The endocrine and autonomic systems and stress response L6 Flashcards
What is the hypothalamus-pituitary axis?
Hypothalamic nuclei, infundibulum, posterior pituitary, anterior pituitary
What the veins between the hypothalamus and the anterior pituitary?
The hypophyseal portal veins (capillaries - portal vein - capillaries)
How many hormones does the hypothalamus have?
9 hormones (releasing and inhibiting hormones to control pituitary)
How many hormones does the pituitary have?
7 hormones (controlling endocrine organs)
What do the hypothalamus and pituitary do together?
Regulate growth, development, metabolism, homeostasis
Process of hormones through the hypothalamus-pituitary axis
From hypothalamic neurosecretory cell -> Releasing and inhibitory hormones released from axon termini -> + blood flow ->
hormones travel through portal vein to secondary plexus then into pituitary target cells
Cross section of the adrenal gland
Capsule, cortex, medulla
What happens in the adrenal medulla?
Sympathetic pre-ganglion neurones that come from the spinal cord and innervate the adrenal medulla (which consists of axon termini). This triggers the cells in the adrenal medulla to release two hormones called epinephrine and norepinephrine, then enter the bloodstream and circulate around the body, which therefore enhances our rapid sympathetic activation.
What is the first stage of the alarm (fight or flight) response?
- Immediate burst
- Sympathetic autonomic activation
[ - mobilising resources for immediate physical activity, glucose and oxygen, alertness and activity, ward off danger or flee ] - Sustained through action of adrenal medulla
What is the second stage of the alarm (fight or flight) response?
Reduce tissue damage (adrenal cortex)
A stress hormone that the adrenal cortex produces
Mineralocorticoids ( eg. aldosterone)
What are mineralocorticoids stimulated by?
Increased K+ and angiotensin II in blood
What are the principal actions of mineralocorticoids?
- Increase Na+ and water and decrease K+ in blood
=> Increase blood volume and pressure
Another hormone that the adrenal cortex produces
Glucocorticoids (eg. cortisol)
What are glucocorticoids stimulated by?
ACTH from pituitary (CRH from hypothalamus)
Actions of Cortisol
- Increase protein breakdown (especially in muscles) = Amino acids available for new protein synthesis
- Gluconeogenesis in liver = Glucose available for ATP production
- Lipolysis in adipose tissue = Triglyceride and fatty acid availability
- Altered blood vessel sensitivity to vasoconstriction = Blood pressure increase
- Anti-inflammatory to limit tissue damage = Slower tissue repair and wound healing
- Alter immune responsiveness = Increased susceptibility to some infections
The negative feedback control of cortisol production
The corticotropin-releasing hormone from the hypothalamus triggers the anterior pituitary to release adrenocorticotropic hormone (ACTH) goes through the bloodstream, stimulates the adrenal cortex to release cortisol.
Elevated cortisol then inhibits release of ATCH by anterior pituitary corticotrophs + elevated cortisol inhibits relase of CRH by hypothalamic neurosecretory cells
Stages of stress response
Alarm response:
- Immediate burst
- Sympathetic activation and adrenal medulla
Resistance reaction:
- Slower, longer lasting
- Associated with hypothalamus, pituitary and adrenal cortex
Stress response in a nutshell
Stress Response Phases:
CRH, ACTH, and the Hypothalamic-Pituitary-Adrenal (HPA) Axis:
CRH (Corticotropin-releasing hormone) is released by the hypothalamus in the brain in response to stress. This hormone stimulates the anterior pituitary gland to release ACTH (adrenocorticotropic hormone).
ACTH then travels through the bloodstream to the adrenal cortex of the adrenal glands, where it stimulates the production of cortisol.
This process is the first step in preparing the body for a stressor.
Sympathetic Nervous System Activation:
The sympathetic nervous system is activated almost immediately in response to stress and acts on the adrenal medulla (the inner part of the adrenal glands) to release epinephrine and norepinephrine (also known as adrenaline and noradrenaline).
These hormones are responsible for the immediate alarm response (often referred to as the “fight or flight” response).
Two Main Phases of the Stress Response:
1. Alarm Response (Fight or Flight):
When the sympathetic nervous system activates the adrenal medulla, epinephrine and norepinephrine are released.
This triggers an immediate physical response, preparing the body to deal with the stressor. The alarm response includes:
Pounding heart (increased heart rate)
Cold sweat
Pale skin
Goosebumps (goose flesh)
Rapid breathing
These reactions help prepare the body to either confront the danger (fight) or flee from it (flight). Blood flow is diverted to muscles and vital organs, and energy resources are mobilized.
2. Resistance Reaction:
This phase involves the adrenal cortex releasing cortisol in response to ACTH.
Cortisol helps sustain the body’s response to long-term stress by providing energy and maintaining homeostasis. The resistance reaction includes:
Increased glucose, fatty acids, and amino acids: Cortisol ensures that energy is available by promoting the release of glucose (via gluconeogenesis), fats, and proteins.
Elevated blood pressure: Cortisol helps maintain proper blood pressure to ensure adequate blood flow to vital organs.
Reduced inflammation: Cortisol has anti-inflammatory effects, preventing excessive tissue damage.
Altered immunity: Prolonged high cortisol levels can suppress the immune system, making the body more susceptible to infections over time.
Neuro-immune links
Cortisol and other hormones help modulate the immune system, particularly during stress, preventing overactivity but potentially weakening immunity if levels remain high.
Autonomic nerves play a role in controlling immune functions, with the sympathetic nervous system stimulating immune responses and the parasympathetic system (via the vagus nerve) often dampening excessive inflammation.
Cytokines are immune system messengers that influence both immune cells and the nervous system, ensuring coordination between these systems during responses to infection or injury.
The image you’ve shared highlights the body’s short-term remedial action during a threat response, commonly known as the fight-or-flight reaction. This response is mediated by the sympathetic nervous system and the release of stress hormones (like adrenaline and cortisol) to deal with immediate danger.
Threat System Arousal:
In response to a perceived threat, the body prioritizes systems that are critical for immediate survival:
Blood (Energy):
Blood flow is redirected to major muscle groups and vital organs that need energy to deal with the threat. This ensures that muscles and the brain have enough glucose and oxygen to respond quickly.
Muscle (Motor Response):
Muscles are primed to either fight or flee, which requires immediate motor activation. Increased blood flow to muscles helps them perform at their peak.
Vigilance (Sensory):
Sensory systems (like eyesight and hearing) become heightened to detect and respond to any potential danger. The brain becomes hyper-focused on the threat, enhancing vigilance and alertness to keep you safe.
Dampen Unnecessary Functions:
To conserve energy for the systems needed in the immediate threat, other functions that are not essential in the short term are dampened:
Digestion:
Digestive processes are slowed or halted because digesting food is not critical during a fight-or-flight situation. The body conserves energy that would otherwise be spent on processing food.
Immunity:
Immune system activity is reduced during acute stress, as resources are focused on immediate survival rather than fighting infections or inflammation. This is why chronic stress can weaken immunity over time, but in the short term, the body prioritizes the immediate need for energy and blood flow.
Overall Concept:
This diagram reflects how the body quickly shifts resources to prioritize survival during a short-term stressor or threat. The systems essential for responding to danger (like muscle activation and heightened senses) are enhanced, while less immediate systems (like digestion and immunity) are suppressed until the threat is resolved.
This response is meant to be short-term, after which the body should return to normal functioning. However, prolonged or chronic stress can lead to long-term suppression of important functions like immunity and digestion, leading to health problems.
Function of eustress and distress
Habitually Hostile People:
People who frequently experience anger, hostility, or stress tend to have their sympathetic nervous system (SNS) chronically activated. This can have harmful effects on their cardiovascular system over time.
Chronic Sympathetic Activation:
The sympathetic nervous system is responsible for the “fight or flight” response, which increases heart rate, blood pressure, and energy mobilization during stress.
In habitually hostile individuals, the SNS is constantly activated, leading to sustained stress on the heart and blood vessels.
Heart Working Harder:
With chronic sympathetic activation, the heart has to work harder to pump blood. This can lead to increased wear and tear on the heart over time, contributing to heart disease.
Blood Flow to Capillaries Constricted:
One of the effects of SNS activation is the constriction of blood vessels, especially in the capillaries (smallest blood vessels). This reduces blood flow to tissues, forcing the heart to work even harder to maintain circulation.
Higher Blood Pressure:
Chronic high blood pressure (hypertension) is a common result of long-term sympathetic activation. Increased pressure in the blood vessels places additional strain on the heart and can damage blood vessels, leading to a higher risk of cardiovascular disease.
Greater Risk of Cardiac Infarct (Heart Attack):
Over time, the combination of a hard-working heart, constricted blood vessels, and elevated blood pressure increases the risk of developing heart disease, particularly myocardial infarction (heart attack).
Habitual hostility and chronic stress are well-documented risk factors for heart attacks due to the ongoing strain on the cardiovascular system.
Summary:
Chronic hostility or frequent anger keeps the sympathetic nervous system activated, leading to increased heart workload, high blood pressure, and constricted blood vessels. Over time, these factors elevate the risk of heart disease and heart attacks.
