Autonomic Innervation of Kidneys and Upper Ureters

Some parasympathetic fibers are carried through the vagal contributions to the celiac plexus and are conveyed onward to the kidneys in the renal branches of this plexus; others emerge through the pelvic splanchnic nerves and may reach the renal collecting tubules, renal calyces and renal pelvis and upper ureter by a more indirect route. Such an arrangement is understandable on embryologic grounds because the structures mentioned are all derived from buds developed from the cloacal ends of the mesonephric (wolffian) ducts. These pelvic parasympathetic fibers join the inferior hypogastric plexuses, ascend in the hypogastric nerves to the superior hypogastric plexus, and exit in fine branches that ascend retroperitoneally to enter the inferolateral parts of the homolateral renal plexus.

Afferent fibers from the kidneys and upper ureter follow similar routes in the reverse direction, but they do not form relays in peripheral ganglia; their cell bodies are located in posterior spinal nerve root ganglia. The central processes of these ganglion cells enter the spinal cord mainly through the posterior nerve roots of the tenth to twelfth thoracic spinal nerves and then ascend in or alongside the spinothalamic tracts and also in the posterior white columns of the cord.

Within the renal hilus and sinus, the renal plexus supplies nerve fibers to the renal pelvis, calyces, and upper ureter. Other nerve fibers form rich plexuses around the renal vessels and their branches and accompany them into the kidney. They contain mostly unmyelinated fibers, and relatively few of the myelinated type. The sympathetic fibers are distributed to the smooth muscle in the renal pelvis and calyces, to the vascular musculature, and possibly to the juxtaglomerular cells and glomeruli. The parasympathetic fibers supply the muscle in the pelvis, calyces, and upper ureter, but it is uncertain whether they supply the vessels and tubules. Sensory nerve endings have reputedly been detected in the pelvis and ureter, in the adventitia of the larger vessels, and near the glomeruli.

Urinary Bladder and Lower Ureter. The preganglionic sympathetic cells concerned with vesical innervation are located in the upper two lumbar segments and perhaps also in the lowest thoracic segment of the spinal cord. The sites where the preganglionic fibers form synapses with the ganglionic neurons that give off the postganglionic fibers have not been determined accurately. The preganglionic parasympathetic cells are located in the second to fourth sacral segments of the spinal cord, and their axons (nervi erigentes) relay in ganglia close to or within the wall of the urinary bladder. The neurons in the anterior gray matter of the sacral spinal cord S1 to S3, Onuf nucleus, provide the motor supply to the external urethral sphincter through the motor branches of the pudendal nerve. Afferent fibers pursue similar pathways, but in the reverse direction; thus some vesical sensory impulses enter the cord through the upper lumbar and last thoracic posterior nerve roots, while others from the neck of the bladder and the lowest parts of the ureters reach the cord via the pelvic splanchnic nerves and the posterior nerve roots of the second to fourth sacral nerve segments.

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