Biochemistry Of Digestion - Dr. Estuart Flashcards
Food is broken down into smaller compounds for absorption by the intestines
Digestion
Uptake of products of digestion by enterocytes and their delivery to blood or lymph
Absorption
Regulated by the nervous system, hormones, and paracrine factors
Digestion and absorption
Food is physically broken down into smaller fragments
Mechanical digestion
- Chewing (mouth), churning (stomach), segmentation (small intestine)
Enzyme-mediated, hydrolysis process that breaks down large macronutrients into smaller molecules.
Chemical digestion
- Hydrolysis, digestive enzymes
Macronutrient for AMYLASE
Carbohydrates
Macronutrient for PROTEASE
Proteins
Macronutrient for LIPASE
Fat
All digestive enzymes are ___________.
Hydrolyases
Any chemical reaction in which a molecule of water ruptures one or more chemical bonds.
Hydrolysis
Low weight for height
Wasting
Low height for age
Stunting
Low weight for age
Underweight
A glucose-polymer cleavage enzyme
Salivary amylase
Comprises a small portion of the total amylase excreted
Salivary amylase
Breaks down starch
Salivary amylase
Begins carbohydrate digestion
Salivary amylase
Alpha 1-4
Amylose
Alpha 1-6
Amylopectin
Amylose a(1-4) undergo HYDROLYSIS:
Dextrins
Maltose
Maltotriose
Glucose
Begins fat digestion
Lingual lipase
Digests triglycerides into diglycerides and free fatty acids
Lingual lipase
Catalytic triad of lingual phase:
aspartate
histidine
serine
Triacylglycerol undergo hydrolysis:
Diacylglycerols Fatty acids
Role in digestion is conduit
Esophagus
(+) mechanical digestion “churning”
Stomach
_______ stops action of salivary amylase
Low pH
Is there a chemical digestion in the stomach?
No.
*NO chemical digestion in the stomach
Mechanical breakdown is ongoing in ___________
Stomach
Strong peristaltic contractions of the stomach mix the carbohydrates into the more uniform mixture of chyme (__________)
Homogenization
Proteins have to be _________ to make them more accessible to proteases
denatured
Inactive precursor to an enzyme
Zymogens / Proenzymes
Prevent auto-digestion
Zymogens or proenzymes
Protein Digestion begins in the _________.
Stomach
From parietal cells
HCl
From chief cells
Pepsin
Hydrophobic
Lipids
Limited surface area for enzyme action
Lipids
Large lipid globules are broken down into several small lipid globules
Emulsification
Digests short and medium-chain fatty acids
Lingual phase or gastric lipase
Stomach can absorb some substances:
Aspirin
Alcohol
breaking down of food into smaller compounds for absorption
Digestion
uptake of products of digestion by enterocytes and their delivery to blood or lymph
Absorption
Macronutrients are broken down into their oligomers, dimers, or monomers through ____________.
Hydrolysis
____________ digestion begins in the mouth due to salivary amylase.
Carbohydrate
_________ digestion begins in the stomach, with denaturation by HCl then hydrolysis by pepsin, into peptides and free amino acids
Protein
_________ digestion begins in the mouth due to lingual lipase, and is further digested by gastric lipase into diglycerides and free fatty acids
Lipid
Liver produces __________.
Bile
Bile stored and concentrated in the _________.
Gallbladder
Enzyme production
Bile and CCK
Bicarbonate-rich fluid
Secretin
Uses ATP, Proteins as pumps, Lower to higher concentration
Active transport
Higher to lower concentration
Passive diffusion
Higher to lower concentration using a carrier protein in cell membrane
Facilitated diffusion
Uses movement of one molecule from Higher to lower to power movement of another from lower to higher
Co-transport/Secondary active transport
Cell membrane engulfs material, uses ATP
Endocytosis
Lactase activity falls __________.
after weaning
Lactose remains in the intestinal lumen and becomes a substrate for bacterial fermentation.
Lactose intolerance or lactase deficiency
Abdominal discomfort, diarrhea, congenital or acquired
Lactose intolerance or lactase deficiency
Two mechanisms for absorption of monosaccharides in the small intestine:
SGLT1
GLUT 5
Exit from the cell for all sugars
GLUT2
Glucose and Galactose
SGLT1 transport protein
Secondary active transport (Na dependent)
SGLT1 transport protein
Duodenum and Jejunum
SGLT1 transport protein
Fructose, Glucose, Galactose via facilitated diffusion
GLUT5
Sodium independent
GLUT5
Down their concentration gradient
GLUT5
Facilitated diffusion
GLUT2
All sugars
GLUT2
Bloodstream —> Portal vein —> Systemic circulation
GLUT2
Increase in blood glucose after a test dose of a carbohydrate compared with that after an equivalent amount of glucose
Glycemic index
Food with _____ glycemic index is beneficial in DM
Low
- Prevents rapid rise in blood glucose
- Prevents rapid fluctuations in insulin secretion
Hydrolyze peptide bonds between specific amino acids
Endopeptides
- Pepsin, Trypsin, Chymotrypsin, Elastase
Hydrolyze peptide bonds from the ends of peptides
Exopeptidases
Carboxypeptidases
Pancreas
Aminopeptidases
Small intestine
Tripeptidases
Small intestine
Dipeptidase
Small intestine
Pepsin product
Peptide fragments
Trypsin / chymotrypsin
Dipeptides
Exopeptidases
Amino acids
Diacylglycerols product:
2 Monoacylglycerols
Fatty acids
Derivative of cholesterol
Bile
Amphipathic
Bile
Contain both hydrophobic (lipid soluble) and polar (water soluble) faces
Bile
Emulsification of lipids —> increased surface area for lipases
Bile
Solubilization and transport of lipids in an aqueous environment
Bile
Lipid absorption occur in two phases:
- Monoglycerides and free fatty acids emulsified by bile, forming micelles, absorbed by the cell, forming __________
Chylomicrons
Lipid absorption occur in two phases:
______________ directly enter the cell.
Short and Medium-chain fatty acids
Cholelithiasis
Gallbladder stones
Most common gallbladder stones:
cholesterol gallstones
Bile supersaturation in cholesterol
Gallbladder stones
Can cause obstruction of biliary tract, complications
Gallbladder stones
- Treatment: Surgery
Released from food during digestion and the Availability depends on the type of food
Vitamins and minerals
Fat-soluble vitamins (ADEK) are absorbed in lipid micelles with fat digestion via ____________.
simple diffusion
Water-soluble vitamins and most mineral salts are absorbed from the SI by __________ or _________ followed by binding to intracellular proteins
active transport or facilitated diffusion
Vitamin B12
Intrinsic factor
Dependent on Vitamin D
Calcium
Zinc-binding ligand secreted by exocrine pancreas
Zinc
Limited absorption
Iron
Required for intestinal absorption of calcium
Vitamin D
Intracellular calcium-binding protein
Calbindin
Induced by Vitamin D
Calbindin
Recruits calcium transports to the cell surface
Calbindin
Increases calcium absorption rapidly
Calbindin
Site of absorption in vitamin B12
Ileum
Requirement for vitamin B12 absorption
Intrinsic factor
Protein secreted by parietal cells in the stomach
Intrinsic factor
Lack of vitamin B12 absorption
Pernicious anemia
A gylcoprotein of M.W 4500
Intrinsic factor
Vit. B12 combine with intrinsic factor forming a complex that resist digestion by GIT enzymes. This complex is absorbed at terminal ileum by ____________
Pinocytosis
Vitamin B12 is transported to the ________ where it is stored.
Liver
Released Vit B12 from Protein by _______ and _______.
HCl and Pepsin
Vitamin B12 binds to ___________
Cobalophilin
Cobalophilin hydrolyzed in __________, releasing Vit B12
Duodenum
Vit B12 is bound to Intrinsic Factor and absorbed in __________.
terminal ileum
Products of nucleic acid digestion:
pentose sugars
nitrogenous bases
phosphate ions
Nucleic acids are transported by carriers across the villi via ____________.
active transport
Alcohol is _____ absorbed in the small intestine and _____ in the stomach.
80%
20%
Slower absorption when stomach is full.
Alcohol
Approximately 5 feet long
Large intestine
Processing chyme after most nutrients are absorbed in the small intestine
Large intestine
3 Primary functions of large intestine:
Absorbing water and electrolytes Producing and absorbing vitamins,
Forming and propelling feces toward the rectum for elimination
Water diffuses in response to an _____________ established by the absorption of electrolytes.
osmotic gradient
Fat soluble vitamin
Vitamin K
Important role in the production of clotting factors to prevent bleeding
Vitamin K
Babies born with low levels of Vitamin K
Hemorrhagic Disease of the Newborn
Absence of the bacterial intestinal flora normally responsible for the synthesis of vitamin K
Hemorrhagic Disease of the Newborn
