Biology of Stress Stage 1 2024 PDF

Biology of Stress Dr Anna Battaglia Faculty of Life Sciences & Medicine  Learning outcomes Definition of stress The autonomic nervous system (ANS) involvement in the stress response The Hypothalamus, Pituitary and Adrenal (HPA) axis The HPA axis in acute and in chronic s...

Biology of Stress Dr Anna Battaglia Faculty of Life Sciences & Medicine  Learning outcomes Definition of stress The autonomic nervous system (ANS) involvement in the stress response The Hypothalamus, Pituitary and Adrenal (HPA) axis The HPA axis in acute and in chronic stress Stress (whetherWhat positiveis or stress? negative) triggers the same physiological/emergence mechanisms in the body. So not just when we perceive a threat but also when the body fights an infection, in stimulating and enjoyable situations (playing tennis etc.). Emotions such as joy, anger and fear are potent stressors. Expectations can also play a role (e.g., an expectation of something unpleasant happening can lead to stress). Stress leads to a biological response in the body. Sympathetic Nervous System and Hypothalamic- Pituitary-Adrenal (HPA) axis activation. The autonomic nervous system (ANS, comprised of the sympathetic and parasympathetic branches) and the HPA axis are highly Activation of the autonomic nervous system and HPA axis in response to a stressor follows a coordinated, temporal sequence. The autonomic nervous system quickly promotes physiological changes through synaptic transmissions by its two branches: the sympathetic and parasympathetic nervous system. The parasympathetic system facilitates the sympathetic response to stress, commonly referred to as the “fight or flight” response, by withdrawing its inhibitory effects. This, in turn, promotes physiological changes including the release of noradrenaline from the locus coeruleus and the stimulation of sympathetic preganglionic neurons to increase heart rate Conversely, the HPA axis is a hormonal system; thus, physiological changes associated with its activation occurs minutes after activation. The HPA axis is initiated by the release of the corticotrophin-releasing hormone from the paraventricular nucleus of the hypothalamus, which results in a series of endocrine events that culminates with the release of cortisol from the adrenal cortex. Cortisol impacts many different physiological systems (e.g., immunity, metabolism) and plays a role in augmenting the activity of the autonomic nervous system, such as enhancing the sympathetically mediated cardiovascular response to stress (e.g., increased heart rate).  Autonomic Nervous System Calm and Stressed and relaxed anxious  Fight or flight response https:// www.simplypsychology.org/stress- biology.html  Autonomic system Acetyl Choline Noradrenalin Calm/relaxed/ Fight or Safe flight/threat ↓heart ↑heart rate rate ↑Blood ↓BP Pressure Iris relaxes Iris contracts so Pupil is so Pupil is smaller larger ↑Gut ↓Gut motility motility Release CRF, ACTH and Cortisol  SYMPATHETIC (heart rate increased) Noradrenaline in neuron terminals PARASYMPATHETIC heart Noradrenali (heart rate falls) ne in the heart blood muscle Terminal of cholinergic neuron heart muscle acetylcholin e What are the main areas of the brain involved in the HPA axis? Amygdala Hypothalamus Pituitary gland Pre-frontal cortex Hippocampus  Amygdala Concerned with emotion, motivation and fear. Receives information on events in the world (e.g., threats), assesses danger and the emotional information is conveyed to other brain regions where defensive action is organised (fight or flight). There are two amygdale, one on each side of the brain. They release Corticotropin Releasing Factor (CRF)  Hypothalamus & Pituitary The hypothalamus is involved in the control of emotional reactions, feeding and drinking. The emotional reactions organised in the hypothalamus trigger hormonal secretions from the pituitary (also called hypophysis) gland like adrenocorticotropic hormone (ACTH).  Hippocampus The hippocampus is involved in organising memory storage in the cortex and retrieving memories stored in the cortex. There is a hippocampus on each side of the brain.  Pre-frontal cortex The front-most region of the frontal cortex. It is involved with planning and organising behaviour based upon the use of working memory.  These brain areas are linked to: Adrenal glands Located outside the brain. Adrenal cortex on outside of the gland releases cortisol directly into the blood stream. It responds to ACTH (adrenocorticotropic hormone) released by pituitary gland. Cortisol and corticosterone are glucocorticoids They bind to glucocorticoid receptors (GR): located on hypothalamus, hippocampus, pre-frontal cortex & pituitary gland in the brain.  The amygdala is concerned with emotion and The hypothalamus is involved in emotional reactions. It has The pituitary secretes ACTH (adrenocorticotropic hormone) into the HPA motivation. links to the bloodstream, during Releases CRF pituitary gland. stress. Releases CRF The hippocampus is involved in The adrenal cortex is the The prefrontal cortex (PFC) carries the formation and storage of outer shell of the adrenal glucocorticoid receptors. The certain kinds of conscious gland. It secretes the constant barrage of memory. The hippocampus hormone cortisol into the glucocorticoids as a consequence contains high levels of bloodstream. of HPA over activity during glucocorticoid receptors. Stress chronic stress makes them more leads to a decline in hippocampal susceptible to damage or death. function, through some combination of decline in hippocampal neurogenesis and HPA- baseline A small amount Hormone cortisol is secreted continuously from the adrenal cortex into blood stream. It is broken down by enzymes in the blood so levels remain low.  HPA- acute stress Stress triggers a cascade release of CRF-CRF-ACTH leading to an increase in cortisol secretion from the adrenal cortex. Cortisol attaches to GR on PFC, Hippocampus, Hypothalamus & Pituitary. Inhibition (direct and indirect) leads to decrease in CRF and ACTH & less cortisol secreted. Cortisol now back to baseline levels. Negative feedback  HPA- chronic stress Chronic Stress: prolonged stress response: HPA -constant release of cortisol. Blood levels elevated (as not enough enzyme breaking it down). Cortisol is toxic on GR so they decrease. This results in less inhibition and CRF and ACTH continue to be released – more cortisol release. Positive SUMMARY https://www.ncbi.nlm.nih.gov/pmc/articles/ PMC5579396/ https://www.frontiersin.org/articles/10.3389/fnbeh.2018.00127/full Zachary M. Harvanek, Nia Fogelman, Ke Xu, Rajita Sinha. Psychological and biological resilience modulates the effects of stress on epigenetic aging. Translational Psychiatry, 2021; 11 (1) DOI: 10.1038/s41398-021-01735-7 Misaki Niu et al. Claustrum mediates bidirectional and reversible control of stress- induced anxiety responses. Science Advances, 2022 DOI: 10.1126/sciadv.abi6375 Summary at: https://www.sciencedaily.com/releases/2023/03/230331131508.htm