Digestion and Absorption in GI Flashcards
Where is the lactase enzyme located?
Brush border
What is lactose intolerance?
- Failure to digest dairy carbohydrates
- 75% of lactose can pass unabsorbed through the intestines
- The lactose in the small intestine is vonverted to SCFAss and H gas in the lumen resulting in the lumen holding water in causing Osmotic diarrhea
What does lactase turn lactose into?
Glucose and Galactose
What digestion occurs in the mouth?
Breakdown of starch with salivary amylase
How does the intestinal mucosa relate to the function of the SI? Where are the villi longest?
- Its ideal for absorbing large amounts of nutrients as the villi and microvilli increase the surface area
- Duodenum has the longest villi
How is the lumen surface of the SI arranged?
Longitudinal folds called folds of kerckring
Describe the path startch takes to glucose?
- Alpha amylase breaks starch into maltose
- Maltase breaks maltose into glucose
How are glucose and galactose absorbed?
- Na/K ATPase creates a gradient
- Secondary active transport through SGLT1 takes in Glu and Gal
How is Fructose absorbed?
GLUT5 via facilitated diffusion
How do carbohydrates get from the lumen to the blood?
Via facilitated transport with GLUT2
What is the purpoe of a D-xylose test?
- D-xylose is drank after an overnight fast and urine is collected for five hours
- We look to see how much is excreted in the urine, if absorption is disrupted there will be little in the urine
- D-xylose is usually absorbed by active Na co transport and passsive diffusion
- This measures the absorptive capacity of duodenum specific to sugars
- Absorbed but not utilized
What test do you use to look for lactose intolerance?
Hydrogen breath test following an oral Lactose test
In general, what causes protein assimilation disorders?
Deficiency of pancreatic enzymes or defect in transporters of intestinal epithelial cells
In a patient who has congenital trypsin absence what will levels of their other pancreatic enzymes look like?
- There are no pancreatic enzymes as they are secreted as zymogens and activated by Trypsin. If ther is no trypsin you will not have Chymotrypsin, Elastase, Carboxypeptidase A or Carboxypeptidaase B.
- Only the zymogen form
What is Cystinuria?
- A defect in the SLC3A1 transporter or absence of di basica AA transporter SLC7A9
- This results in Lys, Ard, Cysteine and Ornithinie not being reabsorbed at the proximal tubule
- Resulting in AA secreted in the urine/feces
What is Hartnup disease?
- Intestines can absorb neutral AA’s such as Trp
- The symptoms are similar to pellagra, Dementia, Diarrhea and Dermatitis, photosensitivity, short stature, urine high in neurtral AA’s
AR disorder of SLC6A19 gene
How is CF related to the pancreas?
- Cystic Fibrosis occurs when theres a defect in CFTR channel which is a Cl channel on apical membrane of the duct cells
- This can result in loss of Bicarb secretion, which protects the pancreas and results in acute and chronic pancreatitis as enzymes cant move from ducts
Where does pepsin come from?
- Chief cells from the stomach secrete pepsinogen and it gets activated into Pepsin at low pH
- it does 10-20% of protien breakdown
What enzymes come from the pancreas and what do they do?
- Trypsin, Chymotrypsin, Carboxypeptidase, elastase
- Breaks proteins down into di and tripeptides and some AA
- Trypsin and chymotrypsin break down in to small polypeptides
- Carboxypeptidase cleaves AA at the carboxyl end
What enzymes come from the brush border of the SI?
`Aminopolypeptidase and dipeptidases
The AA, Di and Trie peptides are then absorbed into the enterocytes
What enzyme activates Trypsionggen and where does it come from?
Enterokinase from the brush border
