week 9 onward.
There is a long transition period, from week 4 to 12, where the placenta gradually
takes over the role of feeding the embryo. The placenta is a hybrid organ containing
both maternal and fetal components. It develops from the deeper layer of the
endometrium and the trophoblast of the embryo. Basically, in week 2, the superficial layer
of the trophoblast - the syncytiotrophoblast - invades and digests the nearby endometrial tissue,
while maternal capillaries at the implantation site begin to dilate, forming sinusoids. As
these events continue, maternal blood vessels surrounding the embryo are slowly dissolved.
The deeper layer of the trophoblast - the cytotrophoblast - then invades the
syncytiotrophoblast to form the primary chorionic villi.
In week 3, extraembryonic mesoderm cells fill the villi and differentiate into fetal blood vessels,
including the three umbilical vessels that connect the embryo to the placenta. The now secondary
villi are submerged in pools of maternal blood. Fetal blood travels to the placenta via 2
umbilical arteries. The exchange between maternal and fetal blood takes place in the capillaries
within chorionic villi. Fetal waste such as carbon dioxide moves into maternal blood, while nutrients
and oxygen move into fetal blood and travel back to the fetus via the single umbilical vein.
The placenta is also permeable to lipid-soluble fetotoxic substances,
which, if consumed by the mother during pregnancy, may cause harm to fetal development.
Note that maternal and fetal blood do not mix because blood cells cannot move across
the placenta. This separation protects the fetus – a genetically-distinct and
hence a “foreign” organism - from being attacked by the maternal immune system.
Fetal circulation is markedly different from neonatal circulation due to the
placental-umbilical circuit and presence of 3 fetal shunts.
The umbilical vein carries oxygen- and nutrient-rich blood from the placenta to
the liver. Because fetal liver is not yet ready for its blood filtering function,
most of the blood bypasses the liver via a shunt called the “ductus venosus”,
which drains into the inferior vena cava. In the inferior vena cava, placental blood
mixes with venous blood of the fetus, and travels to the heart’s right atrium.
While the right heart normally pumps blood to the lungs after birth,
this step is skipped in the fetus because the fetal lungs are not yet functional. Fetal blood
bypasses the pulmonary circuit in 2 ways: - First, part of the blood passes directly
from the right atrium to the left atrium via an opening in the interatrial septum, called
the “foramen ovale”. It then travels through the left ventricle to coronary arteries and the aorta,
which branches to provide blood to the brain. - Second, part of the blood flows to the right
ventricle and is pumped to the pulmonary trunk, but most of this blood is immediately
shunted into the aorta via the so-called “ductus arteriosus”. This happens because
the collapsed fetal lungs put up a much higher resistance than the blood pressure in the aorta.
Blood then enters the systemic circulation. After nourishing the fetus, it returns to the
placenta via 2 umbilical arteries, which are branches of the fetal internal iliac arteries.
At birth, as the lungs expand with air, pulmonary vascular resistance drops rapidly.
At the same time, clamping of the umbilical cord increases systemic vascular resistance.
These 2 changes enable the right heart to pump blood to the now lower-resistant lungs.
The increased systemic resistance also raises the pressure in the left atrium to
a higher value than the right atrium, forcing the foramen ovale to close.
Pressure changes, together with presence of oxygen and decreased prostaglandin levels,
cause the fetal shunts to close and become ligaments.
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