Carbohydrates – Part Two A. Regulation of Blood Glucose B. The Glycemic Index C. ATP Production from CHO

So now we have glucose in the liver and the bloodstream. If glu is to fuel the tissues, how is it done? First… you have “Glucose-dependent tissues” rely on glucose for fuel (not fat)

Storage of CHO is very limited in the body

Average person enough CHO stored to last _______________________ Since we can’t store much, need to rely on dietary CHO.

Blood Glucose Normal range of blood glucose:

Hypoglycemia: Symptoms: nausea, weakness, lightheadedness and dizziness. As a clinical condition: But can be temporarily induced by

Hyperglycemia: Symptoms are few (poor diagnosis) but may include:

Glucose Regulation Pancreas Produces insulin and glucagon, primary hormones involved. Insulin Facilitates entry of glu into liver and muscle cells so it can be stored as glycogen _______________________________

Glucagon Triggers breakdown of liver glycogen Or the synthesis of new glucose …

One more hormone: Epinephrine Produced by adrenal gland increases glu availability to the muscle (via glycogenolysis)

Summary So, in a FED state when blood glucose levels rise insulin levels rise (and glucagon is low) Insulin allows glucose to enters tissues, so blood glucose levels fall as a result Glucose  Glycogen = Glycogenesis Remember: Insulin is the “storage” hormone

In a FASTED state when blood glucose level is low glucagon levels rise (and insulin levels go down) Glucagon stimulates breakdown of Liver glycogen  glucose = Glycogenolysis glucose is released into the bloodstream glucose levels rise as a result

Activity

The Glycemic Effect of Food Glycemic Index A number indicating the extent to which a food raises blood glucose and elicits an insulin response compared with glucose

How to measure it? Each of at least 10 subjects must do two tests. Subjects are fasting 1) Test 1 – 50 g CHO. load of white bread or glucose (standard) 2) Test 2 – 50 g CHO. load of test food

glucose Reference food

Factors influencing glycemic effect Amount of carbohydrate (load) Nature of simple sugars sucrose (65), fructose (23), lactose (46), glucose (100 – this is the reference value)

Physical form of food: -whole apple vs. juice -cubed potato vs. mashed -whole grain vs. refined flour Presence of fiber, fat, protein, other constituents can lower GI

Glycemic Index and Athletes – Practical Applications Research is limited and preliminary GI itself has several limitations E.g. serving sizes to reach 50g CHO

ATP PRODUCTION FROM CARBOHYDRATE Anaerobic: Glycolysis Aerobic: Krebs & ETS

Glycolysis: Anaerobic Glucose-Splitting Occurs in the cytosol glucose is split in half to yield 2 pyruvate + 2 ATP Glu (6C)  2Pyruvate (3C) + 2ATP “Incomplete oxidation” doesn’t break glu down to final products (CO 2 and H 2 O) The coenzyme NAD+ is required

(6C) Glucose (3C) Pyruvate NAD+ NADH 2

Normally, NAD+ is regenerated when we get to aerobic metabolism… but… When O 2 insufficient for aerobic metab., ________________ is formed to help regenerate NAD+ Lactate holds the H ions generated during glycolysis lactate = “hydrogen reservoir”

(6C) Glucose (3C) __________ NAD+ NADH 2 (3C) ____________ (+2H) “hydrogen reservoir” NAD+

So what happens to lactate once it’s formed? Much of it is used for E in the muscle The rest diffuses out into the bloodstream

Muscle: low O 2 Liver glucose pyruvate lactate THE CORI CYCLE pyruvate blood blood lactate glucose glucose pyruvate So, does lactic acid “build up” in the muscle cells, causing muscle soreness?

Summary of Glycolysis Takes place in the cytosol of the cell Is an anaerobic pathway Only glucose (CHO) undergoes glycolysis Glycolysis occurs continuously; only the rate changes Provides a small amount of rapidly generated ATP

Summary of Glycolysis Glycolysis produces: 2 pyruvate or lactate 2ATP (2 H+ ions) (Body Heat) Lactate serves as a temporary storage site for H+ ions during glycolysis The Cori Cycle is the process by which lactate is converted back to glucose

The Krebs Cycle (And ETS): Aerobic, Complete Oxidation

Krebs Cycle & ETS generate ATP aerobically Complete oxidation: When O 2 is adequate, glucose is oxidized to CO 2 and H 2 O NADH 2 is generated; used to generate ATP in ETS

Still talking about CHO metabolism. We left off with pyruvate… This is an IRREVERSIBLE reaction

Then, Acetyl CoA can enter the Krebs Cycle Krebs Cycle Krebs & ETS generate at least 36 ATP

Summary of Aerobic Metabolism Requires Oxygen Acetyl CoA links glycolysis to the Krebs Cycle Krebs occurs continuously; only the rate changes All three macronutrients can be used to produce ATP

Summary of Aerobic Metabolism Krebs and ETS take place in the mitochondria The Krebs Cycle produces: At least 36 ATP (via electron transport) Water Carbon Dioxide (CO 2 ) Body Heat

Krebs

Now… Let’s draw it.

Recall: When intensity of exercise goes up, use of what fuel goes up? Why? Over time (duration), use of what fuel goes up? (assuming there’s plenty of oxygen available) Why?