how does the short term effects of anxiety cause an increase in blood pressure?

Answer 1

Stress causes a short term increase in blood pressure to increase perfusion to the muscles and the brain to better prepare the body to deal with an attack, this is commonly known as the "fight or flight" response.
To do this, the sympathetic nervous system stimulates epinephrine secretion from the adrenal glands, which causes an increase in heart contractility, heartrate, and stroke volume, as well as vasoconstiction, all of which increase blood pressure.

Answer 2

Anxiety and stress causes your adrenal glands to produce cortisol. Cortisol's most important job is to help the body respond to stress. Among its other vital tasks, cortisol helps maintain blood pressure and cardiovascular function, helps slow the immune system's inflammatory response, helps balance the effects of insulin in breaking down sugar for energy, helps regulate the metabolism of proteins, carbohydrates, and fats, helps maintain proper arousal and sense of well-being. It is the cortisol in your blood stream that causes your bp to jump. The amount of cortisol is in turn regulated by your pitutary gland inside the brain, which is affected by your anxiety. Thinking calming thoughts (cool wet grass, mountain streams, etc.) can damp down your pitutary, hence bp.

Answer 3

When you are anxious or stressed your body releases adrenaline (epinephrine) which dilates blood vessels, and allows blood to pumped quicker and faster to the muscles in preparation for the "flight or fight".

Answer 4

by causing an increased production of adrenaline (-> "fight-or-flight" response)