Heart beat is at a fixed rate due to inherent property of the fibres of S A node but it can also be controlled by nervous and hormonal mechanisms. Centre of heart beat regulation is medulla oblongata.
i. Sympathetic nervous system having accelerator nerves increases the heart beat by secreting adrenaline hormone.
ii. Parasympathetic nervous system supplying with vagus nerves decreases the heart beat by secreting acetylcholine (Ach).
i. Thyroxine secreted by thyroid gland increases heartbeat indirectly by increasing basal metabolic rate which requires more oxygen.
ii. Epinephrine and nor-epinephrine secreted by adrenal medulla also have a role in regulation.
iii. Epinephrine increases heart beat in emergency.
iv. Nor-epinephrine increases heart beat under normal condition.
It is wave of distension felt in the arteries with each heart beat. Normally it is counted from radial artery of wrist. Normal pulse rate ranges 70-90 per minute, 72/min in man and 80/min in women.
i. Pulse rate in children is more rapid than adult.
ii. It is more rapid in female than in the male.
iii. When any strong emotion is experienced the pulse rate is increased, for e.g. anger, excitement etc.
iv. Exercise increases the rate of pulse.