Small intestine Flashcards
What does the word ‘small’ in small intestine refer to?
The diameter
what are the 3 components of the small intestine?
Duodenum, jejunum, ileum
What does it mean when describing the small intestine as partially retroperitoneal?
Some parts are behind the peritoneum with only their anterior surface covered, while others are intraperitoneal (enveloped in peritoneum)
Function of small intestine
digestion and absorption
What is the peritoneum?
Serous membrane that lines the abdominal cavity and organs made of 2 layers continuous with each other.
What are the two layers of the peritoneum?
Parietal peritoneum and visceral peritoneum
What is the parietal peritoneum?
The layer of the peritoneum that lines the surface of the abdominal cavity
What is the name of the epithelium making up the peritoneum?
Mesothelium - simple squamous epithelium that produces serous secretions.
What is the visceral peritoneum?
The layer of the peritoneum enveloping organs e.g. liver, stomach, part of small intestine.
What is the mesentery?
A fold/extension of the visceral peritoneum that connects the intraperitoneal organs to the posterior abdominal wall (prevents falling to bottom)
What is the omentum?
Fused folds of the visceral peritoneum that connects the stomach and duodenum to other abdominal organs. Made up of lesser and greater omentum.
What is the greater omentum?
Apron-like structure that connects the greater curvature of the stomach to the transverse colon. Provides protection and insultation to abdomen.
What is the lesser omentum?
Attaches onto the lesser curvature of the stomach. Connects the stomach and duodenum to the liver.
How long is the duodenum?
25-30 cm
Name of glands found in the duodenum?
Brunner’s glands
Function of Brunner’s glands
Brunner’s glands secrete alkaline mucous which protects the duodenum by neutralising the acidity of the chyme from the stomach.
2 secretions which enter at the duodenum
Bile and pancreatic juice
Where is bile produced?
liver
Function of gall bladder
Stores and concentrates bile
4 parts of the duodenum
superior, descending, inferior, ascending
Where does the duodenum end?
At the duodenojejunal junction / flexure at the end of the ascending duodenum
How does bile travel from the gall bladder to the duodenum?
Via the common bile duct which joins with the pancreatic duct at the major duodenal papilla
Which structure controls the release of bile and pancreatic enzymes into the duodenum?
Sphincter of Oddi (found in the major duodenal papilla)
Where is the duodenum located?
From L1 to L3/4 connecting to the stomach. The duodenum is C shaped which wraps around the head of the pancreas.
Where is the major duodenal papilla?
in the descending region of the duodenum
What is an anatomical variation which may be present superior to the major duodenal papilla?
Minor duodenal papilla - may be connected to a second pancreatic duct, not necessarily functional
What is the name of the hormone secreted by cells in the duodenum when chyme enters?
Cholecystokinin.
chole - bile
cysto - gall bladder sac
kinin - move
Function of cholecystokinin
Stimulates gall bladder contraction to release bile, stimulates synthesis and secretion of pancreatic juices, relaxed sphincter of Oddi
Which artery supplies the superior and inferior duodenum and the head of the pancreas?
Superior pancreaticoduodenal artery
Where does the superior pancreaticoduodenal artery originate from?
The abdominal artery branches at the coeliac artery into the hepatic artery, which branches into the gastroduodenal artery, which branches into the superior pancreaticoduodenal artery.
Which artery supplies the inferior duodenum and the inferior pancreas?
Inferior pancreaticoduodenal artery
Where does the inferior pancreaticoduodenal artery originate from?
The abdominal artery branches into the superior mesenteric artery which branches into the inferior pancreaticoduodenal artery.
Significance of anastomosis of superior and inferior pancreaticoduodenal arteries
Blood can still be supplied to the duodenum and pancreas by collateral circulation if there is a blockage in one side. E.g. blood can be supplied via the superior mesenteric artery if there is a blockage at the coeliac trunk.
Where may a duodenal ulcer typically occur?
in the posterior wall of the superior part, nearest to the stomach.
What may cause a duodenal ulcer?
Stomach acid not being neutralised due to ineffective synthesis/secretion of alkaline mucous from Brunner’s glands.
Which drug may increase susceptibility to duodenal ulcers?
Ibuprofen - inhibits alkaline mucous secretion so stomach acid is more likely to aggravate the duodenum.
Consequences of a duodenal ulcer
May perforate the duodenum allowing the digestive contents to escape which may lead to peritonitis (inflammation of peritoneum)
What imaging can be used to identify a duodenal ulcer?
endoscopy (or x-ray if perforated)
How to identify the presence of a GIT perforation using an x-ray?
Dark areas seen under diaphragm caused by gas leaking out of perforation.
Where is the jejunum and ileum located?
In the infracolic compartment (below transverse colon). Jejunum mostly UL, ileum mostly LR.
At which point does the small intestine join to the large intestine?
Ileocaecal junction
Which structure is the start of the large intestine?
Cecum
How does the function of the small intestine change?
Duodenum - mainly digestive, Jejunum - digestive (brush border enzymes) and absorption, Ileum - mainly absorption.
Histological layers of the GIT
mucosa - epithelium, lamina propria, muscularis mucosae. Submucosa (vessels, nerves, glands), Muscularis propria (CILO - and oblique inner in stomach), Serosa
Which epithelium is found in the small intestine?
Simple columnar epithelium
Which cells are found within the epithelium of the GIT?
mucous/goblet cells, endocrine cells
Name of crypts found in the GIT
Crypts of Lieberkuhn
What is found in crypts of Lieberkuhn?
Exocrine glands which secrete antimicrobial and digestive enzymes. Stem cells that differentiate to replace epithelial cells that are destroyed by acid anf abrasion.
What is the submucous plexus (Meissner plexus)?
Collection of parasympathetic nerves found in the submucosa that control blood flow and secretions
What is the myenteric plexus (Auerbach plexus)?
Collection of sympathetic and parasympathetic nerves that control peristalsis and motility. Found between the circular and longitudinal layer in the muscularis propria.
Name of transverse folds on the intestinal surface?
Plicae circulares
Name of finger-like processes that line the mucosa
Villi
What cells line villi?
Epithelial cells which are lined by a brush border
What forms the brush border on the epithelial cells (which line the villi, which line the Plicae circulares)?
Microvilli
Function of Plicae circulares and villi
Increase SA for absorption and digestion (lumen can expand, brush border enzymes secreted from microvilli)
How are the blood vessels and lymphatics supplied to the abdominal viscera?
within the visceral peritoneum including the mesentery
What vessels are found within a villus?
Artery, vein, lacteal (lymph capillary)
How does the superior mesenteric artery branch to supply the small intestine?
Within the mesentery, the superior mesenteric artery branches into arcades (loops) which branch off into straight lines of arteries called vasa recta.
How to distinguish between duodenum and ileum?
Vasa recta longer in duodenum than ileum
Function of the lacteal in the villi?
Helps with fat absorption
Where are crypts of Lieberkuhn located?
Invaginations of the epithelium into the mucosa between villi
What is Peyer’s patch?
Cluster of lymphatic tissue found in the lamina propria extending into the submucosa. Found mostly in the ileum.
Name of the simple columnar / epithelial cells that line the small intestine
enterocytes
How do enterocytes contribute to small intestine function?
Have microvilli which form a brush border to increase SA. Brush border enzymes aid digestion. Contain carrier proteins which aid absorption as they transport substances from the surface to crypts.
How does the muscularis propria aid intestinal motility?
Inner circular layer contracts on top of bolus which propels it and breaks down the contents. Outer longitudinal layer shortens and lengthens to propel the bolus.
Which structure controls the release of bolus from the small intestine to the large intestine?
Ileocecal valve - found in ileocecal junction
Example of absorption still occurring in the large intestine
Cecum involved in absorption of vitamin B12
Examples of intestinal diseases
dietary deficiencies, malabsorption, coeliac disease, Crohn’s disease, Cystic fibrosis, Meckel’s diverticulum.
How may intestinal diseases affect the oral mucosa?
Diseases e.g. malabsorption syndromes, can lead to deficiencies that affect blood e.g. anaemia.
What is Meckel’s diverticulum?
An outpouching of the small intestine, mostly ileal mucosa. May contain acid producing gastric, pancreatic or colonic type mucosa.
What is the rule of 2s relating to Meckel’s diverticulum?
Symptoms before 2 years old, affects 2% of population, within 2 feet of the cecum.
