The endocrine system is a control system of ductless endocrine glands that secrete chemical messengers called hormones that circulate within the body via the bloodstream to affect distant organs. It does not include exocrine glands such as salivary glands, sweat glands and glands within the gastrointestinal tract. The field of medicine that deals with disorders of endocrine glands is endocrinology, a branch of the wider field of internal medicine.

Physiology

The endocrine system consists of a number of ductless glands located in different parts of body, which produce chemical substances called hormones (from Greek word mean-ing 'to excite') directly into the bloodstream, which affect various body functions and activities. Each hormone has a specific role and a target tissue or a target organ to act upon. These target organs respond to the effects of hormones. The hormones are re-leased in very minute concentrations at a time, depending upon the body's require-ment. The hormones are poured directly into the bloodstream, from where they go to their target organs or tissues regulating their activity without affecting any other metabolic activities. The production and release of hormones is controlled by a regulating mechanism called feedback mechanism, which inhibits or accelerates the production of hormones so that overproduction or underproduction does not take place. Over-production (hypersecretion) and underproduction (hyposecretion) of the hormones occurs when this regulating mechanism is not operating well and can lead to many disorders in the body.

List of all endocrine glands and their hormones secreted in both sexes starting from the head and going downwards

Hypothalamus

· Thyrotropin-releasing hormone (TRH)

· Gonadotropin-releasing hormone (GnRH)

· Growth hormone-releasing hormone (GHRH)

· Corticotropin-releasing hormone (CRH)

· Somatostatin

· Dopamine

Pituitary gland

Anterior lobe (adenohypophysis)

· GH (human growth hormone)

· PRL (prolactin)

· ACTH (adrenocorticotropic hormone)

· TSH (thyroid-stimulating hormone)

· FSH (follicle-stimulating hormone)

· LH (luteinizing hormone)

Posterior lobe (neurohypophysis)

· Oxytocin

· ADH (antidiuretic hormone)

Pineal gland

· Melatonin

Thyroid gland

· Thyroxine (T4)

· Triiodothyronine (T3)

· Calcitonin

Parathyroid glands

· Parathyroid hormone (PTH)

Heart

· Atrial-natriuretic peptide (ANP)

Stomach and intestines

· Gastrin

· Secretin

· Cholecystokinin (CCK)

· Somatostatin

· Neuropeptide Y

Liver

· Insulin-like growth factor

· Angiotensinogen

· Thrombopoietin

Islets of Langerhans in the pancreas

· Insulin

· Glucagon

· Somatostatin

Adrenal glands

Adrenal cortex

· Glucocorticoids - cortisol

· Mineralocorticoids - aldosterone

· Androgens (including testosterone)

Adrenal medulla

· Adrenaline (epinephrine)

· Noradrenaline (norepinephrine)

Kidney

· Renin

· Erythropoietin (EPO)

· Calcitriol

Skin

· Calciferol (vitamin D3)

Adipose tissue

· Leptin

In males only

Testes

· Androgens (testosterone)

In females only

Ovarian follicle

1. Estrogens

2. Testosterone

Corpus luteum

· Progesterone

Placenta (when pregnant)

· Progesterone

· Human chorionic gonadotrophin (HCG)

· Human placental lactogen (HPL)

However, endocrine glands of major significance in the human body and also transcription are the pituitary gland, thyroid gland, parathyroid gland, adrenal gland, pancreas, thymus gland, testes (in males) and ovaries (in females).

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