S7) Anatomy for Dissection — Liver, Jejunum, Ileum, Colon Flashcards
Describe the anatomical position of the liver
The liver is located in the right hypochondrium and epigastric areas, extending into the left hypochondrium
There are two surfaces of the liver.
Identify them
- Diaphragmatic surface (anterosuperior surface of the liver)
- Visceral surface (posteroinferior surface of the liver)
The diaphragmatic surface is the anterosuperior surface of the liver.
Describe its structure.
- It is smooth and convex, fitting snugly beneath the curvature of the diaphragm
- A section is not covered by visceral peritoneum (‘bare area’) of the liver
The visceral surface is the posteroinferior surface of the liver.
Describe its structure.
- It is irregular and flat due to the presence of surrounding organs
- It lies in contact with the oesophagus, right kidney, right adrenal gland, right colic flexure, duodenum, gallbladder and the stomach
Describe the superior anatomical relations of the liver
Superior to the liver is the diaphragm (separating the abdominal cavity from the thoracic cavity)
Describe the anterior anatomical relations of the liver
Anterior to the liver is the anterior abdominal wall and ribcage
Describe the posterior anatomical relations of the liver
Posterior to the liver are the oesophagus, stomach, gallbladder, first part of the duodenum (the foregut-derived organs)
Describe the structure and function of the various ligaments of the liver
- Structure: formed by a double layer of peritoneum
- Function: attach the liver to the surrounding structures
Identify the 5 ligaments of the liver
- Falciform ligament
- Coronary ligaments
- Triangular ligaments
- Hepatoduodenal ligament
- Hepatogastric ligament
Describe the anatomical position of the falciform ligament
- Attaches the anterior surface of the liver to the anterior abdominal wall
- Its free edge contains the ligamentum teres (a remnant of the umbilical vein)
Describe the anatomical position of the coronary ligaments
- Anterior and posterior folds
- Attach the superior surface of the liver to the diaphragm
Describe the anatomical position of the triangular ligaments
- Left and right ligaments
- Attach the superior surface of the liver to the diaphragm
What does the lesser omentum consist of (in relation to the liver)?
- Hepatoduodenal ligament attaches the liver to the duodenum
- Hepatogastric ligament attaches the liver to the stomach
Describe the attachment of the liver to the inferior vena cava
The posterior surface of the liver is secured to the inferior vena cava by hepatic veins and fibrous tissue
What is the name of the fibrous layer covering the liver?
Glisson’s capsule
The liver is divided by the attachment of the falciform ligament.
Identify the individual lobes formed
Two ‘accessory’ lobes that arise from the right lobe, and are located on the visceral surface of liver.
Identify them
- Caudate lobe
- Quadrate lobe
Describe the anatomical position of the caudate lobe of the liver
- Located on the upper aspect of the visceral surface
- Lies between the inferior vena cava and a fossa produced by the ligamentum venosum (a remnant of the fetal ductus venosus)
Describe the anatomical position of the quadrate lobe of the liver
- Located on the lower aspect of the visceral surface
- Lies between the gallbladder and a fossa produced by the ligamentum teres (a remnant of the fetal umbilical vein)
What is the porta hepatis and what does it do?
- The porta hepatis is a deep fissure between the caudate and quadrate lobes
- It transmits almost all the vessels, nerves and ducts entering or leaving the liver
Identify the structures in the porta hepatis
- Right and left hepatic ducts (bile)
- Right and left branches of hepatic artery
- Hepatic portal vein
NB. Porta hepatis doesn’t transmit the hepatic veins
What does the hepatic artery do and where is it derived from?
- Hepatic artery supplies the liver with arterial blood
- It is derived from the coeliac trunk
What does the hepatic portal vein do?
Hepatic portal vein is the dominant blood supply to the liver parencyma, supplying the liver with deoxygenated blood and carrying nutrients absorbed from the small intestine
Identify the 3 main tributaries of the hepatic portal vein
Where is the hepatic portal vein formed?
It is formed behind the upper edge of the neck of the pancreas
Describe the structure, function and location of the gallbladder
- Structure: peritoneal structure, gastrointestinal organ
- Function: stores and releases bile
- Location: right hypochondriac region of the abdomen, lies fossa between the right lobe and quadrate lobe of the liver
The gallbladder can usually be divided into three parts.
Identify them
What is the fundus of the gallbladder?
The fundus is the rounded, end portion of the gallbladder; which projects into the inferior surface of the liver
What is the body of the gallbladder?
The body is the largest part of the gallbladder and is occasionally in contact with the transverse colon and proximal duodenum
What is the neck of the gallbladder?
The neck is the tapered region which becomes continuous with the cystic duct, leading to the biliary tree
What is the biliary tree?
- The biliary tree is the series of ducts through which bile is secreted from the gallbladder into the gastrointestinal tract
- These ducts extend from the liver, communicating with the gallbladder and pancreas, and end at an opening into the duodenum
Describe the anterosuperior, posterior, inferior anatomical relations of the gall bladder
- Anteriorly and superiorly: inferior border of the liver and anterior abdominal wall
- Posteriorly: transverse colon and the proximal duodenum
- Inferiorly: biliary tree and duodenum
Describe the anatomical position of the jejunum and ileum
- Distal parts of the small intestine
- Intraperitoneal organs (unlike duodenum)
- Attached to the posterior abdominal wall by mesentery
There is no clear external demarcation between the jejunum and ileum although the two parts are macroscopically different.
Where do these structures start and end?
- The jejunum begins at the duodenojejunal flexure
- The ileum ends at the ileocecal junction
What happens at the ileocecal junction?
- The ileum invaginates into the cecum to form the ileocecal valve
- This valve cannot control movement of material into the cecum but prevents reflux of material back into the ileum
Distinguish between the ileum and jejunum in terms of the following characteristic features:
- Position
- Intestinal wall
- Vasa recta
- Arcades
- Colour
Describe the arterial supply of the jejunum and ileum
The arterial supply to the jejunoileum is from the superior mesenteric artery which arises from the aorta at the level of the L1 vertebrae
Describe the arterial distribution to the jejunum and ileum
- SMA moves in between layers of mesentery, splitting into approximately 20 branches
- These branches anastomose to form loops, called arcades
- From the arcades, long and straight arteries arise, called vasa recta
Describe the venous drainage of the jejunum and ileum
- The venous drainage is via the superior mesenteric vein
- It unites with the splenic vein at the neck of the pancreas to form the hepatic portal vein
The large intestine extends from the caecum to the anal canal.
Identify the 4 different parts of the colon.
Describe three features in the surface anatomy of the colon
- Omental appendices are small pouches of peritoneum, filled with fat, on the colon surface
- Teniae coli are 3 strips of muscle running longitudinally along the surface of the large bowel
- Haustra are sacculations produced by the contraction of the teniae coli to shorten the wall of the bowel
Midgut-derived structures are supplied by the superior mesenteric artery, and hindgut-derived structures by the inferior mesenteric artery.
Hence, describe the arterial supply of the ascending colon
Arterial supply via two branches of the superior mesenteric artery; the ileocolic and right colic arteries
Midgut-derived structures are supplied by the superior mesenteric artery, and hindgut-derived structures by the inferior mesenteric artery.
Hence, describe the arterial supply of the transverse colon
Arterial supply via branches of the superior mesenteric artery and inferior mesenteric artery:
- Right colic artery (SMA)
- Middle colic artery (SMA)
- Left colic artery (IMA)
Midgut-derived structures are supplied by the superior mesenteric artery, and hindgut-derived structures by the inferior mesenteric artery.
Hence, describe the arterial supply of the descending colon
Arterial supply a single branch of the inferior mesenteric artery; the left colic artery
Midgut-derived structures are supplied by the superior mesenteric artery, and hindgut-derived structures by the inferior mesenteric artery.
Hence, describe the arterial supply of the sigmoid colon
Arterial supply via branches of the inferior mesenteric artery; the sigmoid arteries
Describe the formation of the marginal artery
- Terminal vessels of the SMA & IMA split into many vessels as they approach the colon
- Vessels anastomose in loops to form a continuous arterial channel along the length of the colon i.e. the marginal artery
From which blood vessels do the vasa recta arise?
Vasa recta arise from the marginal artery to supply the colon
Describe the venous drainage of the ascending colon
Venous drainage via ileocolic and right colic veins, which empty into the superior mesenteric vein
Describe the venous drainage of the transverse colon
Venous drainage via superior mesenteric vein
Describe the venous drainage of the descending colon
Venous drainage via left colic vein, which drains into the inferior mesenteric vein
Describe the venous drainage of the sigmoid colon
Venous drainage via the sigmoid veins which drain into the inferior mesenteric vein
Describe 5 gross anatomical differences between the small and large intestines
How does the inferior mesenteric artery terminate?
- Superior rectal artery is the terminal continuation of the IMA
- It crosses the left common iliac artery and descends in the mesentery of the sigmoid colon
- It gives rise to branches that supply the rectum
