Posterior body wall
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Fall 1999 Moore, pp280-308

Lecture 20 Dr. C. Dlugos

Overview: We have discussed the anterior abdominal wall and the viscera within the abdominal cavity concerned mainly with the digestion of foodstuffs. In this lecture, the muscles forming the cranial and the posterior walls of the abdominal cavity will be described as well the retroperitoneally located kidneys, the major components of the excretory system. The nerves within the posterior wall, in particular the autonomics, will also be described, as will referred pain, the modality which aids the physician in localizing pain within a visceral organ.

Objectives:

1. knowledge of the gross anatomy of the kidneys

2. knowledge of the embryology and adult anatomy of the diaphragm

3. knowledge of the muscles of the posterior body wall

4. review of the autonomics of the abdominal wall and specifics concerning the dermatomal origin of referred pain.

Embryology (Moore, pp288-289, Sadler 272-279): Kidney tissue is derived from the intermediate mesoderm in the embryo (Figure 15.1, p273). Three kidneys including the pronephros, the mesonephros, and the metanephros are formed in the human at subsequent developmental stages. The pronephric and mesonephric kidneys degenerate. The mesonephric kidney leaves some tubular remnants. The mesonephric duct, a derivative and caudal extension of the pronephric duct, forms the ureteric bud. The vas or ductus deferens in the male also forms from the mesonephric duct. The adult kidneys are developed mainly from the metanephric kidneys which form in the 5^th week of embryonic life.The undifferentiated metanephros forms the nephrons (Sadler Fig.15.6.) while the collecting system (collecting ducts, calyces, and renal pelvis and ureter) is formed from the mesonephric duct (Fig. 15.4. p276) and called the ureteric bud. Unlike the gonads which descend during development, the mesopnephric kidneys originate within the lower lumbar and sacral regions and "ascend" presumably due to a decrease in body curvature and a growth of the body in the sacral and lumbar regions.

The adult location of the kidneys is at vertebral level T12 through L3 (Moore 2.60., p281, 2.61., p282 ). The right kidney is slightly lower than the left kidney due to the position and size of the liver. The adult kidney lies retroperitoneally in a mass of perirenal fat ensheathed by renal fascia. This fascia is attached to the diaphragm superiorly, to the psoas muscle posteriorly, to the inferior vena cava and the aorta medially and to the ureter inferiorly . Because the renal fascia blends with the ureteric fascia, kidney infections may spread to the pelvis. The abdominal wall immediately posterior to the kidney is formed mainly by the quadratus lumborum but the psoas major contacts the kidney on its medial surface.

Regions:

1. Surfaces: anterior and posterior

2. Margins;

a. medial, indented or concave, vessels and ureter enter and leave in the anterior to posterior order from the hilus (renal vein, renal artery, ureter).

b. lateral, convex

3. Poles

a. superior, surprarenal or adrenal gland positioned on superior pole

b. inferior

4. Gross anatomy: ( Moore,Fig. 2.64.,p 285) The kidneys are covered by the renal capsule. Hemisection of the kidney reveals an outer cortex and an inner medulla. Structural subdivisions of the cortex cannot be viewed without a microscope but the medulla is divided grossly into renal pyramids with the renal columns in between adjacrnt pyramids. The tip of each pyramid or renal papilla provides a route of entry for the urine into the minor calyces. Several minor calyces unite to form major calyces which dump the urine into the expanded portion of the ureter, the renal pelvis. Typically humans have 2 to 3 major calyces and 7- 14 minor calyces.

Anterior relationships:

1. Right kidney: (Moore, Fig. 2.63., p284) The superior pole of the right kidney is related to the inferior surface of the liver. The descending part of the duodenum passes across the hilum of the right kidney and the right colic flexure (hepatic flexure) lies anterior to its lateral border and inferior pole.

2. Left kidney: (Moore, Fig.2.63. p284). This kidney is related anteriorly to the suprarenal gland, the stomach, the spleen, pancreas, jejunum, and the descending colon. The left kidney lies in the stomach bed.

Blood Supply:

1. Arterial supply. (Moore, Fig.2.66., p287) The renal arteries arise from the abdominal aorta below the superior mesenteric artery. The renal artery divides into a large anterior and a small posterior branch at the kidney hilus. The anterior branch subdivides further into the apical (superior), upper (anteriosuperior), middle (anterioinferior), and inferior branches. Due to the ascent of the kidneys from the pelvis, anomalies within the vessels are common. Accessory renal arteries form from the aorta as the kidney ascends and are frequently present causing clinical problems when they obstruct the ureter.

2. Venous drainage. The right and left renal veins enter the inferior vena cava.

3. Innervation: Sympathetic little or no parasympathetic

 

 

Ureters (Fig. 3.13, p357)

Gross anatomy: retroperitoneal tubes, 25 cm in length. The ureter begins at the funnel shaped renal pelvis and ends at the urinary trigone within the urinary bladder. In three regions, the ureters are constricted: 1) the transition from pelvis to ureter, 2) the pelvic inlet where it crosses the iliac vessels and 3) the entry to the urinary bladder. These regions have clinical significance since ureteric calculi (kidney stones) can become lodged there.

Arterial supply: Renal, gonadal (testicular or ovarian) and abdominal aorta.

Suprarenal glands: (Moore, Fig.2.65.,p286). The suprarenal glands lie on the superior pole of each kidney. The left suprarenal gland is semilunar in shape and extends more inferiorly than the right one. Each gland is covered by fat and enveloped by renal fascia. The suprarenal gland can be readily separated from the kidney because a layer of renal fascia is interposed between the two organs.

Structure:Embryologically, the suprarenal is derived from mesoderm (cortex) and ectoderm (medulla) and ,thus, is really two glands in one.

cortex-outer layer produces steroid hormones

medulla-inner layer, receives preganglionic sympathetic fibers from the sympathetic trunk via the greatest splanchnic nerve, secretes catecholamines mostly adrenalin or epinephrine. These substances help the sympathetic portion of the nervous system in meeting fright,

flight , or fight situations.

Arterial supply Three branches, superior suprarenal artery from the inferior phrenic artery, middle suprarenal artery from the aorta, and the inferior suprarenal artery from the renal artery

Venous drainage The right suprarenal vein is a tributary of the inferior vena cava, the left suprarenal vein drains into the renal vein.

Diaphragm (Moore, Fig.2.68, p291 and 2.69, p292 ).

Embrology: The diaphragm in the adult is formed from: (1) the septum transversum; (2) the pleuroperitoneal membranes; (3) the mesentery of the esophagus. (Sadler, Fig.11.6, p179).

1. sternal portion, from xiphoid process

2. costal portion, internal surface of lower six ribs and costal cartilages

3. lumbar part, arises from lumbar vertebrae by the right and left crura which attach to the upper two lumbar vertebrae and surround the aorta. The crura of the diaphragm unite with the anterior longitudinal ligament of spinal column.

4. Central tendon of the diaphragm, a sheetlike aponeurosis which has no bony attachments but is fused to the inferior surface of the fibrous pericardium.

Innervation of the diaphragm: The phrenic nerve (ventral rami of C3,4,5)

Ligaments of the diaphragm: (Moore, Fig.2.68., p291)

1. median arcuate ligaments, unites crura opposite the disc of T12 and L1 vertebrae

2. medial arcuate ligament, crura of diaphragm to transverse process of L1 vertebrae

3. lateral arcuate ligaments, tranverse process of L1 to twelfth rib. Superior to this ligament, lies the vertebrocostal triangle , a region where the diaphragm is so thin, that it produces a potential herniation spot. Most diaphragmatic ruptures occur in this area.

Apertures of the diaphragm

1. Inferior vena cava foramen through the central tendon, vertebral level T8

2. Esophageal hiatus, anterior and posterior vagal trunks, vertebral level T10

3. Aortic hiatus, thoracic duct, vertebral level T12

Arterial supply to the diaphragm: The thoracic or superior surface of the diaphragm is supplied by branches from the thoracic aorta,and the musculophrenic and pericardiophrenic arteries from the internal thoracic artery. The abdominal or inferior surface of the diaphragm is supplied by the inferior phrenic arteries (abdominal aorta).

ILIOPSOAS two muscles, the iliacus and the psoas major, share common insertion and action but are not one due to their separate innervation and embryologic origin (Moore, Fig.2.74.,p298)

Proximal Attachment:

1. transverse processes of lumbar vertebrae

2. bodies and discs of T12-L5

Distal Attachment: lesser trochanter of femur

Innervation of psoas major: ventral branches of lumbar nerves

Proximal Attachment: iliac fossa, iliac crest, sacral ala, anterior sacroiliac liagaments

Distal Attachment

1. lesser trochanter of the femur

Innervation of iliacus: femoral nerve

Action of iliopsoas flexes thigh on hip

PSOAS MINOR: present in only 50-60% of humans , muscle deteriorating as evolution progresses, such muscles are marked by long tendons and short bellies.

Proximal Attachment: sides and bodies of vertebrae T12 and L1

Distal Attachment: pectineal line and iliopectineal eminence

Innervation: ventral branches from L1

QUADRATUS LUMBORUM (Moore, Fig.2.74., p298).

Proximal Attachment: 12th rib and lumbar transverse processes

Distal Attachment: iliolumbar ligament and internal lip of iliac crest

Action: extends and laterally flexes vertebral column

Innervation: ventral branches of T12 and L1-4.

Lumbar plexus: formed within the psoas major muscle by the ventral rami of L1-4.(Grants. 2.103, p138)

Branches of lumbar plexus:

1. Iliohypogastric nerve (L1), sensory for skin over buttocks and anterior abdominal wall above pubic symphysis

2. Ilioinguinal nerve (L1), sensory, passes through superficial inguinal ring and supplies groin, scrotum,and labia majora

3. Genitofemoral nerve (L1,2). Genital branch supplies cremaster muscle and scrotum in males and the labia majora in females. The femoral branch is sensory to the skin of the femoral triangle.

4. Lateral femoral cutaneous nerve (L2,3) skin over anterior and lateral parts of thigh

5. Femoral (L2,3,4) Iliacus and anterior compartment of the thigh

6. Obturator (L2,3,4), pierces obturator foramen, and supplies adductor muscles of thigh.

Additional nerves: On the posterior body wall, there are also located the subcostal nerve (T12) and the lumbosacral trunk (ventral rami of L4 (inferior portion only),L5, and S1, 2, and 3. Neither of these is a branch of the lumbar plexus.

Abdominal Autonomics (Grants, Fig.274B, p298).

Most abdominal organs receive both sympathetic and parasympathetic fibers. These fibers tend to congregate around arteries forming nerve plexuses as previously described. For example in the abdomen:

1. celiac plexus; surrounds celiac artery and innervates stomach, liver, pancreas, gallbladder, spleen, and parts of the duodenum

2. the superior mesenteric plexus; surrounds superior mesenteric artery and supplies part of duodenum, remaining small intestine and large intestine to proximal 2/3 of transverse colon

3. the inferior mesenteric plexus; 1/3 of transverse colon, remaining large intestine and rectum.

Sympathetic Nerves: preganglionic fibers originated in thoracic sympathetic trunk, pass through the crura of the diaphragm as the splanchnic nerves and synapse in ganglia located in conjunction with plexi near a major abdominal vessel (eg. solar plexus)?

Four groups of sympathetic splanchnic nerves are important in the abdomen:

Greater splanchnic nerve (T5-9): most preganglionic fibers from this nerve synapse in the celiac ganglia. From the celiac ganglia, postganglionic fibers are distributed with the celiac plexus and communicate with the superior and inferior mesenteric plexuses. Some preganglionic fibers of the greater splanchnic nerve do not synapse in the celiac ganglia but terminate in the adrenal medulla. The adrenal medulla is exceptional since postganglionic sympathetic fibers are totally absent.

Lesser splanchnic nerve (T9-11): Preganglionic fibers from this nerve synapse in the aorticorenal ganglia and join the superior mesenteric plexus.

Least splanchnic nerve (also lowest) (T12): Preganglionic fibers terminate in renal plexus, supply renal arteries and ureters.

Lumbar splanchnic nerves: (L1, 2, (3 ?) preganglionic sympathetics which synapse in the inferior mesenteric ganglia. and provide sympathetic innervation to colon and pelvic viscera.

Parasympathetic Nerves: are found in plexuses and are distributed as follows

1. Vagus: supplies all of abdominal viscera including proximal 2/3 of transverse colon,

2. Pelvic splanchnics: arise from intermediolateral cell column (lateral horn) of S2,3,4 and are distributed to inferior mesenteric plexus, supplies distal 1/3 of transverse colon, remaining large intestine, and rectum.

Referred visceral pain: radiates to dermatomes supplied by somatic sensory fibers associated with the same segment of the spinal cord which received visceral sensory fibers from the affected organ. For example:

Pain in the:

1. diaphragm is referred to dermatome C3,4,5

2. heart is referred to C8-T5

3. stomach is referred to dermatomes T6-9

Therefore, the brain "misdiagnoses" abdominal pain and it is the role of the physician to determine the affected viscera.

Lymphatics of abdomen: (Grants,)

1. Visceral lymph nodes: from abdominal viscera drain into nodes situated along unpaired visceral branches of the aorta

2. Lumbar lymph nodes: receive drainage from the kidneys, testes, ovaries, and posterior body wall and lower limbs through common iliac lymph nodes. Efferent vessels unite to form the right and the left lumbar trunks.

3. The visceral lymph nodes and the lumbar trunks unite at an dilation within the abdomen , the cisterna chyli to form the thoracic duct, the largest lymph vessel in the body. (Moore, Fig.2.77. p307).