PORTAL VENOUS SYSTEM:

· Takes blood from the entire abdomen and dumps it into the liver for processing ------> out the Suprahepatic Inferior Vena Cava.

· Abdominal venous drainage ends in the hepatic sinusoids in the liver.

· Approx 67% of the liver's blood is venous blood from the portal vein. The other 33% comes from the hepatic arteries.

· BLOOD IN THE LIVER:

§ Venous Blood Going into the liver: portal vein branches to left portal vein and right portal vein, to go to the respective functional lobes of the liver. Then it further subdivides until it gets to the hepatic sinusoids.

§ Venous blood leaving the liver: Central Vein à Sublobar Veins à Left and right Hepatic Veins àInferior Vena Cava.

· Tributaries

· Blood going to the portal vein: The anastomose of the splenic vein and superior mesenteric vein.

· Inferior Mesenteric Vein: Joins with the Splenic Vein, 60% of the time, and with the Superior Mesenteric Vein, 40% of the time.

· RELATIONS

· Right at the anastomoses of SMV and Splenic Vein, the portal vein passes posterior to the neck of the pancreas. (CLINICAL) Hence tumors in the head and neck of the pancreas can occlude the portal vein.

· Passes posterior to the common hepatic artery, just south of the liver.

· PORTAL TRIAD: Portal Vein, Proper Hepatic Artery, and Common Bile Duct, going through the Porta Hepatis on the posterior side of the liver, between the caudate and quadrate lobes.

· PORTAL HYPERTENSION: Increased blood flow in hepatic portal system, creating increased pressure in the rest of the venous system.

· Occlusion can be prehepatic, intrahepatic, or posthepatic, depending on where the occlusion occurs.

· THE PORTAL VENUS SYSTEM DOES NOT HAVE VALVES.

· Because the portal system has no valves, the blood can flow back on itself, causing an increase in pressure.

· Blood tries to get back to the heart and winds up taking collateral channels, which creates dilation outside the portal system, causing varicose veins. (This is only one cause of varicose veins).

· CAPUT MEDUSAE: Varicosity of the paraumbilical veins, due to severe portal hypertension. They look like somewhat like small snakes on the skin. They radiate in a wheel-like fashion.

· Ascites: Increased fluid in the peritoneal cavity. Can result from the liver's inability to handle increased blood pressure.

· Hemorrhoids: Varicose veins in the anal regions.

· COUGH UP BLOOD: Blood backflow into esophageal plexus could make you cough up (or vomit) blood from portal hypertension. Important clinical diagnostic sign.

· COLLATERAL VENOUS PATHWAYS: In the event of portal hypertension or portal stenosis.

· Paraumbilical Pathway: The paraumbilical vein feeds into the portal vein, in the left lobe the liver.

o These are usually closed off after birth, but in the event of portal hypertension, they can recanalize.

· Umbilical Veins (recanalized) à Inferior Epigastric Veins à Superficial Epigastric Veins -----> IVA / SVC.

· Esophageal Pathway: Blood back flows into the left gastric and eventually makes its way back to the azygos vein.

o Left Gastric Vein à Esophageal Vein (plexus)à Inferior Thyroid Veins (one on each side) à Azygos system of veins

· Caval/Portal Pathway: At the pectinate line is another collateral pathway.

o Upper portion of anal canal drains via Superior Rectal Vein à IMV

o Lower Portion of anal canal drains via MIddle and Inferior Rectal Veins à Caval System.

· PECTINATE LINE: The two venous systems anastomose with each other, so backflow can take the alternative route at that location.

· HEMORRHOIDS:

o INTERNAL HEMORRHOIDS: Hemorrhoids in the upper anal canal caused by varicosities of the superior rectal vein. They are innervated by autonomic nerves and hence are not painful.

o EXTERNAL HEMORRHOIDS: Varicosities of the inferior and middle rectal veins. They are innervated by somatic nerves and are painful.

Three Hiatuses of the Diaphragm:

• Caval Hiatus: Passage for Vena Cava, T8. The highest, most central hiatus, in the central tendon.
• Esophageal Hiatus: T10.
• Aortic Hiatus: The Descending Aorta passes through the diaphragm most posteriorly and inferiorly. T12.
  

Diaphragmatic Crura: Left and Right Crus of the diaphragm, on posterior wall.

• Thoracic Splanchnic Nerves go through the left and right crura of the diaphragm, to enter the abdomen.
  

Lumbocostal Arches (Arcuate Ligaments): The ligaments connecting the diaphragm to the posterior wall. They are condensations of transversalis fascia.

• Median Arcuate Ligament: Passes anterior to the Aorta as it goes through the diaphragm. It creates the Aortic hiatus.
• CLINICAL: At times it can compress the Celiac trunk, below the diaphragm. In this event blood can still circulate via the Pancreaticoduodenal arcade.
• Medial Arcuate Ligament: Overlies the psoas muscle, lateral to the median arcuate ligament.
• It may also be called the psoas fascia.
• RELATION: The sympathetic trunks enter the abdomen immediately posterior to the medial arcuate ligaments.
• Lateral Arcuate Ligament: Ligament around the Quadratus Lumborum muscle. Extends from the transverse fascia of L1 to the 12th rib.
  

Muscles of the Posterior Abdominal Wall:

Psoas Major Muscle: Chief flexor of the thigh and trunk

• Passes all along vertebral column starting at T12.
• Passes deep to the inguinal ligament and attaches to the lesser trochanter of the femur.
• Innervated by L2-L4.
• Contraction: Pulls the body toward the leg, or the thigh toward the body.
  

Iliacus Muscle: Aids the psoas major in flexing the thigh and trunk

• Attaches to the iliac fossa (anterior surface of the iliac bone).
• Inserts into psoas tendon, and hence the two muscles together are often called the iliopsoas muscle.
  

Quadratus Lumborum: Stabilizes the 12th (floating) rib during inspiration.

• Inserts on the 12th rib.
  

Thoracolumbar Fascia: Actually an extension of the aponeuroses of the transversus abdominis and external abdominal oblique muscles.

• It divides into an anterior plane and posterior plane. It thus serves to compartmentalize the muscles, which lies in between the two planes.
• Anterior plane attaches to the transverse process of the lumbar vertebrae.
• Posterior plane attaches to joins with the other muscles in the back.
  

Nerves of the Posterior Wall:

• Things common to all the nerves: CLINICAL
• They are all related to the psoas muscle. Psoas pathology will irritate those nerves. A patient that relieves pain upon relaxation of the psoas muscle may have retroperitoneal pathology.
• All of the nerves pass from the posterior to wall laterally to the anterior wall.
• Subcostal and lumbar plexus pass through the transversalis fascia and then go in-between the transversus abdominis and internal oblique muscles.
• Subcostal Nerve: T12
• Associated with the 12th (floating) rib.
• This nerve is immediately posterior to the kidney and overlies quadratus lumborum muscle.
• It is the only nerve of the lower posterior wall not associated with the lumbar plexus.
  

• Lumbar Plexus: L1-L3, and the upper half of L4.
• These are spinal nerves, so they have somatic and autonomic branches.
• Somatic Components: Supply iliopsoas and quadratus lumborum muscles.
• Autonomic Components: The lumbar splanchnic nerves.
• Location: The plexus itself is located deep within the psoas muscle.
• Distribution: Lower abdominal wall, genitalia, upper portion of the lower limb
• Nerves of the lumbar plexus:
• Iliohypogastric Nerve: T12-L1.
• Runs superomedial to the Anterior Superior Iliac Spine.
• CLINICAL: Passes over McBurney's Point -- the point of surgical entry for an appendectomy (about 1/4 of the way between the ASIS and umbilicus). It can thus be damaged from an appendectomy.
• In the suprapubic region, it divides into two portions: Iliac Branch and Hypogastric Branch.
• Distribution: Iliac branch gets sensory info from hip. Hypogastric branch innervates the suprapubic region.
• Passes posterior to kidney and overlies quadratus lumborum muscle.
• Sometimes it will be joined with the ilioinguinal nerve from their origin at L1, and sometimes it won't.
• Ilioinguinal Nerve: L1
• Same location as the iliohypogastric. It passes through the inguinal canal and emerges out of the inguinal ring.
• Distribution: Innervates the anterior scrotum / labia majora, and the upper and medial thigh.
• CLINICAL: If you want to anesthetize the pubic area, this is one of the nerves you have to block. Anesthesia would probably be placed in the inguinal canal.
• It maybe joined with genitofemoral nerve.
• Passes posterior to kidney and overlies quadratus lumborum muscle.
• Lateral Femoral Cutaneous Nerves: L2-L3
• Associated with the lateral aspect of the psoas muscle.
• Considered to be a part of the posterior division of the plexus. Has nothing to do with the abdominal cavity.
• Innervates the posterior and lateral thigh.

• Femoral Nerve: L2-L4

• By far the largest branch of the lumbar plexus.
• Location: Located in the cleft between the psoas and iliacus muscles.
• Runs posterior to inguinal ligament and carries fascia with it -- the femoral sheath.
• Distribution: Motor innervation of psoas and iliacus; innervation of the thigh and lower extremities.
• Genitofemoral Nerve: L1-L2
• Location: Anterior surface of the psoas muscle. Very fine string, "ribbon."
• Distribution: Branches into the genital and femoral branches.
• Genital branch goes through inguinal nerve to inguinal canal. It innervates the cremaster muscle.
• Femoral Branch: Innervates skin in upper portion of the thigh.
• CLINICAL: Cremaster Reflex: Gently touch the medial portion of the thigh, and see if the scrotum pulls the testes up. This is a simple way of testing the functionality of the lumbar plexus.
  

§ Obturator Nerve: L2(?), L3-L4

• Deep, medial border of the psoas muscle. Very tight chord that passes along the lateral part of the pelvic wall.
  

• Lumbosacral Trunk: L4-L5
  

• Deep and medial to psoas and obturator nerve.
• Distribution = sensory, to the gluteal region, thigh, leg.
• Not part of the lumbar plexus.

• CNS: The brain and the spinal chord.
• Peripheral Nervous System: All other nerves, consisting of the Autonomic Nervous System (ANS) and Somatic Nervous System (SNS).
• Autonomic Nervous System: Involuntary innervation of visceral structures.
• Innervates smooth (involuntary) muscle, cardiac muscle, and glands.
• GVE: General Visceral Efferent -- Responsible for motor function to visceral tissues.
• "Efferent" refers to flow from CNS to tissues, so that they will stimulate or effect a response.
• GVA: General Visceral Afferent -- responsible for sensory function from visceral tissues.
• "Afferent" refers to flow from the tissues back to the CNS, so they carry the impulse away from the stimulus.
• These are made up primarily of stretch receptors, so that inflammation or distension of organs can be sensed.
• Somatic Nervous System: Voluntary innervation of somatic structures (skeletal muscles and skin).

· GSE: General Somatic Efferent -- responsible for motor function to somatic tissues.

· GSA: General Somatic Afferent -- responsible for sensory function from somatic tissues.

Types of Nerves fibers: There are many types of nerve fibers in a single nerve bundle.

• Motor Fibers
• Sensory Fibers
• Pain receptors -- originating from somatic structures.
• Temperature -- originate from somatic structures.
• Stretch receptors -- originating from visceral structures. These are important to visceral structures, as they constitute the main sensory input from the organs.

MIXED NERVE: Nerves such as vagus and phrenic carry both afferent and efferent fib3ers, and both somatic and autonomic. Therefore they are mixed nerves.

REFERRED PAIN: The interpretation of dermatomal layers in the brain is responsible for the concept of referred pain.

• Sensory input from the visceral organs is interpreted by the brain as originating from one of the dermatomal segments. The brain oversimplifies the stimulus as coming from a cutaneous layer.
• Take Appendicitis as an example:
• Inflamed appendix sends an impulse to T10, which is then sent to brain to be processed.
• Umbilical cutaneous dermatomal region also goes to T10, and in the past the brain has received more info from this region, so it "assumes" that the appendix signal is coming from such a region.
• So, there is an initial referred dull (visceral) pain in the umbilical region.
• Then if the appendix inflames enough to pierce or press against the anterior wall, it will stimulate pain-afferent nerves in the lower right quadrant, so that will create a sharp (somatic) pain in the region of the appendix.
• These two signs together could be taken as signs of appendicitis.

STRUCTURE OF PARAVERTEBRAL GANGLIA:

• Dorsal Root Ganglion: They have afferent (incoming sensory) nerves.
• Two afferent nerves come in -- one from the peripheral tissues and one from the central canal.
• Ventral Root Ganglion: Carries efferent fibers out to the periphery.
• Spinal Nerves form where these two roots come together, to form both sensory and motor fibers in the same nerve.
• All spinal nerves are mixed nerves!
• Soon after forming, the spinal nerve divides into two nerves -- the pre-ganglionic nerves.
• Dorsal primary ramus -- innervates muscles and skin of back.
• Ventral primary ramus -- innervates lateral and anterior.
• Ventral Primary Ramus goes to the White Rami Communicans on the sympathetic chain.
• So the White Rami carries the efferent pre-ganglionic nerves.

• Once the nerve-fiber reaches the sympathetic trunk, it has several options:
• It can synapse with a Grey Rami Communicans and continue as a Sympathetic spinal nerve going out to target viscera.
• It can ascend to a higher level in the sympathetic chain.
• It can descend to a lower level in the sympathetic chain.
• It can pass through and out of the paravertebral ganglion without synapsing, and then continue onto a target organ as a splanchnic nerve -- to go to visceral target organ and form a visceral plexus -- or branch somewhere nearby, like celiac or superior mesenteric arteries.