Digestion and Absorption (6.1)
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Notes and Review:Digestion Notes (SL and HL) |
Digestive System Overview
The digestive system is where all your food is intaken and absorbed to give you energy. It occurs in three steps:
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Digestive System Parts and Functions
You need to be able to draw and label the parts of the digestive system. Also be able to identify the function of each of the parts.
A few pointers in terms of drawing:
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Peristalsis
Peristalsis is the contraction of circular and longitudinal muscle layers of the small intestine. It mixes the food with enzymes and moves it along the gut in waves of muscle contraction. Smooth muscle exert continuous moderate force, allowing the food to move through the body continuoulsy.
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Digestion and Enzymes
Chewing begins the process of digestion, but most of the digestion process occurs through enzymes. [For a review of enzymes see Enzymes (2.5) and Metabolism (8.1).] Enzymes function to build up or tear down macromolecules (anabolic or catbolic reactions) [See Metabolism (2.1) for more information)]. The main types of enzymes within the digestive system are amylase, protease, and lipase. While there are specific enzymes like pepsin, dextrin, endopeptidase, etc each of these fall within the specific type of enzyme and its digestion of a macromolecule.
Note the optimum pH of proteases tend to fall around 2. Which considering that digestion of protein begins in the stomach where it is very acidic, this is ideal for its use and degredation. Most of the rest of the enzymes call within the 7-8 pH range where blood tends to be. Optimum temperature of almost all of these enzymes is generally around 36-40C, body temperature.
Digestion of Starches
Starch digestion begins in the mouth with Sylvatic Amylase and ends in the Small Intestine with Pancreatic Amylase.
3 enzymes in the membranes of microvilli of small intestine have significance in completeing the digestion of starch
- Any 1,4 bond can be broken by amylase in either the mouth or the small intestine.
3 enzymes in the membranes of microvilli of small intestine have significance in completeing the digestion of starch
- Maltase: Maltose ---> glucose
- Glucosidase: Maltotriose --> glucose
- Dextrinase: Dextrin ---> glucose
Digestion of Lipids
Because lipids are non-polar vs carbs and protein are polar and enzymes are also polar, the lipids must be treated differently so that they are accessable to the water soluable enzymes.
Meet the Liver!
NOTE: video below goes through both digestion AND absorption of Lipids. |
The Pancreas
The pancreas produces many of the enzymes used in the digestive system. It also produces a number of hormones necessary for uptake of nutrients, as there are two different types of cells in the pancreas. One type of cell deals with digestion:
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The Villi
The villi are the functional unit of the small intestine.
How do you absorb all those nutrients in such a short area?
Villi and the small intestine |
Absorbtion of Nutrients
Villi absorb the monomers, created by enzymes, and minerals from food that don’t need digestion
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Specifics of Glucose absorption through the villi into blood
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Absorbtion of Lipids
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Triglycerides and cholesterol have to be transported differently than carbohydrates and amino acids. Why? Because they are non-polar and therefore not dissolvable in water!
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