The endocrine system is an integrated system of small organs that involve the release of extracellular signaling molecules known as hormones. The endocrine system is instrumental in regulating metabolism, growth and development and puberty, tissue function, and plays a part also in mood.
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 is an information signal system much like the nervous system. However, the nervous system uses nerves to conduct information, whereas the endocrine system mainly uses blood vessels as information channels. Glands located in many regions of the body release into the bloodstream specific chemical messengers called hormones. Hormones regulate the many and varied functions of an organism, e.g., mood, growth and development, tissue function, and metabolism, as well as sending messages and acting on them.
Types of signaling
The typical mode of cell signaling in the endocrine system is endocrine signaling. However, there are also other modes, i.e., paracrine, autocrine, and neuroendocrine signaling . Purely neurocrine signaling between neurons, on the other hand, belongs completely to the nervous system.
A number of glands that signal each other in sequence is usually referred to as an axis, for example the Hypothalamic-pituitary-adrenal axis.
Typical endocrine glands are the pituitary, thyroid, and adrenal glands. Features of endocrine glands are, in general, their ductless nature, their vascularity, and usually the presence of intracellular vacuoles or granules storing their hormones. In contrast exocrine glands such as salivary glands, sweat glands, and glands within the gastrointestinal tract tend to be much less vascular and have ducts or a hollow lumen.
Other signaling can target the same cell.
Paracrine signaling is where the target cell is nearby.
Juxtacrine signals are transmitted along cell membranes via protein or lipid components integral to the membrane and are capable of affecting either the emitting cell or cells immediately adjacent.
Role in disease
Diseases of the endocrine system are common, including diseases such as diabetes mellitus, thyroid disease, and obesity.
Endocrine disease is characterised by dysregulated hormone release (a productive Pituitary adenoma), inappropriate response to signalling (Hypothyroidism), lack or destruction of a gland (Diabetes mellitus type 1, diminished erythropoiesis in Chronic renal failure), or structural enlargement in a critical site such as the neck (Toxic multinodular goitre). Hypofunction of endocrine glands can occur as result of loss of reserve, hyposecretion, agenesis, atrophy, or active destruction. Hyperfunction can occur as result of hypersecretion, loss of suppression, hyperplastic, or neoplastic change, or hyperstimulation.
Endocrinopathies are classified as primary, secondary, or tertiary. Primary endocrine disease inhibits the action of downstream glands. Tertiary endocrine disease is associated with dysfunction of the hypothalamus and its releasing hormones.
Cancer can occur in endocrine glands, such as the thyroid, and hormones have been implicated in signalling distant tissues to proliferate, for example the Estrogen receptor has been shown to be involved in certain breast cancers. Endocrine, Paracrine, and autocrine signalling have all been implicated in proliferation, one of the required steps of oncogenesis.
Table of endocrine glands and secreted hormones
This is a table of the glands of the endocrine system, and their secreted hormones
| Secreted hormone ||From cells || Effect
| Calcidiol (25-hydroxyvitamin D3)
|| || Inactive form of Vitamin D3
These originate either from the ovarian follicle or the corpus luteum.
| Secreted hormone || From cells || Effect
|| Granulosa cells, theca cells || Support pregnancy:
- Convert endometrium to secretory stage
- Make cervical mucus permeable to sperm.
- Inhibit immune response, e.g., towards the human embryo
- Decrease uterine smooth muscle contractility
- Inhibit lactation
- Inhibit onset of labor.
|| Theca cells || Substrate for estrogen
| Estrogens (mainly estradiol)
|| Granulosa cells || Structural:
- Increase hepatic production of binding proteins
- Reduce bowel motility
- Increase cholesterol in bile
- Support hormone-sensitive breast cancers  (Suppression of production in the body of estrogen is a treatment for these cancers.)
- Promote lung function by supporting alveoli.
|| Granulosa cells || Inhibit production of FSH from anterior pituitary
| Secreted hormone || Abbreviation || From cells || Effect
|| PRL || Decidual cells || milk production in mammary glands
|| || Decidual cells || Unclear in humans
- Journals Designed for Clinical Endocrinologists
- Islet cell antibody
- Binding of antibody to pancreas
- ^ Collier, Judith. et.al (2006). Oxford Handbook of Clinical Specialties 7th edn.. Oxford, 350 -351. ISBN 0-19-853085-4.
- ^ University of Virginia - HISTOLOGY OF THE ENDOCRINE GLANDS
- ^ Kasper et al. (2005). Harrison's Principles of Internal Medicine. McGraw Hill, 2074. ISBN 0-07-139140-1.
- ^ Bhowmick NA, Chytil A, Neilson EG, Moses HL (2004). "TGF-beta signaling in fibroblasts modulates the oncogenic potential of adjacent epithelia.". Science Feb 6 303(5659): 848-51.
- ^ Kosfeld M et al. (2005) Oxytocin increases trust in humans. Nature 435:673-676. PDF PMID 15931222
- ^ Scientific American Mind, "Rhythm and Blues"; June/July 2007; Scientific American Mind; by Ulrich Kraft
- ^ a b c Kaushansky K. Lineage-specific hematopoietic growth factors. N Engl J Med 2006;354:2034-45. PMID 16687716.
- ^ The adipose tissue as a source of vasoactive factors. Frühbeck G. (Curr Med Chem Cardiovasc Hematol Agents. 2004 Jul;2(3):197-208.)
- ^ http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/otherendo/somatostatin.html Colorado State University - Biomedical Hypertextbooks - Somatostatin
- ^ Diabetes-related changes in contractile responses of stomach fundus to endothelin-1 in streptozotocin-induced diabetic rats Journal of Smooth Muscle Research Vol. 41 (2005) , No. 1 35-47. Kazuki Endo1), Takayuki Matsumoto1), Tsuneo Kobayashi1), Yutaka Kasuya1) and Katsuo Kamata1)
- ^ a b Physiology at MCG 5/5ch4/s5ch4_17
- ^ Pentikäinen V, Erkkilä K, Suomalainen L, Parvinen M, Dunkel L. Estradiol Acts as a Germ Cell Survival Factor in the Human Testis in vitro.
The Journal of Clinical Endocrinology & Metabolism 2006;85:2057-67 PMID 10843196
- ^ a b c d http://www.vivo.colostate.edu/hbooks/pathphys/reprod/placenta/endocrine.html
- ^ Physiology at MCG 5/5ch9/s5ch9_13
- ^ Hould F, Fried G, Fazekas A, Tremblay S, Mersereau W (1988). "Progesterone receptors regulate gallbladder motility". J Surg Res 45 (6): 505-12. PMID 3184927.
- ^ http://www.breastcancer.org/tre_sys_hrt_idx.html
- ^ Massaro D, Massaro GD (2004). "Estrogen regulates pulmonary alveolar formation, loss, and regeneration in mice". American Journal of Physiology. Lung Cellular and Molecular Physiology 287 (6): L1154-9. PMID 15298854 url=http://ajplung.physiology.org/cgi/content/full/287/6/L1154.
|Endocrine system: hormones/endocrine glands (Peptide hormones, Steroid hormones)|
|Hypothalamic-pituitary|| Hypothalamus: TRH, CRH , GnRH, GHRH, somatostatin, dopamine - Posterior pituitary: vasopressin, oxytocin - Anterior pituitary: α (FSH, LH, TSH), GH, prolactin, POMC (ACTH, MSH, endorphins, lipotropin)|
|Adrenal axis|| Adrenal medulla: epinephrine, norepinephrine - Adrenal cortex: aldosterone, cortisol, DHEA|
|Thyroid axis|| Thyroid: thyroid hormone (T3 and T4) - calcitonin - Parathyroid: PTH|
|Gonadal axis||Testis: testosterone, AMH, inhibin - Ovary: estradiol, progesterone, inhibin/activin, relaxin (pregnancy)|
|Other end. glands|| Pancreas: glucagon, insulin, somatostatin - Pineal gland: melatonin|
|Non-end. glands|| Placenta: hCG, HPL, estrogen, progesterone - Kidney: renin, EPO, calcitriol, prostaglandin - Heart atrium: ANP - Stomach: gastrin, ghrelin - Duodenum: CCK, GIP, secretin, motilin, VIP - Ileum: enteroglucagon - Adipose tissue: leptin, adiponectin, resistin - Thymus: Thymosin - Thymopoietin - Skeleton: Osteocalcin - Liver/other: Insulin-like growth factor (IGF-1, IGF-2)|
|Target-derived||NGF, BDNF, NT-3|
|Endocrine pathology: endocrine diseases (E00-35, 240-259)|
|Thyroid||Hypothyroidism (Iodine deficiency, Cretinism, Congenital hypothyroidism, Goitre, Myxedema) - Hyperthyroidism (Graves disease, Toxic multinodular goitre, Teratoma with thyroid tissue or Struma ovarii) - Thyroiditis (De Quervain's thyroiditis, Hashimoto's thyroiditis, Riedel's thyroiditis) - Euthyroid sick syndrome|
|Pancreas||Diabetes mellitus (type 1, type 2, coma, angiopathy, ketoacidosis, nephropathy, neuropathy, retinopathy) - Hypoglycemia - Hyperinsulinism - Zollinger-Ellison syndrome|
|Parathyroid||Hypoparathyroidism (Pseudohypoparathyroidism) - Hyperparathyroidism (Primary, Secondary, Tertiary)|
|Pituitary||Hyperpituitarism (Acromegaly, Hyperprolactinaemia, SIADH) - Hypopituitarism (Simmonds' disease/Sheehan's syndrome, Kallmann syndrome, Growth hormone deficiency, Diabetes insipidus) - Adiposogenital dystrophy - Empty sella syndrome|
|Adrenal||Cushing's syndrome (Nelson's syndrome, Pseudo-Cushing's syndrome) - CAH (due to 21-hydroxylase deficiency) - Hyperaldosteronism (Conn syndrome, Bartter syndrome) - Adrenal insufficiency (Addison's disease) - Hypoaldosteronism|
|Gonads||ovarian dysfunction (Polycystic ovary syndrome, Premature ovarian failure) - testicular dysfunction (5-alpha-reductase deficiency) - general (Hypogonadism, Delayed puberty, Precocious puberty)|
|Other||Autoimmune polyendocrine syndrome - Carcinoid syndrome - Short stature (Laron syndrome, Psychogenic dwarfism) - Gigantism - Androgen insensitivity syndrome - Progeria - Multiple endocrine neoplasia (1, 2)|