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62 Cards in this Set

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  • Back
What is the basic chemical process of digestion?
What are the main carbs in the diet?
Disaccharides and polysaccharides
What are the main fats in the diet? How are they formed?
Neutral triglycerides - composed of 3 fatty acids attached to a glycerol backbone by removal of 3 waters.
During digestion what process is similar in all 3 food types? What is different?
Same: hydrolysis
Difference: the enzymes
3 major sources of carbs in the diet:
1. Sucrose from cane sugar
2. Lactose from milk
3. Starches from non-animal foods
What carb cannot be hydrolysed in humans?
What is the first step in digestion of carbs? Where?
Ptyalin containing amylase in saliva mixes with food.
-In mouth/stomach
How much of starch is hydrolyzed in the mouth?
5% - not enough time for anymore.
What happens to salivary amylase as it enters the stomach?
-Acts on more starch - ~35%
-But then low pH inactivates it
Net effect of salivary amylase on carb digestion:
35% of starches digested into maltose (disacchs).
Enzyme for starch digestion in the small intestine:
Pancreatic amylase
How does pancreatic amylase compare to salivary?
Much more powerful
Length of time required for pancreatic amylase to break down starches in sm intestine:
20 min
What cells hydrolyze maltose disacchs into monosachs?
Intestinal epithelial enterocytes lining microvilli of the sm intestine (brush border).
Enzymes in enterocytes for carb digestion:
Product of Lactase:
Galactose and glucose
Product of Sucrase:
Fructose and glucose
Product of maltase:
2 glucose
What happens to the monosaccharide products of carb digestion?
Absorbed immediately into blood
What starts protein digestion?
Chewing in the mouth
Where does enzymatic protein digestion start?
In the stomach
Gastric enzyme for protein digestion:
Activity of pepsin:
Depends on pH range of 2-3
How Pepsin activity is achieved:
Copious secretions of HCl from stomach parietal cells - stimulated by Gastrin/Histamine.
What does pepsin especially digest?
2 Main functions of pepsin:
-digest collagen
-initiate digestion of other proteins
How much of protein digestion is accomplished by pepsin?
Where is the rest of protein digestion done? What enzymes?
In the intestine via Pancreatic enzymes.
4 Major proteolytic enzymes in pancreatic secretions:
1. Trypsin
2. Chymotrypsin
3. Carboxypolypeptidase
4. Proelastase
Which pancreatic proteolytic enzyme digests proteins all the way to amino acids?
Product of majority of pancreatic protein digestion:
Where is the last stage of protein digestion?
The absorption stage at microvilli brush border in the small intestine.
Enzymes for protein digestion on microvilli membrane:
Product of brush border peptidases:
small polypeptides (di/tri) that can esasily transport across the membrane into enterocytes.
What happens to small peptides after uptake by enterocytes?
Intracellular peptidases cleave all polypeptides into single AAs
Final step in amino acid absorption:
easy entrance into bloodstream
Why is protein absorption in its native state rare?
B/c proteins are antigenic.
Dietary fats (4):
-Triglycerides (neutral)
-cholesterol esters
What is the first step in fat digestion?
Lingual lipase breaks down a few triglycerides - less than 10%
1st stage in fat digestion in the small intestine / function?
Emulsification by bile salts and lecithin - to increase surface area for enzyme action on it.
Most important enzyme for lipid digestion:
Pancreatic lipase - acts on triglycerides
What other lipase is found in the small intestine?
Enteric lipase but its significance is questionable.
Product of pancreatic lipase:
2 FA + 2-monoglycerol
Other than emulsifying fats, what is the function of bile salts?
To form micelles and REMOVE fat digestion products from the small intestine - otherwise triglycerides will just reform.
How do bile salt micelles remove fatty acids?
By ferrying them to the brush border where transporters of MG and FFA absorb them into blood.
What digests cholesterol esters?
Cholesterol esterase
What digests phospholipids?
Phospholipase A2
How much fluid do the intestines have to absorb daily?
8-9 liters
-about 1.5 from ingestions
-about 7 from duct secretions
Which intestines absorb more?
Small intestines - about 7
Lg intestines only about 1.5
Why is the stomach a poor absorber?
-No villi
-Tight junctions
What things do get absorbed by the stomach?
-Highly lipid soluble drugs
What enables the small intestine to be such a great absorber?
Folds of Kerckring
Where are valvulae conniventes (kerckring folds) esp developed?
What covers the valvulae conniventes?
Villi - especially in upper SI
What covers the villi on valvulae conniventes?
Microvilli - up to 1000 on each villus
How much does each membrane specialization increase the SA of the small intestine?
Folds - 3X
Villi - 10X
Microvilli - 20X
What is the combined effect of brush border specializations?
The SA is 1000x greater - the size of a tennis court.
What is at the center of a villus?
Central lacteal for lymph absorption
How do villi take up nutrients?
Via pinocytosis
How do villi move?
By continual movements of actin filaments
3 Mechanisms of Villus absorption:
1. Active transport
2. Diffusion
3. Solvent drag
3 important features of villi for their functions:
1. Pinocytic vesicles
2. Endoplasmic reticulum
3. Mitochondria