Feedback mechanisms, Feedback mechanisms, hormones and the hormones and the endocrine systemendocrine system

Biology 12Biology 12

Mr. CMr. C

What is a feedback mechanismWhat is a feedback mechanism

Feedback is Feedback is (generally) (generally) information about information about actions.actions.

In In cyberneticscybernetics and and control theorycontrol theory, , feedbackfeedback is a is a process whereby some proportion or in general, process whereby some proportion or in general, function, of the output signal of a system is function, of the output signal of a system is passed (fed back) to the input. Often this is done passed (fed back) to the input. Often this is done intentionally, in order to control the dynamic intentionally, in order to control the dynamic behaviour of the system. Feedback is observed behaviour of the system. Feedback is observed or used in various areas dealing with complex or used in various areas dealing with complex systems, such as systems, such as engineeringengineering, , architecturearchitecture, , economicseconomics, and , and biologybiology..

Drawing a feedback loopDrawing a feedback loop

Lines are usually drawn, directed from Lines are usually drawn, directed from input through the system and to output. input through the system and to output. The feedback is shown by another The feedback is shown by another arrowed line, directed fromarrowed line, directed from output output outside the system to an input, resulting in outside the system to an input, resulting in a loop on the diagram, called a loop on the diagram, called feedback feedback looploop. This notion is important; for . This notion is important; for example, the feedback loop is a example, the feedback loop is a convenient place for a control device.convenient place for a control device.

In natureIn natureIn In biologicalbiological systems such as systems such as organismsorganisms, , ecosystemsecosystems, or the , or the biospherebiosphere, most parameters , most parameters must stay under control within a narrow range must stay under control within a narrow range around a certain optimal level under certain around a certain optimal level under certain environmental conditions. The deviation of the environmental conditions. The deviation of the optimal value of the controlled parameter can optimal value of the controlled parameter can result from the changes in internal and external result from the changes in internal and external environments. A change of some of the environments. A change of some of the environmental conditions may also require environmental conditions may also require change of that range to change for the system to change of that range to change for the system to function. The value of the parameter to maintain function. The value of the parameter to maintain is recorded by a reception system and conveyed is recorded by a reception system and conveyed to a regulation module via an information to a regulation module via an information channel.channel.

Positive and negative feedbackPositive and negative feedback

Biological systems contain many types of Biological systems contain many types of regulatory circuits, among which positive regulatory circuits, among which positive and negative feedbacks. and negative feedbacks. PositivePositive and and negativenegative don't imply consequences of the don't imply consequences of the feedback have positive or negative final feedback have positive or negative final effect. The negative feedback loop tends effect. The negative feedback loop tends to slow down a process, while the positive to slow down a process, while the positive feedback loop tends to accelerate it.feedback loop tends to accelerate it.

Useful vocabUseful vocab

negative feedback negative feedback The stopping of the The stopping of the synthesis of an enzyme by the accumulation of synthesis of an enzyme by the accumulation of the products of the enzyme-mediated reaction. the products of the enzyme-mediated reaction. negative feedback controlnegative feedback control  Occurs when   Occurs when information produced by the feedback reverses information produced by the feedback reverses the direction of the response; regulates the the direction of the response; regulates the secretion of most hormones.secretion of most hormones.negative feedback loop negative feedback loop A biochemical pathway A biochemical pathway where the products of the reaction inhibit where the products of the reaction inhibit production of the enzyme that controlled their production of the enzyme that controlled their formation.formation.

Negative feedbackNegative feedback

Feedback and regulation are self related. Feedback and regulation are self related. The negative feedback helps to maintain The negative feedback helps to maintain stability in a system in spite of external stability in a system in spite of external changes. It is related to changes. It is related to homeostasishomeostasis. . Positive feedback amplifies possibilities of Positive feedback amplifies possibilities of divergences (evolution, change of goals); divergences (evolution, change of goals); it is the condition to change, evolution, it is the condition to change, evolution, growth; it gives the system the ability to growth; it gives the system the ability to access new points of access new points of equilibriumequilibrium

An example of a simple negative An example of a simple negative feedback loopfeedback loop

What if you get cold?What if you get cold?

What if you blood sugar changes?What if you blood sugar changes?

Integrating organs with feedbackIntegrating organs with feedback

For example, in an organism, most For example, in an organism, most positive feedbacks provide for fast positive feedbacks provide for fast autoexcitation of elements of endocrine autoexcitation of elements of endocrine and nervous systems (in particular, in and nervous systems (in particular, in stress responses conditions) and play a stress responses conditions) and play a key role in regulation of morphogenesis, key role in regulation of morphogenesis, growth, and development of organs, all growth, and development of organs, all processes which are in essence a rapid processes which are in essence a rapid escape from the initial state. escape from the initial state. Homeostasis is especially visible in the Homeostasis is especially visible in the nervousnervous and and endocrine systemsendocrine systems when when considered at organism level.considered at organism level.

Endocrine systemEndocrine systemThe endocrine system is a control system of ductless glands that secrete chemical messengers called hormones that circulate within the body via the bloodstream to 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 glands such as salivary glands, sweat glands and glands within the gastrointestinal tract.

What is a hormone?What is a hormone?

hor·mone (hôrhor·mone (hôr''mōn')mōn')n.n. A substance, usually a peptide or A substance, usually a peptide or steroid, produced by one tissue and steroid, produced by one tissue and conveyed by the bloodstream to another to conveyed by the bloodstream to another to effect physiological activity, such as effect physiological activity, such as growth or metabolism.growth or metabolism.

How are hormones classifiedHow are hormones classified

Hormones are grouped into three classes Hormones are grouped into three classes based on their structure: based on their structure:

steroids steroids

peptides peptides

amines amines

SteriodsSteriods

SteroidsSteroids are are lipidslipids derived from derived from cholesterol. cholesterol. TestosteroneTestosterone is the male is the male sex hormonesex hormone. Estradiol, similar in structure . Estradiol, similar in structure to testosterone, is responsible for many to testosterone, is responsible for many female sex characteristics. Steroid female sex characteristics. Steroid hormones are secreted by the hormones are secreted by the gonadsgonads, , adrenal cortex, and adrenal cortex, and placentaplacenta..

Steroid structureSteroid structure

Peptides and AminesPeptides and Amines

PeptidesPeptides are short chains of are short chains of amino acidsamino acids; ; most hormones are peptides. They are most hormones are peptides. They are secreted by the pituitary, parathyroid, secreted by the pituitary, parathyroid, heart, stomach, liver, and kidneys. Amines heart, stomach, liver, and kidneys. Amines are derived from the amino acid tyrosine are derived from the amino acid tyrosine and are secreted from the thyroid and the and are secreted from the thyroid and the adrenal medulla. Solubility of the various adrenal medulla. Solubility of the various hormone classes varies.hormone classes varies.

The integration of body functions in humans The integration of body functions in humans and other higher organisms is carried out by and other higher organisms is carried out by the nervous system, the immune system, the nervous system, the immune system, and the endocrine system. and the endocrine system.

The endocrine system is composed of a The endocrine system is composed of a number of tissues that secrete their number of tissues that secrete their products, called products, called endocrine hormonesendocrine hormones, , into the circulatory system; from there into the circulatory system; from there they are disseminated throughout the they are disseminated throughout the body, regulating the function of distant body, regulating the function of distant tissues and maintaining homeostasis. tissues and maintaining homeostasis.

In a separate but related system, In a separate but related system, exocrine tissues secrete their products exocrine tissues secrete their products into ducts and then to the outside of into ducts and then to the outside of the body or to the intestinal tract. the body or to the intestinal tract.

Endocrine HormonesEndocrine Hormones

Classically, endocrine hormones are Classically, endocrine hormones are considered to be derived from amino acids, considered to be derived from amino acids, peptides, or sterols and to act at sites distant peptides, or sterols and to act at sites distant from their tissue of origin. from their tissue of origin. However, the latter definition has begun to blur However, the latter definition has begun to blur as it is found that some secreted substances as it is found that some secreted substances act at a distance (classical endocrines), close act at a distance (classical endocrines), close to the cells that secrete them (paracrines), or to the cells that secrete them (paracrines), or directly on the cell that secreted them directly on the cell that secreted them (autocrines). (autocrines). Insulin-like growth factor-I (IGF-I)Insulin-like growth factor-I (IGF-I), , which behaves as an endocrine, paracrine, and which behaves as an endocrine, paracrine, and autocrine, provides a prime example of this autocrine, provides a prime example of this difficulty. difficulty.

What is the amount of hormones in What is the amount of hormones in the blood?the blood?

Hormones are normally present in the plasma Hormones are normally present in the plasma and interstitial tissue at concentrations in the and interstitial tissue at concentrations in the range of 10-7M to 10-10M. range of 10-7M to 10-10M.

Because of these very low physiological Because of these very low physiological concentrations, sensitive protein receptors concentrations, sensitive protein receptors have evolved in target tissues to sense the have evolved in target tissues to sense the presence of very weak signals. presence of very weak signals.

In addition, systemic feedback mechanisms In addition, systemic feedback mechanisms have evolved to regulate the production of have evolved to regulate the production of endocrine hormones. endocrine hormones.

Once a hormone is secreted by an endocrine tissue, it Once a hormone is secreted by an endocrine tissue, it generally binds to a specific plasma protein carrier, with generally binds to a specific plasma protein carrier, with the complex being disseminated to distant tissues. the complex being disseminated to distant tissues.

Plasma carrier proteinsPlasma carrier proteins exist for all classes of endocrine exist for all classes of endocrine hormones. Carrier proteins for peptide hormones hormones. Carrier proteins for peptide hormones prevent hormone destruction by plasma proteases. prevent hormone destruction by plasma proteases.

Carriers for steroid and thyroid hormones allow these Carriers for steroid and thyroid hormones allow these very hydrophobic substances to be present in the very hydrophobic substances to be present in the plasma at concentrations several hundred-fold greater plasma at concentrations several hundred-fold greater than their solubility in water would permit. than their solubility in water would permit.

Carriers for small, hydrophilic amino acid--derived Carriers for small, hydrophilic amino acid--derived hormones prevent their filtration through the renal hormones prevent their filtration through the renal glomerulus, greatly prolonging their circulating half-life. glomerulus, greatly prolonging their circulating half-life.

How do hormones travel in the blood!

Nonsteroid hormones (water soluble) do not enter the cell Nonsteroid hormones (water soluble) do not enter the cell but bind to plasma membrane receptors, generating a but bind to plasma membrane receptors, generating a

chemical signal (second messenger) inside the target cell.chemical signal (second messenger) inside the target cell.

Five different second messenger chemicals, including Five different second messenger chemicals, including cyclic AMP have been identified. cyclic AMP have been identified.

Second messengers activate other intracellular chemicals Second messengers activate other intracellular chemicals to produce the target cell response.to produce the target cell response.

Action of nonsteroid hormonesAction of nonsteroid hormones

Step twoStep two

Step ThreeStep Three

Action of steroid hormoneAction of steroid hormone

The second mechanism involves steroid The second mechanism involves steroid hormones, which pass through the plasma hormones, which pass through the plasma membrane and act in a membrane and act in a two step processtwo step process. .

Steroid hormones Steroid hormones bind, once inside bind, once inside the cell, to the the cell, to the nuclear membrane nuclear membrane receptors, receptors, producing an producing an activated hormone-activated hormone-receptor complex.receptor complex.

The activated The activated hormone-receptor hormone-receptor complex binds to complex binds to DNA and activates DNA and activates specific genes, specific genes, increasing production increasing production of proteins.of proteins.

Tissues capable of responding to endocrines have 2 properties Tissues capable of responding to endocrines have 2 properties in commonin common: they posses a receptor having very high affinity for : they posses a receptor having very high affinity for hormone, and the receptor is coupled to a process that hormone, and the receptor is coupled to a process that regulates metabolism of the target cells.regulates metabolism of the target cells.

Receptors for most amino acid--derived hormones and all Receptors for most amino acid--derived hormones and all peptide hormones are located on the plasma membrane. peptide hormones are located on the plasma membrane. Activation of these receptors by hormones (the first Activation of these receptors by hormones (the first messenger) leads to the intracellular production of a second messenger) leads to the intracellular production of a second messenger, such as cAMP, which is responsible for initiating messenger, such as cAMP, which is responsible for initiating the intracellular biological response. the intracellular biological response.

Steroid and thyroid hormones are hydrophobic and diffuse Steroid and thyroid hormones are hydrophobic and diffuse from their binding proteins in the plasma, across the plasma from their binding proteins in the plasma, across the plasma membrane to intracellularly localized receptors. The resultant membrane to intracellularly localized receptors. The resultant complex of steroid and receptor bind to response elements of complex of steroid and receptor bind to response elements of nuclear DNA, regulating the production of mRNA for specific nuclear DNA, regulating the production of mRNA for specific proteins. proteins.

How do tissue react to hormones?

What we have seen so far..What we have seen so far..

StomachStomach and and intestinesintestines GastrinGastrin SecretinSecretin CholecystokininCholecystokinin (CCK) (CCK) SomatostatinSomatostatin Neuropeptide YNeuropeptide Y

Getting a head start on hormonesGetting a head start on hormones

List of hormones and organs List of hormones and organs related to hormonesrelated to hormones

HypothalamusHypothalamus Thyrotropin-releasing hormoneThyrotropin-releasing hormone (TRH) (TRH) Gonadotropin-releasing hormoneGonadotropin-releasing hormone (GnRH) (GnRH) Growth hormone-releasing hormoneGrowth hormone-releasing hormone (GHRH) (GHRH) Corticotropin-releasing hormoneCorticotropin-releasing hormone (CRH) (CRH) SomatostatinSomatostatin DopamineDopamine

Hypothalamus to PituitaryHypothalamus to Pituitary

Pituitary glandPituitary gland

Anterior lobe (Anterior lobe (adenohypophysisadenohypophysis)) GH (GH (human growth hormonehuman growth hormone) )

PRL (PRL (prolactinprolactin) )

ACTH (ACTH (adrenocorticotropic hormoneadrenocorticotropic hormone) )

TSH (TSH (thyroid-stimulating hormonethyroid-stimulating hormone) )

FSH (FSH (follicle-stimulating hormonefollicle-stimulating hormone) )

LH (LH (luteinizing hormoneluteinizing hormone) )

Posterior lobe (Posterior lobe (neurohypophysisneurohypophysis))

OxytocinOxytocin

ADH (ADH (antidiuretic hormoneantidiuretic hormone))

Integration of blood and hormonesIntegration of blood and hormones

A division of labourA division of labour

Pineal glandPineal gland MelatoninMelatonin

Thyroid glandThyroid gland Thyroxine (T4), a form of Thyroxine (T4), a form of thyroid hormonethyroid hormone Triiodothyronine (T3), a form of Triiodothyronine (T3), a form of

thyroid hormonethyroid hormone CalcitoninCalcitonin

Parathyroid glandParathyroid gland Parathyroid hormoneParathyroid hormone (PTH) (PTH)

HeartHeart Atrial-natriuretic peptideAtrial-natriuretic peptide (ANP) (ANP)

Adrenal glandsAdrenal glands Adrenal cortexAdrenal cortex

GlucocorticoidsGlucocorticoids - - cortisolcortisol

MineralocorticoidsMineralocorticoids - - aldosteronealdosterone

AndrogensAndrogens (including (including testosteronetestosterone) ) Adrenal medullaAdrenal medulla

Adrenaline (Adrenaline (epinephrineepinephrine) )

Noradrenaline (Noradrenaline (norepinephrinenorepinephrine) )

Adrenal gland and kidneyAdrenal gland and kidney

Kidney •Renin •Erythropoietin (EPO) •Calcitriol

LiverLiver Insulin-like growth factorInsulin-like growth factor AngiotensinogenAngiotensinogen ThrombopoietinThrombopoietin http://users.rcn.com/jkimball.ma.ultranet/http://users.rcn.com/jkimball.ma.ultranet/

BiologyPages/L/LiverHormones.htmlBiologyPages/L/LiverHormones.html

Islets of LangerhansIslets of Langerhans in the in the pancreaspancreas InsulinInsulin GlucagonGlucagon SomatostatinSomatostatin

SkinSkin Calciferol (Calciferol (vitamin Dvitamin D3) 3)

Adipose tissueAdipose tissue LeptinLeptin

In males onlyIn males only

TestesTestes AndrogensAndrogens ( (

testosteronetestosterone) )

In females onlyIn females onlyOvarian follicleOvarian follicle OestrogensOestrogens TestosteroneTestosterone

Corpus luteumCorpus luteum ProgesteroneProgesterone

PlacentaPlacenta (when (when pregnantpregnant) ) ProgesteroneProgesterone Human chorionic gonaHuman chorionic gona

dotrophindotrophin (HCG) (HCG)

Human placental lactoHuman placental lactogengen (HPL) (HPL)

Your challenge….Your challenge….

Most hormones turn on and off a responseMost hormones turn on and off a response

You should be able to make feed back loops for You should be able to make feed back loops for regulating levels of major chemical groups in the regulating levels of major chemical groups in the body.body.

What are feedback loops for regulating:What are feedback loops for regulating:

Oxygen and Carbon DioxideOxygen and Carbon Dioxide

Blood sugars ( you have seen it!)Blood sugars ( you have seen it!)

Blood saltsBlood salts

Sexual and growth developmentSexual and growth development

More challenges…More challenges…

Can you link feedback mechanisms to Can you link feedback mechanisms to specific systems?specific systems?

Could you make a comparative table Could you make a comparative table pairing hormones with organ systems?pairing hormones with organ systems?

What disorders are associated with your What disorders are associated with your adrenal gland, thyroid gland, pancreas, adrenal gland, thyroid gland, pancreas, bones and blood sugar imbalance. (see bones and blood sugar imbalance. (see on-line references)on-line references)

A possible end..or beginningA possible end..or beginning

List of on-line referencesList of on-line references

http://www.dentistry.leeds.ac.uk/biochem/thttp://www.dentistry.leeds.ac.uk/biochem/thcme/peptide-hormones.htmlhcme/peptide-hormones.html

http://www.emc.maricopa.edu/faculty/http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookENDOCR.htmlfarabee/BIOBK/BioBookENDOCR.html

http://www.endocrineweb.com/http://www.endocrineweb.com/