Kidneys peritubular capillaries

The vasa recta are modified peritubular capillaries. As with the peritubular capillaries, the vasa recta arise from efferent arterioles. However, these vessels are associated only with the juxtamedullary nephrons and are found only in the medullary region of the kidney. The vasa recta pass straight through to the inner region of the medulla, form a hairpin loop, and return straight toward the cortex. This structure allows these vessels to lie parallel to the Loop of Henle and collecting ducts. 

Figure 8. Transplanted kidney stained for C4d using (a) an ultrasensitive polymer detection system (EnVision) and (b) standard strepavidin-biotin peroxidase system. There was clear staining of peritubular capillaries in (b) compared to the polymer system where the stain extended into the intertubular interstitium masking the capillaries.

Each kidney receives its blood supply from a renal artery, two of which branch from the abdominal aorta. Upon entering the hilum of the kidney, the renal artery divides into smaller arteries which in turn give off still smaller branches. Branching off these are the afferent arterioles supplying the glomerular capillaries, which drain into efferent arterioles. Efferent arterioles divide into peritubular capillaries that provide an extensive blood supply to the renal cortex. Blood from these capillaries collects in renal venules and leaves the kidney via the renal vein. Blood supply is intimately linked to blood pressure. 

Upon gross examination, three major anatomical areas of the kidney are apparent cortex, medulla, and papilla (Figure 29.1). The cortex is the outermost portion of the kidney and contains proximal and distal tubules, glomeruli, and peritubular capillaries. Cortical blood flow is high relative to cortical volume and oxygen consumption the cortex receives about 90% of total renal blood flow. A blood-borne toxicant will be delivered preferentially to the renal cortex and therefore has a greater potential to influence cortical, rather than medullary or papillary, functions. 

Blood flow to the two kidneys is approximately 22-25% of the cardiac output. The kidneys are supplied by the renal artery which enters the kidneys through the hilum and then branches progressively to form the interlobar arteries, arcuate arteries, interlobular arteries (also called radial arteries), and afferent arterioles, which lead to the glomerular capillaries. The distal ends of each glomerulus coalesce to form the efferent arteriole, which leads to a secondary capillary network, the peritubular capillaries which surround the renal tubules. The cortex receives approximately 90% of the blood flow compared to the medulla or papillae so blood-borne toxic molecules reaching the kidneys have a more toxic effect on the cortex, as compared to the medulla or renal papillae. The interstitial space is occupied by the fenestrated peritubular capillaries and a small number of fibroblast-like cells. Increase in thickness of interstitial space in pathological conditions is due to edema, proliferation of fibrous tissue, or infiltration of inflammatory cells (Guyton and Hall, 2006). 

Richman AV, Gerber LI, Balls JU Peritubular capillaries. A major target site of endotoxin-induced vascular injury in the primate kidney. Lab Invest 43 327-332,1980... 

Endogenous erythropoietin (EPO) is produced primarily by the peritubular capillary endothelium of the kidney in response to tissue hypoxia or anemia. EPO is a... 

An indirect measurement of RBF can be made using para-aminohippuric acid (PAH) clearance. This molecule is an ideal marker of the effective renal plasma flow (eRPF), as it freely filters through the glomerulus, and any amotmt remaining in the peritubular capillary plasma is secreted into the proximal tubule. Therefore, essentially aU PAH passing through the kidneys appears in the urine. For this reason, the PAH clearance is directly proportional to the rate of plasma flow through the kidneys. If the hematocrit is known, the total renal blood flow can be easily calculated from the eRPF value. 

Sprague—Dawley 150 ppm—4 weeks then kidney disease creatinine clearance. peritubular capillary loss. et al. (2007)... 

---