Transcript Hepatic function and nutrient absorption (reabsorption) 4/18

Hepatic function and nutrient
absorption (reabsorption) 4/20
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What is the function of the Gallbladder?
How does bile help us digest fatty foods?
How does lipase function?
What are the exocrine secretions of the pancreas?
Why is bicarbonate generated in so many different
places around the duodenum?
What does the intestinal wall look like at the microscopic
level?
How does the intestine move chyme with peristaltic
waves of smooth muscle cell contraction? VIP!!
What enzymes degrade protein, carbohydrates and fat?
Can protein, carbohydrates and fat be absorbed if it is
not broken up into monomers?
What is the function of the large intestine?
Dietary Fiber from plants helps us remove cholesterol from the
blood by preventing ileal/colonic reabsorption of bile! This helps
lower your plasma cholesterol and your heart disease risk!
The diagram below represents digestion without fiber.
Gallbladder: helps store and concentrate bile so extra doses
of bile can be released when chyme passes into the
duodenum. Bile emulsifies fat and greatly improves digestion.
• Concentrates bile X5 to X20 times!
• Smooth muscles around gall bladder contract to release bile to
the cystic duct
• Biliary Calculi (aka Gall stones)
Cholelithiasis and lithotripsy
• In contrast to kidney stones
• Duct Blockages and jaundice!
• If the Gallbladder is removed the bile is dumped into the small
intestine at a constant rate, not bad bud bile isn’t available for
handling meals with lots of fat.
How are large chunks of fat broken down into free fatty acids?
Some good review questions:
1) What are six functions of the liver?
2) What is the difference between a liver
“lobe” and a hepatic “lobule”?
3) What is the function of “bile”?
4) What does the enterohepatic circulation
recycle?
5) Name the digestive enzyme that
degrades triglycerides.
Enzymatic digestion occurs in three places: Mouth, Stomach and
Small Intestine. What enzymes do we use to do this in each of
these three organs? Don’t forget the two types of lipase.
The pancreas is unique because it has BOTH exocrine AND
endocrine functions,,,,, we quickly die without a pancreas.
• 3 Endocrine Hormones Created by Pancreatic Islets:
– 1) Glucagon: to maintain plasma glucose during starvation
– 2) Insulin: to prevent hyperglycemia after a meal
– 3) Somatostatin: inhibits gastrin release and HCl secretion
• CCK gets stomach ready to be empty again (rest) and the
intestine ready to digest food so nutrients can be absorbed
– Acid in duodenum: stimulates CCK secretion!
– Nutrients also promote CCK secretion!
– CCK Functions:
– 1)Contraction of gallbladderBile into duodenum
– 2)Stimulates exocrine secretions by the pancreas:
• +Pancreatic Enzymes, +Bicarbonate and +Flow rate
– 3)Relaxes HEPATOPANCREATIC sphincterBile into
duodenum
The pancreas creates about 1 ½ liters of exocrine secretion/day from
acinar ducts that are rich in water, bicarbonate and zymogens.
• Pancreatic duct and Common bile duct
• Exit pancreatic duct via Sphincter of Oddi
• Why are bile and pancreatic secretions rich
in bicarbonate?
• What are Zymogens? Why make them?
• #1: Trypsinogen>>activated only by
enterokinase in the duodenum!!!!!!
• Secondary Zymogens:
• Carboxylpeptidase and Chymotrypsin
• Bile Activated Pancreatic Enzymes:
• P. amylase, P. lipase, Ribonuclease,
Deoxyribonuclease
• Why do we get so sick without bile?
Intestinal surface promotes four things: 1)Max. surface area,
2)Peristaltic chyme propulsion, 3)Protection against stomach
acid/contents, and 4)Replacement cells (24hr/day-7days/WK)
• Anatomical divisions:
– Circular folds>Villi w Lacteals > Microvilli > Brush Border
• Deep Duodenal glands produce bicarbonate along length of intestine
in case stomach acid should appear.
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Function of brush border and contact digestion
Crypts of Leiberkuhn:
1) 1-2 liters/day with NaCO3 for pH/fluidity
2) Epith. Cell division occurs at bottom of Crypts of Lieberkuhn
– Why extend Crypts so deep into Submucosa?
– What if all Crypts are destroyed?
• The cell turn-over-rate of the GI tract is one of the highest in body (24 days), what happens when GI cells cant divide?
– Consider: Radiation, Toxins, Chemotherapy
– This turnover time is important: never ever forget this!
Circular foldsVilli with LactealsMicrovilliBrush Border
Cell division is most rapid at bottom of crypts! Goblet cells
produce extra mucus to keep surface moist and bacteria free.
GI smooth muscle cells can contract independently of the
CNS because the gut has autorhymicity!
The CNS can only ‘modify’ this rate depending on need.
• Duodenum usually sets rate for the entire intestine! ‘Migrating
Motor Complexes’ are waves of contraction
• 12 MMC/min: Duodenum8MMC/min: Jejunum
• Contractions occur in Circular and Longitudinal SMC
• Contractions mean flow!
– This means bacteria are constantly pushed out!
– Why is a lack of “digestive sounds” a bad clinical sign?
• Irritations in lower intestine may modify gut activity!
– What happens to base-line autorhythmic rate when you
have diarrhea or indigestion?
– What happens to the ability to expel gut material if you are
very weak?
Intestinal autorhythmically generates waves of contraction. Like the heart, areas
with fastest rate determine intestine contraction rate. The Duodenumal region
has the fastest rate and the colonic region has the slowest rate of
autorhythmicity!What happens to colonic motility if the ileum is injured proximal to the IC valve?
The three nutrient types (carbohydrate, proteins and lipids) are broken down into
single monomers for maximal absorption (mostly in the jejunum)!
Triglygerides are broken into free fatty acids by the action of lipase prior to non-enzymatic
All other nutrients (monosaccharides and amino acids) require specific
transport enzymes for significant intestinal absorption to occur.
absorption.
Where are the secretions of the mouth, stomach,
pancreas, liver and small intestine reabsorbed?
Lets Give Thanks to the Colon!!
Some water is reabsorbed with the nutrients along the
length of the small intestine, largely the ileum.
The large intestine is the last chance to reabsorbed needed
materials before you are left with feces in the rectum.
• Bile salts can also be reabsorbed into the Portal
Circulation!
• Ileocecal Valve> entry point to Large Intestine
• Cecum>Ascending>Transverse>Descending>Sigmoid
• Haustra are the large side pockets
Dietary Fiber from plants helps us remove cholesterol from the
blood by preventing ileal/colonic reabsorption of bile! This helps
lower your plasma cholesterol and your heart disease risk!
The diagram below represent digestion without fiber.
The large intestine (colon) lets us adjust the fluid content of our feces.
Problems: Diarrhea (too much H2O) or Constipation (not enough H2O)