USMLE Guide: Endocrine Glands And Their Hormones

Introduction

The endocrine system is a complex network of glands that produce and secrete hormones. These hormones are essential for regulating various bodily functions, such as growth and development, metabolism, reproduction, and maintaining homeostasis. Understanding the endocrine glands and their hormones is crucial for medical students preparing for the USMLE exams. This guide aims to provide a comprehensive overview of the major endocrine glands and their associated hormones to aid in exam preparation.

Endocrine Glands and their Hormones

1. Hypothalamus

• Function: The hypothalamus serves as the control center for the endocrine system, regulating the release of hormones from the pituitary gland.
• Hormones:
  • Gonadotropin-Releasing Hormone (GnRH): Stimulates the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary.
  • Growth Hormone-Releasing Hormone (GHRH): Stimulates the release of growth hormone (GH) from the anterior pituitary.
  • Thyrotropin-Releasing Hormone (TRH): Stimulates the release of thyroid-stimulating hormone (TSH) from the anterior pituitary.
  • Corticotropin-Releasing Hormone (CRH): Stimulates the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary.

2. Pituitary Gland (Hypophysis)

• Function: The pituitary gland is often called the "master gland" as it controls the functions of other endocrine glands. It consists of the anterior pituitary and posterior pituitary.
• Anterior Pituitary Hormones:
  • Growth Hormone (GH): Stimulates growth, protein synthesis, and metabolism.
  • Adrenocorticotropic Hormone (ACTH): Stimulates the release of cortisol from the adrenal cortex.
  • Thyroid-Stimulating Hormone (TSH): Stimulates the release of thyroid hormones (T3 and T4) from the thyroid gland.
  • Follicle-Stimulating Hormone (FSH): Stimulates the growth of ovarian follicles and sperm production.
  • Luteinizing Hormone (LH): Triggers ovulation and stimulates testosterone production in males.
  • Prolactin (PRL): Stimulates milk production in the mammary glands.
• Posterior Pituitary Hormones:
  • Antidiuretic Hormone (ADH): Regulates water balance and blood pressure.
  • Oxytocin: Stimulates uterine contractions during labor and milk ejection during breastfeeding.

3. Thyroid Gland

• Function: The thyroid gland produces hormones that regulate metabolism and growth.
• Hormones:
  • Thyroxine (T4) and Triiodothyronine (T3): Regulate metabolism, growth, and development.
  • Calcitonin: Regulates calcium homeostasis by decreasing blood calcium levels.

4. Parathyroid Glands

• Function: The parathyroid glands control calcium and phosphate levels in the blood.
• Hormone:
  • Parathyroid Hormone (PTH): Increases blood calcium levels and decreases phosphate levels.

5. Adrenal Glands

• Function: The adrenal glands produce hormones that regulate stress response, blood pressure, and metabolism.
• Hormones:
  • Adrenal Cortex:
    • Glucocorticoids (e.g., cortisol): Regulate metabolism and immune response.
    • Mineralocorticoids (e.g., aldosterone): Regulate electrolyte and water balance.
    • Androgens (e.g., DHEA): Precursors for sex hormones.
  • Adrenal Medulla:
    • Epinephrine (adrenaline): Enhances the "fight or flight" response.
    • Norepinephrine (noradrenaline): Enhances stress response and constricts blood vessels.

6. Pancreas

• Function: The pancreas regulates blood glucose levels.
• Hormones:
  • Insulin: Lowers blood glucose levels by promoting glucose uptake by cells.
  • Glucagon: Raises blood glucose levels by promoting glycogen breakdown and gluconeogenesis.

7. Gonads

• Function: The gonads (testes in males and ovaries in females) produce sex hormones and regulate reproductive functions.
• Male Hormones:
  • Testosterone: Promotes male sexual development and sperm production.
  • Inhibin: Inhibits FSH production.
• Female Hormones:
  • Estrogen: Promotes female sexual development and regulates the menstrual cycle.
  • Progesterone: Prepares the uterus for pregnancy and maintains