digestion post midterm 2 Flashcards
what signal is sent to the NS to cause secretion and vasodilation even the food enters the stomach
vago-vagal activation during the cephalic phase
what does distention in the stomach activate?
-activates local enteric reflex and vago-vagal reflex
what are the products of proteins released during protein digestion?
secretogogues
what are secretogogues?
which are AA or partially digestied proteins
what do secretogogues act on?
act on gastrin releasing G-cells which sit in the antrum of the stomach.
what does gastrin effec?
effects parietal cells to produce HCl
what type of hormone is gastrin?
peptide hormone
what is gastrin released by?
released by endocrine cells in the antrum of the stomach by G cells
what causes for gastrin to be released?
- Secretogogues
- Local enteric reflexes (distention in the antrum)
- Vagally-mediated reflexes (vago-vagal reflexes)
what regulates gastrin release?
itself as it is self regulated
what type of feedback mechanism regulates gastrin?
positive feedback and negative feedback
what happens if the pH of the stomach drop below 2?
gastrin release gets inhibited
what will a low stomach pH cause?
release of the somatostatin cells which will inhibit the parietal cells from releasing HCl
what is the tropic effect of gastrin
stimulates production of more parietal cells
where is histamine present in the stomach?
in the gastric mucosa
what does histamine elicit?
large volumes of gastric juices with lots of HCl
how does gastrin ellicit large volumes of gastric juices with lots of HCl?
it sensitized the parietal cells to other stimuli
what can the the blocking of background release of histamine cause
inhibit acid secretion in response to ACh and Gastrin
what are H2 blockers used for?
used to decrease HCl secretions
how can ulcers be treated?
using H2 blockers or as H+/K+ATPase blockers
what is the impact of secretogogues as the food enters the duodenum?
secretogogues will enter circulation and cause a hormone to stimulate a final push of HCl secretion by the parietal cell.
what inhibits gastric secretions?
the enterogastrone hormone complex
what does the enterogastrone hormone complex control?
antral peristalsis & secretion
what are some preintesinal changes made to food?
o Meal is reduced to a semi-liquid consistency
what happens to the osmotic pressure before it reaches the intestine
unchanged
what happens to the cyme before it reaches the intestines
its acidified
what is limited at the level of the stomach?
digestion
what is digested in the stomach?
polysaccharides –> disaccharides by salivary amylase
proteins –> polypeptides by gastric pepsin
lipids into DG/MG by lingual lipases
what happens to chyme once it reaches upper intestine?
must be neutralized
osmotic pressure must be equilibrated
where does absorption take place?
begins in the upper intestine
where do the pancreatic ducts lead to
to the duodenum
what does the pancreas secrete?
pancreatic juices
what is contained in pancreatic juices?
many digestive enzymes
what does the exocrine portion of the pancreas contain?
acini
what is contained in acini
duct cells and acinar cells
what is secreted by acinar cells?
digestive enzymes
what is secreted by duct cells?
bicardbonate rich fluid
what enzymes are contained in the pancreatic juices?
pancreatic amylase trypsin chymotrypsin elastase pancreatic lipase ribonuclease diribonuclease
what breaks down trypsinogen into trypsin?
enterokinase
what is the function of trypsin?
it breaks down other pancreatic enzymes such as chymotrypsin, protelastase, procarboxypeptidase
what does the pancreas produce in order to inhibit trypsin?
trypsin inhibitor
why would the pancreas produce trypsin inhibitor?
to ensure that any trypsin in the pancreas is broken down
what volume of pancreatic juices are secreted daily?
0.5-1.5L/day
what is the osmolarity of pancreatic juices?
isotonic ~300mOsm
what is the main electrolyte found in pancreatic juice?
HCO3-
what is the pH of pancreati juice?
7.2-8.2
what is the concentration of enzymes in pancreatic juices?
~3g%
what is the function o amylase?
breaks down polysaccharides into disaccharides
how must CHO be broken down in order to be absorbed?
as monosaccharides
how are proteases first released as?
proenzymes
why must proteases be secreted into an inactive form?
in order to prevent the breakdown of the pancreatic cells themselves
at what pH is needed for lipases to function?
~8
what is produced by the liver and needed to break down fats?
bile salts
what is released by the exocrine secretions of the pancreased?
cells release large volume of pancreatic juice rich in HCO3- and small volume of juice rich in pancreatic enzymes
what is the largest gland in the body?
the liver
what are the main functions of the liver?
storage, synthesis, detoxification, metabolism
what is secreted by the liver?
bile
where is bile released?
via the hepatic duct and enter common bile duct and then into the SI
what sphincter needs to be open to allow bile to enter through the SI?
sphincter of Oddi
what do the lobules of the liver contain?
hepatocytes
how much bile is secreted daily?
0.5-1L
what ion is most prominent in bile?
HCO3-
what is the pH of bile?
7.8-8.2
what is contained in bile?
disgestive enzymes
what concentration of solids is found in bile
3g%
what solids are found in bile?
bile salts
bile pigments
cholesterol
phospholipids
is bile secretion continuous or intermittent?
continuous
is the enterance of bile in the duodenum continuous of intermittent?
intermittent
how much bile enters the SI daily?
<500-700 ml
what is the function of the gall bladder?
concentrate and store bile
how does the liver synthesize bile salts?
from cholesterol
what are the main fucntions of bile salts?
Facilitate digestion, transport and absorption of Fat (including cholesterol) by forming water-soluble complexes with fats and fat soluble vitamins
what are the fat soluble vitamins?
ADEK
are bile salts polar, non polar, amphipatic?
amphipatic
what does the amphipatic nature of bile salts allow?
it allows to form miscells through aggregation
where would vitamins and choelsterol be found in the micelle?
at the core of it
what is the function of micelles produced by bile salts?
Stabilizes the emulsions so they can be acted on by the lipases
how much bile salts are contained in the body?
3.5g
how much bile salts is synthesized daily?
0.5g
how much bile salts get released daily?
15-20g
how can so much bile be released and so little secreted daily?
bile is recycled and returned to the liver via enterohepatic circulation
how often does the bile salt pool get recirculated dailyy?
a few times a day
what happens by the time they reach the distal ileum
bile salt is reabsorbed
what are the main functions of bile salts
regultaes hepatic bile flow
regulates the synthesis of new bile salts
keeps cholesterol in solution
how is heptatic bile flow regulated?
via positive feedback mechanisms
what would happen to bile secretion if the ileum is removed?
less bile is secreted since, less bile is returned
through what feedback mechanisms does bile synthesis occur?
negative feedback, more that is returned less is synthesized
what happens if cholesterol precipitates?
it may give rise to gallstones
how much is solubility of cholesterol increased in bile?
2x10^6
what is the role of bile salts intraintestinally?
act as a detergent and help for emulsions
aids in transport of fat soluble vitamins
what is the role of bile salts in the colon?
inhibits sodium transport and water absoption`
what happens if we have too much bile salts in the colon?
diarrhea
what are agents which cause the liver to secrete a larger volume of bile
choleretics
what are Agents which cause an increase in the emptying of the gall bladder
colagogues
what is the law of reciprical action?
If the gall bladder is contracted, the sphincter of Oddi will be relaxed and vice versa
how does bile travel from site of production to the organs it needs to reach
The liver produces bile which enters the SI via the sphincter of Oddi, travels via hepatic circulation
From the hepatic portal vein from IT -> liver ->IVC ->Heart
by the time we reach what part of the GIT will most of the bile salts have been reabsorbed?
by the time they reach the distal ileum
how much bile cann the gallbladder store?
50-100ml
what does the gallbladder do to bile?
it concentrates its solids, reduces their pH, increases viscosity
what is the concentration of solids in the gallbladder?
10-20g%
can the gallbladder synthesize bile salts?
no
what is a cholecystectomy?
it involves the removal of a gallbladder
what happens if the gallbladder is removed?
hepatic bile is generally sufficent to break down lipids, however, eating less lipid richs foods would be better
after all the salivary, gastric, pancreatic and hepatic digestion in what state are CHO?
they still need to be broken down into monosaccharides
after all the salivary, gastric, pancreatic and hepatic digestion in what state are proteins?
proteins still need to be broken down into AA, di/tripeptides
after all the salivary, gastric, pancreatic and hepatic digestion in what state are fats?
fats have been broken down into FA/MG/DG and so no need for further steps
what is secreted by the small intestine?
water
mucous
ions
where are the enzymes contained in the SI contained and what are they called?
brush border enzymes which are attached to the villli of the cells
what process is used in the SI to aid in mechanical digestion?
segmentation
how does chemical digestion take place in the SI?
Occurs as chyme mixes with the pancreatic juices, intestinal juices and bile
why is it important to have invaginations and outpushing in the membrane of the SI?
o Large surface area for secretion, digestion and absorption
what takes place in the villi region of the SI?
Complete digestion and absorption
what are villi contained in villi cells?
• Enterocytes in villi synthesize digestive enzymes which remain in the brush border
what enzymes are secreted in the SI?
Enterokinase (lumen) Amylase Lipases Aminopeptidase Dipeptidase Disaccharases -Sucrase -Maltase -Isomalatase -Lactase
where are intestinal cells born?
in the crypt region
when do cells matin in the SI?
Cells mature as they move up to the villi region
how long is cell turnover in the SI?
~3-5 days
what happens to intestinal cells once they reach the tip of the SI?
apoptose
where does absoprtion take place in the SI?
in the lumen of the intestine
what allows for proximity with the circulatory system in the villi of the SI?
capillary loop and lacteal
how are fats carried and absorbed in circulation in the SI?
fats will complex with chylomicorns and be carried by lacteals into lymphatic system until they reach circulation
through what system does the contents of the capillary loop flow through?
flows through the hepatic system
where does the contents of the lacteals drain into?
contents of the lacteal travel through the greater lymphatic vessels and drain into the left subclavian veins
how are lipids tranported?
through lipoproteins
why is it difficult to transport lipids through blood?
due to their hydrophobic nature
what are the different classes of lipoproteins?
chylomicrons
VLDL
LDL
HDL
what do crypt cells lack?
• Lack digestive enzymes
what do crypt cells secrete?
secrete a large volume (3L/Day) of alkaline fluid known as succus entericus
how much volume is secreted in the SI daily?
~3L
what is the most prominent ion in the SI?
HCO3-
what is the ph in the small intestine?
7.5-9
how much is secreted in the colon?
a very small volume
what is the pH in the colon?
• Alkaline
o [HCO3-] = 100-150 mEq/L
o [K]= 100-150 mEq/L
what is there alot of in the colon?
bacteria and mucin
what lack in the colon?
digestive enzymes and no nutrient absorption
what regulates intestinal secretions of the colon?
- Local enteric reflexes
- Vago-vagal reflexes
- Hormonal factors
what is being absorbed through the process of nutrient absorption?
the majority is resabsorbed material
what are the sites of exchange characterized by?
Very large surface area of small intestine
Intimate contact with blood vessels
how does absorption take place?
o Simple diffusion o Facilitated diffusion o Active transport o Pinocytosis (take nutients into the cells) o Osmosis
what factors may limit absorption?
need for adequate digestion, absorption, transit time and cofactors and transporters
what are factors that influence adequate digestion?
the amount of enzymes, the activity of the enzymes, optimal pH and composition, proper motility
how much daily secretions needs to be rebasorbed daily?
~7L
how much content is taken in by the mouth?
~2000mL fluid and 500g solids
how much is excreted by the body
~50g and 100mL
from the solids excreted in the body what are is proportions?
- 30% bacteria
- 30% undigested fiber
- 10-20% lipids
- 10-20% inorganic matter
overall how many L does the body need to absorb daily?
9L
does the body only need to absorb fluid?
no alot of the fluids also contain ions which also need to be absorbed
how manu L are absorbed in the SI daily? what is the max capacity of the SI?
7l
Max: 15L
how manu L are absorbed in the colon daily? what is the max capacity of the colon?
2L
max: 4-5L
how much proteins are released in the lumen daily? what happens to them?
50g enzymes
30g cells
thus overall the 80g of proteins need to be broken down into AA to be reused
by how much is the surface area increased by the vili and microvili
villi: 30x
microvilli: 600x
what is the rate of the post prandial blood flow to the intestine?
1-2L/day
why are villi efficent in absorption?
: each villus has a capillary loop and lacteal
why is it not a good idea to exercise after a fat meal?
slow rate of lymphe flow: 1-2mL/minute
what is mostly absorbed by the duodenum?
Iron Ca2+ CHO PROTEINS Na+ lipids
what is mostly absorbed in the jejunum?
CHO
PROTEINS
Na+
lipids
what is mostly absorbed by the ileum?
CHO VIT B12 PROTEINS BILE SALTS Na+ Lipids
what breaks down lactose?
lactase
what % of CHO is lactose?
6%
what is lactose broken down into?
galactose and glucose
what % of CHO is starch?
60%
what % of CHO is sucros?
30%
what type of protein is more rapidly absorbed?
oligopeptides
how much protein is taken in daily?
~35-200g
what happens to MG ready to be absorbed?
- FA from monoglycerides are taken up by the micelles and will enter the enterocytes and reform TG which will join to the chylomicrons and transported by the lacteal into the lymphatic system
- The glycerol portion of the MG is taken into the blood directly
what is the high efficency of the GIT a result of?
effective coordination of activities (neural, homonal,motor, secretory, enzymatic) within an organ between organs
how does the body function in response to a meal?
- secretory activity before and after
- motor activity will receive, accomodate and convey the meal
what is the transit time in the colon?
hours to days
what is the transit time in the SI?
several hours
what is the transit time in the stomach?
minutes to hours
what is the transit time in the esophagus?
seconds
what is the transit time in the pharynx?
<1s
what is the transit time in the GIT relative to?
the fucntion of the given organ
