Is the ureter's innervation primarily sympathetic (Sympathetic Nervous System) or parasympathetic (Parasympathetic Nervous System)?

Ureter Innervation: Sympathetic vs Parasympathetic

The ureter is primarily innervated by sympathetic nerve fibers, which are distributed throughout its entire length and play a dominant role in ureteral function and regulation.

Anatomical Innervation of the Ureter

• The sympathetic innervation of the ureter is extensive, with sympathetic nerve bundles distributed throughout the entire ureter, with highest density in the distal portion near the bladder (approximately 7-8 nerve bundles/mm) 1
• Sympathetic nerve fibers in the ureter are identified by the presence of tyrosine hydroxylase, an enzyme involved in catecholamine synthesis 1, 2
• The distal (pelvic) ureter receives innervation primarily from the superior hypogastric plexus (SHP), which forms an ascending bundle of nerve fibers that innervate the ureter 2
• Sympathetic innervation of the ureter is adrenergic in nature, with alpha1-adrenergic receptors playing a significant role in ureteral tone regulation 1

Functional Aspects of Ureteral Innervation

• The sympathetic nervous system regulates ureteral tone through alpha-adrenergic receptors, which explains why alpha1-adrenergic receptor antagonists are effective in treating ureteral stones by reducing ureteral tone 1
• While the mechanism of ureteral peristalsis (pyeloureteric peristalsis) is primarily myogenic in origin, it is modulated by both sympathetic and sensory nerve inputs 3
• Peristaltic contractions in the upper urinary tract propagate in a manner that is minimally affected by drugs that block parasympathetic transmission, further supporting the dominance of sympathetic innervation 3
• Sensory innervation of the ureter is also significant, with numerous afferent nerve fibers located in the adventitia, smooth muscle, subepithelial connective tissue, and epithelium of the ureter and renal pelvis 4

Parasympathetic vs Sympathetic Balance

• While both sympathetic and parasympathetic fibers can be identified in the ureter, immunohistochemical analysis confirms that adrenergic (sympathetic) fibers predominate 2
• The pelvic ureter contains adrenergic, cholinergic, and nitrergic fibers, with the adrenergic component being most prominent 2
• In contrast to other parts of the urinary tract like the bladder (which has significant parasympathetic innervation), the ureter's function is more heavily dependent on sympathetic tone 5
• The autonomic innervation may also indirectly modulate pyeloureteric peristalsis via activation of primary sensory nerve nicotinic receptors 3

Clinical Implications

• Understanding the sympathetic predominance in ureteral innervation explains why alpha1-adrenergic receptor antagonists are effective for treating ureteral stones - they reduce ureteral tone throughout the entire ureter 1
• This anatomical information has implications for surgical techniques involving rectal resection and ureteral reimplantation 2
• The sympathetic innervation pattern also informs pharmacological approaches to managing ureteral stones and pain associated with ureteral pathology 1, 2
• The ascending pattern of innervation from the inferior hypogastric plexus to the pelvic ureter is an important anatomical consideration during pelvic surgeries 2

In summary, while the ureter receives both sympathetic and parasympathetic innervation, the sympathetic component is predominant and more functionally significant for ureteral physiology and pathophysiology.