Endocrine Control of Growth: Adrenal Glucocorticoids

Endocrine Control of Growth and Metabolism - Adrenal Glucocorticoids

• Cortisol secretion is controlled by ACTH
• Cortisol is a steroid hormone, synthesized from cholesterol on demand, not stored
• Transported in circulation bound to corticosteroid-binding globulin (produced by the liver)
• Half-life of 60-90 minutes
• Factors affecting release include circadian rhythm and stress
• ACTH, from the anterior pituitary gland, is released in response to CRH (corticotropin-releasing hormone) from the hypothalamus
• Cortisol targets many body tissues and has various effects

Cortisol's Mechanism of Action

• Cortisol acts at the cellular level by binding to intracellular receptors
• This leads to altered gene expression, stimulating transcription, translation, and protein synthesis
• This ultimately affects various physiological processes

Cortisol's Metabolic Effects

• Cortisol's effects are primarily catabolic
• Promotes gluconeogenesis (glucose formation from non-carbohydrate sources)
• Breaks down proteins from skeletal muscle
• Increases lipolysis (fat breakdown)
• Suppresses the immune system
• Causes negative calcium balance
• Influences brain function

Cortisol and Stress

• Cortisol is a key mediator of long-term stress response

Hypercortisolism and Hypocortisolism

• Hypercortisolism (too much cortisol): caused by adrenal tumors, Cushing's disease/syndrome
  • Symptoms include hyperglycemia (high blood sugar) and tissue wasting
• Hypocortisolism (too little cortisol): caused by hyposecretion of adrenal steroid hormones, Addison's disease
  • Symptoms include hypoglycemia (low blood sugar), fatigue, and lack of appetite

Thyroid Hormones

• Thyroid hormone secretion is controlled by the hypothalamic-pituitary-thyroid axis (HPT axis)
• TRH from the hypothalamus stimulates the release of TSH from the anterior pituitary
• TSH stimulates the thyroid gland to produce T3 (triiodothyronine) and T4 (thyroxine)
• Both T3 and T4 have negative feedback mechanisms that regulate their own production
• T3 is the biologically active form (though T4 is initially produced)
• T4 converts to T3 in tissues and has a longer half-life
• Thyroid hormones affect various metabolic processes, including oxygen consumption

Hyperthyroidism and Hypothyroidism

• Hyperthyroidism leads to an overproduction of thyroid hormones; causes may include Graves' disease, accompanied by exophthalmos (eye bulging) and thyroid gland tumors
• Hypothyroidism occurs due to inadequate hormone production; causes might be iodine deficiency, autoimmune issues, or treatment of other disorders
• Goiters (enlarged thyroid glands) can occur in both hyperthyroidism and hypothyroidism

Growth Hormone

• Factors influencing normal growth include growth hormone, adequate diet, absence of chronic stress, and genetics
• Hypersecretion in children results in gigantism, while in adults it leads to acromegaly (disproportionate growth).
• Hyposecretion leads to dwarfism

Calcium Balance

• Calcium (Ca2+) is vital, acting as a signal molecule, a component of cell junctions, a cofactor in coagulation, and affecting nervous system and muscle function
• Calcium is distributed among extracellular fluid, intracellular compartments, and the extracellular matrix (bone).
• Hormones like parathyroid hormone (PTH), calcitriol (vitamin D), and calcitonin regulate calcium levels in different body compartments through bone resorption, intestinal absorption, and renal excretion mechanisms.

This quiz covers the fundamental aspects of adrenal glucocorticoids, particularly cortisol. It explores the mechanisms of cortisol secretion, its action at the cellular level, and its various metabolic effects. Test your understanding of how cortisol functions within the endocrine system and its role in metabolism.