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Endocrine Glands and Hormones
Chapter 20
The endocrine system consists of glands and tissues
that secrete hormones
Endocrine System
Hormones are chemicals that affect other glands or
tissues, many times far away from the site of hormone
production
Endocrine glands
•  Secrete hormones into the bloodstream
•  Hormones cause specific changes in target cells
Birgit Woelker, PhD
The Endocrine System
pineal gland
hypothalamus
pituitary gland
(hypophysis)
thyroid gland
thymus gland
parathyroid glands
(posterior surface o f thyroid)
adrenal glands
pancreas
ovary (female)
testis
(male)
•  Hormones are secreted by endocrine glands
and neurosecretory cells
Secretory
vesicles
Blood
vessel
Target
cell
•  All hormone-secreting cells make up the
endocrine system
Blood
vessel
Neurosecretory
cell
–  Which works with the nervous system in
regulating body activities
Target
cell
Endocrine cell
Hormone
molecules
Hormone
molecules
•  A few chemicals ( e.g. adrenaline /epinephrine)
serve both as hormones in the endocrine system
and as chemical signals in the nervous system
Hormones affect target cells
by two main signaling
mechanisms
•  Water-soluble hormones
such as proteins and
amines
Nerve
cell
Nerve
signals
Neurotransmitter
molecules
–  Bind to plasmamembrane receptors
on target cells
Water-soluble
hormone
(epinephrine)
Target
cell
Receptor
protein
1
2
Plasma
membrane
Signal
transduction
pathway
Relay
molecules
3
Glycogen
Glucose
Cellular response
(in this example, glycogen breakdown)
Nerve
cell
Some endocrine glands and their functions
•  Steroid hormones, such as
the sex hormones
estrogen and testosterone
–  Diffuse through the
plasma membrane of
target cells and bind to
intracellular receptors
Hypothalamus:
Hormones released by the posterior pituitary
gland and those that regulate the anterior pituitary gland
Lipid-soluble
hormone
(testosterone)
1
Target
cell
2
Nucleus
Receptor
protein
Hormonereceptor
complex
3
DNA
4
mRNA
Pituitary gland
posterior lobe :
Oxytocin, Antidiuretic Hormone (ADH),
anterior lobe:
Growth Hormone (GH),
Thyroid stimulating Hormone (TSH),
ACTH (Adrenocorticotropic Hormone)
Pineal gland:
Melatonin
Thyroid gland:
Thyroxine (T4) and Triiodothyronine (T3)
Calcitonin
Adrenal gland:
Epinephrine (Adrenaline), Norepinephrine
Pancreas:
Insulin and Glucagon
Testes:
Androgens (Testosterone)
Ovaries:
Estrogens
Transcription
New
protein
Cellular response: activation
of a gene and synthesis of new protein
The hypothalamus, closely tied to the pituitary,
connects the nervous and endocrine systems
•  The hypothalamus exerts master control over the
endocrine system
–  By using the pituitary gland to relay
directives to other glands
•  The posterior pituitary
–  Secretes oxytocin
and antidiuretic
hormone (ADH)
Hypothalamus
Hormone
Neurosecretory
cell
Posterior
pituitary
Brain
Blood
vessel
Anterior
pituitary
Hypothalamus
Oxytocin
ADH
Uterine muscles
Mammary glands
Kidney tubules
Posterior pituitary
Anterior pituitary
Bone
•  The anterior pituitary
–  Secretes TSH, ACTH, FSH and LH,
growth hormone, prolactin, and
endorphins
•  Releasing and inhibiting hormones from the
hypothalamus
–  Control the secretion of several other
hormones
Neurosecretory
cell
–  TSH for instance controls the secretion of
T4 and T3 from the Thyroid gland
Blood
vessel
Releasing hormones
from hypothalamus
Endocrine cells of
the anterior pituitary
Pituitary hormones
TSH
ACTH
FSH
and
LH
Growth Prolactin Endorphins
hormone (PRL)
(GH)
Thyroid Adrenal Testes or Entire Mammary
Pain
glands
receptors
cortex ovaries body
(in mammals)in the brain
HORMONES AND HOMEOSTASIS
•  Secretion of thyroxine by the thyroid gland
–  Is controlled by a negative-feedback
mechanism
Hypothalamus
Inhibition
TRH
Anterior
pituitary
TSH
Thyroid
Thyroxine
Inhibition
The thyroid regulates development and metabolism
•  Two hormones from the thyroid gland, T4 and T3
–  Regulate an animal’s development and
metabolism
•  Thyroid imbalance can cause disease like
Grave’s disease
•  Negative feedback
–  Maintains homeostatic levels of T4 and
T3 in the blood
No inhibition
Hypothalamus
TRH
No inhibition
Anterior
pituitary
TSH
Marty Feldman
Hormones from the thyroid and parathyroids
maintain calcium homeostasis
•  Blood calcium level is regulated by a tightly
balanced antagonism
–  Between calcitonin from the thyroid and
parathyroid hormone from the parathyroid
glands
Insufficient
T4 and T3
produced
No iodine
Thyroid
Thyroid grows
to form goiter
•  Calcium homeostasis
Calcitonin
Thyroid
gland
releases
calcitonin
Stimulates
Ca2+ deposition
in bones
Stimulus:
Rising
blood Ca2+
level
(imbalance)
Reduces
Ca2+ uptake
in kidneys
Blood Ca2+ falls
Homeostasis: Normal blood
calcium level (about 10 mg/100mL)
Stimulus:
Falling
blood Ca2+
level
(imbalance)
Blood Ca2+ rises
Active
vitamin D
Stimulates
Ca2+ release
from bones
Increases
Ca2+ uptake
in kidneys
Increases
Ca2+ uptake
in intestines
Parathyroid
glands
release parathyroid
hormone (PTH)
Parathyroid
gland
PTH
Pancreatic hormones regulate blood glucose
levels
•  Glucose homeostasis
Body
cells
take up more
glucose
Insulin
•  The pancreas secretes two hormones, insulin
and glucagon that control blood glucose
Beta cells
of pancreas stimulated
to release insulin into
the blood
High blood
glucose level
Stimulus:
Rising blood glucose
level (e.g., after eating
a carbohydrate-rich
meal)
•  Insulin
–  Signals cells to use and store glucose
•  Glucagon
Blood glucose level
declines to a set point;
stimulus for insulin
release diminishes
Liver takes
up glucose
and stores it as
glycogen
Homeostasis: Normal blood glucose level
(about 90 mg/100mL)
Blood glucose level
rises to set point;
stimulus for glucagon
release diminishes
–  Causes cells to release stored glucose
into the blood
Stimulus:
Declining blood
glucose level
(e.g., after
skipping a meal)
Alpha
cells of
pancreas stimulated
to release glucagon
into the blood
Liver
breaks down
glycogen and
releases glucose
to the blood
Glucagon
Diabetes is a common endocrine disorder
•  Diabetes mellitus
•  Diabetes can be detected
– 
–  Results from a lack of insulin or a failure of
cells to respond to it
By a test called a glucose tolerance test
Blood glucose (mg/100mL)
400
350
300
Diabetic
250
200
150
Normal
100
50
0
0
Figure 26.8
1
2
1
2
3
Hours after glucose ingestion
4
5
•  Nerve signals from the hypothalamus
The adrenal glands mobilize responses to stress
–  Stimulate the adrenal medulla to secrete
epinephrine and norepinephrine, which
quickly trigger the fight-or-flight
responses
•  Hormones from the adrenal glands
–  Help maintain homeostasis when the
body is stressed
•  ACTH from the pituitary causes the adrenal
cortex to secrete glucocorticoids and
mineralocorticoids
•  How the adrenal glands control our responses
to stress
Stress
–  Which boost blood pressure and blood
glucose in response to long-term stress
Adrenal
gland
Kidney
Adrenal
medulla
Adrenal
cortex
Nerve
signals
Hypothalamus
Releasing hormone
Anterior pituitary
Nerve
cell
Spinal cord
(cross section)
Blood vessel
Nerve cell
ACTH
Adrenal medulla
Adrenal cortex
ACTH
Epinephrine and
norepinephrine
Short-term stress response
1. Glycogen broken down to glucose;
increased blood glucose
2. Increased blood pressure
3. Increased breathing rate
4. Increased metabolic rate
5. Change in blood-flow patterns,
leading to increased alertness and
decreased digestive and kidney activity
Mineralocorticoids
Glucocorticoids
Long-term stress response
Mineralocorticoids
Glucocorticoids
1. Retention of sodium
ions and water by
kidneys
2. Increased blood
volume and blood
pressure
1. Proteins and fats
broken down and
converted to glucose,
leading to increased
blood glucose
2. Immune system may
be suppressed
Glucocorticoids offer relief from pain, but not
without serious risks
•  Glucocorticoids relieve inflammation and pain
–  But they can mask injury and suppress
immunity
The gonads secrete sex hormones
•  Estrogens, progestins, and androgens are
steroid sex hormones
–  Produced by the gonads in response to
signals from the hypothalamus and
pituitary
Bill Walton
•  Estrogens and progestins stimulate the
development of female characteristics and
maintain the female reproductive system
•  Androgens, such as testosterone
–  Trigger the development of male
characteristics
•  Establishing links between androgens and
human male aggression
–  Has been found to be problematic
Does testosterone
play a role in
aggressive
behavior?