The Endocrine System

RSHWeekend 2Sian Moss

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The Endocrine System

The Nervous and Endocrine systems coordinate to form an information ‘super-system’ which oversees maintenance of

homeostasis

Neuroendocrine System

Historically………..All anatomical structures may be part of a wide functional circuitry, based on "internal secretions”

Toni, R. 2004. J Endocrinol Invest 27(6 Suppl):35-47.2

‘Structure’ of Endocrine System

http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookendocr.html 3

The endocrine system is a collection of ductless

glands that secrete chemical messengers

HORMONES

Local or circulating, hormonal signals pass through

the blood to arrive at a target cell in an organ, which

possesses the appropriate receptor for a specific

hormone

The Endocrine System

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Chemistry of HormonesChemically three types

Steroid hormones in most cases derived from cholesterol secreted by theadrenal cortex (cortisol and aldosterone)ovaries (oestrogen and progesterone)testes (testosterone)placenta (oestrogen and progesterone)

AMINES Derivatives of amino acids TRYPTOPHAN or TYROSINE Thyroid hormones (thyroxine and triiodothyronine)Adrenal medullae hormones (adrenalin and noradrenalin)

Proteins or peptides All remaining important endocrine hormones ( ADH, Insulin,glucagon, pituitary hormones etc)

Local hormonesEicosanoids considered local hormones, derived form Arachidonic acid

Paracrine or Autocrine actioneg Leukotrines and prostaglandins

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Control of hormone secretionInternal control system is generally via NEGATIVE FEEDBACK mechanisms

• There is a tendency for a gland to over secrete its hormone

• Hormone exerts its effect on target organ

• Organ function performed

• Over function causes negative feedback on gland to decrease secretion rate

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It is the degree of organ activity which is important factorIf the organ responds poorly to a hormone, the endocrine gland usually continues to secrete more and more until the appropriate level of activity is reached

Major Endocrine glands

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Pineal glandThe pineal gland is a pine cone shaped gland of the endocrine system, it produces several important hormones including melatonin.

The pineal gland connects the endocrine system with the nervous system in that it converts nerve signals from the sympathetic system of the PNS into hormone signals. It is under control of the hypothalamus

Function include:

• Synthesizes and secretes Melatonin during dark

• Provides an internal calendar regulating seasonal cycles in mammals

• Conversion of Nervous System Signals to Endocrine Signals

• Influences Sexual Development

• Melatonin and immune function theory - increased levels promote immune system and low levels suppress

• Abnormal daily Melatonin profiles found in some psychiatric and neurological disorders Macchi and Bruce 2004. Human pineal physiology and functional

significance of melatonin. Front Neuroendocrinol. Sep-Dec;25(3-4):177-95.

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Hypothalamus and Pituitary gland

http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookendocr.html

Hypothalamus controlsrelease of Pituitary hormones

TSHADH

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Pituitary gland

Thyroid gland

http://www.syncytiabeta.org/~syncyt5/syncytiabeta/index.php?title=Thyroid_Hormone_Regulation

•The Hypothalamus releases Thyrotropin-releasing Hormone TRH, which acts on the Anterior pituitary

•The Anterior pituitary synthesizes and secretes Thyroid Stimulating Hormone TSHwhich acts directly on the Thyroid gland

•The Thyroid gland releases thyroid hormones Thyroxine

•The Thyroid gland mostly releases T4which does not possess much endocrine activity. Target tissues converts T4 to either T3 or reverseT3.

T3 possesses tremendously more endocrine activity than T4 whereas rT3 does not possess any endocrine activity.

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T3 action causes increased basal metabolic rate

Parathyroid gland

http://columbiasurgery.org/parathyroid/patient_education.html

Parathyroid hormone PTH• Increases rate of Ca 2+ reabsorption in Kidney• Increases rate of Ca2+ absorption in gut• Releases Ca2+ from bone• Stimulates release of Calcitriol (active Vit D) from

kidneys for increased absorption of Ca2+ from gut into blood

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The PancreasIslets of Langerhansnormal blood glucose levels 90mgs / 100ml

GLUCAGONA cells

INSULINB cells

Somatostatin (D cells)inhibits both glucagon and insulin

Pancreatic polypeptide (F cells)Inhibits secretion somatostain

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ACTHadrenocorticotropic hormone

AKA corticotropin or adrenocorticotropin formed in the pituitary gland that regulates the activity of the adrenal cortex

In mammals the action of ACTH is limited to those areas of the adrenal cortex in which the glucocorticoid hormones cortisol and corticosterone are formed

The secretion of ACTH by the pituitary is itself regulated by another polypeptide, corticotrophin releasing hormone (CRH), which is discharged from the hypothalamus in response to impulses transmitted by the nervous system

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HPA axis

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Hypothalamus

Pituitary

Adrenal

Axis

Adrenal glands• located superior to each kidney • Pyramid shape • Each adrenal gland has an inner medulla and outer cortex:

Adrenal Cortex Adrenal Medulla

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Adrenal Cortex

Makes and secretes over 30 different steroid hormones (collectively called corticosteroids)

The adrenal cortex has 3 regions that each make a major type of hormones:

Mineralocorticoids (e.g. aldosterone)•Stimulates the kidneys to reabsorb sodium if blood pressure drops •It also secretes (eliminates) potassium

Gonadocorticoids (e.g.testosterone, estrogens, and progesterone )

•The adrenal gland also makes small amounts of the sex hormones (mostly androgens (testosterone) and lesser amounts of estrogens and progesterone)

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Adrenal Cortex

Glucocorticoids (e.g. cortisol)

•These hormones help you to cope with stress •Cortisol increases the level of sugar in the blood by stimulating the production of glucose from fats and proteins•It reduces swelling ie anti inflammatory •In large doses, cortisol inhibits the immune system.

Adrenal medulla

• secretes the hormones Adrenaline and Noradrenaline when stimulated by sympathetic neurons of the autonomic nervous system. Both contribute to the bodies' "fight or flight" response.

They have the same effects as direct stimulation by the sympathetic NS increase heart rateincrease breathing rate and depthincrease blood flow to skeletal musclesincreases glucose in the blood

• Noradrenaline is similar to Adrenaline , but it is less effective in the conversion of glycogen to glucose.

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Schematic overview of the two major arms of the stress response system. ACTH, adrenocorticotropic hormone; BNST, bed nucleus of the stria terminalis; CRH, corticotropin-releasing hormone; HPA axis, hypothalamopituitary–adrenal axis; SAM, sympathoadrenal–medullary system; SNS, sympathetic nervous system. Inhibitory pathways are represented by dashed lines

Robert Murison, in Neuroscience of Pain, Stress, and Emotion, 2016

Stress response

http://www.austincc.edu/rfofi/NursingRvw/PhysText/Endocrine.html 21

General Adaptation Syndrome

Stress = any condition that threatens homeostasis GAS is our bodies response to stress-causing factors

Three phases to GAS:

Alarm Phase (immediate, fight or flight, directed by the sympathetic nervous system)

Resistance Phase body tries tocompensate for the alarm

Exhaustion Phase (breakdown of homeostatic regulation and failure of one or more organ systems and possibly death) http://www.austincc.edu/rfofi/Nursing

Rvw/PhysText/Endocrine.html22

Hans Selye (1907–82) in 1936

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3 stages of GAS

Pathologiesof the

Adrenal glands

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Cushing’s Syndrome

www.potbellysyndrome.com

RememberACTH a polypeptide hormone formed in the pituitary gland that regulates the activity of the adrenal cortex

In mammals the action of ACTH is limited to those areas of the adrenal cortex in which the glucocorticoid hormones cortisol and corticosteroneare formed

The secretion of ACTH by the pituitary is itself regulated by another polypeptide, corticotrophin releasing hormone (CRH), which is discharged from the hypothalamus in response to impulses transmitted by the nervous system

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Addison’s disease

www.studyblue.com

www.cidpusa.org

Sx of Addisonian crisis

• Shock• Severe weakness• Severe dehydration• Confusion• Tachycardia• Loss of consciousness• Coma

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