Reproductive Systems
Hi, and welcome to this video on the male and female reproductive systems.
Male and female reproductive systems have many common anatomic and physiologic features. For example, in men, a penis and scrotum develop, while in women, a clitoris and labia develop. The primary sex organs, the testes and ovaries, are referred to as gonads.
The primary purpose of both the male and female reproductive systems is just that: reproduction.
Male Reproductive System
Let’s look at the male reproductive system first. The external genitalia consist of the penis and the scrotum, which contains the testes.
The appearance of the penis varies slightly depending upon whether the male is circumcised or uncircumcised. The penis consists of the shaft, the glans (which contains the urethral opening), and the corona (which is the base of the glans).
In a circumcised male, the glans is exposed, but in an uncircumcised male, the glans is covered by the foreskin, which retracts during an erection.
The average length of a flaccid penis is about 3.5 inches, and the average length of an erect penis is about 5 inches.
The primary sex organs of the male reproductive system are the testes, which produce the sperm cells (spermatozoa). The other internal reproductive organs and the external genitalia comprise the secondary sex organs.
The scrotum is a saclike structure that hangs free from the body. This allows air to circulate about the scrotum to maintain the temperature about 2 degrees centigrade below body temperature because sperm are immobile at body temperature.
The reproductive system also includes two testes, which are suspended by spermatic cords and are contained within the scrotum. The spermatic cord consists of the vas or ductus deferens, blood vessels, lymphatics, and nerves.
The testes are oval shaped, approximately 3.5 by 5.6 cm in size. Each testis is encased in a tunica albuginea (a tough fibrous capsule). Septa divide each testis into about 250 lobules. These lobules contain one to four tightly-coiled seminiferous tubules which come together to form the epididymis. The seminiferous tubules contain specialized cells that produce sperm and others that secrete male hormones.
The tiny tubes that form the epididymis are about 6 meters long and merge into the vas deferens (also known as the ductus deferens) at the tail end. The sperm that form in the seminiferous tubules are nonmotile and immature when they enter the epididymis, but the rhythmic contractions that cause the sperm to move through the epididymis also cause the sperm to mature so they become motile on ejaculation.
The sperm pass through the vas deferens, which becomes part of the spermatic cord, which then passes through the inguinal canal, into the abdominal cavity, and into the pelvic cavity.
Near the end, the vas deferens merges with the ducts from the seminal vesicles to become the ejaculatory duct. The seminal vesicles are about 5 centimeters long and secrete nutrients, hormones, and an alkaline fluid that controls the pH of the semen. These substances increase the volume of the semen.
The ejaculatory duct passes through the prostate gland and empties into the urethra.
The prostate gland, which is chestnut-shaped and about 4 by 3 centimeters in size, wraps around the urethra right below the bladder. The prostate gland secretes a milky alkaline fluid that neutralizes the semen and increases the motility of the sperm cells. This fluid empties directly into the urethra as the contents of the ejaculatory duct vesicles enter the urethra, further increasing the semen volume.
Beneath the prostate gland, the two bulbourethral glands are about one centimeter in diameter and secrete a mucus-like substance into the urethra to lubricate the glans of the penis.
The penis contains 3 columns of erectile tissue: two corpora cavernosa on the dorsal surface and a single corpus spongiosum, which contains the urethra, on the ventral surface. During sexual stimulation, the vasodilator nitric acid is released, causing the arteries of the penis to dilate and increasing the flow of blood to the erectile tissues.
The increased pressure from the arterial blood flow decreases venous drainage, further causing the penis to swell and elongate so that it becomes rigid enough for penetration into the vagina during sexual intercourse.
The fluid that is ejaculated through the urethra is semen, and the typical volume of an ejaculation ranges from 2 to 5 mL, containing about 120 million sperm. While sperm can live for weeks in ducts in the body, they can generally survive no more than 3 to 5 days after ejaculation.
Female Reproductive System
Now, let’s talk about the female reproductive system.
The primary sex organs of the female reproductive system are the ovaries, which produce the eggs or ova. The other internal reproductive organs and the external genitalia comprise the secondary sex organs.
The external genitalia include the vaginal opening; the labia minora and labia majora, which provide protective lips around the vagina; and the clitoris, which provides sensation during sexual activity.
The clitoris is a complex structure located externally above the urethra. The labia minora provide a hood about the glans clitoris, which is the visible part of the clitoris; however, most of the clitoris is embedded in the tissues. The glans clitoris is very sensitive to touch because of a high concentration of nerves.
Behind the visible glans, the body of the clitoris splits into two halves, each containing a crus (elongated part) and a vestibular bulb (also known as a Bartholin gland). The crura, which are each comprised of two corpora cavernosa (similar to the penis) are located behind the labia minora and the vestibular bulbs are located on either side of the vagina.
Both the crura and the vestibular bulbs contain erectile tissue. The vestibular bulbs secrete mucus, which provides lubrication, similar to the bulbourethral glands in the male.
The vagina is about 3.5 inches long and is a fibromuscular tube that extends from the vaginal opening, or orifice, to the uterus. The vaginal opening is covered by a thin membrane called the hymen.
The hymen has a central opening to allow for drainage of vaginal secretions and menstrual fluids. The hymen typically stretches or tears during physical activities or sexual intercourse. After the hymen is broken, it does not grow back or require repair, as it appears to serve no real purpose and is unrelated to virginity, despite a common misperception.
When a female nears an orgasm, the lower third of the vagina becomes engorged with blood and swells, and this increases friction on the penis during intercourse in order to promote ejaculation.
The cervix is the lower end of the uterus and connects the vagina to the uterus through a short canal. During sexual stimulation, the cervix dilates slightly.
The contractions that occur with orgasm promote the movement of sperm through the cervix and into the uterus and on to the fallopian tubes.
The uterus is typically located behind and above the bladder and in front of the colon. It is a pear-shaped, hollow, muscular organ that is about 7.5 cm by 4.5 cm and 3 cm wide in its normal state but expands greatly with pregnancy.
The ovaries, the primary sex organs, are solid oval-shaped structures that are about 3.5 cm by 2 cm and 1 cm thick and lie on each side of the pelvic cavity and are held in place by ligaments. The outer part of an ovary is the cortex, and the inner part is the medulla. The ovaries produce the hormone estrogen.
When a female is born, each ovary contains about 1 million primordial follicles, which consist of a primary oocyte (also called an egg or ovum) and a layer of follicular cells. More than half of these primordial follicles degenerate before puberty, and this process of degeneration continues with only a few hundred released over the course of a female’s life.
During puberty, maturation continues and the primary oocyte matures into a secondary oocyte, or ovum, and eventually ruptures through the ovary with ovulation. The corpus luteum forms from the remains of the ruptured follicle and secretes hormones and then degrades into the corpus albicans.
Fertilization of an ovum occurs within the fallopian tubes (also known as the uterine tubes or oviducts) when a sperm enters the ovum. The fallopian tubes, which are about 12 cm in length, provide a connection between the ovaries and the uterus so that a fertilized egg can travel to the uterus for implantation.
The funnel-shaped infundibulum at the end of a fallopian tube near the ovary contains a number of extensions called fimbriae, one of which connects directly to the ovary. The fimbriae help draw the ovum into the fallopian tube.
The mammary glands (breasts) are accessory organs of the female reproductive system. Each breast contains 15 to 20 lobules that contain alveoli, or milk glands. The alveoli produce milk after childbirth, and ducts lead from the alveoli to the nipple.
The nipples and areola about the nipples are very sensitive to stimulation and tend to swell during sexual arousal, although this is caused by muscle fibers as the breasts do not contain erectile tissue. The small projections on the areola are the areolar glands (or Montgomery’s tubercles), which produce a nipple lubricant.
The primary purposes of the male reproductive system are to produce sperm, transport the sperm to the female reproductive tract, and secrete hormones. The primary purposes of the female reproductive system are to produce ova, secrete hormones, and provide for the protection and development of a fetus.
That’s all for now.
Thanks for watching and happy studying.