It is pulse per minute. Heart rate varies in animal. The smaller animals have high metabolic rates and hence need greater action of heart to pump more oxygen and nutrients to tissues. This is the reason why smaller animals have much higher heart beat rate than the larger animals.
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Smaller the animal – Higher metabolic rate – Higher heart beat rate/min. Larger the animal – Lower metabolic rate – Lower heart beat rate/min. Eg. Heart rate of elephant – 25 times/min., Heart rate of rat – 300 times/min.
Heart rate increased by:
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(i) Increase in blood pressure in the-vena cava (increase blood in cava => increase blood flow into heart => heart size increases => Frank Starling law causes increase contraction => increase heart rate) Increase in blood CO2 concentration
(ii) Decrease in blood O2 concentration – Stimulates receptors present in blood vessels and in heart wall Decrease in blood pH.
(iii) Increase in body temperature (core temperature).
(iv) Increase in hormone adrenaline.
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(v) Decrease in hormone thyroxin (increase BMR).
(vi) Increase in the nervous input from pain receptors.
Heart rate decreased by:
(i) Increase in blood pressure in aorta and large arteries.
(ii) Decrease in blood CO2 concentration
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(iii) Increase in blood O2 concentration
(iv) Increase in blood pH.
(v) Decrease in body temperature (core temperature).
(vi) Decrease in adrenaline.
(vii) Increase in thyroxin.