In order for milk to flow from the nipple of the mother into the mouth of the nursing infant, which of the following must occur?

Correct Answer: C

Rationale: The correct answer is C because oxytocin is responsible for stimulating the contraction of myoepithelial cells around the alveoli in the mammary glands, causing milk ejection. This process is known as the let-down reflex. In contrast, choice A (myoepithelial cells must relax) is incorrect because they need to contract to push milk out. Choice B (prolactin levels must fall) is incorrect because prolactin is responsible for milk production, not milk ejection. Choice D (the baby's mouth must develop a strong negative pressure over the nipple) is incorrect because it is the mother's hormone release, not the baby's action, that causes milk flow.

Correct Answer: B

Rationale: The correct answer is B: zygote. A zygote is formed when a sperm cell fertilizes an egg cell, marking the beginning of a new individual's development. It is the first cell of the new organism with a full set of chromosomes. A: Blastocyst is a later stage of development after the zygote has undergone several cell divisions. C: Fetus refers to the later stages of development when the embryo has developed recognizable features. D: Embryo is the stage after the zygote when the cells start to differentiate into different tissues and organs.

Correct Answer: C

Rationale: The correct answer is C, the uterine (fallopian) tubes. This is where fertilization usually occurs as it is the site where the egg and sperm meet. The egg is released from the ovary and travels through the fallopian tube where it can be fertilized by sperm. If fertilization occurs, the resulting embryo will then travel to the uterus for implantation. The other choices are incorrect because fertilization does not typically occur in the ovary (A) or vesicular (Graafian) follicle (B). While the uterus (D) is where the embryo implants and develops into a fetus, fertilization itself does not occur there.

Correct Answer: C

Rationale: The correct answer is C: Progesterone. The corpus luteum is a temporary endocrine structure in the ovaries that forms after ovulation. Its main function is to produce progesterone, which helps prepare the uterine lining for implantation of a fertilized egg. Follicle stimulating hormone (FSH) is produced by the pituitary gland to stimulate follicle development, not by the corpus luteum. Testosterone is mainly produced by the testes in males and a small amount by the ovaries in females, not by the corpus luteum. Progesterone is the key hormone produced by the corpus luteum, making choice C the correct answer.

Correct Answer: D

Rationale: The correct answer is D: uterine (fallopian) tubes. These tubes are responsible for receiving the ovulated oocyte (egg) and providing the site for fertilization. The fallopian tubes are specifically designed to transport the egg from the ovary to the uterus for potential fertilization by sperm. Choice A, glans penis, is incorrect as it is part of the male reproductive system and not involved in receiving the ovulated egg. Choice B, shaft, is also incorrect as it refers to the main part of the penis and is not related to female reproductive functions. Choice C, scrotum, is incorrect as it is part of the male reproductive system and has no role in receiving the ovulated egg.