Stress is not directly observable but the results of the bodies adaptation to it is. The hypothalamus activates the autonomic nervous system and the endocrine system. The autonomic nervous system is activated by direct nerves connected from the posterior hypothalamus to the adrenal medulla which secretes adrenaline and nor adrenaline. Cortisol provides fuel for battle by signaling the liver to release glycogen, or if lacking, initiates gluconeogenesis.
Aldosterone increases blood pressure.
In addition the pituitary activates oxytocin and vasopressin which increases the tension in the muscles. White blood cells, namely. Any situation that decreases the number of your white blood cells directly threatens your health. In addition when the stress response is activated heart rate increases, coronary arteries dilate, abdominal arteries constrict, pupils dilate, bronchial tubes dilate, glucose is released from the liver and basal metabolic rate increases. Under these conditions the cerebral cortex makes judgments of the events as either good or bad.