Download Ch 16 Endocrine System Lecture Fa 12

PowerPoint® Lecture Slides
prepared by
Janice Meeking,
Mount Royal College
CHAPTER
16
The Endocrine
System:
Part A
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Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
(on dorsal aspect
of thyroid gland)
Thymus
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
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Figure 16.1
Endocrine System: Overview
• Endo = within
• Crine = to secrete
• Endocrine glands are ductless glands, secrete
into blood stream
• Exocrine glands are glands with ducts,
secrete out of the body (generally)
• Endocrine glands: pancreas, pineal,
hypothalamus, pituitary, thyroid, parathyroid,
and adrenal glands, and ovaries and testes
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Endocrine System: Overview
• Definition: ductless glands and tissues that
secrete hormones which influence metabolic
activities
• Hormones are long distance chemical signals
that travel in blood and lymph
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Endocrine System: Overview
• Hormones
• Regulate growth and development
• Regulate cellular metabolism and energy
balance
• Regulate reproduction
• Mobilize the immune system
• Maintain balance of electrolytes, water, and
nutrients in the blood
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Endocrine System: Overview
• Other tissues and organs that produce
hormones include:
• adipose cells
• thymus
• cells in the walls of the small intestine
• stomach
• kidneys
• heart
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Endocrine System: Overview
• Some organs produce both endocrine
(hormones) and exocrine products (secretions
into ducts)
• e.g., pancreas and gonads
• Some glands have both nervous and
endocrine function
• e.g., the hypothalamus and adrenal glands
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Endocrine System: Overview
Comparison of Endocrine
and Nervous System
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NERVOUS SYSTEM VS. ENDOCRINE SYSTEM
Together, they coordinate functions of all body systems.
- Both send chemical signals
- Both affect specific target organs or tissues
- Both work to maintain Homeostasis in the body
NERVOUS
ENDOCRINE
neurotransmitters
hormones
muscle contractions and glandular
secretions
metabolic activities of cells
acts in milliseconds
acts in seconds to minutes to hours
to days to months
brief effects
long-lasting effects
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Nervous System vs. Endocrine System
• Together the nervous and endocrine systems coordinate
functions of all body systems.
• The nervous system controls homeostasis through nerve
impulses (action potentials) conducted along axons of
neurons.
• In contrast, the endocrine system releases its hormones
into the bloodstream. The circulating blood then delivers
hormones to virtually all cells throughout the body.
• Certain parts of the nervous system stimulate or
inhibit the release of hormones. Hormones in
turn may promote or inhibit the generation of
nerve impulses. (Nervous and Endocrine interact!)
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Nervous System Modulation
• The nervous system can override normal
endocrine controls
• For example, control of blood glucose levels
• Normally the endocrine system maintains
blood glucose
• Under stress, the body needs more glucose
• The hypothalamus and the sympathetic
nervous system are activated to supply
ample glucose
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Endocrine System: Overview
Endocrine action: the hormone is distributed in blood and
binds to distant target cells.
Paracrine action: the hormone acts locally by diffusing from
its source to target cells in the neighborhood.
Autocrine action: the hormone acts on the same cell that
produced it.
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Classes of Hormones
• Two main classes
1. Amino acid-based hormones
• Amines, thyroxine (T4), peptides, and
proteins
• Insulin!
2. Steroids
• Synthesized from cholesterol
• Gonadal and adrenocortical hormones
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Hormone Classification
• All steroid hormones are made
initially from the precursor
cholesterol.
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• Steroid hormone
synthesis from
cholesterol
• Important steroid end
products:
• Aldosterone
• Cortisol
• DHEA
• Testosterone
• Estrone (E3) and
Estraidol (E2)
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Mechanisms of Hormone Action
• Hormone action on target cells
1. Alter plasma membrane permeability of
membrane potential by opening or closing
ion channels
2. Stimulate synthesis of proteins or regulatory
molecules
3. Activate or deactivate enzyme systems
4. Induce secretory activity
5. Stimulate mitosis
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Mechanisms of Hormone Action
•
Two mechanisms, depending on their chemical
nature
1. Water-soluble hormones (all amino acid–based
hormones except thyroid hormone)
•
Act on plasma membrane receptors
•
Cannot enter the target cells (hydrophilic
molecules trying to pass through a hydrophobic
membrane)
•
Use second messenger systems to get message
to target cell
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Mechanisms Of Water-Soluble Hormone Action
Water-soluble hormones
catecholamine, peptide, and protein hormones
target cells use membrane-bound receptors
first messenger vs. second messenger
G protein  adenylate cyclase  cyclic AMP  protein kinase phosphodiesterase
receptor
hormone
adenylate cyclase
G protein
ATP converted to
cAMP
phosphodiesterase
protein kinase
altered cell
function
5’-AMP (inactive)
nucleus
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1 Hormone (1st messenger)
binds receptor.
Adenylate cyclase
Extracellular fluid
G protein (GS)
5 cAMP acti-
vates protein
kinases.
Receptor
GDP
Hormones that
act via cAMP
mechanisms:
Epinephrine
ACTH
FSH
LH
Glucagon
PTH
TSH
Calcitonin
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2 Receptor
activates G
protein (GS).
3 G protein
activates
adenylate
cyclase.
4 Adenylate
cyclase
converts ATP
to cAMP (2nd
messenger).
Active
protein
kinase
Triggers responses of
target cell (activates
enzymes, stimulates
cellular secretion,
opens ion channel,
etc.)
Cytoplasm
Inactive
protein kinase
Figure 16.2
Water Soluble Hormones
• Glucagon
• Insulin
• PTH
• TSH
• Calcitonin
• Epinephrine
• ACTH
• FSH
• LH
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Second Messenger Systems
• 2 main types:
• cAMP (cyclic AMP)
• PIP2-calcium signaling mechanism
• Involves calcium!
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Mechanisms of Hormone Action
2. Lipid-soluble hormones (steroid and thyroid
hormones)
•
Act on intracellular receptors that directly
activate genes
•
Hydrophobic molecule can pass across
hydrophobic membrane
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Mechanisms Of Steroid Hormone Action
Lipid-soluble hormones
steroid and thyroid hormones
target cells use intracellular receptors
hormone-receptor complexes
altered gene expression
receptor
nucleus
diffusion
hormone binds to receptor,
which translocates to gene
mRNA
diffusion
hormone
protein
hormone
DNA
target cell
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target cell
Intracellular Receptors and Direct Gene
Activation
• Steroid hormones and thyroid hormone
1. Diffuse into their target cells and bind with intracellular
receptors
2. Receptor-hormone complex enters the nucleus
3. Receptor-hormone complex binds to a specific region
of DNA
4. This prompts DNA transcription to produce mRNA
5. The mRNA directs protein synthesis
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Target Cell Specificity
• Target cells must have specific receptors for
the hormones to bind to the cell
• ACTH receptors are only found on certain cells
of the adrenal cortex
• Thyroxine (T4) receptors are found on nearly
all cells of the body
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Target Cell Activation
• Target cell activation depends on three factors
1. Blood levels of the hormone
2. Relative number of receptors on or in the
target cell
3. Affinity of binding between receptor and
hormone
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Target Cell Activation
• Hormones influence the number of their
receptors
• Up-regulation—target cells form more
receptors in response to the hormone
• Down-regulation—target cells lose receptors in
response to the hormone
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Hormones in the Blood
• Hormones circulate in the blood either free or bound
• Steroids and thyroid hormone are attached to plasma
proteins (hydrophobic molecules need escorts through
a hydrophilic environment)
• All others circulate without carriers (they are water
soluble)
• The concentration of a circulating hormone reflects:
• Rate of release
• Speed of inactivation and removal from the body
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Hormones in the Blood
• Hormones are removed from the blood by
• Degrading enzymes
• Kidneys
• Liver
• Half-life—the time required for a substance’s
blood level to decrease by half
• Water soluble hormones have the shortest
half life
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Interaction of Hormones at Target Cells
• Multiple hormones may interact in several
ways
• Permissiveness: one hormone cannot exert its
effects without another hormone being present
• Synergism: more than one hormone produces
the same effects on a target cell
• Antagonism: one or more hormones opposes
the action of another hormone
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Control of Hormone Release
• Blood levels of hormones
• Are controlled by negative feedback systems
• Vary only within a narrow desirable range
• Hormones are synthesized and released in
response to
1. Humoral stimuli (body)
2. Neural stimuli
3. Hormonal stimuli
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Humoral Stimuli
• Changing blood levels of ions and nutrients
directly stimulates secretion of hormones
• Example: Ca2+ in the blood
• Declining blood Ca2+ concentration stimulates
the parathyroid glands to secrete PTH
(parathyroid hormone)
• PTH causes Ca2+ concentrations to rise and
the stimulus is removed
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(a) Humoral Stimulus
1 Capillary blood contains
low concentration of Ca2+,
which stimulates…
Capillary (low
Ca2+ in blood)
Thyroid gland
Parathyroid (posterior view)
glands
PTH
Parathyroid
glands
2 …secretion of
parathyroid hormone (PTH)
by parathyroid glands*
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Figure 16.4a
Neural Stimuli
• Nerve fibers stimulate hormone release
• Sympathetic nervous system fibers stimulate
the adrenal medulla to secrete catecholamines
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Hormonal Stimuli
• Hormones stimulate other endocrine organs
to release their hormones
• Hypothalamic hormones stimulate the release
of most anterior pituitary hormones
• Anterior pituitary hormones stimulate targets to
secrete still more hormones
• Hypothalamic-pituitary-target endocrine organ
feedback loop: hormones from the final target
organs inhibit the release of the anterior
pituitary hormones
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(c) Hormonal Stimulus
1 The hypothalamus secretes
hormones that…
Hypothalamus
2 …stimulate
the anterior
pituitary gland
to secrete
hormones
that…
Thyroid
gland
Adrenal
cortex
Pituitary
gland
Gonad
(Testis)
3 …stimulate other endocrine
glands to secrete hormones
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Figure 16.4c
Pineal Gland
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Pineal Gland
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Pineal Gland
• Small gland hanging from the roof of the third
ventricle
• Pinealocytes secrete melatonin, derived from
serotonin
• Melatonin may affect
• Timing of sexual maturation and puberty
• Day/night cycles
• Physiological processes that show rhythmic variations
(body temperature, sleep, appetite)
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Circadian
Rhythm
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PINEAL
Hypothalamus
Pituitary
Adrenal
Ovary/ Testes
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Thyroid
Hypothalamus
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Hypothalamus
• In the lower central part of
the brain
• The main link between the
endocrine and the nervous
systems.
• Nerve cells in the
hypothalamus control the
pituitary gland by
producing chemicals that
either stimulate or
suppress hormone
secretions from the
pituitary.
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Hypothalamic Hormones
• GnRH (gonadotrophic releasing hormone)
• SS (somatostatin)
• PRF (prolactin releasing factor)
• PIH (prolactin releasing inhibiting hormone)
• TRH (thyrotrophin releasing hormone)
• CRH (corticotrophin releasing hormone)
• GHRH (growth hormone releasing hormone)
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Hypothalamic Hormones
Hormones from Hypothalamus
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Pituitary Gland
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Pituitary Gland
• Size of a pea
• Located at the base of the
brain, and the most
important part of the entire
endocrine system.
• AKA: The master gland
because it makes
hormones that control
other endocrine glands.
• The production of hormones
and secretions can be
affected by emotions and
seasons change.
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Pituitary Gland
Pituitary gland and
hypothalamus are connected
via a stalk, also known as the
infundibulum.
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Pituitary Gland
• The pituitary gland (hypophysis) has two
major lobes
1. Posterior pituitary (lobe) (neurohypophysis)
• Neural tissue
• Neuro = nervous
2. Anterior pituitary (lobe) (adenohypophysis)
• Glandular tissue
• Adeno = gland
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Pituitary-Hypothalamic Relationships
• Posterior lobe
• A downgrowth of hypothalamic neural tissue
• Neural connection to the hypothalamus
(hypothalamic-hypophyseal tract)
• Nuclei of the hypothalamus synthesize the
neurohormones oxytocin and antidiuretic
hormone (ADH)
• Neurohormones are transported to the
posterior pituitary
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1 Hypothalamic
Paraventricular
nucleus
Supraoptic
nucleus
Optic chiasma
Infundibulum
(connecting stalk)
Hypothalamichypophyseal
tract
Axon
terminals
Posterior
lobe of
pituitary
Hypothalamus
neurons
synthesize oxytocin
and ADH.
2 Oxytocin and ADH are
Inferior
hypophyseal artery
transported along the
hypothalamic-hypophyseal
tract to the posterior
pituitary.
3 Oxytocin and ADH are
stored in axon terminals
in the posterior pituitary.
4 Oxytocin and ADH are
Oxytocin
ADH
released into the blood
when hypothalamic
neurons fire.
(a) Relationship between the posterior pituitary and the hypothalamus
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Figure 16.5a
Pituitary-Hypothalamic Relationships
• Anterior Lobe:
• Originates as an out-pocketing of the oral mucosa
• Anterior pituitary hormones travel through the blood to
get from the hypothalamus to the pituitary; posterior
pituitary hormones travel directly down neurons
connecting the hypothalamus and pituitary
• Blood route = Hypophyseal portal system
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Hypothalamus
Hypothalamic neuron
cell bodies
Superior
hypophyseal artery
Hypophyseal
portal system
• Primary capillary
plexus
• Hypophyseal
portal veins
• Secondary
capillary
plexus
Anterior lobe
of pituitary
TSH, FSH,
LH, ACTH,
GH, PRL
1 When appropriately
stimulated,
hypothalamic neurons
secrete releasing and
inhibiting hormones
into the primary
capillary plexus.
2 Hypothalamic hormones
travel through the portal
veins to the anterior pituitary
where they stimulate or
inhibit release of hormones
from the anterior pituitary.
3 Anterior pituitary
hormones are secreted
into the secondary
capillary plexus.
(b) Relationship between the anterior pituitary and the hypothalamus
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Figure 16.5b
Anterior Pituitary
(adenohypophosis)
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Anterior Pituitary Hormones
• Growth hormone (GH)
• Thyroid-stimulating hormone (TSH) or
thyrotropin
• Adrenocorticotropic hormone (ACTH)
• Follicle-stimulating hormone (FSH)
• Luteinizing hormone (LH)
• Prolactin (PRL)
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Anterior Pituitary Hormones
• All are proteins
• All except GH activate cyclic AMP secondmessenger systems at their targets
• TSH, ACTH, FSH, and LH are all tropic
hormones (regulate the secretory action of
other endocrine glands)
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Feedback Regulation of the Anterior
Pituitary:
Hypothalamus
-
-
Short
Loop
Feedback
?
+
-
Pituitary
+
Target Organ
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-
Long
Loop
Feedback
Growth Hormone
(GH)
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Growth Hormone (GH)
• Produced by somatotrophs
• Stimulates most cells, but targets bone and
skeletal muscle
• Promotes protein synthesis and encourages
use of fats for fuel (lipolysis or breakdown of
fats)
• Most effects are mediated indirectly by insulinlike growth factors (IGFs)
• elevates blood glucose by decreasing glucose uptake and
encouraging glycogen breakdown (anti-insulin effect of GH)
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Growth Hormone (GH)
• GH release is regulated by
• Growth hormone–releasing hormone (GHRH)
• Growth hormone–inhibiting hormone (GHIH)
(somatostatin)
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Growth Hormone Actions:
Somatostatin
+
IGF-1
Insulin Antagonism
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- GH
Growth
GHRH
+
Lipolysis
Growth
Insulin Antagonism
Inhibits GHRH release
Stimulates GHIH
release
Inhibits GH synthesis
and release
Feedback
Anterior
pituitary
Hypothalamus
secretes growth
hormone—releasing
hormone (GHRH), and
somatostatin (GHIH)
Growth hormone
Direct actions
(metabolic,
anti-insulin)
Indirect actions
(growthpromoting)
Liver and
other tissues
Produce
Insulin-like growth
factors (IGFs)
Effects
Effects
Skeletal
Extraskeletal
Fat
Carbohydrate
metabolism
Increases, stimulates
Increased cartilage
formation and
skeletal growth
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Increased protein
synthesis, and
cell growth and
proliferation
Reduces, inhibits
Increased
fat breakdown
and release
Increased blood
glucose and other
anti-insulin effects
Initial stimulus
Physiological response
Result
Figure 16.6
Homeostatic Imbalances of Growth
Hormone
• Hypersecretion
• In children results in gigantism
• Bone added on before growth plates close, person is very very
tall/large
• In adults results in acromegaly
• Bone added after growth plates close, person accumulates
extra bone, especially at feet, hands, face
• Hyposecretion
• In children results in pituitary dwarfism
• Not enough growth hormone to fully grow
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Thyroid Stimulating
Hormone (TSH)
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Thyroid-Stimulating Hormone (Thyrotropin)
• Produced by thyrotrophs of the anterior
pituitary
• Stimulates the normal development and
secretory activity of the thyroid
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Thyroid-Stimulating Hormone (Thyrotropin)
• Regulation of TSH release
• Stimulated by thyrotropin-releasing hormone
(TRH)
• Inhibited by rising blood levels of thyroid
hormones that act on the pituitary and
hypothalamus
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Hypothalamus
TRH
Anterior pituitary
TSH
Thyroid gland
Thyroid
hormones
Target cells
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Stimulates
Inhibits
Figure 16.7
Adrenocorticotrophic
Hormone (ACTH)
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Adrenocorticotropic Hormone
(Corticotropin)
• Secreted by corticotrophs of the anterior
pituitary
• Stimulates the adrenal cortex to release
corticosteroids
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Adrenocorticotropic Hormone
(Corticotropin)
• Regulation of ACTH release
• Triggered by hypothalamic corticotropinreleasing hormone (CRH) in a daily rhythm
• Internal and external factors such as fever,
hypoglycemia, and stressors can alter the
release of CRH
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Gonadotropins
(FSH, LH)
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Gonadotropins
• Follicle-stimulating hormone (FSH) and
luteinizing hormone (LH)
• Secreted by gonadotrophs of the anterior
pituitary
• FSH stimulates gamete (egg or sperm)
production
• LH promotes production of gonadal hormones
• Absent from the blood in prepubertal boys and
girls
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Gonadotropins
• Regulation of gonadotropin release
• Triggered by the gonadotropin-releasing
hormone (GnRH) during and after puberty
• Suppressed by gonadal hormones (feedback)
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Prolactin (PRL)
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Prolactin (PRL)
• Secreted by lactotrophs of the anterior
pituitary
• Stimulates milk production
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Prolactin (PRL)
• Regulation of PRL release
• Primarily controlled by prolactin-inhibiting
hormone (PIH) (dopamine)
• Blood levels rise toward the end of pregnancy
• Suckling stimulates PRH release and
promotes continued milk production
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Posterior Pituitary
(neurohypophosis)
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The Posterior Pituitary
• Contains axons of hypothalamic neurons
• Stores antidiuretic hormone (ADH) and
oxytocin
• ADH and oxytocin are released in response to
nerve impulses
• Both use PIP-calcium second-messenger
mechanism at their targets
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Oxytocin
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Oxytocin
• Stimulates uterine contractions during
childbirth by mobilizing Ca2+ through a PIP2Ca2+ second-messenger system
• Also triggers milk ejection (“letdown” reflex) in
women producing milk
• Plays a role in sexual arousal and orgasm in
males and females
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Antidiuretic Hormone
(ADH)
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Antidiuretic Hormone (ADH)
• Hypothalamic osmoreceptors respond to
changes in the solute concentration of the
blood
• If solute concentration is high
• Osmoreceptors depolarize and transmit
impulses to hypothalamic neurons
• ADH is synthesized and released, inhibiting
urine formation
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Antidiuretic Hormone (ADH)
• If solute concentration is low
• ADH is not released, allowing water loss
• Alcohol inhibits ADH release and causes
copious urine output
• ADH’s job is to conserve water
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Homeostatic Imbalances of ADH
• ADH deficiency—diabetes insipidus; huge
output of urine and intense thirst
• ADH hypersecretion (after neurosurgery,
trauma, or secreted by cancer cells)—
syndrome of inappropriate ADH secretion
(SIADH)
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Thyroid Gland
Hormones
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Thyroid
• The thyroid, shaped like a
butterfly, produces
thyroxine (T4) and
triiodothyronine (T3).
• These control the rate at
which cells burn fuels from
food to produce energy.
• Thyroid hormones are
important because they
participate in the growth
and development of kids’
and teens’ bones and the
nervous system.
• Attached to the thyroid are
the four parathyroids,
which, with the help of
calcitonin, control the
calcium level.
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Figure 16.8
Thyroid Gland
• Consists of two lateral lobes connected by a
median mass called the isthmus
• Composed of follicles that produce the
glycoprotein thyroglobulin
• Colloid (thyroglobulin + iodine) fills the lumen
of the follicles and is the precursor of thyroid
hormone
• Parafollicular cells produce the hormone
calcitonin
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Thyroid Hormone
• Major metabolic hormone
• Increases metabolic rate and heat production
(calorigenic effect)
• Plays a role in
• Maintenance of blood pressure
• Regulation of tissue growth
• Development of skeletal and nervous systems
• Reproductive capabilities
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Thyroid Hormone (TH)
• Actually two related compounds
• T4 (thyroxine); has 2 tyrosine molecules + 4
bound iodine atoms
• T3 (triiodothyronine); has 2 tyrosines + 3 bound
iodine atoms
• Majority of circulating hormone is T4 - 98.5% T4
1.5% T3
• for thyroid hormone to be built, it requires
iodine
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Transport and Regulation of TH
• T4 and T3 are transported by thyroxine-binding
globulins (TBGs)
• Both bind to target receptors, but T3 is ten
times more active than T4
• Peripheral tissues convert T4 to T3
• T3 is more metabolically active than T4
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Transport and Regulation of TH
• Negative feedback regulation of TH release
• Rising TH levels provide negative feedback
inhibition on release of TSH
• Hypothalamic thyrotropin-releasing hormone
(TRH) can overcome the negative feedback
during pregnancy or exposure to cold
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Hypothalamus
TRH
Anterior pituitary
TSH
Thyroid gland
Thyroid
hormones
Target cells
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Stimulates
Inhibits
Figure 16.7
Homeostatic Imbalances of TH
• Hyposecretion in adults
• Hypothyroidism; very common, often the adrenals
need to be supported and the thyroid will correct
• Sxs: weight gain, fatigue, hair brittle and dry/loss,
constipation, depression, cold intolerance (all signs
the metabolism is slow)
• endemic goiter if due to lack of iodine
• myxedema: very, very scary; end stage of
hypothyroidism; dangerously low levels over a long
period of time
• Bags under eyes very puffy, thyroid may be puffy,
severe fatigue; person on the verge of collapse, can
get fluid in lungs and fall into a coma
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Homeostatic Imbalances of TH
• Hyposecretion in infants—cretinism
• Hypersecretion—Graves’ disease
• Opposite of hypothyroidism
• Racing heart/palpitations, anxiety, jitteriness,
sweating, pupil dilation, weight loss
• Over long term, get bulging eyes
• Can see these effects in someone who has
been rxed too much thyroid hormone
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Figure 16.10
Calcitonin
• Produced by parafollicular (C) cells
• Antagonist to parathyroid hormone (PTH)
• Inhibits osteoclast activity and release of Ca2+
from bone matrix
• Ca2+ goes from blood to bone; lowers Ca2+
levels in the blood
• No important role in humans; removal of
thyroid (and its C cells) does not affect Ca2+
homeostasis
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Parathyroid Gland
Hormones
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Parathyroid Glands
• Four to eight tiny glands embedded in the
posterior aspect of the thyroid
• chief cells secrete parathyroid hormone (PTH)
• PTH—most important hormone in Ca2+
homeostasis
• Ca2+ moves from bone to blood; increases
blood levels of Ca2+
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Pharynx
(posterior
aspect)
Thyroid
gland
Parathyroid
glands
Chief
cells
(secrete
parathyroid
hormone)
Oxyphil
cells
Esophagus
Trachea
(a)
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Capillary
(b)
Figure 16.11
Parathyroid Hormone
• Functions
• Stimulates osteoclasts to digest bone matrix
• Enhances reabsorption of Ca2+ and secretion
of phosphate by the kidneys
• Promotes activation of vitamin D (by the
kidneys); increases absorption of Ca2+ by
intestinal mucosa
• Negative feedback control: rising Ca2+ in the
blood inhibits PTH release
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Parathyroid
Hormone
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Hypocalcemia (low blood Ca2+) stimulates
parathyroid glands to release PTH.
Rising Ca2+ in
blood inhibits
PTH release.
Bone
1 PTH activates
osteoclasts: Ca2+
and PO43S released
into blood.
Kidney
2 PTH increases
2+
Ca reabsorption
in kidney
tubules.
3 PTH promotes
kidney’s activation of vitamin D,
which increases Ca2+ absorption
from food.
Intestine
Ca2+ ions
PTH Molecules
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Bloodstream
Figure 16.12
Homeostatic Imbalances of PTH
• Hyperparathyroidism due to tumor
• Bones soften and deform
• Elevated Ca2+ depresses the nervous system
and contributes to formation of kidney stones
• Hypoparathyroidism following gland trauma or
removal
• Results in tetany, respiratory paralysis, and
death
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Adrenal Gland
Hormones
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Adrenal (Suprarenal) Glands
• Paired, pyramid-shaped organs atop the
kidneys
• Structurally and functionally, they are two
glands in one
• Adrenal medulla—nervous tissue; part of the
sympathetic nervous system (short term
stress)
• Adrenal cortex—three layers of glandular
tissue that synthesize and secrete
corticosteroids (long term stress)
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Adrenal Cortex
• Three layers and the corticosteroids produced
• Zona glomerulosa—mineralocorticoids
• Zona fasciculata—glucocorticoids
• Zona reticularis—sex hormones, or
gonadocorticoids
• G: Salt
• F: Sugar
• R: Sex
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Capsule
Zona
glomerulosa
• Medulla
• Cortex
Cortex
Adrenal gland
Zona
fasciculata
Zona
reticularis
Medulla
Kidney
Adrenal
medulla
(a) Drawing of the histology of the
adrenal cortex and a portion of
the adrenal medulla
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Figure 16.13a
Mineralocorticoids: Zona Glomerulosa
• Regulate electrolytes (primarily Na+ and K+) in
ECF
• Importance of Na+: affects ECF volume, blood
volume, blood pressure, levels of other ions
• Importance of K+: sets RMP of cells
• Aldosterone is the most potent
mineralocorticoid
• Stimulates Na+ reabsorption and water
retention by the kidneys
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Hormones of the Adrenal Cortex
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Mechanisms of Aldosterone Secretion
1. Renin-angiotensin mechanism: decreased blood
pressure stimulates kidneys to release renin,
triggers formation of angiotensin II, a potent
stimulator of aldosterone release
2. Plasma concentration of K+: Increased K+ directly
influences the zona glomerulosa cells to release
aldosterone
3. ACTH: causes small increases of aldosterone
during stress
4. Atrial natriuretic peptide (ANP): blocks renin and
aldosterone secretion, to decrease blood pressure
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Primary regulators
Blood volume
and/or blood
pressure
Other factors
K+ in blood
Stress
Blood pressure
and/or blood
volume
Hypothalamus
Kidney
Heart
CRH
Renin
Initiates
cascade
that
produces
Direct
stimulating
effect
Anterior
pituitary
Atrial natriuretic
peptide (ANP)
ACTH
Angiotensin II
Inhibitory
effect
Zona glomerulosa
of adrenal cortex
Enhanced
secretion
of aldosterone
Targets
kidney tubules
Absorption of Na+ and
water; increased K+ excretion
Blood volume
and/or blood pressure
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Figure 16.14
Homeostatic Imbalances of Aldosterone
• Aldosteronism—hypersecretion due to
adrenal tumors
• Hypertension and edema due to excessive
Na+
• Excretion of K+ leading to abnormal function of
neurons and muscle
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Glucocorticoids (Cortisol): Zona Fasiculata
• Keep blood sugar levels relatively constant
• Maintain blood pressure by increasing the
action of vasoconstrictors
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Glucocorticoids (Cortisol)
• Cortisol is the most significant glucocorticoid
• Released in response to ACTH, patterns of
eating and activity, and stress
• Prime metabolic effect is gluconeogenesis—
formation of glucose from fats and proteins
• Promotes rises in blood glucose, fatty acids,
and amino acids
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Glucocorticoids: Cortisol
• Should be high at beginning of day and taper off;
many people (especially students) have
disrupted cortisol rhythms; stress hormone
• Cortisol suppresses the immune system
• If cortisol is high, more likely to get sick
• Same happens if taking corticosteriods (like
prednisone or putting hydrocortisone cream on
eczema)
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Hormones of the Adrenal Cortex
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Homeostatic Imbalances of Glucocorticoids
• Hypersecretion—Cushing’s syndrome
• Depresses cartilage and bone formation
• Inhibits inflammation
• Depresses the immune system
• Promotes changes in cardiovascular, neural, and gastrointestinal
function
• Signs: Abdominal weight gain, thin skin, moon face, red cheeks,
purple stripes, buffalo hump, Na/K levels in a bad ratio in labs
• Hyposecretion—Addison’s disease
• Also involves deficits in mineralocorticoids
• Decrease in glucose and Na+ levels
• Weight loss, severe dehydration, and hypotension, tan skin
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Figure 16.15
Hyper-adrenocorticism
• Cushing’s syndrome
• 3rd - 6th decade, 4 to1
females
• causes
• pharmocologic
• pituitary adenoma 75-90%
• adrenal adenoma, carcinoma
• ectopic ACTH
• treatment based on cause
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Depressed secretion of
glucocorticoids and
mineralocorticoids
• S&S
• Weight loss
• Glucose and
sodium in blood
are low
• Rising blood
levels of K+
• Dehydration and
hypotension
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Gonadocorticoids
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Gonadocorticoids (Sex Hormones)
• Most are androgens (male sex hormones) that are
converted to testosterone in tissue cells or estrogens in
females
• DHEA is also produced, which is the precursor for
androgens
• May contribute to
• The onset of puberty
• The appearance of secondary sex characteristics
• Sex drive
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DHEA and
Androgen
production
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Adrenal Medulla
• Nervous system tissue
• Chromaffin cells secrete epinephrine (80%)
and norepinephrine (20%)
• These hormones cause
• Blood glucose levels to rise
• Blood vessels to constrict
• The heart to beat faster
• Blood to be diverted to the brain, heart, and
skeletal muscle
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Adrenal Medulla
• Epinephrine stimulates metabolic activities,
bronchial dilation, and blood flow to skeletal
muscles and the heart
• Norepinephrine influences peripheral
vasoconstriction and blood pressure
• Both stimulate the fight or flight response or
short term stress response
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Short-term stress
More prolonged stress
Stress
Nerve impulses
Hypothalamus
CRH (corticotropinreleasing hormone)
Spinal cord
Corticotroph cells
of anterior pituitary
To target in blood
Preganglionic
sympathetic
fibers
Adrenal medulla
(secretes amino acidbased hormones)
Catecholamines
(epinephrine and
norepinephrine)
Short-term stress response
1. Increased heart rate
2. Increased blood pressure
3. Liver converts glycogen to glucose and releases
glucose to blood
4. Dilation of bronchioles
5. Changes in blood flow patterns leading to decreased
digestive system activity and reduced urine output
6. Increased metabolic rate
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Adrenal cortex
(secretes steroid
hormones)
ACTH
Mineralocorticoids
Glucocorticoids
Long-term stress response
1. Retention of sodium
and water by kidneys
2. Increased blood volume
and blood pressure
1. Proteins and fats converted
to glucose or broken down
for energy
2. Increased blood glucose
3. Suppression of immune
system
Figure 16.16
Major Events in the General Stress
Response
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Pancreas Hormones
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Pancreas
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Pancreas
• Triangular gland behind the stomach
• Has both exocrine and endocrine cells
• Acinar cells (exocrine) produce an enzyme-rich juice
for digestion
• Pancreatic islets (islets of Langerhans) contain
endocrine cells
• Alpha () cells produce glucagon (a hyperglycemic
hormone)
• Beta () cells produce insulin (a hypoglycemic
hormone)
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Pancreatic
islet (of
Langerhans)
• (Glucagonproducing)
cells
• (Insulinproducing)
cells
Pancreatic
acinar
cells (exocrine)
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Figure 16.17
Glucagon
• Major target is the liver, where it promotes
• Glycogenolysis—breakdown of glycogen to
glucose
• Gluconeogenesis—synthesis of glucose from
lactic acid and noncarbohydrates
• Release of glucose into the blood; increases
blood glucose levels
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Insulin
• Effects of insulin
• Lowers blood glucose levels
• Enhances membrane transport of glucose into
fat and muscle cells
• Participates in neuronal development and
learning and memory
• Inhibits glycogenolysis and gluconeogenesis
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Stimulates glucose uptake by cells
Tissue cells
Insulin
Pancreas
Stimulates
glycogen
formation Glucose Glycogen
Blood
glucose
falls to
normal
range.
Liver
Stimulus
Blood
glucose level
Stimulus
Blood
glucose level
Blood
glucose
rises to
normal
range.
Pancreas
Liver
Glucose Glycogen
Stimulates
glycogen Glucagon
breakdown
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Figure 16.18
Homeostatic Imbalances of Insulin
• Diabetes mellitus (DM)
• Type I (juvenile)
• Due to hyposecretion of insulin
• Autoimmune cause (autoantibodies destroy beta cells of
pancreas)
• Will initially cause weight loss
• Type II (adult onset)
• Due to hypoactivity of insulin; the cells may have
become resistant to insulin from constant stimulation, or
less sensitive (less receptors for insulin)
• Tendency toward obesity, unhealthy diet and lifestyle
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Homeostatic Imbalances of Insulin
• Three cardinal signs of DM
• Polyuria—huge urine output
• Body trying to get rid of excess glucose
• Polydipsia—excessive thirst
• Body trying to dilute high glucose in the blood
• Polyphagia—excessive hunger and food consumption
• Cells are starving because insulin is not transporting
sugar into cells
• Hyperinsulinism:
• Excessive insulin secretion; results in hypoglycemia,
disorientation, unconsciousness
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Table 16.4
Gonadal Hormones
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Ovaries and Placenta
• Gonads produce steroid sex hormones
• Ovaries produce estrogens and progesterone
responsible for:
• Maturation of female reproductive organs
• Appearance of female secondary sexual
characteristics
• Breast development and cyclic changes in the uterine
mucosa
• The placenta secretes estrogens, progesterone, and
human chorionic gonadotropin (hCG)
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Testes
• Testes produce testosterone that
• Initiates maturation of male reproductive
organs
• Causes appearance of male secondary sexual
characteristics and sex drive
• Is necessary for normal sperm production
• Maintains reproductive organs in their
functional state
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Other Hormone
Producing Tissues
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Other Hormone-Producing Structures
• Heart
• Atrial natriuretic peptide (ANP) reduces blood
pressure, blood volume, and blood Na+
concentration
• Gastrointestinal tract enteroendocrine cells
• Gastrin from stomach stimulates release of
HCl
• Secretin from SI stimulates liver and pancreas
• Cholecystokinin from SI stimulates pancreas,
gallbladder, and hepatopancreatic sphincter
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Other Hormone-Producing Structures
• Kidneys
• Erythropoietin signals production of red blood cells
• Renin initiates the renin-angiotensin mechanism
• Skin
• Cholecalciferol, the precursor of vitamin D
• Adipose tissue
• Leptin is involved in appetite control, and stimulates
increased energy expenditure
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Other Hormone-Producing Structures
• Skeleton (osteoblasts)
• Osteocalcin prods pancreatic beta cells to
divide and secrete more insulin, improving
glucose handling and reducing body fat
• Thymus
• Thymulin, thymopoietins, and thymosins are
involved in normal the development of the T
lymphocytes in the immune response
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Developmental
Aspects
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Developmental Aspects
• Hormone-producing glands arise from all three germ
layers
• Exposure to pesticides, industrial chemicals, arsenic,
dioxin, BPA, plastics, and soil and water pollutants
disrupts hormone function
• Sex hormones, thyroid hormone, and glucocorticoids
are vulnerable to the effects of pollutants
• Interference with glucocorticoids may help explain
high cancer rates in certain areas
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Developmental Aspects
• Ovaries undergo significant changes with age
and become unresponsive to gonadotropins;
problems associated with estrogen deficiency
begin to occur
• Testosterone also diminishes with age, but
effect is not usually seen until very old age
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Developmental Aspects
• GH levels decline with age and this accounts
for muscle atrophy with age
• TH declines with age, contributing to lower
basal metabolic rates
• PTH levels remain fairly constant with age,
but lack of estrogen in older women makes
them more vulnerable to bone-demineralizing
effects of PTH
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QUESTIONS TO TEST
WHAT YOU NOW KNOW!!!
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A major difference between
neurotransmitters and hormones is that
hormones are secreted ____________.
A. directly onto their target cell
B. into the cerebrospinal fluid
C. into ducts
D. into the blood
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A major determinant of a hormone’s
mechanism of action is __________.
A. whether the hormonal molecule is
hydrophobic or hydrophilic
B. its size
C. whether it is rapid acting or slow acting
D. if it activates gene activity or not
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Receptors for steroid hormones are
commonly located _________.
A. inside the target cell
B. on the plasma membrane of the target cell
C. in the blood plasma
D. in the extracellular fluid
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Interaction with a membrane-bound
receptor will transmit the hormonal
message via __________.
A. depolarization
B. direct gene activation
C. a second messenger
D. endocytosis
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Which of the following molecules act as
second messengers?
A. cAMP
B. Ca2+
C. Na+
D. A and B
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It’s possible for a steroid hormone and a
protein hormone to affect the same
intracellular protein because:
A. the steroid hormone may direct the
synthesis of the protein.
B. the protein hormone may activate the
protein.
C. the protein hormone may direct the
synthesis of the protein.
D. of all of the above.
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In order for a hormone to activate a target
cell, the target cell must possess _______.
A. a receptor
B. a second messenger
C. the hormone
D. a chaperone
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The most common form of endocrine
malfunction is __________.
A. failure of the gland to produce the hormone
B. insensitivity of the target cell to the hormone
C. overproduction of the hormone by the gland
D. All of the above are common disorders.
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When the pancreas releases insulin in
direct response to blood glucose, this is an
example of ________ stimulation.
A. humoral
B. neural
C. hormonal
D. negative feedback
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When two people kiss, their
neurohypophyses releases oxytocin. This
is an example of __________ stimulation.
A. humoral
B. neural
C. hormonal
D. negative feedback
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When the ovaries secrete estrogen in
response to the hormone GnRH, this is an
example of __________ stimulation.
A. humoral
B. neural
C. hormonal
D. negative feedback
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Blood levels of hormone are kept within
very narrow ranges by _________
mechanisms.
A. humoral
B. neural
C. hormonal
D. negative feedback
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Hormones secreted into the hypophyseal
portal system are delivered directly to the
________.
A. neurohypophysis
B. adenohypophysis
C. median eminence
D. infundibulum
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A patient is displaying high volumes of urine
output and severe dehydration. The most
likely cause is _________.
A. hyposecretion of oxytocin
B. hypersecretion of oxytocin
C. hyposecretion of ADH
D. hypersecretion of ADH
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Common secretion(s) of the thyroid gland is
(are) _________.
A. calcitonin
B. Triiodothyronine (T3)
C. Thyroxine (T4)
D. all of the above
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A patient is losing weight rapidly, sweating
profusely, and is always anxious. The
patient may be suffering from _______.
A. hypothyroidism
B. cretinism
C. hyperthyroidism
D. hypersecretion of calcitonin
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Two hormones govern calcium regulation.
________ acts to elevate blood calcium
levels, whereas ________ lowers blood
calcium levels.
A. PTH; calcitonin
B. Thyroid hormones; calmodulin
C. Calcitonin; PTH
D. Calcitonin; thyroid hormone
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__________ is the adrenal hormone
responsible for maintaining appropriate
blood sodium levels.
A. Cortisol
B. DHEA
C. Aldosterone
D. Epinephrine
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_________ trigger(s) secretion of
aldosterone.
A. Increased K+
B. Angiotensin II
C. ANP
D. Both a and b
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During times of stress, elevated levels of
_______ often occur, which explains why
we get a cold during final exam time.
A. cortisol
B. aldosterone
C. ACTH
D. androgens
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Along with the sympathetic nervous
system, the _________ is the other primary
mediator of acute stress.
A. adrenal medulla
B. adrenal cortex
C. zona glomerulosa
D. zona reticularis
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The secretion of ________ helps regulate our
circadian rhythms.
A. estrogen
B. testosterone
C. thyroid hormones
D. melatonin
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The thymus secretes the hormone(s)
______________.
A. thymopoietin
B. thymosin
C. thymic factor
D. all of the above
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Which of the following structures produces
a hormone responsible for stimulating red
blood cell production?
A. Stomach
B. Heart
C. Kidney
D. Skin
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Which of the following structures produces
a precursor to hormonal vitamin D,
important for Ca2+ regulation?
A. Stomach
B. Heart
C. Kidney
D. Skin
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