Final answer:
The diver's symptoms of a rapidly beating heart and dry mouth are due to increased adrenaline, which stimulates heart rate and blood pressure, and prepares the body for fight-or-flight response.
Step-by-step explanation:
The competitive diver is experiencing symptoms associated with increased levels of adrenaline. This hormone, also known as epinephrine, is released during stressful or exciting situations and activates the body's fight-or-flight response. It has a stimulatory effect on heart rate and blood pressure, dilates the bronchi of the lungs to allow more air exchange, and increases blood flow to the brain and muscles, enhancing physical performance and awareness.
If someone takes ß-blockers, they work antagonistically to adrenaline and can produce an inhibitory effect on these bodily responses.