The male reproductive system and the testis

One cell from each parent

Every person began as a single cell. It was made when a sperm from the father joined an ovum from the mother. Sperms and ova are called gametes, the sex cells. The organs that make and carry them are the reproductive system.

The male system has three jobs. It makes sperms, it makes the male hormones, and it carries the sperms to the female body. Let us follow the organs one by one.

The testes and the scrotum

A man has two testes. They are the primary sex organs of the male, because they make both the sperms and the hormones. They do not lie inside the abdomen. They hang in a pouch of skin, the scrotum.

Why outside? Sperms are made well only at a temperature lower than the body temperature. The scrotum keeps the testes about 2 to 2.5 °C below the temperature inside the abdomen.

• Each adult testis is oval, about 4 to 5 cm long and 2 to 3 cm wide.
• A tough covering surrounds it.
• Inside it are about 250 compartments, the testicular lobules.

Inside a testis

Each lobule holds one to three highly coiled tubes, the seminiferous tubules. Sperms are made in these tubules.

Now look at one tubule cut across.

The wall of a seminiferous tubule has two kinds of cells.

• Male germ cells, the spermatogonia. They divide, and some of their daughter cells become sperms.
• Sertoli cells. These are large supporting cells. They give food and support to the germ cells that are changing into sperms.

The spaces between the tubules are the interstitial spaces. They hold small blood vessels and the interstitial cells, also called Leydig cells. The Leydig cells make the male hormones called androgens, of which the chief one is testosterone. Some cells of the immune system also lie here.

The ducts

The sperms must travel out of the body. The tubes that carry them are the male sex accessory ducts.

1. The seminiferous tubules open into the rete testis.
2. The rete testis leads to the vasa efferentia, small ducts that leave the testis.
3. The vasa efferentia open into the epididymis, a coiled tube on the back of the testis. Sperms are stored and ripen here.
4. The epididymis leads to the vas deferens. It rises into the abdomen and loops over the urinary bladder.
5. The vas deferens receives a duct from the seminal vesicle, and together they form the ejaculatory duct.
6. The ejaculatory duct opens into the urethra. The urethra starts at the urinary bladder and runs through the penis to the urethral opening, also called the urethral meatus.

In a man the urethra carries both urine and semen, but not at the same time.

The penis and the glands

The penis is the male external organ that places the sperms in the female body. The swollen tip is the glans penis. A loose fold of skin, the foreskin, covers it.

Three kinds of accessory glands add their fluid to the sperms: a pair of seminal vesicles, one prostate gland and a pair of bulbourethral glands. Their fluid is the seminal plasma. It is rich in fructose, calcium and certain enzymes. The fructose is food for the sperms. The bulbourethral glands also make a fluid that makes the penis slippery. The sperms and the seminal plasma together are called semen.

The hormones in one line

Two hormones of the pituitary gland, LH and FSH, control the testis. LH acts on the Leydig cells, which make androgens. FSH acts on the Sertoli cells. You will meet them again in the lesson on spermatogenesis.

You should find that only one kind of gland has added its fluid when the sperm is in the ejaculatory duct, and three kinds by the time it is in the urethra.

Try it in Python

The program lists the parts on the route of a sperm, in order.

Practise with new numbers

Common mistakes

• Saying that the scrotum keeps the testes warm. It keeps them 2 to 2.5 °C cooler than the inside of the body.
• Saying that Leydig cells make sperms. Leydig cells make androgens. The germ cells make the sperms.
• Mixing the vasa efferentia with the vas deferens. The vasa efferentia are small ducts inside the testis region. The vas deferens is the long tube that rises into the abdomen.
• Leaving out the epididymis. Sperms are stored and ripen there before the vas deferens carries them on.
• Saying that the glands make sperms. The glands make the fluid. The sperms come only from the testes.

Remember these

• The testes lie in the scrotum, 2 to 2.5 °C below body temperature. Each has about 250 lobules, and each lobule has one to three seminiferous tubules.
• Seminiferous tubule: germ cells (spermatogonia) and Sertoli cells. Interstitial (Leydig) cells make androgens.
• Route: seminiferous tubules, rete testis, vasa efferentia, epididymis, vas deferens, ejaculatory duct, urethra.
• Glands: seminal vesicles, prostate, bulbourethral. The seminal plasma is rich in fructose, calcium and enzymes.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. Why do the testes lie outside the abdomen?

2. Name the two kinds of cell in the wall of a seminiferous tubule, and give the work of each.

3. Which cells lie outside the seminiferous tubules, and what do they make?

4. Write the route of a sperm from the seminiferous tubule to the outside.

5. Name the three kinds of accessory gland of the male system. Give one thing that the seminal plasma is rich in.

References

• NCERT (2023). Biology, Textbook for Class XII, chapter 2, Human Reproduction.
• Betts J. G. et al. (2022). Anatomy and Physiology 2e, OpenStax, chapter 27, The Reproductive System.
• Hall J. E. and Hall M. E. (2021). Guyton and Hall Textbook of Medical Physiology, 14th edition, Elsevier, chapter 80.