PHTY251 - Exercise and temperature regulation

Define endotherm

warm blooded

Define exotherm

Cold-blooded

Roles of cortex

Behaviour modification, awareness, choice, action

Roles of hypothalamus

Homeostatic mechanisms; autonomic control of thermoregulation

What is the thermoneutral zone?

The range of environmental temperatures over which a constant basal metabolic rate can be maintained

In humans, 21-30 degrees (depending on clothing)

When is our body temperature the highest?

4am

When is our body temperature the lowest?

4pm

What is cardiac rhythm controlled by?

Thought to be controlled by melatonin, secreted by the pineal gland

What are the 4 types of heat loss?

1. Conduction

2. Convection

3. Radiation

4. Evaporation

What are the 4 types of heat gain?

1. Conduction

2. Convection

3. Radiation

4. Metabolism

Define conduction and give an example

Transmission of heat through a physical surface (requires a gradient), e.g. leaning against a cold wal or holding a hot metal bar

Define convection and give an example

Transmission of heat through the movement of fluid or air, e.g. cool wind or heat from fire

Define radiation and give an example

Transmission of heat through electromagnetic waves, e.g. head/feet radiating in cold

Define evaporation and give an example

Loss of heat through conversion of water (sweat) to gas.

How much sweat is secreted onto the skin per day in a neutral environment?

~600mL

What are the two factors that influence the speed of evaporation?

Temperature and moisture gradient

E.g. at 30 degrees, low humidity, lots of evaporation. At 30 degrees, high humidity, low evaporation

Define metabolism

Gain of heat through oxidation of nutrients to make ATP, and hydrolysis of ATP. Heat produced as a byproduct.

Describe shivering thermogenesis

Cold-induced involuntary muscle contractions increases ATP production and use

Describe non-shivering thermogenesis

Main mechanism of heat gain for infants under 1.

Hypothalamus activates the SNS when core body drops, release noradrenaline and thyroid hormone causing activation of uncoupling proteins in the mitochondria of brown fat cells. Oxidizes fatty acids, generating heat rather than ATP

Describe hypothermia

Core body temperature less than 35 degrees

More heat loss than heat gain

Exercising in cold increases chance of hypothermia (sweating leader to greater heat loss in the cold)

What is the effect of hypothermia on physiological functions?

Slows all physiological functions:

↓ metabolic rate, HR and ventilation.

Electrolyte disturbances leading to acidosis.

Slower neural conduction

What is the negative feedback to correct heat loss?

- Shivering via motor nerves and skeletal muscles

- Vasoconstriction via skin arterioles

- Sweat glands ↓ sweat production

- Increased adrenaline -> metabolic rate (minor importance in adults)

Describe thermoregulation during exercise

Heat production: ↑

Heat loss: sweating ↑ (evaporation), blood vessels vasodilate (convection/radiation)

Core body temperature: ↑

When heat production = heat loss, core body temperature stabilises

What is the heat tolerance limit?

When heat loss mechanisms can't keep up with heat production and core body temperature climbs to dangerous levels leading to fatigue and/or heat stroke

What can increase the heat tolerance limit?

Exercise training

Describe hyperthermia

Heat exhaustion

Core body temperature more than 40 degrees

More heat gain than heat loss

Symptoms attributed to hypotension (vasodilation of skin arterioles ↓TPR, sweating causes dehydration and loss of plasma volume, causing ↓in preload and SV)

How do fevers from infection occur?

Macrophages release chemical messengers which stimulate the vagus nerve (hypothalamus), causing the release of prostaglandins within the hypothalamus

↑ the core body temperature set point

Effectors: skeletal muscle (feel cold, shivering), skin arterioles (vasoconstriction to reduce blood flow to skin)

True/false: Endotherms rely on the environment for heat gain

False

Which part of the brain contains the thermoregulatory cortex

a. Cerebellum

b. Cerebral cortex

c. Hypothalamus

d. Medulla

Hypothalamus

An increase in humidity makes it more difficult to lose heat by evaporation of sweat BECAUSE in humid environments the water gradient between the skin surface and environment is decreased

a. Both statements true and causally related

b. Both statements true, not causally related

c. First statement true, second false

d. First statement false, second true

e. Both false

a. Both statements true and causally related

True/false: the core body set point increases at the onset of a fever

True

Which statement about thermoregulation is INCORRECT?

a. At the start of exercise, heat production exceeds heat loss

b. Heat stroke can occur when core body temperature exceeds 40 degrees

c. The symptoms of heat exhaustion are largely a result of hypotension

d. After temperature acclimation sweating decreases

d. After temperature acclimation sweating decreases

Exercising in very cold weather increases the risk of developing hypothermia BECAUSE exercise increases heat production

a. Both statements true and causally related

b. Both statements true, not causally related

c. First statement true, second false

d. First statement false, second true

e. Both false

Both statements true, not causally related

Define oxygen debt

The extra O2 required after exercise to restore the body to its pre-exercise state. Size of O2 debt depends on exercise intensity

During muscle debt, replenishing of the muscle stores of what occurs?

- ATP

- Cr-P

- O2 (bound to myoglobin

- Glycogen

What is lactic acid used for in oxygen debt?

- Used in the liver to be converted into glucose via Cori cycle

- Used by other cells to create more ATP by concerting it back to pyruvate

Explain Excess Post-Exercise Oxygen Consumption (EPOC)

The body continues higher than normal O2 consumption and ventilation after exercise

What happens to oxygen debt after high-intensity, short-duration exercise (e.g. 100m sprint)?

Proportionally larger O2 debt → longer and more intense EPOC

How does oxygen debt compare after low-intensity, long-duration exercise (e.g. marathon)?

Proportionally smaller O2 debt → shorter and lower intensity EPOC.

According to the Fick Principle, what factors determine oxygen consumption?

Cardiac output (CO) and the difference in O2 content between arteries (CaO2) and veins (CvO2).

What is the Fick Principle equation for calculating oxygen consumption (VO2)?

VO2 = CO × (CaO2 - CVO2)

True/false: at the end of exercise, one molecule of ATP is required to remove each molecule of lactate that was accumulated during exercise

False. The Cori cycle uses 6 ATP (3ATP per lactate)

Aerobic metabolism utilises fat and glucose stores for ATP production during exercise lasting longer than ~2 minutes BECAUSE the aerobic system provides all the energy for longer duration exercise.

a. if both statements are true, and the second causes the first.

b. if both statements are true, but the second does not cause the first.

c. if the first is true and the second is false. (anaerobic system provides some)

d. if the first is false and the second is true.

e. both statements are false.

b. if both statements are true, but the second does not cause the first.

True/false: during low intensity exercise, the alveolar partial pressure of O2 (PAO2) should not change

True.

The arterial partial pressure of O2 stays the same throughout low, medium and high intensity exercise because lungs replace the O2 that we use, topping up the PAO2. Shows that alveoli have normal function

During high intensity exercise the increase in ventilation is not proportional to the increase in oxygen consumption (V̇O2) BECAUSE during high intensity exercise O2 extraction from the systemic blood increases, causing a decrease in the venous partial pressure of oxygen (PvO2).

a. if both statements are true, and the second causes the first.

b. if both statements are true, but the second does not cause the first.

c. if the first is true and the second is false.

d. if the first is false and the second is true.

e. both statements are false.

b. if both statements are true, but the second does not cause the first.

How does parasympathetic output to the heart change during exercise?

It decreases (less "rest and digest" influence).

How does sympathetic output change during exercise?

It increases → heart, veins, and arterioles in abdominal organs and kidneys are activated ("fight or flight").

What happens to cardiac output (CO) during exercise?

Increases

What happens to blood flow in abdominal organs during exercise?

Vasoconstriction increases → decreased abdominal organ blood flow.

What happens to skeletal muscle blood flow during exercise?

Vasodilation increases → greatly increased blood flow → O₂ & nutrients delivered, CO₂ & waste removed.

What happens to skin blood flow during exercise?

It increases → heat loss.

What happens to blood flow to the heart and brain during exercise?

It increases → supports heart's increased demand and maintains brain function.

What happens to heart rate during exercise?

It increases from resting rate (~60 bpm) → up to 3-4 times resting; max HR = 220 - age.

What happens to stroke volume during exercise?

It increases from ~70 mL → 1.5-2 times resting.

What happens to cardiac output during exercise?

Increases from ~5 L/min → up to ~40 L/min (up to 8 times resting).

Define functional sympatholysis

Local vasodilation of skeletal muscle overrides the vasoconstriction from sympathetic vasoconstrictor nerves

What happens to cardiac output (CO) during moderate, steady-state exercise?

Increases

How does total peripheral resistance (TPR) change during moderate exercise?

Decreases

How does mean arterial blood pressure (MABP) behave during moderate, steady-state exercise?

Remains relatively constant

What happens to CO and TPR during high-intensity exercise?

CO increases more than TPR decreases.

How does mean arterial blood pressure (MABP) respond to high-intensity exercise?

MABP increases, mainly due to increased systolic pressure.

What is anaerobic strength training?

High intensity low rep training

What are the effects of anaerobic (strength) training?

Muscle hypertrophy - ↑ in size and strength of skeletal muscles

Lactate threshold - ↑ in exercise intensity before reaching lactate threshold

Describe hypertrophy

- Increased protein synthesis → more actin and myosin → ↑ contractile strength

- Satellite cell activity → fuse to fibers → repair micro-tears → ↑ fiber size and strength

- Sarcoplasmic hypertrophy → ↑ sarcoplasm volume → ↑ anaerobic capacity

Describe how increase of lactate threshold occurs

With high-volume, steady-state, and interval training at 80-90% VO2 max → stimulates anaerobic glycolysis → muscle adapts by improving lactate tolerance (buffering)

What is the cause of muscle atrophy? How?

Myostatin. Prevents excessive muscle growth. Increases with inactivity

What is aerobic (cardio) training?

Low intensity training, high rep, longer endurance training

What are the goals of aerobic training?

↑ aerobic capacity: aerobic threshold and VO2 max

Explain how an increased VO2 max (aerobic training) occurs

↑ O2 supply (cardiovascular adaptations)

↑ muscle O2 use (cellular metabolic adaptations)

Explain how an in increase in stroke volume (due to aerobic training) occurs

Remodelling of ventricular walls, moderate hypertrophy → ↑ ventricular volume and contractility

What are the muscle cell adaptations that occur due to aerobic training?

↑ oxidative ATP synthesis capacity

↑ Type 1 fibres (oxidative)

↑ Mitochondria

↑ production of oxidative enzymes

↑ oxidative phosphorylation