small intestine Flashcards
what is the other name for the small intestine?
small bowel
what are the three parts of the small intestine?
- duodenum
- jejunum
- ileum
describe the small instestine
- part of GIT
- around 6metres long
- primary site for absorption
- starts at pylorus and extends to the ileocaceal junction
- partially retroperitoneal
what is the peritoneum?
- Continuous membrane lining the abdominal cavity and covers abdominal viscera
- Supports those organs and provides a route for blood vessels
- 2 layers that are continuous with each other – made up of simple squamous epithelial cells called MESOTHELIUM
PARIETAL peritoneum is sensitive to pressure, pain, temp.
VISCERAL peritoneum covers majority of abdominal viscera. Pain from this is referred to dermatomes (areas of skin supplied by a single spinal nerve)
INTRAPERITONEAL ORGANS – enveloped by visceral peritoneum
RETROPERITONEAL ORGANS – eg duodenum, pancreas, rectum
MESENTERY – Double layer of visceral peritoneum – connects structure to posterior abdominal wall. Mesentery contains blood vessels, nerves and lymphatics
OMENTUM – Sheets of visceral peritoneum extending from the stomach and proximal duodenum to other abdominal organs.
describe the duodenum
- Receives chyme from the stomach
- Short length
- Contains Brunner’s glands (found above where pancreatic and biliary secretions enter the duodenum):
- alkaline and mucous secretion to protect the duodenum from acidity of chyme, provide optimal condition for intestinal enzymes to be active and for lubrication - Receives common bile duct (Sphincter of Oddi)
- Bile- produced and stored in the gall bladder and then passes into the Sphincter of Oddi. This muscular valve controls the flow of bile and the pancreatic juice, or enzymes as they pass into the duodenum.
- Pancreatic “juice” - Ends at duodenojejunal junction
describe the duodenum
- Receives chyme from the stomach
- Short length
- Contains Brunner’s glands (found above where pancreatic and biliary secretions enter the duodenum):
- alkaline and mucous secretion to protect the duodenum from acidity of chyme, provide optimal condition for intestinal enzymes to be active and for lubrication - Receives common bile duct (Sphincter of Oddi)
- Bile- produced and stored in the gall bladder and then passes into the Sphincter of Oddi. This muscular valve controls the flow of bile and the pancreatic juice, or enzymes as they pass into the duodenum.
- Pancreatic “juice” - Ends at duodenojejunal junction
describe the location of the duodenum
Sits between the first lumbar vertebra i.e. L1 and the third/fourth lumbar vertebra i.e. L3/4
It is described as C shaped as it comes from the pyloric sphincter through to the duodenojejunal flexure
what is the Sphincter of Oddi?
Muscular valve controlling pancreatic and biliary secretions
what parts of the duodenum is the sphincter of oddi found?
2nd and 4th
what is surrounded by the sphincter of oddi?
major duodenal pipilla - rounded projection at the opening of the common bile duct and pancreatic duct
what is the minor dueodenal pipilla?
the opening of the accessory pancreatic duct and is typically present in 10% of people- 2cm proximal to major
what is CCK?
- cholecytokinin
- a peptide hormone and helps digest fat and protein
- secreted by cells of the duodenum and highest secretion when there is fatty acids in the chyme entering the duodenum
- inhibits gastric emptying but increases the release of pancreatic enzymes, as well as increases the production of bile, contraction of the gall bladder and relaxes the Sphincter of Oddi resulting in better fat digestion
what are the four parts of the duodenum?
- superior
- descending
- inferior
- ascending
describe the superior part of the duodenum
- also known as the cap
- ascends upwards from the pylorus
- this area that is most common to have a duodenal ulcer
- sits at the level of L1
describe the descending part of the duodenum
- passes downwards around the head of the pancreas
- lying behind the transverse colon and in front of the right kidney
- at this site where the major duodenal papilla lies
- sits at the level of L1-L3
describe the inferior part of the duodenum
- passes to the left over the inferior vena cava and aorta
- lies behind the superior mesenteric artery (supplying the midgut)
describe the ascending part of the duodenum
- crosses the aorta and curves up to join the jejunum at the duodenojejunal flexure)
what is the second part of the duodenum (prior to the major duodenal papilla) supplied by?
gastroduodenal artery
what supplies the duodenum distal to the major duodenal papilla?
superior mesenteric artery and its branch, the inferior pancreaticoduodenal artery
where is the venous drainage of the duodenum to?
the portal system either through the splenic or superior mesenteric vein to the portal vein
describe a duodenal ulcer
- mostly in the posterior wall of the superior part- red, inflamed
- possibility of perforation (hole)
- peritonsis- fever, nausea and vomiting
- pain worse at night
- caused by infection and non-steroidal inflammatory drugs eg ibruprofen
- can lead to air under diaphragm
- could rupture
what is the diagnosis and treatment for a peptic ulcer?
- CT scan can help
- treatment is surgery
what quadrant is the jejunum in?
more upper left
what quadrant is the ileum in?
more lower right
what is the infracolic compartment?
contains the coils of small bowel which is separated from paracolic gutter on either side by ascending and descending colon
what is the duodenojejunal flexure?
sharp angle in the small intestine between the duodenum and the jejunum
what are the main functions of the parts of the small intestine?
Duodenum
- mainly digestion
- pancreatic enzymes and bile
Jejunum
- digestion (brush border enzymes)
- absorption
Ileum
- mainly absorption
what is the structure of the jejunum and ileum?
Lumen
Mucosa
- epithelium
- lamina propria
- muscularis mucosae
Submucosa
Muscularis externa
- innermost oblique (stomach only)
- inner circular
- outer longitudinal
Adventitia (serosa)
describe the mucosa
- enterocytes – tall columnar epithelium and have an absorptive function
- goblet cells – exocrine glands which secrete mucin and Crypts of Lieberkuhn (where hormones are secreted and new stem cells found)
describe the mucosa
- enterocytes – tall columnar epithelium and have an absorptive function
- goblet cells – exocrine glands which secrete mucin and Crypts of Lieberkuhn (where hormones are secreted and new stem cells found)
describe the submucous plexus
(Meissner’s plexus)- these nerves come from the parasympathetic nervous system.
describe the myenertic plexus
motor innervation to both layers of muscle and has both parasympathetic and sympathetic innervation
describe the myenertic plexus
(Auerbach plexus)- motor innervation to both layers of muscle and has both parasympathetic and sympathetic innervation
what features on the intestinal surface area?
plicae circulares
villi
what are pilicae circulares?
Permanent circular folds of mucous membranes which are most numerous in the latter part of the duodenum through the upper part of the jejunum. These increase the surface area in the small intestine by 2-3x
what is the function of villi?
increase surface area by approimmately 10x – 30x and microvilli x600
what is serosa?
The outer lining of organs and body cavities of the abdomen and chest, including the stomach. Also called serous membrane.
2 layers of mesothelium.
describe the jejunum
Thick intestinal wall
Longer vasa recta (straight arteries)
Less arcades (arterial loops)
describe the ileum
Thin intestinal wall
Shorter vasa recta
More arcades
what are peyer’s patches?
groupings of lymphoid follicles in the mucus membrane that lines your small intestine
involved with thickening of the intestinal epithelium and part of immune response
what are peyer’s patches?
groupings of lymphoid follicles in the mucus membrane that lines your small intestine
involved with thickening of the intestinal epithelium and part of immune response
what are enterocytes and their functions?
a cell of the small intestine
Microvilli (“brush border”)
Digestion – brush border enzymes
Absorption – carrier proteins
describe intestinal mobility
segmentation
- differing role for musculature in movement of chyme:
- circular- local contraction and breakdown
- longitudinal- moves further along as well as breakdown
what occurs at the ileo-caecal junction/
Vitamin B12 and bile acid absorption occurs here.
describe intestinal diseases
- Dietary deficeinces
- Malabsorption syndromes can lead to deficeinces that affect blood e.g. anaemia
- Can therefore affect oral mucosa
- Coeliac disease
- Crohn’s disease
- Cystic fibrosis
what is Meckel’s diverticulum?
Rule of 2’s:
- Usually presents before age of 2yrs old
- 2% of population
- Within 2 feet from ileocaecal valve
- 2 inches long
- 2 types of mucosa- mostly ilial mucosa
- May contain acid producing gastric, pancreatic or colonic type mucosa
