Section VI—Urogenital System
The urogenital system includes the excretory and reproductive systems, which perform distinct roles. The excretory system mainly functions in helping to maintain homeostasis by maintaining water balance and ridding the body of nitrogenous waste products.
The reproductive system functions in producing gametes (sperm or ova), meeting all the needs of the fetuses during gestation (in the female), and maintaining gender-specific features, mainly through the production of hormones. Despite the fact that the two systems are distinct, their accessory structures, particularly in the male, become intimately associated. Thus, it is convenient to consider them together as the urogenital system.Excretory System
The kidneys (Figures 7.58, 7.68, 7.69, 7.71), the main organs of the excretory system, were exposed during the dissection of the circulatory system. They are retroperitoneal, lying dorsal to the parietal peritoneum in the lumbar region. The kidneys are surrounded by considerable fat that protects them from mechanical injury. Note that the left kidney lies slightly posterior to the right kidney, which abuts anteriorly against the caudate lobe of the liver.
Each kidney is bean-shaped and covered by a thin, tough, fibrous renal capsule. The hilus is a medial inden-
subscapular vein superficial temporal artery
superficial temporal vein sympathetic trunk thoracic aorta thyrocervical artery transverse facial artery transverse facial vein transverse jugular vein
(hyoid venous arch) transverse scapular artery transverse scapular vein umbilical artery umbilical vein vagosympathetic trunk vagus nerve ventricle vertebral artery vertebral vein
FIGURE 7.68 Frontal section through left kidney of the cat.
tation through which the ureter and blood vessels pass.
Follow one of the ureters posteriorly to the urinary bladder. It passes dorsal to the ductus deferens in the male (Figure 7.69) and uterine horn in the female (Figure 7.71) (see below), and then through the fat of the lateral ligament to enter the dorsal surface of the urinary bladder. Dissect carefully through the fat; recall that the umbilical artery was also traced to the bladder (page 205). The urinary bladder is a sac-like reservoir for urine. Its broad anterior portion gradually narrows posteriorly into the urethra, a narrow tube that passes through the pelvic canal (see below).Return to one of the kidneys, preferably the left. Remove the renal capsule, cutting carefully around
FIGURE 7.69 Abdominopelvic cavity of the male cat with many of the viscera removed and urinary bladder reflected to the right to show vessels and urogenital structures, in ventral view.
the structures passing through the hilus. Section the kidney in the frontal plane (i.e., so that you have dorsal and ventral halves) and examine one of the sectioned surfaces (Figure 7.68). The substance of the kidney is subdivided into a lighter peripheral zone, the renal cortex, and the darker renal medulla. The medullary portion constitutes a renal pyramid, which tapers toward the hilus into the renal papilla.
The ureter and renal vessels enter the hilus, which expands within the kidney into a space termed the renal sinus. The expanded proximal portion of the ureter within the kidney is the renal pelvis. If it is not evident in the section you are studying, examine the other half of the kidney.
Key Terms: Excretory System
ductus deferens hilus kidneys renal capsule renal cortex renal medulla renal papilla
renal pelvis renal pyramid renal sinus ureter urethra urinary bladder uterine horn
FIGURE 7.70 Cross-section through the penis of the cat.
Male Reproductive System
The paired testes (Figure 7.69) are the male gonads and lie in the scrotum, which is a skin-covered sac just ventral to the anus. Externally, the penis, the copulatory organ, lies midventrally with respect to the scrotum. Skin the scrotum by making a small incision toward the ventrolateral side of one of the testes. Extend the incision longitudinally and peel the ventral skin of the scrotum. This exposes the left and right cremasteric pouches, sac-like extensions of the abdominopelvic cavity in which the testes descend from their abdominal position in the embryo.
The testes, as well as other structures, are contained within the pouches. The posterior end of each pouch contains a testis and so is expanded. Follow the pouches anteriorly. Each narrows into a thin tube that passes toward the abdominal wall along the ventral surface of the pelvis, just to one side of the pubic symphysis, and passes through the wad of fat present in the groin. You were cautioned against removing this fat during skinning of the cat precisely because the cremasteric pouches pass through it. Now, follow the pouches, teasing away the fat as needed.
The penis will still have its sheath of skin attached. Remove it by making a cut through the sheath and picking through the connective tissue with needle and forceps. Work your way anteriorly until you have exposed the penis and can appreciate that it passes toward the pelvic canal.
Return to the posterior end of one of the pouches, slit its ventral surface longitudinally, and continue the cut onto its narrowed portion. The space within the pouch, the vaginal cavity, is analogous to the space of the abdominopelvic cavity. It is lined by parietal tunica vaginalis. The structures within the pouch are lined by visceral tunica vaginalis. The mesorchium is the mesentery supporting these structures. The most notable structure within the pouch is the testis. Pull the posterior end of the cremasteric pouch. The short connective tissue extending to the testis is the gubernaculum.
The epididymis is a thin, flattened band of tissue on the dorsomedial part of the testis. It consists of expanded head and tail regions and a central, narrower body. As it may be difficult to discern the epididymis in ventral view, turn the testis over by reflecting its lateral surface dorsally. The concave margin of the epididymis is easily apparent. Grasp it with a forceps and return the testis to its anatomical position.
Spermatozoa, the male gametes, from the testis pass through the head, body, and tail of the epididymis and then enter the strand-like ductus deferens, which passes mainly along the medial side of the testis. This portion of the ductus is highly convoluted. A thicker strand-like
FIGURE 7.71 Abdominopelvic cavity of the female cat with many of the viscera removed and urinary bladder reflected to the right to show vessels and urogenital structures, in ventral view.
structure passes to the anterior end of the testis. This is the pampiniform plexus, formed by the intertwining of the convoluted distal ends of the internal spermatic artery and vein. Follow the artery, vein, and ductus deferens anteriorly by slitting the narrow part of the cremasteric pouch. These structures, bound together by the visceral tunica vaginalis, constitute the spermatic cord. The cord passes through the inguinal canal, a short passageway in the abdominal wall, into the abdominopelvic cavity. Within the abdominopelvic cavity, the vessels and ductus deferens go their separate ways. The vessels extend anteromedially. The ductus deferens loops around the ureter and then extends posteriomedially, passing through the fat within the lateral ligament of the urinary bladder. Locate the ductus on the other side so that both ducti deferentes may be traced as they extend into the pelvic canal and meet the urethra (see below).
Opening the Pelvic Canal
The pelvic canal must be opened in order to continue following the structures of the urogenital system.
Doing so involves cutting through the pelvic symphysis, which is fairly easy, as the symphysis is not fused. Finding the symphysis, however, can be tricky. The most direct way is to continue the incision cut through the body wall posteriorly, all the way to the symphysis. In doing so, try to cut along the sagittal plane (recall that originally you cut to one side of the sagittal plane). Exposing the bladder and urethra may help, as the latter, which lies more or less sagittally, can serve as a guide. When you find the anterior end of the pelvis, attempt to push through the symphysis with a scalpel. (Scraping the pubes a little can help show the symphysis as distinct from the bones.) If you are not precisely on the symphysis, the scalpel will meet with resistance. Do not attempt to force the scalpel through. Instead, move it over slightly to one side or the other and try again; it will pass through fairly easily if it is on the symphysis. Keep trying until you cut through the symphysis. Spread the symphysis by grasping the thighs and twisting them dorsally.Male Reproductive System, Continued
Once the pelvic canal has been opened, follow the urethra posteriorly, clearing away connective tissue and fat as you do so. Just within the canal, the urethra seems to expand laterally. Careful dissection reveals that the expansion is actually the prostate gland. Return to the ducti deferentes and trace them through the canal. They converge and pass along the dorsal surface of the urethra. The prostate gland surrounds their entrance into the urethra. The urethra continues posteriorly and enters the penis very near the end of the pelvic canal.
The penis is formed by three columns of erectile tissue that, when filled with blood, cause its erection (Figure 7.70). The corpus spongiosum penis is the mid-dorsal column; the urethra is embedded within it. Posteriorly, the corpus forms the free end of the penis, the glans penis, from which the urethra emerges. The other two columns, the corpora cavernosa penis, lie side by side on the ventral surface.
The dorsal position of the urethra and corporus spongiosum is a peculiarity of the posterior-pointing penis of the cat. In most other mammals the urethra and corpus lie ventrally, and the corpora cavernosa are dorsal. Posteriorly, the corpora cavernosa diverge laterally as the crura (sing., crus) of the penis, which anchor the organ to the ischia. The small, paired bulbourethral glands lie just dorsal to the crura. Cut and reflect a crus to see them. Then section the penis near its center to view the three columns of spongy tissue. The os penis is a small bone (3-7 mm long) lying in the glans penis.Key Terms: Male Reproductive System
bulbourethral glands corpora cavernosa penis corpus spongiosum
penis cremasteric pouches crus (plur., crura) of the
penis ductus deferens epididymis glans penis gubernaculum inguinal canal
mesorchium
os penis (baculum) pampiniform plexus parietal tunica vaginalis penis
prostate gland
scrotum
spermatic cord
testis (plur., testes) vaginal cavity
visceral tunica vaginalis
Female Reproductive System
The small, oval ovaries are the female gonads (Figure 7.71) and lie in the abdominal cavity just posterior to the kidneys. Follow the ovarian artery and vein of one side to an ovary. As in most vertebrates, ova produced by the ovaries pass posteriorly through paired tubes that have become longitudinally differentiated into several distinct regions in mammals. The uterine tube, the most anterior portion, is a thin, convoluted tube lying lateral to the ovary. Its proximal end enlarges into the infundibulum, which forms a hood-like expansion over the anterior end of the ovary. Its margin bears fimbriae, frill-like projections that help ensure the ovum passes through the ostium tubae, which is the opening of the infundibulum, and into the uterine tube.
Each uterine tube leads posteriorly into the larger uterine horn. These will be narrow unless the female is gravid or has previously carried a litter. The horns of each side pass posteromedially and merge dorsal to the urinary bladder. The short, tough ovarian ligament anchors the ovary and the anterior end of the horn. At first glance, however, it appears to form a connection between the uterine horn and ovary. Thus, carefully follow the uterine horn into the uterine tube.
The union of the uterine horns posteriorly form the body of the uterus, a wider canal that then leads into the vagina. As there is no external division of these structures, their separation will be seen when they are opened. Note that the ureters pass dorsal to the uterine horns.
The reproductive tract is supported by various mesenteries. The main supporting structure is the broad ligament, of which several portions are recognized. Lift the reproductive structures to clearly observe the following mesenteries. The portion of the broad ligament supporting the ovary is the mesovarium. The mesosalpinx attaches to the uterine tube, and the mesometrium attaches to the uterus, including the uterine horn. Lift the uterine horn near its center and tug it medially, as shown in Figure 7.71. The round ligament is the fibrous band in the mesometrium that extends diagonally from the uterine horn posterolaterally toward the body wall. Also, note the suspensory ovarian ligament, which supports the ovary anteriorly, as it extends to the dorsal body wall just lateral to the kidney.
Open the pelvic canal by cutting through the pubic symphysis following the instructions given for the male on page 216. Pick away connective tissue to reveal and separate the structures passing through the canal (see Figure 7.71). The urethra and vagina unite toward the posterior end of the pelvic canal to form a common passageway, the urogenital sinus, which opens to the outside through the urogenital aperture. Dissect dorsal to the vagina and urogenital sinus to separate them from the rectum. On each side, dissect the tissue lateral to the rectum, very near the anus, to reveal the anal glands. Then completely separate the urogenital sinus from the rectum so that it can be turned over. Make a slit along one side of the body of the uterus, vagina, and urogenital sinus, and spread the flaps apart (Figure 7.72). Find the urethral orifice, the entrance of the urethra. The vagina extends anteriorly from this point to the cervix of the uterus, which is the distally tapered, sphincterlike portion of the uterus. Directly posterior to the urethral orifice, and just before the urogenital aperture, lies the small clitoris, which may be difficult to see. It is the female homologue of the penis and generally considerably smaller, but in hyenas it exceeds the penis in size.
The mammary glands are important reproductive structures in mammals. They were observed beneath the skin of the thorax and abdomen during skinning of the cat (see page 157).
FIGURE 7.72 Distal portion of female urogenital tract of the cat in ventral view. The tract has been cut along its lateral margin and opened to the right to reveal the internal anatomy.
Key Terms: Female Reproductive System
anal glands body of the uterus broad ligament cervix of the uterus clitoris fimbriae
infundibulum mammary glands mesometrium mesosalpinx mesovarium ostium tubae
ovarian ligament ovary round ligament suspensory ovarian
ligament urethral orifice urogenital aperture
(vulva)
urogenital sinus (vaginal vestibule, urogenital canal)
uterine horn
uterine tube (fallopian tube)
vagina