Endocrine SystemEndocrine SystemDr Khamis Al HashmiDr Khamis Al Hashmi

Department of physiologyDepartment of physiologyRoom # 006Room # 006

Ext. 3435Ext. 3435Email: kh@squ.edu.omEmail: kh@squ.edu.om

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Nervous Vs Endocrine system

Nervous and endocrine systems acts Nervous and endocrine systems acts together to coordinate functions of body together to coordinate functions of body system. system.

Nervous system releases; Nervous system releases; NeurotransmitorsNeurotransmitors

Endocrine system releases; Endocrine system releases; HormonesHormones

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Nervous Vs Endocrine system (cont.)

Characteristic Nervous system Endocrine system

Mediators molecules

Neurotransmitters Hormones

Site of mediator action

Close to site of release

Far from site of release

Types of target cells Muscle cells, gland cells, other neurons

Cells throughout the body

Time to onset of action

Within milliseconds

Seconds to hours

Duration of action Briefer (milliseconds)

Longer (seconds to days) 33

Endocrine Vs Exocrine glands

Exocrine gland:Exocrine gland: secrete their products into secrete their products into ducts that carry the secretion into body ducts that carry the secretion into body cavities, into lumen of organs, or to the outer cavities, into lumen of organs, or to the outer surface of the body.surface of the body.

E.g. Sweat, sebaceous, mucus, digestive E.g. Sweat, sebaceous, mucus, digestive glands.glands.

Endocrine glands:Endocrine glands: secrete their products into secrete their products into the interstitial fluid surrounding the secretory the interstitial fluid surrounding the secretory cells diffused into blood capillaries cells diffused into blood capillaries carried to target cells.carried to target cells.

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Definitions

Hormone: Hormone: is a mediator molecule that is released in is a mediator molecule that is released in

one part of the body but regulates activity of cells in one part of the body but regulates activity of cells in

other parts of the body.other parts of the body.

Target cell: Target cell: A cells whose activity is affected by aA cells whose activity is affected by a

particular hormone.particular hormone.

Receptor:Receptor: A specific molecule or cluster of moleculesA specific molecule or cluster of molecules

that recognizes and binds a particular ligand (hormone) that recognizes and binds a particular ligand (hormone)

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Circulating hormones Vs Local hormones

A) Circulating hormones

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B) Local hormones:

1) Paracrines

E.g. Nitric oxide.

IL2 77

2) Autocrines

E.g. IL2

Local hormones usually are inactivated quickly 88

Chemical classes of hormonesChemical classes of hormones

a) Water-soluble hormones: Amine hormones Amine hormones (Retain an amino group (Retain an amino group

(NH(NH33++))

Peptide and protein hormonesPeptide and protein hormones Eicosanoid hormones Eicosanoid hormones (derived from (derived from

arachidonic acid. Eg. Prostaglandins, leukotrienes)arachidonic acid. Eg. Prostaglandins, leukotrienes)

b) Lipid-soluble hormones: Steroid hormonesSteroid hormones Thyroid hormonesThyroid hormones Nitric oxideNitric oxide

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a) Water soluble hormone

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b) Lipid soluble hormone

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Hormone transport in the blood

Water soluble hormones circulate in a Water soluble hormones circulate in a free form (free form (UnUnbound).bound).

Lipid soluble hormones bound to Lipid soluble hormones bound to transport proteins. (>90%).transport proteins. (>90%).

Importance:Importance:- Increase the solubility in blood.Increase the solubility in blood.- Slow the rate of excretion by kidney or Slow the rate of excretion by kidney or

degradation by liver.degradation by liver.- Provide a ready reserve of hormone. Provide a ready reserve of hormone.

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Responsiveness of a target cell to a hormonedepend on:

1) Concentration of the hormone2) Number of receptors3) Influence by other hormone (hormones interaction)

1) Concentration of the hormone

– The hormone’s rate of secretion (all hormones)

– Rate of metabolic inactivation and excretion (all hormones)

– Rate of metabolic activation (few hormones)

– Extent of binding to plasma protein (lipophilic hormones)

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Control of hormone secretion Important to prevent overproduction or

underproduction

Three types of signals:1. Signals from the nervous systemEg. Nerve impulse to adrenal medulla Epinephrine

2. Chemical changes in the blood.Eg. Blood Ca2+ level parathyroid hormone

3. Other hormoneEg. Ant. Pituitary hormones hormones of other

glands 1414

Negative-feedback control control

Short loop feedback

long loop feedback1515

Positive-feedback control

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Diurnal (circadian) rhythm The secretion rate of many hormones rhythmically The secretion rate of many hormones rhythmically

fluctuate up and down as function of time.fluctuate up and down as function of time.– Diurnal (or circadian),Diurnal (or circadian), i.e. “day-night”. characterised i.e. “day-night”. characterised

by repetitive oscillations in hormone levels that are by repetitive oscillations in hormone levels that are very regular and have a frequency of one cycle every very regular and have a frequency of one cycle every 24 hours24 hours.. Eg. Cortisol secretion. Eg. Cortisol secretion.

– Other rhythmOther rhythm. Monthly menstrual period.. Monthly menstrual period.

Negative feedback control mechanisms operate toNegative feedback control mechanisms operate to

maintain whatever set point is established for that time.maintain whatever set point is established for that time.

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Clearance of hormones from the bloodClearance of hormones from the blood– Metabolic destruction by the tissuesMetabolic destruction by the tissues

– Binding with the tissues.Binding with the tissues.

– Excretion by the liver into the bile.Excretion by the liver into the bile.

– Excretion by the kidneys into urine. Excretion by the kidneys into urine.

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2) Number of receptors

Down regulation:Down regulation:A hormone present in excess Receptors

– Destruction of the receptor by lysosomesDestruction of the receptor by lysosomes– Decrease production of receptors Decrease production of receptors – Inactivation of some of the receptor moleculesInactivation of some of the receptor molecules– Inactivation of some of the intracellular signaling moleculesInactivation of some of the intracellular signaling molecules– Temporary sequestration of the receptor to the inside of the Temporary sequestration of the receptor to the inside of the

cell.cell.

Up regulation:Up regulation:A hormone is deficient Receptors

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3) Hormones interaction:3) Hormones interaction:

Permissiveness (permissive effect):Permissiveness (permissive effect): powerful action of a powerful action of ahormone on target cells require a simultaneous or recenthormone on target cells require a simultaneous or recentexposure to a second hormone.exposure to a second hormone.Eg. Epinephrine and thyroid hormones in lipolysis. Eg. Epinephrine and thyroid hormones in lipolysis.

Synergism (synergistic effect): Synergism (synergistic effect): the effect of two hormonesthe effect of two hormonesacting together is greater or more extensive than the effect ofacting together is greater or more extensive than the effect ofeach hormone acting alone.each hormone acting alone.Eg. FSH and estrogen for normal development of oocytes in Eg. FSH and estrogen for normal development of oocytes in ovaries.ovaries.

Antagonism (antagonistic effect):Antagonism (antagonistic effect): one hormone opposes the one hormone opposes theaction of another hormone. action of another hormone. Eg. Insulin and glucagon.Eg. Insulin and glucagon.

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Endocrine dysfunctionEndocrine dysfunction

a) Decrease in hormone activity Decrease in hormone secretion by the

endocrine gland (hyposecretion). Increase removal of the hormone from the

blood Abnormal tissue responsiveness to the

hormone:- Lack of target cell receptors. Lack of an enzyme essential to the target cell

response

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b) Increase in hormone activity Increase in hormone secretion by the Increase in hormone secretion by the

endocrine gland (hypersecretion)endocrine gland (hypersecretion) Reduced plasma protein binding of the Reduced plasma protein binding of the

hormone (too much free, biologically active hormone (too much free, biologically active hormonehormone

Decreased removal of the hormone from the Decreased removal of the hormone from the blood:-blood:-

Decreased inactivation.Decreased inactivation. Decreased excretionDecreased excretion

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Location of endocrine glandsLocation of endocrine glandsOrgan Hormones secreted

Hypothalamus Releasing and inhibitory hormones (e.g. thyrotropin releasing hormones, growth hormone inhibitory hormone), ADH, oxytocin.

Anterior pituitary gland Tropic hormones: ACTH, TSH LH,FSH), GH, prolactin.

Posterior pituitary gland Oxytocin, ADH (vasopressin)

Thyroid gland Thyroxine, Tri- iodothyronine.

Adrenal gland Mineralocorticoids (e.g. aldosterone), glucocorticoids (e.g. cortisol), catecholamines (e.g. epinephrine, nor-epinephrine).

Parathyroid glands Parathyroid hormone.

Pancreatic Islets Insulin, glucagon.

Gonads Testosterone, estradiol.

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Hypothalamus and pituitary glandHypothalamus and pituitary gland

Anterior pituitary

Hypothalamic-Hypophyseal portal system

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Posterior Pituitary

Hypothalamohypophyseal tract

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HypothalamusHypothalamus

HormonesHormones Target cells Target cells Major functionMajor function

Releasing hormones:Releasing hormones:

TRH, CTR, GnRH, GHRH, TRH, CTR, GnRH, GHRH, PRHPRH

Anterior pituitaryAnterior pituitary Stimulate release of Stimulate release of particular anterior particular anterior pituitary hormone.pituitary hormone.

Inhibiting hormones:Inhibiting hormones:

GHIH, PIHGHIH, PIHAnterior pituitaryAnterior pituitary inhibit release of inhibit release of

particular anterior particular anterior pituitary hormone.pituitary hormone.

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Anterior pituitary glandAnterior pituitary glandHormonesHormones Target cells Target cells Major functionMajor functionThyroid stimulating hormone (TSH)Thyroid stimulating hormone (TSH) Thyroid follicular cellsThyroid follicular cells Stimulates TStimulates T33 and T and T44 secretion secretion

Adrenocorticotropic hormone (ACTH)Adrenocorticotropic hormone (ACTH) Zona fasciculata and reticularis Zona fasciculata and reticularis of adrenal cortexof adrenal cortex

Stimulates cortisol secretionStimulates cortisol secretion

Growth hormone (GH)Growth hormone (GH) Bone; soft tissueBone; soft tissue

LiverLiver

Essential for growthEssential for growth

Metabolic effects; protein Metabolic effects; protein metabolism, fat mobilization and metabolism, fat mobilization and glucose conservationglucose conservation

Stimulates IGF secresionStimulates IGF secresion

Follicle-stimulating hormone (FSH)Follicle-stimulating hormone (FSH) Female: ovarian folliclesFemale: ovarian follicles

Males: Seminiferous tubules in Males: Seminiferous tubules in testestestes

Promote follicular growth and Promote follicular growth and development; stimulates estrogen development; stimulates estrogen secretionsecretion

Stimulates sperm productionStimulates sperm production

Luteinizing hormoneLuteinizing hormone Females: ovarian follicle and Females: ovarian follicle and corpus luteumcorpus luteum

Males: inerstitial cells of leydig Males: inerstitial cells of leydig in testes in testes

Stimulates ovulation, corpus luteum Stimulates ovulation, corpus luteum development, estrogen and development, estrogen and progesterone secresionprogesterone secresion

Stimulates testosterone secretionStimulates testosterone secretion

ProlactinProlactin Females: mammary glands Females: mammary glands (breast)(breast)

MalesMales

Promotes breast development; Promotes breast development; stimulates milk secresionstimulates milk secresion

UncertainUncertain 2727

Posterior pituitaryPosterior pituitary

HormonesHormones Target cells Target cells Major functionMajor function

Antidiuretic hormone Antidiuretic hormone (ADH), Vasopressin (ADH), Vasopressin

Kidney tubulesKidney tubules

ArteriolesArterioles

Increase water Increase water reabsorptionreabsorption

Produces Produces vasoconstrictionvasoconstriction

OxytocinOxytocin UterusUterus

Mammary glands Mammary glands (Breast)(Breast)

Increase contractilityIncrease contractility

Causes milk ejectionCauses milk ejection

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Thyroid GlandThyroid GlandHormonesHormones Target cells Target cells Major functionMajor functionTetraiodothyronine (TTetraiodothyronine (T44 or or thyroxin); Tri-thyroxin); Tri-iodothyronine (Tiodothyronine (T33))

Most cellsMost cells Increase metabolic Increase metabolic rate; essential for rate; essential for normal growth and normal growth and nerve developmentnerve development

CalcitoninCalcitonin BoneBone Decrease plasma Decrease plasma calcium concentrationcalcium concentration

Parathyroid GlandParathyroid GlandHormonesHormones Target cells Target cells Major functionMajor function

Parathyroid hormone Parathyroid hormone (PTH)(PTH)

Bone, kidneys, intestine.Bone, kidneys, intestine. Increases plasma Increases plasma calcium concentration; calcium concentration; decrease plasma decrease plasma phosphate concentration; phosphate concentration; stimulates vitamin D stimulates vitamin D activationactivation 2929

Adrenal glandAdrenal glandHormonesHormones Target cells Target cells Major functionMajor function

Cortex:Cortex:

Zona Zona glomerulosaglomerulosa

Zona Fasiculata Zona Fasiculata and reticularisand reticularis

Mineralocorticoid Mineralocorticoid (Aldosterone)(Aldosterone)

Glucocorticoid Glucocorticoid (cortisol)(cortisol)

AndrogensAndrogens

Kidney tubulesKidney tubules

Most cellsMost cells

Female: bone Female: bone and brainand brain

Increases NaIncreases Na++ reabsorptionand Kreabsorptionand K++ excresionexcresion

Increases blood Increases blood glucose at the glucose at the expense of protein expense of protein and fat store; and fat store; contributes to contributes to stress adaptationstress adaptation

Pubertal growth Pubertal growth spurt and sex drivespurt and sex drive

MedullaMedulla Epinephrine and Epinephrine and norepinephrinenorepinephrine

Sympathetic Sympathetic receptor site receptor site throughout the throughout the bodybody

Contributes to Contributes to stress adaptation stress adaptation and blood pressure and blood pressure regulation regulation

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Pancreas (Islets of langerhans)Pancreas (Islets of langerhans)

HormonesHormones Target cells Target cells Major functionMajor function

Beta (Beta (ββ) cells) cells

Alpha (Alpha (αα) cells) cells

D cellsD cells

InsulineInsuline

GlucagonGlucagon

SomatostatinSomatostatin

Most cellsMost cells

Most cellsMost cells

Digestive Digestive systemsystem

Pancreatic islet Pancreatic islet cellscells

Promotes cellular Promotes cellular uptake, use and uptake, use and storage of storage of absorbed nutrientsabsorbed nutrients

Important for Important for maintain nutrient maintain nutrient levels in blood levels in blood during during postabsorptive postabsorptive state state

Inhibits digestion Inhibits digestion and absorption of and absorption of nutrientsnutrients

Inhibits secretion Inhibits secretion of all pancreatic of all pancreatic hormoneshormones

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OvariesOvaries

HormonesHormones Target cells Target cells Major functionMajor functionEstrogenEstrogen Female sex organs; Female sex organs;

body as whole.body as whole.

BoneBone

Promotes follicular Promotes follicular development, development, development of development of secondary secondary characteristics, characteristics, stimulate uterine and stimulate uterine and breast growth.breast growth.

Promotes closer of Promotes closer of epiphyseal plateepiphyseal plate

ProgesteroneProgesterone UterusUterus Prepare for pregnancyPrepare for pregnancy

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TestesTestes

HormonesHormones Target cells Target cells Major functionMajor function

TestosteroneTestosterone Male sex organs; body Male sex organs; body as wholeas whole

Stimulate sperm Stimulate sperm production; production; development of development of secondary secondary characteristics; characteristics; Promotes sex drivePromotes sex drive

Testes and ovaries secret inhibin that acts on the anterior Testes and ovaries secret inhibin that acts on the anterior pituitary to inhibit secretion of follicle stimulating hormonepituitary to inhibit secretion of follicle stimulating hormone. .

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