Endocrine system

Image:Illu endocrine system.png The endocrine system is a control system of ductless glandsthat secrete chemical messengers called hormonesthat circulate within the body via the bloodstreamto 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 glandssuch as salivary glands, sweat glandsand glands within the gastrointestinal tract.

The field of medicinethat 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 ligandactivated 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.

Table 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)
  • 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 hormone
  • Calcitonin

• Parathyroid gland
  • Parathyroid hormone(PTH)

• Heart
  • Atrial-natriuretic peptide(ANP)

• Stomachand intestines
  • Gastrin
  • Secretin
  • Cholecystokinin(CCK)
  • Somatostatin
  • Neuropeptide Y

• Liver
  • Insulin-like growth factor
  • Angiotensinogen
  • Thrombopoietin

• Islets of Langerhansin 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
  • Oestrogens
  • Testosterone

• Corpus luteum
  • Progesterone

• Placenta (when pregnant)
  • Progesterone
  • Human chorionic gonadotrophin(HCG)
  • Human placental lactogen(HPL)

Role in disease

Diseases of the endocrine system are common, such as diabetes mellitusand thyroiddisease.

Endocrineopathies 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.

Endocrineopathies 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.

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 myocytesin the heart (atria) and epithelial cellsin 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.

See also

• Receptors
• Releasing hormones
• Nervous system
• Endocrine disruptor
• Neuroendocrinology
• Endocrinology
• Hormones

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This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Endocrine+system Wikipedia article Endocrine system.