Sympathetic Innervation of the Abdomen

Sympathetic innervation to the abdominal organs originates from the thoracolumbar spinal cord segments (T5–L2) and is transmitted via a series of splanchnic nerves and prevertebral plexuses. These nerves carry preganglionic fibers that synapse in ganglia located around major abdominal arteries, with postganglionic fibers traveling along blood vessels to reach target organs. The sympathetic system modulates vasoconstriction, inhibits gastrointestinal motility, reduces secretions, and contracts sphincters.

Pathway Overview

Sympathetic fibers destined for abdominal viscera follow this general pathway:

Originate in the lateral horn of T5–L2 spinal cord segments
Exit via ventral roots and pass through white rami communicantes
Enter the sympathetic chain but do not synapse there
Exit the chain as splanchnic nerves (thoracic, lumbar)
Synapse in prevertebral ganglia within plexuses (e.g., celiac, aorticorenal)
Postganglionic fibers follow arteries to target organs

Major Components

Structure	Origin	Target Organs
Greater splanchnic nerve	T5–T9	Celiac plexus → foregut (stomach, liver, pancreas, spleen)
Lesser splanchnic nerve	T10–T11	Aorticorenal plexus → kidneys, midgut organs
Least splanchnic nerve	T12	Renal plexus → kidneys, upper ureters
Lumbar splanchnic nerves	L1–L2	Inferior mesenteric & hypogastric plexuses → hindgut, pelvic organs

Prevertebral Plexuses

Celiac plexus: Largest plexus; supplies foregut organs
Aorticorenal plexus: Surrounds renal arteries; innervates kidneys and suprarenal glands
Superior mesenteric plexus: Midgut organs (small intestine to transverse colon)
Inferior mesenteric plexus: Hindgut organs (descending colon to rectum)
Intermesenteric plexus: Connects superior and inferior mesenteric plexuses
Hypogastric plexuses (superior and inferior): Pelvic organs and lower rectum

Functions of Sympathetic Input

Sympathetic nerves exert multiple regulatory functions across the abdominal viscera:

Vasoconstriction: Reduces blood flow to abdominal organs during stress
Inhibition of peristalsis: Slows gastrointestinal motility
Reduced secretions: Inhibits glandular activity in the GI tract and pancreas
Sphincter contraction: Promotes closure of pyloric, ileocecal, and internal anal sphincters
Adrenal stimulation: Greater splanchnic nerve directly innervates adrenal medulla (releases epinephrine)

Clinical Significance

Celiac plexus block: Used for managing chronic upper abdominal pain (e.g., pancreatic cancer)
Sympathectomy: Surgical disruption of sympathetic pathways for vascular disorders or hypermotility
Visceral referred pain: Sympathetic afferents travel alongside sensory fibers and can refer pain to thoracolumbar dermatomes (e.g., T10–T12 → umbilical region)
Autonomic dysfunction: Injury to sympathetic fibers may cause motility issues, impaired vascular tone, or organ dysfunction

Sympathetic innervation in the abdomen is critical for modulating organ function, blood flow, and stress responses. Understanding these pathways is essential in pain management, surgical planning, and diagnosing autonomic disorders.