Endocrine System: Major Glands and Hormones

Endocrine System Overview

The endocrine system is composed of glands that secrete hormones directly into the bloodstream to regulate various physiological processes. This guide summarizes the major endocrine glands, their hormones, and key functions, along with practice questions for review.

Anterior Pituitary Gland

Major Hormones and Functions

• Follicle-Stimulating Hormone (FSH): Stimulates sperm formation in males and egg development in females.

• Luteinizing Hormone (LH): Triggers ovulation and stimulates the release of sex hormones.

• Adrenocorticotropic Hormone (ACTH): Stimulates the adrenal cortex to release cortisol.

• Thyroid Stimulating Hormone (TSH): Stimulates the thyroid gland to produce thyroid hormones.

• Prolactin (PRL): Stimulates milk production in mammary glands.

• Growth Hormone (GH): Stimulates cell division and growth throughout the body.

Example: Growth hormone is essential for normal physical development in children.

Posterior Pituitary Gland

Major Hormones and Functions

• Antidiuretic Hormone (ADH): Promotes water reabsorption in the kidneys, reducing urine output and conserving body water.

• Oxytocin: Stimulates uterine contractions during childbirth and milk ejection during breastfeeding.

Additional info: ADH is also known as vasopressin.

Pineal Gland

Major Hormone and Function

• Melatonin: Regulates circadian rhythms and sleep-wake cycles. Derived from the amino acid tryptophan.

Thyroid & Parathyroid Glands

Major Hormones and Functions

• Thyroxine (T4) & Triiodothyronine (T3): Increase metabolic rate and are essential for normal growth and development.

• Calcitonin: Lowers blood calcium levels by promoting calcium deposition in bones.

• Parathyroid Hormone (PTH): Increases blood calcium levels by stimulating bone resorption and increasing calcium reabsorption in the kidneys.

Example: Calcitonin and PTH have opposing effects on blood calcium homeostasis.

Pancreas

Major Hormones and Functions

• Insulin: Lowers blood glucose by promoting uptake of glucose into cells and conversion to glycogen.

• Glucagon: Raises blood glucose by stimulating glycogen breakdown in the liver.

Additional info: The pancreas has both endocrine (hormone-secreting) and exocrine (digestive enzyme-secreting) functions.

Adrenal Glands

Major Hormones and Functions

• Epinephrine (Adrenaline) & Norepinephrine: Mediate the "fight or flight" response, increasing heart rate, blood pressure, and energy availability.

• Glucocorticoids (e.g., Cortisol): Help regulate metabolism, reduce inflammation, and assist in stress response.

Gonads (Ovaries & Testes)

Major Hormones and Functions

• Ovaries: Produce estrogen and progesterone, which regulate female reproductive cycles and secondary sex characteristics.

• Testes: Produce testosterone, which regulates male reproductive functions and secondary sex characteristics.

Hormone-Organ Matching Table

This table summarizes which gland produces each hormone.

Hormone	Gland/Organ
Insulin	Pancreas
Oxytocin	Posterior Pituitary
Melatonin	Pineal Gland
Calcitonin	Thyroid Gland
Growth Hormone	Anterior Pituitary
Progesterone	Gonads (Ovaries)
Parathyroid Hormone	Parathyroid Glands

Practice Questions

1. Which hormone is NOT produced by the gonads?

   • a) Testosterone

   • b) Prolactin (Correct Answer)

   • c) Estrogen

   • d) Progesterone

   Explanation: Prolactin is produced by the anterior pituitary gland, not the gonads.

2. Which hormone is derived from tryptophan and helps regulate circadian rhythm?

   • a) Epinephrine

   • b) Thyroxine

   • c) Melatonin (Correct Answer)

   • d) Growth hormone

   Explanation: Melatonin is synthesized from tryptophan in the pineal gland and regulates sleep-wake cycles.