2.8 Endocrine MNR

8/18/2019 2.8 Endocrine MNR

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• The endocrine system and the nervous system actindividually and together in regulating an animal’sphysiology

• Animals have two systems of internal communicationand regulation – The nervous system and the endocrine system

• Hormones may reach all parts of the body – But only certain types of cells, target cells, are equipped to

respond

• Endocrine: ductless glands, secreting hormones directly into blood.• Hormone: substance that is produced by one tissue and transported to another tissue

where it induces a specific physiological response. Is a chemical signal that issecreted into the circulatory system and communicates regulatory messages withinthe body

Hormones and theEndocrine ystem


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• Hormone can be assigned to four chemicalgroups – teroid hormones are synthesi!ed from cholesterol,

and include testosterone, estradiol and ecdysone" – Amino acids derivatives include amines, which are the

simplest hormones• Amines are synthesi!ed from tyrosine• Thyroid hormones, and epinephrine and norepinephrine are

amines"

– #rotein $peptide% hormones include short chains suchas o&ytocin and A'H and longer chains such asgrowth hormone and T H

– #rostaglandins are fatty acid derivatives"


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• (ertebrate hormones regulate growth, development, fluid balance, metabolism andreproduction" – Endocrine disorders may involves too little or too much hormone"

• Hypersecretion may cause overstimulation of target cells"• Hyposecretion may cause understimulation of target cells"• )f the receptors do not function properly, symptoms similar to hyposecretion

may result" – The hypothalamus integrates neural and endocrine regulation

• The hypothalamus lin*s the nervous and endocrine systems• +eurons of the hypothalamus secrete neurohormones which target the

release of hormones by the pituitary gland• The pituitary secretes at least distict hormones that have a wide variety

of target cells and effects – The pituitary of human consist of an interior and posterior lobe

•The hypothalamus secretes releasing hormones and release-inhibitinghormones which regulate the anterior lobe of the pituitary via a portalsystem"


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• .A TE/ 01 23A+'• .A TE/ 40+T/03 4E+TE/


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– The posterior lobe of the pituitary gland release two hormones• 0&ytocin and A'H are peptide hormones released by the posterior

lobe"• These hormones are produced by neurons in the hypothalamus, and

travel to the posterior lobe via the a&ons of the neurons"

• 0&ytocin stimulates uterine contraction during labor" – 0&ytocin also stimulates contraction of muscle cells in the breast

while nursing, resulting in e&pulsion of mil*"• A'H affects the collecting tubules of the nephron and results in a more

concentrated urine" – The anterior lobe of the pituitary gland regulates growth and other endocrine

glands"

• Tropic hormones stimulate other endocrine glands"• T H, A4TH, 1 H and 3H are tropic hormones"• T H stimulates the thyroid to produce thyroid hormones"• A4TH stimulates the adrenal corte& to produced adrenal cortical

hormones"• 2onadotrophic hormones $1 H and 3H% stimulate gonad function"• The nontropic hormones produced by the anterior pituitary

include – #rolactin – .elanocyte-stimulating hormone $. H% β-endorphin


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– 2rowth hormone stimulates protein synthesis"• 2rowth hormone $2H, also called somatotropin%

stimulates protein synthesis and therefore growth"

• 2H stimulates liver cells to produce somatomedins,which stimulate s*eletal growth at the epiphyseal platesand general growth of tissues"

• 2H promotes mobili!ation of fat and carbohydratesmetabolism

– 2rowth is affected by many factors• 2H is secreted in pulses during the day in both adults

and children"• The hypothalamus secretes 2H/H $growth hormone

releasing hormone% and 2H)H $growth hormone

inhibiting hormone, also called somatostatin% whichsignals the pituitary"


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• ecretion of 2H increases during e&ercise andduring sleep"

• Emotional support is necessary for productionof 2H5 lac* results in psychosocial dwarfism"

• Thyroid hormones and se& hormone alsointeract in the growth process"

– )nappropriate amounts of growth hormonesecretion result in abnormal growth"

• #ituitary dwarfs are a result of hyporsecretion

– /ecombinant 2H may now be used to treat thiscondition

• 2igantism results from 6uvenile hypersecretion• Acromegaly result in adult hypersecretion


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– Thyroid hormones increase metabolic rate"• The thyroid produces thyro&ine $T 7% and

triiodothyronine $T8% collectively *nown as thyroid

hormones" – These hormones increase the metabolic rate"

• Thyroid secretion is regulated by negativefeedbac* mechanism

– Even thyroid hormone concentration drops, thepituitary produces T H, which stimulates the thyroid toproduce thyroid hormones"

– The hypothalamus is also involved in the loop as thehypothalamus produces T H-releasing hormone"

• .alfunction of the thyroid gland leads to specificdisorders"

– 9uvenile hypothyroidism may lead to cretinism, whichis characteri!ed by retarded mental and physical

development"


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– Adult hypothyroidism is characteri!ed bya a sluggishmetabolic rate"

– E&treme adult hypothyroidism causes my&edema and maybe treated by thyroid hormone administration

– Hyperthyroidism increases metabolism but not growth – An enlarged thyroid is a goiter and can be associated with

either hypersecretion or hyposecretion: )odin deficiency is a common cause of goiter"

– The parathyroid glands regulate calciumconcentartion

• The parathyroid glands are embedded in tissuesurrounding the thyroid gland

• #arathyroid hormone $#TH% is produced by cells of the

parathyroid gland, and stimulates calcium release fromthe bones and calcium reabsorption from the *idneytubules"

• 4alcitonin produced by the thyroid acts in opposition to#TH"


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– The islet of the pancreas regulate glocose concentration• The islet of 3angerhans are the endocrine tissues of the

pancreas

– Beta cells secrete insulin and alpha cells secreteglu*agon"• )nsulin lowers the concentration of glucose in the blood"• 2lucagon raises the concentration of glucose in the

blood"

– The adrenal glands helps the body adapt to stress• The paired adrenal glands are locataed above the

*idneys"• The adrenal corte& helps the body deal with the chronic

stress" – 4ortical hormones are steroids made from

cholesterol – The tree classes of hormones include androgen,

mineralocorticoids and glucocorticoids"


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– 'HEA accounts for the ma6ority of the androgen infemales"

– .ineralocorticoids include aldosterone, which

regulates fluid balance – 4ortisol is the primary glucocorticoid which

stimulates gluconeogenesis as well as mobili!ationof fats and transportation of amino acids to livercells"

– tress causes by the hypothalamus to secretecorticotropin releasing hormone factor $4/1% whichstimulates the anterior lobe of the pituitary to secrete

A4TH" – Hyposecretion of adrenal cortical hormones causes

Addisons disease"


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• The ma6or human endocrine glands

Hypothalamus

#ineal gland#ituitary gland

Thyroid gland#arathyroid glands

Adrenal glands

#ancreas

0vary$female%

Testis$male%

Figure 45.6


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• .a6or human endocrine glands and someof their hormones

Table 45.1


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Table 45.1


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/elation Between the Hypothalamus and#ituitary 2land

• The hypothalamus, a region of the lowerbrain – 4ontains different sets of neurosecretory cells


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• ome of these cells produce direct-actinghormones – That are stored in and released from the posterior

pituitary, or neurohypophysis

Figure 45.7

Hypothalamus

+eurosecretorycells of thehypothalamus

A&on

Anterior pituitary

#osterior pituitary

H0/.0+E A'H 0&ytocin

TA/2ET ;idney tubules .ammary glands,uterine muscles


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• 0ther hypothalamic cells produce tropichormones

– That are secreted into the blood and transportedto the anterior pituitary or adenohypophysis

Tropic Effects nly1 H, follicle-stimulating hormone3H, luteini!ing hormoneT H, thyroid-stimulating hormone

A4TH, adrenocorticotropic hormone

!ontropic Effects nly#rolactin. H, melanocyte-stimulating hormoneEndorphin

!ontropic and Tropic Effects2rowth hormone

+eurosecretory cellsof the hypothalamus

#ortal vessels

Endocrine cells of theanterior pituitary

Hypothalamicreleasinghormones

$red dots%

H0/.0+E 1 H and 3H T H A4TH #rolactin . H Endorphin 2rowth hormone

TA/2ET Testes or ovaries

Thyroid Adrenalcorte&

.ammaryglands

.elanocytes #ain receptorsin the brain

3iver Bones

#ituitary hormones$blue dots%

Figure 45."


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• #rolactin stimulates lactation in mammals

– But has diverse effects in different vertebrates• . H influences s*in pigmentation in some

vertebrates

– And fat metabolism in mammals• Endorphins

– )nhibit the sensation of pain


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Thyroid Hormones• The thyroid gland

– 4onsists of two lobes located on the ventral surface ofthe trachea

– #roduces two iodine-containing hormones,triiodothyronine $T 8% and thyro&ine $T 7%


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• The hypothalamus and anterior pituitary – 4ontrol the secretion of thyroid hormones

through two negative feedbac* loops

Hypothalamus

Anterior pituitary

T H

Thyroid

T8 T7<Figure 45.#


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#arathyroid Hormone and 4alcitonin= 4ontrolof Blood 4alcium

• Two antagonistic hormones, parathyroid hormone $#TH% and calcitonin

– #lay the ma6or role in calcium $4a >


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• 4alcitonin, secreted by the thyroid gland

– timulates 4a><

deposition in the bones andsecretion by the *idneys, thus lowering blood4a >< levels

• #TH, secreted by the parathyroid glands – Has the opposite effects on the bones and

*idneys, and therefore raises 4a >< levels – Also has an indirect effect, stimulating the

*idneys to activate vitamin ', which promotesintestinal upta*e of 4a >< from food


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)nsulin and 2lucagon= 4ontrol ofBlood 2lucose

• Two types of cells in the pancreas – ecrete insulin and glucagon, antagonistic hormones that help

maintain glucose homeostasis and are found in clusters in the isletsof 3angerhans

• 2lucagon – )s produced by alpha cells

• )nsulin – )s produced by beta cells


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• .aintenance of glucose homeostasis

Beta cells of pancreas are stimulatedto release insulininto the blood"

)nsulin

3iver ta*esup glucoseand stores itas glycogen"

Body cellsta*e up moreglucose"

Blood glucose leveldeclines to set point5stimulus for insulin

release diminishes"

T).?3? =/ising blood glucose

level $for instance, after eating a carbohydrate-

rich meal%

$omeostasis%Blood glucose level

$about mg @ m3%

Blood glucose levelrises to set point5

stimulus for glucagonrelease diminishes"

T).?3? ='ropping blood glucoselevel $for instance, after

s*ipping a meal%

Alpha cells of pancreasare stimulated to releaseglucagon into the blood"

3iver brea*sdown glycogenand releasesglucose intoblood"

2lucagonFigure 45.1&


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Target Tissues for Insulin andGlucagon

• )nsulin reduces blood glucose levels by – #romoting the cellular upta*e of glucose – lowing glycogen brea*down in the liver – #romoting fat storage

• 2lucagon increases blood glucose levelsby – timulating the conversion of glycogen to

glucose in the liver – timulating the brea*down of fat and protein

into glucose


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Diabetes Mellitus• 'iabetes mellitus( perhaps the best)*no+n

endocrine disorder – )s caused by a deficiency of insulin or a decreasedresponse to insulin in target tissues

– )s mar*ed by elevated blood glucose levels

• Type ) diabetes mellitus $insulin-dependentdiabetes% – )s an autoimmune disorder in which the immune

system destroys the beta cells of the pancreas

• Type )) diabetes mellitus $non-insulin-dependentdiabetes% – )s characteri!ed either by a deficiency of insulin or,

more commonly, by reduced responsiveness of

target cells due to some change in insulin receptors


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Adrenal Hormones= /esponseto tress

• The adrenal glands – Are ad6acent to the *idneys – Are actually made up of two glands= the adrenal medulla and the adrenal

corte&


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atecholamines from the !drenal Medulla

• The adrenal medulla secretes epinephrineand norepinephrine – Hormones which are members of a class of

compounds called catecholamines• These hormones

– Are secreted in response to stress-activated

impulses from the nervous system – .ediate various fight-or-flight responses


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"tress Hormones from the !drenal orte#

• Hormones from the adrenal corte& – Also function in the bodyCs response to stress – 1all into three classes of steroid hormones

• 2lucocorticoids, such as cortisol – )nfluence glucose metabolism and the immune

system

• .ineralocorticoids, such as aldosterone – Affect salt and water balance• e& hormones

– Are produced in small amounts


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• tress and the adrenal gland

pinal cord$cross section%

+ervesignals

+ervecell

/eleasinghormone

,tress

Hypothalamus

Anterior pituitary

Blood vessel

A4TH

Adrenalgland

;idney

Adrenal medulla

secretes epinephrineand norepinephrine" Adrenal corte&

secretesmineralocorticoidsand glucocorticoids"

Effects of epinephrine and norepinephrine=

@" 2lycogen bro*en down to glucose5 increasedblood glucose

>" )ncreased blood pressure

8" )ncreased breathing rate

7" )ncreased metabolic rate

D" 4hange in blood flow patterns, leading to increased alertness and decreased digestive and *idney activity

Effects of mineralocorticoids=

@" /etention of sodiumions and water by*idneys

>" )ncreased bloodvolume and bloodpressure

Effects of glucocorticoids=

@" #roteins and fatsbro*en down andconverted to glucose,leading to increasedblood glucose

>" )mmune system maybe suppressed

-b /ong)term stress response-a ,hort)term stress response

+erve cell

Figure 45.10a(b


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2onadal e& Hormones• The gonads testes and ovaries

– #roduce most of the bodyCs se& hormones=androgens, estrogens, and progestins


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• The testes primarily synthesi!eandrogens, the main one beingtestosterone – Fhich stimulate the development and

maintenance of the male reproductive system


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• Testosterone causes an increase in muscleand bone mass

– And is often ta*en as a supplement to causemuscle growth, which carries many health ris*s

Figure 45.14


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2.8 Endocrine MNR