Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
62 Cards in this Set
- Front
- Back
|
What is the basic chemical process of digestion?
|
Hydrolysis
|
|
|
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?
|
Cellulose
|
|
|
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:
|
-Lactase
-Sucrase -Maltase -a-dextrinase |
|
|
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:
|
Pepsin
|
|
|
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?
|
Collagen
|
|
|
2 Main functions of pepsin:
|
-digest collagen
-initiate digestion of other proteins |
|
|
How much of protein digestion is accomplished by pepsin?
|
10-20%
|
|
|
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?
|
Carboxypolypeptidase
|
|
|
Product of majority of pancreatic protein digestion:
|
Polypeptides
|
|
|
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:
|
-Aminopolypeptidase
-Dipeptidases |
|
|
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)
-phosphoipids -cholesterol esters -cholesterol |
|
|
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
-Alcohol |
|
|
What enables the small intestine to be such a great absorber?
|
Folds of Kerckring
|
|
|
Where are valvulae conniventes (kerckring folds) esp developed?
|
-Duodenum
-Jejunum |
|
|
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 -villi -microvilli |
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 |
