5 Digestion and Absorption in the GI Flashcards
What enzymes are mainly found in the mouth
Amylase and lingual lipase
What enzymes are found in the stomach
Pepsin and gastric lipase
What proteins are found in the pancreas
Amylase, trypsin, chymotrypsin, carboxypeptidase, elastase, lipase-colipase, phospholipase A2, cholesterol esterase
What enzymes are found in the SI
Enterokinase, disacharidases (maltase, sucrase, lactase, trehalase, isomaltase), peptidases (aminooligopeptidase, dipeptidase)
What are cavital/luminal enzymes
Enzymes secreted by salivary glands, stomach, and panreas
What are membrane enzymes
Brush border enzymes (found attached to cell surfaces)
Longitudinal folds of the SI are called
Folds of Kerckring
Villi are longest where
Duodenum
What is the turnover rate of enterocytes
3-6 days
What are enterocytes susceptible to
Radiation and chemotherapy
What is the unstirred layer
A layer of thick mucous that surrounds enterocytes
Lactose is broken down by lactase into
Glucose and galactose
What is responsible for glucose uptake
SGLT1
What is responsible for update of galactose
SGLT1
What is responsible for uptake of fructose
GLUT5
What moves glucose into the blood from the cells
GLUT2
What moves galactose into the blood from the cell
GLUT2
What moves fructose from the cell into the blood
GLUT2
What is the result of lactose intolerance
Osmotic diarrhea
What is a test for carbohydrate assimilation
D-xylose test
Abnormal when low amounts are found in the urine (suggests that it wasn’t taken up)
Why is trypsin such an important enzyme
It activates all the other proteases
What is normally co-transported with the different types of AA
Na
What is co transported with di- and tri-peptides
H
There are separate AA transporters based on
AA type
Neutral, acidic, basic, imino
How is CF linked to pancreatitis
The CFTR Cl transporter doesn’t allow Cl to leave the cell which makes the HCO3 out/Cl in antiporter not work correctly
This means enzymes cannot move from ducts and this can lead to acute or chronic pancreatitis
What does congenital trypsin absence do
Lack of trypsin means no active pancreatic enzymes
Cystinuria is caused by
Defect or absence of Dibasic (Cys, Lys, Arg, Ornithine) AA transporters in SI and kidney
What is Hartnup disease
- cannot absorb neutral AA
- pellagra (resembles niacin deficiency
- tryptophan and thus serotonin deficiency
What initiate the digestion of lipids in the stomach
Lingual and gastric lipases
What hormone is primarily involved in lipid digestion
CCK
What does CCK do
Slows rate of gastric emptying and allows for more mixing
Activates gallbladder secretions
Where does most lipid digestion occur
SI
What are the pancreatic lipases that are secreted
Pancreatic lipase (secreted as active)
Colipase (activated by trypsin)
-once active, displaces bile salts by binding to pancreatic lipse
Cholesterol ester hydrolase
- catalyzes production of cholesterol
- hydrolyzes triglycerides to glycerol
Phospholipase A2 (activated by trypsin)
Lack of ApoB leads to abetalipoproteinemia which leads to
No lipid absorption
Problems with lipid assimilation can manifest as
Steatorrhea
What is pancreatic insufficiency
Failure to secrete proper amounts of pancreatic enzymes
What is Zollinger Ellison syndrome
- gastrin secreting tumor of pancreas
- increased H secretion by parietal cells
- overload of acid into duodenum
What is pancreatitis
Impaired HCO3 and enzyme secretions
Why does ileal resection affect bile salts
The ileum plays a large role in recycling the bile salts into the portal circulation
How does small intestinal bacterial overgrowth cause bile salt issues
Bacteria can deconjugate bile salts which results in poor micelle formation
Overgrowth damges intestinal mucosa (where the bile salts are supposed to be reabsorbed)
What deficiencies are present with tropical sprue
Loss or decreased number of intestinal epithelial cells
Folate and B12
Celiac sprue relates to poor absorption of
Folate, iron, calcium, vitamins A, B12, D
How are most water-soluble vitamins absorbed
Na dependent co-transport
What does Vitamin B12 deficiency cause
Demyelination of the large nerve fibers of spinal cord and important in DNA synthesis in RBC
What is pernicious anemia
Failure of maturation of RBC when B12 is deficient
What can cause issues with B12 absorption
Gastrectomy (partial loss of parietal cells)
Gastric bypass (exclusion of the stomach, duodenum, and proximal jejunum)
What are the common causes of pernicious anemia
Atrophic gastritis-chronic inflammation of the stomach mucosa that leads to loss of parietal cells
Autoimmune metaplastic atrophic gastritis - immune system attacks IF protein or gastric parietal cells
What can poor Vit D absorption cause
Inadequate Ca abs
Rickeys
Osteomalcia
How is iron absorbed
Liver secretes apotransferrin into bile
Binds to free iron and forms transferrin
Binds to receptors on enterocytes
What is primarily absorbed in proximal SI
Fats, sugars, peptides and AA, Iron, Folate, Ca, Water, Electrolytes
What is primarily absorbed in the middle SI
Sugars, peptides and AA, Ca, water, electrolytes
What is primarily absorbed in the distal SI
Bile acids, B12, water, electrolytes
What is primarily absorbed in the colon
Water, electrolytes, MCT, Ca, AA
