Altered Hormone Function and the General Adaptation Syndrome

Mechanisms of Altered Hormone Function

• Hypofunction (Hormone Deficit): This condition is fundamentally associated with a deficit in hormone production. Various mechanisms can lead to hypofunction:

  • Congenital Defects: These may result in the total absence of a gland or significantly impaired development during the fetal stage.

  • Enzymatic Deficiency: The absence of specific enzymes required for hormone synthesis prevents the gland from producing the necessary active chemicals.

  • Glandular Destruction: The gland may be physically destroyed or rendered non-functional by disruption in blood flow, infections, inflammatory processes, autoimmune responses, or neoplastic (cancerous) growth.

  • Functional Decline and Atrophy: Glandular function naturally declines with aging. Alternatively, a gland may atrophy as a direct result of drug therapy or for idiopathic (unknown) reasons.

  • Receptor and Sensitivity Issues: Hormone receptors may be entirely absent, the binding process between receptors and hormones may be defective, or the target cell's internal responsiveness to the hormone may be impaired.

  • Biologically Inactive Hormone: The gland may synthesize and secrete a hormone that lacks the necessary biological activity to trigger a response.

  • Antibody Destruction: Circulating antibodies may target and destroy active hormones before they can reach and act upon target tissues.

• Hyperfunction (Hormone Excess): This is characterized by excessive hormone production and secretion.

  • Excessive Stimulation: Over-stimulation of an endocrine gland can lead to hyperplasia (increase in cell number), resulting in hypersecretion.

  • Ectopic Hormone Production: Hormone-producing tumors located outside the normal endocrine pathways (ectopic) can secrete hormones autonomously without normal regulatory control.

• Hormone Resistance: This occurs when target cells fail to respond to a hormone despite its presence.

  • Receptor Defects: Receptors are either absent or have defective binding capabilities.

  • Intracellular Responsiveness: The internal cell mechanisms triggered by a hormone are impaired, preventing the intended physiological effect.

Classification of Endocrine Disorders

• Primary Defects/Disorders:

  • These originate directly within the target gland responsible for producing the hormone in question.

  • Example: A total thyroidectomy (the surgical removal of the thyroid gland) results in a primary deficiency of thyroid hormones because the source organ is gone.

• Secondary Defects/Disorders:

  • The target gland itself is essentially normal and functional; however, its activity is altered because it is receiving inadequate or excessive stimulation from the pituitary system.

  • Example: The removal or destruction of the pituitary gland eliminates the production of ACTH, which in turn leads to a secondary deficiency of the adrenal cortex.

• Tertiary Defects/Disorders:

  • These result specifically from hypothalamic dysfunction.

  • Since the hypothalamus regulates the pituitary, which then regulates the target organ, a tertiary defect impacts the entire signaling chain (both pituitary and target organ).

Diagnostic Considerations and Sources of Damage

• Key Diagnostic Questions for Altered Hormone Function:

  1. Is there impairment within the hypothalamic-pituitary axis?

  2. Is there impairment of the specific endocrine gland?

  3. Is the hormone production/secretion too high or too low?

  4. Is the hormone produced currently active?

  5. Is the receptor binding adequate at the target site?

  6. Is the target cell responding appropriately to the hormone?

  7. Is the negative feedback loop mechanism impaired?

  8. Is the hormone being produced by an ectopic source?

  9. Is hormone metabolism (inactivation) or elimination by the body impaired?

• Damage to the Hypothalamic-Pituitary Axis (HPA):

  • Sources of Damage: Genetic defects, degeneration, atrophy, infection, inflammation, neoplasms (tumors), hypoxia, hemorrhage, radiation, or medication.

  • Terminology:

    • Hypopituitarism: A generic term indicating the decreased secretion of one or more pituitary hormones.

    • Hyperpituitarism: An excess of pituitary hormone secretion.

    • Panhypopituitarism: Indicates a comprehensive decrease in ALL pituitary hormones.

• Damage to Endocrine Glands:

  • Causes: Autoimmune conditions, genetic defects, atrophy, inflammation, and medication.

  • Manifestations: The gland becomes incapable of responding to neuroendocrine messages; hormone secretion is decreased, missing, or excessively high; or produced hormones lack biological activity due to antibody interference.

• Damage to Cell Receptors:

  • Impairment Mechanisms: Decreased quantity of receptors, lack of receptor sensitivity, or the presence of antibodies that block the receptor site (or mimic the hormone, causing unintended stimulation).

  • Tumor Interference: Tumor cells may have receptor activity that essentially "steals" the available hormone, depriving the healthy, unaffected cells.

  • Signs: Serum hormone levels appear appropriate or normal, but no physiological response is elicited. Intracellular inadequacies may involve impaired enzyme or protein usage within the target cell.

• Damage to Feedback, Metabolism, and Elimination:

  • Feedback Loops: Impairment can occur at the HPA axis, secreting gland, or receptors. Ectopic hormones produced by tumors are particularly dangerous because they are not regulated by feedback controls and continue production regardless of high serum levels.

  • Metabolism/Elimination: Kidney or liver disease can impair the body's ability to metabolize and eliminate hormones, leading to an excess of circulating hormones.

Clinical Manifestations of Pituitary and Endocrine Imbalance

• General Manifestations: Altered hormone function commonly manifests as changes in growth, reproductive function, metabolism, and energy levels.

• Hypopituitarism Specifics:

  • Onset is usually gradual; clinical manifestations may not appear until approximately $75\%$ of the anterior pituitary gland is destroyed.

  • Sequence of Loss ("Go Look For The Adenoma"):

    1. GH (Growth Hormone): Secretion is typically the first to be lost.

    2. LH (Luteinizing Hormone): Leads to sex hormone deficiency.

    3. FSH (Follicle-Stimulating Hormone): Results in infertility.

    4. TSH (Thyroid-Stimulating Hormone): Leads to secondary hypothyroidism.

    5. ACTH (Adrenocorticotropic Hormone): Usually the last to become deficient; leads to secondary adrenal insufficiency.

Detailed Manifestations of Hormone Excess and Deficit

• Antidiuretic Hormone (ADH):

  • Excess: Results in fluid retention, low urine output, and hyponatremia.

  • Deficit: Excessive water loss through urine, excessive thirst, dehydration, and potential progression to shock.

• Glucocorticoids (Cortisol):

  • Excess: Truncal obesity, "moon face," "buffalo hump," glucose intolerance, atrophic skin, striae (stretch marks), osteoporosis, psychological changes, poor wound healing, and increased infection risk.

  • Deficit: Hypoglycemia, anorexia, nausea, vomiting, fatigue, weakness, weight loss, and poor stress response.

• Growth Hormone (GH):

  • Excess (Before Puberty - Gigantism): Excessive skeletal growth.

  • Excess (After Puberty - Acromegaly): Bony proliferation of the spine, ribs, face, hands, and feet; enlarged tongue; edema; overactive sebaceous glands; coarse skin/hair; hypertension; and potential left heart failure.

  • Deficit (Children): Short stature, obesity, immature facial features, delayed puberty, hypoglycemia, and seizures.

  • Deficit (Adults): Obesity, insulin resistance, and high circulating lipids.

• Mineralocorticoids (Aldosterone):

  • Excess: Hypertension, hypokalemia, hypernatremia, muscle weakness, fatigue, polyuria, polydipsia, and metabolic alkalosis.

  • Deficit: Weakness, nausea, anorexia, hyponatremia, hyperkalemia, dehydration, hypotension, shock, and death.

• Thyroid Hormone:

  • Excess: Hypermetabolism, weight loss, diarrhea, exophthalmos (bulging eyes), anxiety, and goiter.

  • Deficit: Hypometabolism, weight gain, constipation, goiter, dry skin, and coarse hair.

• Parathyroid Hormone:

  • Excess: Hypercalcemia, excessive osteoclastic activity (bone resorption), pathologic fractures, and renal calculi (kidney stones).

  • Deficit: Hypocalcemia, muscle spasms, hyperreflexia, seizures, and bone deformities.

Diagnosis and Treatment Strategies

• Detection Methods:

  • History and Physical Exam: Checking for clinical signs.

  • Laboratory Values: Measuring serum or urine hormone levels over a $24$-hour period.

  • Stimulation/Suppression Tests: Directly testing the gland's ability to respond to regulatory signals.

  • Indirect Indicators: Measuring electrolytes, glucose, and calcium levels.

  • Imaging: Using CT/MRI to identify the presence of tumors.

  • Genetic Testing: Identifying underlying genetic alterations.

• Treatment Approaches:

  • Hormone Excess: Pharmacologic intervention (medications that block effects) or surgical intervention (removing the tumor or the gland itself).

  • Hormone Deficits: Pharmacologic intervention to stimulate release or hormone replacement therapy (often requiring lifelong administration).

The Stress Response: General Adaptation Syndrome (GAS)

• General Adaptation Syndrome (GAS): An adaptive response consisting of a generalized set of physiological processes that occur regardless of the initial cause of stress.

• Three Successive Stages of GAS:

  1. Alarm Stage:

     • Immediate arousal of body defenses (the "fight or flight" response).

     • The stressor triggers the hypothalamus and the sympathetic nervous system (SNS).

     • Leads to the release of adrenaline (epinephrine) and cortisol.

  2. Resistance (Adaptation) Stage:

     • Occurs when stress lasts for an extended period.

     • Hormones are utilized to extend and enhance the fight-or-flight response while the body attempts to adapt to the persistent stressor.

  3. Exhaustion Stage:

     • Characterized by a progressive breakdown of compensatory mechanisms.

     • Adaptation is unsuccessful, resulting in the onset of disease.

Physiological Pathways and Specific Hormonal Mediators

• Short-Term Stress Response (SNS Dominant):

  • Heart rate and blood pressure increase.

  • Liver converts glycogen to glucose, raising blood glucose levels.

  • Bronchioles dilate to improve oxygen intake.

  • Blood flow is diverted away from digestive and urinary systems (decreasing urine output).

  • Metabolic rate increases.

• Long-Term Stress Response (Adrenocortical Dominant):

  • Mineralocorticoids: Kidneys retain sodium and water, increasing blood volume and pressure.

  • Glucocorticoids: Proteins and fats are converted to glucose/broken down for energy; blood glucose remains elevated; and the immune system becomes suppressed.

• Key Stress Hormones:

  • CRH (Corticotropin-Releasing Hormone): Secreted by the hypothalamus.

  • ACTH (Adrenocorticotropic Hormone): Secreted by the anterior pituitary.

  • Cortisol: Secretion stimulated by ACTH; the most significant contributor to undesired chronic effects.

  • Catecholamines: Adrenaline and noradrenaline released by the sympathetic nerves and the adrenal medulla.

Impact of Stress on Immunity and Pain Suppression

• Innate Immune Response:

  • The SNS and HPA axis have opposing effects on inflammation. While stress can initially enhance pro-inflammatory cytokines, therapeutic levels of cortisol inhibit innate responses, suppressing inflammatory and allergic reactions.

• Adaptive Immune Response:

  • Stress hormones decrease cell-mediated immunity (decreased $T_1$ activity, decreased lymphocytes, and decreased Natural Killer cell activity).

  • This leads to an increased risk of new infections, viruses, and cancer.

  • Stress increases humoral immunity (increased $T_2$ activity and antibody response), but decreases the production of new antibodies, which can exacerbate autoimmune diseases.

• Suppression of Pain:

  • During acute intense stress or traumatic injury, $\beta$-endorphins (endogenous opiates) are released into the blood.

  • Immune cell-derived endorphins in inflamed tissue activate receptors on peripheral sensory nerves to provide analgesia (pain relief).

Chronic Stress and Related Pathophysiological Conditions

• Gastric (Stress) Ulcers:

  • The SNS causes vasoconstriction in the stomach.

  • Cortisol increases gastric acid secretion while decreasing the protective secretion of mucus, leading to ulcer formation.

• Wound Healing and Osteoporosis:

  • Wound Healing: Deteriorates because cortisol increases the breakdown of proteins and decreases the production of new proteins needed for repair.

  • Osteoporosis: Cortisol increases the breakdown of bone (resorption) to release amino acids into the blood. It also decreases intestinal calcium absorption and increases renal calcium excretion.

• Metabolic Syndrome:

  • The combined effects of Glucagon, Cortisol, Thyroid Hormone, GH, and the SNS lead to increased blood glucose and lipid levels.

  • This contributes to visceral obesity and may lead to Type $2$ Diabetes Mellitus.

• Cardiovascular Health: Chronic stress leads to an increased circulation of pro-inflammatory chemicals, contributing to coronary heart disease and other aging-related diseases.

Relaxation vs. Stress Response

• Stress Pathway: Interpreted by the cerebral cortex and limbic system, leading to the Hypothalamus/Pituitary activation of the SNS and Endocrine system, resulting in increased heart rate, ventilation, and metabolic rate, but decreased immune function.

• Relaxation Pathway: The body moves toward homeostasis with decreased heart rate, ventilation, muscle tone, and metabolic rate, while increasing immune function.

• Cyclic Nature: The central nervous system "remembers" physical responses to stress and relaxation, creating a cycle that influences long-term physical consequences.