D4 - Chemical Digestion Flashcards
What is chemical digestion?
The breakdown of macromolecules using enzymes into smaller, absorbable nutrients.
Who is known as the “father of gastroenterology” and why?
William Beaumont—he studied digestion through a patient with a stomach fistula.
What are accessory digestive organs?
Pancreas, liver, gallbladder—they secrete digestive substances but food does not pass through them.
What is the function of the pancreas?
Secretes pancreatic fluid (~1L/day) containing enzymes and bicarbonate into the duodenum.
What is the function of the liver in digestion?
Produces bile, which emulsifies fats.
What does the gallbladder do?
Stores and releases bile when fat-containing chyme enters the small intestine.
What are the main types of digestive enzymes?
• Amylases → Digest polysaccharides (e.g. salivary amylase)
• Carbohydrases → Break down simple sugars (e.g. maltase, lactase, sucrase)
• Lipases → Digest fats (e.g. pancreatic lipase)
• Proteases → Digest polypeptides (e.g. trypsin, chymotrypsin)
• Peptidases → Break peptides into amino acids
• Nucleases → Digest nucleic acids into nucleotides
• Nucleosidases → Further break nucleotides into bases, sugars, and phosphates.
Where does carbohydrate digestion begin?
In the mouth with salivary amylase breaking down starch.
Why does carbohydrate digestion stop in the stomach?
Salivary amylase is denatured by stomach acid.
What enzymes digest carbohydrates in the small intestine?
• Pancreatic amylase → Breaks down polysaccharides.
• Sucrase, maltase, lactase → Convert disaccharides into monosaccharides.
What enzyme begins protein digestion?
Pepsin (stomach).
What enzymes digest proteins in the small intestine?
• Proteases (Trypsin & Chymotrypsin) → Break polypeptides into shorter peptides.
• Peptidases → Convert peptides into amino acids.
What enzyme breaks down fats?
Lipase (from pancreas).
What is the role of bile in lipid digestion?
Emulsifies fats (physical digestion) to increase surface area for lipase action.
What are fats broken down into?
Glycerol & fatty acids.
What enzymes break down nucleic acids?
• Nucleases → Break nucleic acids into nucleotides.
• Nucleosidases → Break nucleotides into bases, sugars, and phosphates.
How are carbohydrates absorbed?
Glucose and monosaccharides are actively transported into the bloodstream and sent to the liver.
How are proteins absorbed?
Amino acids are actively transported into the bloodstream and sent to the liver.
How are lipids absorbed?
- Fatty acids & glycerol diffuse into intestinal cells.
- Reassembled into lipoproteins for transport.
- Moved into lymphatic system → Bloodstream.
What regulates digestive processes?
The nervous system (stimulates gastric secretions) and endocrine system (hormone release).
What does Gastrin do?
Stimulates HCl and pepsin secretion in response to food.
How does Secretin help digestion?
• Responds to acidic chyme in the duodenum.
• Stimulates bicarbonate release from pancreas to neutralize acid.
What is the function of Cholecystokinin (CCK)?
• Responds to high fat chyme.
• Increases bile secretion & stimulates digestive enzyme release.
What does Gastric Inhibitory Peptide (GIP) do?
• Slows stomach movements for fat digestion.
• Stimulates insulin release in response to glucose.
What is negative feedback in digestion?
A regulatory mechanism where high HCl levels inhibit gastrin secretion, preventing excessive acid production.
How do hormonal responses slow digestion?
• Secretin, CCK, and GIP slow stomach contractions to regulate chyme release into the intestine.
• Helps ensure better digestion and nutrient absorption.
