Sympathetic Innervation of the Abdomen
Abdominal sympathetic innervation arises from thoracolumbar splanchnic nerves and prevertebral plexuses.
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.
Last updated on May 9, 2025
