Session 5: The Intestines Flashcards
Blood supply of the midgut
Superior mesenteric artery
Branches of the superior mesenteric artery
Inferior pancreaticoduodenal artery
Middle colic artery
Right colic artery
Ileocolic artery
Jejunal and ileal arteries
What does the inferior pancreaticoduodenal artery anastomose with?
The superior pancreaticoduodenal artery
What does the inferior pancreaticoduodenal artery supply?
Inferior region of the head of the pancreas
The uncinate process
The duodenum
Explain the jujenal and ileal arteries.
The arteries pass between the layers of the mesentery and form what is called anastomotic arcades which is a vast network of arteries.
Fom these anastomoses straight arteries arise called vasa recta to supply the organs.
What does the middle colic artery supply?
The transverse colon
What does the right colic artery supply?
The ascending colon
What does the ileocolic artery supply?
Gives rise to branches for ascending colon, caecum, appendix and ileum.
At what vertebral level does the SMA arise?
L1
Explain the venous drainage of the small intestines.
The anastomotic loops drain into the jejunal and ileal veins which will join to drain into the superior mesenteric vein.
The inferior mesenteric vein drains into the splenic vein.
The splenic vein and the superior mesenteric vein join to drain into the portal vein. Here blood will go to supply the liver.
The portal vein does not empty into the heart but instead supplies the liver by ending up in the sinusoids. The venous drainage of the liver is then via the hepatic veins.
Explain how the surface area of the intestines is maximised.
The intestine folds called valvulae conniventes, plicae circulares or fold of Kerckring.
Lining the epithelium and therefore also the folds are villi.
Each villi will have a brush border which are thousands of microvilli covering the villi.
All of this greatly increases the surface area of the intestines.
Give components of the epithelium of the intestines
Enterocytes
Goblet cells
Crypts of Liberkühn
Role of the enterocytes.
Absorption
Role of the goblet cells.
Mucus producing to protect the small intestines from the acidic chyme and also for lubrication.
What cells can be found in the crypts of Lieberkühn?
Stem cells at the base
Paneth cells at the base
Enteroendocrine cells
Explain the role of the stem cells of the crypts of Lieberkühn.
Produce new cells that are lost due to abrasion
Explain the role of the paneth cells.
Protection from pathogens
Secrete antimicrobial peptides and Peyer’s patches
Peyer’s patches contain mucosal-associated lymphatic tissue (MALT) with white blood cells and lymphocytes.
What are the enteroendocrine cells?
Found in the crypts of Lieberkühn.
I cells
S cells
K cells
Enterochromaffin cells.
What do I cells produce?
CCK
What do S cells produce?
Secretin
What do K cells produce?
Gastric-inhibitory peptide (GIP)
What do enterochromaffin cells produce?
Stimulated mechanically by the presence of chyme in the intestines.
Release serotonin acting on the enteric nervous system to stimulate CFTR.
This ion channel secretes Cl- into the lumen of the intestines with Na+ and water following.
What does starch consist of?
Straight chains of glucose called amylose.
Branches chains of glucose called amylopectin.
What kind of bond can be found between amylose?
alpha 1-4 bonds
What kind of bond can be found between amylopectin?
alpha 1-6 bonds
What breaks the bonds between amylose (alpha 1-4 bonds)?
What does this produce?
Amylase
Produces maltose (disaccharide of glucose)
What happens when amylase breaks the alpha 1-4 bonds in amylopectin?
Shorter chains are created but still branched.
They are now called alpha dextrins
What breaks the alpha 1-6 bonds?
Isomaltase
From where is maltase and isomaltase produced?
From the brush border of the intestines
What is lactose broken down by?
Lactase from the brush border
What is sucrose broken down by?
Sucrase from the brush border
How can lactose intolerance lead to diarrhoea?
In the case of insufficient amounts of lactase lactose will remain in the lumen of the intestines.
Lactose is osmotically active which means if it remains in the intestinal lumen it water will move to the lumen because of the presence of lactose.
Also lactose is ferment in the gut which produce flatus/bloating
Explain how glucose and galactose is absorbed.
Along with Na+ through a SGLT-1 transporter. The Na+ moves into the cell because the Na+/K+-ATPase on the basolateral membrane maintains a lower intracellular Na+.
The glucose and galactose is then transported into the blood via a GLUT2 transporter on the basolateral membrane.
Explain how fructose is absorbed.
Facilitated diffusion via GLUT5.
Then transported into blood via GLUT2 in same way as galactose and glucose
Briefly explain the protein digestion in the stomach.
Pepsinogen released from chief cells gets converted to pepsin by HCl.
The pepsin then digest the proteins into oligopeptides. They then move on to small intestines.
Explain the protein digestion in the duodenum.
The pancreas releases zymogens.
Trypsinogen is converted into trypsin via enterokinase.
Trypsin will then activate proelastase, chymotrypsinogen, procarboxypolypeptidase.
The trypsin, chymotrypsin and elastase will digest proteins and oligopeptides into shorter peptides.
The carboxypolypeptidase will then digest the peptides into dipeptides, tripeptides and individual amino acids.
Explain the absorption of proteins.
Absorbed mainly as amino acids and not as proteins or peptides.
The amino acids are transported into the enterocytes similarly to glucose with Na+.
Although peptides can be absorbed by peptide transporter 1.
What can happen in the rare occassion of absorption of whole protein molecules?
Allergic respone or immunological disturbance
Explain the movement of water in the small intestines.
Driven by the movement of sodium into enterocytes both transcellular and paracellular.
What is the difference in the water movement between the large intestines and small intestines?
They both have Na+/K+-ATPase on their basolateral membrane in order to set up a gradient for the movement of sodium ions.
On the apical membrane in the small intestines the Na+ is co-transported with glucose, amino acids etc..
On the apical membrane in the large intestines there are Na+ channels which allows the absorption of Na+ and therefore also water.
What are the Na+ channels in the large intestines regulated by?
Aldosterone.
Aldosterone upregulates the Na+ channels in the large intestines to enhance Na+ absorption and water absorption similarly to its function in the kidneys.
Explain the principle of maximal oral rehydration.
A mixture of glucose and salt will stimulate maximum water uptake.
Explain the secretion of water in the intestines.
Driven by chloride movement where cloride enters the the epithelial cells by co-transport with Na+ and K+ (NKCC1).
This leads to an increase in cAMP inside the cells and this activates CFTR.
Cl- ions are secreted via the CFTR.
This leads to a negative enviroment inside the lumen of the intestines. Na+ is drawn into the lumen across tight junctions to make the electrical gradient neutral again.
The NaCl creates an osmotic gradient which allows water movement into the lumen.
Complications of vitamin b12 deficiency.
Megaloblastic anaemia and neurological symptoms
Causes of vitamin b12 deficiency.
Lack of intrinsic factor which is released by parietal cells in the stomach. Intrinsic factor is essential because it bind the vitamin b12 to be absorbed.
Hypochlorhydria which is inadequate stomach acid. The acid is important in initially releasing vitamin b12. This can happen in gastric atrophy or PPIs.
Inadequate intake of vitamin b12 in food
Inflammatory disorders of the ileum where it is absorbed like Crohn’s disease.
Symtpoms of irritable bowel syndrome.
Abdo pain
Bloating
Flatulence
Diarrhoea/constipation
Rectal urgency
Causes of IBS.
More common in females than in males
20-40s most affected age range
More comon in association with psychological disorders
Explain coeliac disease
Immunological response to the gliadin fraction of gluten.
When gluten is absorbed it is broken down into smaller constituents. One of those constituents is gliadin.
In coeliac disease gliadin is presented to T cells of the immune system as a foreign antigen.
This leads to production of antibodies to gliadin and inflammatory response.
Where can gluten be found?
In wheat, rye and barley.
Explain the pathogenesis of coeliac disease.
The immunological response causes damage to the mucosa of the intestines.
This leads to absence of intestinal villi and hypertrophy of the intestinal crypts.
Lymphocytes infiltrate epithelium and lamina propria.
This leads to impaired digestion and malabsorption.
Symptoms coeliac disease.
Diarrhoea
Weight loss
Flatulence
Abdo pain
Anaemia due to impaired iron absorption
Neurological symptoms due to hypocalcaemia
Investigations for coeliac disease
Bloods for IgA antibodies to smooth muscle endomysium and tissue transglutaminase
Upper GI endoscopy and biopsies
Treatment of coeliac disease
Strict gluten free diet
