Which of the following functions of amniotic fluid are critical for fetal lung development? Select all that apply
It acts as a mechanical buffer against external trauma.
It allows the fetus to practice breathing movements.
It contributes to the symmetrical growth of the musculoskeletal system.
It prevents the compression of the umbilical cord.
It provides the necessary fluid medium for lung maturation.
Correct Answer : B,E
Amniotic fluid plays an essential role in fetal development, particularly in the respiratory system. It provides a fluid medium that fills the fetal lungs, necessary for lung tissue expansion and maturation. The fetus practices breathing movements by inhaling and exhaling amniotic fluid, which stimulates the growth and differentiation of the pulmonary alveoli. Normal amniotic fluid volume ranges from 500 to 1000 mL in the third trimester, and abnormalities in volume can impair lung development, leading to conditions like pulmonary hypoplasia.
Rationale for correct answers
B. Amniotic fluid allows the fetus to perform breathing movements, critical for stimulating lung expansion and promoting structural and functional maturation of the lungs.
E. It provides the necessary fluid medium inside the lungs, which maintains lung distension and facilitates alveolar growth, essential for postnatal respiratory function.
Rationale for incorrect answers
A. Acting as a mechanical buffer protects the fetus from external trauma but does not directly affect lung development.
C. While amniotic fluid supports symmetrical growth of the musculoskeletal system, this is unrelated to pulmonary maturation.
D. Prevention of umbilical cord compression ensures adequate blood flow and oxygen delivery but is not directly linked to lung development.
Take home points
- Amniotic fluid is essential for fetal lung growth by providing a fluid medium within the lungs.
- Fetal breathing movements in amniotic fluid stimulate pulmonary development.
- Mechanical protection and musculoskeletal support are important but not lung-specific functions.
- Adequate amniotic fluid volume is crucial to prevent pulmonary hypoplasia.
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Related Questions
Correct Answer is C
Explanation
Amniotic fluid volume is tightly regulated and serves multiple functions, including cushioning the fetus, facilitating movement, and allowing lung development. In the third trimester, the majority of amniotic fluid is produced by fetal urine excreted into the amniotic cavity and lung fluid secreted by the fetal respiratory tract. Normal amniotic fluid volume ranges between 500 to 1000 mL at term. Fluid turnover involves swallowing and absorption by the fetus as well as contributions from membranes and maternal sources.
Rationale for correct answers
C. Fetal urine production significantly increases in the third trimester, contributing the bulk of amniotic fluid volume. Additionally, fetal lungs secrete fluid that mixes with the amniotic fluid, ensuring appropriate volume and composition. This combined secretion accounts for the majority of amniotic fluid after 28 weeks gestation.
Rationale for incorrect answers
A. Diffusion of fluid from maternal blood across the placental membranes contributes minimally to amniotic fluid volume, especially in the third trimester, as fetal urine becomes predominant.
B. Secretions from the fetal gastrointestinal tract do not contribute significantly to amniotic fluid volume; rather, swallowed amniotic fluid is absorbed, not secreted into the cavity.
D. Transudation from fetal skin is significant only early in gestation before keratinization, which is complete by about 20 weeks, greatly reducing this source by the third trimester.
Take home points
- The majority of third trimester amniotic fluid is produced by fetal urine and lung fluid secretions.
- Amniotic fluid volume ranges from 500 to 1000 mL near term and is critical for fetal development.
- Maternal diffusion and fetal skin transudation contribute minimally after mid-gestation.
- Fetal swallowing and absorption regulate amniotic fluid volume alongside production.
Correct Answer is B
Explanation
The chorion frondosum is the part of the chorion characterized by proliferation of vascularized villi adjacent to the decidua basalis, which contributes to the formation of the fetal placenta. These villi undergo extensive branching and vascularization to establish maternal-fetal exchange. In contrast, the chorion laeve is the smooth, avascular part away from the decidua basalis. Proper development of the chorion frondosum is essential for adequate placental function, supporting fetal nutrition and gas exchange throughout pregnancy.
Rationale for correct answers
B. The chorion frondosum forms from the proliferation of chorionic villi adjacent to the decidua basalis, developing into the functional fetal placenta with a dense vascular network enabling exchange of nutrients, gases, and waste. This structure is essential for sustaining fetal growth.
Rationale for incorrect answers
A. The chorion laeve, or smooth chorion, forms from villi on the side of the chorion away from the decidua basalis; these villi regress and become avascular, so it does not contribute to placental formation.
C. The yolk sac is an early embryonic structure involved in initial hematopoiesis and nutrient transfer but is not formed from chorionic villi and is distinct from the chorion.
D. The umbilical cord develops from the connecting stalk and contains blood vessels connecting fetus to placenta but is not formed by chorionic villi proliferation adjacent to the decidua basalis.
Take home points
- The chorion frondosum is the vascularized region of chorionic villi adjacent to the decidua basalis forming the fetal placenta.
- The chorion laeve is avascular and forms the smooth chorion on the opposite side of the placenta.
- Proper placental development depends on chorionic villi proliferation and vascularization in the chorion frondosum.
- The yolk sac and umbilical cord are distinct structures not formed from chorionic villi adjacent to decidua basalis.
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