Hypothalamic-pituitary-adrenal axis
Encyclopedia
The hypothalamic-pituitary-adrenal axis (HPA or HTPA axis), also known as the
limbic-hypothalamic-pituitary-adrenal axis (LHPA axis) and, occasionally, as the hypothalamic-pituitary-adrenal-gonadotropic axis, is a complex set of direct influences and feedback
interactions among the hypothalamus
, the pituitary gland
(a pea-shaped structure located below the hypothalamus), and the adrenal (also called "suprarenal") glands (small, conical organs on top of the kidneys).
The interactions among these organs constitute the HPA axis, a major part of the neuroendocrine system
that controls reactions to stress
and regulates many body processes, including digestion
, the immune system
, mood and emotions, sexuality, and energy storage and expenditure. A wide variety of species, from the most ancient organisms to humans, share components of the HPA axis. It is the common mechanism for interactions among glands, hormones, and parts of the midbrain that mediate the general adaptation syndrome (GAS).
CRH and vasopressin are released from neurosecretory nerve terminals at the median eminence
. CRH is transported to the anterior pituitary through the portal blood vessel system of the hypophyseal stalk and vasopressin is transported by axonal transport to the posterior pituitary. There, CRH and vasopressin act synergistically to stimulate the secretion of stored ACTH from corticotrope cells. ACTH is transported by the blood
to the adrenal cortex
of the adrenal gland
, where it rapidly stimulates biosynthesis of corticosteroid
s such as cortisol from cholesterol
. Cortisol is a major stress hormone and has effects on many tissues in the body, including on the brain. In the brain, cortisol acts at two types of receptor - mineralocorticoid receptor
s and glucocorticoid receptors, and these are expressed by many different types of neurons. One important target of glucocorticoids is the hypothalamus
, which is a major controlling centre of the HPA axis.
Vasopressin can be thought of as "water conservation hormone" and is also known as "antidiuretic hormone." It is released when the body is dehydrated and has potent water-conserving effects on the kidney. It is also a potent vasoconstrictor.
Important to the function of the HPA axis are some of the feedback loops:
, by blood levels of cortisol and by the sleep
/wake cycle. In healthy individuals, cortisol rises rapidly after wakening, reaching a peak within 30–45 minutes. It then gradually falls over the day, rising again in late afternoon. Cortisol levels then fall in late evening, reaching a trough during the middle of the night. An abnormally flattened circadian cortisol cycle has been linked with chronic fatigue syndrome
, insomnia
and burnout
.
Anatomical connections between brain areas such as the amygdala
, hippocampus
, and hypothalamus facilitate activation of the HPA axis. Sensory information arriving at the lateral aspect of the amygdala
is processed and conveyed to the central nucleus, which projects to several parts of the brain involved in responses to fear. At the hypothalamus, fear-signaling impulses activate both the sympathetic nervous system
and the modulating systems of the HPA axis.
Increased production of cortisol mediates alarm reactions to stress, facilitating an adaptive phase of a general adaptation syndrome in which alarm reactions including the immune response are suppressed, allowing the body to attempt countermeasures.
Glucocorticoids have many important functions, including modulation of stress reactions, but in excess they can be damaging. Atrophy
of the hippocampus in humans and animals exposed to severe stress is believed to be caused by prolonged exposure to high concentrations of glucocorticoid
s. Deficiencies of the hippocampus
may reduce the memory resources available to help a body formulate appropriate reactions to stress.
s and functional illnesses, including anxiety disorder
, bipolar disorder
, insomnia
, post-traumatic stress disorder
, borderline personality disorder
, ADHD, major depressive disorder, burnout
, chronic fatigue syndrome
, fibromyalgia
, irritable bowel syndrome
, and alcoholism
. Antidepressants, which are routinely prescribed for many of these illnesses, serve to regulate HPA axis function.
Experimental studies have investigated many different types of stress, and their effects on the HPA axis in many different circumstances. Stressors can be of many different types—in experimental studies in rats, a distinction is often made between "social stress" and "physical stress", but both types activate the HPA axis, though via different pathways. Several monoamine neurotransmitters are important in regulating the HPA axis, especially dopamine
, serotonin
and norepinephrine
(noradrenaline). There is evidence that an increase in oxytocin
, resulting for instance from positive social interactions, acts to suppress the HPA axis and thereby counteracts stress, promoting positive health effects such as wound healing.
The HPA axis is a feature of mammals as well as other vertebrates. For example, biologists studying stress in fish showed that social subordination leads to chronic stress, related to reduced aggressive
interactions, to lack of control
and to the constant threat imposed by dominant fish. Serotonin (5HT) appeared to be the active neurotransmitter involved in mediating stress responses, and increases in serotonin are related to increased plasma
α-MSH levels, which causes skin darkening (a social signal in salmon
oid fish), activation of the HPA axis, and inhibition of aggression. Inclusion of the amino acid
L-tryptophan, a precursor of 5HT, in the feed of rainbow trout
made the trout less aggressive and less responsive to stress. However, the study mentions that plasma cortisol was not affected by dietary L-tryptophan.
Studies on people show that the HPA axis is activated in different ways during chronic stress depending on the type of stressor, the person's response to the stressor and other factors. Stressors that threaten physical integrity, are uncontrollable or involve trauma tend to have a high, flat diurnal profile of cortisol release with lower than normal levels of cortisol in the morning and higher than normal levels in the evening, resulting in a high overall level of cortisol release during the day. Controllable stressors on the other hand tend to produce higher than normal morning cortisol. Stress hormone release tends to gradually reduce as time passes since the stress occurred. In post-traumatic stress disorder
there appears to be lower than normal cortisol, and it is thought that a blunted hormonal response to stress may predispose a person to develop PTSD.
Conditions:
limbic-hypothalamic-pituitary-adrenal axis (LHPA axis) and, occasionally, as the hypothalamic-pituitary-adrenal-gonadotropic axis, is a complex set of direct influences and feedback
Feedback
Feedback describes the situation when output from an event or phenomenon in the past will influence an occurrence or occurrences of the same Feedback describes the situation when output from (or information about the result of) an event or phenomenon in the past will influence an occurrence or...
interactions among the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
, the pituitary gland
Pituitary gland
In vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g , in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold...
(a pea-shaped structure located below the hypothalamus), and the adrenal (also called "suprarenal") glands (small, conical organs on top of the kidneys).
The interactions among these organs constitute the HPA axis, a major part of the neuroendocrine system
Neuroendocrinology
Neuroendocrinology is the study of the extensive interactions between the nervous system and the endocrine system, including the biological features of the cells that participate, and how they functionally communicate...
that controls reactions to stress
Stress (medicine)
Stress is a term in psychology and biology, borrowed from physics and engineering and first used in the biological context in the 1930s, which has in more recent decades become commonly used in popular parlance...
and regulates many body processes, including digestion
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....
, the immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
, mood and emotions, sexuality, and energy storage and expenditure. A wide variety of species, from the most ancient organisms to humans, share components of the HPA axis. It is the common mechanism for interactions among glands, hormones, and parts of the midbrain that mediate the general adaptation syndrome (GAS).
Anatomy
The key elements of the HPA axis are:- The paraventricular nucleusParaventricular nucleusThe paraventricular nucleus is a neuronal nucleus in the hypothalamus. It contains multiple subpopulations of neurons that are activated by a variety of stressful and/or physiological changes. Many PVN neurons project directly to the posterior pituitary where they release oxytocin or vasopressin...
of the hypothalamusHypothalamusThe Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
, which contains neuroendocrine neurons that synthesize and secrete vasopressinVasopressinArginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone , is a neurohypophysial hormone found in most mammals, including humans. Vasopressin is a peptide hormone that controls the reabsorption of molecules in the tubules of the kidneys by affecting the tissue's...
and corticotropin-releasing hormoneCorticotropin-releasing hormoneCorticotropin-releasing hormone , originally named corticotropin-releasing factor , and also called corticoliberin, is a polypeptide hormone and neurotransmitter involved in the stress response...
(CRH). These two peptides regulate:- The anterior lobe of the pituitary glandPituitary glandIn vertebrate anatomy the pituitary gland, or hypophysis, is an endocrine gland about the size of a pea and weighing 0.5 g , in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity covered by a dural fold...
. In particular, CRH and vasopressin stimulate the secretion of adrenocorticotropic hormoneAdrenocorticotropic hormoneAdrenocorticotropic hormone , also known as 'corticotropin', 'Adrenocorticotrophic hormone', is a polypeptide tropic hormone produced and secreted by the anterior pituitary gland. It is an important component of the hypothalamic-pituitary-adrenal axis and is often produced in response to biological...
(ACTH), once known as corticotropin. ACTH in turn acts on: - the adrenal corticesAdrenal cortexSituated along the perimeter of the adrenal gland, the adrenal cortex mediates the stress response through the production of mineralocorticoids and glucocorticoids, including aldosterone and cortisol respectively. It is also a secondary site of androgen synthesis.-Layers:Notably, the reticularis in...
, which produce glucocorticoidGlucocorticoidGlucocorticoids are a class of steroid hormones that bind to the glucocorticoid receptor , which is present in almost every vertebrate animal cell...
hormones (mainly cortisolCortisolCortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...
in humans) in response to stimulation by ACTH. Glucocorticoids in turn act back on the hypothalamus and pituitary (to suppress CRH and ACTH production) in a negative feedback cycle.
- The anterior lobe of the pituitary gland
CRH and vasopressin are released from neurosecretory nerve terminals at the median eminence
Median eminence
The median eminence is part of the inferior boundary for the hypothalamus part of the human brain. A small swelling on the tuber cinereum posterior to the infundibulum - atop the pituitary stalk - the median eminence lies in the area roughly bounded on its posterolateral region by the cerebral...
. CRH is transported to the anterior pituitary through the portal blood vessel system of the hypophyseal stalk and vasopressin is transported by axonal transport to the posterior pituitary. There, CRH and vasopressin act synergistically to stimulate the secretion of stored ACTH from corticotrope cells. ACTH is transported by the blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
to the adrenal cortex
Adrenal cortex
Situated along the perimeter of the adrenal gland, the adrenal cortex mediates the stress response through the production of mineralocorticoids and glucocorticoids, including aldosterone and cortisol respectively. It is also a secondary site of androgen synthesis.-Layers:Notably, the reticularis in...
of the adrenal gland
Adrenal gland
In mammals, the adrenal glands are endocrine glands that sit atop the kidneys; in humans, the right suprarenal gland is triangular shaped, while the left suprarenal gland is semilunar shaped...
, where it rapidly stimulates biosynthesis of corticosteroid
Corticosteroid
Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex. Corticosteroids are involved in a wide range of physiologic systems such as stress response, immune response and regulation of inflammation, carbohydrate metabolism, protein catabolism, blood electrolyte...
s such as cortisol from cholesterol
Cholesterol
Cholesterol is a complex isoprenoid. Specifically, it is a waxy steroid of fat that is produced in the liver or intestines. It is used to produce hormones and cell membranes and is transported in the blood plasma of all mammals. It is an essential structural component of mammalian cell membranes...
. Cortisol is a major stress hormone and has effects on many tissues in the body, including on the brain. In the brain, cortisol acts at two types of receptor - mineralocorticoid receptor
Mineralocorticoid receptor
The mineralocorticoid receptor , also known as the aldosterone receptor or nuclear receptor subfamily 3, group C, member 2, is a protein that in humans is encoded by the NR3C2 gene that is located on chromosome 4q31.1-31.2.MR is a receptor with high affinity for mineralocorticoids...
s and glucocorticoid receptors, and these are expressed by many different types of neurons. One important target of glucocorticoids is the hypothalamus
Hypothalamus
The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
, which is a major controlling centre of the HPA axis.
Vasopressin can be thought of as "water conservation hormone" and is also known as "antidiuretic hormone." It is released when the body is dehydrated and has potent water-conserving effects on the kidney. It is also a potent vasoconstrictor.
Important to the function of the HPA axis are some of the feedback loops:
- Cortisol produced in the adrenal cortex will negatively feedback to inhibit both the hypothalamus and the pituitary gland. This reduces the secretion of CRH and vasopressin, and also directly reduces the cleavage of proopiomelanocortinProopiomelanocortinPro-opiomelanocortin is a precursor polypeptide with 241 amino acid residues. POMC is synthesized from the 285-amino acid long polypeptide precursor, pre-pro-opiomelanocortin , by the removal of a 44-amino acid long signal peptide sequence during translation.The POMC gene is located on chromosome...
(POMC) into ACTH and β-endorphins. - EpinephrineEpinephrineEpinephrine is a hormone and a neurotransmitter. It increases heart rate, constricts blood vessels, dilates air passages and participates in the fight-or-flight response of the sympathetic nervous system. In chemical terms, adrenaline is one of a group of monoamines called the catecholamines...
and norepinephrineNorepinephrineNorepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...
are produced by the adrenal medulla through sympathetic stimulation and the local effects of cortisol (upregulation enzymes to make E/NE). E/NE will positively feedback to the pituitary and increase the breakdown of POMCs into ACTH and β-endorphins.
Function
Release of CRH from the hypothalamus is influenced by stressStress (medicine)
Stress is a term in psychology and biology, borrowed from physics and engineering and first used in the biological context in the 1930s, which has in more recent decades become commonly used in popular parlance...
, by blood levels of cortisol and by the sleep
Sleep
Sleep is a naturally recurring state characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles. It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, and is more easily reversible than...
/wake cycle. In healthy individuals, cortisol rises rapidly after wakening, reaching a peak within 30–45 minutes. It then gradually falls over the day, rising again in late afternoon. Cortisol levels then fall in late evening, reaching a trough during the middle of the night. An abnormally flattened circadian cortisol cycle has been linked with chronic fatigue syndrome
Chronic fatigue syndrome
Chronic fatigue syndrome is the most common name used to designate a significantly debilitating medical disorder or group of disorders generally defined by persistent fatigue accompanied by other specific symptoms for a minimum of six months, not due to ongoing exertion, not substantially...
, insomnia
Insomnia
Insomnia is most often defined by an individual's report of sleeping difficulties. While the term is sometimes used in sleep literature to describe a disorder demonstrated by polysomnographic evidence of disturbed sleep, insomnia is often defined as a positive response to either of two questions:...
and burnout
Burnout (psychology)
Burnout is a psychological term for the experience of long-term exhaustion and diminished interest. Research indicates general practitioners have the highest proportion of burnout cases; according to a recent Dutch study in Psychological Reports, no less than 40% of these experienced high levels of...
.
Anatomical connections between brain areas such as the amygdala
Amygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
, hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
, and hypothalamus facilitate activation of the HPA axis. Sensory information arriving at the lateral aspect of the amygdala
Amygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
is processed and conveyed to the central nucleus, which projects to several parts of the brain involved in responses to fear. At the hypothalamus, fear-signaling impulses activate both the sympathetic nervous system
Sympathetic nervous system
The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...
and the modulating systems of the HPA axis.
Increased production of cortisol mediates alarm reactions to stress, facilitating an adaptive phase of a general adaptation syndrome in which alarm reactions including the immune response are suppressed, allowing the body to attempt countermeasures.
Glucocorticoids have many important functions, including modulation of stress reactions, but in excess they can be damaging. Atrophy
Atrophy
Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations , poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply to the target organ, disuse or lack of exercise or disease intrinsic to the tissue itself...
of the hippocampus in humans and animals exposed to severe stress is believed to be caused by prolonged exposure to high concentrations of glucocorticoid
Glucocorticoid
Glucocorticoids are a class of steroid hormones that bind to the glucocorticoid receptor , which is present in almost every vertebrate animal cell...
s. Deficiencies of the hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
may reduce the memory resources available to help a body formulate appropriate reactions to stress.
Stress and disease
The HPA axis is involved in the neurobiology of mood disorderMood disorder
Mood disorder is the term designating a group of diagnoses in the Diagnostic and Statistical Manual of Mental Disorders classification system where a disturbance in the person's mood is hypothesized to be the main underlying feature...
s and functional illnesses, including anxiety disorder
Anxiety disorder
Anxiety disorder is a blanket term covering several different forms of abnormal and pathological fear and anxiety. Conditions now considered anxiety disorders only came under the aegis of psychiatry at the end of the 19th century. Gelder, Mayou & Geddes explains that anxiety disorders are...
, bipolar disorder
Bipolar disorder
Bipolar disorder or bipolar affective disorder, historically known as manic–depressive disorder, is a psychiatric diagnosis that describes a category of mood disorders defined by the presence of one or more episodes of abnormally elevated energy levels, cognition, and mood with or without one or...
, insomnia
Insomnia
Insomnia is most often defined by an individual's report of sleeping difficulties. While the term is sometimes used in sleep literature to describe a disorder demonstrated by polysomnographic evidence of disturbed sleep, insomnia is often defined as a positive response to either of two questions:...
, post-traumatic stress disorder
Post-traumatic stress disorder
Posttraumaticstress disorder is a severe anxiety disorder that can develop after exposure to any event that results in psychological trauma. This event may involve the threat of death to oneself or to someone else, or to one's own or someone else's physical, sexual, or psychological integrity,...
, borderline personality disorder
Borderline personality disorder
Borderline personality disorder is a personality disorder described as a prolonged disturbance of personality function in a person , characterized by depth and variability of moods.The disorder typically involves unusual levels of instability in mood; black and white thinking, or splitting; the...
, ADHD, major depressive disorder, burnout
Burnout (psychology)
Burnout is a psychological term for the experience of long-term exhaustion and diminished interest. Research indicates general practitioners have the highest proportion of burnout cases; according to a recent Dutch study in Psychological Reports, no less than 40% of these experienced high levels of...
, chronic fatigue syndrome
Chronic fatigue syndrome
Chronic fatigue syndrome is the most common name used to designate a significantly debilitating medical disorder or group of disorders generally defined by persistent fatigue accompanied by other specific symptoms for a minimum of six months, not due to ongoing exertion, not substantially...
, fibromyalgia
Fibromyalgia
Fibromyalgia is a medical disorder characterized by chronic widespread pain and allodynia, a heightened and painful response to pressure. It is an example of a diagnosis of exclusion...
, irritable bowel syndrome
Irritable bowel syndrome
Irritable bowel syndrome is a diagnosis of exclusion. It is a functional bowel disorder characterized by chronic abdominal pain, discomfort, bloating, and alteration of bowel habits in the absence of any detectable organic cause. In some cases, the symptoms are relieved by bowel movements...
, and alcoholism
Alcoholism
Alcoholism is a broad term for problems with alcohol, and is generally used to mean compulsive and uncontrolled consumption of alcoholic beverages, usually to the detriment of the drinker's health, personal relationships, and social standing...
. Antidepressants, which are routinely prescribed for many of these illnesses, serve to regulate HPA axis function.
Experimental studies have investigated many different types of stress, and their effects on the HPA axis in many different circumstances. Stressors can be of many different types—in experimental studies in rats, a distinction is often made between "social stress" and "physical stress", but both types activate the HPA axis, though via different pathways. Several monoamine neurotransmitters are important in regulating the HPA axis, especially dopamine
Dopamine
Dopamine is a catecholamine neurotransmitter present in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this substituted phenethylamine functions as a neurotransmitter, activating the five known types of dopamine receptors—D1, D2, D3, D4, and D5—and their...
, serotonin
Serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
and norepinephrine
Norepinephrine
Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...
(noradrenaline). There is evidence that an increase in oxytocin
Oxytocin
Oxytocin is a mammalian hormone that acts primarily as a neuromodulator in the brain.Oxytocin is best known for its roles in sexual reproduction, in particular during and after childbirth...
, resulting for instance from positive social interactions, acts to suppress the HPA axis and thereby counteracts stress, promoting positive health effects such as wound healing.
The HPA axis is a feature of mammals as well as other vertebrates. For example, biologists studying stress in fish showed that social subordination leads to chronic stress, related to reduced aggressive
Aggression
In psychology, as well as other social and behavioral sciences, aggression refers to behavior between members of the same species that is intended to cause humiliation, pain, or harm. Ferguson and Beaver defined aggressive behavior as "Behavior which is intended to increase the social dominance of...
interactions, to lack of control
Impulsivity
Impulsivity is a personality trait characterized by the inclination of an individual to initiate behavior without adequate forethought as to the consequences of their actions, acting on the spur of the moment. Eysenck and Eysenck related impulsivity to risk-taking, lack of planning, and making up...
and to the constant threat imposed by dominant fish. Serotonin (5HT) appeared to be the active neurotransmitter involved in mediating stress responses, and increases in serotonin are related to increased plasma
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
α-MSH levels, which causes skin darkening (a social signal in salmon
Salmon
Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...
oid fish), activation of the HPA axis, and inhibition of aggression. Inclusion of the amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
L-tryptophan, a precursor of 5HT, in the feed of rainbow trout
Rainbow trout
The rainbow trout is a species of salmonid native to tributaries of the Pacific Ocean in Asia and North America. The steelhead is a sea run rainbow trout usually returning to freshwater to spawn after 2 to 3 years at sea. In other words, rainbow trout and steelhead trout are the same species....
made the trout less aggressive and less responsive to stress. However, the study mentions that plasma cortisol was not affected by dietary L-tryptophan.
Studies on people show that the HPA axis is activated in different ways during chronic stress depending on the type of stressor, the person's response to the stressor and other factors. Stressors that threaten physical integrity, are uncontrollable or involve trauma tend to have a high, flat diurnal profile of cortisol release with lower than normal levels of cortisol in the morning and higher than normal levels in the evening, resulting in a high overall level of cortisol release during the day. Controllable stressors on the other hand tend to produce higher than normal morning cortisol. Stress hormone release tends to gradually reduce as time passes since the stress occurred. In post-traumatic stress disorder
Post-traumatic stress disorder
Posttraumaticstress disorder is a severe anxiety disorder that can develop after exposure to any event that results in psychological trauma. This event may involve the threat of death to oneself or to someone else, or to one's own or someone else's physical, sexual, or psychological integrity,...
there appears to be lower than normal cortisol, and it is thought that a blunted hormonal response to stress may predispose a person to develop PTSD.
See also
- Hypothalamic-pituitary-gonadal axisHypothalamic-pituitary-gonadal axisThe hypothalamic–pituitary–gonadal axis refers to the effects of the hypothalamus, pituitary gland, and gonads as if these individual endocrine glands were a single entity as a whole...
- NeuroendocrinologyNeuroendocrinologyNeuroendocrinology is the study of the extensive interactions between the nervous system and the endocrine system, including the biological features of the cells that participate, and how they functionally communicate...
- HypothalamusHypothalamusThe Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
- StressStress (medicine)Stress is a term in psychology and biology, borrowed from physics and engineering and first used in the biological context in the 1930s, which has in more recent decades become commonly used in popular parlance...
- Allostatic loadAllostatic loadThe term allostatic load, coined by McEwen and Stellar in 1993, is defined as the physiological consequences of chronic exposure to fluctuating or heightened neural or neuroendocrine response that results from repeated or chronic stress....
- ACTH stimulation testACTH stimulation testThe ACTH stimulation test is a medical test usually ordered and interpreted by endocrinologists to assess the functioning of the adrenal glands stress response by measuring the adrenal response to adrenocorticotropic hormone...
- Dexamethasone suppression testDexamethasone suppression testThe dexamethasone suppression test is designed to diagnose and differentiate among the various types of Cushing's syndrome and other hypercortisol states.It has also been used in the research of depression.-Physiology:...
- GlucocorticoidGlucocorticoidGlucocorticoids are a class of steroid hormones that bind to the glucocorticoid receptor , which is present in almost every vertebrate animal cell...
s - CortisolCortisolCortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...
- DexamethasoneDexamethasoneDexamethasone is a potent synthetic member of the glucocorticoid class of steroid drugs. It acts as an anti-inflammatory and immunosuppressant...
- Hydrocortisone
- Cortisol awakening responseCortisol awakening responseThe cortisol awakening response is an increase of about 50% in cortisol levels occurring 20–30 minutes after awakening in the morning in some people. This rise is superimposed upon the late-night rise in cortisol which occurs before awakening...
- Sickness behaviorSickness behaviorthumb|350px|right|[[Michael Peter Ancher|Ancher, Michael]], "The Sick Girl", 1882, [[Statens Museum for Kunst]]Sickness behavior is a coordinated set of adaptive behavioral changes that develop in ill individuals during the course of an infection....
Conditions:
- Adrenal insufficiencyAdrenal insufficiencyAdrenal insufficiency is a condition in which the adrenal glands, located above the kidneys, do not produce adequate amounts of steroid hormones , primarily cortisol, but may also include impaired aldosterone production which regulates sodium, potassium and water retention...
- Addison's diseaseAddison's diseaseAddison’s disease is a rare, chronic endocrine disorder in which the adrenal glands do not produce sufficient steroid hormones...
- Cushing's syndromeCushing's syndromeCushing's syndrome is a hormone disorder caused by high levels of cortisol in the blood. This can be caused by taking glucocorticoid drugs, or by tumors that produce cortisol or adrenocorticotropic hormone or CRH...