anatomy and physiology of small bowel Flashcards
where is the small intestine located and what marks the beginning and end of it (anatomically)
located in the abdominopelvic cavity; beginning: pylorus of the stomach
ends: ileocecal junction
what are the 3 main parts of the small intestine
- duodenum
- jejenum
- ileum
what does retroperitoneal mean
abdominal structures that are only partially covered by peritoneum and lie posterior or behind the abdominal peritoneum e.g. distal duodenum (parts 2-4)
what does intraperitoneal mean
structures that have invaginated and are completely covered by the visceral peritoneum e.g. jejenum, proximal duodenum and ileum
what are the 4 parts of the duodenum
- superior part;
- descending part;
- inferior part;
- ascending part
at what vertebral level does the duodenum begin
L1
what are the attachments to the superior duodenum (2)
- hepatoduodenal ligament - part of the lesser omentum
- greater omentum
what is the ampulla/duodenal cap?
The proximal 2cm of the superior part - it is more dilated and freely mobile as it is intraperitoneal
what 2 organs lie over the top and which 3 lie posteriorly to the proximal duodenum
anterior: liver and gall bladder
posterior: Inferior vena cava, bile duct and gastroduodenal artery posterior
what vertebrae does the descending part of the duodenum run between
L1 - L3 -> It curves downward around the head of the pancreas which is medial, and runs inferiorly from the L1 to the L3
what 2 organs lie over the top and which 2 lie posteriorly to the descending duodenum
anterior: transverse colon and the convolutions of the small intestine;
posterior: the hilum of the right kidney and its vessels, and the ureter
what is the major duodenal papilla
a rounded projection in the duodenum into which the common bile duct and pancreatic duct drain -> forms a hepatopancreatic ampulla
what is the function of the major duodenal papilla
to carry the pancreatic juices and bile to the duodenum
what are 2 other names for the major duodenal papilla
papilla of vater and ampulla of vater
what is the minor duodenal papilla
where the accessory pancreatic duct opens - not always present
at what vertebral level does the inferior duodenum travel
L3
what organs lie posteriorly to the inferior duodenum (4)
- inferior vena cava
- the aorta
- the proximal parts of the inferior mesenteric vessels
- body of the L3 vertebra
what lies anteriorly to the inferior duodenum (3)
- superior mesenteric artery
- the superior mesenteric vein
- parts of the jejunum
what is the name for the point of connection between the duodenumand jejenum, and at what vertebral level does this occur
duodenojejunal flexure/junction - occurs at L2
from what ligament does the duodenojejunal flexure hang
ligament of Treitz - made out of the skeletal muscles from the diaphragm and the smooth muscles of the duodenum
what is the duodenal main arterial supply (2)
- celiac trunk
- superior mesenteric artery
what are the different branches of the celiac trunk and what do they supply
- the common hepatic arterywhich gives rise to the supraduodenal and gastroduodenal arteries
- supraduodenal artery - supplies portions of the first and second duodenal parts
- gastroduodenal artery - has a branch called the superior pancreaticoduodenal artery, that supplies the first two parts of the duodenum up until the major duodenal papilla
what is the branch of the superior mesenteric artery and what part of the duodenum does it supply
the inferior pancreaticoduodenal artery, which supplies the other two parts of the duodenum, distal to the major duodenal papilla.
what is the venous drainage of the duodenum
- splenic
- superior mesenteric vein
both eventually drain into the hepatic portal vein
what lymph node does the duodenal lymphatic system ultimately drain into
celiac node
what is the innervation for the duodenum
celiac and superior mesenteric plexuses - both parasymp and symp neurons reside here -> the sympathetic fibers synapse in prevertebral ganglia such as the celiac and superior mesenteric ganglia, and send their postsynaptic sympathetic fibers through the periarterial plexuses;
The parasympathetic fibers, on the other hand just pass through the celiac and superior mesenteric plexuses as well as the periarterial plexuses and eventually synapse in the intrinsic ganglia found in the walls of the duodenum
what abdominal quadrant is the jejenum mostly situated in
left upper quadrant
what abdominal quadrant is the ileum mostly situated in
right lower quadrant
what is the mesentry
a fold of membrane (visceral peritoneum) that attaches the intestine to the wall around the stomach area and holds it in place
what lies within the folds of the mesentry (4)
1.the superior mesenteric vessels
2. lymphatic vessels
3. nerves that supply the small intestine
4. fat tissue
what is ther srterial blood supply for the ilium and jejenum
superior mesenteric artery
what are the branches off the SMA in the mesentery known as
arterial arcades (arterial loops) which give rise to many straight arteries known as the vasa recta
jejenum vs ilieum arteries
jejenum: fewer arcades with larger loops and longer vasa recta;
ileum: more arcades with shorter loops and shorter vasa recta
what are the lymphatic vessels of the jejenum and ilieum known as
lacteals (arise in the intestinal villi)
where is the main lymph node for drainage of teh jejenum and iliuem
superior mesenteric lymphnode
effect of sympathetic stimulation on the small intestine
reduces peristaltic and secretory activity to stop digestion
along side what kind of nerve fibres do visceral sensory afferent travel
alongside parasympathetic fibres
what sympathetic nerves innervate the small intestine
the greater and lesser splanchnic nerves
what is the approximate length of the small intestine of adults
around 6m
how long is the jejenum and ilieum
jejenum - 2.5m
ilium - 3.5m
what are the 4 main layers of the small intestine wall
- mucosa
- submucosa
- muscularis propria
- serosa
what are the differences in villi between the different parts of the small intestine
duodenum and jejunum: very tall and slender villi;
ileum: significantly shorter, broader, and their tips are flat
what are the villi of the entire small intestine lined with
enterocytes (simple columnar cells with microvilli)
what are the components of the villi in the duodenum and jejenum (5)
- enterocytes
- lamina propria - loose connective tissue that supports the enterocytes and forms the middle or core of each villus
- The crypts of Lieberkühn - glands that contain stemcells
- goblet cells - secrete mucous for lubrication and protection
- muscularis mucosa - a thin supporting layer of smooth muscle
how do new cells reach the tops of the villi
arising from stem cells located within the crypt, differentiated cells move up the villi as new cells are continually formed underneath them, and within a week, the cells will reach the tip of the villi where they’re shed into the lumen
what are paneth cells
small, eosinophilic cells that help provide an innate immune defense against intestinal pathogens
what are peyer’s patches
masses of lymphoid tissue within the lamina propria that are only seen in the ileum
what unique components does the mucosa of the ileum contain (3)
- shorter, borader villi
- Peyer’s patches
- lacteals (white spaces of lymphatic capilaries seen in the villi that absorbe dietary fats)
how can the duodenal submucoa be distinguished from the others
the presence of brunner’s glands - thick layer of coiled, tubular glands lying just beneath the muscularis mucosa
where are bunners glands found
oesophagus and duodenum
function of brunner’s glands
they secrete alkaline mucus into the lumen of the small intestine in order to reduce the acidity of the gastric juices and partially digested food coming from the stomach -> occasionally pass through the muscularis mucosa so that secretions can be released into crypts
how are the muscles in the muscularis externa (propria) arranged
two main layers of smooth muscle arranged in different directions:
1. The inner layer has a circular or circumferential arrangement around the wall of the small intestine
2. The muscle cells of the outer layershave a longitudinal arrangement that runs parallel to the length of the small intestine - they have a rounder appearance compared to the inner layer on cross section
what is between the two layers of the muscularis propria
a network of nerves - called the myenteric plexus or Auerbach’s Plexus
function of the serosa
a thin layer of loose connective tissue that allows the small intestine to move more freely within the abdomen and contains blood vessels,nerves, and lymphatic vessels as well
