Home Life Sciences Developmental Biology and Embryology Placental Development: Structure, Function and Disorders

Placental Development: Structure, Function and Disorders

February 22, 2025

Placental Development: Structure, Function and Disorders – A Comprehensive Study for Medical and Health Students

Introduction

The placenta is a vital organ that develops in the uterus during pregnancy, ensuring the exchange of nutrients, gases, and waste between the mother and the fetus. Its proper formation and function are critical for fetal development and maternal health. This study module provides an in-depth exploration of the placenta’s structure, functions, and common disorders, along with links to relevant resources for further reading.

How placenta develops during pregnancy, placental insufficiency symptoms and causes, role of placenta in fetal growth, common placental disorders in pregnancy, maternal blood circulation in placenta, placental barrier function explained, pregnancy complications due to placenta, placental health and fetal well-being

1. Placental Development

1.1 Formation of the Placenta

Placental development begins soon after fertilization and undergoes multiple stages:

Fertilization and Blastocyst Formation: The zygote undergoes cleavage to form a blastocyst, which implants in the uterine wall.
Trophoblast Differentiation: The outer layer of the blastocyst, called the trophoblast, differentiates into two layers:
- Cytotrophoblast: A single layer of cells that provides structural support.
- Syncytiotrophoblast: A multinucleated layer responsible for invading the maternal endometrium to establish nutrient exchange.
Chorionic Villi Formation: These finger-like projections extend into the maternal blood supply, facilitating nutrient and gas exchange.

1.2 Stages of Placental Growth

The placenta undergoes distinct growth phases:

Implantation Stage (0–2 weeks): Initial attachment of the blastocyst to the uterine wall.
Villous Stage (3–12 weeks): Formation of primary, secondary, and tertiary villi for efficient exchange.
Maturation Stage (13 weeks to term): Growth and functional optimization of the placenta.

2. Structure of the Placenta

The placenta consists of two main components:

2.1 Maternal Component: Decidua Basalis

Formed from the maternal endometrium after implantation.
Supplies maternal blood to the placenta.

2.2 Fetal Component: Chorion Frondosum

Contains chorionic villi that facilitate exchange between maternal and fetal blood.
Connected to the fetus via the umbilical cord.

2.3 Placental Circulation

Maternal Circulation: Maternal arteries supply oxygenated blood to the placenta, and maternal veins carry away deoxygenated blood.
Fetal Circulation: The umbilical arteries carry deoxygenated blood from the fetus to the placenta, while the umbilical vein brings oxygenated blood back.

3. Functions of the Placenta

The placenta performs several crucial functions:

3.1 Respiratory Function

Oxygen and carbon dioxide exchange occur via diffusion across the placental membrane.

3.2 Nutritional Function

Transfers essential nutrients, including glucose, amino acids, fatty acids, and vitamins, to the fetus.

3.3 Excretory Function

Removes fetal waste products like urea and carbon dioxide.

3.4 Endocrine Function

Secretes hormones essential for pregnancy maintenance, including:
- Human Chorionic Gonadotropin (hCG): Supports the corpus luteum.
- Progesterone: Maintains the uterine lining.
- Estrogen: Promotes fetal development and maternal adaptations.

3.5 Immunological Function

Acts as a selective barrier, protecting the fetus from maternal immune responses.
Transfers maternal antibodies (IgG) to the fetus for passive immunity.

4. Placental Disorders

Placental abnormalities can significantly impact pregnancy outcomes.

4.1 Placental Insufficiency

Cause: Poor placental blood flow or development.
Effects: Fetal growth restriction (FGR), preeclampsia, or stillbirth.
Management: Regular monitoring, maternal rest, and controlled delivery planning.

4.2 Placenta Previa

Cause: The placenta partially or completely covers the cervix.
Symptoms: Painless vaginal bleeding in the third trimester.
Management: Bed rest, C-section delivery in severe cases.

4.3 Placental Abruption

Cause: Premature separation of the placenta from the uterine wall.
Symptoms: Severe abdominal pain, vaginal bleeding, fetal distress.
Risk Factors: Hypertension, smoking, trauma.
Management: Hospitalization, blood transfusion, emergency C-section.

4.4 Placenta Accreta, Increta, and Percreta

Cause: Abnormal implantation of the placenta into the uterine wall.
Effects: Severe postpartum hemorrhage.
Management: Surgical intervention, possible hysterectomy.

5. Diagnostic Techniques

Several methods help diagnose placental disorders:

Ultrasound Imaging: Identifies placental position and abnormalities.
Doppler Flow Studies: Evaluates blood flow to detect insufficiencies.
Maternal Blood Tests: Measures hormonal and protein markers.
MRI Scans: Provides detailed imaging in complex cases.

6. Preventive Measures and Treatment

Prenatal Care: Regular check-ups and ultrasound screenings.
Healthy Lifestyle: Proper nutrition, avoiding smoking and alcohol.
Medical Interventions: Treatment of underlying maternal conditions like diabetes or hypertension.
Delivery Planning: C-section for high-risk placental disorders.

7. Website URL Links for Further Reading

Understanding Placental Development – National Library of Medicine.
Placental Functions and Hormonal Secretions – Science Direct.
Placental Disorders and Their Management – American Journal of Obstetrics & Gynecology.

Conclusion

The placenta is an essential organ for fetal development, performing numerous functions critical for a healthy pregnancy. Understanding its structure, functions, and potential disorders is crucial for both medical professionals and expecting mothers. Early detection and management of placental disorders can significantly improve pregnancy outcomes. Continuous research and advancements in fetal medicine are enhancing our knowledge and ability to treat placental complications effectively.

MCQs on Placental Development: Structure, Function and Disorders

1. What is the primary function of the placenta?

A) Gas exchange between mother and fetus
B) Production of digestive enzymes
C) Absorption of nutrients from the intestines
D) Contraction of uterine muscles

✅ Answer: A) Gas exchange between mother and fetus
Explanation: The placenta facilitates oxygen and carbon dioxide exchange between maternal and fetal blood, ensuring the fetus receives oxygen for growth and development.

2. Which structure develops into the placenta?

A) Yolk sac
B) Amnion
C) Trophoblast
D) Chorion

✅ Answer: D) Chorion
Explanation: The chorion, derived from the trophoblast, plays a crucial role in forming the placenta, which supports fetal development.

3. Which hormone is primarily produced by the placenta to maintain pregnancy?

A) Oxytocin
B) Human chorionic gonadotropin (hCG)
C) Thyroxine
D) Insulin

✅ Answer: B) Human chorionic gonadotropin (hCG)
Explanation: hCG maintains the corpus luteum, ensuring continued progesterone production, which is essential for sustaining pregnancy.

4. The placenta is classified as which type of organ?

A) Endocrine
B) Exocrine
C) Excretory
D) Digestive

✅ Answer: A) Endocrine
Explanation: The placenta acts as an endocrine organ by secreting hormones such as hCG, progesterone, and estrogen to support pregnancy.

5. What is the term for the fetal part of the placenta?

A) Decidua basalis
B) Chorionic villi
C) Amniotic sac
D) Endometrium

✅ Answer: B) Chorionic villi
Explanation: Chorionic villi contain fetal blood vessels and facilitate nutrient and gas exchange with maternal blood.

6. The maternal portion of the placenta is derived from which structure?

A) Decidua basalis
B) Yolk sac
C) Amnion
D) Myometrium

✅ Answer: A) Decidua basalis
Explanation: The decidua basalis is the maternal tissue that interacts with the chorionic villi to form the placenta.

7. Which of the following does NOT pass through the placenta?

A) Oxygen
B) Nutrients
C) Maternal red blood cells
D) Antibodies

✅ Answer: C) Maternal red blood cells
Explanation: The placenta allows exchange of gases, nutrients, and antibodies, but maternal red blood cells do not cross the placental barrier under normal conditions.

8. Which disorder is characterized by abnormal placenta attachment deeply into the uterine wall?

A) Placenta previa
B) Placenta accreta
C) Eclampsia
D) Preterm labor

✅ Answer: B) Placenta accreta
Explanation: Placenta accreta occurs when the placenta attaches too deeply to the uterus, potentially causing complications during delivery.

9. What condition occurs when the placenta covers the cervix?

A) Placenta previa
B) Placenta abruption
C) Preeclampsia
D) Ectopic pregnancy

✅ Answer: A) Placenta previa
Explanation: Placenta previa is a condition where the placenta partially or completely covers the cervix, leading to potential complications during delivery.

10. Which fetal blood vessel carries oxygenated blood from the placenta to the fetus?

A) Umbilical artery
B) Pulmonary artery
C) Umbilical vein
D) Hepatic vein

✅ Answer: C) Umbilical vein
Explanation: The umbilical vein transports oxygenated blood from the placenta to the fetal heart.

11. What is the approximate lifespan of the placenta?

A) 1 month
B) 3 months
C) 9 months
D) 12 months

✅ Answer: C) 9 months
Explanation: The placenta develops early in pregnancy and is expelled after childbirth, lasting the entire gestation period of approximately 9 months.

12. What is the function of progesterone secreted by the placenta?

A) Stimulates uterine contractions
B) Maintains the uterine lining
C) Induces labor
D) Increases maternal blood pressure

✅ Answer: B) Maintains the uterine lining
Explanation: Progesterone sustains the uterine lining, preventing contractions that could lead to premature labor.

13. The placenta is formed from which two sources?

A) Chorionic villi and decidua basalis
B) Endometrium and myometrium
C) Amnion and yolk sac
D) Corpus luteum and uterus

✅ Answer: A) Chorionic villi and decidua basalis
Explanation: The fetal chorionic villi and maternal decidua basalis form the placenta, ensuring proper maternal-fetal interactions.

14. What is the major function of the umbilical arteries?

A) Carry oxygenated blood to the fetus
B) Transport deoxygenated blood to the placenta
C) Deliver nutrients to the fetus
D) Regulate amniotic fluid levels

✅ Answer: B) Transport deoxygenated blood to the placenta
Explanation: The umbilical arteries carry deoxygenated blood from the fetus to the placenta for gas exchange.

15. Which of the following conditions results from early placental detachment?

A) Placenta previa
B) Placental abruption
C) Gestational diabetes
D) Amniotic band syndrome

✅ Answer: B) Placental abruption
Explanation: Placental abruption occurs when the placenta separates prematurely from the uterine wall, leading to potential complications.

16. What structure allows maternal and fetal blood to exchange nutrients without direct mixing?

A) Endometrium
B) Placental barrier
C) Amniotic sac
D) Corpus luteum

✅ Answer: B) Placental barrier
Explanation: The placental barrier consists of specialized cells that permit the exchange of oxygen, nutrients, and waste products while preventing the direct mixing of maternal and fetal blood.

17. What is the primary role of human placental lactogen (hPL)?

A) Stimulating fetal lung development
B) Increasing maternal insulin resistance
C) Inducing labor
D) Forming the amniotic sac

✅ Answer: B) Increasing maternal insulin resistance
Explanation: hPL helps regulate maternal glucose levels by increasing insulin resistance, ensuring an adequate supply of glucose for fetal development.

18. In which trimester does the placenta take over hormone production from the corpus luteum?

A) First
B) Second
C) Third
D) At birth

✅ Answer: B) Second
Explanation: By the second trimester, the placenta fully assumes the production of hormones like progesterone and estrogen, maintaining pregnancy.

19. What is the term for insufficient blood flow to the placenta, leading to fetal growth restriction?

A) Placental insufficiency
B) Preeclampsia
C) Gestational diabetes
D) Polyhydramnios

✅ Answer: A) Placental insufficiency
Explanation: Placental insufficiency occurs when the placenta cannot supply enough oxygen and nutrients to the fetus, resulting in poor fetal growth.

20. What condition results from abnormal placental blood vessel development, leading to high maternal blood pressure?

A) Placental abruption
B) Preeclampsia
C) Placenta accreta
D) Hydatidiform mole

✅ Answer: B) Preeclampsia
Explanation: Preeclampsia is a pregnancy complication marked by high blood pressure and potential organ damage due to abnormal placental vascularization.

21. The umbilical cord contains how many blood vessels?

A) One artery and one vein
B) Two arteries and one vein
C) Two veins and one artery
D) Three veins

✅ Answer: B) Two arteries and one vein
Explanation: The umbilical cord has two arteries carrying deoxygenated blood to the placenta and one vein transporting oxygenated blood to the fetus.

22. What term describes excessive amniotic fluid often associated with placental disorders?

A) Oligohydramnios
B) Polyhydramnios
C) Ectopic pregnancy
D) Uterine rupture

✅ Answer: B) Polyhydramnios
Explanation: Polyhydramnios refers to an excess of amniotic fluid, which can be linked to placental dysfunction, fetal swallowing issues, or maternal diabetes.

23. What is the fate of the placenta after childbirth?

A) It remains in the uterus permanently
B) It is expelled as the afterbirth
C) It fuses with the uterine wall
D) It is reabsorbed by the mother

✅ Answer: B) It is expelled as the afterbirth
Explanation: After childbirth, the placenta detaches from the uterine wall and is expelled during the third stage of labor.

24. What is the primary role of estrogen secreted by the placenta?

A) Strengthening fetal bones
B) Stimulating uterine growth and blood flow
C) Increasing milk production
D) Triggering uterine contractions

✅ Answer: B) Stimulating uterine growth and blood flow
Explanation: Estrogen promotes uterine enlargement, increases blood flow, and prepares the breasts for lactation.

25. What placental disorder involves the growth of abnormal trophoblastic tissue?

A) Hydatidiform mole
B) Placental abruption
C) Placenta previa
D) Intrauterine growth restriction (IUGR)

✅ Answer: A) Hydatidiform mole
Explanation: A hydatidiform mole is a gestational trophoblastic disease where abnormal placental tissue develops instead of a normal embryo.

26. Which of the following substances can cross the placenta and affect fetal development?

A) Alcohol
B) Insulin
C) Large proteins
D) Maternal red blood cells

✅ Answer: A) Alcohol
Explanation: Alcohol freely crosses the placenta and can cause fetal alcohol syndrome, affecting fetal growth and brain development.

27. What is the consequence of placenta accreta during childbirth?

A) Delayed labor
B) Excessive bleeding (postpartum hemorrhage)
C) Weak fetal movements
D) Abnormal fetal heart rate

✅ Answer: B) Excessive bleeding (postpartum hemorrhage)
Explanation: In placenta accreta, the placenta attaches too deeply into the uterine wall, making its removal difficult and increasing the risk of severe bleeding.

28. Which condition is caused by a failure of the placenta to detach properly after birth?

A) Retained placenta
B) Preterm labor
C) Polyhydramnios
D) Ectopic pregnancy

✅ Answer: A) Retained placenta
Explanation: A retained placenta occurs when the placenta does not expel within 30 minutes after delivery, requiring medical intervention.

29. What is the name of the temporary organ formed at the site of implantation that nourishes the embryo before the placenta develops?

A) Corpus luteum
B) Yolk sac
C) Amnion
D) Trophoblast

✅ Answer: B) Yolk sac
Explanation: The yolk sac provides early nutrition and aids blood cell formation before the placenta fully develops.

30. Which placental hormone plays a role in increasing maternal blood volume?

A) Progesterone
B) Relaxin
C) Estrogen
D) Human chorionic gonadotropin (hCG)

✅ Answer: C) Estrogen
Explanation: Estrogen contributes to maternal cardiovascular adaptations, including increased blood volume, which supports fetal oxygen and nutrient supply.