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
Figure 7-2 (1 of 2)
Anatomy Summary: Hormones
Figure 7-2 (2 of 2)
Anatomy Summary: Hormones
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
receptor1. Peptide or protein hormones
• Insulin from amino acids2. Steroid hormones
Sex steroids; estrogen, lipophilic3. Amine hormones• epinephrine
Table 7-1
Hormones: Classification
Figure 7-3
Peptide Hormone Synthesis, Packaging, and Release
1
mRNA
RibosomeTo target
Prohormone
Signalsequence
Transportvesicle
Active hormone
Endoplasmic reticulum (ER) Golgi complex
Secretoryvesicle
ECFCytoplasm Plasma
Peptidefragment
Releasesignal
Capillaryendothelium
Preprohormone
Messenger RNA on the ribosomes binds amino acids into a peptide chain called a preprohormoneThe chain is directed into the ER lumen by a signal sequence of amino acids.
The secretory vesicle releases its contents by exocytosis into the extracellular space.
The hormone moves into the circulation for transport to its target.
Enzymes in the ER chop off the signal sequence, creating an inactiveprohormone.
The prohormone passes from theER through the Golgi complex.
Secretory vesicles containing enzymes and prohormone bud off the Golgi. The enzymes chop the prohormone into one or more active peptides plus additional peptide fragments.
2 3 4 5 6
1
2
3
4
5
6
Peptide Hormone Synthesis, Packaging, and Release
Figure 7-4
Preprohormone Hormone Other peptides Signal sequence
processes to
PreproTRH (242 amino acids) 6 TRH(3 amino acids each)
(a)
(c)
TRH
(b)
+
+ +
+
Pro-opiomelanocortin
Prohormone Active hormone(s) Other peptide fragments
processes to
ACTH lipotropin endorphin Fragment
+
+
Proinsulin Insulin C-peptide
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
Figure 7-5
TK = Tyrosine kinase
AE = Amplifier enzyme
G = G protein
KEYProteins
Secondmessenger
system
Opens ionchannel
phosphorylate
Cellular response
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
Figure 7-6
Cholesterol is the parent compound for all steroid hormones.
modified by enzymes to make steroid hormones such as
Estradiol (an estrogen)Aldosterone
Adrenalcortex
Ovary
Cortisol
In ovaryIn adrenal cortex
Steroid Hormones: Action
Figure 7-7
1
Cellmembrane
Interstitialfluid
Cytoplasmicreceptor
Endoplasmicreticulum
Nucleus
Nuclear receptor
DNA
Translation
Cell surface receptor
Rapid responses
Transcriptionproduces mRNA
Steroid hormone
Bloodvessel
Proteincarrier
Newproteins
Steroid hormone receptors are in thecytoplasm or nucleus.
Most hydrophobic steroids are bound toplasma protein carriers. Only unboundhormones can diffuse into the target cell.
Translation produces new proteinsfor cell processes.
Some steroid hormones also bind to membrane receptors that use secondmessenger systems to create rapidcellular responses.
The receptor-hormone complex binds toDNA and activates or represses one ormore genes.
Activated genes create new mRNA thatmoves back to the cytoplasm.
2a
2
54
3
1
2a
2
3
4
5
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
Figure 7-8
Tyrosine
Catecholamines
Dopamine
Norepinephrine
Epinephrine
Thyroid hormones
Thyroxine (Tetraiodothyronine, T4)
Triiodothyronine (T3)
Endocrine Reflex Pathways
• Stimulus• Afferent signal• Integration• Efferent signal (the hormone)• Physiological action• Negative feedback
Endocrine Reflex Pathways: Insulin release
Figure 7-9
Receptor
Efferent path
Effector
Tissue response
Stimulus
Efferent neuron
Sensory neuron
Integrating center
Systemic response
KEYEat a meal
Pancreas
Insulin
Stretch receptorin digestive tract
Glucose uptakeand utilization
CNS
Targettissues
Bloodglucose
Afferent neuron
Efferent neuron
Blood glucose
Neg
ativ
e fe
edba
ck