Chapter 7a
Introduction to the
Endocrine System
Endocrinology
• Study of hormones
•
•
•
•
Specialized chemical messengers
Secreted by select cells
Action at distant sites via blood
Effects
• Enzymatic reactions
• Membrane transport
• Gene expression
About this Chapter
• Function and purpose
of hormones
• Classification, structure,
and synthesis of
hormones
• Pathways of nervous to
endocrine regulation
• Effects of hormone
interactions
• Pathologies of the
endocrine system
Anatomy Summary: Hormones
Figure 7-2 (1 of 2)
Anatomy Summary: Hormones
Figure 7-2 (2 of 2)
Chemical Regulating Systems
• Hormones: cell–to–cell communication molecules
•
•
•
•
Made in gland(s) or cells
Transported by blood
Distant target tissue receptors
Activates physiological response
• Pheromones: organism to organism communication
Hormones: Function
• Control of
• Rates of enzymatic reactions
• Transport of ions or molecules across cell
membranes
• Gene expression and protein synthesis
• Exert effects at very low concentrations
• Bind to target cell receptors
• Half-life indicates length of activity
Hormones: Classification
Be able to give types and example.
Compare synthesis, half-life and location of
receptor
1. Peptide or protein hormones
•
Insulin from amino acids
2. Steroid hormones

Sex steroids; estrogen, lipophilic
3. Amine hormones
•
epinephrine
Hormones: Classification
Table 7-1
Peptide Hormone Synthesis, Packaging, and
Release
2 Enzymes in the
1 Messenger RNA on the
ribosomes binds amino
acids into a peptide chain
called a preprohormone
The chain is directed into
the ER lumen by a signal
sequence of amino acids.
ER chop off the
signal sequence,
creating an
inactive
prohormone.
3 The prohormone 4 Secretory vesicles containing
passes from the
ER through the
Golgi complex.
enzymes and prohormone
bud off the Golgi. The enzymes
chop the prohormone into one
or more active peptides plus
additional peptide fragments.
5 The secretory
6 The hormone
vesicle releases
its contents by
exocytosis into
the extracellular
space.
moves into the
circulation for
transport to its
target.
Golgi complex
Endoplasmic reticulum (ER)
To target
Ribosome
Active hormone
Transport
vesicle
Peptide
fragment
3
6
4
Secretory
vesicle
Prohormone
5
Release
signal
Capillary
endothelium
2
1
Signal
sequence
Preprohormone
Cytoplasm
ECF
Plasma
mRNA
Figure 7-3
Peptide Hormone Synthesis, Packaging, and
Release
(a)
Preprohormone
processes to
Hormone
+
Other peptides
+
Signal
sequence
TRH
+
+
6 TRH
(3 amino acids each)
PreproTRH (242 amino acids)
(b)
Prohormone
processes to
Active hormone(s)
+
Other peptide
fragments
+
Pro-opiomelanocortin
ACTH
lipotropin
endorphin
Fragment
(c)
Proinsulin
Insulin
C-peptide
Figure 7-4
Peptide Hormone-Receptor Complex
• Surface receptor
• Hormone binds
• Enzyme activation
• Open channels
• Second messenger systems
• Cellular response
Peptide Hormone-Receptor Complex
• Membrane
receptors and
signal transduction
for peptide
hormones
Opens ion
channel
Second
messenger
system
phosphorylate
KEY
Proteins
TK = Tyrosine kinase
AE = Amplifier enzyme
Cellular
response
G = G protein
Figure 7-5
Steroid Hormones: Features
• Cholesterol-derived
• Lipophilic and can enter target cell
•
•
•
•
Cytoplasmic or nuclear receptors (mostly)
Activate DNA for protein synthesis
Slower acting, longer half-life
Examples
• Cortisol, estrogen, and testosterone
Steroid Hormones: Structure
Cholesterol is the parent compound for all steroid hormones.
modified by enzymes to make
steroid hormones such as
In adrenal cortex
In ovary
Ovary
Adrenal
cortex
Aldosterone
Cortisol
Estradiol (an estrogen)
Figure 7-6
Steroid Hormones: Action
Blood
vessel
Steroid
hormone
1 Most hydrophobic steroids are bound to
plasma protein carriers. Only unbound
hormones can diffuse into the target cell.
Cell surface receptor
2a
Rapid responses
1
2 Steroid hormone receptors are in the
cytoplasm or nucleus.
2
Protein
carrier
Nucleus
Cytoplasmic
receptor
Nuclear
receptor
2a Some steroid hormones also bind to
membrane receptors that use second
messenger systems to create rapid
cellular responses.
DNA
Interstitial
fluid
Cell
membrane
3
Endoplasmic
reticulum
5
New
proteins
Transcription
produces mRNA
4
Translation
3 The receptor-hormone complex binds to
DNA and activates or represses one or
more genes.
4 Activated genes create new mRNA that
moves back to the cytoplasm.
5 Translation produces new proteins
for cell processes.
Figure 7-7
Amine Hormones: Features
• Derived from one of two amino acids
• Tryptophan
• Tyrosine
• Ring structure
Amine Hormones: Examples
• Thyroid hormones
• Catecholamines
• Epinephrine
• Norepinephrine
• Dopamine
Amine Hormones: Structure
Tyrosine
Catecholamines
Thyroid hormones
Dopamine
Thyroxine (Tetraiodothyronine, T4)
Norepinephrine
Epinephrine
Triiodothyronine (T3)
Figure 7-8
Endocrine Reflex Pathways
•
•
•
•
•
•
Stimulus
Afferent signal
Integration
Efferent signal (the hormone)
Physiological action
Negative feedback
Endocrine Reflex Pathways: Insulin release
Blood
glucose
KEY
Eat a meal
Stimulus
Stretch receptor
in digestive tract
Receptor
Efferent path
Effector
Afferent neuron
Tissue response
Sensory neuron
Negative feedback
CNS
Efferent neuron
Integrating center
Efferent neuron
Systemic response
Pancreas
Insulin
Blood
glucose
Glucose uptake
and utilization
Target
tissues
Figure 7-9