Transcript ENDOCRINE SYSTEM - Doctor Jade Main

ENDOCRINE
SYSTEM
Nervous Vs. Endocrine Systems
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NERVOUS
• controlling system
• releases chemical
messengersneurotransmitters
• regulated by negative
feedback
• goal-Homeostasis
• effects appear fast
– can produce effects
in milliseconds
• effects-short duration
– useful for crisis
control
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ENDOCRINE
• controlling system
• releases chemical
messengers-hormones
• regulated by negative
feedback
• goal-Homeostasis
• effects appear slow
– require hours,
months or years
• effects-long lasting
– regulates long
acting changes
such as metabolic
activity
Endocrine Communication
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changes cellular operations by changing
types of enzymes or proteins
quantities of enzymes or proteins
activities of enzymes or structural proteins
accomplishes with hormones
substances released from one tissue and
transported via blood stream to have effects
on distant tissues
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Endocrine System
composed of endocrine glands
– small, ductless glands
widely scattered throughout
body
release secretions-hormones into
circulatory system
hormones make contact with all
cell types
influence only target cells
– contain specific protein
receptors on membranes or
inside cell to which hormones
can bind
some endocrine glands are
discrete organs
– pituitary & thyroid
others contain discrete areas of
endocrine tissue within their
structure
– islet of Langerhans in
pancreas
Chemical Classes of Hormones
• Lipid Soluble
– Steroids
– Thyroid Hormone
– Nitric Oxide
• Water Soluble
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Amines
Peptides
Proteins
Eicosanoid
Steroid Hormones
• derived from
cholesterol
• Estrogen
• Progesterone
• Testosterone
• Adrenocortical
hormones
• transported bound to
blood transport proteins
– keeps them in
circulation longer
Thyroid Hormone
• Made by adding
Iodine to the amino
acid tyrosine
• Soluble in lipid due to
the ring structure
Peptide/Protein Hormones
• Peptide
–chains of 3 to
49 amino acids
• Protein
–chains of 50 200 amino
acids
Amines
Epinephrine
• made from
amino acids
• retain an
amino group
• epinephrine
• norepinephrine
Eicosanoids
• derived from
fatty acid
• Arachidonic
acid
• Prostaglandins
• Leukotrienes
• Local
hormones
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Mechanisms
of
Action
Hormones change cellular operations
by stimulating synthesis of enzymes or structural proteins
by activating genes
by changing rate of transcription or translation
by turning existing enzymes on or off
come into contact with all types of body cells
only have effects at particular target cells
target cells have receptors for particular hormones
found on cell membrane or inside cell
Lipid Soluble Hormones- Direct
Gene Activation
• soluble in lipid
• can cross cell
membrane
• bind to receptors on
inside of cell
• in cytoplasm or
nucleus
• forming hormonereceptor complex
Direct Gene Activation Steps
• 1-hormone diffuses from
blood to cell
• 2-hormone enters cell
• 3-hormone binds to
receptor forming
receptor-hormone
complex
• 4-alters gene expressionmRNA is made
• 5-mRNA leaves nucleusdirects protein synthesis
• 6-new protein alters
metabolic activities of
other protein
Water Soluble HormonesSecond Messenger Mechanism
• cannot enter target cells
– must stimulate target cells indirectly
• second-messenger system
– receptors embedded in cell membrane
• Hormone-first messenger
– responsible for appearance of second
messenger-produces effects of hormone
• Second messengers include
– cAMP
– cGMP
– Ca++
• second messenger activates or inhibits cofactors
which changes rate of metabolic reactions
Second Messenger Mechanism
• hormone binds to plasma
membrane receptor
• activates G proteinregulatory molecule
• activated G protein
activates adenlyate
cyclase
• Activatged adenylate
cyclase converts ATP to
cAMP (cyclic AMP)
• cAMP is the second
messenger
• activates protein kinase
• catalyzes reactions
• degraded by
phosphodiesterase
Control of Endocrine Activity
• neural impulses
• hormones
• humoral stimuli
–changes in blood chemistry
–changes in extracellular body
fluids
Neural Control
• nerve fibers stimulate
hormone release
• neuroendocrine system
• Example-milk-let down
reflex
• stimulation of udder
neural signals spinal
cord brain secretory
neurons in posterior
pituitary oxytocin
releasedblood flows
through venous system to
heartlungs back to
heart arterial
systemuddersmilk let
down
Hormonal Control
• hormones cause the release of other hormones
• releasing hormones from hypothalamus travel to anterior
pituitary causing cells there to release tropic hormones
• GnRh LH & FSHovariessecrete hormones
• ACTHCRHadrenal cortexreleases hormones
Humoral
Control
• changing blood levels of ions & nutrients cause
hormones to be released
• parathyroid gland monitors Ca++ concentration
• when low secretes parathyroid hormoneCa++
increases
• insulin is released by pancreas due to humoral
stimulus of too much glucose in blood
Hypothalamus
• forms floor & walls of
third ventricle of brain
• responsible for
regulation of primitive
body functions:
• reproduction, hunger &
thirst
• many functions are
carried out by pituitary
gland
• master gland
Hypothalamus-Pituitary
• hypothalamus secretes
regulatory hormones
(releasing hormones) which
control endocrine cells in
anterior lobe of pituitary
• also manufactures hormones
which travel via
hypothalamus-hypophyseal
tract to be stored in posterior
pituitary
• hypothalamus has direct
neural control over endocrine
cells in adrenal medulla via
sympathetic nervous system
– neuroendocrine reflex
Hypophyseal Portal
System
• Adenohypohysis has no
direct connection to
hypothalamus
• connected by hypophyseal
portal system
• typically arteries take blood
from heart to capillaries &
veins from capillaries to heart
• portal system-blood flows
from one capillary network
into portal vein then to
secondary capillary network
before returning to heart.
• arrangement ensures all
blood entering portal vessels
will reach target cells before
entering general circulation
Hypothalamic Hormones
• 2 neurohormones
– oxytocin & antidiruretic hormones
– stored in pituitary
• 5 regulating hormones-releasing
hormones (RH)
– stimulate synthesis & secretion of other
hormones in anterior pituitary
• 2 inhibiting hormones (IH)
– inhibit synthesis & secretion of other
hormones from anterior pituitary
Hypothalamic Control of Anterior
Pituitary
• negative feedback loops
• Hypothalamus
releasing hormones 
adenohypophysis
tropic or trophic
hormone  stimulate
other endocrine glands
or tissues
• hormones from other
endocrine glands
feedback to turn off their
own production
Pituitary Gland-Hypophysis
• located in sella turcicadepression in sphenoid
bone
• size & shape of a pea
• connects to
hypothalamus by
infundibulum
• composed of two parts:
• Adenohypothesis
• Neurohypothesis
– separate functions
– separate anatomy
Anterior Pituitary Gland
• three discrete regions
• pars distalis
– largest & most anterior
• pars tuberalis
– wraps around
infundibulum
• pars intermedia
– narrow band bordering
the posterior pituitary
lobe
– atrophies before birth
Growth Hormone-Somatotropin
• secreted by somatotropes
• promote protein synthesis
• influence carbohydrate metabolism by
decreasing glucose uptake
• promote production of somatomedins or IGFsInsulin like growth factors
• stimulate uptake of amino acids & incorporation
into proteins
• overall increase growth rate of skeleton &
skeletal muscles during childhood & teenage
years
• in adults help maintain muscle & bone mass &
help to promote healing & tissue repair
Growth Hormone Secretion
• GHRH (growth
hormone releasing
hormone) stimulates
release of GH
• GHIH (growth hormone
inhibiting factor) or
somatostatin inhibits
release
• GHIH-triggered by
feedback of GH & IGFs
• as GH increasesinhibits its own release
Growth Hormone
TSH-Thyroid Stimulating
Hormone
• TRH (thyrotropin
releasing hormone) is
made by hypothalamus
• thyrotrope cells of
anterior pituitary
TSHthyroid gland
thyroid hormone
• thyroid hormone feeds
backs on TRH &
TSHinhibits secretion
ACTH-Corticotrophin
• released from
corticotrope cells of
anterior pituitary due to
stimulation from CRH
(corticotropin releasing
hormone) made by
hypothalamus
• ACTHadrenal cortex
• glucocorticorticoids
(especially cortisol)
• glucocorticoids feedback
to block secretion of CRH
& ACTH
Gonadotropins-FSH & LH
• regulate activities of gonads
• hypothalamus releases gonadotropin
releasing factors (GnRH)anterior
pituitaryLH & FSH
• FSH (follicle stimulating hormone)
promotes follicle development in
females & with LH stimulates estrogen
secretion
• in males FSH stimulates sperm
differentiation
• production of GnRH is inhibited by
inhibin
– released by cells in gonads
• LHinduces ovulation & promotes
progestin secretion by ovaries
• in males LH-also called ICSH or
interstitial cell stimulating hormone
stimulates interstitial cells of
testesandrogens
• gonadal hormones feedback to suppress
FSH & LH release
Prolactin-PRL
• released from anterior
pituitary due to stimulation
by PRH made by
hypothalamus
• PRL targets lactotropes in
mammary glandsmilk
production
• PRL helps regulate
androgen production in
males by making interstitial
cells more sensitive to LH.
• hypothalamusPIH or
prolactin inhibiting
hormone  prevents
prolactin secretion
• circulating prolactin
stimulates PIH production &
inhibits PRH
MSH-Melanocyte Stimulating
Hormone
• made by pars
intermedia
• stimulates
melanocytes to make
melatin
• no circulating MSH in
adults
• melanin receptors in
the brain suggests it
is involved in brain
activity
Posterior PituitaryNeurohypophysis
• neurons of supraoptic
(ADH) & paraventricular
(oxytocin) nuclei make
hormones
• made in hypothalamus
• transported to pituitary
along nerve axons
• stored in posterior pituitary
• released from posterior
pituitary on demand in
response to nerve
impulses from same
hypothalamic neurons that
made them
ADH-Vasopression or
Antidiuretic Hormone
• involved in water balance
• released in response to increases in
electrolyte concentrations in blood
• neurons responsible for releaseosmoreceptors
• solutes concentrated
osmoreceptors excite supraoptic
nucleisynthesis & release of ADH
• Target-kidney tubulesreabsorb
water from urineless urineblood
volume increasesblood pressure
increases
• solute concentration decreases,
osmoreceptorsend ADH release
• high concentrations of ADH produce
vasoconstriction primarily of
visceral blood vessels-thus it is
named vasopressin
Oxytocin
• produces smooth muscle
contraction in uterus & breasts
• released in high amounts during
childbirth & when nursing
• uterus stretchesimpulse to
hypothalamusoxytoxin made
& released from posterior
pituitary bloodcontractions
increase-positive feed back
control
• also acts for milk ejection via
neuroendocrine reflex-milk let
down reflex
• suckling (stimulus)sensory
neurons
hypothalamusocytoxin
releasedmyoepithelial
cellsrelease milk
• also believed to be cuddle
hormone which promotes
nurturing & affectionate or
bonding behavior
Pituitary Gland Review
• secretes nine
peptide
hormones
• 7 from anterior
pituitary
• 2 from posterior
pituitary
Thyroid Gland
• largest endocrine
gland
• located in anterior
neck
• 2 lobes connected by
an isthmus
• contains large number
of follicles
• lined by simple
cuboidal epithelium or
follicular cells
• follicle cells surround
a follicular cavity
which stores colloid
Thyroid Hormone Formation
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1. Iodide Trapping follicle cells trap I- by active transporting the ion from the blood
2. Thyroglobulin (TGB) Made ribosomes make TGB; packaged by Golgi into vesicles
3. TGB released vesicles undergo exocytosis and release TGB into the lumen of the follicle
4. Iodide oxidation I- loses an electron I2
5. Iodination of tyrosine I2 binds to tyrosine
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6. Coupling of T1 & T2
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T2 & T1 are linked by to produce T3-triiodothyronine & T4-tetraiodothyronine- thyroxin
7. Pinocytosis &Digestion of Colloid droplets of colloid enter the cell by pinocytosis and bind to
lysosome
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attachment of 1monoiodotyrosine
attachment of 2diiodotyrosine
once iodine binds-colloid
Breaks off T3 & T4
8. Secretion of Hormone thyroid hormones are lipid soluble diffuse through membrane
9. Transport of Hormone bind to TBG (thyroxine binding globulins) to be carried to tissues
Release of Thyroid Hormone
• thyroxine levels
fall hypothalamus
 TRH
pituitaryTSH
thyroid cells
thyroid hormones
• 90% is T4-major
thytoid hormone
• 10% is T3
• T3 is more potent
and responsible for
effects of thyroid
hormone
Functions of Thyroid Hormone
• major metabolic hormones
• Increase BMR (basal metabolic rate) which
raises use of oxygen
• calorigenic effect-increases heat production
• involved in long-term regulation of metabolic
turnover
• effects almost every cell in body except-adult
brain, spleen, testes, uterus and thyroid
Control of Thyroid Hormone
Parafollicular Cells of Thyroid
• secrete calcitonin
• lowers blood Ca++ levels
• Ca++ homeostasis is
essential for nerve
transmission, muscle
contraction & blood
clotting
• too lowNa permeability
increasescells become
more excitable
• calcium levels too high,
hypercalcemiaNa
permeability decreases
membranes less excitable
Calcitonin
• C cells respond to
Ca++
concentrations in
blood
• increased Ca++
concentration
increased
calcitonin
• at skeleton
inhibits osteoclast
activity decreases
Ca++ release from
bone
Parathyroid Glands
• 4 embedded in
posterior thyroid
• two cell types
• oxyphil cells
– unknown function
• chief or principal cells
– secrete PTH
(parathyroid
hormone or
parathormone)
Parathyroid Hormone Targets
• single most important agent in
controlling Ca++ balance
• chief cells monitor Ca levels
• lowered blood Ca++hypocalcemia
• stimulates secretion
• increases Ca++ in blood by
stimulating skeleton, kidneys &
intestines
• SkeletonPTH stimulates
osteoclasts to digest bone
matrix releases Ca++
• KidneysPTH enhances
reabsorption of Ca++
• PTH increases Ca++ by
enhancing synthesis of calcitriol
by the kidney which enhances
Ca++ absorption by gut
Adrenal or Suprarenal Glands
• pyramid shaped organs-top
of kidneys
• 2 parts
– structurally & functionally
different
• inner part-adrenal medulla
– part of sympathetic
nervous system
– makes epinephrine &
norepinephrine
• Outer-adrenal cortex
– Makes steroid hormones
called corticosteroids
or adrenocortical
steroids
• vital to life
Adrenal Cortex
• 3 regions or zones
• Zona Glomerulosa
– outer region
– composed of globular cell
clusters called glomeruli
– mineralocorticoids
• Zona Fasciculata
– middle zone
– cells form in linear cords
– glucocorticoids
• Zona reticularis
– inner zone
– cells form net like
arrangement
– gonadocorticoids
Zona Glomerulosa
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Mineralocorticoids
– control mineral & water balance in extracellular
fluids-particularly Na & K
Aldosterone
– main mineralocorticoid
maintains Na balance by reducing excretion of Na &
increasing elimination of K
primary target-distal kidney tubule stimulates
reabsorption of Na & water from urine
enhances Na absorption from sweat, saliva and
gastric juices
Na ion regulation is critical to overall body
homeostasis
where Na goes water follows via osmotic
reabsorption
therefore secondary effect of mineralocorticoids is
reabsorption of water
can lead to blood volume & blood pressure changes
Aldosterone release is stimulated by rising K levels,
low Na levels, decreasing blood volume & blood
pressure
also released in response to angiotensin II
– hormone made & released by kidneys
Zona Fasciculata
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produce glucocorticoids
– influence glucose metabolism
important in helping to resist stressors
absolutely essential to life
main one-cortisol or hydrocortisone
primary metabolic effect is gluconeogenesis\
– formation of glucose from non-carbohydrate
sources
helps body adapt to intermittent food intake by
keeping blood sugar levels constant
does so by breaking down adipose tissuesfatty
acids & proteinsamino acids.
glucocoricoids enhance epinephrine’s
vasoconstrictive effectsrise in blood
pressure and circulatory efficiency
helps maintain blood volume by preventing a
shift of water into tissue cells
Too muchdepresses cartilage & bone
formation, inhibits inflammation, depresses
immune system, and promotes changes in
cardiovascular, neural and gastrointestinal
functions
inhibit activities of WBCs
Cortisol Regulation
• regulated by negative
feedback
• CRH from hypothalamus
ACTH from anterior
pituitaryzona
fasciculatacortisol
• increased cortisol
hypothalamus &
anterior pituitary
prevents CRH release &
ACTH production
Zona Reticularis
• Gonadocorticoi
ds
• DHEAdehydroepiandro
sterone
• sustains libidio
(sex drive)
• release
stimulated by
ACTH
Adrenal Medulla
• secretes
catecholaminesepinephrine &
norepinephrine and
dopamine
• made by chromaffin cells
• sympathetic activity
increases rate of release
• Stress & exercise
hypothalamusmedulla
hormones fight or flight
reaction
• Increase in heart rate and
blood pressure
Pancreas
• elongated, spongy mixed
gland
• exocrine (98%) & endocrine
(2%) functions
• located partially behind
stomach in abdomen
• exocrine cells are found in
clusters called pancreatic
acini
• secrete alkaline, enzyme
rich fluid used in digestion
• endocrine pancreas is
found scattered throughout
gland in groups of cell
clusters called Islets of
Langerhans
Islets of Langerhans
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Alpha cells
– secrete glucagon
– hyperglycemic effect
• increases blood glucose levels by
increasing glycogenolysis in liver
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Beta cells
– secrete insulin
– hypoglycemic effect
• Decreases blood glucose
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Delta cells
– synthesize somatostatin when
blood glucose, fatty acids and
amino acid levels rise after eating
– inhibits digestive functions in
blood & pancreas
– suppresses release of glucagon &
insulin by the neighboring alpha
alpha & beta cells.
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F Cells
– secrete pancreatic polypeptide
– Inhibits somatostatin
Glucagon
• secretion prompted by humoral
stimuli
– falling blood sugar levels &
rising amino acid levels
• secretion suppressed by rising
blood sugar
• in liver& skeletal muscle
stimulates break down of
glycogen into glucoseglycogenolysis
• stimulates break down of
triglycerides in adipose tissue
• stimulates glucose production
from lactic acid & other noncarbohydrate sourcesgluconeogenesis in liver
• Resultless glucose use & more
glucose releaseincreases blood
glucose
Insulin
• decreases blood glucose
levels by increasing rate of
glucose uptake & use
• one effect is to enhance
glucose absorption &
utilization
• accelerates glucose use &
enhances ATP production
• stimulates glycogen
formation in skeletal muscle
and liver cells
• stimulates amino acid
absorption and protein
synthesis
• stimulates triglyceride
formation in adipose tissue
Gonads
• Testes
• Androgens
–testosteronemajor one
• Ovaries
• Estrogens
Testosterone Functions
• maturation of
reproductive organs
• appearance &
maintenance of
secondary sex
characteristics
• effects metabolic
activities
• stimulates protein
synthesis & muscle
growth
Estrogen Functions
• maturation of
reproductive
organs
• Development &
maintenance of
secondary sex
characteristics
Pineal Gland
• tiny, pine coned shaped
structure hanging from roof of
third ventricle
• secretes melatonin at night
• rises & falls in diurnal cycle
• peaks at night inducing sleep
• lowest during day
• pineal receives information
regarding intensity & duration of
day light via
retinasuprachiasmatic
nucleus in
hypothalamuspineal
glandmelatonin
• responsible for setting circadian
rhythm or daily-cycles
Endocrine Tissues of Other Organs
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Heart-atrium
– ANP-atrial natriuretic peptide
• promotes loss of Na & water at kidneys & inhibits renin release & secretion of
ADH & aldosterone
• net result is reduction of blood volume & pressure.
Skin-keratinocytes
– Vitamin D3-first step in production of calcitriol
• hormone that raises blood calcium levels
Stomach & Small Intestine
– Enteroendocrine cells secrete about 10 enteric hormones
• Coordinate different regions & glands of digestive system with each other
Kidney
– Erythropoietin
• released in response to low O2 levels stimulates RBCs production
– renin
• cleaves angiotensinogenangiotensin II adrenal cortexaldosterone
increases blood volume & pressure
Thymus
– thymopoietins & thymosins
• important in development of T lymphocytes important in the immune response
Adipose tissue
– Leptin-appetite control