Carbs, Their digestion and metabolism Flashcards
types of polysaccharides
starch, glycogen, cellulose (fiber)
the goal of breaking down glycosidic bonds
using dietary foods to produce energy for body processes through digestion; various enzymes break down starch and disaccharides to monosaccharides for absorption
carbohydrate digestion
salivary amylase at the mouth, enzymatic digestion by hydrolysis rxns
starch digestion
salivary alpha amylase at the mouth and at the small intestines
pancreatic alpha amylase
digests starch into disaccharides, containing bicarbonate ions to raise the pH of stomach contents as they move into the duodenum
starch digestion in the small intestine
enzymes in the brush border hydrolyze disaccharides into monosaccharides, each. with activity toward a diff. glycosidic bond/oligosaccharide structure
what type of proteins are carbohydrate-digesting enzymes?
integral membrane proteins which are highly glycosylated to prevent digestion from intestinal proteases
what can the body not digest?
dietary fibre (cellulose), which is insoluble (not to be confused w/ soluble fibres such as pectin and gums)
lactose intolerance
impaired ability to digest lactose due to reduced amounts of the enzyme lactase as you age; secondary lactase deficiency occurs w/ injurt to intestinal absorptive cells (e.g. celiac disease)
what occurs with inability to break down lactose?
metabolism of lactose by colonic bacteria (lac operon) into gases and lactic acid
glucose absorption
secondary active transport with sodium ions (sodium-glucose cotransporter, also facilitative diffusion)
glucose transport
secondary active transport; glucose is polar and cannot freely diffuse through the lipid bilayer
GLUTs (glucose transporters)
mechanism used in some glucose transport into the intestine
GLUT4
isoform of GLUT that is insulin-sensitive and important for uptake into muscle and adipose tissue
GLUT3
isoform of GLUT that is NOT insulin-sensitive and important for uptake into brain; can account for potential for low blood glucose in brain (transported at rate not much faster than it is used)
- less glucose transport = less metabolism = situations associated w/ hypoglycemia
how is glycogen synthesized?
in response to blood glucose level signals
what does insulin signal?
glucose uptake by muscle and adipose and promotion of glycogen synthesis
what does glucagon signal?
glycogenolysis in the liver to control regulate blood sugar levels
glycogen utilization
- fuel source in the muscle when ATP is needed
- glycogen in the liver controls blood glucose; muscle glycogen cannot contribute to blood glucose
- the liver (and kidneys) have glucose-6-phosphatase from C6 so glucose can enter the bloodstream
cholera
toxin causes Cl- channels to remain open resulting in watery diarrhea
- oral rehydration/rice takes advantage of secondary active transport to return Na+ to the cell and slow the release of water into the intestines
Starch
long polymer (many subunits) of glucose
Lactose
glucose + galactose- disaccharide
Sucrose
glucose + fructose- disaccharide
T/ F: Animal products contain very little carbohydrate?
true
Where do carbohydrates exist?
fruits, vegetables, and grains
What stores glycogen?
liver and muscles
Cellulose has what type of bond?
B-14 bonds; dont have enzyme for so bond between glucose cant break so it becomes dietary fibre
Amylases breaks down
starch into individual glucose molecules
Sucrases breaks down
glucose and fructose (Sucrose)
Galactose breaks down
galactose and glucose (lactose)
Where is bile salt stored?
made in liver and stored in gallbladder and released in presence of fats in GI tract
T/F: cellulose is soluble?
false; insoluble
T/F: Pectins and gums are solube?
true
How do soluble fibres reduce blood cholesterol?
by binding bile salts or reducing absorption in the intestines
Type One Diabetes
- beta cells are destroyed by autoimmunity
- GLUT are locked inside cell and can only come to surface of cell
- cells are starving and go into ketoacidosis
- blood glucose drops too low- brain not getting enough
- want glucose out of blood stream and stored back in liver or muscle
- want GLUT to go back into the cell so glucose is not being taken out of the blood so glucose wont keep dropping
Does the brain have insulin sensitive glucose transporters?
no
Type Two Diabetes
- insulin circulates but receptors arent as sensitive
- results in hypergylcemia
- drops in blood glucose= less glucose transport and therefore metabolism
What transport does the brain normally use?
GLUT 3; not insulin sensitive
What is broken down in response to blood glucose level signals?
glycogen
Ribonucleotide
source of energy
What is salivary amylases optimal pH? and when is it inactivated?
6; by the acidity in the stomach
When does starch begin to be digested?
in the mouth due to salivary amylases
What breaks starch down into smaller units until maltose is produced?
alpha amylase in the pancreas
Where does maltose reside?
intestinal wall
Villi and microvilli
contain a capillary network and nutrients can get into the rbc and then into the capillary
Carb digesting enzyme function
wait for disaccharides to come by in order to break them down
What happens to the disaccharides that are not digested?
enzymes distributed along here not digested may be metabolized by bacteria in the colon to prod. gases or short chain FAs
Where should lactose never be?
large intestine- it should be digested in the small intestine
too much LDL
get rid of some bile salts so that the liver takes more LDL out of the blood to remake bile salts
Secondary lactase deficiency
results from injury to intestinal absorptive cells; lactase is first to shed and last to come back
Osmotic diarrhea is caused by?
lactose being in small intestine and dragging in water with it to balance the osmolality
What happens when you cant break down lactose?
metabolism by colonic bacteria by lac operon
treatment for diarrhea
rehydration of fluids needs to contain glucose and sodium in water in order for absorption to occur
symptoms of hypoglycemia
- headache
- blurred vision
- hunger
- irritability
- weakness, fatigue, feeling tired
- sweating
- dizziness
- fast heartbeat
- shaking
- anxiety
Blood glucose levels after eating
drop
Can muscle use glycogen to contribute to blood glucose?
NO only use it for energy within the muscle
