When jacob saw shadows of people behind him on the walls of the dark alley, his blood pressure increased and breathing rate sped up. these physical reactions were most directly regulated by his: ?

The answer is amygdala. This is the region of the brain that is responsible for emotional responses such as fear and anxiety. It is part of the limbic system and hence important in decision-making. It processes information and sends signals to the hypothalamus and other regions such as the locus coeruleus (that processes fear and panic as in this case).