01 Stressed Out : The Behavior and Biology of Stress
02 A Biological Close-Up of Those Streesed-Out Feelings
03 Stress and Glucose Metabolism
04 Stress and Weight Gain
05 Stress and Heart Disease
06 Sleep Disruption
01 Stressed Out: The Behavior and Biology of Stress
- When you think about encountering a life−threatening situation on a highway – you would need a mechanism to decide on an appropriate reaction, whether to stay and fight or flee.
- Stress becomes a problem rather than a life−saving response when the brain is deluged with stimuli that it perceives as repeated threats over a long period of time. And this is when stress morphs from an acute response to a specific threatening situation to chronic, a generalized feeling that the daily pressures of life constitute a threat, thus leading to many of the health concerns
- Work, money, marital and health problems, and the pressures of parenthood are all perceived by the brain as significant stressors (any stimulus that triggers the stress reaction), and all elicit the stress response which affects both body and mind.
- The stress response is regulated by the Autonomic Nervous System (ANS), which takes care of the many bodily processes that are “subconscious” or outside of conscious control. This system is charged with increasing heart rate, blood pressure, and blood sugar,and suppressing the digestive, reproductive, and immune systems.
- The autonomic nervous system regulates a variety of body process that take place without conscious effort. The autonomic system is the part of the peripheral nervous system that is responsible, for regulating involuntary body functions such as heartbeat, blood flow, breathing, and digestion.
- Within the brain, the autonomic nervous system is regulated by the hypothalamus. The hypothalamus, just above the brain stem, acts as an integrator for autonomic functions.
- The autonomic nervous system has three branches: the sympathetic nervous system, the parasympathetic nervous system.
- The sympathetic nervous system is often considered the "fight or flight" system, while the parasympathetic nervous system is often considered the "rest and digest" or "feed and breed" system.
02 A Biological Close−Up of Those Stressed–Out Feelings
- On a smaller level, the stress response is controlled by the hypothalamic−pituitary−adrenal (HPA) axis. Hypothalamus receives a stressful stimulus from the outside world, and releases a hormone called corticotrophin−releasing hormone (CRH).
- CRH signals the adjacent pituitary gland to release adrenocorticotropic hormone (ACTH), which travels through the blood to the adrenal glands, which sit on top of each kidney.
- ACTH simulates the adrenals to release the two major stress hormones, adrenaline and cortisol. It is these two hormones that ready the body for reaction during the fight or flight
- response.
- The main function of adrenaline is to increase heart rate and blood pressure: in our evolutionary example above, it prepares the body to kick into high gear almost instantaneously. The effects of cortisol are observed over the longer−term: not only does the hormone increase blood pressure, but it increases blood sugar and mobilizes fat and protein stores to help replenish lost energy gradually as it is needed.
- An important outcome of chronic stress is hyper-glycemia. This may be due to either reduced uptake of glucose by cells or increased synthesis of glucose.
- Hyperglycemia is the immediate effect of stress as it serves energy to meet the energy requirements of the body to chronic stress. In an attempt to maintain the glucose homeostasis in response to elevated adrenocortical activity during stress, all the glucose pathways would be affected.
- Glucose uptake in the body is facilitated in 2 ways, facilitated diffusion and secondary active transport.
- GLUT receptors play a vital role in the uptake of glucose from the blood stream. GLUT-1 and GLUT-3 are shown to have high affinity for glucose and GLUT-1 is the major receptor that acts in brain and GLUT-2 is responsible for the uptake of glucose in pancreas.
- The GLUT-4 is insulin sensitive and is predominantly involved in receptor mediated glucose uptake in muscle. Counter regulatory hormones such as stress hormones (glucocorticoids and catecholamines) and glucagon are reported to inhibit insulin induced glucose uptake.
- Under stressful conditions, the pyruvate produced by glycolysis may be channeled towards the production of glucose or it might end up in producing high lactate because of the reduced activity of pyruvate dehydrogenase (PDH).
- Reduced pyruvate dehydrogenase activity has been observed under chronic stress condition. Stress is known to alter PDH activity by increasing the concentration of pyruvate dehydrogenase kinase which inactivates PDH by phosphorylating it.
- In spite of this, the activity of tricarboxylic acid (TCA) cycle will be high during stress because of the availability of substrates for TCA cycle by the oxidation of lipids. Further the increased activity of TCA cycle provides substrates for gluconeogenesis.
- It is reported that stress induces lipolysis and proteolysis which further elevate the concentration of the substrates for gluconeogenesis. In addition, chronic stress caused hyperlactatemia an indication of hypermetabolism.
- During normal conditions, the dietary glucose and endogenous glucose synthesized by the liver lead to the formation of glycogen in the liver. Stress is known to inhibit the glycogenesis in liver and skeletal muscles by inhibiting activity of glycogen synthase. The activity of glycogen synthase is inhibited by its phosphorylation by glycogen synthase kinase 3 (GSK-3)
- Glycogenolysis is the process of release of glucose from the glycogen. This usually occurs during starvation. Under stress, the glycogenolysis occurs to meet the increased energy demands by the body to withstand the perceived stress. A number of studies have shown the decreased liver glycogen content in response to chronic stress.
Read also : "Metabolism When Stress (Part 2)"
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