HUBS192 Lecture 22 - The Small Intestine Flashcards
why is the small intestine called the small intestine?
because the intestine is small is diameter
what is the diameter of the small intestine?
3-4cm
what is the diameter of the large intestine?
approx. 7cm
what are the 3 main regions of the small intestine?
1) duodenum
2) jejunum
3) ileum
what is the longest section of the small intestine?
the ileum
how long is the small intestine?
total length is approx. 6m
what does the acronym Don’t Jump In mean?
Duodenum (first region) Don’t
Jejunum (middle region) Jump
Ileum (terminal/end region) In
where does the initial segment of the duodenum sit in relation to the peritoneal cavity?
initial segment of the duodenum sits retroperitoneal (posterior the peritoneal cavity)
what is intraperitoneal?
located within the peritoneal cavity
where is the jejunum and the ileum located in relation to the peritoneal cavity?
sits intraperitoneal (inside the peritoneal cavity)
why is the jejunum and the ileum located intraperitoneal?
to allow the jejunum and the ileum to be able to carry out motility and movement associated with peristalsis (motility pattern that helps to propel stuff along the tract) and segmentation (mixing motility pattern)
how is the small intestine held in place?
small intestine held in place by mesentery
what is the function of a mesentery for the small intestine?
allows movement, but prevents the small intestine from getting tangled
what are the 4 components a mesentery contains?
1) arteries
2) veins
3) nerves
4) lymphatics
what is the function of the mesenteric artery?
supplies the small intestine with oxygenated blood
what is the function of mesenteric vein?
drains deoxygenated blood from the small intestine
what is delivered to the small intestine?
chyme
-very acidic
what are the 2 ways the small intestine is protected from the acidic chyme?
1) protect epithelium
2) neutralise pH
how does the small intestine protect the epithelium from acidic chyme?
through mucous secreting cells with the glands located in the submucosa
-specific to the duodenum
what is a feature specific to the duodenum of the small intestine?
mucous secreting cells in the submucosa
-duodenum requires more protection
how does the small intestine neutralise the pH from acidic chyme?
through bicarbonate (HCO3-) secreted from duct cells of the pancreas
what is the function of the plicate circulares (circular folds)?
- increase the surface area of the tube
- spirals food material as it travels through the lumen
- slows down its passage to allow more time digestion and absorption
what are the plicate circulares (circular folds)?
permanent large folds of the small intestine with a core of submucosa (with overlying mucosa)
what are villi?
finger-like projections of mucosa
what is the function of the muscularis mucosae in terms of the villi?
muscularis mucosae contracts to allow the villi to wiggle back and forth to sample and be exposed to the lumen content
where are villi located?
numerous villi, found on the surface of the place circulares (circular layer)
what surrounds the central lymphatic lacteal?
the capillary network
why are the lymph lacteal and capillary network vessels extending into the tip of the villi?
to sit close to the site of absorption
what products are absorbed in the capillary network of the villi?
products of protein and carbohydrate digestion
what products are absorbed in the lymph lacteal of the villi?
products of fat
digestion
e.g fatty acids
what is the core of each villi made up of?
core is made up of FCT which is the lamina propria
what is a portal vein?
a vein that does more than just the usual function of returning blood back to the heart
what enters the mesenteric veins and where does this drain into?
nutrient rich, deoxygenated blood absorbed in the small intestine enters into the mesenteric veins. This then drains into the hepatic portal vein
what is the cisterns chyli?
collecting sac at the base of the thoracic duct
what is the drainage pathway from the lymph lacteals?
lymph lacteals drain into the cisterns chyli –> thoracic duct –> left subclavian vein
what further increases the surface area of the small intestine without changing the volume?
microvilli on the apical surface further increase the surface area
what is another name for the microvilli layer?
brush border (because the microvilli look like bristles on a brush)
what is the glycocalyx?
network of glycoproteins and branched filaments
what is the function of the glycocalyx?
tethers enzymes in place
what is contact digestion?
involves enzymes that are attached to the brush border
what is luminal digestion?
involves enzymes that are in the lumen of the digestive tract
what are the 2 features of the plasma membrane?
1) selectively permeable
2) has proteins - channels and transporters
what is the junction between the epithelial cell in the small intestine?
tight junctions
- very tight
- only small molecules may diffuse through
what are the 5 epithelial cell types in the small intestine?
1) enterocytes
2) goblet cells
3) stem cells
4) panted cells
5) endocrine cells
what is the function of enterocytes?
absorptive cells
what is the function of goblet cells?
secrete mucous for protection
what is the function of stem cells?
makes all cell types
what is the function of paneth cells?
secrete granules and antibacterial enzymes
what is the function of endocrine cells?
secrete hormones
what epithelial cell types are in the intestinal crypt?
- epithelial cell
- stem cell
- paneth cell
what are microvilli?
fold in the apical plasma membrane of the epithelium
what are the 4 key ways the surface area of the small intestine is increased for absorption?
1) very long - 6m in length
2) plicae circulares (circular layer) = permanent folds of the submucosa
3) villi = folds of the mucosa (not the muscularis mucosa)
4) microvilli = fold in the apical plasma membrane of the epithelium
