GI: Digestion, Absorption, and Regulation Flashcards
T/F. Digestion occurs in the stomach and absorption and secretion occur in the colon. Motility occurs throughout the GI tract.
False, Digestion occurs in the stomach and absorption and secretion occur in the SMALL INTESTINE. Motility occurs throughout the GI tract.
What organ produces most of the enzymes importation in digestion?
pancreas
___L flow thru the GI tract daily but only ___L comes from the diet. Where does the rest come from?
8; 2
blood
The GI tissue has the same structure from the mid-___ all the way down.
esophagus
What are the four tissue layers found in the GI system?
- mucosa
- submucosa
- muscularis externa
- serosa
Match the following specialized tissues with the correct GI tissue.
- lamina propria
- submucosal nerve plexus
- circular muscle
- epithelium
- major blood and lymphatic vessels
- longitudinal muscle
- connective tissue
- myenteric nerve plexus
- muscularis mucosa
A. mucosa
B. submucosa
C. muscularis externa
D. serosa
1 - A 2 - B 3 - C 4 - A 5 - B 6 - C 7 - D 8 - C 9 - A
T/F. The epithelial layer of the mucosa GI tissue is made of a single layer of cells.
True.
There are ___ billion new intestinal epithelial cells a day. Complete turnover is every ___ days.
17; 5
The villus is layered with ___ that contain the ___ border.
microvilli; brush
The ___ contains stem cells that make new epi cells which migrate up to the tip of the villus. This process takes 5 days.
crypt
The ___ drain into the lymphatic duct, which empties into the ___ ___ ___.
lacteals; hepatic portal vein
What are the five basic categories of useable food (energy sources)?
- carbohydrates
- protein
- fats
- vitamins
- minerals
T/F. Starch and glycogen are polysaccharides that can be broken down into glycogen and glucose, respectively.
True.
How is cellulose digested into glucose?
by bacteria
Sucrose, Lactose and Maltose are disaccharides. What are they made of?
Sucrose = glucose and fructose Lactose = glucose and galactose Maltose = glucose and glucose
What is essential for digestion and absorption of carbohydrates?
brush border ectoenzymes
Where does alpha-amylase come from? What does alpha-amylase break startch into? Can the products be absorbed into the intestinal cell?
parotid gland
limit dextrins (30%) and oligosaccharides (70%)
No, because only monosaccharides can be absorbed
Where are ectoenzymes found and where is their active site located?
embedded in the brush border membrane
active site points toward the lumen (outside)
Na+, glucose or galactose uses the ___ transporter and fructose uses the ___ transporter, both of which are located on the ___ border. What transporter puts all monosaccharides into the blood?
SGLT1; GLUT5
GLUT2
T/F. GLUT5 has been found to be upregulated in individuals who use articifical sweeteners and may contribute to weight gain.
False, GLUT2 has been found to be upregulated in individuals who use articifical sweeteners and may contribute to weight gain.
Proteins are broken down into peptides in 2 locations. Name them.
- stomach
2. small intestine
___ is produced in the stomach and cleaved into ___, which degrades proteins by unfolding or breaking them down into peptides.
Pepsinogen; pepsin
The pancreas releases ___ into the ___ ___ to digest proteins. List what is released.
pro-enzymes; small intesting
- trypsinogen
- chymotrypsinogen
- procarboxypeptidases A and B
- proelastase
What is needed to convert proenzymes secreted by the pancreas into their active form?
enteropeptidase
T/F. Enteropeptidase is a brush border enzyme that converts trypsinogen into trypsin, which is an essential protease for cleavage of other pro-enzymes.
True.
Oligopeptides interact with ectoenzymes to form ___- or ___- peptides or ___ aas. How are these absorbed?
Di-; Tri-; free
All can be absorbed into the intestinal cells directly by there own transporters that can be found on the brush border or basolateral membrane.
T/F. Amino acid trasporters are only Na+ dependent transporters.
False, they can be Na+ dependent or independent
Proteins are degraded by ___ and ___.
HCL; proteases
Triglycerides, which cannot be absorbed, are broken down by ___ from ___ ___ glands into ___ and 2 ___ ___.
lipase; von Ebner; monoglyceride; fatty acids
What are the different sources of lipases?
lingual, gastric, and pancreatic lipases
Fatty acid absorption occurs in the small intestine, primarily where? Where does digestion occur?
duodenum
stomach and duodenum
T/F. Fats are not water soluble but lipases are.
True.
T/F. Gastric emptying is sped up by fats.
False, it is slowed by fats. The meal needs to be held longer to help with digestion and emulsification.
Describe why bile salts are capable of interacting with fats for emulsification.
Its structure is amphiliic, meaning it has a nonpolar and polar side that allows it to surround a fat droplet (emusion droplet).
In addition to bile salts, what else is used to form an emulsion droplet?
phospholipid
How does lipase interact with fat?
Via Colipase. It is able to embedded between the bile salts of an emulsion droplet. Once attached, it can recruit lipase to break down TG into monoglycerides and fatty acids.
T/F. Micelles are in equilibrium with free fatty acids and are constantly breaking down and reforming.
True.
T/F. Monoglycerides and free fatty acids are found in systemic circulation.
False, Triglycerides are found in systemic circulation.
This means that once monoglycerides and free fatty acids are absorbed into the cell they must be reformed into TG in order to enter the blood.
Once inside the intestinal cell, ___ reform, go to the ___ ___ and get packaged into vesicles called ___, which diffuse into the lacteal/lymphatic system drain into the hepatic portal system and enter the ___.
TGs; endoplasmic reticulum; chylomicrons; blood
What vitamins are fat soluble?
A D E K
How do fat soluble vitamins enter the body?
they are encorporated (solubilized) into micelles, and passively diffuse thru intestinal epi cells and released into the body with chylomicrons
T/F. All fat soluble vitamins are absorbed by facilitated or active transport, except B4.
False, All WATER soluble vitamins are absorbed by facilitated or active transport, except B12.
How is vitamin B12 abosrbed?
It combines with intrinsic factor and is translocated into the cell where it hangs out in the mitochondria for around 6 hrs until it is released into the portal blood.
Where is most water absorbed? How?
small intestine
it follows the concentration gradient of solutes (most of which are dependent on Na+)
T/F. Na+ absorption can only occur in the duodenum.
False, it occurs throughout the entire GI tract
Na+ absorption is highest in areas where ___ and ___ or ___ ___ are being transported. What other ions are absorbed due to Na+?
glucose; galactose; amino acids
Cl-, HCO3, K+
Minerals (Ca2+) are actively absorbed by ___ segments of the intestine. Salts are soluble at ___ pH. Ca2+ is strongly enhanced by vitamin ___.
all; low; D
High levels form insoluble salt however, in acidic environments, it remains soluble (stomach) to be absorbed into the duodenum
Ca2+ enters thru a channel and binds to ___ to keep it insoluble and transport it to the basolateral surface. It then diffuses via ___-ATPase or ___/___ exchanger or it travels in vesicles and is released via ___.
Calbindin; Ca2+; Na+/Ca2+; exocytosis
Fe___+ can not be absorbed.
3 (ferric)
From plants, the ferric (___) form is converted into the ferrous (___) form by iron ___. Once inside, the enzyme ___ converts it back into the ferric form (usable/reactive iron). What two things happens next?
Fe3+; Fe2+; reductase; ferroxidase
- binds to Ferritin for storage
- Binds to iron binding proteins to be absorbed into the blood
What form is iron found in our diet?
heme
Heme is transported via a transporters and is first broken down into ferrous iron (Fe2+) and then ferric (Fe3+) by Ferroxidase enzyme.
What regulates the GI tract’s functions?
- neurons (ANS and enteric nervous system)
- paracrine mediators (produced by local cells and reach target via diffusion)
- hormones (produced by endocrine cells and reach gut via the blood.
T/G. The psymp nervous system slows digestion while the symp nervous system enhances digestion.
False, The SYMP nervous system slows digestion while the PSYMP nervous system enhances digestion.
How does the autonomic nervous system indirectly affect GI function?
via the enteric nervous system
T/F. The enteric nervous system has more neurons that the brain.
False, it has the 2nd largest amount of neurons following the brain.
What three plexuses make up the enteric nervous system?
- submucosal
- myenteric
- mucosal
What type of neurons are found residing as part of the enteric nervous system?
motor (muscle contractions and gland function)
interneurons (regulate interactions between diff layers of GI tissue)
sensory neurons
What receptors are found in the GI reflex arc? What are they initiated by?
Receptors - mechanoreceptors, osmoreceptors, and chemoreceptors
Initiated by - distention of the wall, chyme osmolarity, acidity and concentrations.
Explain the steps that would occur follow mild distention of the GI wall. What would occur if the distention was severe?
Short Reflex:
- mechanoreceptors would detect stretch
- nerve plexus within the GI wall was signal the smooth muscles to contract to squeeze and mix chyme
- the decreases stretch signal will decrease the activation of mechanoreceptors
Long Reflex:
- the mechanoreceptors would bypass the GI nerve plexus and send its signal via afferent neurons to the CNS.
- Efferent autonomic neurons from the PNS and SNS would send stronger contraction signals to the nerve plexus, increasing smooth muscle contraction and decreasing activation of the mechanoreceptors
What four hormones play a large role in regulating digestion?
- gastrin
- CCK
- secretin
- glucose-dependent insulintropic peptide (GIP)
What are some generalizations about GI hormones?
- each hormone participates in a feedback control system to regulate some aspect of the GI lumen
- Each hormone affects more than one type of target cell
- Hormones have synergistic effects (one can potentiate the other)
The ___ phase is controlled by ___ nerve fibers affecting the enteric nervous system. It is initiated when receptors in the ___ are stimulated.
cephalic; parasympathetic; head
The gastric phase contains short and long neural reflexes and ___. What are the components of the phase?
gastrin
distension, acidity, amino acids, peptides
The ___ phase involves short and long neural reflexes, ___, ___ and ___. What are the components of the phase?
intestinal; secretin; CCK; GIP
distension, acidity, osmolarity, various digestive products
