GI Physiology: Digestion and Absorption Flashcards
Where in the GI tract does most digestion occur?
the small intestine!
Is there bacteria in stool?
Yeah a ton!
How much water is lost to stool per day? How much does the colon absorb?
100ml is lost per day. 1L is absorbed by the colon
What cell types are primarily found in the crypts of the small intestine? Name the function of each.
- Enteroendocrine cells - secrete gastrin, CCK, or secretin.
- Stem cells
- Paneth cells - make lysozyme
What cell types are primarily found in the middle or at the top of small intestinal villi? What does each do?
- Enterocytes - absorb nutrients and express membrane enzymes.
- Goblet cells - mucin secretion
Where in the small intestinal villi does DNA synthesis occur? Where does protein synthesis occur? Where is the disaccharidase and peptidase activity found?
DNA synthesis happens in CRYPTS ONLY.
Protein synthesis happens in the middle of the villi as the cells are differentiating.
Disaccharidase and peptidase enzymes are expressed at the top (tips) of the villi.
How often is the epithelial lining of the small intestine replaced?
every 5-6 days
Do stem cells divide and move up villi like a conveyor belt as they differentiate?
Yeah!
Name two important things that are absorbed mainly in the distal ileum.
- B12
2. Bile acids for recycling
What is the purpose of having folds, villi, and microvilli in the small intestine?
To increase surface area!
Name three major membrane bound enzymes found in the small intestine.
- Enterokinase
- Disaccharidases (there are 5 subtypes)
- Peptidases (2 subtypes)
Trypsinogen can be cleaved to its active form, trypsin, by the membrane-bound enzyme called ________ in the small intestine. Trypsin can then _________ many of the other pancreatic proteases.
enterokinase
activate/cleave
Why do you need to use so many different proteases?
To cleave proteins at different AAs!
Can carbs, protein, lipids, sodium, and water be absorbed pretty much anywhere along the small intestine?
Yeah - although absorption in the duodenum is greatest.
Can the body store vitamins?
Just the fat-soluble ones. Water soluble ones are used or excreted in urine.
Is starch a polymer?
Yeah
Amylase begins digesting __________ (a macromolecule) in the mouth, and in the small intestine numerous ___________ (class of enzymes) finish the job.
carbohydrates in the mouth
numerous oligosaccharidases in the small intestine
Are the oligosaccharidases in the small intestine secreted, or are they membrane bound?
Membrane bound
Which two disaccharides are made of something other than glucose?
lactose (glucose + galactose)
sucrose (glucose + fructose)
How are the three monosaccharides transported into enterocytes? What happens after they get into the enterocytes?
Glucose and galactose are transported by a Na+ dependent co-transporter into enterocytes.
Fructose uses a non-Na+ dependent transporter.
After, they get into the capillaries via facilitated diffusion and go to the liver.
Describe how proteins are digested and get into enterocytes. What happens after they get into enterocytes?
Pancreatic proteases break proteins down to smaller bits: large protein bits, small, protein bits, and free AAs.
Free AAs get into enterocytes using Na+ dependent transporters.
Small proteins (3 AAs) get in using a H+ ion dependent co-transporter.
Large proteins don’t really get in, they gotta be broken up more.
After getting into the enterocyte they go to the capillary with the help of both co-transporters and facilitated transporters.
What happens if you can’t make bile salts or can’t get them into your small intestine?
Steatorrhea, fat malabsorption and fat-soluble vitamin deficiency.
What is the major enzyme that is made by the pancreas (secreted into the duodenum) that works with micelles to aid in free fatty acid absorption?
Lipase
What happens after free fatty acids enter enterocytes?
They are packaged into chylomicrons and exocytosed into the lymphatics (the lacteal in the villi)
