Anatomy chapters
Nerves and vessels of the thorax, abdomen and pelvis
The aorta and its branches, the venae cavae, azygos and portal systems, the internal iliac artery, and the phrenic, vagus, intercostal and splanchnic nerves of the trunk.
- The abdominal aorta enters at T12 and divides at L4; its three gut arteries arise at T12 (coeliac), L1 (SMA) and L3 (IMA).
- The diaphragm openings: IVC at T8, oesophagus at T10, aorta at T12.
- The azygos vein links the IVC and SVC systems; the portal vein carries gut blood to the liver.
On this page
Overview
This page covers the main vessels and nerves running through the trunk: the aorta and its branches, the great veins, the portal system, and the phrenic, vagus, intercostal and splanchnic nerves.
Exams love vertebral levels and relations, so this page lists them clearly.
The thoracic aorta
The ascending aorta begins at the aortic valve and gives the right and left coronary arteries.
The arch of the aorta lies behind the manubrium. Its upper border is at about the level of the middle of the manubrium and its ends are at the level of the sternal angle (T4/T5). It gives three branches:
- Brachiocephalic trunk (divides into right subclavian and right common carotid).
- Left common carotid.
- Left subclavian.
The ligamentum arteriosum joins the arch to the left pulmonary artery. The left recurrent laryngeal nerve hooks under the arch beside it.
The descending thoracic aorta gives the posterior intercostal arteries (3rd to 11th), subcostal arteries, bronchial and oesophageal branches.
The diaphragm openings
| Level | Opening | Passes through |
|---|---|---|
| T8 | Caval opening (central tendon) | IVC, right phrenic nerve |
| T10 | Oesophageal opening (right crus) | Oesophagus, vagal trunks, oesophageal branches of left gastric vessels |
| T12 | Aortic opening (behind the median arcuate ligament) | Aorta, thoracic duct, azygos vein |
"I 8 10 Eggs At 12": IVC at 8, oesophagus at 10, aorta at 12.
The abdominal aorta
It enters at T12 and divides into the common iliac arteries at L4, at about the level of the iliac crests.
| Branch | Level | Type |
|---|---|---|
| Inferior phrenic | T12 | Paired |
| Coeliac trunk | T12 | Unpaired, to the foregut |
| Superior mesenteric | L1 | Unpaired, to the midgut |
| Middle suprarenal | L1 | Paired |
| Renal | L1–L2 | Paired |
| Gonadal | L2 | Paired |
| Inferior mesenteric | L3 | Unpaired, to the hindgut |
| Lumbar | L1–L4 | Four pairs |
| Median sacral | L4 | Unpaired |
The coeliac trunk has three branches: left gastric, splenic and common hepatic arteries.
The left renal vein crosses in front of the aorta, just below the superior mesenteric artery. It can be squeezed between them (nutcracker syndrome). The third part of the duodenum also lies in this angle.
The common and internal iliac arteries
At the pelvic brim (in front of the sacroiliac joint), each common iliac artery divides into the external iliac (to the lower limb) and the internal iliac (to the pelvis).
The internal iliac artery supplies the pelvic organs, perineum, gluteal region and medial thigh. Key branches:
- Anterior division: umbilical (gives superior vesical), obturator, inferior vesical (in men), uterine (in women), middle rectal, internal pudendal, inferior gluteal.
- Posterior division: iliolumbar, lateral sacral, superior gluteal (the largest branch).
The ureter passes under the uterine artery near the cervix ("water under the bridge"). It can be clamped or cut in hysterectomy.
The great veins
Inferior vena cava (IVC)
Formed by the union of the two common iliac veins at L5, behind the right common iliac artery. It runs up on the right of the aorta and passes through the diaphragm at T8 to enter the right atrium.
- The right gonadal vein drains into the IVC. The left gonadal vein drains into the left renal vein.
- The right suprarenal vein also drains directly into the IVC; the left into the left renal vein.
A left-sided varicocele is more common because the left testicular vein enters the left renal vein at a right angle and is longer. A sudden left varicocele in an older man can be a sign of a left kidney tumour blocking the renal vein.
Azygos system
The azygos vein begins in the abdomen, enters the thorax through the aortic opening, runs up on the right of the vertebral bodies and arches over the root of the right lung to join the superior vena cava.
It drains the posterior intercostal veins and links the IVC and SVC systems. If either vena cava is blocked, blood can return to the heart this way.
The hemiazygos and accessory hemiazygos veins on the left cross behind the aorta to join it.
Portal vein
The superior mesenteric vein and the splenic vein join behind the pancreatic neck to form it (which usually receives the inferior mesenteric vein).
It runs up in the free edge of the lesser omentum to the porta hepatis. It carries nutrient-rich blood from the gut, spleen and pancreas to the liver.
For the portosystemic anastomoses, see blood vessels and anastomoses.
Nerves of the thorax
Intercostal nerves
The ventral rami of T1 to T11 run in the costal groove under each rib, with the vein and artery above them (from top to bottom: vein, artery, nerve). T12 is the subcostal nerve.
They supply the intercostal muscles, the skin of the chest and abdominal wall, and the parietal pleura and peritoneum next to them.
T4 supplies the skin at the nipple; T10 at the umbilicus; L1 at the groin.
Phrenic nerves (C3, C4, C5)
They run in front of the lung roots, on the pericardium, to the diaphragm. They are motor to the diaphragm and sensory to the central diaphragm, the mediastinal pleura and the pericardium.
Vagus nerves
They run behind the lung roots. The right vagus passes in front of the right subclavian artery (where the right recurrent laryngeal nerve leaves). The left vagus crosses the arch of the aorta, where the left recurrent laryngeal nerve hooks under the arch.
The vagi form the oesophageal plexus and then the anterior and posterior vagal trunks, which pass through the diaphragm at T10.
Phrenic nerves pass in front of the lung roots; vagus nerves pass behind them.
Splanchnic nerves
- Greater (T5–T9), lesser (T10–T11) and least (T12) splanchnic nerves carry sympathetic fibres to the abdominal ganglia (coeliac, aorticorenal).
- Pelvic splanchnic nerves (S2–S4) carry parasympathetic fibres to the hindgut and pelvic organs.
See autonomic nervous system for more.
Clinical relevance
Abdominal aortic aneurysm
How it happens: weakening of the aortic wall, usually below the renal arteries, in older men who smoke.
What you see: a pulsating, expanding mass above the umbilicus. Rupture causes severe back or abdominal pain and shock.
Hoarse voice from a chest lesion
How it happens: an aortic arch aneurysm, lung cancer or enlarged nodes near the arch press on the left recurrent laryngeal nerve.
What you see: a hoarse voice from left vocal cord palsy.
Most questions are about levels and relations: diaphragm openings, levels of the aortic branches and bifurcation, the left renal vein and gonadal veins, how the portal vein forms, the course of the azygos vein, the ureter and uterine artery, and the positions of the phrenic and vagus nerves at the lung roots.
Quick revision
- Arch branches: brachiocephalic, left common carotid, left subclavian.
- Diaphragm: T8 IVC, T10 oesophagus, T12 aorta.
- Coeliac T12, SMA L1, IMA L3; aorta divides at L4.
- Left gonadal vein to left renal vein; left varicocele commoner.
- Portal vein: SMV + splenic vein behind the neck of the pancreas.
- Azygos arches over the right lung root to join the SVC.
- Phrenic in front of lung roots; vagus behind.
Written by The House Job from standard anatomy references (Snell's Clinical Anatomy by Regions is the book named in the UHS PGET syllabus).
FAQ
At what level does the aorta pass through the diaphragm?
At T12, through the aortic opening behind the median arcuate ligament.
Where does the left testicular vein drain?
Into the left renal vein.
How is the portal vein formed?
By the superior mesenteric vein and the splenic vein joining behind the neck of the pancreas.
What is the order of structures in the intercostal space?
From above down: vein, artery and nerve, in the costal groove under the rib.