35 Diaphragm and Lymphatics Quiz

Diaphragm

• The diaphragm is a double dome-shaped muscle, with the right dome higher than the left.
• The diaphragm's central tendon is surrounded by muscle fibers.
• The diaphragm is innervated by the phrenic nerve (C3-5), which provides motor function, and the central portion is innervated by the phrenic nerve, while the peripheral portion is innervated by the intercostal nerves.
• The diaphragm's blood supply is provided by the superior and inferior phrenic arteries, as well as the musculophrenic and pericardiophrenic arteries.
• The diaphragm can function as a collateral pathway for blood return to the heart if the inferior vena cava is blocked.
• The diaphragm has three openings:
  • The esophageal hiatus for the esophagus
  • The aortic hiatus for the aorta and thoracic duct
  • The caval opening for the inferior vena cava

Lymphatics

• Lymphatic vessels in the posterior abdominal region collect lymph from various structures.
• Pre-aortic lymph nodes are arranged around the three major blood vessels:
  • Celiac nodes: drain the foregut
  • Superior mesenteric nodes: drain the midgut
  • Inferior mesenteric nodes: drain the hindgut
• Para-aortic/lumbar/lateral aortic lymph nodes are located lateral to the aorta and receive lymph from the body wall, kidneys, suprarenal glands, and gonads.

Lumbar Plexus

• The lumbar plexus is formed from the anterior rami of L1-3 (L4) and contributions from T12.
• It is located anterior to the psoas major muscle.
• Its main branches include:
  • Sciatic nerve (L4-S3)
  • Pudendal nerve (S2-4)
  • Superior (L4-S1) and inferior (L5-S2) gluteal nerves
  • Posterior cutaneous nerve of the thigh (S1-S3)
  • Pelvic splanchnic nerves (S2-4)

Autonomics

• Sympathetic nervous system (SNS):
  • Preganglionic neurons originate in the thoracolumbar region (T1-L1/2).
  • Postganglionic neurons reside in the paravertebral sympathetic trunk and prevertebral (pre-aortic) ganglia.
• Parasympathetic nervous system (PSNS):
  • Preganglionic neurons originate in the cranial and sacral regions.
  • Postganglionic neurons are located near or at the organ walls (except in the head).

Vagus Nerve

• The vagus nerve is part of the parasympathetic nervous system and supplies the foregut and midgut.
• The vagus nerve branches into the:
  • Celiac plexus
  • Superior mesenteric plexus
  • Inferior mesenteric plexus
• The inferior mesenteric plexus connects to the hypogastric nerve.

Visceral Afferents

• Visceral afferents carry physiological sensations and accompany parasympathetic fibers.
• Visceral afferents carrying pain sensations accompany sympathetic fibers.
• For example, stomach pain is referred to T6-9 dermatomes due to the greater splanchnic nerves carrying the pain signals.
• Pain from the sigmoid colon is referred to S2-4 due to parasympathetic nerve involvement.

Appendicitis & Pain Referral

• The appendix arises from the posteromedial wall of the cecum.
• The appendix receives its blood supply from the appendicular artery, a branch of the ileocolic artery, which itself branches off the superior mesenteric artery.
• Lymph from the appendix drains to superior mesenteric nodes.
• Pain from appendicitis is referred to the paraumbilical region and right upper quadrant due to visceral afferent fibers accompanying the lesser splanchnic nerves to T10-T11 dorsal root ganglia.
• As the inflammation progresses, the pain localizes to the right lower quadrant due to irritation of the parietal peritoneum, which is innervated by somatic afferent fibers in T11-12.
• Pain in the right lower quadrant is more severe when moving due to irritation of the peritoneum around the psoas major muscle.

### Diaphragm

• The diaphragm is a dome-shaped muscle that separates the thoracic cavity from the abdominal cavity.
• It is attached to the vertebral column by the right and left crura, the xiphoid process, and the lower six costal cartilages.
• The right dome of the diaphragm is higher than the left.
• The diaphragm is innervated by the phrenic nerves.
• The diaphragm receives blood supply from the inferior phrenic arteries.

Structures passing through the diaphragm

• The aorta, thoracic duct, and azygos vein pass through the diaphragm at the level of T12.
• The esophagus, vagal trunks, and IVC pass through the diaphragm at the level of T10.
• The right phrenic nerve and IVC pass through the diaphragm at the level of T8.
• The left phrenic nerve pierces the diaphragm through the muscular part.
• The greater, lesser, and least splanchnic nerves, hemi-azygos vein, sympathetic chains, and quadratus lumborum pass through the crura.

Posterior abdominal wall

• The posterior abdominal wall is formed by the lumbar vertebra, sacrum, pelvic bones, and ribs (11 - 12).
• The posterior abdominal wall is covered by the quadratus lumborum, psoas major, psoas minor, and iliacs muscles.

Aorta

• The aorta begins at T12 and bifurcates at L4 into the common iliac arteries.
• The anterior branches of the aorta are the celiac trunk, superior mesenteric artery, and inferior mesenteric artery.
• The paired branches of the aorta are the inferior phrenic arteries, middle adrenal arteries, renal arteries, gonadal arteries, and lumbar arteries.

Lymphatics of the abdomen

• Lymphatic vessels passing through the posterior abdominal region collect lymph from abdominal structures.
• Pre-aortic lymph nodes are arranged around the three major blood vessels and drain the foregut, midgut, and hindgut.
• Para-aortic lymph nodes are located on the lateral side of the aorta and receive lymph from the body wall, kidneys, suprarenal glands, and gonads.

Lumbar plexus

• The lumbar plexus is formed by the anterior rami of L1 - L3 (L4) and T12.
• The lumbar plexus is located lateral to the psoas muscle.
• The nerves of the lumbar plexus include the subcostal nerve, iliohypogastric nerve, ilio-inguinal nerve, lateral cutaneous nerve of the thigh, femoral nerve, obturator nerve, and genitofemoral nerve.

Sacral plexus

• The sacral plexus is formed by the anterior rami of S1 - S4 and the lumbosacral trunk.
• The nerves of the sacral plexus include the superior gluteal nerve, pudendal nerve, and inferior gluteal nerve.

Parasympathetic nervous system

• The parasympathetic nervous system has preganglionic nuclei in the cranial and sacral regions.
• Postganglionic ganglia are near or at the organ walls (except in the head).
• The vagus nerve innervates the thoracic and abdominal regions.
• The pelvic splanchnic nerves innervate the hindgut.

Sympathetic nervous system

• The sympathetic nervous system has preganglionic nuclei in the thoracolumbar regions (T1 - L1/2).
• The sympathetic nervous system has postsynaptic ganglia in the para-vertebral sympathetic trunk and the pre-vertebral ganglia (celiac, superior mesenteric, and inferior mesenteric).
• The greater splanchnic nerve innervates the foregut.
• The lesser splanchnic nerve innervates the midgut.
• The lumbar splanchnic nerve innervates the hindgut.

Visceral afferents

• Visceral afferents carry physiological sensations with parasympathetic fibers.
• Visceral afferents carry pain sensations with sympathetic fibers.

Appendix

• The appendix arises from the posteromedial wall of the cecum.
• The tenia coli merge at the base of the appendix.
• The appendix is located one-third of the distance from the anterior superior iliac spine to the umbilicus, a surface marking used for medical diagnosis.
• The appendix receives blood supply from the appendicular artery which branches from the ileocolic artery
• Lymph from the appendix drains to the superior mesenteric nodes.
• Pain sensations from the appendix are referred to the paraumbilical region, right upper quadrant, and T10-T11 dermatomes.
• If the appendix is inflamed, pain is often felt in the right lower quadrant and is worse when lying still.
• The inflamed appendix can irritate the parietal peritoneum and presents sharp pain in the right lower quadrant.
• The inflamed appendix may irritate the peritoneum around the psoas major causing discomfort when lying still.