Endocrine System

The endocrine system consists of glands that secrete hormones that regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep, and mood, among other things.

Endocrine glands consist of groups of secretory cells which are surrounded by capillary networks. Hormones secreted by the secretory cells move into the bloodstream through the capillary networks.

Endocrine glands are widely separated from each other and are not physically connected. Endocrine glands are referred to as ductless glands because they secrete the hormones directly into the blood rather than through a duct. Hormones move to the target tissues and organs through the bloodstream and regulate cell growth and metabolism.


Major endocrine glands include:

  • Pineal gland
  • Pituitary gland
  • Pancreas
  • Ovaries
  • Testes
  • Thyroid gland
  • Parathyroid gland
  • Hypothalamus
  • Gastrointestinal tract
  • Adrenal glands

The endocrine system along with the autonomic nervous system is responsible for maintaining homeostasis. The response of the autonomic nervous is faster than endocrine control but the latter is more precise.

The hypothalamus is considered to be a part of the brain but it controls the pituitary gland and influences the functioning of other glands.

The testes and ovaries secrete hormones which regulate activities of the reproductive system. The placenta also has an endocrine function. Apart from endocrine glands, many other tissues and organs also secrete hormones. For example, leptin—the hormone which regulates appetite, is secreted by adipose tissue. The heart secretes a hormone called ‘atrial natriuretic peptide’ or ANP which is involved in the homeostatic control of body water, sodium, potassium and fat (adipose tissue).

Topics in this section

  • Pituitary gland and hypothalamus
    • Anterior pituitary
    • Posterior pituitary
  • Thyroid gland
  • Parathyroid gland
  • Adrenal (suprarenal) glands
    • Adrenal cortex
    • Adrenal medulla
    • Response to stress
  • Pancreatic islets
  • Pineal gland or body
  • Thymus gland
  • Local hormones
  • Disorders of the anterior pituitary
    • Hypersecretion of anterior pituitary hormones
    • Hyposecretion of anterior pituitary hormones
  • Disorders of the posterior pituitary
  • Disorders of the thyroid gland
    • Abnormal secretion of thyroid hormones
      • Hyperthyroidism
      • Hypothyroidism
    • Simple goiter
    • Tumors of the thyroid gland
  • Disorders of the parathyroid glands
    • Hyperparathyroidism
    • Hypoparathyroidism
  • Disorders of the adrenal cortex
    • Hypersecretion of glucocorticoids (Cushing’s syndrome)
    • Hyposecretion of glucocorticoids
    • Hypersecretion of mineralocorticoids
    • Hyposecretion of mineralocorticoids
    • Chronic adrenal cortex insufficiency (Addison’s disease)
  • Disorders of the adrenal medulla
    • Tumors
  • Disorders of the pancreatic islets
    • Diabetes mellitus
      • Type I, insulin-dependent diabetes mellitus (IDDM)
      • Type II, non-insulin-dependent diabetes mellitus (NIDDM)
      • Secondary diabetes
      • Effects of diabetes mellitus
      • Acute complication of diabetes mellitus
      • Long-term complications of diabetes mellitus