The Endocrine System: Hormonal Regulation of Stress Response

The Endocrine System: Hormonal Regulation of Stress Response

Learning Objectives

  • Describe the three stages of the stress response (General Adaptation Syndrome).

  • List the hormones released during short-term stress and describe their hormonal actions.

  • List the major hormones released during long-term stress and describe their hormonal actions.

Introduction to Stress

  • Eustress: Good stress that has a positive effect on the individual.

  • Distress: Bad stress resulting in negative effects on the individual.

  • Stress Response: Body's physical, mental, and emotional reactions to stressors, recognized as part of General Adaptation Syndrome (GAS).

General Adaptation Syndrome (GAS)

  • Phases of GAS:

    • Fight-or-Flight Response: Immediate reaction to stress involving adrenaline and rapid response features.

    • Resistance Reaction: Longer-term physiological response to stressors aimed at restoring homeostasis.

    • Exhaustion: Result of prolonged stress leading to depletion of resources, potentially causing health issues.

The Fight-or-Flight Response

  • Triggered by hypothalamus activation involving:

    • Sympathetic Nervous System activation.

    • Adrenal Medulla: Releases hormones like epinephrine and norepinephrine.

  • Neurosecretory cells in the paraventricular nuclei and supraoptic nuclei are important in signaling.

  • Primary and secondary capillary plexus systems facilitate hormone distribution.

Hormones Involved in the Stress Response

  1. Epinephrine (adrenaline)

  2. Norepinephrine

  3. Cortisol

  4. Insulin-like Growth Factors (IGFs)

  5. Thyroid Hormones

Epinephrine and Norepinephrine Actions

  • Produced by: Adrenal Medulla.

  • Regulated by: Sympathetic Nervous System.

  • Target Tissues: Heart, blood vessels, liver, lungs, digestive organs, etc.

  • Actions:

    • Elevate heart rate (HR), blood pressure (BP), and respiratory rate.

    • Converts glycogen into glucose to provide energy.

Stress Response Feedback Loop: Epinephrine and Norepinephrine

  1. Stressors (distress) activate the brain.

  2. Brain sends signals to sympathetic centers in spinal cord.

  3. Sympathetic nerves trigger adrenal medulla to release epinephrine and norepinephrine.

  4. Epinephrine and norepinephrine cause physiological changes (elevated HR, BP).

  5. Negative feedback loop to regulate levels.

Summary of Epinephrine & Norepinephrine

  • Reviewed in video resources covering the fight-or-flight response.

Cortisol for Stress Response

  • Produced by: Adrenal Cortex.

  • Regulated by: Hypothalamic CRH release triggers anterior pituitary ACTH release.

  • Target Tissues: Liver and adipose tissue.

  • Actions:

    • Lipolysis (fat breakdown).

    • Gluconeogenesis (producing glucose).

    • Protein catabolism (breakdown).

    • Reduces inflammation.

Stress Response Feedback Loop: Cortisol

  1. Stressors (distress) activate the system.

  2. Hypothalamus releases CRH.

  3. CRH stimulates release of ACTH from anterior pituitary.

  4. ACTH stimulates cortisol release from adrenal cortex.

  5. Elevated cortisol results in:

    • Lipolysis.

    • Gluconeogenesis.

    • Protein catabolism.

  6. Triggers negative feedback to regulate cortisol levels.

Summary of Cortisol

  • Explored in video resources discussing the role of cortisol in stress reactions.

Insulin-like Growth Factor (IGF) Actions for Stress

  • Produced by: Liver.

  • Regulated by: Hypothalamic GHRH release, stimulating hGH from the anterior pituitary.

  • Target Tissue: Adipose tissue.

  • Actions:

    • Lipolysis.

    • Glycogenolysis (breakdown of glycogen).

Stress Response Feedback Loop: Insulin-like Growth Factors

  1. Stressors (distress) activate the system.

  2. Hypothalamus releases GHRH.

  3. GHRH stimulates hGH release from anterior pituitary.

  4. hGH increases IGF release from liver.

  5. Elevated IGF levels result in:

    • Lipolysis.

    • Glycogenolysis.

  6. Triggers a negative feedback loop.

Thyroid Hormones for Stress Response

  • Produced by: Thyroid Gland.

  • Regulated by: Hypothalamic TRH release triggers TSH from anterior pituitary.

  • Target Tissue: All cells in the body.

  • Actions:

    • Increased glucose use for ATP production.

Stress Response Feedback Loop: Thyroid Hormones

  1. Stressors (distress) activate the system.

  2. Hypothalamus releases TRH.

  3. TRH triggers TSH release from anterior pituitary.

  4. TSH stimulates T3 and T4 release from thyroid gland.

  5. Elevated T3 and T4 increase glucose use for ATP production.

  6. Triggers a negative feedback loop.

Summary of Thyroid Hormones

  • Reviewed in video resources detailing thyroid functions and stress effects.

Comprehensive Stress Summary

  • Eustress: Good stress beneficial to growth and performance.

  • Distress: Adverse stress leading to health issues.

  • Stages of Stress Response: General Adaptation Syndrome (GAS) includes fight-or-flight response, resistance reaction, and exhaustion.

  • Key Hormones Involved:

    • Epinephrine and Norepinephrine: Immediate stress response resulting in heightened alertness and energy.

    • Cortisol: Sustained response with metabolic effects.

    • Insulin-like Growth Factors: Mediate growth responses under stress conditions.

    • Thyroid Hormones: General increase in metabolic activity across tissues.

Additional Hormones Affecting Blood Pressure

EPO – More Blood Cells, More Blood Pressure

  • Produced: Kidney.

  • Regulated by: Drop in blood pressure (BP) and oxygen.

  • Target Tissue: Red bone marrow.

  • Action: Promotes RBC production and increases the O2 carrying capacity of blood.

Feedback Loop of EPO for Blood Pressure

  1. Drop in BP triggers EPO release from the kidneys.

  2. EPO travels through bloodstream to red bone marrow.

  3. EPO stimulates RBC production.

  4. Increased RBC count raises BP through elevated peripheral resistance.

  5. Triggers a negative feedback mechanism.

Angiotensin II – The Potent Vasoconstrictor

  • Produced primarily in the bloodstream.

  • Regulated by: Release of renin from kidneys due to low BP.

  • Target Tissue: Smooth muscle in blood vessels.

  • Actions: Causes vasoconstriction and elevates blood pressure (BP).

Feedback Loop of Angiotensin II for BP Regulation

  1. Drop in BP detected by the kidneys.

  2. Kidneys release renin into the bloodstream.

  3. Renin converts angiotensinogen to angiotensin I.

  4. Angiotensin I is converted to angiotensin II by ACE.

  5. Angiotensin II causes vasoconstriction and increases BP.

  6. Triggers a negative feedback loop.

Aldosterone – The Salt Hormone

  • Produced: Adrenal gland.

  • Regulated by: Positive feedback from angiotensin II and low BP.

  • Target Tissue: Kidney nephron.

  • Action: Reclaims Na+ (and indirectly water) to elevate BP.

Feedback Loop of Aldosterone

  1. Na+ levels drop, leading to a BP drop.

  2. Drop detected by kidneys prompting the Angiotensin II cycle.

  3. Angiotensin II triggers aldosterone release from the adrenals.

  4. Aldosterone acts to reclaim Na+ and raises BP through water retention.

  5. Triggers a negative feedback loop.

Antidiuretic Hormone (ADH) – The Pee Hormone

  • Produced: Posterior pituitary.

  • Regulated by: Drop in BP and during sleep.

  • Target Tissue: Kidney nephron.

  • Action: Reabsorbs H2O to increase BP.

Feedback Loop of ADH for BP Control

  1. Blood pressure decline is detected.

  2. Release of renin triggers the RAA pathway.

  3. Aldosterone influences the posterior pituitary to release ADH.

  4. ADH acts in the kidneys to reclaim water, raising BP.

  5. Triggers a negative feedback loop.

Atrial Natriuretic Peptides (ANP) – The Counter Regulation for Higher BP

  • Produced: Heart (atrium).

  • Regulated by: Elevated BP detected by mechanoreceptors.

  • Target Tissue: Kidney nephron.

  • Actions: Promotes secretion of Na+ (and indirectly water) to decrease BP.

Feedback Loop of ANP for BP Regulation

  1. Increased stretch of the atrial wall from high BP.

  2. Release of Atrial Natriuretic Peptide.

  3. Increase Na+ release from kidneys.

  4. Decreased Na+ leads to reduced H2O reabsorption, lowering BP.

  5. Negative feedback occurs as BP decreases.

Summary of Insulin and Glucagon Hormonal Actions

Insulin (Produced by Beta Cells of Pancreas)

  • Regulated by: Elevated blood glucose levels (nutrient abundance).

  • Target Tissue: Liver, skeletal muscle, adipose tissue.

  • Action: Absorbs glucose, fatty acids, and amino acids from the bloodstream for storage, lowering blood glucose levels.

Feedback Loop of Insulin

  1. Blood sugar rises post-meal.

  2. Pancreas releases insulin.

  3. Insulin facilitates glucose absorption by target tissues.

  4. Decreasing glucose levels trigger negative feedback.

Glucagon (Produced by Alpha Cells of Pancreas)

  • Regulated by: Drop in blood glucose (<100 mg/dL) or rising amino acid levels.

  • Target Tissue: Liver and adipose tissue.

  • Action: Stimulates gluconeogenesis and glycogenolysis to raise blood glucose levels.

Feedback Loop of Glucagon

  1. Blood sugar drops between meals.

  2. Pancreas releases glucagon.

  3. Glucagon triggers glucose release from liver.

  4. Elevated glucose levels trigger negative feedback.

Calcium Regulation Hormones

Calcitonin (From Thyroid Gland)

  • Produced: Thyroid gland.

  • Regulated by: Calcium intake, hGH, and stress on bone.

  • Target Tissue: Bone, specifically osteoblasts.

  • Action: Promotes calcium deposition into bone, leading to growth.

The Feedback Loop of Calcitonin

  1. Elevated calcium levels or bone stress.

  2. Release of calcitonin from thyroid.

  3. Stimulates osteoblastic activity in bone.

  4. Increased calcium incorporation into the bone.

  5. Triggers a negative feedback when calcium levels stabilize.

Parathyroid Hormone (PTH)

  • Produced: Parathyroid glands.

  • Regulated by: Decrease in blood calcium levels.

  • Target Tissues: Bone (osteoclasts), kidneys, and small intestine.

  • Actions: Increases calcium reabsorption in kidneys, enhances calcium absorption in the intestine, and releases calcium from bones.

The Feedback Loop for PTH

  1. Drop in serum calcium detected.

  2. PTH released from the parathyroid gland.

  3. Stimulates osteoclast activity in bone and reabsorption in kidneys.

  4. Increase in serum calcium levels.

  5. Negative feedback mechanism when calcium levels return to normal.

Calcitriol Action on Calcium Regulation

  • Produced: Kidneys.

  • Regulated by: Decrease in blood calcium levels.

  • Target Tissue: Small intestine.

  • Action: Increases intestinal absorption of calcium.

Feedback Loop for Calcitriol

  1. Serum calcium levels drop.

  2. Calcitriol (active Vitamin D) is released from kidneys.

  3. Enhances calcium absorption in the intestine.

  4. Increased calcium levels initiate negative feedback.

Thymosin – Immune Function Regulation

  • Produced by: Thymus gland.

  • Regulated by: Immune response.

  • Target Tissues: T-cell lymphocytes.

  • Action: Stimulates T-cell development and activity.

The Feedback Loop of Thymosin

  1. Immune response is triggered.

  2. Thymosin released from thymus gland.

  3. Increased production and activation of T-cells.

  4. Feedback regulation via T-cell effectiveness in immune response.

Thyroid Cancer Overview

  • Thyroid Gland Characteristics:

    • Butterfly-shaped gland located anterior to C6.

    • Typically presents as a palpable nodule.

  • Treatment Options:

    • Surgical removal of the thyroid.

    • Use of radioactive iodine.

    • Synthetic thyroid hormone post-surgery as needed.