Chapter 5- Gastric Emptying, Digestion, Absorption Flashcards
what is the GI tract’s function?
to provide the body with nutrients
what is the purpose of digestion
break down into smaller particles
what is the purpose of absorption?
transport of nutrients from intestine via lymph or blood vessels
what is the purpose of elimination ?
elimination of waste, undigested food
where does digestion start ?
in mouth
what is the function of the mouth ?
mechanical digestion
what is the function of salivary glands ?
secretion of fluid and digestive enzymes
what is the function of stomach?
secretion of HCl and proteases
what is the function of pancreas
secretion of digestive enzymes and bicarbonate
what is the function of liver
secretion of bile acids
what is the function of gallbladder
temporary storage and concentration of bile
what is the function of small intestine ?
digestion of food, absorption of water, nutrients, electrolytes
what is the function of large intestine
absorption of electrolytes
what are the 3 purposes of chewing
- mechanically reduces the size of food particles, increasing rate of gastric emptying
- increases surface area of food, more digestive enzymes released
- mixes food with saliva and digestive enzymes
what is the function of esophagus ?
push down bolus
is swallowing possible in space or upside down ?
yes thanks to peristalsis in esophagus
what is GERD ?
esophageal sphincter doesn’t work, acid goes into esophagus
what is the function of the pyloric sphincter ?
controls amount of chyme going in small intestine
what people are more affected by GERD ?
runners and cyclists
what are the three parts of the stomach?
fundus, corpus, antrum
what is the function of stomach corpus ?
secrete mucus, pepsinogen, HCl
what is the function of stomach antrum?
secret mucus, pepsinogen, gastrin
what are the three parts of small intestine ?
duodenum, jejunum, ileum
where in the small intestine is the majority of digestion ?
duodenum
what is the function of duodenum
majority of digestion
what is the function of jejunum
little digestion, majority of absorption
what is the function of ileum
majority of absorption
which part of the small intestine doesnt digest
the ileum
what does bicarbonate secreted by pancreas do ?
it is a base that neutralizes acidic chyme
what are the purpose of the folds of Kerkring in the small intestine ?
they increase the surface area of the intestine 3x
covered by villi which increase TSA 10x
what is the brush border ?
cover the villi and increase TSA of small intestine 20x
what is the TSA of small intestine ?
250 m^2 (tennis court)
how big are villi ?
1 mm
what are 2 diseases affecting the brush border ?
lactose intolerance / celiac disease, causing diarrhea (less absorption because brush border wiped out)
what is a lacteal ?
found in each villi, transports insoluble fat particles via lymphatic vessels
how does water-soluble particles get transported in villi ?
transport or diffusion into blood vessels across membranes of epithelial cells that cover the villi, and then transported to liver via hepatic portal vein
how much time does food spend in GI tract
1-3 days
what is transit time ?
time food spends in GI tract
what is transit time for small intestine
3-10h depending on motility
when does peristalsis increase
after a meal
what does bile consist of ? (6)
water electrolytes bile salts cholesterol lecithin bilirubin
where is bile released ?
through hepatic duct into duodenum
when does bile secretion increase ?
after a meal, esp if a lot of fat
what does bile do ?
emulsify fat
in large intestine, what is chyme called ?
feces
what are the 3 components of large intestine
colon
rectum
anal canal
what are 2 functions of large intestine
absorption of electrolytes and temporary storage of feces
where does digestion of carbs start ?
in mouth
which enzyme breaks down starch ?
amylase
where are the two places amylase is made
saliva and pancreas
lactose intolerance = insufficiency of
lactase
what enzyme breaks down lactose
lactase
what enzyme breaks down sucrose
sucrase
we can only absorb this kind of CHO
monosaccharides, so we have to break CHO down
what secretes it and what is the function of gastrin
stomach
stimulates HCl production and pepsinogen production
what secretes it and what is the function of secretin
small intestine
stimulates water and bicarbonate secretion in pancreatic juice
what secretes it and what is the function of cholecystokinin
small intestine
stimulates secretion of enzymes in pancreatic juice, gall bladder contractions
what CHO can’t be digested ?
cellulose, found in fiber
where does digestion of fats start depending on their size
small and med FA in mouth (coconut and palm oil)
long FA in intestine after emulsification
why is gastric lipase not fully efficient ?
bc it is in water, and fats are insoluble
what form do fat particles take on ?
micelles, with hydrophobic legs in middle bc gut is an aqueous environment
where does digestion of proteins start ?
in stomach
what does HCl do ?
denatures proteins, making bonds between aa exposed to enzymes
where does it work and what does it do: protease
stomach/ small intestine
active form from inactive precursor
where does it work and what does it do: pepsin
subcategory of protease
secreted as pepsinogen from stomach wall, activated with HCl and converted into pepsin which hydrolyzes protein
what stimulates HCl-pepsinogen?
food
pepsin = ____% of protein digestion
10-20
majority of digestion is in
small intestine
what do peptidases do ?
catabolize short chains into <3AA
describe carb digestion in stomach
none, bc amylase deactivated
which enzymes digest carbs in small intestine ?
pancreatic amylase and brush border enzymes
which enzymes digest fiber in large intestine ?
bacterial enzymes
describe protein absorption in large intestine
none
what three main substances hydrolyze protein
acid, pepsin, trypsin
when do proteins get completely broken down to amino acid
small intestine
what three lipases break down fat
lingual, pancreatic and gastric lipase
describe fatty acids in large intestine
none
how do CHO and protein get to liver?
from small intestine to portal vein to liver
how do fats get to blood ?
lymph vessels
what are the three main carbs that result from digestion ?
glucose, fructose, galactose
describe transport of fructose in absorption from lumen to epithelial cell
sodium-independent GLUT5 transporter on membrane of epithelial cell
describe transport of glucose and galactose into epithelial cell for absorption
a sodium dependent monosaccharide transporter (SGLT). eg glucose transported with 2 sodium ions into cell and then the sodium ions are actively transporter back into lumen through a Na+ K+ ATPase pump
describe transport of monosaccharides out of epithelial cell and into capillary
GLUT 2 accepts all three monosaccharides on contraluminal side of epithelial cell (no need for special sodium dependent transporter)
where in the body can glucose transporters be found
everywhere
in skeletal muscle, what are the two glucose transporters and when are they active ?
GLUT 1 at rest or low blood insulin
GLUT 4 when glucose and insulin are high or muscle is active
when is glut 4 used in skeletal muscle ?
when glucose and insulin are high or during exercise
how is absorption different without bile salts for fat ?
with bile salts (micelles), fat absorption 97%
without, 50%
how do fats get into blood ?
transport into villi and diffuse across membrane of epithelium into epithelial cells
for small and medium chain fatty acids, how does absorption happen ?
diffusion because more water soluble. then, bound to albumin and transported into blood
what percentage of bile is recycled
94%
for long chain fatty acids, how does absorption happen ?
micelles are formed within the intestinal lumen, performing a ferrying function. diffusion through lipid membrane, and then FA are reesterified into the epithelial cell endoplasmic reticulum. then, the TG are combined with cholesterol and phospholipids to form chylomicrons. chylomicrons move through lacteals in villi and transport through the lymphatic system to the subclavian veins
what is the structure of a chylomicron
fatty sides in center, polar parts form the surface, allowing transport of blood into aqueous blood.
what does lipoprotein lipase do ?
digests TG into fatty acids for storage by breaking down chylomicrons and causing fatty acids to go into adipocytes where they are reesterified
what percentage of amino acids and peptides are absorbed ?
99%
67% as peptides
33% as aa
how many brush border transporters needed for aa
7
between a big aa chain and a small one, who is absorbed first ?
big, with more affinity
between a essential or non essential aa, who is absorbed first ?
essential
peptides vs aa, who is absorbed first ?
peptides
how do peptides get into epithelial cell ?
transported against a concentration gradient (need H+) carrier-mediated transport.
what happens to peptides in epithelial cell ?
broken down to aa by dipeptidase and tripeptidase and then aa transported to liver
how do aa get into epithelial cell ?
Na-dependent transport, then Na gets pumped out with Na+ K ATPase pump, and amino acids transported to liver via portal vein
what becomes of aminoacids in villi ?
may be used for protein synthesis (apoproteins, digestive enzymes, hormones, N-containing compounds, glutamine)
how does the liver use aa ? (amino acid pool turnover)
excess aa stripped of carbon skeleton. amino groups combine with CO2 to make urea, sent to kidneys
use carbon skeletons to make FA or glucose or energy
where does most water absorption take place ?
in duodenum of small intestine by simple diffusion
what law does water absorption obey ?
law of osmosis
what is an osmole (mOsm)
number of solute particles
what is osmolality
mOsm/kg (number of solute/kg)
what is osmolarity
mOsm/L
in gut, water moves according to ________
osmolarity
if you drink something with high osmolarity, what happens ?
body will want to dilute it and drags water to gut- diarrhea, cramping
when is higher osmolarity: gastric fluid/blood or fruit juice and coca cola ?
fruit juice and coca cola (600)
compared to 300
water in intestine by secretions is what volume and where does it come from
7L
from salivary glands, stomach, gallbladder, pancreas, intestine
what is the volume of daily water intake ?
2L
what is total daily water absorption ?
7+2=9L
with diarrhea, will you have more or less absorption of water ?
less, more fluid loss
where does most vitamin absorption take place ?
jejunum and ileum
what are 4 fat soluble vitamins ?
A, D, E, K
what are 2 water soluble vitamins ?
B and C
how are fat soluble vitamins absorbed ?
with FA, incorporated into chylomicrons and transported in lymph system
where is most of the absorption for fat soluble vitamins ?
small intestine
how are water soluble vitamins absorbed ?
diffusion
how are fat soluble vitamins stored ?
similar to fat, in body
how are water soluble vitamins stored ?
they are not, excess excreted in urine
how are minerals absorbed in small intestine ?
not well
what does mineral absorption depend on ?
chemical form
state %absorption of heme iron
15
state %absorption of non heme iron
2-10
state %absorption of calcium
35
state %absorption of magnesium
20-30
state %absorption of zinc
14-41
after what can absorption of vitamin take place ?
after digestion separates vitamin from coenzyme
how is the amount of bacteria in the gut dependent on the pH?
the higher the pH, the more bacteria there will be (so more in the small intestine and colon than the stomach)
how much bacteria in gut do we have at birth ?
GI is sterile at birth
at what age do we start having bacteria in the gut ?
3-4 weeks
what are the three functions of gut bacteria ?
digest CHO, proteins, lipids that escape digestion and absorption
ferment cellulose
produce vitamin K, B12, thiamin, riboflavin
what 4 vitamins are made by gut bacteria ?
vitamin K, B12, thiamin, riboflavin
folic acid absorption requires which enzyme ?
conjugase
are bacteria in gut primarily anaerobes or aerobes ?
anaerobes
how long does food take to leave stomach after digestion
1-4h
what causes gastric emptying ?
contractions from pacemaker cells of stomach increase intragastric pressure, pushing chyme through pyloric sphincter
what is chyme
food mixed with stomach acid
what kind of signals does the stomach get that controls gastric emptying? (2)
positive
- nervous signals caused by stretching and extension of the stomach wall
- gastrin release
what signals does the duodenum get that controls gastric emptying ? what are their purpose ?
negative feedback due to receptors that detect acidity, osmolarity
prevent dumping of excessive chyme into intestine
what is the enterogastric reflex ?
in duodenum, receptors monitor acidity, osmolarity
when they are stimulated, the pylorus increases contractions, preventing dumping of excess chyme into intestine
what psychological factors can affect gastric emptying
smell and sight of food, thought of a food
how does volume of food ingested affect gastric emptying
stomach walls extend to a certain extent to accommodate larger volumes, but when maximal distension is reached, pressure increases.
how does exercise intensity affect gastric emptying
rate not affected by exercise up to 80%VO2max, where there may be a reduction
how does osmolarity affect gastric emptying
increased beverage osmolarity increases gastric secretions which reduce emptying and decrease water absorption
how does energy density affect gastric emptying
some nutrients like fat have an inhibitory effect on gastric emptying
how does meal or beverage temperature affect gastric emptying
extreme temperature decreases the rate
how does stress affect gastric emptying
reduced, due to stress hormones
who has slower gastric emptying- women or men ?
women
what other factors may cause gastric emptying rates to change
hyperthermia or dehydration
30-50% of these people have GI problems
distance runners
what are 3 upper GI problems
heartburn
bloating
vomiting
what are 4 lower GI problems
urge to poop
loose stool
diarrhea
bleeding
what are 4 related GI problems
nausea
dizziness
side ache
urge to urinate
what are 3 causes of GI problems
physiological
mechanical
nutritional
what are 2 physiological causes of GI problems
reduced blood flow to GI
increased anxiety
what are 2 mechanical causes of GI problems
impact and posture
what are 5 nutritional causes of GI problems
fiber, fat, protein, fructose, dehydration
what are 5 ways to prevent GI problems
avoid: milk containing lactose high fiber foods the day of or day before competition (no digestion could cause discomfort) aspirin and NSAIDs high fructose drinks dehydration
