digestive system lecture 8 Flashcards
What do you need in addition to pancreatic lipase to break down triglycerides into fatty acids?
- you need colipase that is made from pro-colipase that is broken down by trypsin
What is the liver?
What are its 4 main functions?
Largest gland of the body
Functions: Storage, synthesis, detoxification, metabolism
where does the liver secrete bile from?
Where does bile travel in?
Where is bile released?
Secretes bile from hepatic ducts
-bile travels in the common bile duct
-bile is released into the SI at the same location as pancreatic juice
What is the liver bile volume per day?
What type of fluid is it?
What is its pH, what does it neutralize?
Volume: 0.5 –1.0 liters/day
ISOTONIC FLUID: Na+, K+, Cl-, HCO3-
-pH: 7.8 – 8.2, Helps neutralize acidic chyme
How much do solids compose in the liver bile?
What are the 4 components of bile?
SOLIDS ~3%but no digestive enzymes
-Bile Acids (Bile Salts)
Bile Pigments (hemoglobulin breakdown products, gives blood/feces its color)
Cholesterol
Phospholipids
What is bile secretion like in the liver vs the entrance into the duodenum?
How much does the liver release per day?
How much enters the SI?
Bile secretion by the liver is continuous.
The liver releases about 0.5 – 1.0 liter/day.
Entrance of bile into duodenum is intermittent and the volume of bile entering the small intestine is < 500-70
How much space does the gallbladder have?
What does the gallbladder do to get around its low storage space?
it has 50-100mL of space
Concentrates Solids :
-Hepatic Bile 3%
-Gall Bladder Bile 10 – 20% (gallbladder concentrates solids)
-Viscosity Increases
What is the pH of hepatic bile and the gallbladder bile?
Reduces pH
Hepatic Bile 7.8 – 8.2
Gall Bladder Bile 7.0 – 7.5
WHat is the role of the gallbladder?
What does CCK do?
Gall Bladder does NOT synthesize, Bile Salts – it stores and concentrates them
-CCK also causes gallbladder concentration, allowing more concentrated bile salts
What can block call bladder duct?
What can be done to fix it?
gallstones can block the duct
-cholecystectomy is gallbladder removal
What do bile salts do?
Where are they synthesized?
What do bile salts facilitate?
-they reduce surface tension of lipid droplets so they can be acted upon by lipase
-are synthesized in the liver from CHOLESTEROL
- facilitate digestion, transport, and absorption of FAT (including cholesterol) by forming water-soluble complexes with the fats
What do bile salts faciliate the transport and absorption of?
WHat do they reduce/stabilize?
- facilitate transport and absorption of fat-soluble vitamins (A, D, E, K)
- reduce surface tension and stabilize emulsions
What do bile salts form and which side is facing inwards/out?
What is charcteristics of bile salt?
an aggregation of bile salts forms a micelle which has non polar surface facing in, and outward surface is polar
-they are amphipaths
WHat is a mixed micelle?
when fats are incorportated in micelles
What happens with the more bile salts that you add?
-the more you add the smaller the lipid molecules you will have
-it allows easier breakdown
What is the bile salt pool in grams?
What is the dailt synthesis and daily release into intestine?
Bile Salt Pool: 3.5 g
Daily synthesis: 0.5 g
Daily release into intestine: 15 – 20 g
Where are most bile salts reabsorbed and returned?
Where is the entire bile pool recirculated?
Most Bile Salt is reabsorbed into the portal blood and returned to the liver via Enterohepatic Circulation (EHC)
-The entire Bile Salt pool is recirculated several times a day between the Liver → GIT → Liver
What is the hepatic circulation path?
spincte of oddi to liver
then heart sends blood to the liver for nutrients (via the aorta)
-then heart sends blood via the aorta to the intestinal tract (SI)
What is the path of venous retunr in hepatic circulation?
-liver via the hepatic vein to inferior vena cava to heart
-then Hepatic portal vein from
intestinal tract to liver
What pathway is bile reabsorbed through?
enterohepatic circulation (EHC)
What are the intraportal functions of bile salts?
What type of feedback?
Regulate hepatic bile flow - the more Bile Salt returned via portal blood, the larger the volume of bile secreted
-positive feedback
What are the intrapotal functions of bile salts when new bile salts are synthesized?
What type of feedback?
What happens to bile salt synthesis if we remove the ileum?
Regulate the synthesis of NEW Bile Salts
- the more Bile Salt returned in Portal Blood, the smaller the amount of NEW Bile Salt being synthesized
-negative feedback
-bile salt synthesis increases
What is the intrahepatic function of bile salts?
What happens if cholesterol precipitates?
Keep cholesterol in solution ;Cholesterol is insoluble in water
-In bile, solubility of cholesterol is increased by 2 x 10^6
-it may give rise to GALLSTONES
What are the Intraintestinal Functions of Bile Salts, what does the lumen contain?
-Intestinal lumen contains a watery medium
-need fat to be in mixed micelle so they can be brokem up
What are the 2 intraintestinal functions of bile salts?
What would happen if we did not have bile salts?
1.Act as detergents and help form stable emulsions
2. Assist in the transport of fat and fat-soluble vitamins A,D,E,K from SI lumen into intestinal cell
-without bile salts fat would be secreted in feces
What are the 2 intracolonic functions of bile salts?
What happens when we have too much bile salt vs too little?
What does colon absorb?
Inhibit Na+ transport and H2O absorption
Excess Bile Salt in colon —>Diarrhea, too little can cause constipaiton
-colon absorbed water+ions but not nutrients
What are the intraportal and intrahepatic functions of bile salts?
What do they regulate/keep?
Intraportal – regulate volume of bile secreted by liver
– regulate synthesis of new bile salts
Intrahepatic – keep cholesterol in solution
What are the intraintestinal and intracolonic functions of bile salts?
Intraintestinal (SI) – emulsify & transport fats
Intracolonic – prevent too much water absorption
How are secertions regulated in the small intestine and liver?
What are the 3 phases of secretion?
-they are regulated by neuronal and hormonal inputs
-cephalic:pyschic and gustatory
-gastric
-intestinal
What does the pancrease contain cells that release what?
A large volume of juice rich in HCO3-
* A small volume of juice rich in enzymes (for protein/fat rich meal)
What are choleretics and cholagogues?
WHat is law of reciprocal activity?
CHOLERETICS – agents which cause the liver to secrete a larger volume of bile
CHOLAGOGUES – agents which cause an increase Gall Bladder emptying
-If the Gall Bladder is contracted the Sphincter of Oddi will be relaxed and vice versa
What happens to the liver, GB, and pancreas when there is vagus (cephalic) input)
liver as minimal secretion
-GB highly contracts and spincter relaxes
-pancrease secretes low volume/high enzyme/low pH fluid
What happens to the liver, GB, and pancreas when there is gastrin released?
it does not affect much in terms of secretion levels, everything secretes/is active slightly
What happens to the liver, GB, and pancreas when there is CCK secretion?
When is it released?
liver secretion is inhibted
-high contraction of GB
-has high enzymatic secretion but inhibts the high pH secretion
-released when we have a protein/fat rich meal
What happens to the liver, GB, and pancreas when there is secretin released/?
When is it usaully reelased?
-liver is is active and more bicarb rich
-inhibition of GB contraction and low pH secretion
-high amount of alkaline secretion
-released when we have acidic contents in SI
What happens to the liver, GB, and pancreas when there is bile salt secretion?
there is increase liver secretion and everything else is inhibited/no secreting
What is the final result of polysaccharides break down?
-Polysaccharides—> (broken down by Salivary and pancreatic amylase) Disaccharides—->Monosaccharide
What is final result of protein breakdown?
Proteins—> (broken down by pepsin, trypsin, chymotrypsin) Small Peptides—>Amino acids, Di, tripeptides
What is final result of fat breakdown?
-Fats —> (broken down by lipase, colipase, bile salts)–>Mono, Diglycerides, FAs
What are final steps in digestion mediated by, what do they produce?
Final steps in digestion mediated by intestinal enzymes produced by mucosa at the site where absorption will take place
What are the 3 main activities of GIT function?
What does the small intestine secrete?
What does it receive?
What does it contain, what are these attached to?
Secretes intestinal juice
* Water
* Mucus
* Ions
-Receives pancreatic juice enzymes to aid digestion
-Contains brush border enzymes: Attached to the microvilli of SI epithelial cells
What type of digestion does the SI help with?
What does it absorb?
-Mechanical digestion
Involves segmentation
-Chemical digestion
Occurs as chyme mixes with pancreatic juice, intestinal juice and bile
-Absorption of digested nutrients
What do the tubular glands increase in the stomach?
increase SA for stomach secretion
What are the absorptive cells in the SI?
villi and enterocytees are the absorptive cells of the SI
What do crypt cells lack and secrete?
-Crypt Cells lack digestive enzymes but secrete a large volume (3 liters/day) of alkaline fluid known as Succus Entericus
What are the secretions in the SI?
the amount?
What type of fluid is it and the pH?
What do villi not secrete?
crypts—>succus entericus
Volume: ~ 3 liters/day
ISOTONIC: Na+, K+, Cl-, HCO3-
-pH: ~7.5 - 9
-fluid
What do the villi cells do?
What do enterocytes in villi do?
do NOT secrete fluid, but complete digestion and absorb nutrients and fluids
-they Synthesize Digestive Enzymes which remain in the brush border
What are the SI enzymes?
-Enterokinase (lumen)
-Amylase
-Lipase
-Aminopeptidases
-Dipeptidases
What are the 4 SI dissarcharides?
-Sucrase
-Maltase
-Isomaltase
-Lactase
where do new cells migrate in the SI?
WHere do the old cells go?
-new cells migrate up into microvilli
-old cells slough off and get recycled into lumen
What is the villi cells turnover time?
What happens in the crypt region vs the villus region?
-turnover=3-5 days
-crypt region=cells mature as they migrate up to the villus regions
-villus region-cells tip apoptose and slough off into lumen
lumen of the small intestine anatomy
What are fats absorbed via?
Where are carbs and sugars absorbed?
What will flow of bloodblow be after a meal?
Where are fats from chylomicron absorbed?
Fats absorbed via the lacteals
-via the capillary
-very rapid flow after ingesting a meal
-at level of lacteal
What is the volume of colonic secretion?
-What are the secretions?
What is mucin important for?
Small Volume
- Alkaline [HCO3] = 100-150 mEq/L
[K+] = 100-150 mEq/L
- Mucin (Lots!!!) (imp for lubricating colon)
What does the colon not have/do?
What is there lots of in the colon?
What helps keep it in the colon
NO Digestive Enzymes
NO Absorption of Nutrients
-bacterial activity, MMC (migrating motor complex) helps keep bacteria in the colon
What are the 3 reflexes that regulate intestinal secretions?
Local enteric reflexes
- Vago-vagal reflexes
- Hormonal factors
What is the composition of the solids excreted daily, and the amount?
solids 50g, h2O 100mL
-30% bacteria
30% undigested fiber
10-20% lipids
10-20% inorganic matter
How many liters of fluids are secreted, and how many are reabsorbed?
-2 liters ingested +fluids entering GIT=7 liter secreted
-9 liters must be reabsorbed in the lume of GIT
What is daily secretion of salivary gland.
stomach, bile, pancrease, and intestine
-salivary gland=1500mL
-stomach=2500
-bile=500
pancreas=1500mL
intestine=1000mL
What is also reabsorbed from lument of GIT?
What is the composition of protein released into GIT?
What is processed by intestine?
water and Very large quantities of ions
-50g as enzymes+30g as cells=80g protein
-lots of amino acids
What are the sites of exchange characterized by?
- Very large surface area of Small Intestine
- Intimate contact with blood vessels
How much do the circular folds, volli and microvilli increase SA of SI by?
What is the only organ essential to life
What can hypertophy lead to?
ciccular folds=3x
villi=30x
microvilli=600x
-Only SI organ essential to life (colon cant take over)
-hypertrophy of SI can increase SA
What is the postparandial flow to intestine?
What does each villus have for efficient absorption
What is the lymph flow?
What does each enterocyte have?
-1-2 liters/minute
Each villus has a capillary loop and lacteal
Large surface area close to blood and lymph flow
-Lymph Flow 1-2 ml/minut
-each enterocyte has capillary network
What are the major areas of absorption, what absorbs iron/Ca2+, CHo, protein/lipids and vitmin b12 and bile acids
duodenum has high level of absorpiton effciency for iron/ca2+, CHO, protein, lipids and na+, h2O
-ileum absorbs mainly vitamin b12 and bile acids
What are the 5 main methods of diffusion/transport in which absorption takes place?
Simple Diffusion
Facilitated Diffusion
Active Transport
Pinocytosis
Osmosis – water always follows the osmotic gradient generated by the movement of ions and nutrients
What are the 4 requirments for absorption?
What do we need adequeate amounts of
Adequate Digestion – Enzymes (activated), optimal pH and ionic composition
Adequate Sites for Absorption
Adequate Transit Time for Absorption
Adequate Co-factors, Transporters
What amount is absorbed in SI and colon?
7 liter in SI and 2 liters in colon
What is the maximum capacity for water absopriton per say in SI and colon
SI: Maximum capacity 15 liters/day
colon: Maximum capacity 4-5 liters/day
What percent of carbs are digested/absorbed/
6% lactose
60% starch
30% sucrose
What is the protein digestion and absorption per day?
35-200 grams per day
What is the amount of carbs, fat and protein absorbed in GIT in percent
WHy is there a high efficiency?
CARBOHYDRATE 99%
FAT 95%
PROTEIN 92%
High efficiency due to effectivev coordination of activities
- neural, hormonal, motor, secretory, enzymatic -within an organ and between organs
What is the fat digestion and absorption photo
What happens to the waves in response to a meal?
What is closed in absence of meal?
-A wave of secretory activity, preceding, accompanying, and trailing behind meal
-A wave of motor activity which receives, accommodates, and conveys meal
-spincter is closed in meal absence
What are the different transit times in the mouth, throat, stomach, large intesttin, colon?
What are the first 3 protective mechanisms in GIT?
Mucin
* Inactive Proteases, Trypsin Inhibitor
* Gastric Mucosal Barrier
What are the last 4 protective GIT mechanims?
Sphincters prevent reflux
* Negative Feedback Inhibition of Gastrin
* Neutralization of duodenal contents
* Myogenic Motor Complex = “HOUSEKEEPiING
