Chapter 14 Flashcards
(31 cards)
Digestion: Creating Cellular Biomolecules
- components of a meal: proteins, lipids, and polysaccharide; must be degraded into small molecules for absorption and transport
- used for growth and repair
- used to make energy
- facilitated by a diverse set of hydrolytic enzymes accomplish this degradation
Digestion: Stage 1 of Energy Production
- Break complex food compounds down to basic subunits
- Fatty acids and glycerol
- Monosaccharides (glucose)
- Amino acids - Eventually these will be converted into acetyl CoA
- Acetyl (COCH3): 2 carbons
- CoA (Coenzyme A): serves as a carrier
- Acetyl CoA can enter citric acid cycle to make energy
Digestive Tract: Main Components
- Mouth
- Esophagus
- Stomach
- Small intestine
- Large intestine
- Anus
Digestive Tract: Accessory Organs
- Salivary Glands
- Pancreas
- Liver/gall bladder
Digestion: Mouth
- Digestion begins in the mouth where food
is mechanically degraded. - Chewing converts the meal into a slurry
that is more readily attacked by hydrolytic
enzymes
Digestion: Stomach
- Temporary storage tank for food; Site of food breakdown
- Chemical breakdown of protein begins
- Delivers chyme (processed food) to the small intestine
- acidic environment generated by a H+/K+ ATPase
Digestion: Stomach (role in protein breakdown
- Pepsinogen → pepsin
- endopeptidase (hydrolyses internal peptide bonds) - Minor role for other nutrients
- Gastric amylase
- Gastric lipase to initiate emulsification
Pepsin
active enzyme
- zymogen: pepsinogen
- site of synthesis: stomach
Chymotrypsin
active site
- zymogen: chymotrypsinogen
- site of synthesis: pancreas
Trypsin
active enzyme
- zymogen: trypsinogen
- site of synthesis: pancreas
Carboxypeptidase
active enzyme
- zymogen: procarboxypeptidase
- site of synthesis: pancreas
elastase
active enzyme
- zymogen: proelastase
- site of synthesis: pancreas
Digestion: Pancreas
- Secretes bicarbonate to neutralize stomach acid
Digestion: Pancreas (Exocrine Role)
- Extensive biochemical breakdown
- Secretes pancreatic enzymes/proenzyme
Digestion: Pancreas (Endocrine Role)
- Coordinate whole body tissue response to feeding
- Secretes hormones:
- Insulin with feeding
- Glucagon when not fed
Digestion: Zymogens or Proenzymes
- Allows synthesis of nonactive enzyme
- Do not destroy cell proteins
- Get activated in site of digestion - Allows control of the location of digestion
- Example of “compartmentalization”
Digestion: Zymogens are activated in
a cascade-like manner
- enteropeptidase is produced in the intestine to activate pancreatic enzymes
Digestion: Small Intestine
- Digestion:
- site of action for pancreatic enzymes
- brush border enzymes - Absorption
- massive surface via villi and microvilli - Intestinal tract with epithelial cells:
- also called enterocytes, intestinal epithelium
Digestive Hormones
Food in the stomach stimulates intestine to
release 2 key digestive hormones:
- Secretin
- Cholecystokinin (CCK)
Secretin
digestive hormone
- stimulates pancreas to release sodium bicarbonate in intestine
Cholecystokinin (CCK)
digestive enzyme
- stimulates pancreas to release digestive enzymes
- stimulates the gall bladder to secrete bile salts
Protein Digestion
- Proteins are digested into small fragments called oligopeptides.
- Peptidases on the surface of intestinal cells cleave the oligopeptides into amino acids and di- and
tripeptides, which are conveyed into the intestinal cell by transporters. - The amino acids are subsequently released into the blood by antiporters
Clinical Insight: Celiac Disease
- an intestinal inflammatory disorder
- inflammatory response to gluten-derived peptides found in wheat, rye, barley
- may be linked to pattern to peptides produced during digestion
- inflammatory response damages intestinal lining and impairs nutrient absorption
Carbohydrate Digestion
- Starch is a main dietary form of carbohydrates (homopolymer of glucose)
- Breakdown to monosaccharides inside the gut lumen and at enterocyte surface
- α-amylase then α-glucosidase and α-dextrinase
- Sucrose and lactose digested by sucrase and lactase - Galactose, glucose and fructose absorbed
into enterocyte via transporters
