A Laboratory Manual of the Anatomy of the Rat/The Urogenital System
THE UROGENITAL SYSTEM
The reproductive and excretory organs are closely associated in structure and function, and are therefore collectively termed the urogenital, or urinogenital, system. In dissecting the urogenital organs be careful not to cut the blood vessels, which will be studied later.
The two kidneys are the two principal excretory organs of the body. The renal arteries carry the blood to the kidneys, where urea, salts, excess water, etc. are removed from the blood, which then passes to the inferior vena cava through the renal veins. Each kidney is a bean-shaped organ, covered ventrally by peritoneum, and attached to the dorsal wall of the abdomen. The hilum, or depression where the renal blood vessels and ureter enter, is on the median surface. The dorsal surface is flattened, the ventral surface is convex. The anterior end of the right kidney fits into the concave surface of the right lateral lobe of the liver. The left kidney is displaced caudad, so that its hilum is slightly posterior to the level of the posterior end of the right kidney. This displacement is probably due to the presence of the stomach on the left side of the body. The ureter is the tubule which conveys the urine from the kidney to the urinary bladder. Find where it leaves the hilum of the kidney and trace it back to the bladder.
The suprarenal gland is a somewhat hemispherical body immediately anterior to each kidney. It lacks a duct. The secretion (adrenalin) known as an internal secretion, enters the blood, which carries it to those parts of the body where it performs its functions.
Remove both kidneys from the body. With a sharp razor or scalpel divide one kidney into its dorsal and ventral halves, and bisect the other by a transverse cut passing through the hilum. The cut surfaces reveal the outer cortical and inner medullary regions of the kidney. Within the latter note the dorsoventrally flattened papilla which projects into the internal cavity, or sinus, of the kidney. The urine collects in the sinus and drains into the ureter through its funnel-shaped anterior end, the pelvis, which is located at the hilum of the kidney. Insert a fine bristle into the pelvis where it surrounds the tip of the papilla and by careful probing locate the lumen of the ureter.
Exercise XXII. Draw the cut surfaces of the bisected kidneys.
THE MALE UROGENITAL ORGANS
The spermatozoa, or male sex cells, are produced in the two testes, which develop in the embryo near the attachment of the mesentery to the dorsal side of the abdominal cavity. In the lower vertebrates the testes remain through- out life near their embryonic position, but in most mammals they come to lie in an integumentary sac, the scrotum, ventral to the anus. This scrotal sac incloses two extensions of the coelom, each of which communicates in the embryo with the abdominal cavity through the inguinal canal. This canal marks the position of the scrotal evagination. The testes usually descend from the abdominal cavity, through the inguinal canals, into the scrotal sac, though in the whale and elephant they remain in the abdominal cavity. Such a condition (cryptorchism) occasionally occurs in man. The inguinal canal remains open in marsupials, bats, rodents (including the rat), insectivores, etc. The descent of the testes in these animals is temporary, and at the close of the breeding season the testes are withdrawn into the abdomen by the cremaster muscle. Rats dissected in the laboratory frequently show the testes more or less completely retracted into the abdomen.
The scrotum of the rat is a prominent swelling, about four centimeters long in a large male, lying on the ventral side of the body between the anus and penis. Like the rest of the integument it is covered with hair. A longitudinal groove on its ventral surface marks the position of the septum scroti, an internal partition which separates one testis from the other.
Carefully slit the scrotum ventrolaterally on one side throughout its entire length, using care to cut no deeper than the integument. Cautiously separate the integument, which is the scrotum proper, from the underlying layer of connective tissue. This connective tissue forms a sac which joins a similar sac surrounding the other testis to form a median partition, the septum scroti. Slit the connective tissue sac lengthwise and determine the number of layers in it. A muscular sac will be observed immediately under the connective tissue. It may be traced forward to the ventral abdominal muscles. Microscopic examination of a piece of this muscle will show that it is two-layered and that the fibers are cross striated. The fibers of one layer cross those of the other nearly at right angles.
Each testis is an ovoid body about two centimeters long. It lies lengthwise of the scrotum. The epididymis is closely associated with the testis phylogenetically, structurally, and functionally. It comprises three parts. The enlarged anterior end, or caput epididymidis (head), curves around the anterior end of the testis, and is attached ventrally and mesially to it by a mesentery. The slender corpus epididymidis (body) passes along the dorsal side of the testis, connecting the caput epididymidis in front with the cauda epididymidis behind. The latter expands posteriorly and curves down around the posterior end of the testis. The ductus deferens is the conspicuous tube which passes forward from the median side of the cauda epididymidis, through the inguinal canal into the abdominal cavity.
The epididymis and ductus deferens are both attached to a mesentery which extends from the dorsal side of the testis to the dorsal wall of the scrotal cavity. Anteriorly this mesentery also incloses the blood vessels which carry blood to and away from the testis. Fat accumulates in consider- able quantity in front of the epididymis and within ventral prolongations of the mesentery which extend through the inguinal canal into the abdominal cavity.
The mammalian scrotal cavity, like the abdominal cavity from which it is derived, is lined with peritoneum, the tunica vaginalis. The testis, like the intestine, is almost completely invested with peritoneum and is suspended in the scrotal cavity by the mesentery, which is covered on both sides by the peritoneal layer. The wall of the testis is a very tough, fibrous, transparent membrane, the tunica albuginea. This incloses a mass of convoluted seminiferous tubules, readily seen through the tunic. Slit the latter lengthwise of the testis and with a needle tease out some of the tubules, noting their convolutions. These tubules produce the spermatozoa.
The epididymis is covered by a tough transparent membrane similar to the tunica albuginea of the testis. Through the membrane may be seen tubular convolutions. The ductus deferens becomes coiled when it enters the cauda epididymidis. Verify this by a careful dissection.
In man the spermatozoa, produced by the epithelial lining of the seminiferous tubules, pass through efferent ducts, the ductuli efferentes testis, to the caput epididymidis, where they are collected into a single duct, the duct of the epididymis. The convolutions of this tube form the body and tail of the epididymis. The tube emerges from the cauda epididymidis, and as the ductus deferens conducts the sperm cells to the urethra. This arrangement doubtless obtains, in all essential details, in the rat also.
The epididymis of Amniotes is homologous to a part of the mesonephros of the adult Ichthyopsida. The mesonephros is a kidney and a sperm carrier in the latter group. The excretory function is retained by the mesonephros in the mammalian embryo, but in the development of the male the organ undergoes partial degeneration, so that in the adult only the sperm-carrying function is retained.
The ductus deferens of the rat, after entering the abdominal cavity through the inguinal canal, turns medianly, curves around the ventral surface of the ureter, and joins the urethra.
There are several accessory glandular structures in this region. The vesicular glands are a pair of conspicuous, warty structures at the posterior end of the abdominal cavity. The anterior end of each gland bends abruptly caudad, so that each gland, as a whole, somewhat resembles an interrogation point. The gland is hard and brittle in a preserved animal. Open it and remove some of the coagulated secretion. It breaks into fine particles when rubbed between the fingers. This secretion is produced by the wall of the gland, which is said to contain a strong mantle of smooth muscle. Find the duct and trace it caudad to its entrance into the anterior end of the urethra. These organs were formerly called seminal vesicles, but they contain no spermatozoa. It is said that the glands produce an alkaline secretion which is mixed with the sperms, upon whose movements the secretion probably exerts a favorable influence. It is claimed that extirpation of the glands reduces the animal's reproductive capacity. Note the elongated flattened gland lying against the concave surface of the vesicular gland. Find its duct and trace it to the anterior end of the urethra. Find also the pair of small glands (probably the ampullary glands), each of which encircles the ductus deferens near its entrance into the urethra.
The prostate gland comprises two regions. One attaches to the dorsal and lateral surfaces of the proximal end of the urethra, and to the dorsal side of the vesicular gland. The other region consists of two prominent lobes lying ventral to the urinary bladder, to which they are attached. The lobes are also fastened to the adjacent body wall. Dissect away the tough external tunic of connective tissue, and note that both parts of the gland are a mass of tubules. The prostatic secretion in man dilutes and lends bulk to the seminal fluid. It has been suggested that in rodents the secretion assists the locomotion of the sperm cells, and also nourishes them.
The urinary bladder is an oval sac attached to the dorsal surface of the ventral part of the prostate gland. The bladder narrows proximally to the neck, which joins the ductus deferentia to form the urethra. Each ureter, or urinary drainage tube of the kidney, joins the corresponding side of the bladder near the neck. Urine entering the bladder through the ureters, is stored there temporarily, then flows through the neck into the urethra, which conveys it to the outside. The urethra also carries the spermatic fluid during copulation.
The descent of the testis carries the ductus deferens ventral to the ureter. This accounts for the way these tubes loop around each other in the adult.
A mesentery in the sagittal plane connects the bladder and posterior part of the prostate gland with the ventral body wall. Divide the pelvic girdle along the symphysis pubis, remove the ventral part of this girdle, clear away the adjacent muscles, and expose the urethra. This runs back through the girdle ventral to the rectum. The urethra joins the penis at the posterior end of the pelvic girdle. At this place the two bulbo-urethral (Cowper's) glands pour their secretion into the urethra through a pair of long ducts. Each of these glands is ovoid in shape and about five millimeters long. It lies lateral to the rectum and just behind the posterior border of the ischium. It has been suggested that the secretion protects the spermatozoa against the harmful effects of traces of urine.
Dissect away on one side the tissues surrounding the penis. Note that it has the form of a figure 7, with the angle anteroventral. Carefully insert one blade of the scissors into the genital orifice and slit the integument lengthwise of the body. Press aside the flaps of skin and note that the terminal section of the penis, the glans, lies loose in a chamber surrounded by the prepuce or foreskin. The surface of the glans is slightly rough. Its blunt free end points backward. The two preputial glands, one on either side of the glans penis, discharge their secretion near the posterior edge of the prepuce. Dissect away the surrounding tissue and locate the duct and its opening. Each gland is dorsoventrally flattened, rounded anteriorly, and tapers back to the edge of the foreskin. Insert a fine pair of scissors into the orifice of the duct and slit it lengthwise. Note the relatively very large calibre of the duct beyond the opening, and the soapy character of the contained secretion. It has been claimed that this secretion protects the integument in this region from being injured by the excretions.
The penis is the structure which is used to carry the seminal fluid from the male to the vagina of the female. Dissect away the muscle and connective tissue surrounding it, including the preputial glands and foreskin. The body of the penis consists of three parts, the two corpora cavernosa penis, and the corpus cavernosum urethrae. The former comprise the dorsal part of the body when in its normal position, the latter lies in a deep groove on the ventral side of the corpora cavernosa penis. Carefully separate the corpora cavernosa penis from the corpus cavernosum urethrae. Cut the former transversely. Observe that they consist of two lateral spongy masses of tissue, firmly united in the middle, but separated above by a groove carrying a blood vessel, and below by the groove inclosing the corpus cavernosum urethrae. Distally the corpora cavernosa penis terminate in one or two bones. These bones extend to the tip of the glans dorsal to the urethra when the glans is turned forward. The corpora cavernosa penis diverge proximally, forming the two crura penis. Each crus penis is a tough body firmly attached to the posterior border of the innominate bone. The corpus cavernosum urethrae terminates distally at the tip of the glans penis. Proximally it expands into a semilunar structure, probably homologous to the bulb of human anatomy. The ducts of the bulborurethral glands enter the urethra in front of the bulb. The urethra traverses the whole length of the corpus cavernosum urethrae and extrudes the urine or seminal fluid through the external urethral orifice.
Slit the urethra lengthwise from the external urethral orifice to the region of the prostate gland. The incision should be lateral in the vicinity of the bladder to avoid cutting into the neck of the bkdder. Within the penis the lumen of the urethra is of small calibre, but between the penis and urinary bladder it expands and contains a plug of secretion. Note the diverticulum leading off into the bulb. Remove the plug of secretion and locate the ventral orifice through which urine enters from the bladder, also near this the openings of the ductus deferentia and ureters. Urethral glands occur in the mucous membrane of the urethra.
Exercise XXIII. Make a full page drawing of the entire urogenital system of the male.
THE FEMALE UROGENITAL ORGANS
Examine the anal region of a female rat and note the three openings. At the base of the tail is the anus, ventral to it the vaginal orifice, and below this the urinary opening at the summit of a prominent elevation. As a rule there is but one external opening for the female urogenital systems in mammals.
Cautiously cut the urinary elevation lengthwise, inserting but one blade of the scissors into the urinary aperture. This elevation is homologous to the prepuce in the male. Note that it surrounds a body resembling the glans of the penis, to which it is probably homologous. One sex among animals frequently possesses rudimentary structures corresponding to functional reproductive organs in the opposite sex. The penis of the male mammal is represented in the female by the diminutive clitoris, which is terminated by the glans clitoridis, the homologue of the glans penis. A pair of prominent glands just beneath the skin correspond in position to the preputial glands of the male. Locate the opening of the duct on the inner surface of the prepuce a short distance in front of the urinary orifice. Insert a bristle into the duct, slit it open, and ex- amine the secretion, which has a waxy feeling when rubbed between the fingers.
Clear away the muscles ventral to the pelvic girdle, slit the symphysis pubis lengthwise, and expose the female ure- thra. Trace it forward to the urinary bladder, and back to its entrance on the dorsal side of the preputial cavity. At the latter end insert a bristle and push it forward to the urinary bladder.
The urinary bladder is connected with the ventral wall of the abdomen by the suspensory ligament. As in the male, it temporarily stores urine which it receives through a pair of ureters, one from each kidney.
Remove the prepuce, its glans, and the clitoris. Pull the cut end of the urethra forward. This exposes the vagina. Separate the vagina from the surrounding tissues and observe that it lies immediately below the rectum. With a pair of scissors slit the vagina throughout its length. The margin of the vaginal orifice is thrown into longitudinal folds, as is also the internal surface of the vagina. The mucous membrane of the vagina is said to be without glands. The two horns of the uterus converge and join the anterior end of the vagina. The latter receives the penis of the male during copulation, and is therefore a temporary receptacle for spermatozoa. Slit each horn of the uterus a short distance in front of the vagina. Insert here a blunt probe into the lumen of each horn until the probe emerges through the external orifice (os uterus) into the vagina. There are two external orifices, one for each horn, showing that the fusion of the posterior part of the horns is superficial and does not involve the lumen (uterus duplex). The orifices are very easy to locate in an animal well advanced in pregnancy. They are surrounded by five lobes, one large dorsal lobe, one large ventral, and three smaller ventral lobes.
Each horn of the uterus is suspended from the dorsal side of the abdominal cavity by the broad ligament, which may contain considerable fat. This ligament extends anterior to the ovary along the lateral surface of the kidney.
A pair of pockets, corresponding in position to the inguinal canals of the male, extends backward from the abdominal cavity. These pockets are probably the homologues of the male vaginal sacs, and therefore probably correspond to the diverticula of Nuck in man. The mesentery whose attachment runs along the posterior third of the broad ligament's lateral surface, and terminates in this diverticulum, is doubtless the round ligament. Are these diverticula found in all female rats?
Slit the anterior end of the uterus and locate the opening of the uterine (or Fallopian) tube. This tube carries the ova from the ovary to the uterus. The aperture is small but may be found fairly easily, in a uterus containing large fetuses, near the anterior end of the uterine horn, for the tube runs in the wall of the uterus a short distance before opening into it. The ovary, the gonad of the female, is incased in a tough transparent capsule, the bursa ovarica. The periovarial space lies between the bursa and the ovary. Trace the coiled uterine tube. It is said to be from two and a half to three centimeters long, and to contain from eight to ten fairly constant major loops. The tube pierces the bursa ovarica and projects into the periovarial space as the infimdihulum tubae. The epithelial lining of the infundibular section of the tube bears long cilia. This is the only ciliated region of the tube. The wall of the tube contains muscles, which are best developed toward the uterine end. Slit open the ovarial capsule and observe the corpora lutea on the surface of the ovary. Each corpus luteum marks the point at which an egg bursts through the wall of the ovary during ovulation. The ovary is attached dorsally to a strong tendinous band of connective tissue which extends in the broad ligament from the anterior end of the uterine horn to the dorsal body wall near its union with the diaphragm.
The ovary of most mammals is not inclosed in a capsule. The ova which break through the wall of the ovary pass directly to the opening (ostium abdominale) of the uterine tube, and are then carried by cilia in the tube to the uterus. The following events, however, are said to accompany ovulation in the rat. The periovarial cavity is filled with fluid at the time of ovulation. The bursa ovarica exerts pressure upon this fluid as the result of the contraction of the muscles located near the infundibulum tubae and the attachments of the uterine tube. Simultaneously muscular contractions expand the opening (ostium) of the infundibulum tubae. Thus the fluid within the bursa ovarica, with the contained eggs, is forced into the uterine tube, where muscular contractions, possibly assisted to some extent by ciliary action, carry them to the uterus.
The fertilized egg is implanted in the wall of the uterus, where it develops. Examine a female rat with well advanced fetuses in the uterus. Note the large size of the uterus, its abundant blood supply, and segmental character. Each segment contains a fetus. Slit a segment lengthwise along its ventral surface and expose the fetus. This is covered with a thin membrane, the amnion. Carefully open the amnion along the back of the fetus. The fluid in the amniotic cavity protects the embryo from sudden jars. Note the discoidal placenta on the dorsal side of the uterus. The umbilical cord connects the belly of the embryo with the center of the placenta. The blood of the fetus passes through the umbilical cord to and from the placenta, where by osmosis, it receives nutriment from the maternal blood and surrenders waste materials to the mother's blood. The blood of fetus and mother do not mix in the placenta, but are everywhere separated from each other by thin membranes. Compare the fetus with the adult, with other rat fetuses of different ages, and if possible with fetuses, or models of them, of other mammals.
Exercise XXIV. Make a full-page drawing of the entire urogenital system of the female.