Respiration and Circulation — BIOLOGY STD 12 Science — Question

1. Normal activities of the heart are auto regulated. The specialized muscles help in this regulation.
2. The heart is said to be myogenic due to this ability.
3. In the medulla oblongata of brain, there is cardiovascular centre,
4. From this centre, sympathetic and parasympathetic nerves innervate the sinoatrial node.
5. Sympathetic nerves secrete adrenaline and it stimulates and increases the heartbeat.
6. Parasympathetic nerves secrete acetylcholine and it decreases the heart rate.
7. Rate of heartbeat is controlled in response to inputs from various receptors like proprio-receptors.
8. These receptors monitor the position of limbs and muscles. There are chemoreceptors which monitor chemical change in blood and baroreceptors that monitor the stretching of main arteries and veins.

Chemical control on heart rate:

1. Hypoxia, acidosis, alkalosis cause decrease in cardiac activity.
2. Hormones like epinephrine and nor epinephrine enhance the cardiac activity.
3. Elevated blood level of K+ and Na+ decreases the cardiac activity.