GI Physiology 6 Flashcards
Summary of nutrient absorption sites - Primary site is the
Small intestine
Summary of nutrient absorption sites - __ of the small intestine impacts the efficiency of absorption
Surface area!
What impacts the sites of absorption throughout the small intestine
Distribution of enzymes and transporters
SA of the SI
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
Digestion of carbs - Our intestine is only set up for
Monosaccharides!
So you have to digest poly and oligosaccharies to the mono in order for it to be absorbed
Digestion of carbs - First primary site of carb digestion is
In the lumen of the intestine
Mediated by alpha amylase which comes from the pancreas (pancreas secretion is stimulated by CCK)
Digestion of carbs - Complete the digestion of carbs
At the brush border
Absorption of carbs - Digestion of carbs - Important regulatory proteins
SGLT1
GLUT5
GLUT 2
Digestion of carbs - SGLT1
Nutrient sodium coupled transporter (or the Na glucose transporter)
Moves glucose and galactose across the apical membrane with Na
Digestion of carbs - GLUT5
Channel that allows for uptake of fructose
Key to Digestion of carbs
You have to break down saccharides into monosaccharides and this is happening in the duodenum and jejunum
Digestion of protein -
Pretty sufficient
At any stage you can absorb protein
Protein digestion begins in stomach with pepsin enzyme (which comes from chief cells)
Digestion of protein - once you have oligopeptides and amino acids - empties from stomach into
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
Digestion and absorption of protein - Amino acids can be absorbed
across the apical membrane and takes place throughout all sections of the intestine
Digestion and absorption of protein - The amino acids are absorbed by
Transporters (referred to as nutrient sodium coupled transporters) and they are highly functional during the fed state
Digestion and absorption of protein compared to carbs
Proteins - you do not have to break them down into amino acids - you can take the oligopeptides
Carbs - have to be monosachharides
Digestion and absorption of protein - Oligopeptides are transported across the membrane by
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
Lipid digestion and emulsification - Lipids primarily come in your diet in the form of
Triglycerides
Lipid digestion and emulsification - In the lumen of the stomach you have
Physical/mechanical disruption called emulsification of the fat
There is not a chemical change of fat in the stomach - just physically disrupting it
Lipid digestion and emulsification - The more fatty the meal,
The longer it is in the stomach
You want to physically disrupt it to get it as small as possible
Lipid digestion and emulsification - After emulsification in the lumen of the stomach
In the duodenum you start mixing with pancreatic lipase and co lipase
And then mix with bile and facilitate absorption
Lipid digestion and emulsification - For fat absorption we want to stimulate what organ
the pancreas because that is where the lipase will come from
Lipid digestion and emulsification Compared to carb and protein
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
Lipid emulsification
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
Delivery of lipid products to enterocytes by micelles - in the absence of bile
Your absorption is less efficient and you are not delivering as much fat to surface of enterocyte
Delivery of lipid products to enterocytes by micelles - If you have impairments in bile production - nutritionally, that will show up as what
Deficiency in fat soluble vitamins (a, d, e, k)
Delivery of lipid products to enterocytes by micelles - once across the membrane what happens
You repackage the fat and package it with lipoproteins to form a chylomicron
Chylomicron taken up into lymph and then gets into circulation
Delivery of lipid products to enterocytes by micelles - After you absorb the fat into the enterocyte, you
repackage it as a chylomicron and that is what shows up in circulation
Intrinsic factor - important for
very important for vit B12 absorption (need to be bound together for vit B12 to be seen)
Vit B12 absoprtion - Vit B12 in complex with IF will move from __ to ___
From the small intestine to the ilium
Vit B12 absoprtion - Ileum
Ileum expresses IF receptor
IF receptor sees the IF (not vit B12)
Two ways to cause a vit B12 deficiency
1 death to parietal cells, atrophy of gastric mucosa (will not secrete IF)
2 damage to the ileum (won’t have the IF receptors)
So if someone is presenting with pernicious anemia could be issue with
stomach or the ileum
Intestinal absorption of iron - Iron is taken up by the
Duodenal enterocytes
Intestinal absorption of iron - what do you need
Vitamin C to convert the iron into an absorbable form
Intestinal absorption of iron - Different ways for Iron to be absorbed
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)
Calcium absorption
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
Lactose intolerance is what type of disorder
Absorption
Lactose intolerance - lactase is expressed
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)
Lactose intolerance - What is the result of lacking lactase enzyme
you get an accumulation of lactose in the lumen
Lactose intolerance - what happens from having an accumulation of lactose in the lumen?
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
Celiac sprue is what kind of disorder
Absorption
Celiac sprue - AKA
Gluten sensitive enteropathy
Celiac sprue - is what
immune reaction to protein component of cereal grains
- results in malabsorption and inflammation
Celiac sprue - what happens
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
Celiac sprue - What happens over time with repeated exposure
You damage and lose the villi so you have dec absorption deficiency of everything
Intestinal transport of fluid and electrolytes - in the small intestine there is a net absorption of ___ and a net secretion of ___
Na, K, Cl
and a net secretion of HCO3
Uptake salt and secrete bicarb
Intestinal transport of fluid and electrolytes - in the large intestine
Still net abs of Nacl
But now you secrete K and Bicarb
Intestinal transport of fluid and electrolytes - What is impacting how the electrolytes are being handled by the enterocytes
Immune system, Enteric nervous system and the endocrine system
SA is important too
Motility is important too - Short transit time - dec amount of abs
Intestinal transport of fluid and electrolytes - In general there is a net ___ of water in the GI tract
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
Intestinal transport of fluid and electrolytes - in disease state - If we dec the salt uptake
You stimulate Cl secretion and now fluid moves into the lumen
Generally still see regular nutrient absorption
Regulation of intestinal ion/fluid transport - what will lead to more fluid secretion??
Active immune system Endocrine regulators (histamines, prostaglandins) Enteric NS (VIP, Ach, 5HT)
Regulation of intestinal ion/fluid transport - Motility and SA
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
S/S of GI pathophys - Define diarrhea
Inc in the number of bowel movements or a decrease in stool consistency
S/S of GI pathophys - Diarrhea can be caused by
Inc intestinal secretion
Dec intestinal absorption
Increased osmotic load
Abnormal intestinal mobility
S/S of GI pathophys - Osmotic diarrhea is what
Diarrhea caused by a non absorbable nutrient
Retention of fluid (can’t absorb it)
S/S of GI pathophys - Secretory diarrhea is what
Diarrhea caused by intestinal secretion of fluid and electrolytes
Secretion of fluid
S/S of GI pathophys - Osmotic diarrhea causes
Disaccharide deficiency (like lactose intolerance)
Pancreatic enzyme deficiency Nutrient binging substances Loss of enterocytes Bacterial overgrowth Antacids
S/S of GI pathophys - Secretory causes
Enterotoxins
Inflammatory cytokines
Tumor
S/S of GI pathophys - If both (secretory and osmotic) at same time, can be caused by
Inflammtory conditions
Infectious disease
S/S of GI pathophys - Constipation is what
Infrequent or difficult evacuation of the feces
S/S of GI pathophys - Constipation causes can be
Diet/lifestyle (fiber for ex, fluid intake)
GI (stricture, hernia, adhesions, CA, inflammation)
Pharmacological
Endocrine
Neurogenic
