Transcript F13_Endocrine1

The Endocrine System Endocrinology = the study of the endocrine system
Unlike the nervous system with which the endocrine works similarly to and in some cases with, the
endocrine system sends messages to cells to perform a necessary action. Hormones are messenger
molecules.
The endocrines system is comprised of small organs dispersed throughout the body and secrete
hormones into the extracellular space to then be picked up by nearby capillaries into the general
circulation to be delivered throughout the body. If the hormone finds a “lock and key” fit on the surface
of a cell membrane, it will fuse at that point and the message will be delivered. Therefore, cells that don’t
have a receptor protein for a particular hormone, it will have no effect.
Hormones only act on “target” cells.
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Figure 17.1 Location of the major endocrine organs.
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
(on dorsal aspect
of thyroid gland)
Thymus
Adrenal glands
Pancreas
Gonads
Ovary (female)
Testis (male)
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Three types of endocrine gland stimuli.
Humoral Stimulus
Hormone release caused by altered
levels of certain critical ions or
nutrients
Neural Stimulus
Hormone release caused by
neural input
Hormonal Stimulus
Hormone release caused by another
hormone (a tropic hormone)
Hypothalamus
CNS (spinal cord)
Capillary (low Ca2+
in blood)
Thyroid gland
(posterior view)
Parathyroid
glands
Preganglionic
sympathetic
fibers
Anterior
pituitary
gland
Thyroid
gland
Adrenal
cortex
Gonad
(Testis)
Medulla of
adrenal gland
Parathyroid
glands
PTH
Capillary
Stimulus: Low concentration of Ca2+ in
capillary blood
Response: Parathyroid glands secrete
parathyroid hormone (PTH), which
increases blood Ca2+
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Stimulus: Action potentials in preganglionic
sympathetic fibers to adrenal medulla
Response: Adrenal medulla cells secrete
epinephrine and norepinephrine
Stimulus: Hormones from hypothalamus
Response: Anterior pituitary gland secretes
hormones that stimulate other endocrine glands
to secrete hormones
The pituitary gland (hypophysis).
Corpus
callosum
Thalamus
Pineal
Hypothalamus
Mammillary
body
Brain stem
Pituitary (hypophysis)
Anterior lobe
Optic chiasma
Median eminence
of hypothalamus
Anterior lobe
Pars tuberalis
Pars intermedia
Pars distalis
Mammillary
body
Tuber cinereum
Posterior lobe
Infundibulum
Pars nervosa
Chromophobe
cells
Basophil
cells
Acidophil
cells
Pituicytes
(neuroglia)
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Posterior
lobe
Figure 17.4a The hypothalamus controls release of hormones from the pituitary gland in two different ways.
Anterior Pituitary: Hypothalamic hormones released into special blood vessels
(the hypophyseal portal system) control the release of anterior pituitary hormones.
Hypothalamus
Hypothalamic
neurons synthesize
releasing and inhibiting
hormones
Anterior lobe
of pituitary
Superior
hypophyseal
artery
1 When appropriately stimulated,
hypothalamic neurons secrete
releasing or inhibiting hormones
into the primary capillary plexus.
2 Hypothalamic hormones travel
through portal veins to the anterior
pituitary where they stimulate or
inhibit release of hormones made
in the anterior pituitary.
Hypophyseal
portal system
Primary capillary
plexus
Hypophyseal
portal veins
3 In response to releasing
hormones, the anterior pituitary
secretes hormones into the
secondary capillary plexus. This in
turn empties into the general
circulation.
Growth Hormone (GH)
Prolactin (PRL)
Thyroid-Stimulating Hormone (TSH)
Luteinizing Hormone (LH)
Adrenocorticotropic Hormone (ACTH)
Follicle-Stimulating Hormone (FSH)
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Secondary
capillary plexus
Anterior lobe
of pituitary
A portal system
is two capillary
plexuses (beds)
connected by
veins.
Figure 17.4b The hypothalamus controls release of hormones from the pituitary gland in two different ways.
Posterior Pituitary: Nerve impulses travel down the axons of hypothalamic
neurons, causing hormone release from their axon terminals in the posterior pituitary.
Paraventricular nucleus
Hypothalamus
1 Hypothalamic neurons synthesize
oxytocin or antidiuretic hormone
(ADH).
Posterior lobe
of pituitary
Optic chiasma
Supraoptic
nucleus
Infundibulum
(connecting stalk)
Hypothalamohypophyseal
tract
Inferior
hypophyseal
artery
2 Oxytocin and ADH are
transported down the axons of the
hypothalamohypophyseal tract to
the posterior pituitary.
Axon terminals
Posterior lobe
of pituitary
3 Oxytocin and ADH are stored in
neurosecretory bodies in the
posterior pituitary.
Oxytocin
Antidiuretic Hormone (ADH)
4 When associated hypothalamic
neurons fire, nerve impulses arriving
at the neurosecretory bodies cause
oxytocin or ADH to be released into
the blood.
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Figure 17.6 The parathyroid glands.
Pharynx
(posterior
aspect)
Capillary
Thyroid
gland
Esophagus
Parathyroid
glands
Photomicrograph
of parathyroid
gland embedded
within the thyroid
gland (2)
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Trachea
Illustration of
parathyroid glands
embedded within
the thyroid gland,
posterior view
Parathyroid
cells
(secrete
parathyroid
hormone)
Oxyphil
cells
Photomicrograph of
parathyroid gland
(205)
Figure 17.7 The adrenal gland, gross and microscopic structure.
Hormones
secreted
Adrenal
gland
Medulla
Cortex
Cortex
Capsule
Zona
glomerulosa
Aldosterone
Zona
fasciculata
Cortisol
and
androgens
Kidney
Medulla
Zona
reticularis
Adrenal
medulla
Drawing of the histology
of the adrenal cortex
and a portion of the
adrenal medulla
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Epinephrine
and
norepinephrine
Photomicrograph (120)
Figure 17.8 Stress and the adrenal gland.
Short-term stress
Prolonged stress
Stress
Nerve impulses
Hypothalamus
CRH (corticotropinreleasing hormone)
Spinal cord
Corticotropic cells
of anterior pituitary
Preganglionic
sympathetic
fibers
To target in blood
Adrenal medulla
(secreted amino acid–
based hormones)
Catecholamines
(epinephrine and
norepinephrine)
Short-term stress response
• Heart rate increases
• Blood pressure increases
• Bronchioles dilate
• Liver converts glycogen to glucose and releases
glucose to blood
• Blood flow changes, reducing digestive system activity
and urine output
• Metabolic rate increases
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Adrenal cortex
(secretes steroid
hormones)
ACTH
Mineralocorticoids
Glucocorticoids
Long-term stress response
• Kidneys retain
sodium and water
• Blood volume and
blood pressure
rise
• Proteins and fats converted
to glucose or broken down
for energy
• Blood glucose increases
• Immune system
suppressed
Figure 17.9 Photomicrograph of a pancreatic islet.
Pancreas
Pancreatic islet
 (Glucagonproducing) cells
 (Insulinproducing) cells
Pancreatic acinar
cells (exocrine)
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Figure 17.10 Disorders of pituitary growth hormone.
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Figure 17.11 Thyroid disorders.
Protrusion of the eyeballs;
symptom of
hyperthyroidism
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An enlarged thyroid
(goiter); due to
iodine deficiency
Figure 17.12 The effects of excess glucocorticoid.
Patient before
onset
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Same patient with
Cushing’s syndrome.
The white arrow shows
the characteristic
“buffalo hump” of fat
on the upper back.
Table 17.1 Pituitary Hormones: Summary of Target Organs and Effects (1 of 4)
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Table 17.1 Pituitary Hormones: Summary of Target Organs and Effects (2 of 4)
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Table 17.1 Pituitary Hormones: Summary of Target Organs and Effects (3 of 4)
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Table 17.1 Pituitary Hormones: Summary of Target Organs and Effects (4 of 4)
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