Digestion And Absorption (Lauren) Flashcards
When food gets to the digestive compartments, is it a size that we can absorb?
No, we need to break foodstuffs down into smaller sizes that can absorbed.
In a molecule of glycogen or starch, glucose molecules are linked to each other by ___,___ linkages and at branch points, there are ___,___ linkages
1,4 glucose to glucose
1,6 at branch points
How do we break down complex polysaccharides like glycogen and starch?
First break them into oligosaccharides
Then break down oligosaccharides into simple sugars (monosaccharides)
What kind of bonds can salivary amylase and pancreatic amylase break down?
1,4 only
What enzyme breaks down lactose?
Lactase
What enzymes break down Dextrins?
Maltase
Dextrinase
What enzymes break down maltotriose and maltose
Maltase
Sucrose
Dextrinase
What enzyme breaks down sucrose?
Sucrose
What are the products of lactose breakdown?
Glucose
Galactose
What are the products of sucrose breakdown?
Glucose
Fructose
What are the 2 main groups of enzymes that break down disaccharides and oligosaccharides
Galactosidases (Lactase)
a-glucosidases (sucrase, maltase, dextrinase)
What is another name for the enzymes that break down disaccharides and oligosaccharides into monosaccharides?
“Intrinsic membrane proteins”
How is glucose brought into the enterocyte from the lumen?
Secondary active transport
Comes in with the sodium gradient
What is the name of the transporter that brings glucose and galactose from the lumen across the apical membrane and into the enterocyte ?
SGLT 1
Comes in with SODIUM
Does SGLT1 use (active/secondary active/passive) transport to bring glucose and galactose into the enterocyte?
Secondary active
How does fructose get into the enterocyte
PASSIVE transport through the GLUT-5 transporter
(Don’t need active transport since there is so much more fructose in the lumen than inside the cell….it just diffuses down its gradient)
How do glucose and galactose travel across the basal membrane into the blood?
Facilitated diffusion using the GLUT-2 transporter
What is the main cause of disorders with carbohydrate digestion?
Enzyme deficiencies
Ex: lactase deficiency
Why do enzyme deficiencies cause you to “liquidate your assets” (aka diarrhea)
The unabsorbed carbs are osmotically active and hold water
🧻~~osmotic diarrhea~~
Is lactose intolerance congenital or acquired?
Its usually congenital (but not evident until later in life for many ppl)
Can also be caused by long-term disease that messes up membrane lactase
True or false: a significant amount of your protein intake comes from sloughed epithelial cells and gastric secretions
True 🍴
What are the products of protein digestion?
Amino acids
Oligopeptides
What enzyme needs to be activated FIRST before any other enzymes can be activated?
Trypsinogen must be turned into Trypsin by ENTEROPEPTIDASE**
*********
What enzymes does Trypsin activate?
Trypsinogen—> Trypsin
Chymotrypsinogen—> Chymotrypsin
Proelastase—> Elastase
Procarboxypeptidases A and B —> Carboxypeptidases A and B
What enzyme is required to activate Trypsin before any other enzymes can be activated
ENTEROPEPTIDASE
What happens to oligopeptidases when they get to the brush border?
Membrane bound peptidases will further break them down into AA’s
OR
Endocytosis of oligopeptides and immunoglobulins (from breast milk)**
When you’re a little baby drinking your mommy’s breast milk and you ingest immunoglobulins, how do you absorb those without first breaking them down into individual amino acids?
Brush border cells can use endocytosis to eat them WHOLE**
How do Amino acids get from the lumen into the enterocytes?
Secondary active transport coupled to sodium transport (just like glucose)
How do dipeptides and tripeptides get from the lumen into the enterocyte?
Coupled to H+ transport**
Once inside the cell, they will get further broken down by peptidases into amino acids
What co-transporters shuttle amino acids from the lumen into the enterocyte?
There are 4 separate ones depending on the type of amino acid:
Neutral AA’s
dibasic AA’s
Dicarboxylic AA’s
Imino (proline)
What are the 3 diseases that can cause problems with protein digestion/absorption?
Pancreatic insufficiency
Hartnup disease
Cystinuria
Why does pancreatic insufficiency inhibit protein absorption?
Insufficient amount of Trypsin= malnutrition
How does Hartnup disease affect protein absorption?
The transporter for neutral amino acids is defective
BUT you can still absorb di- and tripeptides via endocytosis, and those guys will have neutral amino acids in them.
👍 no big deal. no amino acid deficiency here
How does Cystinuria affect protein digestion/absorption?
Transporter for dibasic amino acids (cystine, lysine, and arginine) is absent from gut and kidney= dibasic amino acids lost in urine and feces
BUT di- and tripeptides can still be sucked up via endocytosis :)
What makes the digestion of fats so challenging?
Fats are not water soluble, but the enzymes needed to break them down are.
Fats also tend to coalesce so the surface area is small (reason we must churn and have bile emulsification)
What are the 4 key events in fat digestion?
Secretion of bile and lipases
Emulsification by bile
Hydrolysis of ester linkages
Solubilizing digestion products within micelles for delivery to enterocytes
What are the 3 specific enzymes needed for fat digestion?
Pancreatic lipase
Cholesterol ester hydrolase
Phospholipase A2
What does pancreatic lipase do?
Cleaves FA’s off triglycerades at the 1 and 3 position
What protects pancreatic lipase from being destroyed by bile?
Colipase****
No colipase= no pancreatic lipase
What does cholesterol ester hydrolase do?
Removes fatty acid from:
Cholesterol
Vitamin A, D, E,
Glycerine
(Non-specific esterase)
What does Phospholipase A2 do?
Hydrolyzes phospholipids at the 2 position
How do lipolytic products get through the intestinal mucosa?
Micelles diffuse through the “unstirred” later to the mucosal surface. Then they just diffuse right into the cells down their concentration gradient
95% of fat is removed by the (small/large) intestine
Small
Once all the pieces of triglycerides that were in the micelle diffuse into the cell, what happens to them?
They get reassembled into triglycerides and then turned into chylomicrons
What happens to chylomicrons once they are produced inside the cell?
They get EXOCYTOSED across the basolateral membranes into a lacteal. It gets carried through the lymph system to the thoracic duct where it enters the general circulation
What is a chylomicron?
A core of triglycerides surrounded by phospholipids and apoproteins
How do micelles travel around the body?
THEY FUCKING DON’T!!!!
They are ONLY in the lumen of the intestine!
DO NOT MIX UP MICELLES AND CHYLOMICRONS
What do chylomicrons do once they are in your bloodstream?
They deliver triglycerides to adipose and muscle
What are the 4 ingredients in chylomicrons?
Triglycerides 84%**
Cholesterol 6%
Phospholipids 8%
Apoproteins 2%
Zollinger-Ellison Syndrome is abnormal (digestion/absorption)
Digestion
What happens with Zollinger-Ellison syndrome?
You have a tumor that secretes gastrin which causes the small intestine to be WAY TOO acidic.
All the acidity denatures pancreatic lipase and you can’t digest lipids.
(= lipids in feces=steatorrhea)
Whipple’s Disease is abnormal (digestion/absorption)
Absorption
What happens with Whipple’s disease?
Underdeveloped lymph system impairs the ability to pick up chylomicrons. Leads to steatorrhea
Another name for enterokinase is________
Enteropeptidase
Do these enzymes come from the small intestine or the pancreas:
Enterokinase
Disaccharidases
Maltase
Sucrase
Lactase
Peptidases
Aminooligopeptidase
Dipeptidase
Small intestine (they are membrane proteins)
Do these enzymes come from the pancreas or the small intestine:
Amylase
Trypsin
Chymotrypsin
Carboxypeptidase
Elastase
Lipase-colipase
Phospholipase
Pancreas
How do fat soluble vitamins travel through the lumen of the intestine?
Micelles
If you had no micelles for some reason, would you have a vitamin deficiency?
Yes, you would not be able to absorb fat-soluble vitamins
How do fat soluble vitamins enter the circulation?
In chylomicrons
How do water-soluble vitamins get into the enterocytes?
Na+ dependent co-transport
Secondary active transport, just like glucose
How does B12 get absorbed?
Bound to gastric intrinsic factor and then it gets absorbed in the ileum**
What part of the intestine is B12 absorbed?
ILEUM
Why is vitamin D required for calcium absorption?
It causes the expression of the Calcium binding protein which is the intracellular shuttle for Calcium- we don’t want a bunch of free calcium floating around inside cells
How does calcium get across the brush border?
Facilitated diffusion
How does calcium get across the basolateral membrane and into the blood?
TWO OPTIONS:
Ca+ ATPase
Na+/Ca+ exchanger
What does gastric acid have to do with the intestinal absorption of Iron?
Helps absorption and with solubilization by reducing Fe3 into Fe2
How does Iron travel around the blood
Transferrin
How does iron get stored inside cells?
In ferritin
If an enterocyte has a bunch of iron stored on ferritin, and then it gets sloughed off, what happens to the iron
You just poop it out
Where is water reabsorbed?
Small intestine
Large intestine
NOT stomach
What is the driving force for water reabsorption into enterocytes?
Water follows solutes out the basolateral membrane
How does Na+ get pumped out of the enterocytes?
Na+/K+ ATPase
Requires A LOT of energy
Water reabsorption is (isosmotic/hyposmotic)
Isosmotic
Water and solute absorption are proportional
What part of the intestine is the #1 site for Na+ absorption?
Jejunum*
How does Na+ get absorbed in the jejunum?
TWO OPTIONS:
Co transported with sugar or amino acid
Na+/H+ exchange (NHE)***
What are the 2 important things that happen as a result of the Na-H+ exchanger in the jejunum?
- H+ that gets sent into the lumen neutralizes HCO3-
- Na+ floats through the cell and gets transported into the blood where it will combine with an HCO3- (that came from the production of the H+)
In the jejunum, we end up with a net absorption of _______
NaHCO3
******
(From the Na and the HCO3- that get transported across the basolateral membrane)
How does Cl- get absorbed in the jejunum?
Paracellular absorption driven by a voltage gradient
What additional transporter is on the apical membrane of cells in the ILEUM?
Cl-/HCO3- exchanger
***
(Still have the NHE and the cotransporters for absorption of Na+)
What transporter is present on the basolateral membrane in the jejunum and not the ileum?
HCO3- transporter
What transporter is present on the basolateral membrane in the ileum and NOT in the jejunum?
Cl- transporter
In the ileum, what happens to the acid/base status of the lumen?
Nothing, H+ and HCO3- are both secreted into the lumen
In the ileum we are not trying to recover bicarb, we’re trying to recover Cl-
In the ileum there is a net reabsorption of
_________
NaCl****
Net reabsorption
In Jejunum:
In Ileum:
In Jejunum: NaHCO3
In Ileum: NaCl
What electrolyte gets absorbed in the colon and through what transporter?
Na+ gets absorbed through Epithelial Na+ Channels (ENaC)
True or false: ENaC channels in the colon are sensitive to aldosterone like they are in the kidney
True
What electrolyte gets secreted in the colon?
K+
What will cause an increased amount of K+ to be secreted into the lumen in the colon?
Increased flow/diarrhea
Increased flow will increase Na+ absorption, which will kick out more K+
Severe diarrhea puts you at risk of (hypo/hyper) kalemia
Hypo
What 3 things get lost with diarrhea?
Fluid
HCO3-
K+
Diarrhea puts you at risk for metabolic (acidosis/alkalosis)
Acidosis (loss of HCO3-)
What are 3 possible causes of diarrhea?
- Decreased absorptive surface area (inflammation of small intestine)
- Osmotic diarrhea due to unabsorbable osmolytes (lactase deficiency, MgSO4 etc)
- Excessive secretion of intestinal fluid (Cholera)
How does cholera cause diarrhea?
Cholera toxin binds to apical membrane of crypt cells, and causes adenylyl cyclease to go crazy making cAMP.
All the extra cAMP stimulates Cl- secretion, and water and Na+ will follow Cl-.
How do you treat cholera?
Pedialyte
