Abdomen II Flashcards
What is the longest part of the Gastrointestinal Tract?
Small intestine
Where does the small intestine extend begin and end?
It extends from the pylorus of the stomach to the ileocecal junction
Divisions of the small intestine
Duodenum, Jejunum and the Ileum
Describe the shape and location of the duodenum and the organ that it surrounds.
- It is a C-shaped tube and surrounds the head of the Pancreas.
- It is the shortest, widest, and most fixed part of the small intestine
- The duodenum and the pancreas lie at the junction between the foregut and the midgut and receive blood from the Celiac Trunk + SMA
What connects the duodenum to the liver (externally to these organs)?
The hepatoduodenal ligament of the lesser omentum
The 4 parts of the Duodenum
(1) L1- Duodenal cap- often affiliated with duodenal ulcers. Attachment for hepatoduodenal ligament. Retroperitoneal begins after the first 1-2 inches.
(2) Descending- L2- L3 Receives the major duodenal papilla (opening of the bile duct and main pancreatic duct) and the minor duodenal papilla (the opening of the accessory pancreatic duct)
(3) Inferior- L3- Crosses inferior Vena Cava and Aorta and is crossed by SMA and SMV
(4) Ascending- Ascends back up to left of L3-L2- Tethered by suspensory ligament at duodenojejunal flexure
Location and functioning of the Pancreas
Endocrine (insulin/glycogen) + Exocrine (digestive enzymes)
Located across the posterior abdominal wall, and extends from the duodenum to the spleen
The 4 parts of the Pancreas
(1) Head- lies in the C-shaped concavity of the duodenum. UNICATE is a finger like extension of the head where the SMA and SMV pass anteriorly. From here they go to supply the small intestine.
(2) Neck- lies anterior to the beginning of the portal vein where the splenic vein and SMV join to form the portal vein– VERY IMPORTANT
(3) Body- Forms the major portion of the stomach bed. Splenic artery runs along its upper border and the splenic vein runs posterior to it.
(4) Tail- Ends in the splenorenal (lienorenal) ligament at the hilum of the spleen (touches spleen)
The 2 ducts of the Pancreas
(1) The main pancreatic (of Wirsung)- drains the tail, body, neck and upper part of the head. Joins the bile duct to form a short tune called Hepatopancreatic ampulla (ampulla of Vater). Opens on major duodenal papilla.
(2) The Accessory Pancreatic Duct (of Santorini)- drains the uncinate process and lower part of the head. Opens at the minor papilla.
What covers the Jejunum and Ileum?
Peritoneum (intraperitoneal) as they are suspended by a mesentery from the posterior abdominal wall
Describe the borders of the mesentery which covers the Jejunum and the Ileum
The mesentery is fan-shaped and has 2 borders:
(1) Attached border (root)- 6 inches long, crosses 3rd part of duodenum, aorta, IVC and under the right ureter and psoas major
(2) Free border- 6 meters long, encloses loops of jejunum and ileum
What provides the vascularization of the Jejunum/Ileum?
SMA
Main differences between Jejunum and Ileum
JEJUNUM:
- More vascular
- Long Vasa Recta
- A few large loops of arterial Arcades
- Large, tall, and closely packed circular folds
- Few Lymphoid nodules
- Thinner fat
ILEUM
- Less vascular
- Short vasa recta
- Many short loops of arterial Arcades
- Low and Sparse circular folds which are absent in distant parts
- Many Lymphoid nodules
- Thicker fat
What does the Large Intestine surround?
It surrounds the small intestine like a “picture frame”
Parts of the Large Intestine, and their associated peritoneal coverings (folds)
- Cecum (retroperitoneal)
- Appendix (mesoappendix)
- Ascending colon (retroperitoneal)
- Transverse colon (transverse mesocolon)
- Descending colon (retroperitoneal)
- Sigmoid colon (Sigmoid mesocolon)
- Rectum (Retroperitoneal)
Divisions of the Colon
Ascending colon, right (hepatic) colic flexure, transverse colon, left (splenic ) colic flexure, descending colon, and sigmoid colon
Components of the large intestine which are fixed are within what type of covering?
Retroperitoneal
The parts of the large intestine which are not fixed
- Appendix
- Transverse colon
- Sigmoid colon
Blood supply of the large intestine
SMA + IMA
Small pouches filled with fat around large intestine.
Appendices epiploicaue
Feature of the Large Intestine
Aka Omental appendices
Absent in Cecum, Appendix and Rectum (CAR) [ COLIC PORTION ONLY]
Taeniae Coli
Feature of the Large Intestine
The outer longitudinal muscle layer is thickened to form 3 bands which are shorter than the other layers. The begin at the base of the appendix and end at the sigmoid colon.
Sacculations
Feature of the Large Intestine
Aka Haustra
Found between the Taeniae Coli. The colon bulges outwards forming 3 rows of pouches
Cecum
A blind sac in the right iliac fossa, continuous with the ascending colon. Medially receives the opening of the ileum and appendix
Ileocecal valve (IC)
Guards the ileal opening into the cecum. The valve has 2 lips. The opening of the appendix is 2cm below it.
Appendix
Blind tube rich in lymphoid tissue, suspended by mesoappendix.
Common positioning of appendix
Retrocecal
Useful landmark for appendectomies
The 3 taeniae coli meet at the base of the appendix, so this can serve as a great landmark for surgeons.
Acute Appendicitis
Acute inflammation of the appendix due to viral or bacterial infection. May result in thrombosis of the appendicular artery (branch of ileocolic artery) which can lead to perforation of the appendix
McBurney’s Point
The point of maximum tenderness in acute appendicitis. Pain from the appendix enters the spinal cord through T10 segment so acute appendicitis is referred to the umbilicus region (which also shares T10).
Where is McBurney’s point?
It lies opposite to the junction of lateral and middle thirds of a line joining the Rt. ASIS to the umbilicus. The meeting point of the median 2/3rds and the lateral 1/3rd
Omentum vs Mesentary
Omentum- stomach; Mesentary- Small intestine
If a surgeon doesn’t pay attention during a splenectomy, what might he injure?
The pancreas
Muscle of Treitz
Other name for suspensory ligament. Acts like Sphincter. controls about of food which enters the small intestine
Caput Medusae
Veins popping out around belly button, like Medusa snake head.
Meckel’s diverticulum
Often confused for Appendicitis (it’s a differential diagnosis). Syndrome of Two’s:
- 2 feet from IC valve (which leads to appendicular valve)
- 2 inches long
- 2% of population has this
- 2% of those with it are symptomatic
- 2 types of ectopic tissue (gastric + pancreatic)
- 2 years of age at clinical presentation
- 2 x more common in boys
Parasympathetic innervation of the GIT
Foregut & Midgut- Vagus nerves
Hindgut- Pelvic splanchnic nerves (parasympathetic sacral outflow S2, 3, 4)
[All these fibers are preganglionic]
Sympathetic innervation of the Foregut/midgut
Foregut/Midgut:
Thoracic splanchnic nerves
- Greater (T5-T9- Presynaptic fibers to celiac)
- Lesser (T10- T11- Presynaptic fibers to superior mesenteric)
- Least (T12- Presynaptic fibers to the aorticorenal [prevertebral]
Sympathetic innervation of the Hindgut
Hindgut:
Lumbar splanchnic nerves (L1, L2- Presynaptic fibers to prevertebral ganglia of inferior mesenteric and superior hypogastric plexuses)
Path of the Superior Mesenteric Artery
(SMA)- Artery of the Midgut
- The second unpaired branches of the abdominal aorta at level L1
- Runs downward to the Right Iliac fossa
- Descends across uncinated process of the pancreas, then enters the mesentery and ends by anastomoses with the ileal branch of ileocolic artery
Branches of the Superior Mesenteric Artery
All branches go to the right except the jejunal and ileal branches which go to the left (small intestine left, large intestine right)
(1) Inferior pancreaticoduodenal- 1/2 duodenum and pancreas
(2) Middle colic- right 2/3 of Transverse colon
(3) Right Colic- ascending colon
(4) Ileocolic- Cecum + appendix
- Name the branches of the Ileocolic Artery.
- What does the the Ileocolic branch off from?
- Anterior cecal artery
- Posterior cecal artery
- Appendicular artery (IMPORTANT)
- Ileal artery (IMPORTANT)- anastomoses with the end of SMA
Branches off SMA
Where do the Jejunal and Ileal Branches of the SMA run?
What do they form when they branch?
They run in the mesentery.
They branch and anastomose to form series of arcades. Arcades send straight arteries to the intestine (Vasa Recta)
Path of the Inferior Mesenteric Artery
(IMA)- Artery of the Hindgut
- The third unpaired branches of the abdominal aorta at level of L3
- Runs downwards to the left iliac fossa
- Arise behind the 3rd part of duodenum.
- Ends by crossing the left common iliac artery and becoming the superior rectal artery
Branches of the Inferior Mesenteric Artery
(1) Left colic- left 1/3 of transverse colon + upper of descending colon
(2) Sigmoid arteries (2-3)- lower of descending colon + sigmoid colon
(3) Superior rectal- sigmoid colon + rectum. It is the direct continuation of the IMA
Marginal Artery
Aka the Marginal Artery of Drummond
CONNECTS THE IMA TO THE SMA
It is an arterial arcade along the colon that interconnects the right, middle and left colic
Hepatic portal venous system
System in which blood collected from the intestinal capillary bed passes through the portal vein then through Liver sinusoids (2nd capillary bed) before reaching IVC (systemic circulation)
In other words, IT IS BETWEEN 2 SETS OF CAPILLARIES
How does the Portal Vein forms and what does it end as?
- It begins as a vein after a union of the Superior Mesenteric Vein (SMV) and the splenic vein (of which IMV is a tributary)
- It ends as an artery in the porta hepatis by dividing into 2 branches (right and left) to supply the liver with 75% of its blood and 50% of the required oxygen
Where does the Portal Vein drain blood from and where doe that blood go?
- It drains blood from the GIT tract, pancreas, spleen and gallbladder to the liver
- After passing through the liver sinusoids, blood collects into the Hepatic veins
- Blood then drains to the IVC
Path of the portal vein
- Begins at the neck of the pancreas by union of the SMV and splenic vein
- Ascend in the free border of lesser omentum
- Enters the porta hepatis
Order of structures at the Porta Hepatis
From Posterior to Anterior
VAD (portal Vein, hepatic Artery, hepatic Duct)
Portal vein is always posterior in its course.
- Path of the Celiac Vein.
- Path of the Gastroduodenal Vein
NEITHER OF THESE VEINS EXIST, although there are arteries with the same names.
Tributaries of the Portal Vein
- SMV
- Splenic Vein
- Right & Left Gastric veins (Left is a common site for portostemic anastomosis)
- Cystic vein
- Paraumbilical veins
What vein is a major tributary to the splenic?
Inferior Mesenteric Vein (IMV)
The important sites of Portosytemic Anastomosis and the clinical relevance of these locations.
- These are sites where the portal system anastomosis with the systemic caval system (IVC and Azygos) which allows for rerouting the venous return to the heart.
(1) Left gastric vein/ esophageal vein of the Azygos system
(2) The rectal veins
(3) The paraumbilical veins
In case of liver cirrhosis, the fibrosis disrupts the portal blood flow leading to PORTAL HYPERTENSION which can lead to:
- Esophageal varices (Hematemesis aka vomiting blood)
- Rectal varices (Hemorrhoids- bleeding per rectum)
- Caput medusa- (Varicose veins radiating from the umbilicus - Medusa’s head)
