Which of the following sexually transmitted infections cannot be completely cured?

The correct answer is B, the ampulla of the fallopian tube. The ovum released at ovulation is picked up by the fimbriae of the infundibulum and meets the sperm in the ampulla, the wide middle part of the tube, where fusion takes place to form the zygote. A is wrong because the uterus is the site of implantation, not fertilisation; the blastocyst reaches it about a week later and attaches to the endometrium. C is wrong because the cervix is the narrow neck of the uterus through which the sperms pass on their way up; nothing fuses there. D is wrong because the ovary only releases the ovum; a fertilised egg in or near the ovary would be an abnormal ectopic pregnancy. This single distinction, fertilisation in the tube and implantation in the uterus, is the most repeated question from the chapter.

The correct answer is B, the Leydig or interstitial cells, which lie in the spaces between the seminiferous tubules of the testis and secrete androgens, chiefly testosterone, under the influence of luteinising hormone from the anterior pituitary. A is wrong because Sertoli cells lie inside the tubules and nourish the developing sperms, for which reason they are called nurse cells; this swap is the commonest error in the topic. C is wrong because the prostate is an accessory gland whose secretion forms part of the semen and does not make the hormone. D is wrong because the epididymis is a coiled duct where sperms are stored and mature; it secretes no sex hormone. Pair them once and for all: Sertoli nourishes, Leydig secretes. Testosterone is responsible for the secondary sexual characters of the male, such as the deepening of the voice and the growth of facial hair.

The correct answer is B, to nourish the developing sperms. Sertoli cells line the seminiferous tubules and provide nutrition and support to the germ cells as they divide and change into sperms, which is why they are called nurse cells; they are controlled mainly by follicle stimulating hormone. A is wrong because testosterone comes from the Leydig or interstitial cells outside the tubules. C is wrong because mature sperms are stored in the epididymis and the vas deferens, not within the Sertoli cells. D is wrong because the fluid part of semen is secreted by the accessory glands, namely the seminal vesicles, the prostate and the bulbourethral glands. Remember that the scrotum keeps the testis about two to two and a half degrees below body temperature, which this process needs.

The correct answer is B, enzymes that help it enter the ovum. The acrosome is a cap-like structure over the sperm nucleus filled with enzymes that digest the layers around the egg so that one sperm can fuse with it. A is wrong because the mitochondria are packed into the middle piece of the sperm and supply the energy for the lashing of the tail. C is wrong because the genetic material lies in the haploid nucleus of the head, below the acrosome, and the acrosome itself carries no chromosomes. D is wrong because the sperm draws its energy from the fluid around it and from its own mitochondria rather than from a glucose store in the head. The three parts of a sperm, head with acrosome, middle piece with mitochondria and tail for motion, are a standard diagram question.

The correct answer is C, human chorionic gonadotropin, usually written hCG. It is secreted by the trophoblast of the implanted blastocyst and then by the placenta, appears in the blood and urine within a few weeks of conception, and is unique to pregnancy, so test kits use antibodies against it. A is wrong because oestrogen is secreted through the cycle and in pregnancy as well, so it cannot confirm pregnancy. B is wrong for the same reason: progesterone rises in the luteal phase of every cycle even when there is no conception. D is wrong because prolactin from the anterior pituitary is the hormone of milk secretion and rises late in pregnancy and after birth. Note that the placenta also secretes human placental lactogen, oestrogen, progesterone and relaxin.