Exercise practice 1: Human reproduction

5.1 Exercise practice 1: questions E1 to E11

The chapter closes with one exercise section of twenty-one questions. Each is worked below, in my own words. Try it first, then check the reasoning.

5.1.1 E1 Fill in the blanks

Question. Fill the gaps: (a) humans reproduce ____, (b) the human mode of development is ____, (c) fertilisation in humans is ____, (d) the gametes are ____, (e) the zygote is ____, (f) release of an ovum from a mature follicle is termed ____, (g) the hormone that triggers ovulation is ____, (h) the combining of a male and a female gamete is named ____, (i) in humans the site of fertilisation is ____, (j) after division the zygote forms a ____ that implants in the uterus, and (k) the vascular link between foetus and uterus is the ____.

Answer. (a) sexually, (b) viviparous, (c) internal, (d) haploid, (e) diploid, (f) ovulation, (g) luteinising hormone, (h) fertilisation, (i) the ampulla of the fallopian tube, (j) blastocyst, (k) placenta.

5.1.2 E2 The male reproductive system

Question. Draw a labelled diagram of the male reproductive system.

Answer. A good diagram shows a pair of testes in the scrotum, each giving off the vasa efferentia into the epididymis, then the vas deferens looping over the urinary bladder. Add the seminal vesicle joining the vas deferens to form the ejaculatory duct, the prostate below the bladder, the bulbourethral glands near the urethra, and the penis with the glans. Label the urethra and the urethral meatus at the tip. The testis should be shown opened, because the exam expects the seminiferous tubules and the rete testis inside.

5.1.3 E3 The female reproductive system

Question. Draw a labelled diagram of the female reproductive system.

Answer. Show a pair of ovaries, the fallopian tubes with the infundibulum, fimbriae, ampulla and isthmus, the pear-shaped uterus with the cervix, and the vagina. Label the three layers of the uterine wall if there is space: perimetrium, myometrium and endometrium. The diagram should also show the broad relationships, with the uterus between the bladder and the rectum and the cervical canal opening into the vagina.

5.1.4 E4 Functions of testis and ovary

Question. Write two major functions each of the testis and the ovary.

Answer. The testis produces sperms inside the seminiferous tubules and produces androgens from the Leydig cells. The ovary produces the ovum and secretes ovarian hormones, with oestrogen coming from the growing follicle and progesterone from the corpus luteum. Both organs are therefore at once gamete factories and endocrine glands.

5.1.5 E5 The seminiferous tubule

Question. Describe the structure of a seminiferous tubule.

Answer. A seminiferous tubule is a long, highly coiled tube inside a testicular lobule. Its wall is lined by two cell types. Spermatogonia lie near the basement membrane and multiply by mitosis, and their daughters enter meiosis as primary spermatocytes. Sertoli cells are tall supporting cells that reach between the germ cells and feed the spermatocytes and spermatids as they grow. Maturing sperm heads rest inside these cells until release. Beyond the tubule wall, the interstitial space holds blood vessels and Leydig cells.

5.1.6 E6 Spermatogenesis

Question. What is spermatogenesis? Describe the process briefly.

Answer. Spermatogenesis is the formation of sperm from spermatogonia in the seminiferous tubules. Spermatogonia, which are diploid with 46 chromosomes, multiply by mitosis. Some of them become primary spermatocytes, which complete the first meiotic division to give two haploid secondary spermatocytes with 23 chromosomes each. Meiosis II then yields four haploid spermatids, again two from each secondary spermatocyte. The spermatids are transformed into spermatozoa by spermiogenesis.

5.1.7 E7 Hormones and spermatogenesis

Question. Name the hormones involved in the regulation of spermatogenesis.

Answer. The hypothalamus releases gonadotropin releasing hormone, or GnRH. GnRH causes the anterior pituitary to put out luteinising hormone and follicle stimulating hormone. LH targets the Leydig cells and lifts androgen output, and those androgens push sperm formation along. FSH acts on the Sertoli cells and induces them to release factors that assist spermiogenesis.

5.1.8 E8 Spermiogenesis and spermiation

Question. Define spermiogenesis and spermiation.

Answer. Spermiogenesis is the transformation of a haploid spermatid into a motile spermatozoon. Spermiation is the release of the mature sperm heads from the Sertoli cells into the lumen of the seminiferous tubule.

5.1.9 E9 The sperm

Question. Draw a labelled diagram of a sperm.

Answer. The diagram should show four regions. The head carries the haploid nucleus covered at the front by the acrosome. The short neck follows. The middle piece is packed with mitochondria. The tail is the long motile part. Label the plasma membrane over the whole cell and the acrosome as the enzyme-filled cap that helps the sperm cross the zona pellucida.

5.1.10 E10 What seminal plasma contains

Question. Which substances make up seminal plasma, and where do they come from?

Answer. Seminal plasma is the liquid portion of semen. The seminal vesicles, the prostate and the bulbourethral glands supply most of it, and the epididymis and vas deferens add their own secretions. It is rich in fructose, calcium and several enzymes. Fructose fuels the sperm, calcium supports their activity and the enzymes help the semen to clot and later liquefy. The bulbourethral secretion also lubricates the penis.

5.1.11 E11 Accessory ducts and glands

Question. What are the major functions of the male accessory ducts and glands?

Answer. The duct system runs through the rete testis, the vasa efferentia, the epididymis and the vas deferens; its job is to hold sperm and move them out of the body. The epididymis also lets the sperm mature and become motile. The accessory glands make the seminal plasma that nourishes the sperm, keeps them motile and lubricates the reproductive tract. All these functions are maintained by androgens.