Endocrine Systems12 Endocrine Systems

7/27/2019 Endocrine Systems12 Endocrine Systems

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Hormones &Endocrine System


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endocrine system secretes hormones

slower but longer-acting responses

roles include: reproduction, development,energy metabolism, growth & behavior

nervous system high-speed electrical signals along specialized

cells called neurons

these signals regulate other cells

Two systems communicatethroughout body:


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Signaling by Pheromones

Pheromones: chemicals that are released into the

environment & used to communicate with other individuals

Pheromones serve many functions, including marking

trails leading to food, defining territories, warning of

predators, and attracting potential mates


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MHC-dependent Mate Preferences in HumansCLAUS WEDEKIND, THOMAS SEEBECK, FLORENCE BETTENS AND ALEXANDER J. PAEPKE

(Proceedings of the Royal Society. B, Biological sciences 1995)


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Chemical Classes of

Hormones

Three major classes ofmolecules function as

hormones in

vertebrates

Polypeptides

(proteins and

peptides)

Amines derivedfrom amino acids

Steroid hormones

Water-soluble Lipid-soluble

Steroid:

Cortisol

Polypeptide:

Insulin

Amine:Epinephrine

Amine:Thyroxine

0.8 nm


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Signalreceptor

TARGETCELL

Signal receptor

Transportprotein

Water-soluble

hormone

Fat-solublehormone

Generegulation

Cytoplasmicresponse

Generegulation

Cytoplasmicresponse

OR

(a) NUCLEUS (b)

Water-soluble hormones

are secreted by

exocytosis, travel freely

in the bloodstream &bind to cell-surface

receptors

Lipid-soluble hormonesdiffuse across cell

membranes, travel in the

bloodstream bound to

transport proteins &diffuse through the

membrane of target cells


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Multiple Effects of Hormones

The same hormone may have differenteffects on target cells that have Different receptors for the hormone

Different signal transduction pathways

Different proteins for carrying out the response

A hormone can also have different effects in

different species


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Different receptorsSame receptors but differentintracellular proteins

Different cellular

responses

Different cellular

responses

Epinephrine Epinephrine Epinephrine

receptor receptorreceptorGlycogendeposits

Vesseldilates.

Vessel

constricts.

Glycogen

breaks downand glucoseis releasedfrom cell.

(a) Liver cell (b) Skeletal muscle

blood vessel

Intestinal blood

vessel

(c)


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Major endocrine glands:

Adrenalglands

Hypothalamus

Pineal gland

Pituitary gland

Thyroid gland

Parathyroid glands

PancreasKidney

Ovaries

Testes

Organs containingendocrine cells:

Thymus

Heart

Liver

Stomach

KidneySmallintestine


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Feedback regulation and

antagonistic hormone pairs

are common in endocrine systems

Hormones are assembled into regulatory

pathways

negative feedback loop

inhibits response by reducing initial stimulus regulates many hormonal pathways involved

in homeostasis


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Pathway Example

Stimulus Low pH in

duodenum

S cells of duodenumsecrete secretin ( )

Endocrinecell

Bloodvessel

PancreasTargetcells

Response Bicarbonate release

SimpleHormonePathways

NegativeFeedback


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Pathway

Example

Stimulus Suckling

Sensory

neuron

Positivefeedback

Hypothalamus/posterior pituitary

Neurosecretory cell

Neurohormone

Blood vessel

Targetcells

Response

Posterior pituitary

secretes theneurohormoneoxytocin ( ).

Smooth muscle inbreasts

Milk release

SimpleHormonePathways

PositiveFeedback


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Insulin and Glucagon:

Control of Blood Glucose

Insulin (decreases blood glucose) and glucagon

(increases blood glucose)are antagonistic

hormones that help maintain glucose

homeostasis

The pancreas has clusters of endocrine cells

called pancreatic islets with alpha cells thatproduce glucagon and beta cells that produce

insulin


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Body cellstake up moreglucose.

Insulin

Beta cells ofpancreasrelease insulininto the blood.

Liver takesup glucoseand stores itas glycogen.

Blood glucoselevel declines.

Blood glucoselevel rises.

Homeostasis:Blood glucose level(70110 mg/m100mL)

STIMULUS:Blood glucose level rises(for instance, after eating acarbohydrate-rich meal).

Liver breaksdown glycogenand releasesglucose into

the blood.

Alpha cells of pancreasrelease glucagon intothe blood.

Glucagon

STIMULUS:Blood glucose levelfalls (for instance, after

skipping a meal).


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Insulin & Glucagontarget specific tissues

Insulin reduces blood glucose by promoting uptake by cells

slowing glycogen breakdown in liver

promoting fat storage

Glucagon increases blood glucose by stimulating conversion of glycogen to glucose

stimulating breakdown of fat & protein intoglucose


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Diabetes Mell i tus

Type 1 (insulin-dependent)

autoimmune disorder in

which the immune system

destroys pancreatic beta

cells

Type 2(non-insulin-

dependent)

insulin deficiency or

reduced response of target

cells due to change in

insulin receptors


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In response to a drop in blood glucose belownormal levels, what mechanisms aretriggered to get more sugar into the blood &

restore normal glucose levels?

A. Insulin is released into circulation and, in response,

body cells take in & use up glucose.

B. Glucagon is released into circulation and, in response,

liver cells release glucose into the blood.

C. Secretin is released into circulation and, in response,

the pancreas secretes amylases into the intestine.

D. CCK is released into circulation and, in response,enzymes & bile are released into the intestine.

E. Amylase enzymes are released into circulation and, in

response, starches in the blood are digested to

glucose.


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Coordination of Endocrine and Nervous

Systems in Vertebrates

The hypothalamusreceives information

from the nervous

system and initiates

responses throughthe endocrine

system

The pituitary gland

iscomposed of the

posterior pituitary

and anterior pituitary

Pinealgland

Cerebellum

Spinal cord

Cerebrum

Thalamus

Hypothalamus

Pituitarygland

Posteriorpituitary

Anteriorpituitary

Hypothalamus


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Major Endocrine Glands and Some of Their Hormones


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Major Endocrine Glands and Some of Their Hormones


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Posteriorpituitary

Anteriorpituitary

Neurosecretorycells of thehypothalamus

Hypothalamus

Axon

HORMONE OxytocinADH

Kidney tubulesTARGET Mammary glands,uterine muscles

PosteriorPituitaryHormones


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Anterior Pituitary Hormones


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Tropic effects only:FSH

LHTSHACTH

Nontropic effects only:ProlactinMSH

Nontropic and tropic effects:GH Hypothalamic

releasing andinhibitinghormones

Posteriorpituitary

Neurosecretory

cells of thehypothalamus

Portal vessels

Endocrine cellsof the anteriorpituitary

Pituitaryhormones

HORMONE FSH and LH TSH ACTH Prolactin MSH GH

TARGET Thyroid MelanocytesTestes orovaries

Adrenalcortex

Mammaryglands

Liver, bones,other tissues

Anterior Pituitary Hormones


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Pathway Example

Stimulus Cold

Sensory neuron

Hypothalamus

Neurosecretory cell

Releasing hormone

Blood vessel

Anterior pituitary

Tropic hormone

Endocrine cellHormone

Target

cells

Response

Negative

feedback

Hypothalamus secretes

thyrotropin-releasinghormone (TRH ).

Anterior pituitary secretesthyroid-stimulating

hormone (TSH, also known

as thyrotropin ).

Thyroid gland secretes

thyroid hormone

(T3 and T4 ).

Body tissues

Increased cellularmetabolism

Thyroid Regulation:

A Hormone CascadePathway


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Disorders of Thyroid Function and Regulation

Hypothyroidism can produce symptoms such as

Weight gain, lethargy, cold intolerance Hyperthyroidism can lead to

High temperature, sweating, weight loss,

irritability, and high blood pressure

Graves disease, a form of hyperthyroidism caused

by autoimmunity, is typified by protruding eyes

Thyroid hormone refers to a pair of hormones

Triiodothyronin (T3), with three iodine atoms

Thyroxine (T4), with four iodine atoms Insufficient dietary iodine leads to an enlarged

thyroid gland, called a goiter


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Growth hormone (GH)is secreted by theanterior pituitary gland

and has tropic andnontropic actions

It promotes growthdirectly and has diverse

metabolic effects It stimulates production

of growth factors

An excess of GH can

cause gigantism, whilea lack of GH can causedwarfism


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Parathyroid Hormone and Vitamin D:

Control of Blood Calcium

Two antagonistic hormones regulate the homeostasis ofcalcium (Ca2+) in the blood of mammals

Parathyroid hormone (PTH) is released by the parathyroid

glands increases the level of blood Ca2+ by releasing Ca2+ from

bone

stimulates kidneys to activate vitamin D, which promotes

intestinal uptake of Ca2+

Calcitonin is released by the thyroid gland

decreases the level of blood Ca2+

stimulates Ca2+ deposition in bones and secretion by

kidneys


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Activevitamin D

Increases Ca2uptake inintestines

Stimulates Ca2uptake in kidneys

StimulatesCa2 releasefrom bones

Parathyroidgland (behindthyroid)

PTH

Blood Ca2level rises.

Homeostasis:Blood Ca2 level(about 10 mg/100 mL)

STIMULUS:

Falling bloodCa2 level


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Adrenal Hormones: Response to Stress

The adrenal glands are adjacent to the kidneys

Each adrenal gland actually consists of two

glands: the adrenal medulla (inner portion) andadrenal cortex(outer portion)

The adrenal medulla secretes epinephrine

(adrenaline) and norepinephrine(noradrenaline)


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Spinal cord(cross section)

(a) Short-term stress response and the adrenal medulla

Stress

Nervesignals

Nervecell

Nerve cellAdrenal medullasecretes epinephrineand norepinephrine.

Adrenalgland

Kidney

Effects of epinephrine and norepinephrine:

Glycogen broken down to glucose;

increased blood glucose Increased blood pressure

Increased breathing rate

Increased metabolic rate

Change in blood flow patterns, leading toincreased alertness and decreased digestive,excretory, and reproductive system activity

Hypo-thalamus

Stress and the adrenal gland.

Steroid Hormones from the Adrenal Cortex


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(b) Long-term stress response and the adrenal cortex

Stress

Releasinghormone

Hypothalamus

Anterior pituitary

Blood vesselACTH

Adrenal cortexsecretes mineralo-corticoids andglucocorticoids.

Effects ofmineralocorticoids:

Effects ofglucocorticoids:

Retention of sodiumions and water bykidneys

Increased bloodvolume and bloodpressure

Proteins and fats brokendown and converted toglucose, leading toincreased blood glucose

Partial suppression ofimmune system

Adrenalgland

Kidney

Steroid Hormones from the Adrenal Cortex


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Gonadal Sex Hormones

The gonads, testes and ovaries, produce most ofthe sex hormones: androgens, estrogens, and

progestins

All three sex hormones are found in both males

and females, but in significantly different

proportions


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The testes primarily synthesize androgens,mainly testosterone, which stimulate

development and maintenance of the male

reproductive system

Testosterone causes an increase in muscle and

bone mass and is often taken as a supplement to

cause muscle growth, which carries health risks


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Estrogens, most importantly estradiol, are

responsible for maintenance of the femalereproductive system and the development offemale secondary sex characteristics

In mammals, progestins, which includeprogesterone, are primarily involved in preparingand maintaining the uterus

Synthesis of the sex hormones is controlled byFSH and LH from the anterior pituitary


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Between 1938 and 1971 some pregnant women atrisk for complications were prescribed a syntheticestrogen called diethylstilbestrol (DES)

Daughters of women treated with DES are at higherrisk for reproductive abnormalities, includingmiscarriage, structural changes, and cervical andvaginal cancers

DES is an endocrine disruptor, a molecule thatinterrupts the normal function of a hormone pathway,in this case, that of estrogen

Endocrine Disruptors


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Caster Semenya And The IOCs Olympics

Gender Benderby Jesse Ellison The Daily Beast, Jul 26, 2012


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Melatonin and Biorhythms

The pineal gland, located in the brain, secretesmelatonin

Light/dark cycles control release of melatonin

Primary functions of melatonin appear to relate to

biological rhythms associated with reproduction


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All hormones

a) are lipid-soluble molecules.

b) are protein molecules.

c) elicit the same biological response from

all of their target cells.

d) are carried to target cells in the blood.e) are produced by endocrine glands.


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Thyroxine hormones exert negative feedback on

the production of thyroid stimulating hormone

(TSH), as best exemplified by

A. I.

B. II.

C. III.D. IV.

Thyroxines

Hormones are transported throughout the


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Hormones are transported throughout the

circulatory system, but they affect only

specific tissues or cells because

A. only the capillaries at the target will let thehormones out of the blood.

B. only the target cells have receptors for thehormone.

C. the nontarget tissues catabolize or destroy thehormones.

D. the hormones know where their targets arelocated.


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Epinephrine causes the constriction of someblood vessels and the dilation of others because

A. the target cells have different receptors for the same

hormone with different signal transduction pathways.

B. the vasoconstriction targets are incapable of

vasodilation.

C. the target cells have the same receptor and the same

signal transduction pathway.

D. the hormone is able to enter the cytosol of the

vasodilation targets but not the vasoconstriction targets.


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Thyroid hormones exert negative-feedback effects

at all levels of the hypothalamic-pituitary-thyroid

gland axis, so we should expect to find thyroid

hormone receptors at

A. the hypothalamus.

B. the anterior pituitary gland.

C. the targets of thyroid hormones throughout the

body.

D. all of the above.


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Oxytocin, the milk-release hormone secreted from

nerve endings (axon terminals) in the posterior

pituitary gland, is synthesized in

A. the anterior pituitary gland.

B. the hypothalamus.

C. the mammary glands.

D. the posterior pituitary gland.


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The role of the pancreas as an endocrine gland

that mediates glucose homeostasis is of great

importance to health, but a patient whose

pancreas has been surgically removed also loses

A. the bodys source of epinephrine.

B. the bodys source of growth hormones.

C. the bodys source of most of its digestive enzymes.

D. the ability to coordinate swallowing and breathing.


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The gas that causes vasodilation by

relaxing vascular smooth muscle, thus

enabling male sexual function, is

A. carbon dioxide.

B. nitric oxide.

C. carbon monoxide.

D. oxygen.

E. nitrogen.

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Endocrine Systems12 Endocrine Systems