Endocrine System: Functions of Key Glands and Hormones

Posted on Oct 24, 2025 in Medicine

Hypothalamus: Central Regulator of Body Functions

Regulation of Hunger and Satiety

The hypothalamus regulates hunger, appetite, and satiety through various hormones and peptides, such as cholecystokinin, glucose and fatty acids in the blood, and neuropeptide Y, among others.

• The hunger center is located in the lateral hypothalamus.
• The satiety center is located in the ventromedial portion.

Temperature Control

The hypothalamus plays a crucial role in thermoregulation:

• The anterior hypothalamus is involved in heat dissipation (cooling).
• The posterior hypothalamus is responsible for maintaining constant body temperature by increasing or decreasing respiratory rate and sweating.

Sleep and Wakefulness

The anterior and posterior hypothalamus also regulate the cycle of sleep and wakefulness (the circadian rhythm).

The Pituitary Gland and Its Hormones

The pituitary gland secretes hormones that act directly on target tissues. Key pituitary hormones include:

• Somatotropin (Growth Hormone): Promotes bone growth, stimulates protein synthesis, and promotes the conservation of glucose.
• Prolactin: Stimulates milk production. Its activity is controlled by the hypothalamus, which secretes an inhibitory hormone. As long as the baby is nursing, the hypothalamus prevents milk production from stopping.
• ADH (Antidiuretic Hormone): Reduces urine production.
• Oxytocin: Stimulates the contraction of internal muscles, causes contractions of the muscle fibers of the mammary glands, and induces milk let-down when the baby begins to suckle.

Functions of the Thyroid and Parathyroid Glands

Thyroid Hormones (T3, T4, and Calcitonin)

The thyroid gland secretes three types of hormones: T4 (Thyroxine), T3 (Triiodothyronine), and Calcitonin.

• T4 and T3: Control cellular metabolism by speeding up the process of cellular respiration. These hormones are also involved in regulating body temperature and increasing the overall metabolic rate.
• Calcitonin: Reduces the level of calcium in the blood. When calcium concentration is above normal, Calcitonin:
  • Inhibits the release of calcium from bones.
  • Accelerates the excretion of calcium in the kidneys.
  • Reduces calcium absorption in the intestine.

Parathyroid Hormone (PTH)

The parathyroid gland secretes Parathyroid Hormone (PTH), which plays a fundamental role in controlling the level of calcium and phosphorus in the body. PTH acts to increase blood calcium levels by:

• Releasing calcium from the bones.
• Stimulating the activation of Vitamin D, which in turn increases calcium absorption in the intestine.

Calcium is essential not only as a component of bones and teeth but also for nerve impulse transmission, muscle contraction, and blood clotting.

Functions of the Thymus Gland

The thymus produces hormone-like substances involved in the maturation processes of lymphocytes (T-cells). Its action is most evident in childhood, contributing significantly to immune system enhancement.

Hormones Produced by the Pancreas

The pancreas secretes Insulin and Glucagon, which are crucial for controlling blood sugar levels and the utilization of glucose inside cells.

• Insulin: Promotes the uptake of glucose by cells, lowering blood sugar.
• Glucagon: Promotes the breakdown of glycogen into glucose in liver cells, raising blood sugar.

Hormonal Functions of the Ovaries and Testes (Gonads)

The ovaries (female) and testes (male) secrete sex hormones involved in the production and maturation of gametes (sperm and eggs), as well as the development of secondary sexual characteristics.

• Estrogen: Controls the menstrual cycle and subsequent development of female secondary sexual characteristics.
• Testosterone and Androgens: Affect the development of male secondary sexual characteristics and increase sperm production.

Functions of Hormones Produced by the Adrenal Glands

The adrenal glands consist of two main parts: the cortex (outer layer) and the medulla (inner core).

Adrenal Cortex Hormones (Corticosteroids)

The cortex produces steroid hormones called corticosteroids, divided into two main groups:

• Glucocorticoids (e.g., Cortisol):
  • Stimulate the production of glucose from protein and fat.
  • Reduce the cellular use of glucose.
  • Inhibit inflammatory processes.
• Mineralocorticoids (e.g., Aldosterone):
  • Regulate the level of certain minerals, primarily sodium and potassium, affecting blood pressure.

Adrenal Medulla Hormones

The medulla contains neurosecretory cells that secrete catecholamines:

• Epinephrine (Adrenaline) and Norepinephrine: Prepare the body to react to danger (the “fight or flight” response).

Related Biological Processes

Cellular Respiration

The overall process of cellular respiration is summarized by the following reaction:

Nutrients (Glucose) + Oxygen → Carbon Dioxide + Water + ATP (Energy) + Heat

Comparison: Photosynthesis vs. Respiration