Adrenaline is the human hormone that reduces blood flow to the digestive system and skin during stress. Adrenaline, also known as epinephrine, is a hormone and neurotransmitter produced by the adrenal glands, which are located on top of the kidneys.

Role of Adrenaline during Stress:
During times of stress, the body goes into a "fight or flight" response, which is triggered by the release of adrenaline. This response prepares the body to either confront a threat or flee from it. Adrenaline plays a crucial role in this response by initiating various physiological changes in the body.

Constriction of Blood Vessels:
One of the effects of adrenaline during stress is the constriction of blood vessels in certain parts of the body, including the digestive system and skin. This constriction is achieved by the hormone causing the smooth muscles in the walls of blood vessels to contract. As a result, blood flow to these areas is reduced.

Diversion of Blood Flow:
By reducing blood flow to the digestive system and skin, adrenaline diverts blood to more essential areas of the body during stress. This includes organs that are important for survival in a fight or flight situation, such as the heart, lungs, and skeletal muscles. These organs require increased blood flow to provide them with the necessary oxygen and nutrients to function optimally during times of stress.

Increased Blood Flow to Essential Organs:
By reducing blood flow to the digestive system, adrenaline temporarily shuts down non-essential functions such as digestion. This allows the body to conserve energy and focus its resources on dealing with the immediate threat or stressor. Similarly, by reducing blood flow to the skin, adrenaline helps to limit bleeding in case of injury and prevent excessive heat loss from the body.

In summary, adrenaline is the human hormone that reduces blood flow to the digestive system and skin during stress. This physiological response is part of the body's "fight or flight" response and helps to redirect blood flow to essential organs and conserve energy during times of stress.