Question

How does the body increase heart rate and blood pressure under different circumstances? For example, if you were to start running a 5K race vs if you were to stand up from a seated position (baroreceptors, sympathetic and parasympathetic activity)

Answer 1

• Body responses to exercise – when we start running 5K race.

Cardiovascular response to exercise is a well-orchestrated neuro-hormonal event.

The physiological changes that body endures during exercise is called the “stress-response”. Stress is an unpleasant sensation, like in the case of exercise. When brain senses stress, it triggers cascade of neurological and hormonal changes that prepares the body for “fight or flight”. Body is primed to either counter stress or flee the situation.

So the brain comprehends exercise and communicate it with the rest of the body by-

Sensing (Triggering the alarm): Sensory nerves in the body communicate physical stress of exercise to the portion of brain called Amygdala.

Amygdala is the cognitive and emotional processing center in the brain. It interprets the sensory signals received from the body. If danger is perceived, hypothalamus is alerted to ready the body for fight-or-flight.

Hypothalamus can be thought of as the headquarters that communicates with key organ systems in the body via autonomic nervous system (ANS). ANS controls heart rate, blood pressure and breathing.

Autonomic nervous system has two parts:

Sympathetic nervous system —It prepares the body to fight stress.
Parasympathetic nervous system —It induces relaxation and calm in the body after stress passes.

When hypothalamus receives distress signals from amygdala, it alerts adrenal glands via sympathetic nervous system. They are glands located on top of kidneys.

Adrenal glands release epinephrine (also called as adrenaline) into the blood.

Adrenaline rich blood circulates through rest of the body bringing about several physiological changes.

Adrenaline interacts with receptors on heart and blood vessels causing an increase in heart rate and blood pressure. Pulse rate goes up. Thus, muscles and other vital organs of the body are pumped with increased blood flow.

Adrenaline causes an increase in respiratory rate. Airways in lungs dilate. Wide open airways breath in higher volumes of oxygen which further improves oxygen delivery to the exercising muscles, heart, and brain.

This whole response is commonly called adrenaline rush.

• If you were to stand up from a seated position-

Normally when you sit up to stand, gravity pulls some of your blood down to your belly area, hands and feet. In response, your blood vessels quickly narrow and the baro-receptors in the arch of aorta senses and it sends signals to the brain through the sympathetic nervous system and your heart rate increases slightly to maintain blood flow to the heart and brain, and prevent blood pressure dropping.

The stimulus for increase in heart rate and increase in blood pressure is very less compared to the stimulus produced during exercise.

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