Posterior abdominal wall and retroperitoneal organs Flashcards
Kidneys and suprarenal glands
-Produce urine that is conveyed by the ureters to the urinary bladder in the pelvis
-The suprarenal glands function as part of the endocrine system and have completely different functions from the kidneys despite their close proximity
-Both kidneys and suprarenal glands are primary retroperitoneal structures
Kidney position
-Kidneys are positioned relatively superiorly in the abdominal cavity (T12-L3, overlap the 11th and 12th ribs)
-The renal hilum is situated at the L1-2 level
-Usually the right kidney is lower than the left due to the space occupied by the liver
Relations of the kidney
-Liver, duodenum and maybe ascending colon are anterior to the right kidney
-Stomach, spleen, pancreas and the descending colon are anterior to the left kidney
-The suprarenal glands are typically located superomedially to the kidneys
Surface of kidney
-In addition to being retroperitoneal, kidneys are also surrounded by a large amount of perinephric fat.
-Surface of the kidney is covered by a thin renal fibrous capsule.
Renal hilum
-The renal hilum is the entrance and exit for structures that serve the kidneys
-The hilum of the left kidney lies near the transpyloric plane
-This plane passes through the superior pole of the right kidney
-At the hilum, the renal vein is anterior to the renal artery
Interior of kidney
-When sectioned, the renal pelvis can be seen as the superior expansion of the ureter
-Renal pelvis receives 2/3 major calyces, each of which receives 2/3 minor calyces
-Each minor calyx is indented by a renal papilla, the apex point of the renal pyramid, from which the urine is excreted
-The renal tissue consists of inner medulla, which has renal pyramids and an outer cortex that forms the renal columns between the pyramids
Suprarenal glands
-2 parts: the cortex and medulla
-These have different embryological origins and different functions
-Cortex secretes corticosteroids and androgens. These hormones cause the kidneys to retain salts and water in response to stress, increasing the blood volume and blood pressure
-The medulla has chromaffin cells that secrete mainly adrenaline and nonadrenaline into the bloodstream to active the flight or fight status
Blood supply of kidney and suprarenal glands
-Renal arteries (L1/2) and veins supply the kidneys
-Each artery divides close to the hilum into five segmental arteries
Arterial branches supplying suprarenal glands arise from 3 sources:
-Superior (6-8) from the inferior phrenic arteries
-Middle from the abdominal aorta near where SMA is
-Inferior from the renal arteries
Left suprarenal vein vs right suprarenal vein
-Right suprarenal vein drains into the IVC
-Left suprarenal vein drains into the left renal vein then the IVC
-Left renal vein is longer than the right renal vein
-The SMA descends anterior to the left renal vein
Nerve supply of suprarenal gland
-Nerve supply to suprarenal glands is from the suprarenal plexus. This plexus receives fibres from the coeliac ganglion and aorticorenal ganglion
-However, the sympathetic innervation of the suprarenal medulla is exceptional because the suprarenal medulla is like a sympathetic ganglion itself.
-The chromaffin cells in the medulla receive preganglionic sympathetic fibres directly
-The suprarenal cortex is activated by adrenocorticotropic hormone (ACTH) from the anterior pituitary gland.
Sympathetic and parasympathetic outflow
-Abdominal viscera are supplied by autonomic nerve fibres
-The preganglionic sympathetic and parasympathetic fibres are delivered by several splanchnic nerves and the vagus nerve to the abdominal aortic plexuses and associated sympathetic ganglia
-The peri-arterial extensions of these plexuses deliver postganglionic sympathetic fibres and the continuations of parasympathetic fibres to the abdominal organs, where parasympathetic synapses occur.
-Another source of parasympathetic fibres comes from the pelvic splanchnic nerves (S2-4)
Prevertebral ganglia
-The greater, lesser and least splanchnic nerves convey preganglionic sympathetic fibres to the coeliac, superior mesenteric and aorticorenal sympathetic ganglia
-The lumbar splanchnic nerves convey preganglionic sympathetic fibres to the inferior mesenteric ganglion. It is within these ganglia that the preganglionic sympathetic fibres synapse.
-Parasympathetic fibres are conveyed to the coeliac, superior mesenteric and aorticorenal ganglia by the vagal trunks (predominantly posterior) and to the inferior hypogastric plexus by the pelvic splanchnic nerves
Periarterial plexuses and their destinations
-These are the abdominal aortic plexuses and associated sympathetic ganglia.
-These plexuses are what give rise to peri-arterial plexuses that reach corresponding organs via the branches of the abdominal aorta that supply them
Visceral sensory innervation
-Visceral afferent fibres convey pain sensations accompany the sympathetic visceral efferent fibres
-These visceral afferent fibres pass retrogradely to those of the motor fibres along the peri-arterial plexuses, prevertebral ganglia, splanchnic nerves and to the sympathetic chain
-They then pass into the posterior root to the spinal sensory ganglia and spinal cord
What are the major structures of the posterior abdominal wall?
-Five lumbar vertebrae and their intervertebral discs
-Psoas, quadratus lumborum, iliacus, posterior portions of the oblique and transversus abdominis muscles
-Diaphragm
-Lumbar plexus
-IVC and abdominal aorta
Lumbar vertebrae anatomy
-5 lumbar vertebrae found between the thoracic and sacral segments of the vertebral column
-They are for weight bearing so are generally larger and more robust/sturdy
Differences between the thoracic and lumbar vertebrae
Muscles of posterior abdominal wall
Quadratus lumborum
Action: Laterally flexes vertebral column
Innervation: Subcostal nerve (T12)
Psoas major + iliacus (iliopsoas)
Action:
Psoas – unilateral contraction flexes the vertebral column laterally
Psoas – bilateral contraction raises the trunk from the suspine position
Iliopsoas– hip joint flextion
Innervation:
Psoas – L1-L4 spinal nerves
Iliacus – Femoral nerve (L2-4)
Lumbar plexus
-This nerve network is composed of the anterior rami of L1 to L4 spinal nerves
-The ilioinguinal and iliohypogastric nerves arise from anterior ramus of L1. They supply the anterolateral abdominal muscles and skin of the inguinal and pubic regions
-The genitofemoral nerve pierces the psoas major and runs inferiorly on its anterior surface. The genital branch supplies skin over the scrotum/labia majora but also the cremaster muscle in male
Gonadal vessels
-The abdominal aorta begins at the aortic hiatus and ends at the level of L4 vertebra by dividing into left and right common iliac arteries
-Gonadal arteries are branches of the abdominal aorta
-The IVC begins at the level of L5 vertebra by the union of left and right common iliac veins
-The IVC receives the right gonadal vein directly whereas the left gonadal vein drains into the left renal vein
Renal vein entrapment syndrome
-The left renal vein may get compressed by the SMA during its course to the IVC
-This causes renal vein entrapment syndrome
-Causing left testicular pain in men resulting in left testicular varicocele
