endocrine system

Homeostasis

  • Definition: Ability to maintain a stable internal environment despite external changes.

  • Energy Consumption: Significant energy spent to maintain homeostasis.

  • Factors Involved: Chemical, thermal, and neural interactions.

  • Age Impact: Mechanisms become less efficient, increasing disease susceptibility.

Negative Feedback

  • Definition: Mechanism that shuts off the original stimulus.

  • Prevalence: 99% of homeostatic feedback loops.

  • Examples: Regulation of body temperature, pH, glucose levels, blood pressure, and calcium levels.

Positive Feedback

  • Example: Oxytocin release during childbirth facilitates uterine contractions.

  • Mechanism: Head of fetus pushes against cervix; stimulates hormonal response.

Endocrine System Overview

  • Function: Controls metabolic activities via hormones.

  • Hormones: Chemical messengers that stimulate responses in target tissues.

  • Endocrine Glands: Include pituitary, thyroid, adrenal, and others.

  • Tissue Production: Other tissues like adipose and kidneys also produce hormones.

Endocrine vs. Exocrine Glands

  • Exocrine: Have ducts; secrete substances like digestive enzymes and sweat.

  • Endocrine: No ducts; release hormones into blood or lymphatic systems.

Hormone Classification

  • Amino Acid-Based Hormones: Water-soluble, cannot cross cell membranes (e.g., insulin).

  • Steroid Hormones: Lipophilic, require protein carriers (e.g., testosterone, cortisol).

Hormone Action Mechanisms

  1. Second Messengers: Amino acid-based hormones activate surface receptors, influencing internal cell functions.

  2. Direct Gene Activation: Steroid hormones enter the nucleus and influence gene expression.

Hypothalamus Functions

  • Regulates: Body temperature, blood pressure, growth, reproduction, and hormone production.

  • Hormones Produced: ADH and oxytocin.

Pituitary Gland Overview

  • Structure: Anterior (adenohypophysis) and posterior (neurohypophysis) lobes.

  • Function: Secretes hormones influencing other glands (e.g., TSH, ACTH).

Growth Hormone (GH)

  • Stimuli for Release: Low blood sugar, high stress, increased amino acids.

  • Functions: Promotes growth via IGF-1, maintains metabolism, and electrolyte balance.

  • Conditions: Increased GH can lead to gigantism or acromegaly; decreased levels can cause dwarfism.

Thyroid Gland Functions

  • Hormones: Produces T3 and T4; stimulated by TSH.

  • Actions: Regulates metabolic rate, growth, and development.

  • Diseases: Hyperthyroidism (Graves' disease) and hypothyroidism (goiter).

Adrenal Glands Functions

  • Layers: Cortex (produces corticosteroids) and medulla (produces catecholamines).

  • Stress Hormones: Manage stress responses via cortisol and adrenaline.

Major Hormones and Their Effects

  • Cortisol: Increases blood sugar levels, aids in stress response, suppresses immune function.

  • Aldosterone: Regulates sodium and potassium balance.

  • Catecholamines (epinephrine, norepinephrine): Facilitate fight or flight responses.

Addison's Disease & Cushing's Disease

  • Addison's Disease: Hyposecretion affecting stress response.

  • Cushing's Disease: Hypersecretion causing increased glucose and blood pressure.

Clinical Questions

  • Identifying signs of endocrine disorders based on symptoms and hormone levels.