Digestion and Absorption in GI

Question 1

Where is the lactase enzyme located?

Answer 1

Brush border

Question 2

What is lactose intolerance?

Answer 2

• 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

Question 3

What does lactase turn lactose into?

Answer 3

Glucose and Galactose

Question 4

What digestion occurs in the mouth?

Answer 4

Breakdown of starch with salivary amylase

Question 5

How does the intestinal mucosa relate to the function of the SI? Where are the villi longest?

Answer 5

• Its ideal for absorbing large amounts of nutrients as the villi and microvilli increase the surface area
• Duodenum has the longest villi

Question 6

How is the lumen surface of the SI arranged?

Answer 6

Longitudinal folds called folds of kerckring

Question 7

Describe the path startch takes to glucose?

Answer 7

• Alpha amylase breaks starch into maltose
• Maltase breaks maltose into glucose

Question 8

How are glucose and galactose absorbed?

Answer 8

• Na/K ATPase creates a gradient
• Secondary active transport through SGLT1 takes in Glu and Gal

Question 9

How is Fructose absorbed?

Answer 9

GLUT5 via facilitated diffusion

Question 10

How do carbohydrates get from the lumen to the blood?

Answer 10

Via facilitated transport with GLUT2

Question 11

What is the purpoe of a D-xylose test?

Answer 11

• 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

Question 12

What test do you use to look for lactose intolerance?

Answer 12

Hydrogen breath test following an oral Lactose test

Question 13

In general, what causes protein assimilation disorders?

Answer 13

Deficiency of pancreatic enzymes or defect in transporters of intestinal epithelial cells

Question 14

In a patient who has congenital trypsin absence what will levels of their other pancreatic enzymes look like?

Answer 14

• 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

Question 15

What is Cystinuria?

Answer 15

• 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

Question 16

What is Hartnup disease?

Answer 16

• 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

Question 17

How is CF related to the pancreas?

Answer 17

• 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

Question 18

Where does pepsin come from?

Answer 18

• Chief cells from the stomach secrete pepsinogen and it gets activated into Pepsin at low pH
  
  • it does 10-20% of protien breakdown

Question 19

What enzymes come from the pancreas and what do they do?

Answer 19

• 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

Question 20

What enzymes come from the brush border of the SI?

Answer 20

`Aminopolypeptidase and dipeptidases

The AA, Di and Trie peptides are then absorbed into the enterocytes

Question 21

What enzyme activates Trypsionggen and where does it come from?

Answer 21

Enterokinase from the brush border