Major Endocrine Glands

The major endocrine glands play vital roles in regulating various body functions through hormone production. Understanding these glands helps connect their influence on growth, metabolism, and reproduction to the broader concepts in Anatomy and Physiology II.

1. Pituitary gland

   • Often referred to as the "master gland," it regulates other endocrine glands.
   • Divided into anterior and posterior lobes, each secreting different hormones.
   • Produces hormones such as growth hormone (GH), prolactin, and adrenocorticotropic hormone (ACTH).
   • Plays a crucial role in growth, metabolism, and reproductive functions.
   • Located at the base of the brain, it is connected to the hypothalamus.

2. Thyroid gland

   • Produces thyroid hormones (T3 and T4) that regulate metabolism and energy levels.
   • Influences growth and development, particularly in children.
   • Regulated by thyroid-stimulating hormone (TSH) from the pituitary gland.
   • Located in the neck, it has a butterfly shape and consists of two lobes.
   • Plays a role in calcium homeostasis through the secretion of calcitonin.

3. Parathyroid glands

   • Four small glands located on the back of the thyroid gland.
   • Secrete parathyroid hormone (PTH), which regulates calcium levels in the blood.
   • PTH increases calcium absorption in the intestines and kidneys and releases calcium from bones.
   • Essential for maintaining bone health and preventing osteoporosis.
   • Works in opposition to calcitonin from the thyroid gland.

4. Adrenal glands

   • Located on top of each kidney, they consist of the adrenal cortex and adrenal medulla.
   • Produce hormones such as cortisol (stress response), aldosterone (blood pressure regulation), and adrenaline (fight-or-flight response).
   • Involved in metabolism, immune response, and stress management.
   • The adrenal cortex is responsible for steroid hormone production, while the medulla produces catecholamines.
   • Play a key role in the body's response to stress and maintaining homeostasis.

5. Pancreas

   • Functions as both an endocrine and exocrine gland, located behind the stomach.
   • Produces insulin and glucagon, which regulate blood glucose levels.
   • Insulin lowers blood sugar, while glucagon raises it, maintaining energy balance.
   • Plays a critical role in digestion by secreting digestive enzymes into the small intestine.
   • Dysfunction can lead to diabetes mellitus and other metabolic disorders.

6. Pineal gland

   • A small, pea-shaped gland located in the brain.
   • Produces melatonin, which regulates sleep-wake cycles and circadian rhythms.
   • Influenced by light exposure, with production increasing in darkness.
   • Plays a role in reproductive hormone regulation and seasonal biological rhythms.
   • Often referred to as the "third eye" due to its location and light sensitivity.

7. Thymus

   • Located in the upper chest, behind the sternum, and is largest in childhood.
   • Produces thymosin, which is essential for the development and maturation of T-lymphocytes (T-cells).
   • Plays a critical role in the immune system, particularly in developing adaptive immunity.
   • Gradually shrinks and becomes less active after puberty.
   • Important for the body's defense against pathogens and cancer.

8. Gonads (ovaries and testes)

   • Ovaries produce estrogen and progesterone, while testes produce testosterone.
   • Regulate sexual development, reproductive functions, and secondary sexual characteristics.
   • Involved in the menstrual cycle in females and sperm production in males.
   • Hormonal balance is crucial for fertility and overall reproductive health.
   • Gonadal hormones also influence bone density, muscle mass, and mood.