BLOOD AND NERVE SUPPLY TO THE KIDNEY
The blood supply to the kidney is extensive because of its important role in adjusting the composition of extracellular fluid (including plasma) (Figure 18.3).
The two renal arteries may receive as much as one- fourth of the total cardiac output.
The origin of renal arteries is directly from the abdominal aorta. While passing through the renal sinus, the renal artery divides into many segmental arteries. Each segmental artery subdivides into interlobar arteries. The interlobar artery passes between the medullary pyramids. At the base of the renal pyramid, the interlobar artery forms the arcuate artery. Each arcuate artery gives rise to interlobular arteries. From each interlobular artery, numerous afferent arterioles arise. The afferent arteriole enters the Bowman capsule and forms the glomerular capillary tuft.In the glomerulus, the capillary loops unite and form the efferent arteriole, which leaves the Bowman capsule. After leaving the Bowman capsule, efferent arterioles form a second capillary network called peritubular capillaries, which surround the tubular portions of the nephrons. In this way, the renal circulation forms a portal system by the presence of two sets of capillary networks, namely glomerular capillaries and peritubular capillaries.
18.9.1 Venous System
Venous system runs opposite to the arterial system. It starts with peritubular venules and continues as interlobular veins, arcuate veins, interlobar veins, segmental veins, and finally the renal vein. The renal vein leaves the kidney through the hilus.
18.9.2 Innervation
The innervation to the kidney is mainly by efferent sympathetic nerve fibers. There is no authentic proof for the innervation of the kidney by parasympathetic nerves. Normal physiological stimulation of the efferent sympathetic nerves is involved in maintaining the water and sodium balance in the body. Efferent renal sympathetic nerve activity (ERSNA) produces significant changes in renal hemodynamics, tubular ion and water transport, and renin secretion. The renal nerves are the communication link between the central nervous system and the kidneys. Reno-renal reflexes are defined as responses occurring in one kidney as a result of intervention on the same or the opposite kidney that are mediated by neurohumoral mechanisms.
18.10