733 Metabolic System

liver location

right upper quadrant

liver function

processes nutrients absorbed from the diet, manufactures bile and blood proteins, stores vitamins and minerals, and provides the body with a quick energy source in the form of glycogen

pancreas location

deep in the abdomen behind the stomach

pancreas function

exocrine organ to aid in digestion; endocrine organ to secrete insulin or glucagon regulating blood glucose levels

adipose tissue function

fat storage, secretes hormones of leptin and adiponectin involved in hunger and insulin sensitivity regulation

anaerobic

without oxygen

anaerobic processes of energy production

• glycolysis

glycolysis

the breakdown of glucose to pyruvate for energy which occurs in the cells during exercise. This process converts glucose into pyruvate, producing small amounts of energy captured in ATP and NADH and is active during high intensity, short-duration exercises like sprinting

aerobic

with oxygen

aerobic processes of energy production

• Krebs Cycle

• Oxidative Phosphorylation

Krebs cycle

processes pyruvate into carbon dioxide and high energy electron carriers like NADH and FADH2 which produces small amounts of ATP which then feeds into oxidative phosphorylation

oxidative phosphorylation

the primary energy currency of the cell and is crucial during sustained, low-intensity activities

basal metabolic rate (BMR)

the energy your body needs just to keep the lights on at rest

BMR daily use

accounts for 60-70% of total daily energy use

what sets BMR

• lean body mass → biggest driver / more muscle = higher BMR

• thyroid hormones → set idle speed

• Age→ decreases with age b/c of muscle loss

total energy expenditure (TEE)

all the calories you burn in a 24 hour period

TEE equation

= BMR + TEF + Activity

thermic effect of food (TEF)

the energy used to digest and absorb food (~10%)

activity

the most variable part and includes EAT and NEAT (20-30%)

exercise activity thermogenesis (EAT)

calories burned through planned workouts

non-exercise activity thermogenesis

everything else (walking, fidgeting, chores)

fuel in a fasted state overnight

• insulin lower, glucagon higher

• Liver releases glucose from glycogen

• Adipose releases fat for muscle and sends glycerol to liver

fuel in a prolonged fasted state

• Liver makes new glucose

• Muscles use more fat

• Brain uses ketones

PT relevance for a patient in a fasted state

morning or long-gap sessions may reduce tolerance for hard busts of activity, pace and progress accordingly

fuel during exercise

• Hard and brief efforts rely mostly on muscle glycogen

• Liver supports glucose release

• Moderate work uses carbohydrates and fats

• Long and easy work is mainly fat

PT relevance for a patient doing exercise

match intensity and duration to goals

fuel during recovery immediately after

• Oxygen use remains higher

• Body restores creatine and clears lactate

• Muscles are more sensitive to insulin

fuel during recovery later on

Muscles adapt with better capacity to use fat and handle glucose

PT relevance for a patient in recovery

post session snack with carbohydrates (with or without protein) can support recovery

in a 0-30min workout what system is used

muscle glycogen → the body draws on fuel that is the fastest to access; glycogen stored in working muscle

in a quick fast paced workout like a sprint what system is used

muscle glycogen→ the body makes a quick withdrawal of energy

in a steady 1-3 hour workout what energy system is used

liver glycogen & adipose fat → the body will preserve glycogen and leans mainly on fat from adipose tissue. Liver glycogen keeps working quietly in the background, releasing glucose to keep the blood sugar stable for the brain

exercise onset (0-3 minutes) hormones

• low insulin

• high glucagon

• high catecholamines

sustained moderate exercise hormones

• little to no change in insulin

• high glucagon

• high to moderate catecholamines

• high cortisol

• high growth hormone

recovery (early) hormones

• high insulin

• low glucagon

• low catecholamines

growth hormone

supports lipolysis and tissue building over time

insulin secretion

secreted by the pancreas

insulin dominant state

dominant in fed state

insulin primary action

put fuel into cells for storage and growth

insulin role

• Signals muscle and liver cells to take up glucose from the blood

• Promotes the storage of glucose as glycogen

• Enhances fat deposition in adipose tissue

• Spares protein from being broken down

glucagon secretion

secreted by the pancreas

glucagon dominant state

dominant in fasting state

glucagon primary action

to get fuel out of storage to maintain stability

glucagon role

• Targets the liver to release stored glucose

• Stimulates the breakdown of glycogen

• Promotes the creation of new glucose

• Ensures the brain has a steady supply of blood sugar

catecholamines secretion

by the adrenal medulla

catecholamines dominant state

exercise onset acute stress

catecholamines primary action

to rapidly mobilize all available fuel for immediate, high-intensity use

catecholamines role

• Increases HR and force of contraction

• Stimulates rapid breakdown of glycogen in both the muscles and liver

• Promotes breakdown of fats

• Provides massive fast surge of energy

cortisol secretion

secreted by the adrenal cortex

cortisol dominant state

dominant during state of prolonged stress

cortisol primary action

to ensure fuel availability for the long haul by creating new fuel from other resources

cortisol role

• Strongly stimulates the creation of new glucose in the liver

• Frees up amino acids and fatty acids to be converted into fuel

• Has powerful anti-inflammatory effects to manage stress response

T3/T4 secretion

secreted by the thyroid under pituitary control

T3/T4 role

• Set the basal metabolic rate

• Enhance carbohydrate and fat metabolism

• Influence protein turnover

• affect mitochondrial density and muscle contractile behavior

hypothyroidism

decreased T3/T4 leading to slowed metabolism, fatigue, reduced energy, potential weight gain

hyperthyroidism

increased T3/T4 leading to elevated metabolism, muscle weakness, heat intolerance

how insulin gets glucose into cells

• insulin binds to receptors on skeletal muscle and adipose tissue

• cascade of GLUT-4 transporters

• GLUT-4 allows glucose to enter cell

• *exercise stimulates GLUT-4 movement independent of insulin

muscle as a major glucose sink

During and after exercise, skeletal muscle is the largest site of glucose uptake, helping regulate blood sugar and replenish glycogen stores.

insulin-independent uptake

Exercise stimulates GLUT-4 translocation to the muscle cell membrane through contraction signals. This means the muscle can take up glucose even when insulin levels are low

post-exercise insulin sensitivity

After a workout, muscles become more sensitive to insulin for several hours, making them more efficient at storing glucose as glycogen. This is a key mechanism behind exercise as a treatment for insulin resistance and type 2 diabetes

training adaptations

Regular aerobic and resistance training increases both the number and efficiency of GLUT-4 transporters and improve mitochondrial density, supporting better glucose handling and endurance.

PT relevance of glucose uptake and insulin

Exercise prescriptions (time, intensity, type) can directly influence glucose control in patients with diabetes, metabolic syndrome, or impaired recovery. For example, moderate bouts of exercise can lower blood glucose acutely and improve long-term insulin action

metabolic system infancy & childhood

high metabolic rate because energy demands are significant to support rapid growth and brain development

metabolic system in adolescence

increased energy levels and growth spurt requires more calories

females get more fat for reproductive readiness

males get increased muscle mass and BMR

metabolic system in early adulthood

metabolic peak as the body efficiently balances energy intake with expenditure

metabolic system in middle age

metabolic slow down

metabolic system in old age

further metabolic reduction and increased risk of osteoporosis

type 1 diabetes

an autoimmune disease where the body’s immune system mistakenly attacks and destroys the insulin-producing beta cells in the pancreas and requires lifelong insulin therapy

type 2 diabtetes

primarily results from insulin resistance, where the body’s cells don’t respond properly to insulin, and the pancreas may not produce enough insulin overtime

thyroid hormones, energy, and BMR- affecting gene expression

thyroid hormones bind to receptors within cell nuclei, activating genes that increase the body’s metabolic rate and heat generation

thyroid hormones, energy, and BMR- increasing the activity of the Na/K pump

thyroid hormones stimulates this energy-consuming enzyme in the cell membranes, which boosts oxygen and energy consumption throughout the body

thyroid hormones, energy, and BMR- enhancing mitochondrial activity

by promoting the growth and protein synthesis of mitochondria, thyroid hormones enhance the cell’s ability to produce energy

thyroid hormones, energy, and BMR- influencing macronutrient metabolism

the hormones boost both the breakdown (catabolism) and synthesis (anabolism) of carbs, fats, and proteins