GI 4 Flashcards
More than —% of pancreas is exocrine:
– Acinar cells synthesize
and secrete
– Duct cells secrete
90
hydrolases for digestion
bicarbonate and water
Luminal digestion of (3)
– Impaired function causes (2)
carbohydrate, protein, fat.
maldigestion and malabsorption.
Neutralizes gastric H+:
secretes HCO3- into
duodenum up to
145 mEq/L
Proteolytic enzymes synthesized, stored and secreted as inactive precursors. - Activated in intestinal lumen (2)
- Enterokinase
2. Trypsin
—- synthesized, stored and
secreted with precursors.
Trypsin inhibitor
Regulation of Acinar Cell Secretion
Function =
Digestive Enzyme Secretion
Two Stimuli for Acini Cell Enzyme Secretion (2)
- CCK
2. ACh/GRP (vagovagal reflex)
Two Stimuli for Ductal Cell
Secretion of H2O and HCO3- (2)
- *Secretin (Secretin receptor).
2. Ach (M3 receptor).
Secretin (4)
cAMP Phosphorylation of CFTR increase Cl- conductance increase HCO3- secretion
Secretin released when pH
< 4.5.
Below pH = 3,
secretin release is maximal in segment of duodenum. Further release of secretin depends upon area of small intestine affected. (Maximal bicarbonate response is 30 mEq/hr)
During meal pH rarely
< 3.5 or 4.0.
Phases of Pancreatic Secretion (3)
Cephalic (20%)
Gastric (5-10%)
Intestinal (70-80%)
Cephalic (20%)
Gastric (5-10%)
Both phases mediated by
vagovagal
reflex - low volume, high enzyme
secretion (Ach/GRP)
(2) both potentiate the effects of secretin on water and
bicarbonate secretion.
CCK and Ach
Secretion Rate α
[Secretin] + [Ach] + [CCK]
Low secretion rates - (2)
bicarbonate concentration is low
chloride concentration is high
High secretion rates - (2)
bicarbonate concentration is high
chloride concentration is low
Sodium and potassium concentrations
always same as —
plasma
Pancreatic juice is —
isotonic
Cystic Fibrosis (3)
Abnormal sweat composition. Decreased pulmonary and pancreatic secretion. Mendelian autosomal recessive occurrence.
Defective CFTR: (3)
– Sweat Cl- reabsorption;
– Pancreatic duct cell function;
– Pulmonary mucus clearance.
Disorders of Exocrine Pancreatic
Function (3)
Cystic Fibrosis
Pancreatitis
Duct Obstruction
Pancreatitis (4)
– Acute and chronic – Trypsin activation causes pain, inflammation – Chronic disease destroys acini – Consequences reflect decreased digestive enzyme production
Duct Obstruction (2)
– Gallstones
– Tumors
Without pancreatic
enzymes - (2)
60% fat not absorbed (steatorrhea) 30-40% protein and carbohydrates not absorbed
Functional Unit of liver =
Liver
Lobule
skipped Hepatic Function (7)
Cleansing and storage of blood
Metabolism of nutrients
Synthesis of proteins (coagulation factors,
plasma proteins, angiotensinogen)
Metabolism of hormones, chemicals
Storage of energy, vitamins, iron
Excretion of lipid-soluble waste products
Marked capacity for cellular regeneration
Secretion of bile –
600-1000 ml/day
Liver Has High Blood and Lymph Flow
Total blood input approaches
1,350 ml/min (27% of resting
cardiac output).
Liver Has High Blood and Lymph Flow
Resistance of vessels to blood
flow very —
low
Cirrhosis increases resistance,
produces
portal hypertension.
Hepatic lymph accounts for –%
of total body production.
50
Increased vascular resistance can
cause —.
ascites
Role of Bile (2)
1. Bile salts (acids) and lecithin required for digestion (emulsification) and absorption (micelles) of dietary fat. 2. Excretion of lipophilic metabolites (bilirubin), excess cholesterol, other waste products, drugs, and toxins.
Hepatocytes secrete (5)
bile salts, cholesterol, lecithin, bilirubin, many other lipophilic substances.
Duct epithelial cells modify —, add —
primary secretion
HCO3-
Storage and concentration in —.
gallbladder
— circulation reabsorbs some
components.
Enterohepatic
Hepatocytes secrete
organic component of
bile into bile ducts (3)
- Bile Salts (produced
from cholesterol) - Cholesterol
- Organic substances
Bile Duct cells secrete (3)
water, Na+ and HCO3-
Bile Transported (2)
- Small intestine for
- Gall Bladder for
fat digestion
storage
Bile secreted — by liver
continually
Most stored in
Gall Bladder (max. volume = 30-60 ml)
12 hours of liver bile secretion
or — ml bile (concentrated)
450
(2) reabsorbed from bile while in
Gall Bladder (5-20x more
concentrated)
Electrolytes and water
Cholecystectomy (2)
No problems with fat digestion
Bile flow directly into duodenum
Enterohepatic Circulation Conserves Bile Salts
Substance secreted into
bile by
hepatocytes.
Enterohepatic Circulation Conserves Bile Salts
Delivered to lumen of
—, then reabsorbed.
ileum
Enterohepatic Circulation Conserves Bile Salts
Transported to
hepatocytes via —
sinusoids
Enterohepatic Circulation Conserves Bile Salts
—% of bile salts
recirculated
94
Enterohepatic Circulation Conserves Bile Salts
Bile salts circulate –x
before lost in feces.
17x
Active absorption: (2)
Apical sodium-dependent bile salt
transporter (ASBT)
ASBT also present in renal PT
BARI (Bile Acid Reabsorption Inhibitors) (4)
Drugs that inhibit Bile Recycling
Used to lower LDL levels in blood
Hepatocyte production of bile increases
6-10x if bile salt recycling reduced.
LDL taken up from blood via hepatocytes
as source of cholesterol for bile salts
Types:
1. Bile acid sequestrants
Bind to bile salts in intestinal lumen and
block transport
Benefits: (2)
Drugs work in intestinal lumen (do not
need to be absorbed)
Reduce harmful side effects
Low ASBT Activity Associated with: (4)
Crohn’s disease
Congenital 1° bile acid malabsorption
Idiopathic chronic diarrhea
Irritable Bowel Syndrome
Hepatocyte dysfunction impairs (2) secretion:
bilirubin, bile salt
Hepatocyte dysfunction impairs bilirubin, bile
salt secretion: (2)
– Drugs (acetaminophen), viral hepatitis, toxins;
– Fibrosis, cirrhosis.
Duct obstruction: (2)
– Gallstones, tumors.
Intestinal mucosal defects impair`
bile salt
reabsorption.
Stimuli for Gut Hormone Secretion
Gastrin (stomach) (3)
amino acids and peptides
distention
(H+ inhibits)
Stimuli for Gut Hormone Secretion
Ghrelin (stomach) (2)
absence of nutrients
(inhibited by stretch)
Stimuli for Gut Hormone Secretion
Secretin (Small Intestine) (1)
H+
Stimuli for Gut Hormone Secretion
CCK (Small Intestine) (3)
amino acids and peptides
fatty acids
Indirectly via secretion of CCK-
RP and Monitor peptide
Stimuli for Gut Hormone Secretion
GIP, GLP-1 (Small intestine) (1)
Glucose
Stimuli for Gut Hormone Secretion
Motilin (Small Intestine) (2)
stimulus unknown
some studies suggest that an
alkaline pH in the duodenum
stimulates its release.
Endocrine Regulation: Specific Actions of Each Hormone
Gastrin (4)
↑ Histamine Release (ECL cell)
↑ H+ Secretion (Parietal Cell)
↑ Gastric emptying
Trophic affects on Mucosa
Endocrine Regulation: Specific Actions of Each Hormone
Ghrelin (1)
↑ Hunger
Endocrine Regulation: Specific Actions of Each Hormone
Motilin (2)
↑ Gastric Motility (MMC/Fasting)
↑ Intestinal Motility (MMC/Fasting)
Endocrine Regulation: Specific Actions of Each Hormone
GIP, GLP-1 (3)
↑ Insulin response to glucose
↓ Gastric Acid Secretion
↓ Gastric emptying
Endocrine Regulation: Specific Actions of Each Hormone
Secretin (4)
↑ Panc & Biliary HCO3- secretion
Trophic affects on Exo. Pancreas
↓ Gastric Acid Secretion
↓ Gastric emptying
skipped
Endocrine Regulation: Specific Actions of Each Hormone
CCK (7)
↑ Pancreatic enzyme secretion ↑ Gall Bladder Contraction Trophic affects on Exo. Pancreas ↓ Gastric emptying ↓ Gastric Acid Secretion Relaxation of Sphincter of Oddi Gastric receptive relaxation