1. GI Part 4

Question 1

describe the liver morphologically

Answer 1

liver lobule – portal vein, hepatic artery, bile duct –> sinusoids, hepatocytes, bile canaliculi

endothelial wall – fenestrated –> passage of big molecules (glucose, amino acids, etc)

blood flows from portal triad to central vein

bile flows from center to portal triad

fenestrated capillaries – allow nutrients to pass from blood to cells

Question 2

functions of the liver (8)

Answer 2

1. carbohydrates metabolism - gluconeogenesis, glycolysis
2. amino acids and protein metabolism - synthesis of plasma proteins
3. lipid metabolism - fatty acid oxidation, ketone bodies synthesis
4. storage - glycogen, lipids, vitamins, copper, iron
5. synthesis and secretion of bile acids, bile formation
6. biotransformation - medicaments, xenobiotics, metabolism byproducts
7. synthesis of hormones and mediators
8. synthesis of components of the immune system

Question 3

important plasma proteins synthesized in the liver (6)

Answer 3

1. albumins - produces oncotic pressure
2. lipoproteins - transport of lipids
3. glycoproteins - haptoglobin, transferrin
4. prothrombin and fibrinogen - blood coagulation
5. nonimmune alpha and beta globulins
6. complement components also produced in the liver

Question 4

different types of lipoproteins (3)

Answer 4

1. VLDL - transport of triglycerides from the liver to other organs
2. LDL (“bad”) - transport of cholesterol esters from liver to other tissues
3. HDL (“good”) - remove cholesterol from peripheral tissues and transport it to liver

Question 5

important hormones synthesized in the liver (4)

Answer 5

1. angiotensinogen –> prohormone
2. thrombopoietin –> hormone (growth factor); formation of blood platelets
3. IGF (insulin like growth factor) –> IGF 1 and 2
4. hepcidin –> small peptide hormone (iron homeostasis)

Question 6

what is biotransformation

Answer 6

group of reactions involved in the conversion of toxic molecules in non-toxic water soluble and more excretable substances

Question 7

why do most drugs need to undergo biotransformation

Answer 7

most drugs are liposoluble, so stay in the body long time

biotransformation is essential for the termination of their action and their elimination from the body

Question 8

what is the major site for drug biotransformation

Answer 8

the liver – cytochrome P450 microsomal enzyme

Question 9

what does drug metabolism lead to

Answer 9

drug metabolism leads to increased polarity

makes drugs and their metabolites more water soluble

Question 10

what are the 2 phases of biotransformation

Answer 10

Phase I – oxidation

Phase II – conjugation with glucuronic acid

Question 11

Phase I of biotransformation

what does it entail, where is it performed

Answer 11

oxidation

includes hydroxylation (adding -OH) and carboxylation (adding -COOH) to a foreign compound

performed in SER and mitochondria (reactions with proteins called cytochrome P450)

Question 12

Phase II of biotransformation

what does it entail
what does it do to the product of Phase I

Answer 12

conjugation

includes the addition of glucuronic acid, glycine or taurine to the target substance

makes product of Phase I more water soluble so that it can be easily eliminated

Question 13

where is bile produced and modified

Answer 13

bile is produced in hepatocytes

it is modified in epithelial cells of the gallbladder

Question 14

what happens to bile in the gallbladder

Answer 14

storage and concentration through electrolyte and water resorption

Question 15

why is bicarbonate needed in bile

Answer 15

in duodenum - helps neutralize acidic food coming from the stomach

Question 16

what are bile acids synthesized from

Answer 16

bile acids are synthesized from cholesterol and conjugated with amino acids (glycine, taurine)

Question 17

what are the most important components of bile

Answer 17

bile acids

bile acids are amphipathic (both hydrophobic and hydrophilic parts)

Question 18

where are bile acids secreted and what do they do there

Answer 18

bile acids are secreted into the duodenum

they emulsify fat droplets in the small intestine to form mixed micelles

Question 19

define emulsify

Answer 19

make fat droplets smaller for digestion

Question 20

movement of bile from liver to duodenum

Answer 20

bile is first excreted into the bile canaliculi (small canals between hepatocytes)

bile canaliculi gradually feed into larger canals and finally into the common bile duct (ductus choledochal)

a sphincter of smooth muscle (sphincter of Oddi) guards the entrance of the bile into the duodenum

Question 21

what happens to bile when there is no digestion going on in the duodenum

Answer 21

bile is stored in the gallbladder

Question 22

bile movement after a meal

Answer 22

after taking a meal –> emptying of gallbladder

increased amino acids and fatty acids in duodenum –> increased CCK –> contraction of smooth muscle and relaxation of Oddi’s sphincter

reflectory –> increased Ach –> contraction of the smooth muscle

Question 23

what is enterohepatic circulation of bile acids

Answer 23

bile acid recycling

bile acids get reabsorbed and go back to the liver via portal vein

only 5% of bile acid pool is synthesized de novo in the liver

95% recirculates between the small intestine and the liver (recycling of bile acids)

Question 24

what does the exocrine pancreas do

Answer 24

secretion of digestive enzymes

Question 25

describe the exocrine pancreas

Answer 25

an acinar gland connected by arborizing system of ducts

structure resembles salivary gland

Question 26

what does the pancreas secretion in acinus resemble

where does HCO3 addition occur

Answer 26

primary saliva – CL channel apical, Na/K/2Cl cotransporter basolateral

HCO3 addition occurs in the ducts

Question 27

what are zymogens and why are they needed

Answer 27

zymogens are the inactive forms of the enzymes produced in the pancreas

they are needed because protein digesting enzymes (proteases) produced in the pancreas are potentially harmful to pancreatic cells

Question 28

digestive enzymes produced in the pancreas (4)

Answer 28

1. peptidases - produced in inactive form
   trypsinogen, chymotrypsinogen, proelastase, procarboxtypeptidase A and B
2. nucleases
   ribonuclease, desoxyribonuclease
3. amylases - digestion of polysaccharides
   a-amylase
4. lipases

Question 29

regulation of the exocrine pancreas

Answer 29

pancreatic cells have receptors for acetylcholine, CCK, and secretin

Question 30

pancreatic secretions adjustments to food composition

Answer 30

increased starch leads to increased amylase

increased fat and protein leads to increased lipases and peptidases

Question 31

regulation of the exocrine pancreas and the 3 phases

Answer 31

cephalic phase - smell, sight, imagination

gastric phase - dilation of the stomach

intestinal phase - decreased pH leads to increased secretin; increased amino acids and fatty acids leads to increased CCK

Question 32

the exocrine pancreas – Ach and CCK

Answer 32

Ach and CCK stimulate secretion of an enzyme and chloride-rich formula

Question 33

the exocrine pancreas – secretin

Answer 33

secretin stimulates production of a bicarbonate-rich excretion

Question 34

pancreatic insufficiency

Answer 34

insufficient production of digestive enzymes by the exocrine pancreas; maldigestion

clinical signs: greasy/oily stools (steatorrhea), polyphagia (increased eating), rapid weight loss

Question 35

pancreatitis

Answer 35

relatively frequent in dogs – middle to old age, obese dogs

acini destroyed and replaced by connective tissue because of autodigestion

increased risk when eating too much fat, human food, or garbage