Module 2 Section 2 (Male Reproductive Physiology)

Question 1

Describe the actions of testosterone.

Answer 1

Effects Before Birth;
- It causes the masculinization of the reproductive tract and external genitalia as
well as the descent of the testes into the scrotum.

Effects on sex-specific tissues after birth:
- It maintains the reproductive tract throughout adulthood, promotes spermatogenesis, and promotes maturation of the reproductive system at puberty.

Other reproductive effects:
- Develops sex drive at puberty and controls the secretion of gonadotropin hormone.

Effects on secondary sexual characteristics:
- Causes voice to deepen, development of male pattern of body hair, and promotion of muscle growth (protein anabolism).

Non-reproductive actions:

• Promotes bone growth at puberty and plays a role in the closing of the epiphyseal plates.
• May also induce aggressive behaviour.

Question 2

Outline the process of spermatogenesis.

Answer 2

Spermatogenesis is the process in which diploid (46 chromosomes) primordial germ cells are converted into motile sperm cells with a haploid (23 chromosomes) set of chromosomes.

1) Mitotic Proliferation
- The primordial germ cells = spermatogonia (located in the outermost layer of the
seminiferous tubule). These cells continuously undergo mitotic division to create a constant supply of new germs cells.
- Following each division, one of the daughter cells remains at the outer edge while the other starts to migrate towards the lumen of the tubule.
- This sperm-forming daughter cell will undergo mitotic divisions 2x more to produce 4 identical primary spermatocytes, that enter a resting
phase in preparation for meiosis I.

2) Meiosis
- Each primary spermatocyte forms 2 secondary spermatocytes, each with 23 double stranded
chromosomes.
- During meiosis II, each secondary spermatocyte = in 2 spermatids, each with
23 single stranded chromosomes.
- At this point there are no further divisions.
Therefore, for each spermatogonia, 16 spermatids can be produced.

3) Packaging
- The final maturation of spermatids -> spermatozoa = the process of packaging. During this phase,
the cells are stripped down of all non-essentials such as the cytosol and most organelles.

Question 3

Differentiate between the physiological roles of Sertoli and Leydig cells.

Answer 3

Leydig cells: these are the cells that produce and secrete testosterone under the control of luteinizing hormone. They are also known as interstitial cells.
- Once secreted by
these cells, some testosterone enters the bloodstream and circulates to distant target cells. However,
most of the testosterone enters the lumen of the seminiferous tubules where it supports sperm production.

Sertoli cells
- A single layer of Sertoli cells makes up the walls of the seminiferous tubules.
- Developing sperm cells pass between them as they migrate towards the lumen.
- Developing sperm cells are essentially engulfed in the Sertoli cells as they migrate towards the lumen
where the sperm head remains embedded until it is mature.
- Functions:
1) The tight junctions which exist b/w the Sertoli cells form the blood-testes barrier. For a substance to reach the intratubular fluid it must pass through the Sertoli cells, which allows the
Sertoli cells to control the intratubular environment optimal for developing spermatozoa.
2) Nourish sperm cells.
3) Absorb developing sperm cytoplasm and remove any defective germ cells.
4) Secrete seminiferous tubule fluid into the lumen to flush released sperm into the epididymis for storage.
5) Secrete androgen-binding protein that helps to concentrate testosterone in the lumen.
6) The site of action for testosterone and FSH to regulate spermatogenesis.

Question 4

Describe the components and their functions of the male reproductive tract.

Answer 4

Testes

• Contracts or relaxes depending on temp to protect sperm.
• The majority of the testes consists of coiled seminiferous tubules in which sperm are produced.

Question 5

True or false: in most males, the testes will descend into the scrotum in the last months of fetal life.

Answer 5

True

However, in
some cases, this does not occur.

Question 6

When does the descension of the testes occur? What occurs if they don’t descent?

Answer 6

For the majority of premature male babies, the testes will descend in early childhood.

In some of these
cases, the testes remain within the body cavity. If they stay that way in adulthood, this
condition is called cryptorchidism and results in sterility.

Question 7

From what you have learned about the physiological role of the testes, describe what you would predict to be the significance of the location of the testes.

Answer 7

The location of the testes is physiologically important to one of the primary roles of the testes, spermatogenesis (production of sperm).

The temperature within the scrotum averages several degrees Celsius less than normal
body (core) temperature.
- Descent of the testes into this cooler environment is essential b/c spermatogenesis is temperature sensitive and cannot occur at normal body temp.
- Thus, an
individual with cryptorchidism is unable to produce viable sperm.

The position of the scrotum in relation to the abdominal cavity can be varied by 2 muscles (the cremaster muscle and dartos muscle) and a spinal reflex mechanism that play an important role in regulating testicular temperature.

Question 8

How does temp impact the testes?

Answer 8

Testes are too cold for spermatogenesis, the scrotal muscles (the cremaster muscle and the dartos muscle) contract to bring the testes closer to the body to gain heat.

Testes are too hot for spermatogenesis, the scrotal muscles relax to move the testes away from the body.

Question 9

The majority of the seminiferous tubules are composed of two cell types. What are they?

Answer 9

Germ cells and Sertoli cells

Question 10

Using what you have just learned about spermatogenesis, indicate whether the cell at each step is haploid or diploid, and whether the chromosomes are single or double stranded.

1) Spermatogonium
2) Spermatogonia
3) Primary
Spermatocytes
4) Secondary
Spermatocytes
5) Spermatids
6) Spermatozoa

Answer 10

1) Spermatogonium
- Diploid
- Single

2) Spermatogonia
- Diploid
- Single

3) Primary
Spermatocytes
- Diploid
- Double

4) Secondary
Spermatocytes
- Haploid
- Double

5) Spermatids
- Haploid
- Single

6) Spermatozoa
- Haploid
- Single

Question 11

A mature spermatozoa has four parts. What are they?

Answer 11

Head
- Consists of the nucleus.

Acrosome
- Enzyme-packed vesicle at the tip of the head that is needed to penetrate the ovum.

Midpiece
- Packed full of mitochondria to provide energy for locomotion.

Tail (flagellum)
- Movement of this provides propulsion (a process that requires lots of ATP).

Question 12

True or false: the testes are under the control of luteinizing hormone (LH) and follicle stimulating hormone (FSH).

Answer 12

True

Question 13

Discuss the hormonal regulation of testosterone.

Answer 13

Testosterone:
- In males, LH stimulates the Leydig cells to secrete testosterone.
- Meanwhile, FSH acts on the Sertoli cells to stimulate spermatogenesis and to secrete inhibin.
- Testosterone has a direct negative-feedback
pathway at the level of both:
• the hypothalamus to decr GnRH release
• at the anterior pituitary to decr LH and FSH release.
- The inhibin released by the Sertoli cells feeds back to the anterior pituitary to decrease FSH release

Question 14

Using what you know about hormonal regulation in males, match the hormone to its function in males:

• FSH
• GnRH
• LH
• Testosterone
• Inhibin

1) Released by Sertoli cells, feeds back to the anterior pituitary to decrease FSH release
2) Stimulates the Leydig cells to secrete testosterone

3) Has a direct negative-feedback pathway at the level of both the hypothalamus and
the anterior pituitary

4) Acts on the Sertoli cells to stimulate spermatogenesis and to secrete inhibin
5) Stimulates the anterior pituitary to release LH and FSH

Answer 14

1) Released by Sertoli cells, feeds back to the anterior pituitary to decrease FSH release
- Inhibin

2) Stimulates the Leydig cells to secrete testosterone
- LH

3) Has a direct negative-feedback pathway at the level of both the hypothalamus and
the anterior pituitary
- Testosterone

4) Acts on the Sertoli cells to stimulate spermatogenesis and to secrete inhibin
- FSH

5) Stimulates the anterior pituitary to release LH and FSH
- GnRH

Question 15

The remainder of the male reproductive tract is designed to deliver the sperm to the female reproductive tract. What does the rest of the male reproductive tract consist of?

Answer 15

The male reproductive tract consists of the epididymis and ductus deferens, the accessory sex glands, and the penis.

Question 16

Discuss where the sperm goes after it’s produced.

Answer 16

After sperm are produced in the seminiferous tubules -> swept into the epididymis (a tightly coiled tube around 5m in length), where the sperm can be stored for months and are not motile b/c of the low pH -> the epididymal ducts from each testis converge to form the ductus
deferens -> the ductus deferens of each testis empties -> into the urethra.

Question 17

There are 3 primary accessory sex glands whose secretions make up the bulk of semen, and they function to provide support for the continuing viability of sperm inside the female reproductive tract. What are they?

Answer 17

1) Seminal Vesicles
- There are 2 seminal vesicles, one that empties into each of the ductus deferens just before the
urethra.
- Purpose:
• to provide the bulk of the semen
• supply fructose as an energy source for ejaculated sperm
• secrete prostaglandins to cause smooth muscle contractions in both the male and female reproductive tracts
• to secrete fibrinogen (a precursor of the protein fibrin, which forms the meshwork of a clot)

2) Prostate Gland: this is a large gland that surrounds the ejaculatory ducts and urethra.
- To secrete an alkaline fluid to neutralize the acidic environment of the vagina.
- Secretes clotting enzymes which act on the fibrinogen from the seminal vesicles to produce fibrin, which clots the semen and keep it within the female reproductive tract.

3) Bulbourethral Glands: also called Cowper’s glands.
- They’re a pair of glands that both empty
into the urethra, one on each side, before the urethra enters the penis.
- They secrete a clear substance during sexual arousal and this fluid helps to lubricate the urethra for sperm to pass through.

Question 18

What is sperm?

Answer 18

A mixture of accessory gland secretions and sperm.

Question 19

Review vids on slide 16

Answer 19

** Check 2 vids for an overview **