digestion, absorption, transport Flashcards
List all relevant enzymes, where they are produced, where they act, and their substrates and products.
a-amylase: produced by the salivary glands, act in the mouth, hydrolyses a-1,4 bonds of starches and glycogen produces dextrins.
pancreatic a-amylase: produced by the pancreas, acts in the small intestine, hydrolyses dextrins and produces maltose or glucose.
Maltase: produced by enterocytes, acts in small intestine, hydrolyzed maltose (a-1,4 bonds) forms 2 glucose molecules.
a-dextrinase: produced by enterocytes, acts in small intestine, hydrolyses a-1,6 bonds forming free glucose molecules
Describe the process of CHO digestion from the mouth to the brush border.
CHO undergo chemical transformations as they move through the GI tract. The glycosidic bonds that hold disaccharides and starches together are broken.
Process requires a serious of enzymes produced in the salivary glads, pancreas and small intestine.
Chemical digestion of starch begins in the mouth when the salivary glands release the enzyme a-amylase (breaks a-1,4 bonds) forming dextrins.
Once dextrins enter the stomach, the acidic environment stops the enzymatic activity of salivary a-amylase where dextrins then pass unchanged from the stomach into the small intestine.
Pancreatic a-amylase hydrolyzes a-1,4 glycosidic bonds transforming dextrins into disaccharide maltose.
Last maltase a brush border enzyme produced by enterocytes, finishes the job of starch digestion by hydrolyzing the last chemical bonds into two glucose molecules.
a-dextrinase, a brush border enzyme, hydrolysis a-1,6 glycosidic bonds .
**Now numerous glucose molecules are ready to be transported into the enterocytes.
Explain lactose intolerance and its treatment options.
Lactose intolerance: lactose enters the large intestine undigested. Bacteria ferment lactose producing
*gas
*abdominal cramps
*diarrhea
*bloating
Products such as lactose-free milk and over the counter lactase enzyme tablets
Describe the mechanisms by which each mono- is transported across the enterocyte. Specify all transporters and ions involved, whether each process is active, facilitated, and/or hormone mediated, and why?
Glucose and galactose are absorbed into the enterocyte by carrier-dependent, energy-requiring active transport. They move from a lower to higher concentration with assistance of transport proteins
Fructose is absorbed by facilitated diffusion. they move from a higher to lower concentration with the assistance of transport proteins
*once absorbed, mono- are circulated to the liver via hepatic portal system
Explain how insulin resistance could impact absorption.
Insulin resistance hinders glucose from being absorbed into cell membranes. This is called hyperglycemia when abnormally high levels of glucose is in the blood.
Describe what happens to mono- after they are absorbed.
After mono- are absorbed they circulate directly to the liver via the hepatic portal system, where the majority of galactose and fructose is converted into glucose.
Some mono- are converted to ribose (ATP, RNA, DNA)
Describe the glycemic response to CHO ingestion.
A rise in blood glucose levels can be detected shortly after we eat CHO-rich foods. Some foods cause blood glucose to rise quickly and remain elevated, while other elicit a more gradual increase.
Describe the terms glycemic index (GI) and glycemic load (GL), including how each is calculated, how they differ, and limitations of each.
glycemic index: a rating system used to categorize foods according to the relative glycemic responses they elicit
glycemic load: rating system used to categorize the bodies glycemic response to foods that takes into account GI as well as the amount of CHO
Explain how the glycemic index would affect glucose curves in individuals.
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List examples of low and high GL and GI foods
High GL: *French fries *baked potato *white rice Low GL: *oat bran bread *apple *cherries High GI: *baked potato *french fries *waffles Low GI: *oat bran bread *cherries *apple
Explain how one food item could be both high GI and a low GL food
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Define: absorptive state postprandial state postabsorptive state fasted state
absorptive state: when full, proceeds anabolic process postprandial state: 3-4 hours post-absorptive state: 12-18 hours fast state: 18 hours up to 2 days starvation: several weeks
Describe how blood glucose levels are maintained, how cells take up glucose, and how energy storage in the body is regulated.
Blood glucose levels are maintained by the hormones insulin (b-cells) & glucagon (a-cells) that are secreted from the pancreas. Cells take up glucose through transport proteins.
^glucose - ^ insulin - v glucose
v glucose - ^ glucagon - ^ glucose
when meals provide more glucose than required, insulin stimulates storage of glycogen. Once muscle & liver reach storage capacity excess glucose is converted to fat.
Describe the GLUT transporters, including how they function, which subtypes are expressed in which tissue; which subtypes are insulin resistant.
GLUT 2: monosaccharides facilitated transportation
GLUT 5: enables fructose to be transported to the intestinal lumen into enterocyte by facilitated transportation
GLUT 4: insulin responsive, skeletal muscle
SGLT-1: Active transport, glucose and galactose, apical membrane of kidney
Explain how insulin and glucagon work to maintain homeostasis. List where and which state each is produced.
Insulin and glucagon assist in blood glucose regulation and energy storage. When blood glucose levels increase, the pancreas takes action by releasing more insulin. Insulin in return lowers blood glucose by facilitating the uptake of glucose into many kinds of cells.
glucagon stimulates the breakdown of glycogen stores in the liver.
