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Anatomy and Physiology:
The Endocrine System
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Overview
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Endocrine System Overview
Hormone Secretion/Pos. & Neg. Feedback
Hypothalamus and Anterior Pituitary
Posterior Pituitary
Thyroid Gland
Parathyroid Glands
Adrenal Cortex
Pancreas
Gonads
Pineal Gland
Essential Terms
hormone
 chemical mediator that helps maintain homeostasis
target cell
 cell with a receptor that responds to the presence of a hormone
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General Characteristics
 Glands that secrete chemical signals
(hormones) into circulatory system
 Hormone characteristics
 Produced in small quantities
 Secreted into intercellular space
 Transported some distance in
circulatory system
 Acts on target tissues elsewhere in
body
 Regulate activities of body structures
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Endocrine System Functions
 Metabolism and tissue maturation
 Ion regulation
 Water balance
 Immune system regulation
 Heart rate and blood pressure regulation
 Control of blood glucose and other nutrients
 Control of reproductive functions
 Uterine contractions and milk release
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Endocrine Glands
exocrine glands secrete products onto a surface
endocrine glands secrete products into the body fluids
hormones are carried to target tissues where activity is
carried out
pituitary, thyroid, parathyroid, adrenal, pineal
Other hormone secreting structures
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hypothalamus, thymus, pancreas, ovaries, testes, kidneys,
stomach, liver, small intestine, skin, heart, adipose tissue,
placenta
Figure 17.1
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Regulation of Activities:
Comparison of Endocrine
and Nervous Systems
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Endocrine: amplitude modulated signals.
 Amount of hormone determines strength of
signal
 Onset within minutes of secretion of
hormone
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Nervous: frequency-modulated signals.
 Frequency of action potentials produced by
neurons determines strength of signal.
 Onset within milliseconds
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Two systems actually inseparable
 Nervous system secretes neurohormones
into circulatory system
 Nervous system uses neurotransmitters and
neuromodulators as ligands
 Some parts of endocrine system innervated
directly by nervous system
Intercellular Chemical Signals
 Hormones: type of intercellular signal. Produced by cells of endocrine
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glands, enter circulatory system, and affect distant cells; e.g., estrogen
Autocrine: released by cells and have a local effect on same cell type from
which chemical signals released; e.g., prostaglandin
Paracrine: released by cells and affect other cell types locally without
being transported in blood; e.g., somatostatin
Pheromones: secreted into environment and modify behavior and
physiology; e.g., sex pheromones
Neurohormone: produced by neurons and function like hormones; e.g.,
oxytocin
Neurotransmitter or neuromodulator: produced by neurons and
secreted into extracellular spaces by presynaptic nerve terminals; travels
short distances; influences postsynaptic cells; e.g., acetylcholine.
Functional Classification of Intercellular
Chemical Signals
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Functional Classification of Intercellular
Chemical Signals
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Control of Secretion Rate
 Most hormones controlled by negative feedback systems
 Most hormones are not secreted at constant rate, but their
secretion is regulated by three different methods
1. The action of a substance other than a hormone on an endocrine
gland.
2. Neural control of endocrine gland.
3. Control of secretory activity of one endocrine gland by hormone or
neurohormone secreted by another endocrine gland
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Positive and Negative Feedback
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POSITIVE
During the menstrual cycle, before
ovulation, small amounts of
estrogen are secreted from the
ovary.
Estrogen stimulates the release of
gonadotropin-releasing hormone
(GnRH) from the hypothalamus
and luteinizing hormone (LH)
from the anterior pituitary
GnRH also stimulates the release
of LH from the anterior pituitary
LH causes the release of additional
estrogen from the ovary. The
GnRH and LH levels in the blood
increase because of this positivefeedback effect.
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Positive and Negative Feedback
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NEGATIVE
During the menstrual cycle,
after ovulation, the ovary
begins to secrete
progesterone in response to
LH.
Progesterone inhibits the
release of GnRH from the
hypothalamus and LH from
the anterior pituitary.
Decreased GnRH release
from the hypothalamus
reduces LH secretion from
the anterior pituitary. GnRH
and LH levels in the blood
decrease because of this
negative-feedback effect.
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Table 17.1
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Receptors
hormones only affect target cells
water soluble hormone receptors on outside
surface and trigger response inside the cell
 lipid soluble hormone receptors on inside of
cell and trigger response inside cell
 target cells generally have between 2,000 and
100,000 receptors for a given hormone
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Chemical Classes of Hormones
water soluble
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amino acid based
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lipid soluble
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steroids
thyroid hormones
nitric oxide
transported in blood by transport proteins
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slow rate of loss in kidneys
ready reserve of hormone in blood stream
Table 17.2 pt 1
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Table 17.2 pt 2
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Hormone Action
variable depending on hormone and target cell
 various targets respond differently to same
hormone
 some hormones activate synthetic or
stimulatory processes
 others activate degradation or inhibitory
processes
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Figure 17.2
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Figure 17.3
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Hormone Interactions
permissive effects
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synergistic effects
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one hormone intensifies the effects of the other
antagonistic effects
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one hormone allows the other to function
one hormone inhibits or reduces the effects of the
other
Control of Hormone Secretion
hormones secreted in bursts
 as stimulation increases bursts increase in
frequency
 in absence of stimulation, bursts are minimal or
inhibited
 regulated by
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neural signals
chemical changes in blood
other hormones
Hypothalamus & Pituitary
Gland
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Hypothalamus
controls the activity of the pituitary gland
 major integrating link between the nervous and
endocrine systems
 hormones that stimulate anterior pituitary are
all either releasing hormones or inhibiting
hormones
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Releasing and Inhibiting Hormones
 Tropins or tropic hormones: hormones that regulate the hormone secretions of target
endocrine tissues. All anterior pituitary hormones are tropins.
 Releasing hormones:
 GHRH. Growth hormone-releasing hormone. Causes the anterior pituitary to
release growth hormone.
 TRH. Thyroid-releasing hormone. Causes the anterior pituitary to release thyroidstimulating hormone (TSH).
 CRH. Corticotropin-releasing hormone. Causes anterior pituitary to produce
adrenocorticotropic hormone.
 GnRH. Gonadotropin-releasing hormone. Causes anterior pituitary to produce
FSH (follicle stimulating hormone) and LH (luteinizing hormone).
 PRH. Prolactin-releasing hormone. Causes the anterior pituitary to release
prolactin.
 Inhibiting hormones:
 GHIH. Growth hormone-inhibiting hormone, somatostatin. Causes the anterior
pituitary to decrease release of growth hormone.
 PIH. Prolactin-inhibiting hormone. Causes the anterior pituitary to decrease release
of prolactin.
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Figure 17.4
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Pituitary Gland
two lobes
 anterior lobe
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posterior lobe
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stimulated by tropic hormones from hypothalamus
hypophyseal portal system
neural tissue that releases hormones produced in
the hypothalamus
neurosecretory cells
Table 17.3
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Figure 17.5
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Figure 17.6
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Figure 17.11
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FSH & LH
released by the anterior pituitary
triggered by GnRH
target tissue gonads
FSH
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LH
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in females initiates development of ovarian follicles
in males stimulates sperm production
in females triggers ovulation
in males triggers testosterone secretion
PRL
released by the anterior pituitary
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trigger is PRH and PIH from hypothalamus
initiates and maintains milk secretion and
production by mammary glands in females
 in males can cause erectile dysfunction
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ACTH
secreted by anterior pituitary
 triggered by CRH
 also triggered by stress
 controls production and secretion of hormones
called glucocorticoids
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cortisol from adrenal cortex
cause negative feedback regulation of CRH and
ACTH release
Figure 17.16
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MSH
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secreted by anterior pituitary
function unknown in humans
presence of MSH receptors in brain suggests it
may influence brain activity
excessive CRH stimulates MSH release
PIH inhibits MSH release
Table 17.4 pt 1
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Table 17.4 pt 2
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Posterior Pituitary
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Posterior Pituitary
AKA neurohypophysis
 store and release two hormones produced by
hypothalamus
 ADH
 OT
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Figure 17.4
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OT
oxytocin
targets uterus and mammary glands during and after delivery
uterus contracts
milk ejection (“let down”)
function in non-reproducing women and in men is unknown
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animal studies seem to indicate parental caretaking behavior
toward offspring
sexual pleasure during and after intercourse
ADH
antidiuretic hormone
decreases urine production
kidneys return water to blood
decreases sweating
causes constriction of arterioles
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increases blood pressure
AKA vasopressin
Figure 17.8
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Table 17.5
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Thyroid Gland
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TSH
follicular cells produce
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thyroxine (T4)
triiodothyronine (T3)
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parafollicular cells produce
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calcitonin
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involved in calcium homeostasis
brings calcium levels down when too high
Figure 17.11
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Actions of Thyroid Hormones
thyroxine and triiodothyronine
 regulate oxygen use and BMR
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Abnormal Thyroid Conditions
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Parathyroid
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PTH
parathyroid hormone
 major regulator of calcium, magnesium, and
phosphate ions in blood
 PTH brings blood levels of calcium up when
too low
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Figure 17.13
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Table 17.7
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Causes and Symptoms of
Hypersecretion and Hyposecretion
of Parathyroid Hormone
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Adrenal Gland
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Adrenal Cortex
divided into three zones
 each secretes its own hormone
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mineralocorticoids
glucocorticoids
androgens
Figure 17.15
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Figure 17.16
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Figure 17.5
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Glucocorticoid Functions
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Protein breakdown
Glucose formation
Triglyceride breakdown
Resistance to stress
Anti-inflammatory effects
Depression of immune responses
Adrenal Medulla
modified sympathetic ganglion of ANS
 epinephrine
 norepinephrine
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Symptoms of Hypersecretion and
Hyposecretion of Adrenal Cortex Hormones
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Pancreas
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Figure 17.17a
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Figure 17.17b
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Figure 17.17c
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Figure 17.17d
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Blood Glucose Level Regulation
glucagon released when
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insulin released when
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blood glucose is low
blood glucose is high
Figure 17.18
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Table 17.9
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Gonads
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FSH & LH
estrogens
 progesterone
 testosterone
 androgens
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Table 17.10
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Pineal Gland
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Pineal Gland
hormone secreted is melatonin
 contributes to setting the body’s biological
clock
 promotes sleepiness in small doses
 in animals with breeding seasons, melatonin
inhibits reproductive functions outside the
season
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