The Pancreas, Liver, and Gallbladder Flashcards
name 3 gastrointestinal digestive organs. of those, which are endocrine organs?
- pancreas (endocrine)
- liver (endocrine)
- gallbladder
what general functions do gastrointestinal digestive organs do?
regulate digestion and maintain metabolic homeostasis
what are characteristics of exocrine glands?
- secretion onto a surface
- made up of epithelial cells
- diverse secretion types
what are characteristics of endocrine glands?
- secretion into the vasculature
- made up of epithelial and non-epithelial cells
- exocytosis
describe the basic structure of exocrine glands
- acinus (secretory portion) containing secretory vesicles
- duct (conducting portion)
what are 3 types of exocrine glands?
- merocrine glands
- holocrine glands
- apocrine glands
- remember, it is the cells themselves within the glands that are producing the secretions
describe merocrine glands
- most common exocrine gland that releases products via exocytosis at the apical end of secretory cells
- ex. salivary glands, pancreas
describe holocrine glands
- secretory cells disintegrate to form secretion
- ex. sebaceous glands
describe apocrine glands
- secretion of membrane-enclosed apical cytoplasm containing proteins and lipids
- ex. mammary glands (also merocrine in function)
T or F:
the pancreas has endocrine and exocrine functions
true
describe the cells and the products they release of the endocrine and exocrine functions of the pancreas
- endocrine: islets of langerhans, protein and polypeptide hormones
- exocrine: acinar cells, releases digestive molecules into the duodenum
what is the function of acinar cells?
- exocrine function in the pancreas
- they exocytose zymogen granules into intercalated ducts
name 4 zymogen granules
- alpha-amylase
- lipases
- nucleases
- proteases
what is the function of alpha-amylase?
hydrolyze long-chain carbohydrates
what is the function of lipases?
hydrolyze lipids
what is the function of nucleases?
hydrolyze DNA and RNA
what is the function of protease? what is the cascade responsible for the functional process?
- proteases are zymogens
- they are inactive until they reach the duodenum
- they hydrolyze proteins
- trypsinogen enters the duodenum; activated by enterokinase (turns trypsinogen into trypsin)
- activated trypsin cleaves chymotrypsinogen into chymotrypsin
- activeated trypsin activates elastase
T or F:
zymogens are activated in the liver to protect acinar cells
false:
they are activated in the duodenum to protect acinar cells
what are contracinar cells?
- produce HCO3 to create an alkaline solution that flushes secretions into the duodenum
what 2 molecules induce acinar and contracinar exocrine activity?
- cholecystokinin (CCK) - neuropeptide of the central and enteric nervous system; I cells
- secretin - S cells
islets of langerhans include which 4 major cell types?
- alpha cells
- beta cells
- delta cells
- PP cells
what is the function of alpha cells?
- islets of langerhans cell type
- secrete glucagon
- 30% of islet cells
what is the function of beta cells?
- islets of langerhans cell type
- secrete insulin
- 65% of islet cells
what is the function of delta cells?
- islet of langerhans cell type
- secrete somatostatin - inhibit GI and pancreatic endocrine and exocrine secretion
- 4% of islet cells
what is the function of PP cells?
- islets of langerhans cell type
- secrete pancreatic polypeptide - inhibits exocrine secretion, reduce GI motility, inhibit gastric acid secretion
- <1% of islet cells
what are 4 main functions of the liver?
- blood reservoir
- bile secretion
- detoxification
- metabolic homeostasis
how does the liver function in metabolic homeostasis?
- carbohydrate metabolism
- lipid metabolism
- protein metabolism
- storage
- serum protein production
the liver has vasculature coming from how many different places?
- 2 (dual blood supply)
- hepatic artery and portal vein
- receives 30% of cardiac output
- this is important in the liver’s detoxification function
T or F:
the liver is the largest organ in the body
true
T or F:
the liver cannot regenerate
false:
the liver is highly regenerative
what are 3 major cell types of the liver?
- hepatocyte
- kupffer cell
- sinusoidal epithelial cell
what are hepatocytes?
- polarized epithelial cells
- metabolism of carbohydrates, proteins, and lipids
- produces bile from cholesterol
- detoxifies endogenous and xenobiotic molecules
what are kupffer cells?
- liver-specific macrophage
- removes pathogens and debris from the blood
- help prevent infection
what is the Couinaud system?
- it divides the lobes of the liver into lobules
- lobules are 3mm wide and 7mm long
what are sinusoidal epithelial cells?
- line sinusoids in liver
- large pores between cells (fenestrae)
- no basement membrane
- allows the liver to take on excess blood
describe blood flow through the liver
- blood flows into liver via portal vein and hepatic artery
- blood diffuses through hepatic sinusoids
- contacts hepatocytes, kupffer cells, and sinusoidal cells
- filtered through into bile duct or blood leaves via the central vein
the hepatic artery and portal vein supply the liver. what percent of the blood supply of the liver is coming from each source?
- 70% from portal vein
- 30% from hepatic artery
blood from the portal vein enters the liver, but it first drains blood from which 5 organs?
- stomach
- spleen
- pancreas
- small intestine
- colon
describe the blood flow and resistance of the liver
- high blood flow
- low resistance
which blood vessel allows first-pass metabolism?
- portal vein
- this allows the liver to conduct rapid assessment of dietary products
kupffer cells filter the blood. blood from which 2 organs does it primarily filter?
clears colon and intestinal bacteria
T or F:
the liver provides rapid assessment of dietary products
true
is the liver a blood buffer and reservoir?
- yes
- normal volume: 450mL
- expansion: 0.5-1L
what are the 3 structure-function liver architecture classifications?
- classic hepatic lobule
- portal lobule
- hepatic acinus
describe the classic hepatic lobule structure-function liver architecture classification
- hexagonal prism of portal canals
- blood drains from the portal vein and hepatic artery to the central vein
- endocrine focus - when endocrine products are released from the liver, they are released into the central vein
describe the portal lobule structure-function liver architecture classification
- bile drains from hepatocytes to the bile ducts
- exocrine focus - production and drainage of bile
describe the hepatic acinus structure-function liver architecture classification
- microvascular liver unit divided into circulatory zones
- gradient of hepatocyte oxygenation
- hepatic functions differ across zones
what are the 3 hepatic acinus zones?
- zone I - periportal zone; oxygen and nutrient rich; most active in regulating blood sugar and protein metabolism
- zone II - intermediate zone
- zone III - peripheral zone; oxygen poor; high concentration of detoxifying enzymes
the liver maintains systemic metabolic homeostasis in which 5 major ways?
- carbohydrate metabolism
- fatty acid metabolism
- protein metabolism
- storage
- protein production
describe how the liver maintains metabolic homeostasis via carbohydrate metabolism
- glycogen storage
- gluconeogenesis
- normalizes blood glucose
describe how the liver maintains metabolic homeostasis via fatty acid metabolism
- oxidizes fatty acids
- produces ketone bodies
- synthesizes fatty acids
- synthesizes triglycerides, phospholipids, and cholesterol
- forms lipoproteins to transport lipids and fatty acids
describe how the liver maintains metabolic homeostasis via protein metabolism
- deaminates amino acids
- forms urea to remove ammonia from the blood
- synthesizes non-essential amino acids
describe how the liver maintains metabolic homeostasis via storage
- vitamins
- fatty acids
- iron
describe how the liver maintains metabolic homeostasis via protein production
- acute phase proteins
- clotting factors
- albumin
- apolipoproteins
the liver detoxifies endogenous and exogenous molecules. describe phase I and II of hepatocyte xenobiotic (drug)/molecule elimination
phase I:
- drugs/molecules converted to more polar compounds; oxidized
- cytochrome p450 and microsomal oxidases
phase II:
- drugs/molecules/phase I metabolites conjugated to hydrophilic molecules
- transferases
some drugs/molecules are directly transported into the bile
metabolites are eliminated in the bile or urine
what is bile?
a heterogenous liver secretion containing bile salts, cholesterol, phospholipids, bilirubins, and waste
bile salts are the products of what?
cholesterol metabolism
what cell produces bile?
hepatocytes
T or F:
bile is a mixed micelle solution
true
T or F:
bile acidifies intestinal contents
false:
it alkalanizes it
what is the function of bile acting as a detergent?
it solubilizes dietary lipids and fatty acids
bile from the liver eliminates toxic _____ waste and _____
- endogenous
- xenobiotics
describe the path bile takes from the gallbladder to the duodenum
- gallbladder
- cystic duct
- common bile duct
- merges with main pancreatic duct
- major duodenal papilla
- duodenum
what is the function of CCK relative to bile?
- stimulates bile release
- contracts gallbladder smooth muscle
- relaxes hepatopancreatic sphincter
what is the function of secretin relative to bile?
- it stimulates HCO3 secretion into the bile
- serves to neutralize the acids from the stomach
what is a zymogen?
- an inactive enzyme precursor
- activated in the duodenum
- activated form serves to protect acinar cells
in the hepatic acinus model, which zone contains hepatocytes that are most susceptible to damage during hypoxia or toxic conditions?
- zone III
- this region is oxygen poor and rich in detoxifying enzymes, and therefore regeneration and repair of hepatocytes here is inefficient
describe how bile is recycled
- via the enterohepatic pathway
- bile is released from the gallbladder into the duodenum
- reuptake of bile salts into the liver
- production of bile in the liver
- bile stored in the gallbladder
list the following in order of decreasing % in bile:
chenodeoxycholic acid
lithocholic acid
deoxycholic acid
cholic acid
- cholic acid - 50%
- chenodeoxycholic acid - 30%
- deoxycholic acid - 15%
- lithocholic acid - 5%
