The Intestines Flashcards
What are the differences between the jejunum and the ilium?
Jejunum: -Upper left quadrant -Thick intestinal wall -Long vasa recta Less arcades
Ilium:
- Lower right quadrant
- Thin intestinal wall
- Shorter vasa recta
- More arcades
What is the blood supply to ilium and jejunum?
Superior Mesenteric artery.
This comes off the abdominal gives of branches that form a plexus.
What is the venous drainage of the ileum and jejunum?
Superior mesenteric vein
It eventually drains into the portal vein which enters the liver and supplies 70-80% fall blood going into the liver. (hepatic arteries supply the rest).
What are placate circulares?
The numerous permanent crescentic folds of mucous membrane found in the small intestine especially in the lower part of the duodenum and the jejunum.
What are the types of intestinal epithelia?
Enterocytes (most of the cells in the small intestine) -absorptive tall columnar cells.
Goblet cells -mucus producing
Enteroendocrine cells -produce hormones
What are the crypts of Lieberkuhn?
Intestinal glands
High turnover of cells - every 3-6 days.
Contain stem cells at the base which migrate to the surface and mature as they migrate into a variety of cell types.
Paneth cells at base (innate mucosal defence cells) produce antimicrobial peptides.
How do you absorb carbs?
As monosacchides with Na+.
What does starch consist of?
Straight chain (amylose - alpha 1-4 bonds) and branched chains (amylopectin- alpha 1-6 bonds) of glucose
How is starch first broken down?
Salivary and pancreatic amylase breaks the a-1-4 bonds in amylose producing maltose.
What are alpha dextrin?
Shorter but still branched chains of glucose.
What is isomaltase used for?
Break the branched alpha 1,6 bonds.
What enzymes are found in the brush border that help with the digestion of starch
Maltese
Isomaltase
How are monosaccharides absorbed?
Na+/K+ ATPase on basolateral membrane. which maintains low intracellular Na+.
SGLT-1 binds Na+ which allows glucose so Na+ and glucose moves into cell.
GLUT2 transports glucose out of enterocyte. This diffuses down gradient into capillary blood.
Fructose uses GLUT5 transporter to enter enterocyte via facilitated diffusion.
Where does protein digestion begin?
In stomach - pepsinogen released from chief cells gets converted to pepsin by HCl.
Pepsin acts on proteins to covert them to oligopeptides / amino acids so they can move to the small intestine.
Why is trypsinogen important?
Once trypsinogen is converted to trypsin, it catalyses the conversion of zymogens
Trypsinogen to trypsin is catalysed by enteropeptidase (enterokinase).
Give some examples of endopeptidases
Trypsin
Chymotrypsin
Elastase
-Cut in middle of chain
Give some examples of exopeptidases
Carboxypeptidases
-chop off end of chain
How does the brush border of SI help to digest proteins?
Contain proteases
Sometimes cannot completely digest proteins down to amino acids. But, Intestine can absorb short peptides as well as amino acids by PepT1.
Amino acids are transported into cell (similar to glucose) via Na+AA co-transporters.
How does the cytosol of enterocytes contribute to protein digestion?
Small peptides are acted on by cytosolic peptidases (broken down into amino acids)
Certain di- and tri- peptides can also be absorbed into blood.
Was is the difference between water uptake in the small and large intestine.
Both have NaKATPase on basolateral membrane
Apical membrane:
SI : Na+ is co-transported with glucose, amino acids ect..
LI: Na+ channels induced by aldosterone.
How does oral rehydration fluid work?
Mixture of glucose and salt will stimulate maximum water uptake.
Uptake of Na+ generates osmotic gradient - water follows.
Glucose uptake also stimulates Na+ uptake via NaGlucose cotransporters.
What drives water secretion?
Chloride ions
What can B12 deficiency lead to?
Megaloblastic anaemia and neurological symptoms.
What can cause B12 deficiency?
Lack of intrinsic factor mean B12 cannot bind in the stomach - pernicious anaemia
Hypochlorhydra (inadequate stomach acid) -caused by Gastrin atrophy, PPIs
Inadequate intake in food (strict vegetarians)
Inflammatory disorders of ileum (where it is absorbed) - Crohns disease
