Lecture 5

Vocabulary flashcards covering key terms related to pancreatic digestive enzymes, their regulation, cystic fibrosis, and liver–biliary structure and function.

Pancreas

Exocrine gland that produces the major enzymes required to digest carbohydrates, proteins, fats, and nucleic acids.

Proteases

Pancreatic enzymes that hydrolyze proteins into peptides and amino acids.

Amylolytic enzymes

Pancreatic enzymes, such as pancreatic amylase, that break starches into sugars.

Lipases

Pancreatic enzymes that split triglycerides into free fatty acids and monoglycerides.

Nucleases

Pancreatic enzymes that cleave nucleic acids into free nucleotides.

Acinar cells

Pancreatic cells that synthesize digestive enzymes and package them into zymogen granules.

Zymogen

Inactive precursor form of an enzyme stored in granules until secretion (proenzyme).

Enterokinase

Duodenal brush-border enzyme that converts trypsinogen to active trypsin.

Trypsinogen

Inactive pancreatic proenzyme activated by enterokinase to form trypsin.

Trypsin

Active protease that activates many other pancreatic proenzymes.

Chymotrypsinogen

Proenzyme converted by trypsin into chymotrypsin.

Pro-elastase

Inactive precursor converted by trypsin into elastase.

Pro-carboxypeptidase A/B

Proenzyme forms activated by trypsin into carboxypeptidase A and B (exopeptidases).

Pancreatic amylase

Enzyme that cleaves starches to disaccharides (maltose, maltotriose) and α-limit dextrins.

Pancreatic lipase

Enzyme that hydrolyzes triglycerides into free fatty acids and monoglycerides.

Phospholipase A₂

Pancreatic enzyme that splits phospholipids into free fatty acids and lysophospholipids.

Cholesterolesterase

Pancreatic enzyme that hydrolyzes cholesterol esters into cholesterol and free fatty acids.

S-cells

Duodenal epithelial cells that secrete secretin in response to acid.

Secretin

Hormone that stimulates pancreatic duct cells to secrete bicarbonate-rich fluid and inhibits gastrin release.

I-cells

Duodenal/jejunal cells that release cholecystokinin (CCK) when exposed to fat and protein.

Cholecystokinin (CCK)

Hormone that triggers pancreatic enzyme secretion, gallbladder contraction, and Oddi relaxation; slows gastric emptying.

Sphincter of Oddi

Muscular valve controlling the flow of bile and pancreatic juice into the duodenum.

Cephalic phase

First phase of pancreatic secretion initiated by sight, smell, or taste of food via parasympathetic nerves.

Gastric phase

Pancreatic secretory phase stimulated by stomach distension via vagal reflexes.

Intestinal phase

Major phase where duodenal acid triggers secretin and luminal fat/protein trigger CCK release.

Cystic fibrosis

Genetic disease with defective Cl⁻ channel leading to thick pancreatic secretions, enzyme retention, and pancreatic insufficiency.

Hepatic artery

Vessel supplying oxygen-rich, nutrient-poor arterial blood (~25 %) to the liver.

Hepatic portal vein

Vessel delivering nutrient-rich, oxygen-poor venous blood (~75 %) from GI tract to the liver.

Hepatic lobule

Hexagonal functional unit of the liver centered on a central vein with portal triads at corners.

Portal triad

Set of three structures—hepatic artery branch, portal vein branch, and bile duct—found at each lobule corner.

Hepatocytes

Liver epithelial cells that metabolize nutrients, detoxify substances, and secrete bile constituents.

Canalicular network

Tiny channels formed by adjacent hepatocytes that collect newly secreted bile.

Bile

Exocrine secretion containing bile acids, phospholipids, cholesterol, bile pigments, salts, and water; essential for fat digestion.

Bile acids

Amphipathic molecules synthesized from cholesterol that emulsify dietary fat and form micelles.

Emulsification

Process of breaking large lipid droplets into small ones and preventing re-aggregation using bile acids and phospholipids.

Micelle

Small, single-layered cluster of bile acids, phospholipids, and lipid digestion products that keeps fatty acids and monoglycerides soluble.

Mixed micelle

Micelle containing bile acids, phospholipids, free fatty acids, and monoglycerides formed during fat digestion.

Gallbladder

Muscular sac beneath the liver that stores and concentrates bile between meals.

Bile duct cells

Epithelial cells lining bile ducts that add bicarbonate, salts, and water to bile.

Secretin negative feedback

Neutralization of duodenal acid by HCO₃⁻ reduces secretin release, limiting further bicarbonate secretion.

CCK negative feedback

Absorption of fats and amino acids lowers luminal stimuli, decreasing CCK release and enzyme secretion.

Secretin effect on stomach

Hormone inhibits gastrin secretion, reducing gastric motility and acid production.

CCK effect on stomach

Hormone inhibits gastrin secretion, slowing gastric emptying and decreasing acid secretion.

Systemic circulation (liver)

Arterial route supplying oxygenated blood to the liver via the hepatic artery.

Hepatic sinusoids

Specialized liver capillaries where arterial and portal blood mix en route to the central vein.

Bile pigments

Breakdown products of heme, principally bilirubin, excreted in bile.

Phospholipids (in bile)

Amphipathic molecules that aid bile acids in emulsifying fats.

Detoxification (liver)

Hepatic process of chemically modifying drugs, toxins, and hormones for excretion.

Exocrine gland (liver)

Role of the liver in secreting bile into the digestive tract.

Blood coagulation factors

Proteins synthesized by the liver essential for normal blood clotting.

Lipoproteins

Liver-produced complexes that transport lipids in blood, such as Very Low-Density Lipoprotein (VLDL) and High-Density Lipoprotein (HDL)

Autodigestion prevention

Pancreatic safeguards: storing enzymes as proenzymes, secreting trypsin inhibitors, and self-degradation of prematurely activated trypsin.