GI Exam Lecture 4

Question 1

Two major factors contribute to inhibition or slowing of gastric emptying:

1.

2.

The effect of fat is mediated by the hormone _____ (which is secreted when fat is present in duodenum)

_______ slows gastric emptying

Also regulates _____

Answer 1

Two major factors contribute to inhibition or slowing of gastric emptying:

1. presence of fat in duodenum
2. presence of H+ (low pH) in duodenum

The effect of fat is mediated by CCK (which is secreted when fat is present in the duodenum)

CCK slows gastric emptying and also stimulates bile secretion into duodenum by sphincter of oddi

Question 2

Explain the endocrine vs exocrine pancreas:

Endocrine pancreas : islets of _____

Exocrine pancreas (___% of volume): secretes ___

Answer 2

Pancreas:

Endocrine: islets of lagerhans (2% of total volume): secretes insulin, glucagon, etc

Exocrine pancreas: 90% of total volume secretes enzymes

Question 3

Explain where the sphincter of oddi is

Answer 3

Sphincter of oddi is in between pancreas and duodenum

Remember, liver produces bile, bile is stored in gallbladder

gall bladder can be stimulated to contract to release bile down bile duct and through sphincter of oddi into duodenum

Question 4

Exocrine/endocrine pancreas has significant contributions towards the digestion process

Pancreatic secretion has two components:

1.

2.

Answer 4

EXOCRINE pancreas has significant contributions towards digestive process

Pancreatic secretion has two components:

1. HCO3- (to buffer the H+ from stomach contents)
2. enzymes (to digest carbs, lipids, proteins)

Question 5

The acinar part of the pancreas is stimulated by _____ (what does it secrete?)

The ductal part of the pancreas is stimulated by _____ (what does it secrete)

Answer 5

Acrinar part of pancreas is stimulated by CCK, stimulates enzyme release

Ductal part of pancreas is stimulated by secretin, releases bicarb

Question 6

Cystic Fibrosis:

cystic fibrosis results in a defective _____ transporter

Due to that, the pancreas ductal cells cannot secrete as much ____

As a result, the pancreas gets ____

Answer 6

Cystic Fibrosis:

DEFECTIVE CFTR transporter

the transport of bicarb from ductal cells gets impaired

thus, the pancreas gets destroyed essentially because of the high H+ content that can’t be buffered now

Question 7

CCK released from ___ cells is triggered by what?

CCK stimulates pancreatic ____ cells

CCK can also stimulate the vagus nerve to release what?

Answer 7

CCK release from I cells is triggered by the presence of fat in the duodenum (or amino acids)

CCK stimulates pancreatic acinar cells (to secrete enzymes)

CCK can also stimulate vagus nerve to release ACh, GRP or VIP

Question 8

The enzymes released by the pancreatic acinar cells are not mature/full mature (pick the correct answer)

The activation of those enzymes occurs by _____. How does that enzyme get activated?

How does this relate to pancreatitis?

Answer 8

Enzymes released by acinar cells are PROENZYMES (not mature) trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidase A and B, etc

Trypsin is what activates these enzymes (and enterokinase activates trypsin

Also, if these enzymes are activated too early –> pancreatitis

pancreatic enzymes contain trypsin inhibitors to prevent this

Question 9

What is the major constituent of bile?

Bile acids are made in the ____, stored in the ____, get secreted into the duodenum from the sphincter of ____

In the duodenum, bile acids are important to digest _____, they form what is called a _____

Answer 9

Major constituent of bile: bile acid

Bile is produced in liver, it is stored in gall bladder (CCK can stimulate the contraction of gallbladder and relaxation of sphincter of oddi so that bile can enter the duodenum)

bile is important in digestion of fats, forms what is called a micelle

Question 10

IMPORTANT:

We don’t produce a bunch of bile acids, they need to get recycled to the liver via enterohepatic circulation

Conjugated bile acids are unable to passively cross the intestinal epithelial layer

When chyme reaches ileum, conjugated bile acids are reabsorbed by a symporter known as the ____

Answer 10

We don’t produce a lot of bile acids, they need to be recycled back into the liver via the enterohepatic circulation

Conjugated bile acids can’t passively cross the intestinal lumen

Once chyme gets to the terminal ileum, conjugated bile acids get actively transported across via a symporter known as the apical Na dependent bile acid transporter (abst)

Question 11

Two contractile activities exists in the small intestine during digestion:

1.

2.

Answer 11

Two contractile activities exist in the small intestine:

1. Segmentation (only happens in small and large intestine… mixing propels chyme in up and down direction.. no forward movement)
2. Peristalsis (to move food along)

Question 12

What is MMC within the small intestine

MMC occurs during ______

It is mediated by the hormone called _____

It occurs at 90 minute intervals to clear remaining contents in the small intestine and into the colon

Answer 12

MMC occurs during fasting

It is mediated by a hormone called motilin

It occurs every 90 minutes to clear any reamining gastric contents and intestinal contents within small intestine into colon

Question 13

Carbs:

Only ___saccharides are absorbed through intestinal cells

Therefore carb digestion is focused on breaking things down into _____

Answer 13

Only monosaccharides can be absorbed through intestinal epithelial cells

(only glucose, galactose, and fructose)

Question 14

Maltose consists of _______

Lactose consists of _______

Sucrose consists of?

What ___-ose can humans not digest?

Answer 14

Maltose: 2 molecules of glucose

Lactose: glucose-galactose

sucrose: glucose and frucose

Celluose cannot be digested by humans (gets excreted)

Question 15

Digestion of starch begings with _______

Salivary starts the process, but insignificant

Pancreatic _____ is the most significant, yielding mixture of oligo, tri, and disaccharides (also called dextrins, maltose, and maltitriose)

These are further digested on brush border enzymes

Answer 15

Digestion of starch begings with alpha-amylase

Salivary amylase starts it but is insignificant

Pancreatic amylase is most significant starch enzyme: breaks down starches into maltose, maltitriose, and dextrins

These are further digested on brush border enzymes (isomaltase, maltase, and sucrase)

Question 16

The three disaccharides in food at trehalose, sucrose and lactose (these don’t require amylase digestion)

Maltose is digested by _____ into ____

Lactose is digested by _____ into ______

Sucrose os digested by ____ into _____

What are the three end products of carb digestion?

Answer 16

Maltose is digested by maltase into two glucoses

Lactose is digested by lactase into glucose and galactose

Sucrose is digested by sucrase into glucose and fructose

The three end products of carb digestion are glucose, galactose and fructose

Question 17

Explain what the following transporters do within each border

Brush border: SGLT-1 and GLUT 5

Basolateral Membrane: Na-K pump and GLUT 2

Answer 17

Basolateral Membrane:

SGLT-1 is a symporter of sodium and glucose and galactose

GLUT 5 is the transporter for fructose across the epithelial layer

Basolateral membrane: GLUT2 transporters glucose, galactose, and fructose all into the blood

Question 18

Lactose intolerance:
lack or defeciency in ___ in brush border

Lactose can;t be broken down into glucose-galactose

lactose remains undigested and causes ______

Answer 18

Lactose Intolerance:

lack of or defeciency in lactase on brush border

lactose can’t be broken down into glucose and galactose

Lactose remains undigested and causes osmotic diarrhea

Question 19

Protein digestion starts in the ____ with ______

First step in intestinal protein digestion is activation of trypsinogen—> trypsin by ______

The most important enzyme in protein degradation is ________, without it you cannot digest proteins at all

Answer 19

Protein digestion starts in stomach with pepsin in the stomach

(pepsinogen released by chief cells, activated into pepsin via acidic enviornment)

First step in intestinal protein digesion is activation of trypsinogen—> trypsin by enterokinase

Enterokinase is most important enzyme in protein degradation