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Endocrine System
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Endocrine system - glands, tissues, and cells thatsecrete hormones
Endocrinology the study of this system and the
diagnosis and treatment of its disorders Endocrine glands organs that are traditional sources of
hormones
Hormones - chemical messengers that are transported
by the bloodstream and stimulate physiological responsesin cells of another tissue or organ, often a considerabledistance away
Endocrine System Components
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Hypothalamus
Organs of the endocrine system (purple) and other organscontaining tissues that secrete hormones (tan)
Thyroid Gland
Adrenal Glands
Pancreas (Pancreatic Islets)
Organs with Secondary
Endocrine Functions
Parathyroid Glands
Pineal Gland
Pituitary Gland
Secretes hormones involved with
fluid balance, smooth muscle
contraction, and the control ofhormone secretion by the
anterior pituitary gland
Secretes multiple hormones that
regulate the endocrine activities
of the adrenal cortex, thyroid
gland, and reproductive organs,
and a hormone that stimulates
melanin production
Secretes hormones that affect
metabolic rate and calcium levels in
body fluids.
Secretes hormones involved with
mineral balance, metaboliccontrol, and resistance to stress;
the adrenal medullae release E
and NE during sympathetic
activation
Secretes hormones regulating
the rate of glucose uptake and
utilization by body tissues
Testis
Ovary
Gonads: Secrete hormones
affecting growth, metabolism,
and sexual characteristics, as
well as hormones coordinating
the activities of organs in the
reproductive system
Kidneys: Secrete hormones that
regulate blood cell productionand the rates of calcium and
phosphate absorption by the
intestinal tract
Digestive Tract: Secretes
numerous hormones involved in
the coordination of system
functions, glucose metabolism,
and appetite
Thymus: Secretes hormones
involved in the stimulation and
coordination of the immune
response
Heart: Secretes hormones
involved in the regulation of
blood volume
Secrete a hormone important
to the regulation of calcium ion
concentrations in body fluids
Secretes melatonin, which
affects reproduction function
and helps establish circadian
(day/night) rhythms
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Anatomy of Hypothalamus
Provides highest level of endocrine control Shaped like a flattened funnel Forms floor and walls of third ventricle of
the brain Regulates primitive functions of the body
from water balance and thermoregulation tosex drive and childbirth
Many of its functions carried out bypituitary gland
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The three mechanisms by which the hypothalamus integrates the activitiesof the nervous and endocrine systems
The hypothalamus func-
tions as an endocrine
organ. Hypothalamic
neurons synthesize two
hormonesantidiuretic
hormone (ADH) and
oxytocin (OXT)
andtransport them along axons
within the infundibulum.
The hypothalamus secretes
regulatory hormones,
special hormones that control
endocrine cells in the pituitary
gland. The hypothalamic
regulatory hormones control
the secretory activities ofendocrine cells in the anterior
lobe of the pituitary gland.
The hypothalamus contains
autonomic centers that
exert direct neural control
over the endocrine cells of
the adrenal medullae. When
the sympathetic division is
activated, the adrenalmedullae are stimulated
directly and immediately.
Preganglionic
motor fibers
Adrenal gland
HYPOTHALAMUS
Adrenal cortex
Adrenal medulla
Posterior lobe
of pituitary gland
Infundibulum
Anterior lobeof pituitary gland
Hormones released
control the activities of
endocrine cells in the
thyroid gland, adrenal
cortex, and reproductive
organs.
ADH and oxytocin
are released into
the circulation.
Upon direct neuronal
stimulation, the
adrenal medullae
secrete epinephrine
and norepinephrine
into the circulation.
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Once within the anterior lobe, these
vessels form a second capillary
network that branches among the
endocrine cells.
The vessels between the median
eminence and the anterior lobe
carry blood from one capillary
network to another. Blood vessels
that link two capillary networks are
called portal vessels; in this case,
they have the histological structure
of veins, so they are called portalveins.
The capillary networks in the
median eminence are supplied by
the superior hypophyseal artery.
Before leaving the hypothalamus,
the capillary networks unite to form
a series of larger vessels that spiral
around the infundibulum to reach
the anterior lobe.
Hypophyseal Portal System
Control of the production of anterior
pituitary hormones by hypothalamic
regulatory hormones
Neurons of these structures manufacture
antidiuretic hormone and oxytocin,
respectively, which are released by
synaptic terminals at capillaries in the
posterior lobe of the pituitary gland
Supraoptic
nuclei
Paraventricular
nucleiNeurosecretory
neurons
HYPOTHALAMUS
Superior
hypophyseal artery
Infundibulum
Inferior
hypophyseal artery
Posterior lobe of
pituitary gland
Endocrine cells
Anterior lobe of
pituitary gland
Hypophyseal veins
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Pituitary Gland (Hypophysis)
Suspended from hypothalamus by a stalk
infundibulum Location and size
Housed in a depression of the sphenoid bonecalled sella turcica
Size and shape of kidney bean 1.3 cm wide
Composed of two structures withindependent origins and separate functions adenohypophysis (anterior or glandular pituitary)
- three-quarters of pituitary Fleshy and glandular
neurohypophysis (posterior or neural pituitary) one quarter of pituitary
Down growth from brain Neural composition
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Pituitary Gland
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Histology of Pituitary Gland
Chromophobe
Basophil
Acidophil
(b) Posterior pituitary
Unmyelinatednerve fibers
Glial cells(pituicytes)
(a) Anterior pituitary
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Histology of Anterior Pituitary Gland
Acidophilshave cytoplasm that stains red or orange
Cells that contain the polypeptide hormones : growthhormone and prolactin
Basophils have cytoplasm that stains a bluish colour
Cells that contain the glycoprotein hormones :thyroid stimulating hormone, luteinizing hormone,follicle stimulating hormone and adrenocorticotrophichormones
Chromophobes have cytoplasm that stains very poorly
These are cells that have minimal or no hormonalcontent. Some chromophobes may also representstem cells that have not yet differentiated intohormone-producing cells
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Hypothalamic Hormones
Eight hormones produced in hypothalamus Six regulate the anterior pituitary Two produced in hypothalamus and via axoplasmic transport
are stored in the posterior pituitary from where they arereleased into the blood circulation (Oxytocin andAntidiuretic Hormone)
Six releasing and inhibiting hormones stimulate orinhibit the anterior pituitary TRH, CRH, GnRH, and GHRH are releasing hormones that
affect anterior pituitary secretion of TSH, PRL, ACTH,FSH, LH, and GH
PIH inhibits secretion of prolactin SOMATOSTATIN (growth hormone-inhibiting hormone
(GHIH) or somatotropin release-inhibiting factor (SRIF)inhibits secretion of growth hormone & thyroid stimulatinghormone by the anterior pituitary
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Hypophyseal Portal System
Portal venules
Posterior lobe
Anterior lobe
Hypothalamic hormones
Anterior lobe hormones
Primary capillariesGonadotropin-releasing hormoneThyrotropin-releasing hormone
Corticotropin-releasing hormoneProlactin-inhibiting hormoneGrowth hormonereleasing hormoneSomatostatin
Follicle-stimulating hormoneLuteinizing hormoneThyroid-stimulating hormone(thyrotropin)
Adrenocorticotropic hormoneProlactinGrowth hormone
Axons toprimarycapillaries
Neuroncell body
Hypophysealportal system:
Secondarycapillaries
Superior hypophysealartery
Hypothalamic releasing and inhibiting
hormones travel in hypophyseal portalsystem (system of blood vesselsthat link the hypothalamus and theanterior pituitary in the brain) fromhypothalamus to anterior pituitary Hormones secreted by anteriorpituitary
Portal venules
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Hypothalamic Hormones
Two other hypothalamic hormones are oxytocin(OT) and antidiuretic hormone (ADH) secreted byposterior pituitary gland
Produced by neurosecretory neurons
Transported to posterior pituitary by axoplasmictransport Both stored and released by posterior pituitary
Right and left paraventricular nuclei produce oxytocin(OT)
Supraoptic nuclei produce antidiuretic hormone (ADH) Posterior pituitary does not synthesize them but merely
stores these hormones
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ADH (antidiuretic hormone) increases water retention thus reducing urine volume and
prevents dehydration also called vasopressin because it can cause vasoconstriction
OT (oxytocin) surge of hormone released during sexual arousal and orgasm
stimulate uterine contractions and propulsion of semen promotes feelings of sexual satisfaction and emotional bonding
between partners stimulates labor contractions during childbirth stimulates flow of milk during lactation promotes emotional bonding between lactating mother and
infant
Posterior Pituitary Hormones
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Anterior lobe of the pituitary synthesizesand secretes six principal hormones Two gonadotropin hormones that target
gonads FSH (follicle stimulating hormone)
stimulates secretion of ovarian sex hormones,development of ovarian follicles, and spermproduction
LH (luteinizing hormone) stimulates ovulation, stimulates corpus luteum to
secrete progesterone, stimulates testes to secrete
testosterone TSH (thyroid stimulating hormone)
stimulates secretion of thyroid hormone whichincreases metabolic rate, stimulates appetite, increasegrowth of hair, skin, teeth, increase respiratory rate,increase heart rate
Anterior Pituitary Hormones
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Anterior Pituitary Hormones
ACTH (adrenocorticotropic hormone) stimulates adrenal cortex to secrete
glucocorticoids e.g. cortisol which stimulates fatand protein metabolism, gluconeogenesis, helps to
repair damaged tissues and has an anti-inflammatory effect PRL (prolactin)
after birth stimulates mammary glands tosynthesize milk, enhances secretion of
testosterone by testes GH (growth hormone)
stimulates mitosis and cellular differentiation
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Hypothalamo-Pituitary-Target Organ Relationships
Figure 17.6
PRL
GH
ACTHTSH
Liver
TRHGnRHCRH
Hypothalamus
Adrenal cortex
OvaryTestis
Thyroid
IGF
GHRH
Mammarygland
Fat,muscle,bone
LHFSH
Principle hormones and target organs
PRL
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An overview of the relationships between hypothalamic and pituitaryhormones, and some effects of pituitary hormones on target tissues
Hypothalamus
Indirect Control through Releaseof Regulatory Hormones
Direct Releaseof Hormones
Corticotropin-releasinghormone
(CRH)
Thyrotropin-releasinghormone
(TRH)
Growthhormone-releasinghormone(GH-RH)
Growthhormone-inhibitinghormone(GH-IH)
Prolactin-releasing
factor(PRF)
Prolactin-inhibitinghormone
(PIH)
Gonadotropin-releasinghormone(GnRH)
Sensorystimulation
Osmoreceptorstimulation
Regulatory hormones are released intothe hypophyseal portal system for delivery
to the anterior lobe of thepituitary gland.
Posterior lobeof pituitary gland
Kidneys
Males: Smoothmuscle in ductusdeferens andprostate gland
Females: Uterinesmooth muscle andmammary glands
Melanocytes (uncertainsignificance in healthyadults)
Ovariesof femaleTestes
of maleMammaryglands
Bone, muscle,other tissues
Thyroidgland
Adrenalglands
Adrenal cortex Anterior lobe ofpituitary gland
ACTH
TSHGH
PRLFSH LH
MSH
OXT
ADH
Liver
Somatomedins
Glucocorticoids(steroid
hormones)
Thyroidhormones
Inhibin Testosterone Estrogen Progesterone Inhibin
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The control ofhypothalamic andpituitary hormone
secretion by negativefeedback
Hypothalamus
RH
Pituitary
gland
Anterior
lobe
Hormone 1
Hormone 2
Endocrine
organ
Target cells
KEY
Stimulation
Inhibition
Negative feedback
Releasinghormone(RH)
Hormone 1(frompituitary)
Hormone 2(from targetorgan)
Endocrinetargetorgan
TRH
CRH
GnRH
LH
FSH
ACTH
TSH
Testes
Ovaries
Ovaries
Testes
Adrenalcortex
Thyroidgland
Thyroidhormones
Gluco-corticoids
Inhibin
InhibinEstrogens
ProgestinsEstrogens
Androgens
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The secretion of growth hormone(GH), involves both releasing
and inhibiting hormones. Thisprovides a more rapid and preciseregulation of GH.
Stimulation
Inhibition
Stimulates growth of skeletal muscle,cartilage, and many other tissues
Epithelia,adipose tissue,liver
Anteriorlobe
GH
GH-IH
GH-RH
Liver
Somatomedins
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Growth Hormone
GH has widespread effects on the body tissues especially cartilage, bone, muscle, and fat
Stimulates liver cells to synthesize somatomedinswhich increase uptake of amino acids and theirincorporation into proteins by various tissues
Suppresses protein catabolism (breakdown)
Lipid metabolism increased fat catabolized byadipocytes (protein-sparing effect) provides energyfor growing tissues
In liver stimulates breakdown of glycogen
Bone growth, thickening, and remodeling influenced,especially during childhood and adolescence
GH levels decline gradually with age
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Pituitary Disorders Hypersecretion of growth hormone (GH)
Acromegaly due to hypersecretion of GH in adultscausing thickening of bones and soft tissues
especially hands, feet and face
problems in childhood or adolescence gigantism if hypersecretion (excessive production of GH in
chlidren) pituitary dwarfism if hyposecretion rare since growthhormone is now made by genetically engineered bacteria
Age 33Age 16Age 9 Age 52
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Gigantism
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PRL
PRF
PIHStimulation
Inhibition
Stimulatesmammary
glands
Anteriorlobe
The control ofprolactin (PRL)secretion by a pairof regulatoryhormones
PIH (dopamine) inhibits release ofprolactin most of the time. Each
month before menstruationbegins, secretion of PIHdiminishes and levels of prolactinincrease. During pregnancyprolactin levels rise due toincrease secretion of PRF
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Pineal Gland
Pineal Gland
Pi l Gl d
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Pineal Gland
Pineal gland - attached to roof of third ventriclebeneath the posterior end of corpus callosum
After age 7, it undergoes involution (shrinkage) down 75% by end of puberty tiny mass of shrunken tissue in adults
Produces melatonin, a hormone that affects themodulation of wake/sleep patterns and photoperiodic(seasonal) functions i.e. it regulates the gonads andthe annual breeding cycle
It regulates the hormonal changes that usher in
sexual maturity puberty during adolescence i.e. mayregulate timing of puberty in humans Today it is associated with the sixth chakra whose
awakening is linked to prophecy and increased psychicawareness as consciousness ascends.
Th
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Thymus Bilobed gland in the mediastinum superior to the heart
goes through involution after puberty
Site of maturation of T lymphocytes important in immune defense
Secretes hormones (thymopoietin, thymosin, and thymulin) thatstimulate development of other lymphatic organs and activity of T-lymphocytes
Thymus
Thyroid
Trachea
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Thyroid Gland Largest endocrine gland
composed of two lobes and an isthmusbelow the larynx
dark reddish brown color due to richblood supply
Secretes thyroxine (T4 because of 4iodine atoms) and triiodothyronine(T3) T4 which is converted to T3
increases metabolic rate, O2consumption, heat production(calorigenic effect), appetite, growthhormone secretion, alertness andquicker reflexes
Parafollicular (C or clear) cellssecrete calcitonin with rising bloodcalcium stimulates osteoblast activity and
bone formation
Inferior thyroid vein
Isthmus
Thyroidcartilage
Thyroidgland
Trachea
Superior thyroidartery and vein
l f P
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Control of Pituitary:Feedback from Target Organs
Negative feedback -increased target organhormone levels inhibits
release of hormones+
+
+
+
TRH
TSH
Target organs
Thyroid hormone
Stimulatory effect
Inhibitory effect
2
3
4
1
5
6Negative feedbackinhibition
-
-
Th id Gl d Di d
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Thyroid Gland Disorders
Goiter any pathological enlargement of the thyroid
gland- Hashimoto's thyroiditis or chronic lymphocytic thyroiditis
is an autoimmune disease in which the thyroid gland isgradually destroyed by a variety of cell and antibody mediated
immune processes Endemic goiter
dietary iodine deficiency, no TH, no - feedback,increased TSH stimulates hypertrophy
Toxic goiter (Graves disease) autoantibodies mimic the effect of TSH on the thyroid
causing hypersecretion
overgrown thyroid produces functional TH (increasedlevels)
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Goiter
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Parathyroid Glands
Usually four glands partially
embedded in posteriorsurface of thyroid gland can be found from as high as
hyoid bone to as low as aorticarch
Secrete parathyroidhormone (PTH) increases blood Ca2+ levels
promotes synthesis ofcalcitriol
increases absorption of Ca2+
decreases urinary excretion increases bone resorption increases osteoclast
activity
Thyroid gland
Esophagus
Trachea
Pharynx(posterior view)
Parathyroidglands
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Parathyroid Disorders
Hypoparathyroidism surgical excision during thyroid surgery
fatal tetany in 3 - 4 days due to rapid decline in
blood calcium level Hyperparathyroidism - excess PTH
secretion
parathyroid tumor bones become soft, fragile, and deformed
Ca2+ and phosphate blood levels increase
promotes renal calculi formation
l l
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(a)
(b)
Adrenal gland
Kidney
Adrenal cortex
Adrenal medulla
Connectivetissue capsule
Adrenal cortex
Adrenal medulla
Zonaglomerulosa
Zona
fasciculata
Zonareticularis
Suprarenal vein
Adrenal Gland
Small gland that sits on top of each kidney
They are retroperitoneal like the kidney
Ad l M d ll
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Adrenal Medulla Adrenal medulla inner core, 10% to 20% of gland which is
surrounded by a much thicker adrenal cortex constituting 80% -
90% Consists primarily of modified sympathetic neurons calledchromaffin cells (neuroendocrine cells) which have no dendrites oraxons but receive sympathetic input and release their productsdirectly into the blood stream. When stimulated releasecatecholamines (epinephrine and norepinephrine)
Effect is longer lasting than neurotransmitters increases alertness (fight and flight) and prepares body for
physical activity mobilize high energy fuels, lactate, fatty acids, and glucose glycogenolysis and gluconeogenesis boost glucose levels glucose-sparing effect because inhibits insulin secretion
muscles use fatty acids saving glucose for brain increases blood pressure, heart rate, blood flow to muscles,
pulmonary air flow and metabolic rate decreases digestion and urine production
Ad l C t
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Adrenal Cortex Surrounds adrenal medulla and produces major
steroid hormones called corticosteroids Secretes 3 major categories of steroid hormones
from three layers of glandular tissue zona glomerulosa (thin, outer layer)
cells are arranged in rounded clusters
secretes mineralocorticoids e.g. aldosterone regulate thebodys electrolyte balance i.e. sodium retention
zona fasciculata (thick, middle layer) cells arranged in fascicles separated by capillaries secretes glucocorticoids e.g. cortisol regulate metabolism
of glucose, suppresses immune system, helps body adapt tostress and repair tissues
zona reticularis (narrow, inner layer) cells in branching network secretes sex steroids e.g. androgens, estrogen (estradiol).
DHEA is converted to testosterone in other tissues.
Adrenal Disorders
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Adrenal Disorders Cushing syndrome - excess cortisol secretion
hyperglycemia, hypertension, weakness, edema
rapid muscle and bone loss due to protein catabolism
abnormal fat deposition moon face and buffalo hump
Adrenogenital syndrome (AGS)
adrenal androgen hypersecretion (accompanies Cushing)
enlargement of external sexual organs in children and early onset of
puberty masculinizing effects on women
increased body hair, deeper voice and beard growth
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