Lecture Notes: The Endocrine System and Hormones

Introduction

• Hormones: Critical chemical messengers in the body.
• Endocrine System: Consists of glands that secrete hormones.

Major Endocrine Glands and Their Hormones

Brain

• Hypothalamus & Pituitary Complex: Regulates the rest of the endocrine system.
  • Posterior Pituitary: Secretes hormones made by the hypothalamus.
    • Oxytocin: Uterine contractions during childbirth.
    • Antidiuretic Hormone (ADH): Stimulates kidneys to reabsorb water.
  • Anterior Pituitary: Makes its own hormones but regulated by hypothalamus.
    • Growth Hormone (GH): Promotes growth.
    • Prolactin (PRL): Milk production from mammary glands.
    • Thyroid-Stimulating Hormone (TSH): Stimulates thyroid to release its hormones.
    • Follicle Stimulating Hormone (FSH): Stimulates gonads to make gametes.
    • Luteinizing Hormone (LH): Stimulates gonads to make androgens.
    • Adrenocorticotropic Hormone (ACTH): Stimulates adrenal cortex to release hormones.
• Pineal Gland:
  • Melatonin: Regulates circadian rhythm (sleep-wake cycle).

Neck

• Thyroid:
  • T4 (Thyroxine) & T3 (Triiodothyronine): Control metabolic processes.
  • Calcitonin: Lowers blood calcium levels.
• Parathyroid:
  • Parathyroid Hormone (PTH): Raises blood calcium levels.

Upper Chest

• Thymus: Active before puberty; important for T cell development.
  • Thymosin: Stimulates the production of T cells.

Abdomen

• Adrenal Glands:
  • Adrenal Medulla: Secretes epinephrine and norepinephrine (fight or flight response).
  • Adrenal Cortex: Secretes glucocorticoids (e.g., cortisol) and mineralocorticoids (e.g., aldosterone).
• Pancreas:
  • Insulin: Lowers blood glucose levels.
  • Glucagon: Raises blood glucose levels.

Reproductive Glands

• Gonads:
  • Ovaries: Produce estrogen and progesterone (female reproductive system).
  • Testes: Produce androgens such as testosterone (male reproductive system).

Endocrine vs. Exocrine Glands

• Endocrine Function: Releases hormones into surroundings without ducts.
• Exocrine Function: Uses ducts to carry secretions to body surfaces (e.g., sweat glands).
• Some glands, like the pancreas, have both endocrine and exocrine functions.

Hormone Classes and Functions

• Hormones can be derived from different biomolecules (amino acids, polypeptides, lipids).
• Hormone structure influences hormone function and receptor binding.
• Hormones bind to specific target cells, triggering various responses.

Example of an Endocrine Disorder

• Hypothyroidism: Underactive thyroid leading to low production of thyroid hormones.
  • Symptoms: Extreme fatigue, slowed heart rate.
  • Treatment: May include thyroid hormone replacement.