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NRSG 202-Chapter 18 Endocrine System

Chapter 18: The Endocrine System

Learning Objectives

  • Understand the differences between hormonal and neural body controls.

  • List major endocrine organs and their locations in the body.

  • Describe how hormones impact target tissues.

  • Distinguish between hormones, paracrine, and autocrine signaling.

  • Explain hormone classification based on chemical structure.

  • Discuss the regulation mechanisms for hormone release.

  • Identify how target cells respond to hormones.

  • Overview interactions of multiple hormones on the same target cell.

Introduction to the Endocrine System

  • Definition: A chemical messenger system that secretes hormones to maintain homeostasis across long distances in the body.

  • Importance of endocrine hormones in regulating various functions, including metabolism and mood.

  • Structure: Endocrine system functions through the release of hormones into the circulatory system.

Homeostasis

  • Definition: Maintenance of stable internal conditions despite external environmental changes.

  • Functions include regulation of body temperature, pH, blood glucose, blood pressure, and blood volume.

  • Involves feedback mechanisms:

    • Negative feedback: Stabilizes system conditions.

    • Positive feedback: Amplifies changes for specific processes.

Consequences of Homeostasis Disruption

  • Disorders can arise from unregulated hormone levels.

  • Potential conditions: Heart failure, diabetes, ulcers, alkalosis, acidosis, etc., which can lead to severe health issues, including death.

Comparing the Nervous and Endocrine Systems

  • Both systems coordinate body functions but differ in operation:

    • Nervous system: Utilizes neurotransmitters.

    • Endocrine system: Utilizes hormones.

Overview of Endocrine Glands

  • Endocrine glands secrete hormones directly into interstitial fluid without ducts.

  • They play a key role in regulating longer-term processes such as growth and metabolism.

  • Hormones affect target cells possessing specific protein receptors, which may undergo regulation:

    • Down-regulation: Reduces receptor sensitivity in response to hormone excess.

    • Up-regulation: Increases sensitivity with low hormone levels.

Types of Hormones

  • Classification of hormones includes:

    • Local hormones (paracrines): Act quickly on neighboring cells.

    • Autocrines: Affect the same cell that secretes them.

Hormone Structure Types

  • Hormones categorized by solubility:

    • Lipid-soluble: e.g., steroid hormones.

    • Water-soluble: e.g., peptide and protein hormones.

Mechanisms of Hormone Action

  • Lipid-soluble hormones: Diffuse into cells and bind to intracellular receptors affecting gene expression.

  • Water-soluble hormones: Bind to surface receptors, activating second messengers like cAMP that amplify the hormone's effect.

Target Cell Response

  • A target cell's response is based on:

    • Hormone concentration in blood.

    • Number of receptors on the target cell.

    • Interactions with other hormones, which may have synergistic or antagonistic effects.

Control of Hormone Secretion

  • Hormone release can be stimulated through:

    • Neural signals: Nervous system prompts gland activation (e.g., epinephrine).

    • Humoral stimuli: Changes in blood chemistry (e.g., calcium regulation).

    • Hormonal stimuli: One hormone triggers the release of another.

  • Negative feedback mechanisms: Commonly regulate hormone levels to maintain balance.

  • Positive feedback examples: Increased oxytocin release during childbirth enhances contractions.

Endocrine Organs Overview

  • Hypothalamus: Coordinates the endocrine system with the pituitary gland.

  • Pituitary Gland: Divided into anterior and posterior lobes, each releasing specific hormones.

    • Anterior lobe secretes seven hormones affecting growth, metabolism, and reproductive functions.

    • Posterior lobe stores and releases hormones like oxytocin and ADH produced by the hypothalamus.

Hormones of the Thyroid and Parathyroid Glands

  • Thyroid Gland: Produces T3 and T4 to regulate metabolism and calcitonin for calcium control.

  • Parathyroid Glands: Secrete PTH to increase calcium levels in the bloodstream.

Adrenal Glands

  • Adrenal Cortex: Produces hormones regulating sodium and potassium, blood volume, and stress response (cortisol).

  • Adrenal Medulla: Releases epinephrine and norepinephrine in response to stress.

Pancreas Functions

  • Acts as both endocrine and exocrine gland, regulating blood glucose levels via insulin and glucagon.

  • Pancreatic islets consist of various cell types:

    • Alpha cells: Glucagon

    • Beta cells: Insulin

    • Delta cells: Somatostatin

Gonadal and Other Hormones

  • Ovaries: Produce estrogens and progesterone.

  • Testes: Produce testosterone, influencing male characteristics and reproductive functions.

  • Pineal Gland: Produces melatonin, regulating sleep patterns.

The Stress Response

  • Eustress: Beneficial stress motivating action; Distress: Harmful stress needing management.

  • The body's initial stress response (fight-or-flight) engages energy reserves and prepares for immediate actions.

  • Longer-term stress can shift into a resistance phase, utilizing hormones for sustained energy.

Endocrine Disorders and Aging

  • Age-related changes can affect hormone levels and gland structure.

  • Disorders can arise from imbalances, such as adrenal hyperactivity leading to Cushing's syndrome or thyroid dysfunction leading to goiter.