Small Intestine and pharmacology Flashcards
Describe blood supply to jejunum and ileum
Supplied by SMA
Branches into ileocolic artery
Which branches into jejunal and ileal
What is SGLT1?
Na/glucose co transporter in small intestine which takes these molecules from lumen to blood. Na down conc gradient, glucose against
How can one distinguish between jejunum and ileum?
Jejunum - long vasa recta, 1/2 arcades, wide bore, thick folded wall
Ileum - short vasa recta, multiple arcades, narrow bore, thin smooth wall
What is the risk of proximal duodenal ulcers?
Perforation of gastroduodenal artery which will bleed profusely
Describe the blood supply to the duodenum
Proximal supplied by coeliac trunk - gastroduodenal and superior pancreaticoduodenal
Distal supplied by SMA - inferior pancreaticoduodenal
What does the Ligament of Treitz provide a good landmark for? And where does it originate?
Duodenal-Jejunal flexure
Originates at diaphragm
Name 4 symptoms of malabsorption
Weight loss Abdominal distension Diarrhoea Steatorrhoea Pernicious anaemia Hypochromic anaemia
What deficiencies can cause malabsorption?
Brush border enzyme deficiency
Poor absorption
Pancreatic enzyme secretion deficiency
Bile secretion deficiency
What happens to the SI in coeliac disease?
Lining becomes sensitive to gluten
This causes damage to the mucosa
So the ability of the SI to absorb fats is affected
Why does lactose intolerance result in diarrhoea?
Bacteria in colon digest lactose which the SI is unable to due to a deficiency of lactase brush border enzymes. The monosaccharides cannot be absorbed here and so create an osmotic drag, pulling water into the lumen and causing diarrhoea
What is Vit B12 bound to in the stomach and how is that different from the SI?
R protein in stomach
Intrinsic factor in SI
What 3 things are required for the absorption of fat to take place?
Bile salts
Phospholipids
Pancreatic lipase
What are micelles in the SI?
Globule containing monoglycerides and fatty acids
Surrounded by bile salts and phospholipids
Formation and break down of micelles in equilibrium so some free fatty acids which can diffuse into the epithelial cells
Can also carry fat soluble vitamins
How do reassembled fats in the epithelial cells get out?
Triglycerides are packaged into chylomicrons which are exported across the basolateral membrane to leave intestinal villus via lymph vessel as they are too big to pass into the blood stream
How does the emulsification of fats aid absorption?
Larger surface area for pancreatic lipase to have its effect
Make it more water soluble
Which 4 enzymes are responsible for protein/peptide digestion in the SI?
Trypsin
Chymotrypsin
Aminopeptidase - brush border enzyme
Carboxypeptidase
Which ion are amino acids usually cotransported with during absorption?
Na
What are maltase, lactase and fructase?
Brush border enzymes which convert disaccharides into monosaccharides
Which vitamin facilitates the absorption of Ca?
Vit D
Which molecule does iron bind to within epithelial cells for storage?
Ferritin
In what circumstance would iron storage be depleted?
Reduced iron content in blood eg haemorrhage
What are alginates?
Anionic polysacharrides which form a raft like gel layer on top of the stomach contents to reduce the symptoms of acid reflux
What do magnesium salts, aluminium salts and bicarbonate salts have in common?
Antacids used to reduce acidity of stomach acid to help reduce acid reflux
Give 2 uses of Misoprostol
Abortion drug
Prevent gastric damage caused by chronic NSAID use
What is cimetidine?
Histamine H2 antagonist
What caution should be taken when prescribing cimetidine?
Dose given to those with hepatic and renal impairment
And in women who are pregnant or breast feeding
What would bismuth chelate be used for generally?
In a combination regimen to treat H pylori involvement of peptic ulcers
Give 4 ways that bismuth chelate has its desired effect
Mild antibiotic Coats mucosa Enhances local prostaglandin synthesis Stimulates bicarbonate secretion Absorbs pepsin
Name 2 side effects of bismuth chelate
Nausea and vomiting
Reversible blackening of tongue and faeces
What is Omeprazole?
Proton pump inhibitor used to treat acid reflux
Why are proton pump inhibitors the gold standard for acid reflux treatment?
Specific local effects - accumulate in parietal cell canaliculi and are only active at low pH
Provide irreversible inhibition so longer lasting effect
More effective than H2 antagonists at decreasing basal and stimulated acid secretion
How are proton pump inhibitors usually delivered?
Orally via enteric coated tablet as they are degraded rapidly at the low pH of the stomach so are absorbed in SI and enter cells via the blood
What are the enteric hormones?
CCK, secretin, GIP, VIP, motilin
What effect does secretin have on the pancreas and liver?
Causes secretion of HCO3 from pancreas and stimulates bile production in liver
What effect does CCK have on pancreas and gallbladder?
Causes secretion of digestive enzymes from the pancreas and causes contraction of the gallbladder
What effect do secretin and CCK have on motility?
Inhibit gastric motility and secretion
What is the function of VIP?
Increases blood flow to the GI tract
What do Brunners glands do?
Secrete mucus in the duodenum
Which enteric hormone is responsible for clearing out the system between meals and stimulating migrating motor complexes?
Motilin
Which part of the duodenum has a mesentery?
4th
Where do the SMA and SMV emerge?
Behind pancreas and duodenum
What are the branches of the SMA?
Middle colic Inferior pancreaticoduodenal Ileocolic which branches into: Jejunal Right colic Ileal Appendicular
What sphincter guards the entrance to the bile duct from the duodenum?
Hepato pancreatic sphincter
What are the secretions of the proximal small intestine?
Mucus - Brunners glands
Water
Enteric hormones
What does Motilin do?
Stimulates migrating motor complexes via enteric and autonomic nervous systems
What does gastric inhibitory peptide do?
Inhibits gastric secretion
Stimulates insulin secretion
What digestion occurs in the duodenum and proximal jejunum?
Fats are digested by pancreatic lipase to monoglyceride and fatty acids
Starch digestion is completed by pancreatic amylase. Disaccharides are broken down into monosaccharides by brush border enzymes
Proteins are broken down to peptide fragments by trypsin and chymotrypsin. Peptide fragments are digested to free amino acids by carboxypeptidase (pancreas) and aminopeptidase (luminal membranes of small intestine epithelial cells)
What 2 factors are required for fat emulsification?
Bile salts
Phospholipids
Describe the absorption of fat
Monoglycerides and fatty acids are held in micelles
They diffuse into an unstirred layer next to the epithelial cells in equilibrium of free and micelle bound
Free fatty acids and monoglycerides can diffuse into cells
Here they are reassembled into fats and packaged into chylomicrons
These are transported across the basolateral membrane and leave via lymph vessels
Describe the digestion of carbohydrates
Amylase from the mouth and pancreas digests the carbohydrate into disaccharides and monosaccharides. The monosaccharides are absorbed via channels. Disaccharides are converted to monosaccharides by brush border enzymes and then absorbed
What channels are responsible for absorption of monosaccharides?
SGLT1 is a Na and glucose co transporter
GLUT5 is a fructose channel
GLUT2 channels transport glucose, galactose and fructose out of the cell into the blood
Describe the digestion of proteins and absorption of amino acids
Digested by pepsin from stomach and peptidases from the pancreas and duodenum
Amino acids are absorbed by co transport with Na or H
What is the absorbable form of iron?
Fe2+ so any Fe3+ is first reduced
What are the fat soluble vitamins?
Vitamins A, D, E and K follow the pathway for fat absorption
What defects in digestion and absorption occur as a result of coeliac disease?
Fat absorption
Lactose hydrolysis
What defects in digestion and absorption occur as a result of pancreatitis?
Fat digestion
What defects in digestion and absorption occur as a result of ileum resection or Crohn’s disease?
Vitamin b12 and bile salt/acid absorption
