Term
| Explain why digestion of large food molecules is essential. |
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Definition
- large food molecules are usually polymers, such as polysaccharides, proteins and lipids, which are too large to be absorbed from the digestive tract into the circulatory system for transport because they are simply too large to move across the membrane of small intestine epithelial cells
- after digestion: polysaccharides are broken down into monosaccharides, polypeptides are broken down into amino acids and lipids are broken down into glycerol and fatty acids
- monomers, such as monosaccharides, amino acids, glycerol and fatty acids, are small enough to be absorbed by small intestine epithelial cells, moving these substances by either diffusion, facilitated diffusion or active transport through membrane proteins |
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Term
| Explain: need for enzymes in digestion |
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Definition
- at body temperature (37 degrees C in mammals) reaction rates are too slow to be efficient at hydrolysis reactions of large food molecules
- hydrolyctic reactions in the digestion of large food molecules, such as polysaccharids, proteins and lipids into their monomers, are exothermic but occur very slowly due to considerable activation energy
- enzymes lower activation energy, catalyzing hydrolysis reactions of large food molecules into their monomers |
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Term
| State: source, substrate, optimum pH for one amylase, one protease, and one lipase. |
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Definition
Enzyme: Salivary amylase
Source: Salivary glands
Substrate: Starch
Products: Maltose
Optimum pH: 7-8
Enzyme: Pepsin
Source: stomach cells
Substrate: proteins
Products: Polypeptides
Optimum pH: 2-3
Enzyme: phospholipase A2
Source: pancreas cells
Substrate: phospholipids
Products: glycerol, fatty acids, phosphate
Optimum pH: 8 |
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Term
Outline the function of the stomach, small intestine and large intestine.
A. Stomach |
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Definition
- a large, expandable, muscular and glandular organ
- stores and mixes food, aiding in both physical and chemical digestion
- gastric pits secrete:
a) HCl, producing a stomach pH of about 2, facilitating pepsin activity and killing foreign pathogens such as bacteria
b) pepsinogen: inactive precursor which is converted into pepsin under acidic conditions
c) pepsin catalyzes the hydrolysis of large proteins and oligopeptides and polypeptides into smaller polypeptides
d) mucus: which protects stomach cells from acidic conditions
e) chyme: product of stomach digestion, an acid fluid released from stomach into small intestine via pyloric sphincter |
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Term
Outline the function of the stomach, small intestine and large intestine.
B. Small Intestine |
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Definition
- digestion:
a) pancreas releases bicarbonate ions = NaHCO3-
b) which neutralizes acidic chyme, producing a pH = 8, optimizng activities of intestinal enzymes
c) enzymes from pancreas, and small intestine epithelial cells hydrolyze large molecules into smaller molecules
d) polypeptides and oligopeptides digested into amino acids
e) polysaccharides and disaccharides digested into monosaccharides
f) triglycerides digested into fatty acids and glycerol
g) bile produced in liver, stored in gall bladder, released through bile duct
h) emulsifying fat droplets into smaller particules on which pancreatic lipase can act more efficiently
- motility by peristalsis: rhythmic contractions of circular and longitudinal smooth muscles lining small intestine slowly force chyme down the intestinal tract
- absorption: lining of small intestine is folded, increasing surface area for absorption, and each fold is folded again into villi, with each villus acting as an absorptive unit |
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Term
Outline the function of the stomach, small intestine and large intestine.
C. Large Intestine |
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Definition
- absorption of vitamin K produced by mutualistic bacteria
- reabsorption of water, Na+, K+ from intestinal lumen to capillaries
- motility by peristalsis: rhythmic contractions of circular ad longitudinal smooth muscles lining large intestine slowly force fecal matter down intestinal tract |
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Term
| Distinguish between absorption and assimilation. |
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Definition
- absorption: movement of chemical substances from the lumen of the digestive tract across the membranes of cells lining the digestive tract by diffusion, facilitated diffusion or active transport, and then either into the circulatory or lymphatic systems for distribution to all somatic cells
- assimilation: following digestion and absorption, nutrients are taken into somatic cells and converted to the biomass of the organism |
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Term
Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion.
A. Surface Area |
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Definition
- folding: intestinal folding increases surface area by 3X
- villi: within each fold, a second set of folds creates a series of villi, with each villus being a finger-like projection, increasing intestinal surface area by an additional 10X
- microvilli: along the lumen side of each small intestine epithelial cell a brush border of microvilli additionally expands surface area by another 20X
-thus, the total surface area increase = 3 x 10 x 20 = 600X |
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Term
Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion.
B. Membranes of epithelial cells |
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Definition
- diffusion of fatty acids, monoglycerides, fat-soluble vitamins, some mineral ions thruogh membrane phospholipid bilayer
- facilitated diffusion of some monosaccharides, some vitamins adn mineral ions using membrane proteins
- active transport of amino acids, most monosaccharides, some mineral ions, using membrane proteins and ATP produced by mitochondria in epithelial cells |
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Term
Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion.
C. Blood capillaries |
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Definition
- oxygenated blood enters villus supplying oxygen for cellular respiration:
- cell growth replacign lost/injured cells
- ATP for active transport
- deoxygenated blood leaves villus rich in absorbed nutrients: amino acids, monosaccharides, mineral ions, vitamins |
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Term
Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion.
D. Lacteals |
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Definition
- fatty acids and glycerol are reformed into triglycerides in epithelial cell smooth ER/Golgi apparatus
- triglycerides, with phospholipids and cholesterol, aggregate into chylomicrons, which are coated with proteins and then leave epithelial cells and enter lacteals |
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