Adrenal Glands: Medulla & Catecholamines

Adrenal Glands - Medulla & Catecholamines

• Catecholamines are produced:
  • Epinephrine (Adrenaline): 80%
  • Norepinephrine (Noradrenaline): 20%
  • Dopamine: A precursor to norepinephrine, but in smaller amounts.

Functions of Catecholamines

• Fight-or-Flight Response:

  • Epinephrine: Increases heart rate, dilates airways, increases blood flow to muscles, raises blood glucose levels.
  • Norepinephrine: Primarily increases vasoconstriction (narrowing blood vessels), raising blood pressure.

• Metabolic Effects:

  • Stimulates glycogen breakdown in the liver (glycogenolysis).
  • Increases lipolysis (fat breakdown).
  • Promotes increased glucose release for energy.

• Central Nervous System Effects:

  • Increase alertness, arousal, and focus.
  • Enhances memory formation in response to stress.

• Cardiovascular Effects:

  • Epinephrine: Increases heart rate and force of contraction.

Stimuli for Release of Catecholamines

• Stress (physical or emotional, acute or chronic)
• Exercise
• Hypoglycemia (Low blood glucose)
• Hypoxia (Low oxygen)
• Pain (Acute)
• Fear/Anxiety

Inhibitors of Catecholamine Release

• Parasympathetic Nervous System Activity: Counteracts the fight-or-flight response, reducing catecholamine secretion.
• High Cortisol Levels: Chronic high cortisol may dampen acute catecholamine release.
• Negative Feedback: High levels of catecholamines reduce further release through negative feedback mechanisms.
• Beta-Blockers: Medications that block catecholamine receptors, reducing their effects.

Adrenal Cortex

• Produces steroid hormones crucial for metabolism, immune function, and salt balance.
• Divided into three zones: Zona Glomerulosa, Zona Fasciculata, Zona Reticularis.

Zona Glomerulosa

• Hormones Produced: Aldosterone (mineralocorticoid).
• Function: Regulates sodium and potassium balance. Increases sodium reabsorption in kidneys, leading to water retention and increased blood volume. Promotes potassium and hydrogen ion excretion by kidneys, maintaining electrolyte balance.
• Stimuli: Renin-Angiotensin-Aldosterone System (RAAS):
  • Low blood pressure or low sodium levels stimulate the kidney to release renin.
  • Renin converts angiotensinogen, to angiotensin I. To angiotensin II in the lungs.
  • Angiotensin II stimulates the zona glomerulosa to release aldosterone.
  • High potassium levels (hyperkalemia) stimulate aldosterone secretion.
• Inhibitors: Low potassium levels (hypokalemia) inhibit aldosterone release. Increased blood pressure or adequate blood volume (via negative feedback from RAAS).

Zona Fasciculata

• Hormones Produced: Cortisol (glucocorticoid).
• Function: Regulates metabolism (carbohydrate, protein, and fat). Stimulates gluconeogenesis, increases blood glucose levels, antiinflammatory, and a role in body adaptation to stress.
• Stimuli: ACTH (Adrenocorticotropic Hormone) from the anterior pituitary, stress (physical, emotional, metabolic). Circadian rhythm, peaking in morning, decreasing at night.
• Inhibitors: Negative feedback, high cortisol levels inhibit ACTH release via feedback to the hypothalamus and pituitary, increased blood glucose can suppress cortisol secretion.

Zona Reticularis

• Hormones Produced: Androgens (DHEA and androstenedione - weak male sex hormones).
• Function: Development of secondary sexual characteristics, especially in females, precursor to sex hormones like testosterone and estrogen.
• Stimuli: ACTH, stress. Increased ACTH during stress leads to more androgen production.
• Inhibitors: Negative feedback from high cortisol levels, estrogen/testosterone feedback (in both men and women). Suppresses ACTH release, decreasing androgen production.

Insulin Overview

• Produced by beta cells of the islets of Langerhans in the pancreas.
• Primary Role: Regulates blood glucose levels by promoting glucose uptake and storage.

Insulin Functions

1. Lowers Blood Glucose Levels: Promotes glucose uptake by cells, stimulates glucose storage (glycogen) In liver/muscle, inhibits gluconeogenesis.
2. Promotes Fat Storage: Stimulates lipogenesis (fat synthesis) and inhibits lipolysis (fat breakdown).
3. Promotes Protein Synthesis: Stimulates amino acid uptake into cells and enhances protein synthesis.
4. Regulates Metabolism: Facilitates nutrient storage (glucose, fats, proteins) during the fed state, counteracts glucagon, cortisol, and epinephrine.

Stimuli for Insulin Release

1. High Blood Glucose (Hyperglycemia): The primary stimulus, after meals glucose levels rise.
2. Amino Acids: Elevated amino acid levels (especially after protein-rich meals) stimulate insulin secretion.

Inhibitors of Insulin Release

1. Low Blood Glucose (Hypoglycemia): Low blood sugar inhibits further lowering of glucose levels.
2. Sympathetic Nervous System: Stress, exercise and fight or flight stimulate the sympathetic nervous system, inhibiting insulin release.
3. Somatostatin: Released by delta cells in the pancreas, inhibits both insulin and glucagon secretion.
4. High Cortisol Levels: Cortisol can indirectly inhibit insulin release or reduce its effectiveness (insulin resistance).
5. Fasting: During fasting states, insulin secretion is low to promote use of stored energy.

Glucagon Overview

• Produced by alpha cells of the islets of Langerhans in the pancreas.
• Primary role: Raises blood glucose levels by promoting the release of glucose from storage sites in the body.

Glucagon Functions

1. Increases Blood Glucose Levels: Stimulates glycogenolysis, breaking down glycogen to raise blood sugar.

• Also stimulates gluconeogenesis, producing new glucose from non-carbohydrate sources.

Stimuli for Glucagon Release

1. Low Blood Glucose (Hypoglycemia): The primary stimulus for glucagon release.
2. High Amino Acid Levels: Elevated amino acid levels stimulate glucagon release. Helps in conversion of amino acids into glucose (gluconeogenesis).
3. Exercise: Body requires more energy, leading to increased glucose availability.

Inhibitors of Glucagon Release

1. High Blood Glucose (Hyperglycemia): Sufficient glucose levels inhibit further glucagon release.
2. Insulin: Insulin secreted by beta cells inhibits glucagon release.
3. Somatostatin: Released by delta cells; inhibits glucagon & insulin secretion to stabilize blood glucose levels.
4. High Fatty Acid Levels: Sufficient energy from fats reduce glucagon release. Also, inhibits glucagon release.

Other Topics (from the provided text)

• Incretin Hormones: GLP-1 & GIP are secreted by the gut in response to food intake, enhancing insulin release.

• Parasympathetic Nervous System: Increases insulin secretion during the feeding state.

• Physiological Effects of Insulin & Glucagon: Include glucose regulation, fat metabolism, and protein metabolism. These effects demonstrate their regulatory roles in maintaining homeostasis.

• Diabetes Mellitus: Overview, Type 1 Diabetes, Type 2 Diabetes. Physiological effects in each type, focusing on hyperglycemia, ketosis, and ketoacidosis.

• Note: The provided text spans multiple pages of endocrinology information; these points summarize the concepts.

Explore the crucial functions of catecholamines produced by the adrenal glands, including epinephrine, norepinephrine, and dopamine. This quiz focuses on their roles in the fight-or-flight response, metabolic effects, and impacts on the central nervous system and cardiovascular health.