Kidney of giraffes

Abstract

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 ϫ 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. Anat Rec 267: 94 -111, 2002.

The giraffe kidney tolerates high arterial blood pressure by high renal interstitial pressure and low glomerular filtration rate

“…). Nevertheless, the thickness of the renal capsules in our study (0.20 mm) is even lower than the 0.75 mm reported by Maluf (Maluf ). This difference in thickness could be age‐related as the age of the animals in the latter study was 18 and 22 years.…”

“…) and mice (Sallstrom & Friden ). Also, both our present study and that of Maluf (Maluf ) show normal microscopic structure of the giraffe cortex and glomeruli, leaving no evidence for peculiar mechanical properties of the giraffe glomerular membrane. Instead, our measurements of the high renal interstitial hydrostatic pressure could account for a reduction in transmural pressure across Bowman's capsule that would reduce GFR in spite of the high MAP.…”

“…We relied on the terminology of Maluf (Maluf ) to describe the giraffe kidney. The microscopic structure of the cortex was very similar to the human kidney cortex; occasionally, the glomeruli were close to the wall of the cortical radial arteries.…”

Harvey Cushing and the regulation of blood pressure in giraffe, rat and man: introducing ‘Cushing's mechanism’

“…If it was correct, then all mammals with legs as long as those of giraffes, such as elephants and camels, would have as high a MAP and TPR, but they do not (Seymour & Blaylock, 2000). In addition, giraffe renal and cerebral vasculature is normal (van Citters et al 1969; Maluf, 2002), so hypertension of renal origin or because of increased cerebrovascular resistance is unlikely. The best explanation in our view is that as neck length and the effects of gravitational hypotension increase, the Cushing mechanism secures increased sympathetic outflow and an increase in TPR.…”

Insights into Biomedicine from Animal Adaptations

“…Arterial structural changes very similar to those in the giraffe are observed in patients with essential hypertension (83,100,106). Interestingly the interlobular arteries and afferent arterioles of the giraffe kidney do not show structural remodeling (reduction in lumen size and thickening of the media) despite the high mean arterial pressure (69), whereas small vessel structural changes have been well documented in the kidneys of patients with essential hypertension (110).…”