Chapter 18: The Endocrine
System
Copyright 2009, John Wiley & Sons, Inc.
Nervous and Endocrine Systems


Act together to coordinate functions of all body
systems
Nervous system



Nerve impulses/ Neurotransmitters
Faster responses, briefer effects, acts on specific target
Endocrine system


Hormone – mediator molecule released in a part of the
body to regulates activity of cells in other parts
Slower responses, effects last longer, broader influence
Copyright 2009, John Wiley & Sons, Inc.
Nervous and Endocrine Systems
Copyright 2009, John Wiley & Sons, Inc.
Body Glands

2 kinds of glands

Exocrine – ducted


Endocrine – ductless


Secrete products into interstitial fluid, diffuse into blood
Endocrine glands include


Sweat, mucous, and digestive glands.
Pituitary, thyroid, parathyroid, adrenal and pineal glands
Organs not exclusively endocrine glands

Hypothalamus, thymus, pancreas, ovaries, testes, kidneys,
stomach, liver, small intestine, skin, heart, adipose tissue,
and placenta.
Copyright 2009, John Wiley & Sons, Inc.
Hormone Activity



Hormones work through receptors
Hormones affect only specific target tissues
with specific receptors
Receptors constantly synthesized and
broken-down
Copyright 2009, John Wiley & Sons, Inc.
Hormone Activity



Hormones work through receptors
Hormones affect only specific target tissues
with specific receptors
Receptors constantly synthesized and
broken-down

Down-regulation &
Up-regulation
Copyright 2009, John Wiley & Sons, Inc.
Hormone Activity





Hormones work through receptors
Hormones affect only specific target tissues
with specific receptors
Receptors constantly synthesized and
broken-down
They operate within feedback systems to
maintain an optimal internal environment
They are excreted by the kidney, deactivated
by the liver or by other mechanisms
Copyright 2009, John Wiley & Sons, Inc.
Hormone types


Circulating : circulate in
blood throughout body
Local hormones : act
locally


Paracrine – act on
neighboring cells
Autocrine – act on the
same cell that secreted
them
Copyright 2009, John Wiley & Sons, Inc.
Chemical classes of hormones


Lipid-soluble – use transport proteins
 Steroid
 Thyroid
 Nitric oxide (NO)
Water-soluble – circulate in “free” form
 Amine
 Peptide/ protein
 Eicosanoid
Copyright 2009, John Wiley & Sons, Inc.
Lipid-soluble Hormones
• Steroids
– lipids derived from
cholesterol on SER
– different functional
groups attached to core of
structure provide
uniqueness
• Thyroid hormones
– tyrosine ring plus attached
iodines are lipid-soluble
• Nitric oxide is gas
18-12
Water-soluble Hormones
• Amine, peptide and
protein hormones
– modified amino acids or
amino acids put together
– serotonin, melatonin,
histamine, epinephrine
– some glycoproteins
• Eicosanoids
– derived from arachidonic
acid (fatty acid)
– prostaglandins or
18-13
leukotrienes
Hormone Transport in Blood
• Protein hormones circulate in free form in blood
• Steroid (lipid) & thyroid hormones must attach
to transport proteins synthesized by liver
– improve transport by making them water-soluble
– slow loss of hormone by filtration within kidney
– create reserve of hormone
• only .1 to 10% of hormone is not bound to transport
protein = free fraction
18-14
18-15
Mechanisms of Hormone Action




Response depends on both hormone and target cell
Water-soluble hormones bind to receptors on the
plasma membrane
 Activates second messenger system
 Amplification of original small signal
Lipid-soluble hormones bind to receptors inside target
cells
Responsiveness of target cell depends on
 Hormone’s concentration
 Abundance of target cell receptors
 Influence exerted by other hormones

Permissive, synergistic and antagonistic effects
Copyright 2009, John Wiley & Sons, Inc.
Blood capillary
1 Binding of hormone (first messenger)
to its receptor activates G protein,
which activates adenylate cyclase
Water-soluble
hormone
Adenylate cyclase
Receptor
Second messenger
G protein
ATP
cAMP
2 Activated adenylate
cyclase converts
ATP to cAMP
Protein kinases
6 Phosphodiesterase
inactivates cAMP
3 cAMP serves as a
second messenger
to activate protein
kinases
Activated
protein
kinases
4 Activated protein
Protein
kinases
phosphorylate
cellular proteins
ATP
ADP
Protein— P
5 Millions of phosphorylated
proteins cause reactions that
produce physiological responses
Target cell
Amplification of Hormone Effects
• Single molecule of hormone binds to receptor
• Activates 100 G-proteins
• Each activates an adenylate cyclase molecule
which then produces 1000 cAMP
• Each cAMP activates a protein kinase, which
may act upon 1000’s of substrate molecules
• One molecule of epinephrine may result in
breakdown of millions of glycogen molecules
into glucose molecules
18-18
Mechanisms of Hormone Action




Response depends on both hormone and target cell
Water-soluble hormones bind to receptors on the
plasma membrane
 Activates second messenger system
 Amplification of original small signal
Lipid-soluble hormones bind to receptors inside target
cells
Responsiveness of target cell depends on
 Hormone’s concentration
 Abundance of target cell receptors
 Influence exerted by other hormones

Permissive, synergistic and antagonistic effects
Copyright 2009, John Wiley & Sons, Inc.
Free hormone
Blood capillary
1 Lipid-soluble
Transport
protein
hormone
diffuses into cell
2 Activated
Nucleus
Receptor
receptor-hormone
complex alters
gene expression
DNA
Cytosol
mRNA
3 Newly formed
mRNA directs
synthesis of
specific proteins
on ribosomes
Ribosome
New
protein
4 New proteins alter
cell's activity
Target cell
General Mechanisms of Hormone Action


Hormone binds to cell surface or receptor
inside target cell
Cell may then




synthesize new molecules
change permeability of membrane
alter rates of reactions
Each target cell responds to hormone
differently


liver cells---insulin stimulates glycogen synthesis
adipose---insulin stimulates triglyceride synthesis
Mechanisms of Hormone Action




Response depends on both hormone and target cell
Lipid-soluble hormones bind to receptors inside target
cells
Water-soluble hormones bind to receptors on the
plasma membrane
 Activates second messenger system
 Amplification of original small signal
Responsiveness of target cell depends on
 Hormone’s concentration
 Abundance of target cell receptors
 Influence exerted by other hormones

Permissive, synergistic and antagonistic effects
Copyright 2009, John Wiley & Sons, Inc.
Hormonal Interactions

Permissive effect



Synergistic effect



a second hormone, is needed and strengthens the
effects of the first
thyroid strengthens epinephrine’s effect upon lipolysis
Two hormones work together to produce a particular
result. May be complimentary or as a greater effect
estrogen & LH are both needed for oocyte production
Antagonistic effects


two hormones with opposite effects
insulin promotes glycogen formation & glucagon
stimulates glycogen breakdown
Control of Hormone Secretion

Regulated by




Signals from nervous system
Chemical changes in the blood
Other hormones
Chronotropic

Most hormonal regulation by negative feedback
(Few examples of positive feedback)

Irregular control will lead to Disorders
Copyright 2009, John Wiley & Sons, Inc.
Types of endocrine disorders
1.
Hypo-secretion

Primary hypo-secretion



Secondary hypo-secretion

2.
3.
Deficiency in tropic “regulatory” hormone
Hyper-secretion
Hypo-responsiveness


4.
Deficiency in resources for hormone production
Malfunction in hormone producing organ
Abnormal or deficiency in receptors
Lack of activation enzyme
Hyper-responsiveness
Hormonal upregulation of receptor population
(Example) Thyroid hormone to epinephrine receptor
