Renal anatomy of the manatee, Trichechus manatus, linnaeus

Abstract

The manatee kidney is composed of several closely apposed lobes. These are formed by cortical folds (plicae corticales) that completely isolate the medullae, except where the medullae of adjacent lobes are partially fused. The cortex is continuous; its folds usually are separated, but only partially, by interlobar septa extending from the renal capsule. The cortex makes up approximately 57% of renal mass in adults and 68% in the calf. There are about 3 million glomeruli per kidney. The average is somewhat less than that expected of an adult eutherian of equal mass. The glomeruli, however, are large; they form 7.38% +/- 1.33 of cortical mass, which is above that for at least ten unrelated adult eutherians. The number of glomeruli per gram of cortex is considerably greater in the calf than in the adult. The medullae are about 43% of renal mass. The cortico-medullary thickness ratio is 0.08 to 0.24. All terminal collecting ducts open at a crater (cratera cribrosa) of varying depth. Hair-pin loops occur at all levels of medulla, and apparently all loops bend at their thick segment. Cortical loops occur in the medullary rays. Vascular bundles were evident at the cortico-medullary border and thin tubules extended into the medulla from the central ends of the medullary rays (cortical) in seven out of the nine kidneys. The renal pelvis is separated from the central ends of the cortical folds by delicate fascia through which pass the interlobar vessels. There are no fornices and no infundibula. The collagenous tissue of the pelvic wall extends across most of the pelvic surface of the outer medulla.

Kidney of elephants

“…Glomeruli were counted as previously described (Maluf, 1989a(Maluf, , 1991a(Maluf, ,b, 1993. Briefly, a few grams of the central cortex of the previously frozen, thawed, and formaldehyde-fixed kidney were thoroughly mopped with absorbent paper and weighed to the nearest 0.1 mg.…”

“…The present author, however, cannot corroborate Sperber's 9/10 ratio for cortexlkidney in Elephas. Furthermore, in the adult manatee, the cortex of which is rich in medullary loops, the cortical fraction of the renal parenchyma is relatively low (Maluf, 1989a). It is not clear how Sperber obtained the above ratio, since he noted that "the weight of the kidneys is not known either in my own alcohol kidneys or in most data from the literature.…”

Amazonian Manatee Urinalysis: Conservation Applications

“…Although little is known about the maintenance of water in manatees, Maluf (1989) analyzing the anatomy of nine manatee kidneys (Trichechus manatus), suggested that they have an increased ability to concentrate urine. Since Trichechus manatus inhabits both freshwater and marine, it can be considered an interesting model for osmoregulation study in Sirenians.…”

Further studies on the kidney of the hook‐lipped African rhinoceros, Diceros bicornis

“…This is a relatively large fraction. In the writer's experience this fraction is outstripped by the adult manatees (Maluf, 1989a). In the two other adult Diceros bicornis females the medulla averaged 34.9% of the parenchymal mass (Maluf, 1991a).…”

“…Counting of glomeruli has been described in detail (Maluf, 1989a(Maluf, , 1991a. Pieces of central cortex, checked by dissecting microscope to exclude possible residual medulla, were carefully mopped on absorbent paper and weighed to the nearest mg and then disintegrated at room temperature with 7.4 N (27%) HC1.…”