Lecture 29 - Male Reproductive System

Although male and female reproductive organs are different, the have a common purpose of what?

Producing offspring.

What are the four tasks of the reproductive systems?

- Form gametes (sperm or ova/eggs)
- Bring gametes together via sexual intercourse
- Combine genetic information (fertilization occurs to form a zygote)
- Support fetal development (gestation) and the birth of baby(ies) (parturition).

What are the gonads in males?

The testes.

What are the gonads in females?

Ovaries.

Gonads produce what?

Gametes (sex cells).

What are the gametes in males?

Sperm.

What are the gametes in females?

Ova (eggs).

Gonads also secrete what?

Steroid sex hormones.

What do sex hormones do?

They stimulates the development of secondary sex characteristics.

What is the sex hormone secreted by the testes?

Androgens (mainly testosterone).

What are the sex hormones secreted by the ovaries?

Estrogens and progesterone.

What are accessory reproductive organs?

Ducts, glands, and external genitalia.

What is the hypothalamic-pituitary-gonadal (HPG) axis?

The axis in what initiates the secretion of sex hormones.

Is the HPG axis the same in males and females?

Yes.

What is gonadotropin releasing hormone (GnRH)?

A hormone that stimulated the release of gonadotropin from the hypothalamus.

What are the gonadotropins released from the pituitary gland?

Follicle stimulating hormone (FSH) and lutenizing hormone (LH).

What do gonadotropins do?

They act on gonads to stimulate gamete production and sex hormone secretion.

Sex hormones have what type of control at the hypothalamus and the anterior pituitary?

Negative feedback control.

Gametes are formed using what division process?

Meiosis.

Where does nuclear division of gametes occur?

In the gonads.

From one spermatocyte, how many spermatids are produced via meiosis?

Four spermatids.

From one oocyte, how many ova are produced via meiosis?

One ova (the rest of the cells produced are polar cells and are degenerated).

Meiosis of gametes produce what?

Haploid cells and introduces genetic variation.

What is the primary sex organ in males?

The testes.

What are the accessory ducts of the male reproductive system? (5)

- Epididymis
- Ductus (vas) deferens
- Ejactulatory duct
- Urethra

What are the accessory glands on the male reproductive system? (3)

- Seminal vesicles
- Prostate gland
- Bulbourethral glands

What is the scrotum?

A sac of skin and superfical fascia that hangs outside the abdominopelvic cavity at the root of the penis.

The scrotum houses what?

The testes.

Why do the testes sit inside the scrotum?

Because they require a temperature 3 degrees Celsius colder than the core body temperature.

The scrotum can respond to what?

Temperature changes.

When it is cold, what does the scrotum do?

They become shorter and more wrinkled. They also pull closer into the body.

When it is hot, what does the scrotum do?

They become flaccid and loose to increase heat loss when it is too warm. They also hang further away from the body.

The testes produce what?

Sperm and testosterone.

Testes are divided into how many lobules?

~ 250

Each testis lobule contains how many seminiferous tubules?

1-4.

What do seminiferous tubules do?

The converge into a tubule that conveys sperm into the rete testis.

Within the epithelial tissue of the seminiferous tubules are what two types of cells?

Spermatogenic cells and sertoli cells.

What do spermatogenic cells do?

Give rise to sperm.

What do sertoli cells do?

They are support cells that nourish and protect spermatogenic cells.

What are the two functions of sertoli cells?

- Promote sperm production by germ cells
- From blood-testis barrier

What does the blood-testis barrier do?

It protects sperm cells from toxins in blood and potential autoimmune reactions.

Testicular tissues make up the testis. How many layers of smooth muscle surrounds the seminiferous tubules?

Three to five layers of smooth muscle like myoid cells.

What are myoid cells?

Smooth muscle-like cells that may squeeze sperm and testicular fluids out of testes.

What cells are found within connective tissue surrounding the seminiferous tubules?

Interstitial cells (AKA Leydig cells).

What do interstitial cells (Leydig cells) do?

They produce androgens, mainly testosterone.

What is the pampiniform venous plexus?

Testicular veins the surround the testicular artery.

Since blood from the heart is at core body temperature, and sperm require a cooler temperature to be produced at, what cools down blood?

The pampiniform venous plexus brings "cold" blood from testes to the heart. As it travels, the "warm" blood in the testicular artery runs alongside it and some of the heat diffuses to warm up the "cold" blood and thus cools.

What is the spermatic cord?

A bundle of autonomic nerve fibres, blood vessels, and lymphatic passes through the inguinal canal to each testis.

Hypothalamic GnRH stimulates what?

The anterior pituitary to release FSH and LH.

What does LH do in males?

It stimulates testosterone synthesis by interstitial endocrine cells.

What does FSH do?

It indirectly stimulates spermatogenesis.

How does FSH indirectly stimulate spermatogenesis?

It stimulates sertoli cells to release an androgen-bining protein. This keeps increased testosterone around spermatogenic cells.

What is the final trigger for spermatogenesis?

Testosterone.

When there is high blood testosterone, what happens?

This inhibits the hypothalamic release of GnRH and anterior pituitary release of gonadotropins.

The HPG axis is regulated by what?

Negative feedback control (dictated by testosterone).

What is inhibin?

An FSH inhibiting protein that is released by sertoli cells when sperm count is high.

What is testosterone?

A steriod hormone that is synthesized by cholesterol.

Testosterone does what?

It binds to androgen receptors, causing intracellular transcription factors. This activates specific genes and increases specific protein synthesis.

Testosterone must be converted into what hormone in the prostate gland?

Dihydrotestosterone (DHT)

Testosterone must be converted into what hormone in some neurons of the brain?

Estradiol (a form of estrogen).

Testosterone targets what?

Accessory organs (ducts, glands, and penis), causing them to grow to adult size and function.

What also is needed to to maintain the size of organs and prevent atrophy (decrease in size or wasting away of body part or tissue) of the male reproductive system (and all body tissues as a matter of fact)?

Normal plasma levels.

Before birth, how many testosterone is found in male infants?

Two-thirds of the level found in adult males.

What does the increase of testosterone in male infants do?

Helps them to generate their male reproductive system.

Soon after birth of a male infant, what happens to testosterone levels?

They recede and remain low until puberty.

What are some of the secondary sex characteristics testosterone causes?

- Pubic, axillary, and facial hair
- Deepening of the voice, thickening of the skin, and increase in oil production (causes acne)
- Increase in bone/skeletal muscle size and mass

Testosterone also increase the basal metabolic rate which means what?

That it can cause more hunger to be able to supply the energy that is now needed.

Sperm goes from the seminiferous tubules to where?

The rete testis and then to the epididymis via efferent ductules.

Each tesis is connected to epididymis of what length?

Longer than 6 meters (20 feet).

Coiled tubes of the epididymis does what?

It provides a place for immature sperms to develop until they are expelled during ejactulation.

Immature sperm takes how long to pass through the epididymis?

Two to six days.

The epididymis has fluid that contains what?

Antimicrobial proteins and deefnsins.

While is the epididymis, sperm gain the ability to do what?

Swim.

What is the ductus deferens (vas deferens)?

Part of the spermatic cord, it extends from the epididymis, through the inguinal canal, into the pelvic cavity where it passes over the bladder, and into the ejactulatory duct which passes through the prostate gland to join the urethra.

What is the urethra?

A tube that carries urine and sperm (in males, not at the same time) from the bladder to the outside of the body.

The urethra is the terminal portion of that?

The testis-associated duct system.

What is semen?

It is a milky white, sticky mixture of sperm and accessory gland secretions.

What does semen do?

It is a transport medium for sperm. It also supports and protects sperm in the uterine reproductive tract.

Where are seminal glands found?

On the posterior bladder surface.

What do seminal glands do?

They produce seminal fluid.

Describe seminal fluid. (5)

- Alkaline
- Contains fructose (to provide energy for the sperm)
- Ascorbic acid
- A coagulating enzyme
- Prostaglandins

What percentage of semen is made out of seminal fluid?

60%.

Where is the prostate gland?

It encircles the urethra inferior to the bladder.

What does the prostate gland do?

Produces prostatic fluid.

Describe prostatic fluid. (5)

- Milky
- Slightly acidic
- Contains citrate
- Several enzymes
- Prostate-specific antigens.

What does prostatic fluid do?

It plays a role in sperm activation.

What percentage of semen is made out of prostatic fluid?

25%.

What are the bulborethral glands?

Glands that produce s thick, clear mucus prior to ejactulation.

What is the purpose of the secretion from the bulborethral glands?

To neutralize the urethra of the male (since urine is also using this tube) and to help neutralize the acidic environment of the vagina so that sperm can live and make its way through the system.

Overall, is semen alkaline or acidic?

Alkaline (basic).

What is the penis?

The male copulatory organ that is made of an attached root and a free body that ends in an enlarged tip.

What is the enlarged tip of a penis called?

The glans penis.

What is prepuce?

Foreskin.

What does prepuce do?

It covers the penis and may be slipped back to form a cuff around the glans.

What is circumcision?

The surgical removal of foreskin. This is often done for cultural or religious reasons.

What are the erectile tissues of the penis?

The corpus sponginosum and the corpora cavernosa.

Where is the corpus spongiosum located?

Surrounding the urethra. It expands distally to form the glans and proximally to form the bulb of the penis.

What does the corpora cavernosa make?

Proximal ends form the crura of the penis.

What is the crura surrounded by?

An ischiocavernosum muscle that anchors it to the pubic arch.

How does erection occur?

When there is engorgement of erectile tissue with blood during sexual intercourse.