Advanced Endocrine System

Endocrine System - Advanced Notes

• Hypothalamus-Pituitary Axis:
  • The hypothalamus directly innervates the posterior pituitary, releasing hormones such as ADH and oxytocin.
  • The hypothalamus indirectly regulates the anterior pituitary by releasing hypothalamic releasing hormones (RHs) and inhibiting hormones (IHs).
  • These RHs and IHs regulate the anterior pituitary's hormone secretion, which in turn influences a wide range of bodily functions.
• Thyroid Hormone Regulation:
  • T3 and T4 from the thyroid gland play a crucial role in regulating their own production through negative feedback mechanisms.
  • T3 and T4 inhibit the secretion of both TRH from the hypothalamus and TSH from the anterior pituitary, effectively controlling their own levels.
• Pancreatic Hormones and Metabolism:
  • Insulin is the main hormone released after eating, facilitating glucose uptake and lowering blood glucose levels.
  • Glucagon has an opposing effect, increasing blood glucose by stimulating glycogenolysis, gluconeogenesis, and lipolysis, primarily during fasting or prolonged starvation.
  • Glucocorticoids (cortisol) also contribute to gluconeogenesis and lipolysis during prolonged starvation.
• Mineralocorticoid Action:
  • Mineralocorticoids, primarily aldosterone, target the kidneys.
  • Aldosterone regulates electrolyte balance by promoting sodium reabsorption and potassium excretion.
• Parathyroid Hormone (PTH):
  • PTH is the main regulator of calcium levels in the blood.
  • Its secretion is stimulated by low calcium levels, promoting calcium reabsorption from the bones and kidneys, as well as calcium absorption from the gut.
• Hormone Mechanisms:
  • Steroid hormones, being lipid-soluble, can easily pass through cell membranes due to their hydrophobic nature.
  • Hormone release is typically governed by negative feedback mechanisms, maintaining a balanced level of hormones within the body.
• Hormonal Functions:
  • Hormones play a crucial role in regulating metabolism, stimulating gamete production, controlling growth, and mediating many other physiological processes.
• Hypothalamus and Hormone Inhibition:
  • The hypothalamus can inhibit the release of several hormones, including TSH, ACTH, FSH, and GH, ensuring a balanced endocrine system.
• Peptide Hormones:
  • Most peptide hormones exert their effects by binding to membrane receptors on target cells, triggering intracellular signaling cascades.
• Angiotensin II Action:
  • Angiotensin II, a potent vasoconstrictor, is countered by natriuretic peptides like ANP and BNP, promoting vasodilation and lowering blood pressure.
• Pituitary Gland:
  • The pituitary gland comprises two lobes: the anterior lobe (adenohypophysis) and the posterior lobe (neurohypophysis).
  • The anterior lobe produces various hormones, while the posterior lobe stores and releases hormones produced by the hypothalamus.
• FSH in Males:
  • Follicle Stimulating Hormone (FSH) in males directly influences sperm maturation, contributing to healthy sperm production.
• Hormonal Sensitivities:
  • A cell's response to a hormone is dictated by the presence of specific receptors that bind to the hormone, not just the hormone's structure or circulating levels.
• Endocrine Pancreas:
  • The endocrine pancreas consists of four main cell types: alpha, beta, delta, and gamma cells.
  • Alpha cells secrete glucagon, beta cells secrete insulin, delta cells secrete somatostatin, and gamma cells produce pancreatic polypeptide.
• Pancreatic Hormones:
  • The pancreas secretes insulin, glucagon, somatostatin, and pancreatic polypeptide, playing essential roles in regulating blood glucose levels and other metabolic processes.
• Nervous System (NS) vs. Endocrine System (ES):
  • The NS uses neurotransmitters for rapid, short-lived, and specific transmission, while the ES utilizes hormones for slower, longer-lasting, and widespread effects.
• Sympathetic-Endocrine Integration:
  • The adrenal gland is under dual control: the sympathetic nervous system directly stimulates the adrenal medulla, while the endocrine system (via ACTH) influences the adrenal cortex.
• Hypothalamus as Integrator:
  • The hypothalamus acts as the crucial bridge between the nervous and endocrine systems, integrating their responses to maintain overall homeostasis.
• Endocrine Hormone Mispairing:
  • Progesterone, a sex hormone, does not directly increase plasma glucose levels. While it influences glucose tolerance, it is not the primary hormone responsible for increasing blood glucose levels.