Human Reproductive Systems The functions of the human reproductive system are multifold. The male's reproductive role is to manufacture male gametes called sperm and deliver them to the female reproductive tract. The female produces female gametes called ova or eggs.

The female also provides an environment for a fertilized ovum, a zygote, to develop. Both the male and the female produce sex hormones that affect sexual behavior, drive, development and function.

Anatomy of the Testes and Scrotum The male gonads (primary sex organs) are the testes. They're housed in the scrotum. The major function of the testes is the production of sperm and the sex hormone, testosterone.

Effect of Temperature The temperature in the scrotum is about 3 degrees Centigrade cooler than normal body temperature. This low temperature facilitates sperm production. Within the scrotum, attached to the testes, are the cremaster muscles. They function to raise or lower the testes within the scrotum in response to changes in body temperature.

For example, if body temperature increases, the cremaster muscles relax, allowing the testes to descend farther from the body so that they maintain their cool temperature.

Testis Each testis sits within its own compartment in the scrotum. Inside the the testis are 250-300 lobules. Each lobule contains one to four coiled seminiferous tubules. These are the sites of sperm synthesis. Surrounding the seminiferous tubules are the interstitial cells, or Leydig cells. These cells produce testosterone.

Freshly made sperm are conveyed from the seminiferous tubules into the rete testis, a network of tubes on the posterior of the testis. From there, the sperm will travel to the epididymis.

Interestingly, as the testicular arteries descend to the scrotum, they're wrapped by a network of testicular veins. The network of veins absorbs heat from the arterial blood, preventing testis temperature from increasing. These blood vessels, along with nerves and lymphatics, descend to the testes in a connective tissue wrapping called the spermatic cord.

If the testis fails to descend, it's known as cryptorchidism If the testis fails to descend, it's known as cryptorchidism. This drastically increases the likelihood of testicular cancer, but can be surgically corrected.

Seminiferous Tubule Shows spermatogenesis

Notice the Metaphase

spermatogenesis occurs within the seminiferous tubules. Developing sperm cells actually make up the walls of the seminiferous tubules, with the stem cells at the outer edge of the wall and the newly formed sperm cells lining and being pushed into the lumen.

Seminiferous Tubule sperm in lumen (center duct)

Why are there mitochondria?

Anatomy of the Penis The penis and the scrotum collectively make up the external genitalia. The function of the penis is to deliver sperm into the female reproductive tract during copulation. The penis consists of an attached root, a shaft, and an enlarged tip called the glans penis. The skin covering the penis is loose, and at the glans there is a cuff called the prepuce, or foreskin, which is typically removed at circumcision.

The penis contains three erectile bodies: the corpus spongiosum and two corpora cavernosa. The corpus spongiosum is ventral and surrounds the urethra. The corpora cavernosa are dorsal. Each of these erectile tissues consists of a network of connective tissue and smooth muscle filled with vascular sinuses.

Where is the urethra?

Anatomy of the Accessory Ducts and Glands During ejaculation, sperm is conveyed from the testes through a system of accessory ducts. These ducts include the epididymis, the ductus deferens (also known as the vas deferens), the ejaculatory duct, and the urethra.

The path of the Sperm Each epididymis sits on the back of a testis and consists primarily of a highly coiled duct. Sperm arriving at the epididymis are immature and immotile. Within the epididymis, sperm mature and learn how to swim. The maturation process takes about three weeks. However, sperm can be stored within the epididymis for several months.

From the epididymis, sperm enter the ductus deferens From the epididymis, sperm enter the ductus deferens. It's about 18 inches long. The ductus deferens runs upward as part of the spermatic cord and enters the pelvic cavity via the inguinal canal.

At the posterior wall of the bladder, the end of the ductus deferens connects with the duct of the seminal vesicle to form the ejaculatory duct. The ejaculatory duct enters the prostate gland and within it, empties into the urethra.

What is a Vasectomy? A popular method of birth control is to make a small incision in the scrotum, slice the ductus deferens, and then tie off the ends.

The final accessory duct is the urethra The final accessory duct is the urethra. It has three sections: the prostatic urethra, the membranous urethra, and the penile urethra. Its exterior opening is the external urethral orifice.

Several Accessory Glands: prostate gland paired seminal vesicles paired bulbourethral or cowper's glands.

The prostate gland is shaped like a glazed donut and sits inferior to the bladder. As mentioned before, it completely surrounds the prostatic urethra. It functions in activating sperm and produces 30% of the components of semen.

The seminal vesicles lie on the posterior bladder and function to secrete about 60% of the components of semen. The bulbourethral glands are pea-sized and sit in the urogenital diaphragm. They produce an alkaline mucus that neutralizes the acidity of the urethra.

Composition and Path of Semen Semen is approximately 10% sperm and testicular fluid 30% prostatic secretions 60% seminal vesicle secretions

seminal vesicle secretions include Fructose: Provides energy for the sperm coagulating enzyme: helps turn semen into a bolus that can be readily propelled into the vagina Prostaglandins: decrease cervical mucus viscosity and stimulate reverse peristalsis of the uterus

Prostatic secretions include Citrate :food source Fibrinolysin: acts to "decoagulate" the semen, which helps the sperm begin their journey.

So, How many sperm are produced? Typically 2-5 mL of semen are expelled per ejaculation. Each mL of semen can contain 50-130 million sperm. Do the math!! 4 ml x 100 million= 4 million sperm

Remember 7 Up

Trace the path of sperm from synthesis to maturation to ejaculation. Synthesis occurs in the seminferous tubules of the testes. Sperm then move onward to the epididymis, where they mature. During ejaculation, they travel through the ductus deferens to the ejaculatory duct to the urethra and out to the body exterior.

Think Seven Up For a handy mnemonic, think of that refreshing soda, 7-Up: (S)emiferous tubules, (E)pididymis, (V)as deferens, (E)jaculatory duct, (N), (U)rethra, and (P)enis.

Physiology of Erection and Ejaculation The main phases of the male sexual response are erection and ejaculation. Erection results from engorgement of the erectile bodies with blood. Activation of parasympathetic nerves to the penis increases local nitric oxide release. This causes dilation of the penile arterioles.

The expansion of the penile arterioles compresses penile veins The expansion of the penile arterioles compresses penile veins. Thus, more blood enters, while less blood leaves. This results in an erection, which allows the penis to penetrate the vagina. During erection, the bulbourethral glands are induced to secrete their alkaline solution. Erection can be a simple spinal reflex and it may also be influenced by higher cortical centers.

When sexual stimuli reach a certain threshold, a massive sympathetic discharge occurs. The reproductive ducts and accessory glands contract, emptying their secretions into the urethra. The internal urethral sphincter contracts, preventing semen from entering the bladder or urine from entering the semen. The bulbospongiosus muscles of the penis contract rapidly. This expels semen from the penis and causes the accompanying orgasm.

Hormones of the Male Reproductive System The hypothalamus releases gonadotropin-releasing hormone (GNRH). GNRH travels to the anterior pituitary gland and causes it to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

LH binds to the interstitial cells of the testes and causes them to secrete testosterone. For this reason, LH can be referred to as interstitial cell-stimulating hormone (ICSH).

Testosterone will promote spermatogenesis Testosterone will promote spermatogenesis. However, it must be concentrated within the seminiferous tubules.

FSH acts on the sertoli cells, causing them to release androgen-binding protein (ABP). ABP binds to and concentrates testosterone within the seminiferous tubules.

enlargement of the larynx increased bone and muscle mass Testosterone acts on other body tissues to create secondary sexual characteristics: pubic, axillary and facial hair enlargement of the larynx increased bone and muscle mass

If testosterone levels rise too high, it begins to inhibit the release of GNRH from the hypothalamus and FSH and LH from the anterior pituitary. If sperm count rises too high, the sertoli cells release the hormone inhibin, which inhibits GNRH and FSH release. These negative feedback processes prevent testosterone levels from rising too high and spermatogenesis from going too fast.