Flashcards in 8. The Intestines Deck (94)
What happens to the chyme that is emptied into the duodenum?
It is conditions, acidity is correct by HCO3- secretion from pancreas, liver, and duodenal mucosa. Hypertonicity corrected by osmotic movement of water into duodenum across wall. Partly digested nature correct for by complete digestion by enzymes from pancreas and duodenal mucosa, with bile acids from liver.
What makes the small intestines good for absorption?
Large surface area that contents is exposed to through gentle agitation for hours.
How is the small intestine surface area so big?
Millons of villi project into the lumen.
How is the brush border of the small intestines formed?
The epithelial cells arise by rapid division in the crypts between villi and migrate towards the tips to be shed. They mature as they migrate and the luminal surface gets covered with millions of microvilli.
What is the purpose of the small intestine brush border?
Increasing the surface layer, it forms an 'unstirred layer' where nutrients meet and react with enzymes secreted by enterocytes, completing digestion prior to absorption.
What is the function of the large intestines?
Absorb water from the indigestible residues of chyme and convert them into semi-solid stool or faeces that is stored temporarily.
What are teniae coli?
Thickened bands of smooth muscle, running the length of the large intestines.
What are haustra?
The shortened part of the walls that are sacculated between the teniae.
What are the functions of the whole small intestine?
Secrete protease/ carbohydrase enzymes to complete digestions, secrete hormones - secretin, gastrin, cholecystokinin.
What are the functions of the duodenum?
Bile and pancreatic secretions added via ampulla of vater, secrete HCO3- to neutralise chyme, osmotic movement of water in to make chyme more hypotonic, absorption of iron.
What are the functions of the jejunum?
Absorption fo carbohydrate and amino acids. Fatty acids, vitamins, mineral, electrolytes, and water soak through vili.
What are the functions of the ileum?
Absorption of vitamin B12, bile, and anything not absorbed by the jejunum.
How long is food in the large intestine for?
16 hours to finish digestion.
What are the functions of the large intestines?
Absorption of water, any remaining absorbable nutrients, vitamins created by colonic bacteria (vitamin K, B12, thiamine, riboflavin). Sends indigestible matter to the rectum.
What is the function of the rectum?
To store and compact faecal matter for defaecation.
How are a-amylases important in absorption?
They break a1-4 bonds and are secreted in saliva and by the pancreas. They yield glucose and maltose from amyloses and a-limit dextrins from amylopectins.
How do brush border enzymes complete breakdown of glucose?
Isomaltase breaks down branched molecules at a1,6 bonds. Maltase breaks maltose to glucose. Sucrase breaks sucrose to glucose and fructose diamer. Lactase breaks lactose to glucose and galactose diamer.
How is glucose absorbed in the gut?
Actively using energy from the Na+ gradient from the Na+K+ATPase in the basolateral membrane. Glucose enters the epithelial cell across its apical membrane via Na+/glucose symptorter - SGLT1.
How does glucose leave the epithalial cell into the bloodstream across the basolateral membrane?
Via facilitated diffusion through GLUT2 transporter.
How does fructose enter cells from the lumen?
Via facilitated diffusion.
How are proteins digested to short peptides in the stomach?
By pepsin from chief cells.
How are proteins digested to short peptides in the duodenum?
By peptidases from the pancreas.
Which bonds do the following enzymes prefer breaking? Pepsin, trypsin, chymotrypsin, carboxypeptidase.
Pepsin - bonds near aromatic AA side chains. Trypsin - bonds near basic AA side chains. Chymotrypsin - bonds near aromatic AA side chains. Carboxypeptidase - C-terminal AA with basic side chains.
Why is it useful that neonate guts are open?
They can pick up whole proteins, helpfully including IgA from mother's breast milk for passive immunity.
How are amino acids uptaken?
Using Na+/amino acid co-transporters that use the Na+ gradient from the Na+/K+ATPase. Or by facilitated passive diffusion.
How are dipeptides and tripeptides taken up?
By active mechanisms associated with pumping H+ into the lumen - then returns by co-transport with the peptide.
Why is it hard to digest fats?
Fats are insoluble in water so aggregate into large globules so digestive enzymes can't effectively get at them and the problem is made worse by acid in the stomach.
How does the duodenum help with fat digestion?
Bile acids enable fats to be incorporated into small micelles that have a higher surface area for lipases and carry fats to the unstirred layer to slowly diffuse into epithelial cells.
What happens to fatty acids when in epithelial cells?
They are reconstituted into triacylglycerols and re-expelled as chylomicrons into the lymphatic system and then systemic veins.