Small Intestine Flashcards
What is the main site of action in the SI?
Jejenum
Which part of the duodenum do the bile duct and pancreatic duct drain into?
second part
What are the pile circulares?
mucosal layer is thrown into huge circular folds which increase SA and create turbulence for mixing of fluids
What is the role of crypts between microvilli?
small mucosal glands that secrete bicarb and mucus to neutralise acid and facilitate smooth fluid movement
What are microvilli?
further increase SA of villi
have brush borer enzymes that break down materials
What is the role of segmentation in motility?
Mixes food up and mixes it with intestinal secretions
Alternate contraction of neighbouring segments churns and fragment the bolus
What stimulates migrating motor complexes (slow, strong peristaltic waves)?
Motilin
Peptide secreted by M cells in the crypts
How often are migrating complexes?
Every 90 mins when gut is empty
What suppresses motilin?
feeding
what is the role of migrating motor complexes stimulated by motilin?
keep the gut clean
prevent reflux
prevent bacterial growth
What do amylases break down?
Carbohydrates
1,4 internal bonds
this leaves alpha limit dextrin (small chains with 1,6 links)
After amylase partially breaks down carbohydrates, what breaks down the short chains?
Specific enzymes on the burns border membrane break down disaccharides into monosaccharides so they can be actively transported into the cell
What protein absorbs glucose and galactose? Is this active or passive?
Specific glucose transporter 1 (SGLT1)
active
What protein absorbs fructose? actively or passively?
Glut5 transporter
passive
Where does proteolysis begin?
Stomach
What protease is secreted by crypt cells?
Enterokinase - cleaves trypsinogen into trypsin which then cleaves pancreatic enzymes into active forms
e.g. proelastase - elastase
Why is pepsin inactivated in the duodenum?
Higher pH
Where do endopeptidases cut?
Within a protein chain (usually within a certain pair of amino acids)
e.g. trypsin
chymotrypsin
elastase
Where do exopeptidase cut?
(ex = exit)
at the last peptide bond to cleave off the last amino acid
Where are small peptides taken up in the SI?
Diffuse to brush border, where membrane bound peptidases chop them up into amino acids. These amino acids are taken up by sodium linked secondary active transporters.
Di peptides are taken up by proton linked secondary active transporters.
What happens to the small amount of protein taken up into the cell by endocytosis?
Most is degraded
Except in M cells which overly Peyer’s patches (immune tissue under mucosa)
This allows the immune cells to detect how to handle the food - to respond or not?
What is the role of bile salts?
Break up lipid droplets, creating a single layer of lipids and increasing surface area so enzymes can break down the lipids
What is the role of pancreatic lipase in fat digestion?
Cleaves off fatty acids from the outside of lipids leaving a monoglyceride + 2 free fatty acids
Where do mixed micelles (monoglycerides, fatty acids + bile salts) diffuse to and how?
Close to the brush border where they deliver their contents across the membrane
Bile salts make the molecule soluble
