Embryology: Development of the Placenta and Fetal Circulation, Animation

Summary

The 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

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🍼 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.

Keywords

💡Prenatal nutrition

Prenatal nutrition refers to the nourishment a developing fetus receives in the womb. It is crucial for the growth and development of the fetus and is divided into two phases: the trophoblastic phase and the placental phase. In the video, prenatal nutrition is the central theme, highlighting the importance of the nourishment process during different stages of fetal development.

💡Trophoblastic phase

The trophoblastic phase is the first major phase of prenatal nutrition, occurring from week 2 to week 8. During this phase, the trophoblast, a part of the placenta, digests and derives nutrition from the endometrial tissue. The script explains how the syncytiotrophoblast invades and digests the endometrial tissue, which is vital for the early nourishment of the embryo.

💡Placental phase

The placental phase is the second major phase of prenatal nutrition, beginning from week 9 onward. The placenta, a hybrid organ containing both maternal and fetal components, takes over the role of feeding the embryo. The script describes the gradual transition of the placenta taking over the nourishment process, emphasizing its importance in the later stages of fetal development.

💡Placenta

The placenta is a vital organ in prenatal nutrition, responsible for providing nutrients and oxygen to the fetus while removing waste products. It develops from the endometrium and the trophoblast of the embryo. The script details the structure and function of the placenta, including its role in the exchange of substances between maternal and fetal blood.

💡Syncytiotrophoblast

The syncytiotrophoblast is the superficial layer of the trophoblast, which invades and digests the nearby endometrial tissue during the trophoblastic phase. The script mentions this layer as being crucial for the initial nourishment of the embryo by digesting the endometrial tissue and forming sinusoids.

💡Cytotrophoblast

The cytotrophoblast is the deeper layer of the trophoblast that invades the syncytiotrophoblast to form the primary chorionic villi. As explained in the script, the cytotrophoblast plays a key role in the development of the placenta by contributing to the formation of the villi, which are essential for nutrient exchange.

💡Chorionic villi

Chorionic villi are projections from the placenta that contain fetal blood vessels and are essential for the exchange of nutrients, oxygen, and waste between the mother and the fetus. The script describes the formation of primary and secondary villi and their role in the placental phase of prenatal nutrition.

💡Umbilical vessels

Umbilical vessels, including the umbilical arteries and vein, connect the fetus to the placenta and are responsible for the transport of blood between the two. The script explains how fetal blood travels to the placenta via the umbilical arteries and returns via the umbilical vein, highlighting the importance of these vessels in prenatal nutrition.

💡Fetal circulation

Fetal circulation refers to the unique blood flow pattern in the fetus, which is adapted to the in-utero environment. The script discusses the differences between fetal and neonatal circulation, emphasizing the presence of fetal shunts that allow for efficient nutrient and oxygen delivery to the fetus.

💡Fetal shunts

Fetal shunts are temporary blood vessels that allow blood to bypass certain organs in the fetus, such as the lungs and liver, which are not yet functional. The script describes three fetal shunts: the ductus venosus, the foramen ovale, and the ductus arteriosus, explaining their role in facilitating blood flow and the changes that occur at birth.

💡Foramen ovale

The foramen ovale is an opening in the interatrial septum of the fetal heart that allows blood to pass directly from the right atrium to the left atrium. The script explains how this shunt facilitates the bypass of the pulmonary circuit, ensuring that oxygenated blood reaches the brain and other vital organs.

💡Ductus arteriosus

The ductus arteriosus is a shunt that allows blood to be diverted from the pulmonary trunk to the aorta, bypassing the fetal lungs. The script describes how this shunt operates due to the high resistance in the collapsed fetal lungs and the changes that lead to its closure after birth.

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.