Physiology - Pancreas & Liver

Question 1

Both the pancreas and liver secrete into the:

Answer 1

• duodenal lumen

- (pancreas secretes pancreatic juice, liver secretes bile)

Question 2

What type of gland tissue does the pancreas have?

Answer 2

• both exocrine and endocrine tissue
• exocrine pancreas is dominant: secretory cells (acini) connect to ducts and empty in the duodenum
• endocrine pancreas is smaller: islets of Langerhaans (insulin and glucagon hormone secretion)

Question 3

What are the two components of pancreatic juice? Which cell type secretes each?

Answer 3

• pancreatic digestive enzymes (secreted by the acinar cells) and an aqueous alkaline solution rich in NaHCO3 (secreted by the duct cells)

Question 4

The 3 Pancreatic Digestive Enzymes

Answer 4

• proteolytic enzymes (protein digestion), pancreatic amylase (carbohydrate digestion), and pancreatic lipase (fat digestion)

Question 5

What are the three pancreatic proteolytic enzymes? How are they activated?

Answer 5

• trypsinogen, chymotrypsinogen, and procarboxpeptidase
• (each attacks a different peptide linkage)
• trypsinogen gets activated into tryspin by enterokinase/enteropeptidase, which is found in the lumen –> trypsin can then go on to activate chymotrypsin, carboxpeptidase, and other trypsin molecules

Question 6

All cells have proteins, so how does the pancreas protect itself from its own proteolytic enzymes?

Answer 6

• 1) the enzyme needed to activate trypsinogen (enterokinase/enteropeptidase) is only found in the duodenal lumen
• 2) the pancreas secretes trypsin inhibitor, blocking any trypsin activity in the pancreas due to spontaneous activation

Question 7

What is the function of pancreatic amylase and pancreatic lipase? Are these enzymes secreted in an active or inactive form? Why?

Answer 7

• pancreatic amylase: converts polysaccharides into maltose (a disaccharide)
• pancreatic lipase: converts triglycerides into monoglycerides and free fatty acids (pancreatic lipase is the ONLY fat digesting enzyme involved in digestion!)
• both are secreted in an active form because the pancreatic cells lack both polysaccharides and triglycerides, and are therefore not in danger

Question 8

The aqueous alkaline solution makes up the largest part of pancreatic juice. Which compound is it rich in? What role does it play in digestion?

Answer 8

• the solution is rich in sodium bicarbonate (NaHCO3)
• it neutralizes the acidic gastric contents as they enter the duodenum; this is necessary to insure proper functioning of the pancreatic enzymes (they don’t work well in acidic environments) and also to protect the duodenal mucosa from the acid

Question 9

What regulates pancreatic exocrine secretion?

Answer 9

• secretin increases alkaline solution secretion and CCK increases the enzyme secretion; both are major enterogastric hormones
• these hormones are released when chyme is present in the small intestine (secretin release stimulated by presence of acid, CCK release stimulated by presence of fat and protein)
• (carbohydrates have no effect on CCK release)
• somatostatin decreases pancreatic secretion (is released with excess acidity)

Question 10

10 Liver Functions

Answer 10

• secretion of bile salts to aid in fat digestion and absorption; metabolic processing of carbohydrates, fats, and proteins after their absorption; detoxing wastes, hormones, drugs, and foreign compounds; synthesis of plasma proteins, clotting factors, and angiotensinogen; storing glycogen, fats, iron, copper, and vitamins; activating vitamin D; removing bacteria and old RBCs; secreting thrombopoitein (platelet production), hepcidin (inhibits iron uptake), and growth-factors; producing acute phase proteins for inflammation; and excreting cholesterol and bilirubin

Question 11

What are the specialized residual macrophages of the liver called? Where do they reside?

Answer 11

• Kupffer cells
• they are found in the sinusoids
• (they engulf any bacteria and old RBCs passing through)

Question 12

What connects the portal veins to the central vein in each lobule?

Answer 12

• sinusoids

Question 13

When is bile produced? What determines whether bile enters the duodenal tract or the gallbladder for storage?

Answer 13

• bile is continuously produced by the liver
• the sphincter of Oddi, when closed, prevents bile from entering the GIT, diverting it into the gallbladder (the sphincter opens during digestion)

Question 14

5 Components of Bile

Answer 14

• bile salts, bilirubin, cholesterol, and lecithin (a phospholipid) in an aqueous alkaline fluid

Question 15

How do bile salts aid in the digestion of fats? How about in fat absorption?

Answer 15

• digestion: bile salts exhibit detergent action, breaking up large fat goblets into a liquid emulsion (increases surface area for pancreatic lipase)
• absorption: bile salts promote the formation of micelles

Question 16

What is bilirubin

Answer 16

• the end waste product of breaking down RBCs’ heme

Question 17

What role does bile play in excretion?

Answer 17

• bile allows the body to excrete non-water soluble wastes that are unable to be excreted by the kidneys (because they are hydrophobic)

Question 18

Cholerectic Substances

Answer 18

• these are substances that up-regulate bile secretion

- the most potent cholerectic substance is bile salts, themselves

Question 19

Roles of secretin and CCK in bile production/secretion.

Answer 19

• secretin: increases alkaline fluid component of bile
• CCK: increases secretion of pancreatic enzymes, and causes contraction of gallbladder and relaxation of the sphincter of Oddi = bile enters the duodenum

Question 20

The liver is constantly producing bile, so how can the gallbladder store it without filling up?

Answer 20

• the gallbladder actually concentrates the bile by actively transporting salt out (water follows salt = concentrated bile)

Question 21

What are the three zones of the liver? What type of injury is each prone to?

Answer 21

• zone I: periportal zone; contains the portal triad (bile ductule, branch of portal vein, branch of portal artery); affected 1st by viral hepatitis and ingested toxins (cocaine)
• zone II: intermediate zone
• zone III: pericentral vein/centrilobular zone; contains the central vein; affected 1st by ischemia and metabolic toxins

Question 22

What type of blood do the sinusoids contain?

Answer 22

• mixed, but largely deoxygenated, blood; 80% from the central vein and 20% from the hepatic artery

Question 23

Where do ALT and AST originate from? What about GGT and ALP? Where else is ALP produced?

Answer 23

• alanine transaminase (ALT) and aspartate transaminase (AST) originate in the cytoplasm of hepatocytes
• gamma glutamyl transferase (GGT) and alkaline phosphatase (ALP) originate from the bile/canalicular surface of hepatocytes
• ALP is also produced in bone, intestines, and placenta