🩺

Comprehensive Overview of Endocrine System

May 29, 2025

Endocrine System Overview

Introduction

  • The endocrine system involves glands, tissues, and cells that secrete hormones.
  • It's compared to the nervous system as a control system.
  • Communication mechanisms include:
    • Gap Junctions: Cell-to-cell communication via pores.
    • Neurotransmitters: Chemicals released from neurons.
    • Paracrine: Local hormones affecting nearby cells.
    • Hormones: Chemical messengers in the bloodstream affecting distant organs.

Endocrine vs. Exocrine Glands

  • Endocrine Glands: Ductless, secrete hormones directly into the bloodstream.
  • Exocrine Glands: Have ducts, secrete substances onto epithelial surfaces.
  • Mixed Glands: Function as both endocrine and exocrine (e.g., pancreas, gonads).

Nervous System vs. Endocrine System

  • Nervous System: Fast, targeted, uses electrical signals.
  • Endocrine System: Slower, widespread, uses chemical signals (hormones).
  • Some chemicals function in both systems (e.g., epinephrine).

Endocrine Glands Overview

  • Includes pineal, hypothalamus, pituitary, thyroid, parathyroid, thymus, adrenals, pancreas, gonads.
  • Study of endocrine system is known as endocrinology.

Pituitary and Hypothalamus

  • Hypothalamus: Connects to pituitary via infundibulum.
  • Pituitary Gland: Has anterior (adenohypophysis) and posterior (neurohypophysis) lobes.
    • Anterior Pituitary: Hormones regulated by hypothalamic releasing/inhibiting hormones.
    • Posterior Pituitary: Stores and releases hormones made by the hypothalamus.
  • Hormones include FSH, LH, TSH, ACTH, GH, PRL.

Hormone Function and Regulation

  • Hormones have specific target cells/organs with receptors.
  • Negative Feedback: Primary mechanism regulating hormone secretion.
  • Positive Feedback: E.g., oxytocin during labor.

Major Endocrine Glands and Hormones

  • Thyroid: Secretes T3, T4 (increase metabolism), calcitonin (lowers blood calcium).
  • Parathyroid: Secretes PTH (increases blood calcium).
  • Adrenal Glands: Cortex secretes aldosterone, cortisol; medulla secretes epinephrine/norepinephrine.
  • Pancreas: Secretes insulin (lowers blood glucose) and glucagon (raises blood glucose).
  • Gonads: Ovaries produce estrogen, progesterone; testes produce testosterone.

Hormone Classes

  • Steroids: Derived from cholesterol (e.g., sex hormones).
  • Monoamines and Peptides: Derived from amino acids.

Hormone Transport

  • Hydrophilic Hormones: Travel freely in blood (e.g., monoamines, peptides).
  • Hydrophobic Hormones: Require transport proteins (e.g., steroids, thyroid hormones).

Hormone Action

  • Membrane Receptors for Peptides/Monoamines: Activate second messenger systems.
  • Intracellular Receptors for Steroids: Directly influence gene transcription.

Stress and Adaptation

  • General Adaptation Syndrome (GAS): Body's response to stress in three stages (alarm, resistance, exhaustion).
  • Stress Hormones: Include epinephrine, norepinephrine, cortisol.

Disorders

  • Hypo/Hypersecretion: Disorders due to too little or too much hormone production (e.g., diabetes insipidus, Cushing syndrome).
  • Diabetes Mellitus: Type 1 (insulin deficiency), Type 2 (insulin resistance).

Eicosanoids and Signaling Molecules

  • Local Hormones: Paracrine and autocrine actions (e.g., histamines, prostaglandins).
  • Anti-inflammatory Treatments: Steroids and NSAIDs affect eicosanoid pathways.

This structured note provides a comprehensive overview of the endocrine system's structure, function, and disorders, along with key comparisons to the nervous system.

Full transcript