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The Endocrine System
Chapter 46
Types of Chemical Messengers
A hormone is a chemical that is secreted
into extracellular fluid and carried by the
blood
-Can therefore act at a distance from source
-Only targets with receptor can respond
Paracrine regulators do not travel in blood
-Allow cells of organ to regulate each other
Pheromones are chemicals released into the
environment to communicate among
individuals of a single species
2
Types of Chemical Messengers
-Some neurotransmitters
are distributed by the
blood and act as
neurohormones
-Norepinephrine coordinates
the activity of heart, liver
and blood vessels
during stress
-Hormone production
and release is often
regulated directly or indirectly
by the nervous system
3
Endocrine System
The endocrine system
includes all the
organs and tissues
that produce hormones
-Includes endocrine glands,
which are specialized to
secrete hormones
-Also organs, like the liver,
that secrete hormones
in addition to other functions
Exocrine glands secrete
their
products, such as
saliva or milk, into a duct for
transport to the outside
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Three Chemical Classes of
Hormones
1. Peptides and proteins
-Glycoproteins
2. Amino acid derivatives
-Catecholamines
-Thyroid hormones
-Melatonin
3. Steroids
-Sex steroids
-Corticosteroids
5
Two Classes of Hormones & Their mode of Action
6
Hydrophilic
Lipophilic
Paracrine Regulators
The endothelium of blood vessels is a rich
source of paracrine regulators
-Nitric oxide (NO) which promotes
vasodilation
-Endothelin which stimulates
vasoconstriction
-Bradykinin which promotes vasodilation
7
Lipophilic Hormones
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for reproduction or display.
Blood
plasma
1. Hormone passes
through plasma
membrane
Lipophilic hormones
Plasma membrane
Cytoplasm
-Hormones circulate
in the blood, bound
to transport proteins
-Dissociate from carrier
at target cells
Nucleus
2. Inside target
Receptor
5. Change in protein
synthesis is
cellular response
cell the hormone
binds to a
receptor protein
in the cytoplasm
or nucleus
Protein
3. Hormone-receptor
mRNA
complex binds to
hormone response
element on DNA,
regulating gene
transcription
DNA
4. Protein synthesis
Hormone response element
-Pass through the cell membrane and bind to
an intracellular receptor, either in the cytoplasm
or the nucleus
-Hormone-receptor complex binds to hormone response
elements in DNA
-Regulate gene expression
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Hydrophilic
Hormones
2. Receptors Activate G Proteins
1. Receptors Function as Kinase Enzymes
Hormones
Hormone
Second messengerGPCR generating enzyme
GPCR
Receptor
b g
GDPa
Inactive
Active kinase
domain
ATP
Target
protein
Inactive G
protein
ADP
Phosphorylated
protein
Cellular
response
GTP
GTP
Active G
protein
Second
messenger
Active
Protein
kinase
Inactive
protein kinase
Target
proteins
Cellular
response
Hydrophilic hormones include the peptide, protein and catecholamine
hormones...Too large or polar to cross cell membrane
Hormones bind to extracellular receptors...Initiate signal transduction
pathways through Kinase or G Protein Receptors
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G-Protein Receptor Signal
Transduction
Second-messenger systems
-Many hydrophilic hormones work through
second messenger systems
-Two have been described:
-One involving cyclic adenosine
monophosphate (cAMP)
-One that generates 2 lipid messengers:
inositol triphosphate (IP3) and diacyl
glycerol (DAG) – muscle contract and
calcium release
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The Pituitary Gland
The pituitary gland is also known as the
hypophysis
-It hangs by a stalk from the hypothalamus
The pituitary gland consists of two parts:
-Anterior pituitary (adenohypophysis)
-Appears glandular
-Posterior pituitary (neurohypophysis)
-Appears fibrous
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The Posterior Pituitary (or
neurohypophysis)
Releasese 2 Neurohormones
Made in Hypothalamus
Antidiuretic hormone (ADH)
-A peptide hormone that stimulates water
reabsorption by the kidney, and thus inhibits
diuresis (urine production)
Oxytocin
-In mammals, it stimulates the milk ejection
reflex and uterine contractions during labor,
12
and it regulates reproductive behavior
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Effects of
Antidiuretic
Hormone
Stimulus
Stimulus
Stimulus
Osmotic
concentration of
blood increases
Dehydration
Lowers blood
volume and
pressure
Sensor
Sensor
Baroreceptors
in aorta
monitor pressure
Osmoreceptors
in CNS monitor
concentration
(–)
Negative
feedback
Response
Water returned to
blood
Effector
• ADH reduces
urine volume
(–)
Integrating Center
ADH synthesized
by neurosecretory
cells in the
hypothalamus
is released
from neurohypophysis into
blood
Negative
feedback
Response
Increases
blood pressure
Effector
• ADH increases
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vasoconstriction
The Anterior Pituitary
It produces at least seven essential hormones
-Collectively called tropic hormones or
tropins
•
•
•
•
•
•
•
Adrenocorticotropic hormone (ACTH)
Melanocyte Stimulating homone (MSH)
Growth hormone (GH)
Prolactin (PRL)
Thyroid-stimulating hormone (TSH)
Luteinizing hormone (LH)
Follicle-stimulating hormone (FSH)
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The Anterior Pituitary
The activity of the anterior pituitary is
controlled by hormones of the
hypothalamus
-Neurons secrete releasing hormones and
inhibiting hormones, which diffuse into
blood capillaries at the hypothalamus’ base
15
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Negative Feedback @ The Anterior Pituitary &
Hypothalamus
(–)
Hypothalamus
Releasing hormones
(TRH, CRH, GnRH)
(+)
Pituitary
Adenohypophysis
(–)
Tropic hormones
(TSH, ACTH, FSH, LH)
Anterior Pituitary is
the
Adenohypophysis
Target ( + )
cells
(+)
Target Glands
Thyroid, adrenal
cortex, gonads
Hormones
Negative
feedbac
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Anterior Pituitary Disorders
Growth hormone stimulates growth of
muscles and connective tissue
-It also promotes the production of insulinlike growth factors
-Stimulate cell division in the epiphyseal
growth plates, and thus bone elongation
Gigantism is caused by an excessive
secretion of growth hormone in a child
Pituitary Dwarfism - deficiency
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Anterior Pituitary Disorders
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The Thyroid Gland
In humans, the thyroid gland is shaped like a
bow tie, and lies just below the Adam’s
apple in the front of the neck
-It secretes:
-Thyroid hormones
-Thyroxine
-Triiodothyronine
-Calcitonin
-Stimulates the uptake of calcium
(Ca2+) into bones
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The Thyroid Gland
Thyroid hormones bind to nuclear receptors
-Regulate carbohydrate & lipid metabolism
-Adults with hypothyroidism have low
production of thyroxine
-Reduced metabolism and overweight
-Adults with hyperthyroidism have high
production of thyroxine
-High metabolism and weight loss
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Thyroxine
-Trigger metamorphosis in amphibians
-Forelimbs emerge on Tadpole
-Tail is reabsorbed
21
The Adrenal Glands
The adrenal glands are located just above each
kidney
-Medulla = Inner portion
-secrete epinephrine and norepinephrine
– -These trigger “alarm” responses
– Increase heart rate, blood pressure, and glucose
levels
-Cortex = Outer portion
-Stimulated by the anterior pituitary, through the
hormone ACTH
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The Adrenal Glands
The Cortex secretes steroid hormones called
corticosteroids
-Glucocorticoids (such as cortisol)
maintain glucose homeostasis and modulate
some aspects of the immune response
-Mineralocorticoids (such as aldosterone)
regulate mineral balance by stimulating the
kidneys to reabsorb Na+ and excrete K+
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Insulin
-Secreted by beta
(b) cells of the islets
The Pancreas
-Stimulates cellular uptake
of blood glucose and its
storage as glycogen in the
liver and muscle cells or
as fat in fat cells
Glucagon
-Secreted by alpha
(a) cells of the islets
-Promotes the hydrolysis
of glycogen in the liver
and fat in adipose tissue
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Diabetes Mellitus
Diabetics cannot take up glucose from blood
-Type I (insulin-dependent diabetes)
-Individuals lack insulin-secreting b cells
-Treated by daily injections of insulin
-Type II (noninsulin-dependent diabetes)
-Most patients have this form
-Very low number of insulin receptors
-Treated by diet and exercise
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The Gonads
The ovaries and testes in vertebrates
-Produce sex steroids that regulate
reproductive development
-Estrogen and progesterone
-“Female” hormones
-Androgens
-“Male” hormones
-Testosterone and its derivatives
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The Pineal Gland
The pineal gland is located in the roof of the
third ventricle of the brain
-Functions as an endocrine gland by
secreting the hormone melatonin
-Reduces dispersal of melanin granules
-Regulates biological clocks
-Synchronizes various body
processes to a circadian rhythm
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Insect Hormones
Insects undergo two types of transformations
during post-embryonic development
-Molting = Shedding of old
exoskeleton and secretion of
a new larger one (Ecdysone
hormone)
-Metamorphosis = Radical
transformation from the larval to the
adult form (Ecdysone hormone)
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