Digestion 1 - BIO210

Gastrointestinal Tract

extracts and absorbs nutrients needed; lots of hydrolysis reaction happen to depolymerize macromolecules

protease

enzymes that break down proteins

Stomach lumen

Mouth and Salivary glands mechanical or absorption?

mechanical breakdown of food

Lysozyme

cuts peptidoglycan in many bacterial cell walls

How does the chewing with teeth and tongue help break down food?

increases SA:V ration (volume remains the same)

Salivary/pancreatic Amylase

cuts glucose a1 → 4 glucose bonds so that starch is depolymerized to glucose

Salivary/pancreatic Lipase

cuts triglycerides to glycerol and 3 fatty acid tails (cuts lipids)

How does food go from mouth to stomach?

when swallowing, food is pushed out the mouth into stomach by the peristalsis

Peristalsis

wave like contractions of muscle rings (pushes food into stomach)

Epiglottis

flap that keeps food out of the trachea

Esophagus

muscular tube that transfers food from mouth to stomach

What is the stomach surface made up of?

Deep pits that increase SA:V ratio that are lined with various types of epithelial cells

What types of epithelial cells are on the stomach surface?

mucous cells, parietal cells, chief cells

Mucous cells

thick material that secrets mucous to protect stomach cells

Parietal cells

Secrete HCl to acidify the stomach to a pH of 2

Chief cells

secretes inactive enzyme, pepsinogen (a precursor of pepsin)

• pepsinogen does nothing b/c it’s inactive due to its attatched amino terminus

Pepsinogen

inactive enzyme produced by chief cells; activated when amino terminus falls off and produces pepsin

Pepsin

active enzyme that cuts other proteins (protease) and shows low specificity, cutting almost any peptide bond

Entry to the stomach is controlled by?

Gastroesophageal sphincter: rings of muscle that only opens briefly when food comes down esophagus

Why is it important that the stomach is highly acidic?

protects the body by denaturing proteins, killing microbes, and dissociate large complexes

Carbonic anhydrase

enzyme for parietal cells that catalyzees the chemical reaction of combining CO2 and H2O for the production of carbonic acid

What does carbonic acid (H2CO3) quickly break down into?

bicarbonate (H3CO-)

H+/K+ ATPase

transporter in parietal cells that moves H+ ions across the membrane to the stomach lumen

How is Cl- imported from the blood into the cell?

by the HCO3/Cl- antiporter

Cl- Facilitated transporter

transporter on apical side of parietal cell that moves Cl- ions to stomach lumen

Duodenum

first part of the small intestine joined by ducts to the pancreas, liver, and gallbladder

Pancreas

small organ underneath the stomach that contains two secretory tissues (exocrine and endocrine)

Exocrine (part of exocrine pancreas)

aids in digestion with two cell types: duct cells and acinar cells

Endocrine (part of pancreas)

no duct, aids in digestion

Duct cells

part of exocrine pancreas; lines the duct, neutralizes stomach acid by secreting H3O-

Acinar cells (bicarbonate acinar)

part of exocrine pancreas; makes various enzymes to assist digestion (trypsin and chymotrypsin, pancreatic amylase, and pancreatic lipase)

Trypsin and Chymotrypsin Protease

proteases activated in the small intestine, secreted in active form, low specificity

Hepatocyte

liver cells that produce bile

Bile

produced by hepatocytes, contain bile salts, are amphipathic

When is bile produced and released?

continuously produced and stored in gallbladder; released upon eating

Bile salts

acts as detergent to breaks down fat globules (lipids) by emulsification ( to increase SA:V ratio)

Which enzyme facilitates the connection of a water molecule with carbon dioxide?

carbonic anahydrase