Digestive system-7 Flashcards
What is enzymatic hydrolysis and what is it’s purpose?
▪ Digestion: catabolic process that breaks macromolecules → monomers (chemical building blocks) small enough for absorption(ex. polysaccharide broken to disaccharide broken to monosaccharide)
▪ Intrinsic & accessory gland enzymes are involved
▪ Enzymes carry out hydrolysis -water is added to break chemical bonds
What is absorption in the gut and how does it occur? Which molecule can be asborbed passively?
▪ Absorption: moving substances from lumen of gut into body
▪ Tight junctions: molecules pass through rather than between cells
• Materials enter cell through apical membrane (lumen side) and exit through basolateral
membrane (blood side)
▪ Lipid molecules can be absorbed passively through membrane, but other polar molecules are absorbed by active transport
What are the 3 types of saccharide? What is the most common polysaccharide in the body? What is the only type that can be absorbed? How are the other 2 types absorbed?
Three classes
▪ Mono-, di- and polysaccharides
▪ the principal polysaccharide in human body is glycogen
▪ Only monosaccharides can be absorbed
Poly and di saccharides are broken down by salivary enzymes in the mouth, then pancreatic enzymes and lastly brush border enzymes, both in the small intestine
What do pancreatic amylase and brush border enzymes break down the food stuff into?
Pancreatic amylase
o breaks down starch/ glycogen that escaped salivary amylase into oligosaccharides &
disaccharides
Brush border enzymes
o (dextrinase, lactase, glucoamylase, maltase & sucrase)
o further break these into lactose, maltose & sucrose; and then into monosaccharides
(glucose, fructose, galactose)
How do monosaccharides enter the bloodstream?
▪ Monosaccharides are cotransported across apical membrane of absorptive epithelial cell, mostly by secondary active transport with Na+
▪ Monosaccharides exit across the basolateral membrane by facilitated diffusion and enter the capillary via intercellular clefts
What is the cause of lactose intolerance? what are the consequences? what is the common treatment?
• People with lactose intolerance have deficient amounts of lactase and cannot consume lactose
• Any lactose eaten remains undigested and creates an osmotic gradient in intestine that prevents water from being absorbed, resulting in diarrhea
– Can also can pull water from interstitial space into intestinal lumen
• Bacterial metabolism of undigested solutes produces large amounts of gas, resulting in
bloating, flatulence, and cramping pain
• Treatment: add lactase enzyme “drops” to milk or take a lactase tablet before
consuming milk products
What do proteins look like? What are the 3 sources of protein? What are the 3 steps of protein breakdown? Where does digestion begin?
3D coiled up chain of amino acids (aa) arranged in a precise sequence
▪ Source of protein: diet, digestive enzymes & from breakdown of mucosal cells
▪ Proteins are broken into:
▪ Large polypeptides
▪ Small polypeptides and small peptides
▪ Finally into amino acid monomers, with some dipeptides and tripeptides
▪ Digestion begins in stomach when pepsinogen is converted to pepsinat pH 1.5–2.5
– Becomes inactive in high pH of duodenum
What do pancreatic proteases and brush border enzymes break down the food stuff into?
Pancreatic proteases
▪ trypsin & chymotrypsin cleave protein into smaller peptides
▪ carboxypeptidase takes off one aa at a time from end
Brush border enzymes
▪ aminopeptidases, carboxypeptidases & dipeptidases break oligopeptides
and dipeptides into amino acids
How do proteins and carbohydrates enter the blood stream differently?
Trick question, they have the same pathway
What is the most abundant kind of fat in the diet? What is the process of emulsification? What are the 3 steps of fat digestion?
▪Triglycerides: most abundant fats in diet
▪ Need pre-treatment with bile salts that break large fat globules into smaller
ones → emulsification
▪ lipid droplets are coated with bile salts & lecithin, forming emulsion droplets
(larger surface area → digestive action of lipases) that are water soluble -
micelles
▪ Digestion: pancreatic lipases break down fat into monoglyceride plus two free FAs (all are ________ in H2O)
▪ Micelle formation: products from digestion become coated with bile salts and lecithin
▪ Diffusion: lipid products leave micelles and cross epithelial membrane via diffusion
What are the 2 domains of bile salts? Are micelles soluble in water?
▪ Bile salts have both hydrophilic & hydrophobic domains
o The hydrophobic part → to the lipids
o The hydrophilic part → the surface
▪ The molecules in micelles are clustered together exposing polar ends toward H2O
making micelles soluble in water
o in this form FA & monoglycerides reach the intestinal epithelial cells
What is the difference between chylomicron formation and chylomicron transport?
▪ Chylomicron formation: lipid products are converted back into TGs and
packaged with lecithin and lipoproteins, forming chylomicron
▪ Chylomicron transport: chylomicrons are exocytosed from basolateral
side and enter lymphatic lacteal
▪ Eventually emptied into venous blood at thoracic duct
▪ Once in blood, chylomicrons are broken into free fatty acids and glycerol
by lipoprotein lipase so they can be used by cells
▪ Short-chain fatty acids can diffuse directly into blood
What is the structure of nucleic acids? How are they broken down?
▪ coiled up chains of nucleotides linked together in a precise arrangement
▪ Nuclei of ingested cells in food contain DNA and RNA
▪ Pancreatic nucleases hydrolyze nucleic acid to nucleotide monomers
▪ Brush border enzymes, nucleosidases, and phosphatases break nucleotides down into free nitrogenous bases, pentose sugars & phosphate ions
▪ Breakdown products are actively transported by special carriers in epithelium
of villi
How are vitamins absorbed in the small and large intestine?
▪ In small intestine:
- Fat-soluble vitamins (A, D, E, and K) are carried by micelles; diffuse into absorptive cells
- Water-soluble vitamins (C and B) are absorbed by diffusion or by passive or active transporters
- Vitamin B12 (large, charged molecule) binds with IF (produced where?) and is
absorbed by endocytosis
▪ In large intestine:
- vitamin K and B vitamins from bacterial metabolism are absorbed
How are electrolytes absorbed?
▪ Most ions are transported actively along length of GI
• Amount in intestine is amount absorbed regardless of nutritional state except for Fe and Ca
▪ Na+ absorption is coupled with active absorption of glucose and amino acids
▪ Cl−is transported actively
▪ K+ diffuses (facilitated) in response to osmotic gradients; lost if water absorption is poor
▪ HCO3- actively secreted into the lumen
▪ Fe and Ca2+ : absorption in duodenum is related to need
• Ionic Fe actively transported into mucosal cells and stored bound to ferritin (local storehouse)
• Normal state: 10-20% pass into portal blood; most lost with epithelial cells
• Fe depleted: ↑ uptake and release; transported in blood by transferrin
▪ Ca+ absorption: regulated by vitamin D & parathyroid hormone (PTH)
• Vitamin D promotes absorption
• PTH releases Ca from the bone matrix
