Carbohydrates – Part Two

A. Regulation of Blood GlucoseB. The Glycemic IndexC. 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 sugarssucrose (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: GlycolysisAerobic: 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 (CO2 and H2O)

The coenzyme NAD+ is required

(6C) (6C) GlucoseGlucose

(3C) (3C) PyruvatePyruvate

NAD+NAD+

NADHNADH22

Normally, NAD+ is regenerated when we get to aerobic metabolism… but…

When O2 insufficient for aerobic metab., ________________ is formed to help

regenerate NAD+ Lactate holds the H ions generated

during glycolysis lactate = “hydrogen reservoir”

(6C) (6C) GlucoseGlucose

(3C) (3C) ____________________

NAD+NAD+

NADNADHH22

(3C) (3C) ____________ ____________ (+2H)(+2H)

““hydrogen hydrogen reservoir”reservoir”

NAD+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 OMuscle: low O22

LiverLiver

glucoseglucose

pyruvatepyruvate

lactatelactate

THE CORI CYCLETHE CORI CYCLE

pyruvatepyruvate

bloodblood

bloodblood

lactatelactate

glucoseglucose

pyruvatepyruvate

So, does lactic acid “build up” in the So, does lactic acid “build up” in the muscle cells, causing muscle soreness?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 O2 is adequate, glucose is

oxidized to CO2 and H2O NADH2 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 Krebs CycleCycle

Krebs & ETS generate Krebs & ETS generate at least 36 ATPat 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 (CO2) 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?