The brain includes two major components: the cerebral cortex and the subcortex. The subcortex includes the cerebellum, medulla oblongata, pons, and diencephalon. The diencephalon is made up of the thalamus and the hypothalamus.
When the hypothalamus experiences a stressor, it releases corticotropin releasing factor, which instructs the pituitary to secrete adrenocorticotropic hormone. In addition, the hypothalamus directly activates the adrenal medulla.
Once instructed by the hypothalamus and pituitary, the adrenal cortex secretes glucocorticoids and mineralocorticoids. The primary glucocorticoid is cortisol, and the primary mineralocorticoid is aldosterone. In addition, the hypothalamus instructs the adrenal medulla to secrete the catecholamines epinephrine and norepinephrine.
Adrenal hormones cause a number of physiological changes that include accelerated heart rate, dilation of coronary arteries, dilation of bronchial tubes, increased basal metabolic rate, constriction of blood vessels in the limbs, increased oxygen consumption, increased blood sugar, and increased blood pressure.
In addition to the adrenal gland response to stress, the thyroid gland releases thyroxin, and the pituitary secretes oxytocin and vasopressin. These hormones also help prepare the body for a physical response to the stressor.
Stress results in secretions of oxytocin and vasopressin, which cause contractions of smooth muscles (such as in the walls of the blood vessels). Therefore, blood vessel constriction occurs. Vasopressin secretion also results in a greater blood volume. The combination of these effects leads to increased blood pressure, which can threaten the cardiovascular system.
The autonomic nervous system is made up of the sympathetic nervous system (generally in charge of expending energy—such as during stress) and the parasympathetic nervous system (generally in charge of conserving energy—such as during relaxation).
Stress decreases the amount of saliva in the mouth, leaving a feeling of cotton mouth. It may also lead to uncontrollable contractions of the esophagus, making swallowing difficult. Stress also causes greater secretions of hydrochloric acid, which can result in ulcers.
The contraction of skeletal muscle that results from stress can lead to tension headaches, backaches, and fatigue. The smooth muscle contractions of the walls of blood vessels can lead to hypertension.
The skins ability to conduct electrical currents and the skins temperature are both affected by stress.
