Section 1A Flashcards
Alimentary Tract consists of:
mouth, tongue, teeth and throat
Alimentary tract contributes to …
MECHANICAL digestion of food - preparing a food bolus by biting, chewing, and swallowing
salivary enzymes released when chewing:
large amounts of CHO-hydrolyzing amylase
very small amounts of lipid-hydrolyzing lipase
Amylase is to __________ as Lipase is to ________
Amylase - CHO
Lipase - Lipids
Esophagus
tube from mouth to stomach lined with mucus and smooth muscle
NO digestion
pushes food down to stomach via peristaltic wave-like contractions
Regurgitation of food back to throat is prevented by…
upper and lower esophageal sphincters
PRIMARILY by the LES !
Lower Esophageal Sphincter (LES)
between esophagus and stomach preventing stomach acids to come back up
Chemical and Enzymatic Hydrolysis of food in the _____________
stomach
Chemical and enzymatic hydrolysis of food includes:
holding, preparing, and mixing food material
regulating osmolarity of ingested food
reducing bacterial load through acid secretion
_________ of the stomach secrete lipase
chief cells
Chief cells —-
stomach
secrete lipase
break down dietary triglycerides (triacylglycerols) into FFAs and diglycerides (diacylglycerols), and pepsinogen (precursor of pepsin)
Pepsinogen is the precursor of….
pepsin
pepsin initiates ….
the hydrolysis of food proteins
_______ of the stomach secrete intrinsic factor
parietal cells
Intrinsic factor
small protein required for absorption of B12 and HCl
_________ of the stomach secrete mucus containing glycoproteins and bicarbonate
mucous cells
Secretions from Mucous cells
mucus containing glycoproteins and bicarbonate that PROTECT the gastric mucosa from acid damage and autodigestion
Gastric Acid requires what kind of environment
performs a # of preliminary digestive roles that require an acidic environment
Gastric acid roles
- destruction of microorganisms
- activation of pepsinogen to pepsin
- activation of intrinsic factor
- denaturation (loss of three-dimensional conformation) of macromolecules
- facilitation of the breakdown of protein and polypepides by pepsin
presence of food protein in the stomach triggers ______
gastric secretion
Gastrin secreted by _____
gastric endocrine cells
Gastrin acts on
- gastric parietal and chief cells to stimulate intragastric secretion of HCl and Pepsinogen
- stimulates gastric peristalsis and maintains the proliferation of gastric parietal cells
__________ intragastric acidity inhibits (hinders) continued gastrin secretion
increasing
Peristaltic contractions of the _____________________ propel digesta toward the gastric pylorus
distal stomach
while food is propelled towards the gastric pylorus, the gastric pylorus contracts in opposition to gastric peristalsis, but_______ which causes _____
it does not close – causes sufficiently small particles, liquids, and liquified digesta to pass through into the proximal small intestine
After the stomach — digesta goes into the _______
small intestine
If foods particles are too big to make it through the residual pyloric opening into the small intestine, they _____________
are retropelled back into the stomach for further preliminary digestion
ingested fats can also turn into fine lipid droplets (<5 mm diameter)
what is the major anatomical site of food digestion and nutrient absorption
small intestine
Brush Border — what is it, what is it composed of
luminal surface of the SI
composed of microvilli that dramatically increase available absorptive surface area of the small intestine
Microvilli
extravaginations of the plasma membranes of the absorptive cells of the intestinal mucosa
Absorptive enterocytes originate from __________________________ in the ______________
originate from stem cells in the intervillar crypts
Where do enterocytes differentiate?
at the luminal surface of the mucosa
How long do enterocytes survive
about 72 hours — then they undergo apoptosis and lose their attachment to the mucosal basement membrane (desquamation)
Most proximal upper section of the small intestine?
the short duodenum
Chemical degradation of partially digested food into individual nutrients begins in ….
the short duodenum
seconds section of the SI
jejunum
Third and distal part of the SI
ileum
Major sites of nutrient absorption
jejunum and ileum
_______ transfers any undigested food materials into the large intestine
distal ileum
________ entering ________ stimulates the enteric secretion of secretin into systemic circulation
Acidic chyme entering the proximal duodenum stimulates secretion of secretin into systemic circulation
Secretion stimulates……
pancreatic secretion of bicarbonate into the ductal system
the ductal system
terminates in the common bile duct
Fat or Protein entering the proximal duodenum stimulate ________ of _____ into systemic circulation
Fat or Protein entering the proximal duodenum stimulate duodenal secretion of cholecystokinin (CCK) into systemic circulation
cholecystokinin (CCK)
stimulates pancreatic secretion of zymogens into the ductal system
stimulates gall bladder contraction, propelling bile into the common bile duct
Zymogens
inactive digestive enzyme precursors
Common bile duct empties into the ____ (and what does it do there)
proximal duodenum, transferring pancreatic zymogens and hepatic bile constituents into the duodenal lumen
In the duodenal lumen, the pancreatic zymogens and hepatic bile constituents mix with the digesta to ___________ the conversation of food components into __________
In the duodenal lumen, the pancreatic zymogens and hepatic bile constituents mix with the digesta to ACCELERATE the conversation of food components into ABSORBABLE INDIVIDUAL NUTRIENTS AND SMALL MOLECULES
___________ duodenal distension triggers secretion of gastric inhibitory peptide which ________ gastric motility and _________ the rate of further gastric emptying
INCREASING duodenal distension triggers secretion of gastric inhibitory peptide which INHIBITS gastric motility and SLOWS the rate of further gastric emptying
So increasing the pressure in the duodenum (inflammation) triggers secretion of gastric inhibitory peptide. This hinders gastric motility and slows down gastric emptying – think inflammation in your SI
Pancreatic zymogens that play a major role in food digestion are —- (6)
Trypsinogen
Proelastase
Chymotrypsinogen
Procolipase
Procarboxypeptidase A
Procarboxypeptidase B
When pancreatic zymogens reach the SI ______ secreted by duodenal enterocytes converts _______ to _______
When pancreatic zymogens reach the SI, ENTEROKINASE secreted by duodenal enterocytes converts TRYPSINOGEN to TRYPSIN
Enterokinase Enzyme
secreted by the duodenal enterocytes
triggered by pancreatic zymogens reaching the SI
REQUIRED for trypsin activation
Trypsin
converts the OTHER zymogens to:
- Proelastase TO elastase
- Chymotrypsinogen TO chymotrypsin
- Procolipase TO colipase
- Procarboxypeptidase A TO carboxypeptidase A
- Procarboxypeptidase B TO carboxypeptidase B
Trypsin NEEDED to convert the others so in turn enterokinase is required to activate all of the pancreatic zymogens
Serine Proteases
trypsin, chymotrypsin, and elastase (same as the endopeptidases)
means that a serine is required at the enzymes’ active site
Endopeptidases
trypsin, chymotrypsin, and elastase (same as the serine proteases)
hydrolyze peptide bonds within polypeptides
carboxypeptidases are
zinc-requiring metalloenzyme exopeptidases —- they cleave single carboxyterminal amino acids from polypeptides
Amylase
secreted by the pancreas
performs initial digestion of starches to produce glucosyl oligosaccharides and disaccharides
Lipase
secreted by the pancreas
hydrolyzes dietary fats that have been emulsified by bile salts into fatty acids and glycerol
Cholesteryl Esterase
secreted by the pancreas
cleaves cholesteryl esters
Secreted by the Pancreas
amylase, lipase, cholesteryl esterase, ribonuclease deoxyridonuclease, zymogens
Brush Border Enzymes
Ectozymes
Ectozymes
brush border enzymes
associated with and attached to microvillar surfaces of the SI
Produced by enterocytes
complete the final steps in hydrolysis of amylase-digested CHOs to monosaccharides and of protease-digested PROTEINS to absorbable free AAs, dipeptides, and tripeptides
Oligosaccharidases, disaccharidases, and pepidases
ectozymes
What completes the final steps in hydrolysis of amylase-digested CHOs to monosaccharides and of protease-digested PROTEINS to absorbable free AAs, dipeptides, and tripeptides
Ectozymes
What buffers gastric HCl into a weaker acid, H2CO3, maintaining duodenal pH near the neutrality optimum for digestive enzyme function
pancreatic bicarbonate
in other words - this helps to keep the pH of the duodenum near optimum for digestive enzyme function
Efficiency of digestive enzymes is affected primarily by
local pH
_______ availability affects the ionization of the active state of an enzyme
proton
if an enzyme and substrate have the greatest affinity when the enzyme is in a protonated form, an alkaline pH will cause the enzyme to become depronated, substrate affinity will decrease and the rate of the rxn will decline
Extremes of pH can lead to _____ of enzymes
denaturation
Salivary amylase works best at what pH
6.75 - 7.00
gastric pepsin and lipase function optimally at what pH
1.5 - 3.5
enzyme that is activated by protons_____
gastric pepsin – because a strong acid like gastric HCl will liberate all H+ in water component of the digesta
this then dramatically decreases the pH
Enzymes that are deactivated by presence of free protons include : (3)
gastric lipase
salivary amylase
lingual lipase
these function most efficiently at neutral or higher alkaline pH
Bile
a watery greenish fluid stored in the gallbladder
contains cholic acid, chenodeoxycholic acid, taurine, glycine, cholesterol, electrolytes, and water (6-7 L/day on average in adults)
Primary role of liver in food digestion and nutrient absorption is excretion of
bile
organic and mineral components of bile form
bile salts
usually electrolyte salts of cholic and chenodeoxycholic acids
bile salts
emulsify the fine lipid droplets reaching the intestine from the stomach which increases the droplet surface area exposed to the combined actions of pancreatic lipase and colipase and is required for these enzymes to be effective
________ and ______ hydrolyze triglycerides to release monoglycerides (monoacylglycerols) and free fatty acids
pancreatic lipase and colipase hydrolyze triglycerides to release monoglycerides (monoacylglycerols) and free fatty acids
What things cannot penetrate the unstirred water layer that separates the epithelial surface of the SI from the intestinal lumen (and how they can be absorbed) (5)
monoglycerides
FFAs
cholesterol
phospholipid digestion products
other fat-soluble food components
their absorption depends on ability to aggregate spontaneously with bile salts and become incorporated with micelles
Micelles
vaguely spherical clusters of bile salts
collections of lipid soluble dietary subcomponents surrounded by a layer of water soluble bile salts
why are micelles helpful in absorption of the things that cannot penetrate the water layer?
solubility characteristics of the bile salt layer allows ready penetration of the unstirred water layer by micelles; the complex breaks down upon reaching the brush border, allowing rapid diffusion of their lipid components down concentration gradients into enterocytes
Where are lipids and lipid compounds repackaged into large protein-coated chylomicrons that are secreted into the lacteals?
endoplasmic reticulum of the enterocytes
protein-coated on the chylomicrons means …..
it is water soluble
Chylomicrons get secreted into the lacteals then ….
flow through the lymphatic system and enter the circulation via the thoracic duct
most of the water and bile salts excreted into the intestine are reabsorbed in the ______
ILEUM
Bile salts are transported back to the liver via
enterohepatic circulation
portion of cholesterol in bile is not incorporated into micelles and is excreted in the ______
feces
as is 1% to 2% of the water that was delivered to the proximal small intestine)
what utilizes the potential energy associated with the diffusion of water through a SEMIPERMEABLE membrane from an area of HIGH osmotic pressure to LOWER osmotic pressure
Osmosis
Osmotic movement of nutrients is limited to the _______ pathway
paracellular pathway
where water and electrolytes cross tight junctions between adjacent enterocytes
what uses HYDROSTATIC PRESSURE to drive the movement of solutes and water through a SEMIPERMEABLE membrane from a region of HIGHER hydrostatic pressure to a region of LOWER hydrostatic pressure
Filtration
What utilizes the potential energy created by a difference in nutrient concentration across a membrane to move nutrients from an area of HIGHER concentration to an area of LOWER concentration?
Passive diffusion (simple diffusion)
_________ compounds enter intestinal cells by passive diffusion from brush border into the cell cytosol
lipid soluble compounds
What utilizes a lipid soluble membrane carrier protein to pass through membranes moving down its concentration gradient?
facilitated diffusion (carrier-mediated transport)
_______ are transported across biological membranes via facilitated diffusion
Most Carbohydrates utilize facilitated diffusion
In what does a nutrient move through MUCOSAL cell membranes AGAINST a concentration gradient requiring the participation of a membrane carrier protein (receptor) and consumes biochemical energy provided by ATP
active transport (solute transport)
Active - needs ATP
_______ and ______ are absorbed via active transport
amino acids and ions
Active transport, uses Atp, Amino Acids and ions, Against the concentration gradient
What prevents components of ingesta and their degradation products from penetrating into the GI circulation (and most importantly the portal vein)
Intestinal Barrier
An intact intestinal barrier maintains –
relative impermeability of the GI tract to exogenous materials and organisms
prevents absorption and translocation of intact microorganisms, microbial endotoxins, and food allergens
Factors that preserve intestinal barrier function: (6)
antibacterial and antiviral secretions of nonpathologic microflora
endogenous mucous secretions
intercellular “tight junctions”
intestinal epithelial secretion of lectins and anti-adhesion glycoproteins
peristaltic movement of digesta
enterocytic filtration (lysosomal hydrolysis of pathogens and toxins within enterocytes)
Antimicrobial defenses within the intestinal tract rely heavily on the secretion of ________ by _____________
secretory IgA (sIgA) by gut-associated lymphoid tissue (GALT)
GALT contains about __________ of the total number of immune cells in the body, scattered throughout the intestinal tract
50-60%
What is the first line of defense against environmental assault?
GALT (gut-associated lymphoid tissue)
What is the first line of defense against environmental assault?
GALT (gut-associated lymphoid tissue)
provides both cell-mediated immunity and humoral immunity via secretory IgA
When intestinal permeability increases secondary to compromise of intestinal barrier function, what happens?
failure of exclusion
increased intestinal permeability
antigen-induced disease
_______________ diseases may occur when food components or bacterial antigens share a common antigenic determinant (epitope) with both a virus or other pathogenic microorganisms to which the host has been exposed previously and a host cell membrane components
Autoimmune-like diseases
Small molecules (like monosaccharides) are absorbed by _______ via _____________
enterocytes via direct transcellular uptake
measuring the rate of __________ of a test dose of a nonmetabolizable small molecules (monosaccharide, mannitol) provide information on _________
urinary excretion
the rate of transcellular uptake by enterocytes and, indirectly, the overall health status of small intestinal villi
Large molecules do not undergo transcellular uptake and normally are prevented from _______
passing between enterocytes (paracellular uptake) by intercellular “tight junctions”
Urinary excretion of:
Mannitol NORMAL or HIGH
Lactulose HIGH
Dx?
increased small intestinal permeability
Urinary excretion of:
Mannitol LOW
Lactulose LOW
Dx?
small intestinal malabsorption
Urinary excretion of:
Mannitol LOW
Lactulose HIGH
Dx?
increased small intestinal permeability and small intestinal malabsorption
use of lactulose to detect increased intestinal permeability may be associated with ____
high incidence of false positive results
Intestinal impermeability may be restored by any means that will either :
reduced the amount of proteinaceous residue reaching the ileum,
increase epithelial integrity
support the GALT
Examples: increasing the effectiveness of digestive enzymes by oral supplementation with purified or semi-purified enzyme preparations and maintaining adequate intraepithelial glutamine concentrations
Glutathione
intestinal antioxidant
short peptide
major intestinal extracellular antioxidant
highest tissue content of GSH (glutathione) is in:
human gastric and duodenal epithelia
Where does GSH activity reside
on the outer (luminal) enterocyte cell membrane and rapidly neutralizes oxidizing ingesta and breakdown of products of digestion
Within enterocytes – GSH synthesis produces an alternative pathway for________
utilization of homocysteine that is independent of B-vitamin status (but only with adequate intracellular glutamine concentration)
What is utilized to make glutathione
Homocysteine —> cystathione
cystathione —–> cysteine
Glutamine —-> glutamate
Cysteine + glutamate —-> y-glutamylcysteine
y-glutamylcysteine + glycine –> glutathione
intact glutathione administered via parenteral nutrition contributes to whole-body glutathione — oral glutathione ——–
undergoes proteolytic digestion before it can be absorbed
intact glutathione may neutralize toxins within?
the intestinal lumen
Primary fuel source for enterocytes?
glutamine
Glutamine
Amino Acid
required primary fuel source for enterocytes
provides substrates for the enteric tricarboxylic acid cycle
high intraenterocyte glutamine concentration is required to supply substrates for the production of polyamines and DNA in support of normal rates of cell desquamation and replication
During illness, trauma, and stress _____________________ is diverted to the immune system, depleting enterocytes of _________ and __________
During illness, trauma, and stress, GLUTAMINE is diverted to the immune system, depleting enterocytes of GLUTAMINE and GLUTATHIONE
Glutamine inadequacy is associated with
acceleration of apoptosis in the SI
causing accelerated cell death and desquamation without compensatory acceleration of stem cell proliferation
imbalance in tissue turnover produces thinning of villi with deccreased digestive function, decreased absorptive function, loss of intestinal barrier integrity, and increased translocation of antigens and pathogens from the intestinal lumen into the extravellular fluid and blood
Maintenance of intra-intestinal glutamine supply prevents—-
disruption in intestinal function
Examples: very low birth weight infants have immature intestinal anatomy, incomplete barrier function, and increased incidence of septic infections —- oral supplementation with L-glutamine decreases incidence of septic infections in very-lower-birth weight infants
Large intestine is composed of: (4)
ascending colon
transverse colon
descending colon
sigmoid colon
Major functions of the large intestine (4)
reabsorb water from the digesta
absorb vitamins produced in intestinal bacteria
provide an environment conducive to the fermentation of dietary fiber by resident microbes
eliminate dried residues (undigested and unabsorbed material) as feces
products of dietary fiber fermentation that AVOID microbial ingestion are: (3)
primary energy sources for colonocytes
support colonocyte metabolism
maintain colonocyte apoptotic synchrony
_________________ of ingested dietary fiber exhibit the “classical” function of stool softening and binging for fecal excretion of bile salts, cholesterol, and steroid hormones and their metabolic derivatives
Unfermented Fractions
Categories of dietary fiber:
soluble
insoluble
nonfermentable
What type of fiber:
beta-glucans (arabinogalactans, lactoferrin), gums, mucilages, and pectins
Soluble
Which dietary fiber comprises 10-20% of the total dietary fiber content of fruit, okra, beans, turnips, oats, parsnips, sea weeds, and prunes
soluble
Which dietary fiber include the celluloses and the lignins
insoluble
what is classified as both soluble and insoluble
hemicellulose
Most adults with healthy colons should ingest _____ to ______ g of soluble fiber daily
25-35 g
foods rich in soluble fiber often contain ____________ that prevent the digestion of dietary fat and may induce deficiencies in essential fatty acids and fat - soluble vitamins
lipase inhibitors
Soluble fiber intake greater than ______ g/day may inhibit the digestion of non-fiber CHO, increasing the amount of sugar and starch reaching the colon
50 g/day
What type of dietary fiber includes oat hulls, methylcellulose, and wood pulp cellulose
nonfermentable
Which dietary fiber functions in the colon to increase the bacterial mass of the stool (by adhesion), decrease the absorption of glucose, and increase the glucose content of stool (by interfering with CHO digestion in the small intestine), dilute pathogens and toxins in digesta and stool, increase rate of passage stimulating peristaltic concentrations, inhibit the inflammatory responses to bacterial infections by blocking microbial access to the intestinal mucosa, and inhibit phagocytotic capacity of intestinal macrophages (possibly by interfering with macrophage-secreted oxidizing compounds
nonfermentable
What happens at the colon?
human colonocytes and immune cells, microbes and ingested foods interact in the near-absence of oxygen
GI tract contains ____ living bacteria, representing over ____ individual species
GI tract contains 10^14 living bacteria, representing over 400 individual species
goal of dietary maintenance of colon health
foster stable steady-state, with the human host and its microbial symbiotes and pathogens in harmonic balance
the most common microorganisms in the stomach and duodenum are: (3)
Lactobacilli
streptococci
yeasts
Small pH differences along the small intestine favor:
Lactobacilli
Enterobacteriaceae
streptococci
bacteroides
bifidobacteria
fusobacteria
in the human jejenum and ileum
the most common microorganisms in the colon are: (11)
bifidobacteria,
lactobacilli,
Streptococci
Bacteroides
Fusibacteria
Enterobacteriaceae
Pseudomonas
Clostridia
Proteus species
yeasts
protozoa
Colon harbors larger diversity of organisms
The most beneficial individual species for the GI tract:
Bifidobacterium bifidus (bifidum),
Bifidobacterium infantis
Lactobaacillus acidophilus,
Lactobacillus bulgaricus
Lacto brevis
Lacto casei
lacto cellobiosus
lacto fermenti
lacto leichmannii
lacto plantarum
lacto rhamnosus,
lact saliverius
lacto sporogenes
Saccharomyces boulardii
Enterococcis faecium
Streptococcus Thermophilus
Most common microorganism in healthy human digestive tract
predominant microbes in human breast milk
Bifidobacteria
what comprises about 50% of all intestinal microflora and ferments dietary fiber CHOs to short chain fatty acids
Bifidobacteria
Bifidobacteria function (8)
enhance epithelial barrier fxn by reducing pathogenic load
reduce risk for developing colon cancer by metabolizing carcinogens and pro-carcinogens
suppress growth of pathogenic species by maintaining a slightly acidic colonic pH
binding to adhesion proteins on pathogens (competitive exclusion)
secretion of adhesion-inhibiting proteins
secretion of broad-spectrum antibiotics (like bulgarican)
secretion of antiviral L-bifidus factor (also found in cow’s milk)
and stimulation of GALT phagocytosis of pathogens
What comprises about 25% of all intestinal microflora
Lactobacilli
Types of Lactobacilli that are most common (5)
L. brevis
L. acidophilus
L. bulgaricus
L. casei
L. rhamnosus
Lactobacilli roles (
ferments dietary fiber CHOs to lactic acid and short chain fatty acids – contributes to the slightly acidic colonic pH
enhance epithelial barrier integrity by reducing pathogenic load
reduce risk of colon cancer by binding heterocyclic mutagens, deconjugating bile acids and binding and metabolizing cholesterol
Also ameliorate symptoms of lactose intolerance in individuals with inadequate lactase production by secretion of beta-galactosidase (lactose –> glucose + galactose)
suppresses growth of pathogenic species by a variety of mechanisms, including maintaining a slightly acidic colonic pH, binding to adhesion proteins on pathogens (“competitive exclusion”), secretion of adhesion-inhibiting proteins, competing for adhesion sites on enterocytes, secretion of species-specific antibiotics (acidolin, acidophilin, lactobacilin, and lactocidin)
secretion of hydrogen peroxide
stimulation of DALT production and secretion of secretory IgA (sIgA)
inhibition of bacterial enzymes (glucuronidase, beta-glucuronidase, and nitroreductase)
stimulation of colonic peristalsis (reducing time for colonocyte-pathogen interactions)
Saccharomyces boulardii also known as_____
yeast !
found both in small and large intestine
Saccharomyces boulardii (yeast)
Saccharomyces boulardii (yeast)
antagonistic to Candida albicans
inhibit effects of cholera toxin
inhibit adhesion of amoeba to intestinal brush border
stimulate enterocyte secretion of brush border enzymes (sucrase, lactase, maltase)
stimulate GALT production and secretion of sIgA
Oral supplements with what have been found to reduce severity and duration of childhood rotaviral diarrhea
Saccharomyces boulardii (yeast)
Colon obtains 70% of its nutrients directly from _________
the digesta
Microbial fermentation of fermentable dietary fibers results in the production of ?
SCFAs – acetate, propionate, butyrate
the relative proportions of the SCFA’s produced reflect substrate supply and the relative proportions of the microbial species present
What is especially important to human colonocytes?
butyrate
what is metabolized to Acetyle CoA within Colonocytes?
butyrate
what is the primary energy source for colonocytes and is required for the formation and maintenance of intercellular tight junctions
Acetyl CoA
Within the colon, butyrate stimulates: (7)
secretion of enteroglucagon (hormone that is trophic for intestinal villi)
stimulate T-lymphocyte proliferation in GALT
attenuates B-lymphocyte reactivity in GALT
inhibits TNF-alpha-induced activation of the nuclear transcription factor (procarcinogenic) NF-kB in colonocytes
inhibits TNF-alpha-induced secretion of pro-inflammatory IL-8 by colonocytes
inhibits growth of pro-inflammatory Clostridium species
required for maintenance of colonocyte apoptotic destiny
Hormone that is trophic (stimulating for activity) for intestinal villi?
enteroglucagon
Butyrate insufficiency within the colon results in - (5)
depletion of intracolonocyte acetyl-CoA
increased introcolonocyte cyclic AMP concentration
inhibition of apoptosis
failure of intercellular “tight junctions”
impairment of epithelial barrier integrity in the colon and increased large intestinal epithelial permeability
Consequence of butyrate insufficiency secondary to inadequate fermentation of butyrate precursor dietary fiber include: (3)
intraepithelial inflammation
systemic illness
inflammatory syndromes that mimic autoimmune dx
balance within the colon
ecologic harmony
dietary and medical practices that disturb the balance within the colon (ecologic harmony) include:
infant formula feeding
low fiber diets
diets high in resistance starch content (starches resistance to digestion by amylase)
inadequate intake of glutamine
Starches that are resistant to digestion by amylase
resistance starches
things that desensitize the colon
inadequate production of pancreatic zymogens that results in poor digestion of dietary sugars
oral antibiotic therapy
ingestion of zenobiotics and exotoxins
The human GI tact is ________ at birth
sterile
Parturition
action of giving birth
the tract is seeded initially by maternal vaginal organisms to child
When does mammary gland microflora contribute to early Bifidobacteria for a newborn?
breastfeeding
When else contributes to early intestinal ecology (besides breastfeeding and childbirth)
foodborne microflora and self-inoculation via coprophagy (eating of feces or dung)
maternal antibodies get transferred in
colostrum
In breastfed infants, over ____ of intestinal bacteria consist of ____________
In breastfed infants, over 90% of intestinal bacteria consist of Bifidobacterium infantis
In non-breast fed infants there are ______ #s of Bifidobacteria and Lactobacilli and ________ numbers of Enterococci, Coliforms, and Clostridia
In non-breast fed infants there are LOW #s of Bifidobacteria and Lactobacilli and HIGH numbers of Enterococci, Coliforms, and Clostridia
Clinically, feeding with infant formula instead of breast mild is associated with : (3)
Sepsis, necrotizing enterocolitis, and gastroenteritis
what causes a lack of substrate for fermentation that prevents the beneficial mild acidification of the colonic lumen and results in its relative alkalinization
low fiber diet
the rise in colon intraluminal pH is accompanied by :
decreased supply of butyrate to colonocytes with disruption of colonocyte apoptotic synchrony and persistence of senescent colonocytes with increased probability of undergoing precarcinogenic and carcinogenic change
what decreases the rate of passage, increases the time available for absorption of water by colonocytes, and provides increased exposure of colonocytes to toxins, mutagens and carcinogens
lack of sufficient amounts of dietary fiber in the colon
decreased water absorption to stool results in increased stool hardness and incidence of ______
constipation
what will increase the amount of fermentable nonfiber CHO reaching the colon
incomplete digestion of dietary sugars
fermentation of sugars within the colon result in
hyper-acidification of intraluminal pH and an increase in microbial production of SH2
SH2 readily enters colonocytes where it acts as an::
inhibitor of enzymatic conversion of butyrate to acetyl CoA
what produces leaky tight junctions with an increase in intestinal permeability, increased risk for energy deficit in colonocytes
Intracolonocyte acetyl CoA deficiency
decreased colonocyte oxidation of butyrate produces
delayed colonocyte apoptosis with increased colonocyte exposure to toxins, mutagens, procarcinogens, and carcinogens and increased risk for colorectal carcinoma
what kills Lactobacilli and Bifidobacteria although usually targeted at pathogenic organisms
oral antibiotics
as the numbers of Lacobacilli and Bifidobacteria decrease due to oral antibiotic, what increases?
the pathogenic bacterial species
when this happens it has a severe impact on Colon health and causes colonocytes to have increased exposure to pathogens
most pathogenic species are insufficient fermenters of
dietary fibers
When taking antibiotics, intestinal permeability increases leading to
increased exposure of intestinal mucosa to pathogen-produced irritants decreases the synchrony of colonic smooth muscle contractions and commonly induces diarrhea
environmental toxins can damage the:
colonic mucosa both directly and following their conversion to reactive metabolites in the liver and excretion into the intestinal tract via the bile
the proportion of reactive metabolites in the colon reflect the interplay of the genetic diversity of hepatic mixed function oxidases and:
the extent of exposure to environmental toxins
environmental toxins and their metabolites also interact with?
pathogens
for example: bacteria may deconjugate reactive metabolites reaching the colon via the bile, liberating highly reactive (and usually highly oxidizing or DNA damanging) compounts
environmental toxins and their metabolites also interact with?
pathogens
for example: bacteria may deconjugate reactive metabolites reaching the colon via the bile, liberating highly reactive (and usually highly oxidizing or DNA damaging) compounds
non-digestible fermentable CHOs that encourage beneficial change in the host’s microbial balance
prebiotics
non-digestible food ingredients that beneficially affect the host by selectively stimulating the growth and activity of one or more bacterial species in the colon, thereby improving the host health
prebiotics
most widely available prebiotic:
CHOs (usually oligomers) that are not hydrolyzed or absorbed in the stomach or intestines and that are selectively fermented by non-pathogenic microbes
the fermentation of prebiotic CHOs produces ________ that are beneficial to the human colon
metabolic byproducts
Common sources of prebiotic fructans (fructooligosaccharides; FOS) and inuilin
wheat, onions, asparagus, chicory, banana, and artichoke
Oligofructoses from other plant sources include:
galactooligosaccharides and levans
These compounds get converted to SCFAs by intestinal microbes and provide about 70%of the metabolizable energy of an equal weight of sucrose
GRAS
generally recognized as safe
__ to ___ % of the population is sensitive to oligofructoses
1-4%
Fructooligosaccharides (FOS)
specifically fermented SCFA’s by Bifidobacteria and are not converted to lactic acid and do not induce lactic acidosis
Supplimenting with 4g/day of FOS
increases the proportion of bifidobacteria in the colon
Oligofructose roles:
increases calcium absorption in men and women
reduce the number of aberrant crypt foci in the colon
reduces the incidence of inducible mammary tumors in animal models of cancer
products of oligofructose fermentation inhibit:
hepatic triglyceride synthesis
oral deitary supplements containing live microbes that beneficially affect the hosts microbial balance
probiotics
when effective, probiotics can”
increase the numbers of intestinal Bifidobacteria and Lactobacilli
decrease microbial species that do not ferment fiber to SCFAs
Probiotic supplement should survive passage through:
the stomach and small intestine to reach the large intestine
produce SCFAs from dietary fiber
maintain colonic pH at about 6
prevent the adherence of pathogens to the colonic mucosa
adhere to human colonocytes in situ
be capable of eventually permanently repopulating the colon
Reseeding with adherent probiotic species required at least ____ (time and how)
6 months of daily ingestion of at least 10 billion colony forming units (10^10 CFU) per species
Is reseeding possible for all people?
no, some will require life-long daily supplementation
supplementation with a pre/probiotic combo consistently has either:
prevented or produced significant reductions in the severity and duration of colonic diarrheas, including infant formula induced diarrheas, childhood viral diarrhea, traveler’s nonbacterial diarrhea, antibiotic-induced diarrhea, diarrhea accompanying AIDS enteropathy and diarrhea caused by Clostridium difficile infection (C.diff)
Has helped with reducing need for parenteral feeding in pts with small bowel bacterial overgrowth (dysbacteriosis) and inflammatory bowel disease
what is the leading cause of nosocomially acquired infection
C. diff
C.diff is found in ____ % of all inpatients, and infection with it causes more than_____% of all interic infections
20, 70
supplementation with oral combination of pre/probiotic is _________ in the prevention or treatment of most other bacterial (small intestinal) diarrheas
ineffective
system that plays important role in regulation of digestive system function:
nervous system
Extrinsic nerves to the digestive system from the unconscious part of the brain or spinal cord respond to the presence of food in the alimentary tract by
stimulating the local release of acetylcholine, which causes intestinal smooth muscle contraction, squeezing and pushing food and fluids along the digestive tract and stimulating the release of digestive enzymes
in response to the emptying of the digestion tract,
adrenaline (epinephrine) is secreted centrally, which relaxes the muscles of the stomach and intestine and decreases the flow of blood to the organs
intrinsic nerves in the walls of the esophagus, stomach, small intestine, and colon are excited when
the walls of the hollow organs are stretched by food; in response, the movement of food may be increased or decreased
premature infants have decreased ability to secrete
gastric pepsin, lipase, pancreatic trypsinogen, lipase, amylase, and chymotrypsinogen
they are unable to form micelles with dietary fat
enterocyte secretion of the ectoenzymes, enterokinases, and lactase, also are reduced
normal term infants exhibit _____ and _____ activities similar to those in adults, while ____, ____, and _____ secretion is impaired compared to that of an adult.
pepsin and lipase
pancreatic enzyme, bile, and enterokinase
therefore the ability to digest dietary starches and animal fats is minimal until about 6 months of ago
Enterokinase activity reaches adult levels at about ___ years of age
4
examples of dietary nutrients that are NOT absorbed directly into the enterohepatic portal blood system include:
long-chain fatty acids
examples of dietary nutrients that ARE absorbed directly into the enterohepatic portal blood system include:
amino acids
medium-chain fatty acids
monosaccharides
hormone responsible for the decrease in GI smooth muscle tone and motility during pregnancy is
progesterone
ingestion of a meal containing large amounts of saturated fat will result in a transient increase in the serum concentration of
chylomicrons
product of enterokinase rxns is
trypsin
most iron is transported in the blood via the plasma carrier:
transferrin
organs most active in the synthesis of endogenous cholesterol are the liver and the _____
intestinal mucosa
lactulose is a CHO that is
nonabsorbable laxative
digested dietary protein is absorbed primarily in the
jejenum
monosaccharides are transported across the placenta from the maternal circulation to the fetal circulation by the process of
facilitated diffusion
if a bolus containing 600 mOsm/L enters the jejunum, the net direction of fluid movement in the intestinal tract will be:
from the circulation to the intestinal lumen
excessive production of gas within the intestines may be caused by excessive colonic bacterial fermentation of unabsorbed
CHO
a major intracellular antioxidant is the nutrient
glutathione
a required prereq to the digestion of proteins is the HCl-dependent process called
denaturation
the true digestibility of dietary fatty acids is
> 95%
