3/30: Accessory GI Organs Flashcards
Is the pancreas exocrine or endocrine?
More than 90% is exocrine
What do acinar cells synthesize and secrete?
Hydrolases for digestion
What do duct cells secrete?
Bicarbonate and water
What does the pancreas have luminal digestion of?
Carbohydrate, protein, fat
What does impaired digestion function of the pancreas cause?
Maldigestion and malabsorption
What does the pancreas neutralize?
Gastric H+: secretes HCO3- into duodenum up to 145 mEq/l
How are proteolytic enzymes synthesized, stored, and secreted as?
Inactive precursors
Where are proteolytic enzymes activated in/
Intestinal lumen
1. Enterokinase
2. Trypsin
What is trypsin inhibitor synthesized, stored, and secreted with/
Precursors
What is the function of acinar cells?
Digestive enzyme secretion
What are the two stimuli for acini cell enzyme secretion?
- CCK
- ACh/GRP (Vagovagal reflex)
What are CCKs function in the gallbladder?
Contraction
What do CCKs do in the pancreas?
Acinar secretion
What do CCKs do in the stomach?
Stimulates receptive relaxation
Reduce emptying
Reduce HCl secretion
What do CCK do in the sphincter of Oddi?
Relaxation
What cells secrete CCK?
I cells
What two substances stimulate I cells to secrete CCK?
Monitor peptide
CCK-RP
What does CCK-RP need to function?
Fatty acids
Amino acids
What are the two stimuli for ductal cell secretion of H2O and HCO3?
- Secretin (secretin receptor)
- ACh (M3 receptor)
What does secretin induce when bound?
cAMP
Phosphorylation of CFTR
Increase Cl conductance
Increase HCO3- secretion
What is HCO3 bicarbonate output used as an index of?
Secretin release
What pH is secretin released at?
pH <4.5
At what pH is secretin release maximal in segment of duodenum?
Below pH of 3
What does further release of secretin depend upon?
Area of small intestine affected
When is pH rarely <3.5 or 4?
During a meal
Compare the rate of pancreatic secretion of CCK and secretin
HCl-
- increases levels of Water and HCO3 because HCl stimulates secretin which stimulates ductal cells to secrete water and NaHCO3
Soap-
- fatty acids
Acids secrete secretin
Fats secrete CCK
Peptone-
- increases levels of enzymes because peptides stimulate CCK which stimulates acinar cells to secrete enzymes
What are cephalic and gastric phases mediated by?
Vagovagal reflex
What kind of secretion is vagovagal secretion?
Low volume, high enzyme (Ach/GRP)
What does acid in the intestine stimulate?
Secretin -> HCO3-/H2O
What do fats/proteins stimulate in the intestine?
CCK -> Enzymes
(indirectly via CCK-RP and monitor peptide)
What is secretion rate proportional to?
[secretin], [Ach], [CCK]
What is bicarb and chloride concentration at low secretion rates?
Bicarbonate concentration is low
Chloride concentration is high
What is bicarb and chloride concentration at high secretion rates?
Bicarbonate concentration is high
Chloride concentration is low
What concentrations are always the same as the plasma?
Sodium and potassium concentrations
What tonicity is pancreatic juice?
Isotonic
What abnormal composition is caused by cystic fibrosis?
Abnormal swear composition
Decreased pulmonary and pancreatic secretion
What is the inheritance trait of cystic fibrosis?
Mendelian autosomal recessive occurrence
What does a defective CFTR cause?
Sweat Cl- reabsorption
Pancreatic duct cell function
Pulmonary mucus clearance
What are disorders of exocrine pancreatic function?
Cystic fibrosis
Pancreatitis
Duct obstruction
What are types of pancreatitis?
Acute and chronic
What causes pain and inflammation in pancreatitis?
Trypsin activation
What does chronic pacreatitis destroy?
Acini
What do consequences of pancreatitis reflect?
Decreased digestive enzyme production
What are types of duct obstruction?
Gallstones
Tumors
What happens if there are no pancreatic enzymes?
60% fat not absorbed (steatorrhea)
30-40% protein and carbs not absorbed
What is the functional unit of the liver?
Liver lobule
What are hepatic functions?
- 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 cell regenerations
Describe the resistance of vessels to blood flow in liver
Very low
What does cirrhosis do?
Increases resistance, produces portal hypertension
What can increased vascular resistance cause?
Ascites
What are bile salts (acids) and lecithin required for?
Digestion (emulsification) and absorption (micelles) of dietary fat
What is the role of bile with excretion?
Excretion of lipophilic metabolites (bilirubin), excess cholesterol, other waste products, drugs, and toxins
What do hepatocytes secrete?
Bile salts, cholesterol, lecithin, bilirubin, many other lipophilic substances
What do duct epithelial cells modify?
Primary secretion, add HCO3
Where is bile stored and concentrated?
Gallbladder
What reabsorbs some components of bile?
Enterohepatic circulation
What synthesizes and secretes bile?
Liver hepatocytes
What are organic compounds that hepatocytes secrete?
Bile salts (produced from cholesterol)
Cholsterol
Organic substances
What do bile duct cells secrete?
Water, Na and HCO3
Describe the transport of bile
- Small intestine for fat digestion
- Gall bladder for storage
What happens to someone whos had a cholecystoectomy?
- no problems with fat digestion
- bile flow directly into duodenum
What does secretin stimulate in the gallbladder?
Liver ductal secretion
What does vagal stimulation cause?
Weak contraction of gallbladder
What does cholecystokinin via blood stream cause?
- Gallbladder contraction
- Relaxation of sphincter of Oddi
How are substances secreted into bile by?
Hepatocytes
Where are substances that are secreted into bile delivered to?
Lumen of ileum, then reabsorbed
Where and how are bile salts transported?
To hepatocytes via sinusoids
What transporter helps with active absorption of bile salts?
Apical sodium-dependent bile salt transporter (ASBT)
What are BARI (bile acid reabsorption inhibitors)?
Drugs that inhibit bile recylcing
What is BARI used for?
To lower LDL levels in blood
How is LDL taken up from blood?
Via hepatocytes as source of cholesterol for bile salts
What are the two types of drugs that inhibit bile recycling?
- BIle acid sequestrants
- ASBT inhibitors
What do bile acid dequestrants bind to?
Bile salts in intestinal lumen and block transport
What are benefits of bile acid sequestrants?
- drugs work in intestinal lumen (do not need to be absorbed)
- reduce harmful side effects
What do ASBT inhibitors do?
Promising new drugs to reduce cholesterol levels in ECF
What is low ASBT activity awssociated with?
- Crohn’s dsease
- congenital primary bile acid malabsorption
- idiopathic chronic diarrhea
- Irritable bowel syndrome
What are disorders of biliary secretion?
- hepatocyte dysfunction impairs bilirubin, bile salt secretion:
drugs (acetaminophen), viral hepatitis, toxins
fibrosis, cirrhosis - duct obstruction
Gallstones, tumors - intestinal mucosal defects impair bile salt reabsorption
