Kidney of giraffes.

This study focuses on certain aspects of the renal structure of the giraffe, with some implications as to its function. About 4,000 collecting ducts open at the truncated end of a curved crest that juts into the renal pelvis as the inner medulla (IM). Extensions of the pelvis pass between the medullary (MP) and vascular (VP) processes almost to the corticomedullary border. The MPs contain an IM and an outer medulla (OM) containing clusters of capillaries (vascular bundles). The VPs contain the interlobar arteries and veins. All of the IM and almost all of the OM, with its vascular bundles, are bathed with pelvic urine. The cortex comprises 63% of the parenchyma. The OM has nine times the mass of the IM. The IM comprises 4% of the parenchyma. The ratio of mass of the adult cortex to the medulla is 1.7:1.0, and the number of glomeruli per kidney is 6.6 x 10(6). Glomerular mass is 6.2-6.7% of renal mass in the adult and 5.2% in the 6-month-old calf. The dimensions of the glomerular capsules are the same across the thickness of the cortex. Every terminal collecting duct drains an estimated 1,650 nephrons. In the adult giraffe the ratio of thickness of the muscularis of the main renal artery (RA) to its diameter is 0.117 (right RA) and 0.132 (left RA). These ratios are close to those in rhinoceros and ox but greater than in man. The visceral arteries (celiac, anterior mesenteric, and renal) have about the same muscularis : diameter ratio. Giraffes have arterial hypertension, but atherosclerosis is apparently absent and serum lipid fractions are low.