Hepatic function and nutrient absorption reabsorption 416

1
Hepatic function and nutrient absorption
(reabsorption) 4/16

• 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?

2
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.
3
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) Cholelithiasi
  s 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 isnt available for handling meals
  with lots of fat.

4
How are large chunks of fat broken down into free
fatty acids?
5
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.

6
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? Dont forget the two types of lipase.
7
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

8
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 Trypsinogengtgtactivated 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?

9
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 foldsgtVilli w Lacteals gt Microvilli gt
  Brush Border
• Deep Duodenal glands produce bicarbonate along
  length of intestine in case stomach acid should
  appear.
• 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 (2-4 days), what happens when
  GI cells cant divide?
• Consider Radiation, Toxins, Chemotherapy
• This turnover time is important never ever
  forget this!

10
Circular folds?Villi with Lacteals?Microvilli?Brus
h Border Cell division is most rapid at bottom
of crypts! Goblet cells produce extra mucus to
keep surface moist and bacteria free.
11
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?

12
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?
13
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
absorption. All other nutrients (monosaccharides
and amino acids) require specific transport
enzymes for significant intestinal absorption to
occur.
14
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 Valvegt entry point to Large Intestine
• CecumgtAscendinggtTransversegtDescendinggtSigmoid
• Haustra are the large side pockets

15
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.
16
The large intestine (colon) lets us adjust the
fluid content of our feces.Problems Diarrhea
(too much H2O) or Constipation (not enough H2O)