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Physiology II Digestion
Duke's Ch 26
54
Veterinary Medicine
Professional
01/23/2013

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Term
What anatomical mechanisms increase the small-intestine surface area?
Definition
microvilli
Term
The large intestine has villi but no _______.
Definition
microvilli
Term
The small intestine (jejunum and ileum) is capable of surface digestion via _______.
Definition
microvilli
Term
Almost all nutrient absorption occurs in the
Definition
small intestine
Term
Sodium absorption occurs
Definition
in the small and large intestine
Term
The large intestine has the ability to _______ sodium.
Definition
conserve
Term
Four phenotypes on the small intestine epithelium
Definition
columnar absorptive cells (most numerous), enterochromaffin (endocrine) cells, mucous (goblet cells), and undifferentiated cells
Term
Why does the tip of the villus receive blood with the lowest arterial PO2?
Definition
as blood flows up the central arteriole, oxygen diffuses down the concentration gradient into the veins draining the villous
Term
During what period is there a depletion in the high energy phosphate bonds required for the production of protective substances such as mucus?
Definition
ischemic period
Term
Depressed cell pH regulation lead to ________ ________ in the small intestine.
Definition
tissue acidosis
Term
During tissue acidosis there is
Definition
release of lysosomal enzymes and tissue digestion
Term
Name the 3 end products of carb digestion that are absorbed into portal blood?
Definition
glucose, galactose, and fructose
Term
What is the function of bile in the jejunum?
Definition
emulsify fats by forming a negatively charged aggregate called a micelle to dissolve water insoluble material
Term
After emulsified fats are dissolved inside the micelle how are they absorbed across the brush border?
Definition
micelles diffuse from the emulsion particle to the brush border where the fat is released to diffuse across the lipid membrane into the cell
Term
What is pinocytosis?
Definition
uptake of large amounts of intact molecules (usually proteins) by engulfing them via invaginations by phagosomes
Term
What happens after a phagosome has performed pinocytosis?
Definition
merging with lysosomes to form phagolysosomes where cellular digestion can occur
Term
Why is absorption of intact protein important for the neonate?
Definition
for obtaining antibodies (passive immunity) from the mother
Term
Pancreatic enzymes adapt quickly to changes in diet, especially when
Definition
solid food is introduced
Term
During the introduction of solid food there is an increase in
Definition
pancreatic and brush border enzymes
Term
Adaption to dietary protein and fat is mediated by the intestinal hormones
Definition
CCK and secretin
Term
CCK and secretin induce gene expression of
Definition
pancreatic proteases and lipases
Term
Initiation of brush border enzymes is due to an intrinsic program in the enterocyte regulated by levels of
Definition
glucocorticoids or thryoxine
Term
What are the carbohydrate sources and absorbable end products of microbial digestion of carbs?
Definition
sources are soluble starches and insoluble fiber and end products are SCFA's and gases
Term
Horses cannot utilize microbial protein because
Definition
there is no amino acid transport system in the small intestine
Term
Ruminants can recover the microbial protein in the
Definition
small intestine
Term
The purpose of protein in the large intestine of the horse is to provide
Definition
nitrogen for microbial protein synthesis
Term
Most of the salt and water that the gut has to reabsorb is derived from what sources?
Definition
endogenous sources
Term
Herbivores secrete larger amounts of fluid such as saliva that are necessary for
Definition
forestomach fermentative process
Term
In carnivores and omnivores, the proximal small intestine recovers at least _____% of total absorbed substances
Definition
60
Term
The remainder of what has not been absorbed by the small intestine of the carnivore/omnivore is absorbed by
Definition
ileum and large intestine
Term
In herbivores, the proximal small intestine absorbs
Definition
very little
Term
The major sites of fluid absorption in herbivores are
Definition
distal small intestine and large intestine
Term
Bulk water flow is strictly a consequence of osmotic and hydrostatic gradients set up by
Definition
basolateral membrane Na-K pumps
Term
Where is the site and what is the basic driving force for intestinal secretion of salt and water?
Definition
Na-ATPase on the basolateral membrane provides a low intracellular Na concentration and negative intracellular electrical potential establishing a large electrochemical gradient for Na diffusion across the apical membrane
Term
How do the mechanisms for Ca absorption differ from those for other electrolytes?
Definition
does not use Na electrochemical gradient
Term
Since Ca absorption does not use Na in the electrochemical gradient, it facilitates diffusion regulated by Ca binding protein is used to
Definition
translocate the Ca across the membrane
Term
Ca can be endocytosed or diffused by Ca binding protein, both of which are affected by
Definition
vitamin D concentrations
Term
How do the SCFAs become undissociated (lipid soluable) in the large intestine lumen?
Definition
they become undissociated by protonating
Term
SCFAs can become undissociated by protonation by two different sources
Definition
H+ - hydration of CO2 and apical Na-H exchanger present in the forestomach and proximal colonic epithelium
Term
Name some paracrine mediators that promote intestinal secretion.
Definition
Prostaglandins, leukotrienes, histamine, serotonin, active oxidants, platelet activating factor, bradykinin, cytokines
Term
What class of systemic hormones mediates intestinal absorption?
Definition
Epinephrine, coricosteroids, angiotensin, aldosterone, norepinephrine
Term
How does the central nervous system regulate intestinal electrolyte transport?
Definition
cholenergic agonists decrease absorption of elicit secretion and adrenergic agonists modify cholinergic transmission
Term
Intestinal epithelium is innervated by cholinergic nerves that decreat the action of the _____ absorptive process on the villi and elicit ___ secretion in the crypts.
Definition
NaCl; Cl
Term
What is the mechanism of producing diarrhea in association with a rotovirus infection
Definition
cause diarrhea by causing villous atrophy that leads to maldigestion and malabsorption
Term
What is the mechanism of producing diarrhea in association of enterotoxigenic E. coli?
Definition
secretes enterotoxins that occupy apical membrane receptors on enterocytes which in turn raise cAMP or cGMP and massive hypersecretion by the intestine
Term
Phagocytes release soluable mediators such as TNF alpha and reactive oxygen metabolites taht are capable of causing epithelial injury causing
Definition
malabsorption
Term
Reactive ocygen metabolites can stimulate epithelial secretion directly and also signal ________ cells to secrete ________ that sets off second messengers to cause secretion
Definition
mesenchymal; prostaglandin
Term
What second messenger in the epithelial cells mediate intestinal secretion?
Definition
cAMP and Ca ions
Term
How is cAMP and Ca ions activated in inflammation?
Definition
by release of prostaglandins
Term
How are cAMP and Ca ions activated by enterotoxins?
Definition
binding of receptors to enterotoxins
Term
What is epithelial restitution?
Definition
immediate response of mucosa to injury and loss of epithelium
Term
How does the process of restitution repair damaged epithelial barrier?
Definition
viable cells beneath the denuded area are capable of ameboid locomotion and rapidly migrate over the defect, over time increased renewal or proliferation of enterocytes at the base at the base of the crypts to replenish the lost cells
Term
How does proliferation differ from restitution?
Definition
actual growth and replication of cells vs. initial movement of cell's cytoplasm to cover damaged areas
Term
Why does villous contraction assist the repair process in a damaged epithelium
Definition
decreases villous height and facilitates restitution by lessening the total surface area for the migrating cells to cover
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