Biochem 510 - Exam 1

What is digestion?

in the GI tract, the series of mechanical, chemical, and enzymatic processes that break food down for absorption

Primary organs of the GI tract

oral cavity, esophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine

Function of oral cavity (Primary)

mastice food, mix with saliva, which contains enzymes (amylase to digest carbs) and mucus (lubricant), mostly mechanical digestion, very little enzymatic or chemical digestion

Function of the esophagus (Primary)

tube to the stomach, lined with muscles for swallowing, peristalsis

Peristalsis (Primary)

the coordinated (wave-like) series of muscle contractions that move food through the GI tract beginning in the esophagus

Function of the stomach (Primary)

holding tank (50ml-1.5L), controls delivery to small intestine (pyloric sphincter), site of some mechanical (~3 contractions per min), some enzymatic (salivary amylase, pepsin, gastric lipase), but mostly chemical (HCl secretion, protein denaturation, mineral release, kills most bacteria)

Function of the small intestine (Primary)

major site of digestion (and absorption), some mechanical digestion (8-12 contractions per minute), but mostly enzymatic digestion

Function of Colon (Primary)

lots of digestion performed by intestinal bacteria, also an important site of absorption, water, electrolytes (K, Cl, Na)

Accessory organs of the GI tract

salivary glands, pancreas, liver, gallbladder, the microbiota, and appendix

Function of salivary glands

excretion of saliva, which contains enzymes and mucus-lubricant

Function of the pancreas

endocrine function (1%) - production of insulin and glucagon, released into blood stream, and control glucose metabolism

exocrine function (99%) - produces secretions for digestion that are released into the duodenum, contains enzymes (lipases, proteases, amylases, etc.) and bicarbonate (to buffer stomach acid, critical for enzyme activity, protect small intestine from acidity)

Acinar cells and ductal cells

part of the exocrine function of the pancrea, duct cells secrete aqueous bicarbonate solution, and acinar cells secrete digestive enzymes

Why don’t pancreatic enzymes pancreas?

zymogens - inactive enzymes

Zymogens

enzymes are first made in inactive forms, and are then activated by proteolysis after their release into the duodenum

Functions of the liver and gallbladder

liver makes bile acid and bile salts (made from cholesterol), stored and concentrated in the gallbladder and emptied into the intestine when needed

Bile acids and salts

act as detergents to break up fat “blobs” vie emulsification, needed for lipid absorption and absorption of fat-soluble vitamins

The microbiota

lots of microbes live in GI tract, which can train our immune systems, make vitamins so we can use them, digest unused energy sources to convert into usable energy, but composition can affect risk of obesity

Appendix

proposed vestigial nature, but new theory is that potentially a reservoir of good intestinal bacteria that can repopulate your intestine after diarrhea or antibiotic treatment

Absorption

the process where nutrients are taken up into the body, occurs in the stomach, small intestine, and large intestine, though different nutrients are absorbed in different organs

Why is the small intestine the major site of nutrient absorption?