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someone who is in year 13 and does Alevel AQA Biology

Lol i need help with the control of the heart for the chemoreceptors bit.
So if the high respiration leads to more co2 in the blood, and a signal is sent to increase the heart rate, then surely wouldn't the heart rate already be high anyway due to the rate of respiration? literally so confused lmao
Original post by m2105
Lol i need help with the control of the heart for the chemoreceptors bit.
So if the high respiration leads to more co2 in the blood, and a signal is sent to increase the heart rate, then surely wouldn't the heart rate already be high anyway due to the rate of respiration? literally so confused lmao

High heart rate means oxygen can be transported to the muscles quickly and co2 can be taken away quickly. The heart rate is high because of the co2 produced in respiration.
Reply 2
Original post by ashvinsingh
High heart rate means oxygen can be transported to the muscles quickly and co2 can be taken away quickly. The heart rate is high because of the co2 produced in respiration.

i get that, but i dont understand why a signal should be sent in order to increase the heart rate if its already high lol
@m2105

Hello m [I am also M - Snap! [tho upper case lol]],

Ok let me explain -

1. The human body works as a combined group of systems that work jointly [in conjunction with one another] to achieve a steady state during rest or to prepare for action in case a fight, flight, [or fright - a third reaction I have added] reaction is needed, yeah?

2. In addition, biology/medicine are not precise sciences - the degree of an effect or e.g. the weight or height of a group of people are not discrete whole numbers [categorical data] but are RATHER continuous data. So you cannot necessarily draw a line anywhere to distinguish between "black and white" - there is always a grey area, with me?

Ok now taking your specific Q, first [as in 1) above, the respiratory system, the cardiovascular system and the musculoskeletal system work together as a unit to e.g. run for your life if a lion jumps in through the window [v unlikely in UK, but has been known to happen where I was born :mad:; (just round the corner [Kenya - only 5000 miles away lol]), so the heart beats faster by the action of many mechanisms, NOT ONE [there are nerves that increase the slope of the resting potential of the heart muscle cells and of the sinoatrial node [the normal pacemaker - i.e. the part that determines the heart rate] so the potential reaches the threshold earlier and thus heart rate goes up PLUS more adrenaline is released and stimulates the heart to beat faster PLUS the chemoreceptors in the carotid body are stimulated PLUS central nervous system gets excited and sends noradrenaline to the heart, etc. In addition, the lungs provide more O2, the blood vessels dilate to provide more blood to the muscles [and to the heart], vessels in the skin constrict to leave more blood for the muscles, etc etc.

Taking 2) you say that "wouldn't the heart rate already be high" BUT what is high? The normal heart rate is 60-100 at rest so is 90 beats/min high or is 124 high or what? You cannot draw a line, yeah? The heart rate will be lower to start with in a fitter person [mine is 41 bpm cos I play a number of sports and train regularly, but my sis's is 75 odd cos she sits watching TV and eats Mac lol]; so it might rise from 75 to 130 in my sis in case of the lion scenario cos she will bolt while mine might just rise from 41 to 65 to calmly pick up my "rungu" [go to google translate [Kiswahili]] and smash the lion's face in, with me? It is a continuum.

On the other hand, if I cycle at 35 mph on the flat in a 50 mile race, my heart rate will probs go to 150 bpm or faster.

So it is a Q of resting level and the degree of demand, yeah? If a greater amount of O2 is needed by the muscles, then more than one mechanism might come into play, happy?

I hope this answers your Q!
Be safe!

M.

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