Endocrine system
The
endocrine system is a control system of
ductless glands that secrete chemical "instant messengers" called
hormones that circulate within the body via the
bloodstream to affect distant cells within specific
organs. Endocrine glands secrete their products immediately into the blood or interstitial fluid, without storage of the chemical. Hormones act as "messengers," and are carried by the bloodstream to different cells in the body, which interpret these messages and act on them. Typical endocrine glands are
pituitary,
thyroid, and
adernal glands, but not
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.
The endocrine system provides an electrochemical connection from the
hypothalamus of the brain to all the organs that control body
metabolism,
growth and development, and
reproduction.
There are two types of hormones secreted in the endocrine system: (1) steroidal and (2) nonsteroidal, or protein based hormones. 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.Nonsteriodal hormones bind to
receptor sites on the external surface of the cell membrane and use a
second messenger method of altering internal cell functions.
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.
Reference: http://www.hormoneprofile.com/howhormoneswork.htm
In both sexes
*
Hypothalamus produces
**
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 produces
**
Anterior pituitary lobe (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 lobe (neurohypophysis)
***
Oxytocin (ocytocin)
***
Arginine vasopressin (AVP; also ADH, antidiuretic hormone)
* Also within the brain,
Pineal gland produces
**
Melatonin*
Thyroid gland produces
**Triiodothyronine (T3), the potent form of
thyroid hormone**Thyroxine (T4), a less active form of
thyroid hormone**
Calcitonin*
Parathyroid gland produces
**
Parathyroid hormone (PTH)
*
Heart produces
**
Atrial-natriuretic peptide (ANP)
*
Stomach and intestines produce
**
Cholecystokinin (CCK)
**
Gastrin**
Ghrelin**
Neuropeptide Y (NPY)
**
Secretin**
Somatostatin*
Liver produces
**
Insulin-like growth factor (IGF)
**
Angiotensinogen**
Thrombopoietin*
Islets of Langerhans in the pancreas produce
**
Insulin**
Glucagon**
Somatostatin*
Adrenal glands produce
**
Adrenal cortex***
Glucocorticoids (chiefly
cortisol)
***
Mineralocorticoids (chiefly
aldosterone)
***
Androgens (including
DHEA and
testosterone)
**
Adrenal medulla***
Adrenaline (epinephrine)
***
Noradrenaline (norepinephrine)
**
Testosterone*
Kidney produces
**
Renin**
Erythropoietin (EPO)
**
Calcitriol (the active form of vitamin D
3)
*
Skin produces
**
Vitamin D3 (calciferol)
*
Adipose tissue**
Leptin**
Estrogens (mainly
estrone)
In males only
*
Testes**
Androgens (chiefly
testosterone)
In females only
*
Ovarian follicle**
Estrogens (mainly
estradiol)
*
Corpus luteum**
Progesterone**
Estrogens (mainly
estradiol)
*
Placenta (when
pregnant)
**
Progesterone**
Estrogens (mainly
estriol)
**
Human chorionic gonadotropin (HCG)
**
Human placental lactogen (HPL)
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.
*
Hormones*
Releasing hormones
*
Endocrinology*
Neuroendocrinology*
Nervous system*
Endocrine disruptor
