ATI RN

1. If pregnancy does not occur, the corpus luteum shrinks, and the __________.

• A. cells begin to duplicate
• B. one-celled zygote multiplies and forms a blastocyst
• C. germinal period lasts only about two weeks
• D. lining of the uterus is discarded

Correct Answer: D

Rationale: If pregnancy does not occur, the corpus luteum will shrink. As a result, the lining of the uterus is discarded through the process of menstruation. This shedding of the uterine lining is what causes menstrual bleeding. Choices A, B, and C are incorrect because they do not describe the physiological response of the body when pregnancy does not occur. The corpus luteum shrinking and the subsequent shedding of the uterine lining are part of the menstrual cycle, not processes related to cell duplication, zygote multiplication, or the duration of the germinal period.

2. Which statement about a blastocyst is true?

• A. It consists of a single cell.
• B. It is a structure that feeds the developing organism.
• C. Between the seventh and ninth days, it burrows deep into the uterine lining.
• D. It is a membrane that helps to keep the temperature of the prenatal world constant.

Correct Answer: C

Rationale: The statement that is true about a blastocyst is that between the seventh and ninth days, it burrows deep into the uterine lining. This process, known as implantation, is essential for the blastocyst to establish a connection with the mother's body and receive nutrients for further development. It is a critical stage in prenatal development and sets the foundation for pregnancy. Choices A, B, and D are incorrect. A blastocyst is not a single cell but rather a structure composed of many cells. It is not a structure that feeds the developing organism; instead, it implants in the uterine lining to receive nutrients. It is not a membrane that regulates temperature but plays a crucial role in the initial stages of pregnancy by implanting in the uterus.

3. The force of blood flowing through the __________ keeps it firm.

• A. amnion
• B. umbilical cord
• C. yolk sac
• D. embryonic disk

Correct Answer: B

Rationale: The force of blood flowing through the umbilical cord keeps it firm. The umbilical cord is the connection between the placenta and the fetus, providing essential nutrients and oxygen to the developing baby. Blood flow through the umbilical cord helps maintain its structure and function throughout the prenatal period. Choices A, C, and D are incorrect as they do not play a role in providing nutrients and oxygen to the developing baby or in maintaining its firmness.

4. During prenatal development, the ectoderm folds over to form the __________, or primitive spinal cord.

• A. mesoderm; neuron tract
• B. neural tube
• C. endoderm; neural tube
• D. neuron tract

Correct Answer: B

Rationale: The correct answer is B. During prenatal development, the ectoderm folds over to form the neural tube, which eventually develops into the brain and spinal cord. The neural tube is the precursor to the central nervous system, including the primitive spinal cord. Choices A, C, and D are incorrect because the mesoderm does not form the neural tube, the endoderm is not involved in the formation of the central nervous system, and neuron tract is not the structure that forms the primitive spinal cord.

5. During the second trimester, a white, cheeselike substance called __________ emerges on the skin.

• A. lanugo
• B. corpus luteum
• C. vernix
• D. chorion

Correct Answer: C

Rationale: During the second trimester of pregnancy, a white, cheeselike substance called vernix emerges on the skin of the developing fetus. Vernix is a protective layer that helps prevent the skin from becoming waterlogged during the time in the amniotic fluid. Choice A, lanugo, is incorrect as lanugo refers to the fine, soft hair that covers the body of a fetus. Choice B, corpus luteum, is incorrect as it is a temporary endocrine structure involved in the menstrual cycle. Choice D, chorion, is incorrect as it is one of the membranes that surround the embryo and later the fetus.