Endocrine System Study Guide

General Functions of the Endocrine System

• Regulates bodily functions through hormone production and secretion.

• Works with the nervous system to maintain homeostasis controlling the following:

  • Metabolism: Thyroid hormones regulate energy use.

  • Growth and Development: Growth hormone promotes tissue growth.

  • Reproduction: Estrogen and testosterone manage reproductive functions.

  • Homeostasis: Insulin regulates blood glucose levels.

  • Response to Stress: Cortisol aids in managing prolonged stress.

Memory Trick: Think of the endocrine system as a "slow WiFi signal"; it sends messages (hormones) that take longer to arrive but create long-lasting effects!

Chemical Families of Hormones

• Hormones categorized by chemical structure and solubility:

  1. Lipid-Soluble Hormones

  • Description: Derived from cholesterol (steroids) or amino acids (thyroid hormones).

  • Examples: Cortisol, Estrogen, Testosterone, Thyroxine (T3/T4).

  • Receptor Location: Inside the cell (cytoplasm/nucleus).

  2. Water-Soluble Hormones

  • Description: Peptides and proteins that cannot pass through membranes; require surface receptors.

  • Examples: Insulin, Glucagon, Growth Hormone, ADH, Epinephrine.

  • Receptor Location: On the cell membrane.

Memory Tricks:

• "Water rides outside" – water-soluble hormones bind to receptors outside the cell.

• "Lips slip in" – lipid-soluble hormones enter the cell membrane easily.

Control Mechanisms of Hormonal Secretion

• Regulation of hormone secretion occurs through three principal mechanisms:

  1. Negative Feedback (Most Common):

  • Example: High blood glucose leads to insulin release, lowering glucose, which stops insulin secretion.

  1. Positive Feedback:

  • Example: Oxytocin increases contractions during childbirth, stimulating more oxytocin release.

  1. Stimuli-Based Control:

  • Humoral: Changes in blood levels, e.g., low calcium stimulates PTH release.

  • Neural: Direct nerve signals trigger hormone release, e.g., adrenal medulla releases epinephrine.

  • Hormonal: One hormone stimulates the release of another, e.g., TRH -> TSH -> T3/T4.

Memory Trick: Remember "H-N-H" for hormone regulation: Humoral, Neural, Hormonal.

Role of the Hypothalamus in the Endocrine System

• The hypothalamus acts as the "command center" linking the nervous and endocrine systems by:

  • Producing releasing and inhibiting hormones to regulate the pituitary gland.

  • Controlling the autonomic nervous system.

  • Releasing oxytocin and ADH, which are stored in the posterior pituitary.

Hypothalamic Hormones and their Effects:

• TRH (Thyrotropin-Releasing Hormone): Stimulates TSH release.

• CRH (Corticotropin-Releasing Hormone): Stimulates ACTH release.

• GnRH (Gonadotropin-Releasing Hormone): Stimulates FSH and LH release.

• GHRH (Growth Hormone-Releasing Hormone): Stimulates GH release.

• Somatostatin (GHIH): Inhibits GH release.

• Dopamine: Inhibits prolactin release.

Memory Trick: "The Crazy Giant Goes Sleeping During Pregnancy" for hypothalamic hormones.

Functions and Effects of Hormones

Memory Trick: For thyroid disorders: "Hypo is slow, Hyper is high" - remembering the difference in metabolic effects.

Endocrine vs. Nervous System in Homeostasis

Memory Trick: Nervous = Netflix (instant streaming), Endocrine = Email (delayed but long-lasting).

Endocrine and Nervous Response to Stress

1. Short-Term Stress (Nervous System - Fight or Flight):

   • Mediated by the Sympathetic Nervous System.

   • The adrenal medulla releases epinephrine and norepinephrine, resulting in:

     • Increased heart rate and blood pressure.

     • Dilated pupils and airways.

     • Release of glucose for energy.

2. Long-Term Stress (Endocrine System - HPA Axis):

   • Hypothalamus releases CRH -> Pituitary releases ACTH -> Adrenal cortex releases cortisol.

   • Cortisol helps the body adapt by:

     • Increasing blood sugar.

     • Suppressing the immune system.

     • Altering metabolism for prolonged energy.

Memory Trick: "Fight Fast, Adapt Slow" – Epinephrine for quick response, Cortisol for long-term adaptation.