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Endocrine system

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.^[1] The field of medicine that deals with disorders of endocrine glands is endocrinology, a branch of the wider field of internal medicine.

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Function

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 ^[2]. Purely neurocrine signaling between neurons, on the other hand, belongs completely to the nervous system.

Endocrine

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.

Autocrine

Main article: Autocrine signalling

Other signaling can target the same cell.

Paracrine

Main article: Paracrine signalling

Paracrine signaling is where the target cell is nearby.

Juxtacrine

Main article: Juxtacrine signalling

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

Main article: Endocrine diseases

Diseases of the endocrine system are common,^[3] 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.^[4]

Table of endocrine glands and secreted hormones

This is a table of the glands of the endocrine system, and their secreted hormones

Hypothalamus

Secreted hormone	Abbreviation	From cells	Effect
Thyrotropin-releasing hormone	TRH	Parvocellular neurosecretory neurons	Release thyroid-stimulating hormone from anterior pituitary (primarily) Stimulate prolactin release from anterior pituitary.
Gonadotropin-releasing hormone	GnRH	Neuroendocine cells of the Preoptic area	Release of FSH and LH from anterior pituitary.
Growth hormone-releasing hormone	GHRH	Neuroendocrine neurons of the Arcuate nucleus	Release GH from anterior pituitary
Corticotropin-releasing hormone	CRH	Parvocellular neurosecretory neurons	Release ACTH from anterior pituitary
Vasopressin		Parvocellular neurosecretory neurons	Release ACTH from anterior pituitary
Somatostatin, also growth hormone-inhibiting hormone	SS or GHIH	Neuroendocrince cells of the Periventricular nucleus	Inhibit release of GH and TRH from anterior pituitary
Prolactin inhibiting hormone or Dopamine	PIH or DA	Dopamine neurons of the arcuate nucleus	Inhibit release of prolactin and TRH from anterior pituitary
Prolactin-releasing hormone	PRH		Release prolactin from anterior pituitary

Pineal body

Secreted hormone	From cells	Effect
Melatonin (Primarily)	Pinealocytes	antioxidant and causes drowsiness

Pituitary gland (hypophysis)

Anterior pituitary lobe (adenohypophysis)

Secreted hormone	Abbreviation	From cells	Effect
Growth hormone	GH	Somatotropes	stimulates growth and cell reproduction Release Insulin-like growth factor 1 from liver
Prolactin	PRL	Lactotropes	milk production in mammary glands sexual gratification after sexual acts
Adrenocorticotropic hormone or corticotropin	ACTH	Corticotropes	synthesis of corticosteroids (glucocorticoids and androgens) in adrenocortical cells
Lipotropin		Corticotropes	lipolysis and steroidogenesis, stimulates melanocytes to produce melanin
Thyroid-stimulating hormone or thyrotropin	TSH	Thyrotropes	stimulates thyroid gland to secrete thyroxine (T4) and triiodothyronine (T3)
Follicle-stimulating hormone	FSH	Gonadotropes	In female: stimulates maturation of Graafian follicles in ovary. In male: spermatogenesis, enhances production of androgen-binding protein by the Sertoli cells of the testes
Luteinizing hormone	LH	Gonadotropes	In female: ovulation In male: stimulates Leydig cell production of testosterone

Posterior pituitary lobe (neurohypophysis)

Secreted hormone	Abbreviation	From cells	Effect
Oxytocin		Magnocellular neurosecretory cells	Contraction of cervix and vagina Involved in orgasm, trust between people.^[5] and circadian homeostasis (body temperature, activity level, wakefulness) ^[6]. release breast milk
Vasopressin or antidiuretic hormone	AVP or ADH	Magnocellular neurosecretory cells	retention of water in kidneys moderate vasoconstriction

Intermediate pituitary lobe (pars intermedia)

Secreted hormone	Abbreviation	From cells	Effect
Melanocyte-stimulating hormone	MSH	Melanotroph	melanogenesis by melanocytes in skin and hair.

Thyroid

Secreted hormone	Abbreviation	From cells	Effect
Triiodothyronine	T3	Thyroid epithelial cell	potent form of thyroid hormone: increase the basal metabolic rate & sensitivity to catecholamines, affect protein synthesis
Thyroxine or tetraiodothyronine	T4	Thyroid epithelial cells	less active form of thyroid hormone: increase the basal metabolic rate & sensitivity to catecholamines, affect protein synthesis, often functions as a prohormone
Calcitonin		Parafollicular cells	Construct bone reduce blood Ca²⁺

Parathyroid

Secreted hormone	Abbreviation	From cells	Effect
Parathyroid hormone	PTH	Parathyroid chief cell	increase blood Ca²⁺: *indirectly stimulate osteoclasts Ca²⁺ reabsorption in kidney activate vitamin D (Slightly) decrease blood phosphate: (decreased reuptake in kidney but increased uptake from bones activate vitamin D)

Heart

Secreted hormone	Abbreviation	From cells	Effect
Atrial-natriuretic peptide	ANP	Cardiac myocytes	Reduce blood pressure by: reducing systemic vascular resistance, reducing blood water, sodium and fats
Brain natriuretic peptide	BNP	Cardiac myocytes	(To a minor degree than ANP) reduce blood pressure by: reducing systemic vascular resistance, reducing blood water, sodium and fats

Striated muscle

Secreted hormone	From cells	Effect
Thrombopoietin	Myocytes	stimulates megakaryocytes to produce platelets^[7]

Skin

Secreted hormone	From cells	Effect
Calcidiol (25-hydroxyvitamin D₃)		Inactive form of Vitamin D3

Adipose tissue

Secreted hormone	From cells	Effect
Leptin (Primarily)	Adipocytes	decrease of appetite and increase of metabolism.
Estrogens^[8] (mainly Estrone)	Adipocytes

Stomach

Secreted hormone	Abbreviation	From cells	Effect
Gastrin (Primarily)		G cells	Secretion of gastric acid by parietal cells
Ghrelin		P/D1 cells	Stimulate appetite, secretion of growth hormone from anterior pituitary gland
Neuropeptide Y	NPY		increased food intake and decreased physical activity
Secretin		S cells	Secretion of bicarbonate from liver, pancreas and duodenal Brunner's glands Enhances effects of cholecystokinin Stops production of gastric juice
Somatostatin		D cells	Suppress release of gastrin, cholecystokinin (CCK), secretin, motilin, vasoactive intestinal peptide (VIP), gastric inhibitory polypeptide (GIP), enteroglucagon Lowers rate of gastric emptying Reduces smooth muscle contractions and blood flow within the intestine ^[9]
Histamine		ECL cells	stimulate gastric acid secretion
Endothelin		X cells	Smooth muscle contraction of stomach ^[10]

Duodenum

Secreted hormone	From cells	Effect
Cholecystokinin	I cells	Release of digestive enzymes from pancreas Release of bile from gallbladder hunger suppressant

Liver

Secreted hormone	Abbreviation	From cells	Effect
Insulin-like growth factor (or somatomedin) (Primarily)	IGF	Hepatocytes	insulin-like effects regulate cell growth and development
Angiotensinogen and angiotensin		Hepatocytes	vasoconstriction release of aldosterone from adrenal cortex dipsogen.
Thrombopoietin		Hepatocytes	stimulates megakaryocytes to produce platelets^[7]

Pancreas

Secreted hormone	From cells	Effect
Insulin (Primarily)	ß Islet cells	Intake of glucose, glycogenesis and glycolysis in liver and muscle from blood intake of lipids and synthesis of triglycerides in adipocytes Other anabolic effects
Glucagon (Also Primarily)	a Islet cells	glycogenolysis and gluconeogenesis in liver increases blood glucose level
Somatostatin	d Islet cells	Inhibit release of insulin ^[11] Inhibit release of glucagon^[11] Suppress the exocrine secretory action of pancreas.
Pancreatic polypeptide	PP cells	Unknown

Kidney

Secreted hormone	From cells	Effect
Renin (Primarily)	Juxtaglomerular cells	Activates the renin-angiotensin system by producing angiotensin I of angiotensinogen
Erythropoietin (EPO)	Extraglomerular mesangial cells	Stimulate erythrocyte production
Calcitriol (1,25-dihydroxyvitamin D₃)		Active form of vitamin D3 Increase absorption of calcium and phosphate from gastrointestinal tract and kidneys inhibit release of PTH
Thrombopoietin		stimulates megakaryocytes to produce platelets^[7]

Adrenal glands

Adrenal cortex

Secreted hormone	From cells	Effect
Glucocorticoids (chiefly cortisol)	zona fasciculata and zona reticularis cells	Stimulation of gluconeogenesis Inhibition of glucose uptake in muscle and adipose tissue Mobilization of amino acids from extrahepatic tissues Stimulation of fat breakdown in adipose tissue anti-inflammatory and immunosuppressive
Mineralocorticoids (chiefly aldosterone)	Zona glomerulosa cells	Increase blood volume by reabsorption of sodium in kidneys (primarily) Potassium and H⁺ secretion in kidney.
Androgens (including DHEA and testosterone)	Zona fasciculata and Zona reticularis cells	Virilization, anabolic

Adrenal medulla

Secreted hormone	From cells	Effect
Adrenaline (epinephrine) (Primarily)	Chromaffin cells	Fight-or-flight response: Boost the supply of oxygen and glucose to the brain and muscles (by increasing heart rate and stroke volume, vasodilation, increasing catalysis of glycogen in liver, breakdown of lipids in fat cells) Dilate the pupils Suppress non-emergency bodily processes (e.g., digestion) Suppress immune system
Noradrenaline (norepinephrine)	Chromaffin cells	Fight-or-flight response: Boost the supply of oxygen and glucose to the brain and muscles (by increasing heart rate and stroke volume, vasoconstriction and increased blood pressure, breakdown of lipids in fat cells) Increase skeletal muscle readiness.
Dopamine	Chromaffin cells	Increase heart rate and blood pressure
Enkephalin	Chromaffin cells	Regulate pain

Testes

Secreted hormone	From cells	Effect
Androgens (chiefly testosterone)	Leydig cells	Anabolic: growth of muscle mass and strength, increased bone density, growth and strength, Virilizing: maturation of sex organs, formation of scrotum, deepening of voice, growth of beard and axillary hair.
Estradiol	Sertoli cells	Prevent apoptosis of germ cells^[12]
Inhibin	Sertoli cells	Inhibit production of FSH

Ovary

These originate either from the ovarian follicle or the corpus luteum.

Secreted hormone	From cells	Effect
Progesterone	Granulosa cells, theca cells	Support pregnancy^[13]: 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^[13] Inhibit lactation Inhibit onset of labor. Other: Raise epidermal growth factor-1 levels Increase core temperature during ovulation^[14] Reduce spasm and relax smooth muscle (widen bronchi and regulate mucus) Anti-inflammatory Reduce gall-bladder activity^[15] Normalize blood clotting and vascular tone, zinc and copper levels, cell oxygen levels, and use of fat stores for energy Assist in thyroid function and bone growth by osteoblasts Increase resilience in bone, teeth, gums, joint, tendon, ligament, and skin Promote healing by regulating collagen Provide nerve function and healing by regulating myelin Prevent endometrial cancer by regulating effects of estrogen
Androstenedione	Theca cells	Substrate for estrogen
Estrogens (mainly estradiol)	Granulosa cells	Structural: Promote formation of female secondary sex characteristics Accelerate height growth Accelerate metabolism (burn fat) Reduce muscle mass Stimulate endometrial growth Increase uterine growth Maintain blood vessels and skin Reduce bone resorption, increase bone formation Protein synthesis: Increase hepatic production of binding proteins Coagulation: Increase circulating level of factors 2, 7, 9, 10, antithrombin III, plasminogen Increase platelet adhesiveness Increase HDL, triglyceride, height growth Decrease LDL, fat depositition Fluid balance: Regulate salt (sodium) and water retention Increase growth hormone Increase cortisol, SHBG Gastrointestinal tract: Reduce bowel motility Increase cholesterol in bile Melanin: Increase pheomelanin, reduce eumelanin Cancer: Support hormone-sensitive breast cancers ^[16] (Suppression of production in the body of estrogen is a treatment for these cancers.) Lung function: Promote lung function by supporting alveoli^[17].
Inhibin	Granulosa cells	Inhibit production of FSH from anterior pituitary

Placenta (when pregnant)

Secreted hormone	Abbreviation	From cells	Effect
Progesterone (Primarily)			Support pregnancy^[13]: Inhibit immune response, towards the fetus. Decrease uterine smooth muscle contractility^[13] Inhibit lactation Inhibit onset of labor. Support fetal production of adrenal mineralo- and glucosteroids. Other effects on mother similar to ovarian follicle-progesterone
Estrogens (mainly Estriol) (Also Primarily)			Effects on mother similar to ovarian follicle estrogen
Human chorionic gonadotropin	HCG	Syncytiotrophoblast	promote maintenance of corpus luteum during beginning of pregnancy Inhibit immune response, towards the human embryo.
Human placental lactogen	HPL	Syncytiotrophoblast	increase production of insulin and IGF-1 increase insulin resistance and carbohydrate intolerance
Inhibin		Fetal Trophoblasts	suppress FSH

Uterus (when pregnant)

Secreted hormone	Abbreviation	From cells	Effect
Prolactin	PRL	Decidual cells	milk production in mammary glands
Relaxin		Decidual cells	Unclear in humans

References

^ 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.

v • d • e Human organ systems
Cardiovascular system • Digestive system • Endocrine system • Immune system • Integumentary system • Lymphatic system • Muscular system • Nervous system • Reproductive system • Respiratory system • Skeletal system • Urinary system

v • d • e Human anatomy, endocrine system: endocrine glands
Hypothalamic/pituitary axes	Adrenal axis: Adrenal gland Thyroid axis: Thyroid gland (Parafollicular cell, Thyroid epithelial cell) - Parathyroid gland (Oxyphil cell, Chief cell) Gonadal axis: Testes - Ovaries - Corpus luteum
Other	Pineal gland • Islets of pancreas

v • d • e 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

v • d • e 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)

v • d • e cell signaling
Key concepts	Ligand - Cell signaling networks - Signal transduction - Apoptosis - Second messenger system (Ca²⁺ signaling, Lipid signaling)
Processes	Paracrine - Autocrine - Juxtacrine - Neurotransmitters - Endocrine (Neuroendocrine)
Types of proteins	Receptor (Transmembrane, Intracellular) - Transcription factor (General, Preinitiation complex, TFIID, TFIIH) - Adaptor protein

v • d • e Endocrine system intervention (ICD-9-CM V3 06-07)
Operations, surgeries	Thyroidectomy - Parathyroidectomy - Adrenalectomy - Hypophysectomy - Thymectomy
Hormone therapy	in oncology - sex reassignment (female-to-male, male-to-female)
Other medication	Replacement therapy

Categories: Cell signaling | Signal transduction

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Endocrine_system". A list of authors is available in Wikipedia.