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Urogenital System of the Rat
The urogenital system consists of an excretory or urinary system and the reproductive or genital system. Excretory products consisting primarily of nitrogenous metabolic wastes produced in the tissues are transported in the blood to the excretory organs, the kidneys. Urine, consisting of these metabolic wastes plus variable amounts of water, passes through a network of small uriniferous tubules and collecting ducts within the kidney. Urine is carried posteriorly, usually in a single excretory duct from each kidney. In most cases, a urinary bladder for temporary storage is present.
The reproductive system consists of paired gonads which produce gametes, and ducts leading to the exterior. Accessory organs and glands that may be present include those for transferring and receiving gametes; for storage or nutrition of gametes, zygotes or embryos and glands producing secretions neccessary for reproductive function.
In reptiles, birds and mammals, the ureter drains the kidney. In the males of these classes, the Wolffian duct has become exclusively genital in function, whereas in the female, the Wolffian duct is vestigial and non-functional. The Mullerian duct functions as the genital duct in the female of these classes.
Find the two bean-shaped kidneys that lie up against the dorsal body wall. The ureter connects the kidney with the bladder, while the urethra allows for the passage of urine from the bladder to the exterior. The ureter is a fine thread-like duct which runs posterior from the kidney along the dorsal body wall to the bladder.
In male specimens, the testes are located within the scrotum. Along each testis, from top to bottom lies a tightly coiled duct, the epididymis. From the epididymis, sperm pass into the vas deferens (Wolffian duct), which in turn empties into the urethra. At this latter junction are the seminal vesicles and prostate gland.
In the female rat, locate the external orifices of the vagina and urethra. Follow the urethra from the bladder to the external orifice. Trace the vagina anteriorly to where it joins the two uterine horns (cornua of uterus) that together form a duplex uterus. Each of the uterine horns leads into a coiled oviduct (Fallopian tube) which in turn leads to the ovary (there is one at the end of each uterine horn).
i) Kidney
Canadian Campbell, Fig 44.14
Examine the section of mammalian kidney:
At low magnification you will note that the kidney is divided into two regions, an outer cortex and an inner medulla. The nephron (the functional unit of the kidney) is organized so that Bowman's Capsule and the proximal and distal tubules are located in the cortex and the loop of Henle and the collecting tubules are located primarily in the medulla (Campbell 7th Ed., Fig. 44.13). In the cortical region Bowman's capsules are relatively abundant and appear as spherical structures with a coiled mass of capillaries, the glomerulus in the center. Surrounding the Bowman's capsules will be elements of proximal and distal convoluted tubules cut in various plains of section. The cells making up the walls of the tubules are cuboid in shape and contain a prominent nucleus. In the medulla you should find elements from the loop of Henle and the collecting tubules cut mostly in longitudinal section. Remember this is a section and you will not find all parts of the nephron appearing together as in illustrations such as Figure 44.22 on page 946 in Campbell 6th Ed., or Figure 44.14 on page 933 of Campbell 7th Ed.
Study the slides and make a sketch labelling as many of the above features as possible.
Examine the section of mammalian testis
The testis is enclosed by a capsule and contains within it, sections of seminiferous tubules (view C.S.). Within these tubules spermatogenesis occurs (see Lab 3). Note the mature tailed spermatozoa (sperm). Between the tubules are interstitial cells which are responsible for secretion of the male hormone, testosterone.
iii) Ovary
Examine the maturing follicle with ovum in the section through ovary
This is where oogenesis occurs A space is present between the follicular layers and the ovum. The ovum is, however, embedded at one side of the follicle in a "little hill" of follicle cells, the cumulus oophorous. As the follicle matures, the cumulus becomes more elevated, finally forming a slender stalk bearing the ovum. The ovum is spherical and contains little yolk.
