< Male genital system >
Male genital system sets out from the testis which produces sperms. The testis is also an endocrine organ to secrete male hormone called androgen (Fig. 9-24).
Before birth, the testes descend from the abdominal cavity into the scrotum, a part of skin (Fig. 7-5). The testes pass the inguinal canal.
Fig. 7-3. Inguinal ligament, superior inguinal ring.
The anterior superior iliac spine is anterior end of the iliac crest (Fig. 1-31); the pubic tubercle is a part of the pubis (Fig. 1-34). The inguinal ligament between the two bone structures serves as the boundary between the abdomen and lower limb (Fig. 10-55) (Fig. 13-98).
Fig. 7-4. Sheets forming inguinal canal (anterosuperior view).
Review the abdominal wall muscles (Fig. 3-28). Holes in the external oblique muscle and transversalis fascia (Fig. 3-33) are the superficial inguinal ring (Fig. 7-3) and deep inguinal ring, respectively.
The two rings serve as openings of the inguinal canal that runs inside the inguinal ligament (Fig. 7-3). The superficial inguinal ring is medial to the deep inguinal ring, which means that the inguinal canal is oblique. This obliquity prevents the small intestine from herniating through the inguinal canal (Fig. 7-5).
Fig. 7-5. Shortening of male gubernaculum.
In case of male, a string called gubernaculum connects the testis with the scrotum. During development, the gubernaculum gets shorter and shorter until it disappears, to pull the testis down into the scrotum (Fig. 7-2). During the descent, the testis drags the following three structures into the scrotum.
First, the testis takes along with the ductus deferens (Fig. 7-2). Second, the testis takes along with the peritoneum to the scrotum.
Fig. 7-6. Isolated tunica vaginalis. (External structures are omitted.)
The extended peritoneum becomes obliterated later. Third, the testis takes along with the external oblique muscle, internal oblique muscle (rather than transversus abdominis), and transversalis fascia (Fig. 3-33) (Fig. 7-4) (Fig. 7-5).
Extension of the internal oblique muscle is the cremaster (Fig. 7-5) that is a skeletal muscle, but is an involuntary muscle. The cremaster elevates the testis in the cold environment. The testis works best at temperature slightly lower than abdominal cavity temperature (Fig. 7-2).
Unlike the ovary which produces countable ova (Fig. 7-23), the testis produces uncountable sperms. The ova and sperms are made by meiosis (Fig. 8-8).
The produced sperms are waiting in the epididymis for ejaculation.
Long journey of the sperms (ejaculation) is made possible by peristalsis of the ductus deferens. The word “deferens” means “carrying away” in Latin.
Fig. 7-11. Urinary bladder, prostate, ductus deferens.
The ductus deferens passes the inguinal canal (Fig. 7-2) and reaches the back of the urinary bladder. The ductus deferens then encounters the duct of seminal vesicle to become the ejaculatory duct. The short ejaculatory duct penetrates the prostate to enter the urethra (concretely, prostatic urethra) (Fig. 6-21).
Fig. 7-12. Prostatic urethra.
The bilateral ejaculatory ducts open on the seminal colliculus that is grossly identifiable in the prostatic urethra (Fig. 7-15). The several prostatic ducts open on both sides of the seminal colliculus.
During ejaculation, the seminal vesicle and prostate discharge the useful secretions, a part of semen.
In clinics, the ductus deferens is called the vas deferens. Therefore, the excision of the ductus deferens for contraception is vasectomy. The amount of semen is barely reduced after vasectomy, because secretions from the seminal vesicle and prostate are much larger than sperms in volume.
Fig. 7-15. Urinary bladder, male urethra.
The male urethra is surrounded by the prostate, external urethral sphincter (skeletal muscle), and penis. Proximal to the urethra, there exists the internal urethral sphincter (smooth muscle) (Fig. 6-18).
During ejaculation, the internal urethral sphincter contracts while the external urethral sphincter relaxes (Fig. 7-15), so that semen containing sperms would not go into the urinary bladder.
Fig. 7-17. Penis (transverse plane).
The SPONGy urethra is covered by the corpus SPONGiosum of penis. The other two erectile tissues are the corpora cavernosa.
Regardless of their names, all the corpus spongiosum and corpora cavernosa are spongy tissue for erection.
Erection is caused by the widened artery and the narrowed vein. Parasympathetic nerve is responsible for the control of the blood vessels, causing erection (Fig. 13-64).
The corpus spongiosum is smaller than each corpus cavernosum. If the corpus spongiosum were too large, its erection would obliterate the spongy urethra located inside, which would interrupt the ejaculation (Fig. 7-17).
Fig. 7-20. Body and root of penis.
In the body of penis, the corpus spongiosum is longer than the corpora cavernosa because of its distal end (glans penis). The glans penis including the urethra is surrounded by skin called the prepuce.
In the root of penis, a skeletal muscle called “bulbospongiosus” encloses the “bulb” of penis and corpus “spongiosum.” This muscle squeezes urine and semen to the body of penis so as to finish urination and ejaculation voluntarily. It also squeezes blood to the body of penis to contribute to erection voluntarily (Fig. 7-19).
The skeletal muscle that originates from the “ischial” tuberosity (Fig. 1-38) and encloses the corpus “cavernosum” is called “ischiocavernosus.” The ischiocavernosus also squeezes blood to the body of penis in order to assist erection.
Unlike the root of penis, the body of penis does not have skeletal muscle (Fig. 6-22) (Fig. 7-20).
< Female genital system >
The ovary is ovum-producing organ found in female. The ovary in female is analogous to the testis in male (Fig. 7-1) in that they are both genital organs and endocrine glands (Fig. 9-24).
The bilateral ovaries make and send ovum regularly (ovulation). Although about one million ova are present at birth in the ovaries, only a few are ovulated.
The ovarian follicle containing ovum is periodically initiated to grow and develop, culminating in ovulation. The corpus luteum is remnant of the ovarian follicle that has released the ovum.
As a woman ages, the ovary experiences a decline in reproductive performance, which leads to menopause.
Fig. 7-26. Parts of uterine tube, ovulation.
The uterine tube is divided into the fimbriae, infundibulum, ampulla, and isthmus. Just after ovulation, the ovum enters the peritoneal cavity (Fig. 4-38). Then, the ovum is swallowed by the fimbriae of uterine tube which is opened to the peritoneal cavity (Fig. 7-34).
The uterine tube allows only passing of the ovum and sperm (Fig. 7-28). The size of an ovum is only 0.1 mm (much larger than a sperm) (Fig. 8-11), even if it is the biggest human cell (Fig. 16-1).
The ampulla of uterine tube is the longest and widest part which provides a good environment for fertilization of the ovum and sperm (Fig. 8-13).
The ovary and labium majus (Fig. 7-22) (Fig. 7-36) are homologous organs of the testis and scrotum (Fig. 7-2), respectively.
Fig. 7-30. Not shortening of female gubernaculum.
Like the male gubernaculum connects the testis with the scrotum, the female gubernaculum connects the ovary with the labium majus. Unlike the male gubernaculum (Fig. 7-5), the female one never gets shorter.
The distal part of the gubernaculum becomes the round ligament of uterus that passes the inguinal canal (between the deep and superficial inguinal rings) (Fig. 7-4). Content of the female inguinal canal (round ligament of uterus) is definitely thinner than that of the male inguinal canal (ductus deferens, etc.) (Fig. 7-2). Consequently, the female inguinal canal is thinner than the male one.
The menstrual cycle is the regular natural change that occurs in the female genital system. The cycle is required for production of the ovum, and for preparation of the uterus wall that makes pregnancy possible (Fig. 8-15).
Menstrual phase is the first phase of the cycle. Menstruation is the sign that a female is not pregnant.
The follicular phase and luteal phase of ovary corresponds to the proliferative phase and secretory phase of uterus, respectively. The “follicular” phase is influenced by the estrogen, a hormone secreted by the ovarian “follicle.” The “luteal” phase is influenced by the progesterone, a hormone secreted by the corpus “luteum” (Fig. 7-24).
Fig. 7-34. Female genital system.
Size of the not pregnant uterus is nearly equivalent to that of a woman’s fist. The uterus consists of the body and cervix. Border between the body and cervix is the isthmus where the uterine cavity narrows. The cervix protrudes into the vagina to form the luminal corner (vaginal fornix) (Fig. 7-35).
Fig. 7-35. Female genital and urinary systems (midsagittal plane).
The uterus is anteverted to form an angle with the vagina. Accordingly, the uterus covers the urinary bladder from above. This is why a pregnant woman feels the urge to urinate frequently.
In the midsagittal plane, peritoneum around the uterus forms the rectouterine and vesicouterine pouches that are parts of the peritoneal cavity (Fig. 4-38). The rectouterine pouch is close to the vaginal fornix (Fig. 7-34).
At the inferior end of the vagina, there are three structures: the labium majus, the labium minus, and hymen.
The space between the bilateral labia minora is the vestibule of vagina; the greater “vestibular” glands open into the “vestibule” (Fig. 7-38) (Fig. 7-39).
Fig. 7-38. Vestibule of vagina, adjacent structures.
Anterior to the hymen (ruptured in the above figure), the urethral opening and glans clitoris are located in order. The glans clitoris equal to the body of clitoris (Fig. 7-39), although the glans penis is a part of the body of penis. The glans clitoris is covered by the prepuce, like the glans penis (Fig. 7-20).
Fig. 7-39. Clitoris, bulb of vestibule.
The clitoris is homologous with the male corpora cavernosa. The body of clitoris is continuous with the root of clitoris on both sides like the male corpora cavernosa (Fig. 7-20).
The bulb of vestibule is homologous with the male corpus spongiosum. But unlike the male corpus spongiosum (Fig. 7-17) (Fig. 7-20), the bulbs of vestibule are double and do not contain the urethra.
Female also has the two muscles, bulbospongiosus and ischiocavernosus (Fig. 7-20). The “bulbospongiosus” covers the “bulb” of vestibule (female corpus “spongiosum”) to help constriction of the vagina. The “ischiocavernosus” which originates from the “ischial” tuberosity and covers the root of clitoris (female corpus “cavernosum”) squeezes the blood and helps the body of clitoris erect (Fig. 7-38).
While the plural form of labium majus is labia majora (Fig. 7-38), the plural form of corpus cavernosum is corpora cavernosa (Fig. 7-17).