How HR varies

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Heart usually beats at 70 bpm

when we exercise our muscles must release more energy and so they need more O2 for aerobic respiration

To deliver more O2 the HR must inc and stroke volume must inc

when we are stressed/angry/afraid/nervous our HR also inc

the inc output supplies extra blood to the muscles enabling them to release more energy through aerobic respiration gland

this is triggered by the secretion of the hormone adrenaline from the adrenal

Adrenaline produces several changes to the body. They are:

breathing rate inc and breathes becme deeper

heart beats faster, sending more blood to the muscles, so that they can recieve more glucose and O2 for respiration

blood diverted from intestines to muscles

in the liver, stored carbohydrates are changed in the glucose and released into blood. muscles cells absorb it and use it for respiration

pupils dilate, inc visual sensitivity to movement

mental awareness inc, so reactions are faster

When we sleep our HR dec as all of our organs are working slower, they need to release less energy and so we need less O2.

these changes in HR are brought by nerve impulses from the MEDULLA in the brain

when we exercise we produce a lot more CO2 in aerobic respiration

sensors in the aorta and the Carotid Arteery detect this inc and send an impulse to the medulla

the medulla responds by sending nerve impulses along the accelerator nerves

when CO2 production returns to normal the medulla recieves fewer impulses

it responds by sending nerve impulses along the decelerator nerve

why when we exercise does HR inc

there is inc muscle contraction

HR inc so more O2 and C6H12O6 are taken to muscles

so more respiration

to release more energy- for inc muscle contraction

inc O2 means O2debt can be repaid

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