GI digestion & absorption Flashcards
What is the area of the intestines and lungs?
Tennis court - 300 sq meters
What is the function of a lacteal?
Absorption of fats in a villus
What are the roles of nerves in villi?
To get sensory info (mechanical, chemical) coming in from the villus; to give motor instructions for secreting substances
Which enteric nerve layer are the nerves of the villi derived from?
submucosal plexus
Which segment of the small intestine has the least absorptive ability?
ileum - less surface area than the duodenum & jejunum
Villi are found throughout the GI tract.
T/F
False - villi are exclusive to small intestine.
Crypts are common to small intestine and large intestine.
T/F
True - crypts are necessary for cell turnover
“Fiber” refers to a complex polysaccharide (carbohydrate) that cannot be broken down by enzymes.
T/F
True
How are glucose and galactose transported across the intestinal epithelium?
Secondary active transport, SGLT1
How is fructose transported across the intestinal epithelium?
What is necessary for this to happen?
Facilitated transport, GLUT5 - is dependent on a fructose gradient, so as soon as fructose is brought into the cell it is pumped out to the interstitial fluid side
How do glucose, galactose, and fructose leave intestinal epithelial cell to the interstitial fluid side?
facilitated diffusion transporters in the basolateral membrane, GLUT2
What causes lactose intolerance?
Lactase brush-border enzymes are missing or decreased….lactose stays in the lumen. It’s osmotically active, so it draws water into the lumen (diarrhea). Also, it provides a sugar supply to the bacteria in the large intestine, and they create gas as they anaerobically metabolize it.
There is no problem created if we fail to absorb all the glucose from the lumen in the small intestines.
T/F
False. Passing on any nutrient source to the large intestines can be a problem (cellulose is not a nutrient source - it’s indigestible).
Enzymes and their locations of actions?
Starch
salivary amylase - mouth
pancreatic amylase - duodenum
Enzymes and their locations of actions?
Cellulose
NONE - NOT DIGESTED
Enzymes and their locations of actions?
Disaccharides
hydrolytic enzymes in ileum
Enzymes and their locations of actions?
Proteins
pepsin - stomach
trypsin - duodenum
chymotrypsin - duodenum
carboxypeptidase - duodenum
aminopeptidase - ileum
Pancreas releases trypsin, chymotrypsin, carboxypeptidase, and aminopeptidase.
T/F
FALSE! Pancreas releases inactive versions of these enzymes, so that we don’t start digesting ourselves.
trypsinogen
chymotrypsinogen
procarboxypeptidase
proaminopeptidase
All of the proteolytic enzymes result in peptide fragments.
T/F
FALSE
the peptidases result in free amino acids
Enzymes and their locations of actions?
triacylglycerol
pancreatic lipase - duodenum
How do amino acids enter the intestinal epithelium?
Via co-transport with sodium
How are peptide fragments brought into the intestinal epithelium?
absorbed by secondary active transport coupled to H+ gradient
How do peptides leave the intestinal epithelial cells?
di- and tri-peptides are hydrolyzed to amino acids before leaving cell in facilitated diffusion carrier
The components of a micelle include all of the following EXCEPT:
A. Bile salt
B. Triglycerides
C. Phospholipid
D. Fatty acids
B - Micelles do not contain triglycerides.
Why are free fatty acids and monoglycerides converted back into triglycerides within the epithelial cell?
To maintain a steep concentration gradient
The components of a chylomicron include all of the following EXCEPT:
A. Cholesterol
B. Triglycerides
C. Phospholipid
D. Fatty acids
D - Fatty acids
How & where is vitamin B12 absorbed?
Vitamin B12 is too large and is a charged molecule. It must bind to intrinsic factor protein before being endocytosed by epithelium in lower portion of ileum.
Emulsification
Prevents small fat droplets from reaggregating in the intestinal lumen. This is achieved by the action of bile salts and phospholipids present in bile (from liver).
Describe the process of fat absorption starting with emulsified fatty acids.
~fatty acids move into cell
~fatty acids form triglycerides
~triglycerides form a chylomicron inside the cell
~chylomicrons are exocytosed to the interstitium and enter lacteals and portal system.
How are fat-soluble vitamins absorbed?
Fat-soluble vitamins are solubilized in micelles and are absorbed with fatty acids & monoglycerides into chylomicrons.
Protein digestion and absorption is completed in the _____ portion of small intestines (upper, lower)
upper
How are water-soluble vitamins absorbed (in general)?
Water-soluble vitamins are absorbed by diffusion or mediated transport except vitamin B12.
What are the circulation forms of the fat-soluble vitamins?
- Vit. A (retinol) converted to ester for incorporation into chylomicron
- Vit. D (calciferol) transferred to binding protein before conversion in liver
- Vit. E (a-tocopherol) transported with lipoproteins and erythrocytes
- Vit. K is incorporated in VLDL in liver
Where is intrinsic factor secreted?
secreted by gastric parietal cells into lumen of tract - it’s not in the blood
We absorb all of the calcium and iron that we eat.
T/F
False. Absorption of these minerals is regulated.
How do mother’s IgA antibodies get into the fetus?
endocytosis/exocytosis of intact IgA
Which of the following transporters are essential in the luminal membrane for protein absorption?
A. Sodium-amino acid symporter
B. Sodium-proton antiporter
C. Proton-peptide symporter
D. All of above are essential
All
What are the products of pancreatic lipase activity?
2 free fatty acids
1 monoglyceride
How do we increase our absorption of iron?
Stop producing the iron-binding molecule (when it’s bound, it gets sloughed off and pooped out).
