The small intestine Flashcards
how is the pancreas attached to the small intestine
via the common bile duct
what is the function of the brush border enzymes
intergral memnbrane proefins
on surfaces of microvilli
break down material n contact with brush border
what is peristalsis
waves of muscular contraction which move contents along the length of the GIT
describe the muscles involved in peristalsis
circular muscles contract behind bolus while circular muscles ahead of bolus relax
longitudinal muscles ahead of the muscles contract shortening adjacent segments
wave of contraction in circular muscles forces bolus forward
which muscles contract first in peristalsis
longitudinal then circular behind the bolus
what is segmentation
alternative contraction of neighbouring segments which churn and mix contents with intestinal secretions
describe the migrating motor complex
when the gut is empty
MMC’s generate every 90 mins stimulated by motion (22 aa peptide secreted by M cells and erythromycin)
these are to help clean the gut, slow strong peristaltic waves
what inhibits MMC’s
feeding
what hormones are secreted from APUD cells
CCK from I cells
secretin from S cells
MOtilin from M cells
gastrin from G cells
where does bicarbonate come from
pancreas
where does mucus come from
goblet cells
what foods must be digested before absorption
carbs
lipids
proteins
describe carb digestion
soluble amylases only break down internal a1-4 bonds, remaining short china carbs are broken down by enzymes on the brush border
glucose and galactose actively absorbed by SGLT1
fructose passively via GLUT5 transporter
where does protein digestion start
in the stomach -15% but pepsin is inactivated in the duodenum
where is enterkinase secreted from
crypt cells
what is the role of trypsinogen (released from the pancreas) in protein digestion
converted to trypsin by enterokinase which converts proenzymes to the active enzymes
what are 5 proenzymes in protein digestion
trypsinogen chymotrypsinogen proelastase procarboxypeptidase a procarboxypeptidase b
what are large proteins digested by within the protein chain
typsin
chymotrypsin
elastase
what is the role of carboxypeptidases
cut at the last peptide bond
what is the specific role of carboxy A
cuts peptide with C terminal neutral AA such as serine
what is the specific role of carboxy b
peptide cut with C terminal basic AA such as arginine
how are amino acids taken up into the cell
via sodium linked secondary active transporters
how are di/tri peptides taken up by cells
proton linked secondary active transport
what is the role of M cells in protein absorption
phagocytose large proteins into cells
how are fats digested
bile slats break up lipid droplets increasing surface area as fats cannot dissolve in water
amphipathic bile slats causes emulsification
what is the role of the pancreas in fat digestion
pancreatic lipase cells off outside fatty acids leaving a monoglyceride plus 2 free fatty acids
once fats are turned into monglycerides or mixed with bile salts what happens to them
diffuse close to the brush border and are resythesised and packaged in into chylomicra which are exocytosied which drain into lymphatic lacteals
describe bile salt recycling
conjugated bile salts are actively absorbed in the distal ileum
describe how iron is absorbed
absorbed in fe 2 state and starts in the duodenum
Dcytb reduces iron from fe3+
either absorbed within haem or via cotransport with H+
iron leaves the cell via FP1 and ends to plasma transferrin
bilirubin is a bi product of absorbing iron
how is calcium absorbed
actively reabsorbed in the dude which is regulated by vit D
in the rest of the small bowel it is reabsorbed paracellularly
Ca binds to calbindin in the cell
leaves cell via na / ca anti porter
how are fat soluble vitamins absorbed
ADEK
absorbed with lipids as they are dissolved in lipid droplets and enter into chylomicrons
how are water soluble vitamins absorbed
require special transport proteins usually Na+ linked
how is Vit B12 absorbed
absorbed only hone bound to intrinsic factor which is released from gastric parietal cells in the ileum
what is the role of aldosterone in digestion
absorption of Na and K secretion in colon are aldosterone regulated
what happens to acidity as you move through the GIT
acid in stomach and becomes more alkaline
how much is absorbed in the small intestine compared to large
7L/day
1.9L/day
