Urogenital System

The excretory and reprodutive systems of vertebrates are closely integrated and are usually studied together as the urogenital system. However, they do have different functions: the excretory system removes wastes and the reproductive system produces gametes (sperm & eggs). The reproductive system also provides an environment for the developing embryo and regulates hormones related to sexual development.

Excretory Organs

1. The primary organs of the excretory system are the kidneys. Locate these large bean shaped structures located toward the back of the abdominal cavity on either side of the spine. Renal arteries and veins supply the kidneys with blood.

2. Locate the delicate ureters that attach to the kidney and lead to the bladder. Wiggle the kidneys to help locate these tiny tubes.

3. Procedure: Remove a single kidney (without damaging the other organs) and dissect it by cutting it longitudinally. Locate the cortex (the outer area) and the medulla (the inner area).

4. The urethra carries urine from the bladder to the urethral orifice (this orifice is found in different areas depending on whether you have a male or female rat).

5. The small yellowish glands embedded in the fat atop the kidneys are the adrenal glands.

**You are responsible for knowing the structures of both sexes. Locate the structures in your own rat and then observe the structures of the opposite sex from another group's rat.

The Reproductive Organs of the Male Rat

1. The major reproductive organs of the male rat are the testes (singular: testis) which are located in the scrotal sac. Cut through the sac carefully to reveal the testis. On the surface of the testis is a coiled tube called the epididymus, which collects and stores sperm cells. The tubular vas deferens moves sperm from the epididymus to the urethra, which carries sperm though the penis and out the body.

2. The lumpy brown glands located to the left and right of the urinary bladder are the seminal vesicles. The gland below the bladder is the prostate gland and it is partially wrapped around the penis. The seminal vesicles and the prostate gland secrete materials that form the seminal fluid (semen).

The Reproductive Organs of the Female Rat

1. The short gray tube lying dorsal to the urinary bladder is the vagina. The vagina divides into two uterine horns that extend toward the kidneys. This duplex uterus is common in some animals and will accomodate multiple embryos (a litter). In contrast, a simple uterus, like the kind found in humans has a single chamber for the development of a single embryo.

2. At the tips of the uterine horns are small lumpy glands called ovaries, which are connected to the uterine horns via oviducts. Oviducts are extremely tiny and may be difficult to find without a dissecting scope.

Procedure: Pin the organs of the urogenital system.