Urinary System

The urinary system of the porpoise, like other mammals, consists of paired kidneys, ureters, a urinary bladder, and urethra. Unlike most other mammals however, marine mammals have reniculate, or lobed, kidneys.

 The function of reniculate kidneys may be associated with increased body size or may have other unknown functions (see Ortiz, 2001 for a review). Upon gross dissection, reniculate kidneys appear like a “sack of grapes” held together by an outer membrane. Each reniculi is composed of cortex (the outer, darker margin) and medulla (the inner lighter) margin. Urine produced within each reniculi is collected into a common renal pelvis and drains into the ureter. In the porpoise, the kidney’s are located just deep to the hypaxial muscles and during necropsy, careful dissection of the hypaxial muscle will permit access to the kidney (see image below). The adrenal glands are situated at the cranial pole of each kidney.

Urine drains from the kidney through the ureters to the urinary bladder. In the harbor porpoise the bladder is located ventrally, against the abdominal wall. In males, it is fairly easy to locate the bladder by looking for the paired testes located laterally to the bladder. In females, the bladder lies ventral to the reproductive organs which may be laid back to reveal the bladder.

During necropsy, collection of urine can be most easily achieved by locating the bladder and then, using a large gauge needle, puncturing the bladder near the cranial margin. If the bladder is not very full, moving the needle around or trying lower on the bladder can sometimes help with collection. In addition, the kidneys should be removed and cross sectioned at various points (bread loafing) to look for lesions as well as to examine the color of the organ. These observations can be useful to the pathologist when determining COD.

 Detailed annotated images of the urinary system in a harbor porpoise are shown below.  CLICK on an image to see an enlarged view.