Human Anatomy Chapter on Liver and Vascular System

Abdominal Cavity Organs

• The abdominal cavity is bordered by abdominal walls, diaphragm, and pelvis.
• It forms the major portion of the abdominopelvic cavity, which is continuous with pelvic cavities.
• It contains most digestive organs, spleen, kidneys, and ureters.

Digestive Tract

• The viscera of the abdomen make up most of the digestive tract.
• The digestive tract components are listed in the figure.

Abdominal Quadrants

• The abdomen is often divided descriptively into four quadrants by imaginary vertical and horizontal lines that cross at the umbilicus.
• Each quadrant contains specific organs. Right upper quadrant (RUQ) contains liver, gall bladder, pylorus, duodenum, hepatic flexure of colon, and head of pancreas. Left upper quadrant (LUQ) contains spleen, splenic flexure of colon, stomach, body & tail of pancreas. Right lower quadrant (RLQ) contains terminal ileum, cecum, appendix, ascending colon, and right ovary. Left lower quadrant (LLQ) contains descending colon, sigmoid colon, and left ovary.

Abdominal Regions

• The abdomen can be subdivided into nine regions for more precise localization of organs. These regions are epigastric, right hypochondriac, left hypochondriac, umbilical, right lumbar, left lumbar, hypogastric/suprapubic, right iliac/inguinal, and left iliac/inguinal.

Peritoneum

• The peritoneum consists of parietal peritoneum (lining the abdominopelvic cavity) and visceral peritoneum (investing the viscera).
• The peritoneal cavity is the potential space between parietal and visceral peritoneum, containing a small amount of peritoneal fluid (~50mL).
• The space is closed in males and females with an opening for oocytes to travel from ovaries to fallopian tubes.

Peritoneum: Mesentery & Ligaments

• Mesentery is a double layer of peritoneum that encloses an organ and connects it to the posterior abdominal wall, providing pathways for nerves, vessels, and lymphatics.
• Peritoneal ligaments are another double layer of peritoneum that connect one organ to another or to the abdominal wall.

Intraperitoneal vs. Retroperitoneal Organs

• Retroperitoneal organs are partly external to the peritoneal cavity and posterior to the peritoneum. They are connected to the abdominal wall. Examples are kidneys.
• Intraperitoneal organs are completely within the peritoneal sac and are almost entirely invested by visceral peritoneum. Examples of these are stomach and liver.

Intraperitoneal Organs

• This list gives examples of intraperitoneal organs: Liver, Tail of Pancreas, Spleen, Stomach, Portion of Duodenum(1st part), Jejunum & Ileum, Cecum, Appendix, Sigmoid Colon, and Upper 1/3 of Rectum.

Retroperitoneal Organs

• This list provides examples of retroperitoneal organs: Suprarenal glands, Aorta/IVC, Parts of Duodenum(2nd, 3rd, 4th part), Pancreas (except tail), Ureters, Colon (Ascending and Descending only), Kidneys, Esophagus, and Rectum. Use "SAD PUCKER" as a memory aid.

Liver

• The liver has four anatomical lobes: Right, Left, Quadrate, and Caudate.
• The liver is divided into 8 surgically resectable hepatic segments, each supplied by tertiary branches of the portal triad (portal vein, hepatic artery, and bile duct).
• Liver functions: Detoxification, glycogen storage, hormone production, plasma protein synthesis, and bile production.
• The liver can be divided into 4 anatomical lobes, right, left, quadrate, and caudate.
• The bare area portion of the liver sits directly against the diaphragm and is not covered by peritoneum.
• Ligaments associated with the liver include the falciform ligament, coronary ligaments, right and left triangular ligaments, and the round ligament. The round ligament is a fibrous remnant of the umbilical vein.

Liver: Blood Supply

• Hepatic portal vein brings 75-80% of blood to liver containing nutrients absorbed by Gl tract, formed by superior mesenteric vein & splenic vein, and terminates by dividing into right & left branches.
• It carries absorbed nutrients or other substances

Portal Venous System

• The portal venous system carries blood from GI visceral structures to the liver. The hepatic portal vein is formed by superior mesenteric vein & splenic vein. It typically sends blood to the liver for filtration.

Caval Venous System

• The caval venous system drains blood from structures of posterior abdominal wall, kidneys, suprarenal glands, gonads, pelvic region, and lower limbs.
• This blood bypasses the liver en route to the right atrium of the heart.
• The inferior vena cava is formed by union of left & right common iliac veins.

Portal-Caval Anastomoses

• Anastomoses between caval and portal veins enable collateral circulation in cases of liver or portal vein obstruction.
• Different anastomotic connections (points where veins meet or communicate) may or may not form as a result of obstruction.

Stomach

• The stomach stores and chemically and mechanically breaks down food.
• Four parts of the stomach are cardia (first part), fundus (dome-shaped superior portion), body (largest/middle section), and pylorus (terminal end).
• Ligaments connected to the stomach are greater omentum (double-layered peritoneal sheet), gastrosplenic ligament (connects stomach to spleen), gastrophrenic ligament (connects stomach to diaphragm), gastrocolic ligament (apron-like part of greater omentum, connects stomach to transverse colon), hepatogastric ligament, and hepatoduodenal ligament.

Small Intestine

• The small intestine is the primary site of nutrient absorption and consists of duodenum, jejunum and ileum.
• Duodenum is C-shaped and short (about 1 foot).
• Jejunum is ~8 feet
• Ileum is ~12 feet
• Small intestine is divided into 3 parts: Duodenum (first/shortest part), Jejunum, and Ileum.

Small Intestine: Mesentery

• The small intestine's mesentery is a fan-shaped peritoneum fold that attaches the jejunum and ileum to the posterior abdominal wall—carrying blood vessels, lymphatics, and nerves.

Pancreas

• The pancreas is an accessory digestive gland located behind the stomach between the duodenum and spleen.
• It produces pancreatic juice (exocrine secretion) that enters the duodenum & endocrine secretions (glucagon & insulin)
• The pancreas is divided into Head, Neck, Body, and Tail.

Large Intestine

• The large intestine absorbs water and electrolytes, produces and absorbs vitamins, and propels feces toward the rectum for elimination. It consists of Cecum, Ascending colon, Transverse colon, Descending colon, Sigmoid colon, & Rectum.

Kidneys

• Kidneys remove excess water, salts, and wastes from the blood and return nutrients and chemicals to the blood. They lie retroperitoneally on the posterior abdominal wall.
• They are positioned on either side of the vertebral column at the level of T12-L3.
• The left kidney is slightly more superior than the right kidney.
• The different capsules surrounding the kidneys include fibrous capsule, perinephric fat, renal fascia, and paranephric fat.

Blood Supply (of Foregut, Midgut, and Hindgut)

• The foregut is supplied by Celiac Trunk.
• The midgut is supplied by Superior Mesenteric artery.
• The hindgut is supplied by Inferior Mesenteric artery.

Celiac Trunk

• The Celiac Trunk arises from the abdominal aorta at T12 level. The Celiac Trunk branches into Left Gastric artery, Splenic artery, and Common Hepatic artery.

Superior Mesenteric Artery (SMA)

• Arises from abdominal aorta at L1 level and runs between the layers of the mesentery. Its branches include ileocolic, right colic, middle colic, and intestinal arteries.

Inferior Mesenteric Artery (IMA)

• Arises from the abdominal aorta at L3 level. This artery provides a supply of blood for descending colon, sigmoid colon, and the superior rectum.

Innervation (of Abdominal Organs)

• Sympathetic innervation is involved in inhibiting peristalsis, constricting blood vessels to GI, and contracting internal anal sphincters.
• Parasympathetic innervation is involved in promoting peristalsis, secretion of digestive juices, and relaxing internal anal sphincters.

Splanchnic Nerves: Sympathetic and Parasympathetic

• These nerves carry both visceral efferent & visceral afferent fibers to/from organs in the abdominopelvic cavities.
• Sympathetic pathways run through cardiopulmonary, abdominopelvic, greater, lesser, least, lumbar and sacral splanchnic nerves.
• Parasympathetic pathways run through pelvic nerves as presynaptic parasympathetic pathways.

Autonomic Plexuses

• Include abdominal aortic plexus (celiac, superior, inferior mesenteric & renal).
• Superior and Inferior hypogastric plexuses carry autonomic innervation.

Ganglia

• Prevertebral/preaortic/collateral ganglia include celiac, aorticorenal, superior, and inferior mesenteric ganglia.

Parasympathetic Nervous System

• The parasympathetic system involves presynaptic neurons in cranial nerve nuclei (III, VII, IX, X) & sacral region (S2-S4) and postsynaptic neurons near or within target organs.