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.