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What is the primary function of the placenta during fetal development?
What primarily forms the chorionic leave from the capsular decidua?
Which structure is responsible for connecting the fetus to the placenta?
Which of the following methods is commonly employed for placental separation during the third stage of labor?
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Which structure stabilizes the placenta by anchoring it to the decidua?
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What hormonal change primarily triggers the onset of labor?
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At term, how thick is the placenta at its center?
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What is the main function of the placenta during intrauterine life regarding gas exchange?
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Which factor is NOT associated with congenital abnormalities during fetal development?
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How does the mother's body prepare for postpartum bleeding control?
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At what stage of fetal development are major organs primarily formed?
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What is the approximate diameter of the placenta at term?
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What impact does the hormone relaxin have during labor?
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Which fetal development milestone occurs between 28-32 weeks?
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What forms the blood-filled spaces known as sinuses in the placenta?
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Which layer of tissue prevents the mixing of fetal and maternal blood?
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What is the primary function of the placenta during fetal development?
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Which type of villi are responsible for absorbing nutrients and oxygen from maternal blood?
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When does the placenta become fully formed and functional?
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Which phase describes the changes in fetal circulation at the time of birth?
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At what gestational age can early fetal movements typically be seen on ultrasound?
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What changes occur to the fetus's skin between 28-32 weeks?
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Which statement about the chorionic villi is correct?
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What characteristic of the placental development is most critical for fetal survival?
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Study Notes
Fetal Development
- 0-4 weeks: Rapid development occurs, with the formation of the embryonic plate and the primitive central nervous system. Limb buds form during this period. The embryo is vulnerable to damage from drugs, radiation, and viruses.
- 4-8 weeks: Very rapid cell division takes place, leading to the development of head and facial features. All major organs are laid down in their primitive form. External genitalia are present, but sex is not distinguishable. Early movements begin. The embryo is visible on ultrasound from 6 weeks.
- 8-12 weeks: Eyelids fuse, and the kidney begins to function. The fetus passes urine from 10 weeks. Fetal circulation functions properly. Sucking and swallowing begin. Sex becomes apparent. The fetus moves freely, though not felt by the mother. Primitive reflexes appear. The fetus is 0-6 cm in length and weighs 30g. The spleen produces red blood cells.
- 12-16 weeks: Rapid skeletal development occurs, visible on X-ray. Meconium is present in the gut. Lanugo (fine hair) appears. The nasal septum and palate fuse. The fetus is 10-16 cm in length and weighs 120g.
- 20-24 weeks: Most organs become capable of functioning. Periods of sleep and activity occur. The fetus responds to sound.
- 26-28 weeks: Survival is possible if the fetus is born prematurely. Eyelids reopen, and respiratory movements begin. The fetus weighs 1000-1200g.
- 28-32 weeks: Fat and iron begin to be stored. The testes descend into the scrotum. Lanugo disappears from the face. Skin becomes paler and less wrinkled.
- 32-36 weeks: Increased fat leads to a rounder body shape. Lanugo disappears from the body. Head hair lengthens. Nails reach the tips of fingers. Ear cartilage remains soft. Plantar creases become visible.
Placenta Development
- The placenta develops from the trophoblastic layer of the fertilized ovum, forming the chorionic villi, which become more profuse in the area with the richest blood supply. This area is known as the chorionic frondosum and develops into the placenta.
- The chorionic villi erode the maternal blood vessels, creating a pool of maternal blood in which they float.
- The maternal blood circulating around the villi allows for the absorption of oxygen and nutrients and the excretion of waste.
- Nutritive villi absorb nutrients, while anchoring villi stabilize the placenta.
- The placenta is fully formed and functional by 10 weeks. It initially is soft and loose, becoming more compact as it matures.
Placenta At Term
- The placenta at term is a round, flat organ approximately 20 cm in diameter and 2.5 cm thick at the center. It weighs about 1/6th of the newborn's weight.
- It is made up of the chorionic frondosum, fetal blood vessels, and the decidua basalis.
- Fetal Surface: Smooth, whitish, and shiny, covered by the amnion and chorion. The umbilical cord is attached at the center, and fetal blood vessels radiate from the cord insertion to the edge of the placenta.
- Maternal Surface: The surface is rough and bluish-red, made up of chorionic villi arranged in 20 cotyledons or lobes separated by sulci.
Placenta Functions
- Respiratory: The placenta facilitates gas exchange for the fetus, as the lungs are not functioning in utero.
- Nutritive: The placenta absorbs nutrients from the maternal blood and transfers them to the fetus.
- Excretion: Waste products from the fetus are transferred to the maternal blood for elimination.
- Hormonal: The placenta produces hormones necessary for pregnancy maintenance, including human chorionic gonadotropin (hCG), estrogen, and progesterone.
- Protective: The placenta provides a barrier against some harmful substances, such as bacteria and viruses, although many substances can cross the placental barrier.
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Description
Test your knowledge on the stages of fetal development from conception to 16 weeks. This quiz covers critical changes and milestones in embryonic and fetal growth, including organ formation and early movements. Challenge yourself and learn more about this fascinating aspect of human biology!
