GI Physiology 6

Question 1

Summary of nutrient absorption sites - Primary site is the

Answer 1

Small intestine

Question 2

Summary of nutrient absorption sites - __ of the small intestine impacts the efficiency of absorption

Answer 2

Surface area!

Question 3

What impacts the sites of absorption throughout the small intestine

Answer 3

Distribution of enzymes and transporters

Question 4

SA of the SI

Answer 4

Is very large - the villi allow for such a large SA of the SI (no villi with LI)
If you damage the villi, you dramatically change SA and impact abs capacity

Question 5

Digestion of carbs - Our intestine is only set up for

Answer 5

Monosaccharides!

So you have to digest poly and oligosaccharies to the mono in order for it to be absorbed

Question 6

Digestion of carbs - First primary site of carb digestion is

Answer 6

In the lumen of the intestine

Mediated by alpha amylase which comes from the pancreas (pancreas secretion is stimulated by CCK)

Question 7

Digestion of carbs - Complete the digestion of carbs

Answer 7

At the brush border

Question 8

Absorption of carbs - Digestion of carbs - Important regulatory proteins

Answer 8

SGLT1
GLUT5
GLUT 2

Question 9

Digestion of carbs - SGLT1

Answer 9

Nutrient sodium coupled transporter (or the Na glucose transporter)

Moves glucose and galactose across the apical membrane with Na

Question 10

Digestion of carbs - GLUT5

Answer 10

Channel that allows for uptake of fructose

Question 11

Key to Digestion of carbs

Answer 11

You have to break down saccharides into monosaccharides and this is happening in the duodenum and jejunum

Question 12

Digestion of protein -

Answer 12

Pretty sufficient
At any stage you can absorb protein
Protein digestion begins in stomach with pepsin enzyme (which comes from chief cells)

Question 13

Digestion of protein - once you have oligopeptides and amino acids - empties from stomach into

Answer 13

Into duodenum and then you have trypsin enzyme (coming from the pancreas) activated in the duodenum to trypsinogen

CCK is primary stimulus for trypsinogen secretion

Question 14

Digestion and absorption of protein - Amino acids can be absorbed

Answer 14

across the apical membrane and takes place throughout all sections of the intestine

Question 15

Digestion and absorption of protein - The amino acids are absorbed by

Answer 15

Transporters (referred to as nutrient sodium coupled transporters) and they are highly functional during the fed state

Question 16

Digestion and absorption of protein compared to carbs

Answer 16

Proteins - you do not have to break them down into amino acids - you can take the oligopeptides
Carbs - have to be monosachharides

Question 17

Digestion and absorption of protein - Oligopeptides are transported across the membrane by

Answer 17

H linked cotransportes (or H oligopeptide cotransporters) such as PEPT1

The intracellular oligopeptides are further digested into amino acids by intracellular peptidases

And then can be transported across membrane into the blood

Question 18

Lipid digestion and emulsification - Lipids primarily come in your diet in the form of

Answer 18

Triglycerides

Question 19

Lipid digestion and emulsification - In the lumen of the stomach you have

Answer 19

Physical/mechanical disruption called emulsification of the fat
There is not a chemical change of fat in the stomach - just physically disrupting it

Question 20

Lipid digestion and emulsification - The more fatty the meal,

Answer 20

The longer it is in the stomach

You want to physically disrupt it to get it as small as possible

Question 21

Lipid digestion and emulsification - After emulsification in the lumen of the stomach

Answer 21

In the duodenum you start mixing with pancreatic lipase and co lipase

And then mix with bile and facilitate absorption

Question 22

Lipid digestion and emulsification - For fat absorption we want to stimulate what organ

Answer 22

the pancreas because that is where the lipase will come from

Question 23

Lipid digestion and emulsification Compared to carb and protein

Answer 23

With carb and protein - there is no role for the liver

With fat - we need the bile, so there is a role for the liver

Question 24

Lipid emulsification

Answer 24

water and fat do not mix well - so bile acids serve as an emulsifying agent

We will inc water solubility of our fat by mixing the digestive fat with the bile and bile will help emulsify it until you end up with a micelle - micelle can move through aqueous environment toward surface of enterocyte

Change in pH at surface causes micelle to fall apart and then you can have active and passive transport of your fats

Question 25

Delivery of lipid products to enterocytes by micelles - in the absence of bile

Answer 25

Your absorption is less efficient and you are not delivering as much fat to surface of enterocyte

Question 26

Delivery of lipid products to enterocytes by micelles - If you have impairments in bile production - nutritionally, that will show up as what

Answer 26

Deficiency in fat soluble vitamins (a, d, e, k)

Question 27

Delivery of lipid products to enterocytes by micelles - once across the membrane what happens

Answer 27

You repackage the fat and package it with lipoproteins to form a chylomicron Chylomicron taken up into lymph and then gets into circulation

Question 28

Delivery of lipid products to enterocytes by micelles - After you absorb the fat into the enterocyte, you

Answer 28

repackage it as a chylomicron and that is what shows up in circulation

Question 29

Intrinsic factor - important for

Answer 29

very important for vit B12 absorption (need to be bound together for vit B12 to be seen)

Question 30

Vit B12 absoprtion - Vit B12 in complex with IF will move from __ to ___

Answer 30

From the small intestine to the ilium

Question 31

Vit B12 absoprtion - Ileum

Answer 31

Ileum expresses IF receptor IF receptor sees the IF (not vit B12)

Question 32

Two ways to cause a vit B12 deficiency

Answer 32

1 death to parietal cells, atrophy of gastric mucosa (will not secrete IF) 2 damage to the ileum (won't have the IF receptors)

Question 33

So if someone is presenting with pernicious anemia could be issue with

Answer 33

stomach or the ileum

Question 34

Intestinal absorption of iron - Iron is taken up by the

Answer 34

Duodenal enterocytes

Question 35

Intestinal absorption of iron - what do you need

Answer 35

Vitamin C to convert the iron into an absorbable form

Question 36

Intestinal absorption of iron - Different ways for Iron to be absorbed

Answer 36

Can be taken up when associated with heme (endocytic process) Can be taken up by transferrin receptor Can be taken up by divalent cation transporter 1 (DCT1)

Question 37

Calcium absorption

Answer 37

In duodenum through a Ca channel Expression of Ca channel is regulated by vitamin D (which is a fat soluble vitamin) So if you have impairments in fat soluble abs, you can also have impairments in Ca absorp

Question 38

Lactose intolerance is what type of disorder

Answer 38

Absorption

Question 39

Lactose intolerance - lactase is expressed

Answer 39

At the brush border It will take lactose and covert it to glucose and galactose and then those are taken up by SGLT1 Lactose intolerance - you are not expressing the lactase enzyme anymore, so you cannot convert lactose to glucose and galactose (and we can't absorb these - need to be monosaccharides)

Question 40

Lactose intolerance - What is the result of lacking lactase enzyme

Answer 40

you get an accumulation of lactose in the lumen

Question 41

Lactose intolerance - what happens from having an accumulation of lactose in the lumen?

Answer 41

Osmotic pressure changes and you retain water in the lumen intestinal bacteria will rbeak down the lactose and this will release CO2 and hydrogen gas - leading to bloating and distention that is painful

Question 42

Celiac sprue is what kind of disorder

Answer 42

Absorption

Question 43

Celiac sprue - AKA

Answer 43

Gluten sensitive enteropathy

Question 44

Celiac sprue - is what

Answer 44

immune reaction to protein component of cereal grains | - results in malabsorption and inflammation

Question 45

Celiac sprue - what happens

Answer 45

GLuten stimulates an immune response at the mucosal surface so enterocyte takes up the gluten and you have a change in those cells and they start to act like antigen presenting cells System thinks something is wrong and attacks and kills the enterocytes

Question 46

Celiac sprue - What happens over time with repeated exposure

Answer 46

You damage and lose the villi so you have dec absorption deficiency of everything

Question 47

Intestinal transport of fluid and electrolytes - in the small intestine there is a net absorption of ___ and a net secretion of ___

Answer 47

Na, K, Cl and a net secretion of HCO3 Uptake salt and secrete bicarb

Question 48

Intestinal transport of fluid and electrolytes - in the large intestine

Answer 48

Still net abs of Nacl But now you secrete K and Bicarb

Question 49

Intestinal transport of fluid and electrolytes - What is impacting how the electrolytes are being handled by the enterocytes

Answer 49

Immune system, Enteric nervous system and the endocrine system SA is important too Motility is important too - Short transit time - dec amount of abs

Question 50

Intestinal transport of fluid and electrolytes - In general there is a net ___ of water in the GI tract

Answer 50

Absorption NaCl absorbed through the villus and water follows But you can also secrete fluid by regulating Cl (done within the crypts) Generally net abs Regulate abs by uptake Na Regulate secretion by secreting Cl ions

Question 51

Intestinal transport of fluid and electrolytes - in disease state - If we dec the salt uptake

Answer 51

You stimulate Cl secretion and now fluid moves into the lumen Generally still see regular nutrient absorption

Question 52

Regulation of intestinal ion/fluid transport - what will lead to more fluid secretion??

Answer 52

``` Active immune system Endocrine regulators (histamines, prostaglandins) Enteric NS (VIP, Ach, 5HT) ```

Question 53

Regulation of intestinal ion/fluid transport - Motility and SA

Answer 53

Have a huge impact Opiods for example will slow motility and lead to longer time for abs If you reduce SA, you dec time for abs

Question 54

S/S of GI pathophys - Define diarrhea

Answer 54

Inc in the number of bowel movements or a decrease in stool consistency

Question 55

S/S of GI pathophys - Diarrhea can be caused by

Answer 55

Inc intestinal secretion Dec intestinal absorption Increased osmotic load Abnormal intestinal mobility

Question 56

S/S of GI pathophys - Osmotic diarrhea is what

Answer 56

Diarrhea caused by a non absorbable nutrient Retention of fluid (can't absorb it)

Question 57

S/S of GI pathophys - Secretory diarrhea is what

Answer 57

Diarrhea caused by intestinal secretion of fluid and electrolytes Secretion of fluid

Question 58

S/S of GI pathophys - Osmotic diarrhea causes

Answer 58

Disaccharide deficiency (like lactose intolerance) ``` Pancreatic enzyme deficiency Nutrient binging substances Loss of enterocytes Bacterial overgrowth Antacids ```

Question 59

S/S of GI pathophys - Secretory causes

Answer 59

Enterotoxins Inflammatory cytokines Tumor

Question 60

S/S of GI pathophys - If both (secretory and osmotic) at same time, can be caused by

Answer 60

Inflammtory conditions | Infectious disease

Question 61

S/S of GI pathophys - Constipation is what

Answer 61

Infrequent or difficult evacuation of the feces

Question 62

S/S of GI pathophys - Constipation causes can be

Answer 62

Diet/lifestyle (fiber for ex, fluid intake) GI (stricture, hernia, adhesions, CA, inflammation) Pharmacological Endocrine Neurogenic