Endocrine system

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

This article needs to be developed more. It should be a more substantial article, as it deals with one of the main systems. It can be a portal article to some extent, as we will develop other articles on the various glands, heart, etc. But it should be at least 2,000 words. Also, a question: Does endocrine system refer only to humans or does it also reference other animals?

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. 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.

Endocrine glands and the hormones secreted

In both sexes

Hypothalamus
- Thyrotropin-releasing hormone (TRH)
- Gonadotropin-releasing hormone (GnRH)
- Growth hormone-releasing hormone (GHRH)
- Corticotropin-releasing hormone (CRH)
- Somatostatin (SS; also GHIH, growth factor-inhibiting hormone)
- Dopamine (DA)

Pituitary gland
- Anterior pituitary (adenohypophysis)
  - Growth hormone (GH)
  - Prolactin (PRL)
  - Adrenocorticotropic hormone (ACTH, corticotropin)
  - Thyroid-stimulating hormone (TSH, thyrotropin)
  - Follicle-stimulating hormone (FSH, a gonadotropin)
  - Luteinizing hormone (LH, a gonadotropin)
- Posterior pituitary (neurohypophysis)
  - Oxytocin (ocytocin)
  - Arginine vasopressin (AVP; also ADH, antidiuretic hormone)

Pineal gland
- Melatonin

Thyroid gland
- Triiodothyronine (T3), the potent form of thyroid hormone
- Thyroxine (T4), a less active form of thyroid hormone
- Calcitonin

Parathyroid gland
- Parathyroid hormone (PTH)

Heart
- Atrial-natriuretic peptide (ANP)

Stomach and intestines
- Cholecystokinin (CCK)
- Gastrin
- Ghrelin
- Neuropeptide Y (NPY)
- Secretin
- Somatostatin

Liver
- Insulin-like growth factor (IGF)
- Angiotensinogen
- Thrombopoietin

Islets of Langerhans in the pancreas
- Insulin
- Glucagon
- Somatostatin

Adrenal glands
- Adrenal cortex
  - Glucocorticoids (chiefly cortisol)
  - Mineralocorticoids (chiefly aldosterone)
  - Androgens (including DHEA and testosterone)
- Adrenal medulla
  - Adrenaline (epinephrine)
  - Noradrenaline (norepinephrine)

Kidney
- Renin
- Erythropoietin (EPO)
- Calcitriol (the active form of vitamin D₃)

Skin
- Vitamin D₃ (calciferol)

Adipose tissue
- Leptin
- Estrogens (mainly estrone)

In males only

Testes
- Androgens (chiefly testosterone)

In females only

Ovarian follicle
- Estrogens (mainly estradiol)
- Testosterone

Corpus luteum
- Progesterone
- Estrogens (mainly estradiol)

Placenta (when pregnant)
- Progesterone
- Estrogens (mainly estriol)
- Human chorionic gonadotrophin (HCG)
- Human placental lactogen (HPL)

Role in disease

Diseases of the endocrine system are common, such as diabetes mellitus and thyroid disease.

Endocrinopathies can occur with any of these. Hypofunction can occur as result of loss of reserve, hyposecretion, agenesis, atrophy, destruction, etc. Hyperfunction can occur as result of hypersecretion, loss of suppression, tumor, hyperplasia, etc.

Endocrinopathies are classified as primary, secondary, or tertiary.

Primary is target organ dysfunction and is normally associated with increased or decreased secretory hormones. Secondary is a dysfunction that originates elsewhere like the pituitary gland and is normally associated with increased or decreased production of trophic factors. Tertiary is associated with dysfunction of the hypothalamus and its releasing hormones.

Diffuse 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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