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Endocrine Control
Chapter 26
Endocrine System
Major Components
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Hypothalamus
Pituitary gland
Pineal gland
Thyroid gland
Parathyroid glands
Thymus gland
Adrenal glands
Pancreatic islets
Ovaries
Testes
hypothalamus (part
of the brain)
pituitary gland,
anterior lobe
pituitary gland,
posterior lobe
pineal gland
thyroid gland
parathyroid glands (four)
thymus gland
adrenal gland (one pair)
cortex
medulla
ovaries
(one pair of female gonads)
pancreatic islets
testes (one pair of
male gonads)
Fig. 26-1, p.449
Hormones
• Secreted by endocrine glands, endocrine cells,
and hypothalmic neurons
• Travel through bloodstream to target cells
• Bind to receptors on target cells
Other Signaling Molecules
• Neurotransmitters
– From axon endings of neurons
• Local signaling molecules
– Prostaglandins
– Nitric oxide (NO)
Three-Step Hormonal Action
• Activation of a receptor as it binds the
hormone
• Transduction of signal into a molecular form
that can work inside the cell
• Functional response of target cell
signal
reception
signal
transduction
cellular
response
Responses to Hormones Vary
• Different hormones activate different
responses in the same target cell
• Not all types of cells respond to a particular
hormone
Main Hormone Types
Steroid hormones
– Lipids derived from cholesterol
Peptide hormones
– A few amino acids
Amine hormones
– Modified amino acids
Protein hormones
– Longer amino acid chains
Receptors
• Intracellular
– Steroid hormones
– Diffuse across plasma membrane
• Plasma membrane
– Peptides and proteins
– Too big or polar to diffuse
– Second messengers (cAMP)
Steroid
Hormones
hormone
• Most diffuse across the
plasma membrane and
bind to a receptor
• Hormone-receptor
complex acts in nucleus to
inhibit or enhance
transcription
receptor
hormone-receptor
complex
gene product
1 A steroid hormone
molecule moves from
the blood into
interstitial fluid that
bathes a target cell.
2 Being a lipidsoluable molecule,
the steroid
hormone diffuses
across the target
cell’s plasma
membrane.
5 The mRNA
transcript moves from
the nucleus into the
cytoplasm. There it
becomes translated
into a gene product
that
is required for the
response to the
hormone signal.
3 The hormone
diffuses through the
cytoplasm, then on
through the nuclear
envelope. Inside the
nucleus, it will bind
with a receptor
molecule.
receptor
hormone-receptor
complex
4 Now the hormonereceptor complex
triggers transcription
of gene regions in the
DNA.
gene product
Fig. 26-2a, p.451
Peptide Hormone
• Hormone binds to a
receptor at cell surface
• Binding triggers a change
in activity of enzymes
inside the cell
glucagon
glucagon receptor
cyclic AMP + Pi
ATP
The cAMP activates
protein kinase A.
Protein kinase A converts phosphorylase
kinase to active form and inhibits an
enzyme required for glucagon synthesis.
1 A glucagon molecule diffuses from
blood into the interstitial fluid that
bathes the plasma membrane of a liver
cell.
unoccupied glucagon receptor at target
cell’s plasma membrane
cyclic
AMP
+Pi
ATP
2 Glucagon binds with the receptor, and the binding
activates adenylate cyclase. This enzyme catalyzes 3 The cAMP now activates protein kinase
the formation of cAMP inside the target cell.
A.
4 Protein kinase A converts phosphorylase
kinase to active form. This enzyme activates
a different enzyme, which breaks down
glycogen to its glucose monomers.
5 Protein kinase A also inhibits an enzyme
required for synthesis of glycogen.
Fig. 26-2b, p.451
Hypothalamus and Pituitary
• Glands in brain
– Structurally and functionally linked
• Master integrating center for endocrine and
nervous systems
• Hypothalmic neurons produce
– Neurotransmitters
– Hormones
Pituitary Gland
• Pea-sized gland at base of hypothalamus
• Two lobes
– Posterior lobe stores and releases hormones
made in hypothalamus
– Anterior lobe produces and secretes its own
hormones
Posterior Pituitary
Secretions
• Antidiuretic hormone
(ADH)
• Oxytocin (OCT)
cell body in
hypothalamus
axons
to the general circulation
Cell bodies in hypothalamus
synthesize ADH or oxytocin
cell body
axon
ADH, oxytocin move down
axons, accumulate in axon
endings
capillaries
Action potentials cause release
of hormones, which capillaries
pick up
Small vessels carry hormones to general circulation
Stepped Art
Fig. 26-3, p.452
a Cell bodies of
secretory neurons in
hypothalamus synthesize
ADH or oxytocin.
muscles in
uterus wall
b The ADH or oxytocin
moves downward inside
the axons of the
secretory neurons and
accumulates in the axon
endings.
oxytocin
c Action potentials
trigger the release of these
hormones, which enter
blood capillaries in the
posterior lobe of the
pituitary.
mammary glands
ADH
d Small blood vessels
deliver the hormone
molecules to the general
circulation.
nephrons in kidney
Fig. 26-3, p.452
Anterior Pituitary
• Responds to hypothalmic signals
• Releasers
– Stimulate secretion of pituitary hormones
• Inhibitors
– Inhibit release of pituitary hormones
Anterior Pituitary
Secretions
• Adrenocorticotropin (ACTH)
• Thyroid stimulating hormone
(TSH)
• Follicle-stimulating hormone
(FSH)
• Luteinizing hormone (LH)
• Prolactin (PRL)
• Growth hormone (GH)
a Cell bodies of
different secretory
neurons in the
hypothalamus secrete
releasing and inhibiting
hormones.
b The hormones are picked up
by a capillary bed at the base of
the hypothalamus.
c Bloodstream delivers hormones
to a second capillary bed in anterior
lobe of pituitary.
e Hormones secreted
from anterior lobe
cells enter small blood
vessels that lead to the
general circulation.
ACTH
TSH
d Molecules of the releasing or
inhibiting hormone diffuse out of
capillaries and act on endocrine cells in
the anterior lobe.
FSH
LH
PRL
GH (STH)
most cells
(growthpromoting
effects)
adrenal
glands
thyroid
gland
testes in males mammary
ovaries in females glands
Fig. 26-4, p.453
Abnormal Pituitary Output
• Pituitary gigantism
• Pituitary dwarfism
• Acromegaly
Abnormal Pituitary Outputs
Thymus, Thyroid and Parathyroid
• Thymus
– Immune function
• Thyroid
– Development and metabolism
– Regulated by feedback loops
• Parathyroid
– Calcium levels
Negative Feedback and Thyroid Function
Stimulus
Blood level of thyroid
hormone falls below a
set point.
Response
Hypothalamus
–
+
TRH
Anterior Pituitary
TSH
Thyroid Gland
Thyroid hormone
is secreted
–
Rise in the blood
level of thyroid
hormone inhibits
secretion of TRH
and TSH.
Thyroid
Function
• Requires mineral
iodine
– Deficiency causes
goiter
Parathyroid and Calcium
• Parathyroid hormone (PTH)
– regulates blood calcium
– secreted when calcium levels drop
– causes bone cells to release calcium from bone
tissue
– stimulates calcium reabsorption by kidneys
Calcium and Vitamin D
• Without vitamin D, not enough calcium is
absorbed
• Low blood calcium causes oversecretion of
PTH
– Breaks down existing bone
– Causes rickets
Adrenal Glands and Stress
• Adrenal cortex secretes cortisol and
aldosterone
• Negative feedback maintains blood cortisol
levels
Negative Feedback Control of Adrenal Glands
Stimulus
a Blood level of
cortisol falls
below a set point
–
Hypothalamus
+
Response
b CRH
–
Anterior Pituitary
adrenal
cortex
adrenal
medulla
ACTH
Adrenal Cortex
f Both the hypothalamus
and pituitary detect rise in
blood level of cortisol and
slow its further secretion.
Cortisol is secreted, with these effects:
c Cellular uptake of glucose from blood slows in many
tissues, especially muscles (not the brain).
d Proteins degraded in many tissues, especially in muscles.
The free amino acids are converted to glucose and used in the assembly or
repair of cell structures.
kidney
e Fats in adipose tissue degraded to fatty acids that enter blood as an
alternative energy source, indirectly conserving glucose for the brain.
Stress Response
• Stress can cause nervous system to override
feedback loop
• Cortisol levels rise above normal, suppress
inflammation
• Persistent high cortisol levels may harm health
The Pancreas and
Glucose Homeostasis
stomach
pancreas
small
intestine
Pancreatic Hormones
and Glucose Balance
• Glucagon
– Secreted by alpha cells in islets
– Raises blood glucose level
• Insulin
– Secreted by beta cells in islets
– Lowers blood glucose level
• Somatostatin
– Secreted by delta cells
– Blocks insulin and glucagon secretion
a Stimulus
f Stimulus
Increase in blood glucose
Decrease in blood glucose
PANCREAS
b alpha cells
–
glucagon
LIVER
c beta cells
+
insulin
g alpha cells
+
glucagon
h beta cells
–
insulin
i Cells in liver break down
glycogen faster. The
released glucose
monomers enter blood.
MUSCLE FAT CELLS
d Body cells, especially in muscle and
adipose tissue, take up and use more glucose.
Cells in skeletal muscle and liver store glucose
j Response
in the form of glycogen.
Increase in blood glucose
e Response
Decrease in blood glucose
Fig. 26-9, p.456
Diabetes Mellitus
Excess glucose accumulates
Type 1
Type 2
• Autoimmune disease
• Target cells don’t
respond
• Usually appears in
childhood
• Insulin injections
• Usually appears in
adults
• Diet, drugs
Table 26-2, p.457
Sex Hormones
• Testes and ovaries synthesize the same sex
hormones in different amounts
– Estrogens
– Progesterone
– Testosterone
• Influence sexual traits
The Pineal Gland
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Photosensitive gland embedded in brain
In absence of light, secretes melatonin
Influences seasonal behaviors
Affects human biological clock
– sleep-wake cycles
– seasonal affective disorder
Deformed Frogs
• Something in water triggers deformities
• Problem thyroid function?
• Tadpoles from “hotspots” developed normally
when given extra thyroid hormones
• UV, parasites also play a role
Effects of Pollution on Frogs
Table 26-3, p.459