Overview of the Endocrine System

Introduction

• Endocrine System: A collection of cells and glands producing and releasing hormones.
• Hormones: Chemicals released into the bloodstream to have effects on distant areas of the body.
• Communication Network: Similar to the nervous system but slower, less direct, and with longer-lasting effects.

Key Characteristics

• Nervous System: Fast, direct, short-acting.
• Endocrine System: Slow, indirect (via bloodstream), long-lasting (effects can last hours to weeks).

Major Endocrine Glands and Hormones

Brain Region

1. Hypothalamus:

• Located at the base of the brain below the thalamus.
• Master regulator of the endocrine system.
• Produces 5 major hormones:
  • Thyrotropin Releasing Hormone (TRH)
  • Corticotropin Releasing Hormone (CRH)
  • Growth Hormone Releasing Hormone (GHRH)
  • Prolactin Releasing Hormone (PRH)
  • Gonadotropin Releasing Hormone (GnRH)

2. Pituitary Gland:

• Anterior Pituitary: Connected to the hypothalamus via blood supply.
  • Hormones:
    • Thyroid Stimulating Hormone (TSH)
    • Adrenocorticotropic Hormone (ACTH)
    • Growth Hormone (GH)
    • Prolactin
    • Gonadotropins (Luteinizing Hormone (LH), Follicle Stimulating Hormone (FSH))
• Posterior Pituitary: Connected via nerves.
  • Hormones:
    • Oxytocin
    • Antidiuretic Hormone (ADH, also known as vasopressin)

Thyroid Gland

• Located in front of the trachea.
• Produces:
  • T3 (Tri-iodothyronine) and T4 (Thyroxine):
    • T3 is the most active form, responsible for metabolism, development, and catecholamine release.
  • Calcitonin: Lowers blood calcium levels.

Adrenal Glands

• Cortex (outer part): Produces corticosteroids.
  • Hormones:
    • Cortisol: Increases blood glucose, suppresses immune system, stimulates fight or flight response.
    • Aldosterone: Increases reabsorption of salt and water in kidneys, raises blood pressure.
• Medulla (inner part): Produces catecholamines.
  • Hormones: Adrenaline (epinephrine) and Noradrenaline (norepinephrine)

Other Important Glands and Hormones

• Parathyroid Glands: Located behind the thyroid, releases Parathyroid Hormone (PTH) to increase blood calcium levels (opposes calcitonin).
• Pancreas:
  • Endocrine function: Releases insulin (lowers blood glucose) and glucagon (raises blood glucose).
  • Exocrine function: Releases digestive enzymes.
• Kidneys: Release hormones like renin (regulates blood pressure and volume) and erythropoietin (stimulates red blood cell production).

Specific Functions of Key Hormones

1. Thyroid Stimulating Hormone (TSH): Stimulates thyroid to release T3 and T4.
2. Adrenocorticotropic Hormone (ACTH): Stimulates adrenal cortex to produce cortisol and aldosterone.
3. Growth Hormone (GH): Stimulates growth and metabolic processes.
4. Prolactin: Stimulates milk production.
5. Gonadotropins: LH and FSH regulate reproductive functions:

• LH: Stimulates ovulation and progesterone in females; testosterone in males.
• FSH: Stimulates follicle maturation and estrogen in females; androgen binding protein in males.

6. Oxytocin: Causes uterine contractions, milk ejection, and affects social behaviors.
7. ADH (Vasopressin): Reduces urine production, maintains water balance and blood pressure.
8. Cortisol: Manages stress response, increases glucose levels.
9. Aldosterone: Helps with water reabsorption to increase blood volume and pressure.
10. Calcitonin: Lowers blood calcium levels.
11. Parathyroid Hormone (PTH): Raises blood calcium levels.
12. Insulin: Lowers blood glucose by facilitating cellular absorption.
13. Glucagon: Raises blood glucose by releasing stored glucose.
14. Renin: Part of a system that controls blood pressure and volume.
15. Erythropoietin: Stimulates red blood cell production.

Summary

• The endocrine system plays a crucial role in maintaining homeostasis and regulating various physiological activities.
• Hormone interactions and balances are essential for proper bodily functions.