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By Root 974 0

response in multicellular organisms is not an either/or proposition—not all of our 50 trillion cells have to be in growth or protection mode at the same time. The proportion of cells in a protection response depends on the severity of the perceived threats. You can survive while under stress from these threats but chronic inhibition of growth mechanisms severely compromises your vitality. It is also important to note that to fully experience your vitality it takes more than just getting rid of life’s stressors. In a growth-protection continuum, eliminating the stressors only puts you at the neutral point in the range. To fully thrive, we must not only eliminate the stressors but also actively seek joyful, loving, fulfilling lives that stimulate growth processes.

The Biology of Homeland Defense

In multicellular organisms, growth/protection behaviors are controlled by the nervous system. It is the nervous system’s job to monitor environmental signals, interpret them, and organize appropriate behavioral responses. In a multicellular community, the nervous system acts like the government in organizing the activities of its cellular citizens. When the nervous system recognizes a threatening environmental stress, it alerts the community of cells to impending danger.

The body is actually endowed with two separate protection systems, each vital to the maintenance of life. The first is the system that mobilizes protection against external threats. It is called the HPA axis, which stands for the Hypothalamus-Pituitary-Adrenal Axis. When there are no threats, the HPA axis is inactive and growth flourishes. However, when the brain’s hypothalamus perceives an environmental threat, it engages the HPA axis by sending a signal to the pituitary gland, the “Master Gland,” which is responsible for organizing the fifty trillion cells of the community to deal with the impending threat.

Think back to the cell membrane’s stimulus-response mechanism, the receptor-effector proteins—the hypothalamus and pituitary gland are behavioral equivalents. Similar to the role of a receptor protein, the hypothalamus receives and recognizes environmental signals; the pituitary’s function resembles that of the effector protein in that it launches the body’s organs into action. In response to threats from the external environment, the pituitary gland sends a signal to the adrenal glands, informing them of the need to coordinate the body’s “fight or flight” response.

The technical details of how stress stimuli engage the HPA axis follow a simple cascade: In response to perceptions of stress registered in the brain, the hypothalamus secretes a corticotropinreleasing factor (CRF), which travels to the pituitary gland. CRF activates special pituitary hormone-secreting cells causing them to release adrenocorticotropic hormones (ACTH) into the blood. The ACTH then makes its way to the adrenal glands, where it serves as the signal to turn on the secretion of the “fight-flight” adrenal hormones. These stress hormones coordinate the function of the body’s organs, providing us with great physiologic power to fend off or flee from danger.

Once the adrenal alarm is sounded, the stress hormones released into the blood constrict the blood vessels of the digestive tract, forcing the energy-providing blood to preferentially nourish the tissues of the arms and legs that enable us to get out of harm’s way. Before the blood was sent to the extremities, it was concentrated in the visceral organs. Redistributing the viscera’s blood to the limbs in the fight or flight response results in an inhibition of growth-related functions; without the blood’s nourishment the visceral organs cannot function properly. The visceral organs stop doing their life-sustaining work of digestion, absorption, excretion, and other functions that provide for the growth of the cells and the production of the body’s energy reserves. Hence, the stress response inhibits growth processes and further compromises the body’s survival by interfering with the generation of vital energy reserves.

The body