Endocrine System from MobileReference

The endocrine system is a control system of ductless glands that secrete chemical messengers called hormones that circulate within the body via the bloodstream to affect distant organs. Hormones act as "messengers", and are carried by the bloodstream to different cells in the body, which interpret these messages and act on them.

Major endocrine glands. (Male left, female on the right.)
1. Pineal gland
2. Pituitary gland
3. Thyroid gland
4. Thymus
5. Adrenal gland
6. Pancreas
7. Ovary
8. Testis

The endocrine system 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 links the brain to the organs that control body metabolism, growth and development, and reproduction.

Signal transduction of some hormones with steroid structure involves nuclear hormone receptor proteins that are a class of ligand activated proteins that, when bound to specific sequences of DNA serve as on-off switches for transcription within the cell nucleus. These switches control the development and differentiation of skin, bone and behavioral centers in the brain, as well as the continual regulation of reproductive tissues.

The endocrine system regulates its hormones through negative feedback. Increases in hormone activity decrease the production of that hormone. The immune system and other factors contribute as control factors also, altogether maintaining constant levels of hormones.

List of endocrine glands and the 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).
Pituitary gland>Posterior lobe (neurohypophysis): Oxytocin, ADH (antidiuretic hormone)
Pineal gland: Melatonin
Thyroid gland: Thyroxine (T4), a form of thyroid hormone, Triiodothyronine (T3), a form of thyroid hormonem, Calcitonin.
Parathyroid gland: 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 glands>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: Oestrogens, Testosterone
Corpus luteum: Progesterone
Placenta (when pregnant): Progesterone, Human chorionic gonadotrophin (HCG), Human placental lactogen (HPL)

Difuse Endocrine System

Organs aren't the sole way for hormones to be sent into the body; there are a host of specific cells which secrete hormones independently. These are called the "diffuse" endocrine system, and include myocytes in the heart (atria) and epithelial cells in the stomach and small intestines. In fact, if one were to classify any chemical excretions in the term "hormone," every cell in the human body could be considered a part of the endocrine system.

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