1. Chapter 16: The Endocrine System Part I System: Part A
Information primarily from:
Human Anatomy & Physiology
Ninth Edition
Elaine N. Marieb & Katja Hoehn

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3. Endocrine System: Overview
Nervous System
Integrate and coordinate activity of the body
Hormones secreted from cells
Electrochemical signals are
sent from neurons
Secreted into the bloodstream
Transferred in the synapses of the nervous system
Regulates the function of other cells
Hormone binds to a receptor on or within a target cell to
initiate a response
Neurotransmitters bind to receptors on post-synaptic membrane
Last seconds to days (long)
Milliseconds of time (short)
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4. Endocrine System: Overview
Controls and integrates
Growth and development; Example: Pituitary Gland
Maintenance of electrolyte, water, and nutrient balance of blood; Example: Hypothalamus and Pituitary Gland
Regulation of cellular metabolism and energy balance; Example: Thyroid Gland
Mobilization of body defenses; Example: Thymus
Reproduction ; Example: Ovaries and Testes
Hypothalamus
Pituitary
Pineal
Thyroid
Parathyroid
Thymus
Adrenal Glands
Pancreas
Ovaries
Testes
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5. Fun Fact
To collect 1 kilogram (2.2 pounds) of hormone producing tissue – you would need to collect all of the endocrine tissue from 8 – 9 adults.
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6. Endocrine System: Overview
Exocrine glands
Nonhormonal substances (sweat and saliva)
Have ducts to carry secretion to membrane surface
Endocrine glands (endo –within; crine – to secrete)
Produce hormones
Lack ducts (ductless)
Hormone producing cells arranged in cords/branching networks
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7. Anatomy of the pancreas. Source: McKinley M. and O'Loughlin
Anatomy of the pancreas. Source: McKinley M. and O'Loughlin. Human Anatomy, 2nd ed. New York: McGraw Hill Figure
Source: Pathology of the Pancreas, Pathology: A Modern Case Study
Citation: Reisner HM. Pathology: A Modern Case Study; 2015 Available at: Accessed: April 18, 2017
Copyright © 2017 McGraw-Hill Education. All rights reserved

8. Endocrine System: Overview
Endocrine glands: pituitary, thyroid, parathyroid, adrenal, and pineal glands
Hypothalamus is neuroendocrine organ
Some have exocrine and endocrine functions
Pancreas, gonads, placenta
Other tissues and organs that produce hormones
Adipose cells (leptin), thymus, and cells in walls of small intestine, stomach, kidneys, and heart
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9. Chemical Messengers
Hormones: long-distance chemical signals; travel in blood or lymph
Autocrines: chemicals that exert effects on same cells that secrete them; Example: prostaglandins are released by smooth muscle cells in order to make them contract.
Paracrines: locally acting chemicals that affect cells other than those that secrete them; somatastatin released by one population of insulin cells inhibits the release of insulin by another population of insulin cells.
Autocrines and paracrines are local chemical messengers; not considered part of endocrine system
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11. eicosanoids Includes leukotrienes and prostaglandins
Biologically active lipids made from Arachnidonic Acid
Leukotrienes are signaling chemicals that mediate inflammation and some allergic reactions.
Prostaglandins – raise blood pressure; increase uterine contractions; enhance blood clotting, pain, and inflammation
Generally are listed into the paracrines and autocrines, but some researches add them as a class of hormones.
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12. Chemistry of Hormones Two main classes Amino acid-based hormones
Amino acid derivatives, peptides, and proteins
Steroids
Synthesized from cholesterol
Gonadal and adrenocortical hormones
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13. Mechanisms of Hormone Action
Though hormones circulate systemically only cells with receptors for that hormone are affected.
Target cells
Tissues with receptors for specific hormone
Hormones alter target cell activity
Hormones increase or decrease a cellular response
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14. Mechanisms of Hormone Action
Hormone action on target cells may be to
Alter plasma membrane permeability and/or membrane potential by opening or closing ion channels
Stimulate synthesis of enzymes or other proteins
Activate or deactivate enzymes
Induce secretory activity
Stimulate mitosis
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15. Review of G-Protein Cell communication
Animation: G-Proteins udent_view0/chapter17/animation__membrane- bound_receptors_that_activate_g_proteins.html
Second Messenger: udent_view0/chapter10/animation__second_messeng er__camp.html
Here is another (my high school student’s favorite): Signal Transduction Pathways
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16. Review of G-Protein Cell communication
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17. Mechanisms of Hormone Action
Hormones act at receptors in one of two ways, depending on their chemical nature and receptor location
Water-soluble hormones (all amino acid–based hormones except thyroid hormone)
Act on plasma membrane receptors
Act via G protein second messengers
Cannot enter cell
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18. Mechanisms of Hormone Action
2. Lipid-soluble hormones (steroid and thyroid hormones)
Act on intracellular receptors that directly activate genes
Can enter cell
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19. Plasma Membrane Receptors and Second-messenger Systems
cAMP signaling mechanism:
Hormone (first messenger) binds to receptor
Receptor activates G protein
G protein activates adenylate cyclase
Adenylate cyclase converts ATP to cAMP (second messenger)
cAMP activates protein kinases that phosphorylate proteins
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20. Hormone is the first messenger. When it binds the receptor, the
Figure Cyclic AMP second-messenger mechanism of water-soluble hormones.
Slide 2
Recall from Chapter 3 that
G protein signaling mechanisms
are like a molecular relay race.
Hormone
(1st messenger)
Receptor
G protein
Enzyme
2nd
messenger
Hormone (1st messenger) binds receptor. 1
Extracellular fluid
Receptor
Hormone is the first messenger.
When it binds the receptor, the
Receptor change will bind (conformation)
Cytoplasm
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21. This conformation (change in shape), allows it to bind the
Figure Cyclic AMP second-messenger mechanism of water-soluble hormones.
Slide 3
Recall from Chapter 3 that
G protein signaling mechanisms
are like a molecular relay race.
Hormone
(1st messenger)
Receptor
G protein
Enzyme
2nd
messenger
Hormone (1st messenger) binds receptor. 1
Extracellular fluid
G protein (Gs)
Receptor
GTP
GDP
GTP
This conformation (change in shape), allows it to bind the
Inactive G Protein. GTP now replaces GDP .
GTP – Guanine Triphosphate is a high Energy molecule.
Cytoplasm
Receptor activates G protein (Gs). 2
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22. The activated G-protein moves along the
Figure Cyclic AMP second-messenger mechanism of water-soluble hormones.
Slide 4
Recall from Chapter 3 that
G protein signaling mechanisms
are like a molecular relay race.
Hormone
(1st messenger)
Receptor
G protein
Enzyme
2nd
messenger
Hormone (1st messenger) binds receptor. 1
Adenylate cyclase
Extracellular fluid
G protein (Gs)
GTP
Receptor
GTP
GDP
GTP
The activated G-protein moves along the
Membrane and binds to enzyme adenylate
Cyclase. GTP is hydrolyzed to GDP and P.
G Protein is now inactive again.
Cytoplasm
Receptor activates G protein (Gs). 2
G protein activates adenylate cyclase. 3
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23. Adneylate cyclase converts ATP to cAMP for as long as
Figure Cyclic AMP second-messenger mechanism of water-soluble hormones.
Slide 5
Recall from Chapter 3 that
G protein signaling mechanisms
are like a molecular relay race.
Hormone
(1st messenger)
Receptor
G protein
Enzyme
2nd
messenger
Hormone (1st messenger) binds receptor. 1
Adenylate cyclase
Extracellular fluid
G protein (Gs)
cAMP
GTP
Receptor
GTP
ATP
GDP
GTP
Adneylate cyclase converts
ATP to cAMP for as long as
GTP is bound to the enzyme.
Cytoplasm
Receptor activates G protein (Gs). 2
G protein activates adenylate cyclase. 3
Adenylate
cyclase converts
ATP to cAMP (2nd messenger). 4
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24. cAMP activates protein kinases.
Figure Cyclic AMP second-messenger mechanism of water-soluble hormones.
Slide 6
Recall from Chapter 3 that
G protein signaling mechanisms
are like a molecular relay race.
Hormone
(1st messenger)
Receptor
G protein
Enzyme
2nd
messenger
Hormone (1st messenger) binds receptor. 1
Adenylate cyclase
Extracellular fluid
G protein (Gs)
cAMP
cAMP activates protein kinases. 5
GTP
Receptor
GTP
ATP
Inactive
protein
kinase
Active
protein
kinase
GDP
GTP
cAMP activates protein kinases.
Protein kinases are enzymes that phosphorylate
(add a phosphate group to) other proteins.
Activated protein kinases activates cellular
Processes.
Triggers responses of
target cell (activates
enzymes, stimulates
cellular secretion,
opens ion channel, etc.)
Cytoplasm
Receptor activates G protein (Gs). 2
G protein activates adenylate cyclase. 3
Adenylate
cyclase converts
ATP to cAMP (2nd messenger). 4
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25. Your turn!
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26. Plasma Membrane Receptors and Second-messenger Systems
cAMP signaling mechanism
Activated kinases phosphorylate various proteins, activating some and inactivating others
cAMP is rapidly degraded by enzyme phosphodiesterase
Intracellular enzymatic cascades have huge amplification effect
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27. Plasma Membrane Receptors and Second-messenger Systems
PIP2-calcium signaling mechanism (Calcium acts as the Second messenger
Involves G protein and membrane-bound effector – phospholipase C
Phospholipase C splits PIP2 into two second messengers – diacylglycerol (DAG) and inositol trisphosphate (IP3)
DAG activates protein kinase; IP3 causes Ca2+ release
Calcium ions act as second messenger
Ca2+ alters enzyme activity and channels, or binds to regulatory protein calmodulin
Calcium-bound calmodulin activates enzymes that amplify cellular response
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28. DAG activates protein kinases like cAMP
Phospholipase C, a membrane bound effector, splits A plasma membrane (PIP2), Phosphophatidyl inositol Biphosphate, into DAG, diacylglycerol and inositol Trisphosphate (IP3)
DAG activates protein kinases like
cAMP
IP3 releases Ca2+ from storage. Then binds
To Calmodulin, and activates enzymes
For cellular response.
Calmodulin is a Calcium modulated messenger.
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29. Other Signaling Mechanisms
Cyclic guanosine monophosphate (cGMP) is second messenger for some hormones
Some work without second messengers
E.g., insulin receptor is tyrosine kinase enzyme that autophosphorylates upon insulin binding  docking for relay proteins that trigger cell responses
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30. Intracellular Receptors and Direct Gene Activation
Steroid hormones and thyroid hormone
Diffuse into target cells and bind with intracellular receptors
Receptor-hormone complex enters nucleus; binds to specific region of DNA
Prompts DNA transcription to produce mRNA
mRNA directs protein synthesis
Promote metabolic activities, or promote synthesis of structural proteins or proteins for export from cell
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31. Steroid hormone Extracellular Plasma fluid membrane 1
Figure Direct gene activation mechanism of lipid-soluble hormones.
Slide 2
Steroid
hormone
Extracellular
fluid
Plasma
membrane 1
The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor.
Cytoplasm
Receptor
protein
Receptor-
hormone
complex
Nucleus
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32. hormone complex enters the nucleus.
Figure Direct gene activation mechanism of lipid-soluble hormones.
Slide 3
Steroid
hormone
Extracellular
fluid
Plasma
membrane 1
The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor.
Cytoplasm
Receptor
protein
Receptor-
hormone
complex 2
The receptor-
hormone complex enters the nucleus.
Nucleus
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33. hormone complex enters the nucleus.
Figure Direct gene activation mechanism of lipid-soluble hormones.
Slide 4
Steroid
hormone
Extracellular
fluid
Plasma
membrane 1
The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor.
Cytoplasm
Receptor
protein
Receptor-
hormone
complex 2
The receptor-
hormone complex enters the nucleus.
Receptor
Binding region
Nucleus 3
The receptor- hormone complex binds a specific DNA region.
DNA
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34. Cytoplasm Nucleus mRNA
Figure Direct gene activation mechanism of lipid-soluble hormones.
Slide 5
Steroid
hormone
Extracellular
fluid
Plasma
membrane 1
The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor.
Cytoplasm
Receptor
protein
Receptor-
hormone
complex 2
The receptor-
hormone complex enters the nucleus.
Receptor
Binding region
Nucleus 3
The receptor- hormone complex binds a specific DNA region.
DNA 4
Binding initiates transcription of the gene to mRNA.
mRNA
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35. Cytoplasm Nucleus mRNA New protein
Figure Direct gene activation mechanism of lipid-soluble hormones.
Slide 6
Steroid
hormone
Extracellular
fluid
Plasma
membrane 1
The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor.
Cytoplasm
Receptor
protein
Receptor-
hormone
complex 2
The receptor-
hormone complex enters the nucleus.
Receptor
Binding region
Nucleus 3
The receptor- hormone complex binds a specific DNA region.
DNA 4
Binding initiates transcription of the gene to mRNA.
mRNA
The mRNA directs protein synthesis. 5
New protein
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36. Target Cell Specificity
Target cells must have specific receptors to which hormone binds, for example
ACTH receptors found only on certain cells of adrenal cortex
Thyroxin receptors are found on nearly all cells of body
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37. Target Cell Activation
Target cell activation depends on three factors
Blood levels of hormone
Relative number of receptors on or in target cell
Affinity of binding between receptor and hormone
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38. Target Cell Activation
Hormones influence number of their receptors
Up-regulation—target cells form more receptors in response to low hormone levels
Down-regulation—target cells lose receptors in response to high hormone levels
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39. Control of Hormone Release
Blood levels of hormones
Controlled by negative feedback systems
Vary only within narrow, desirable range
Endocrine gland stimulated to synthesize and release hormones in response to
Humoral stimuli
Neural stimuli
Hormonal stimuli
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40. Humoral Stimulus
Hormone release caused by altered
levels of certain critical ions or
nutrients.
Stimulus: Low concentration of Ca2+ in
capillary blood.
Parathyroid
glands
Capillary (low Ca2+
in blood)
Thyroid gland
(posterior view)
PTH
Response: Parathyroid glands secrete
parathyroid hormone (PTH), which
increases blood Ca2+.
Humoral Stimuli
Changing blood levels of ions and nutrients directly stimulate secretion of hormones
Example: Ca2+ in blood
Declining blood Ca2+ concentration stimulates parathyroid glands to secrete PTH (parathyroid hormone)
PTH causes Ca2+ concentrations to rise and stimulus is removed
Humor – various body fluid
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Figure 16.4a Three types of endocrine gland stimuli. 40

41. Neural Stimuli Nerve fibers stimulate hormone release
Neural Stimulus
Hormone release caused by neural input.
Stimulus: Action potentials in preganglionic
sympathetic fibers to adrenal medulla.
CNS (spinal cord)
Preganglionic
sympathetic
fibers
Medulla of
adrenal gland
Capillary
Response: Adrenal medulla cells secrete
epinephrine and norepinephrine.
Neural Stimuli
Nerve fibers stimulate hormone release
Sympathetic nervous system fibers stimulate adrenal medulla to secrete catecholamines
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Figure 16.4b Three types of endocrine gland stimuli.

42. Hormonal Stimuli
Hormones stimulate other endocrine organs to release their hormones
Hypothalamic hormones stimulate release of most anterior pituitary hormones
Anterior pituitary hormones stimulate targets to secrete still more hormones
Hypothalamic-pituitary-target endocrine organ feedback loop: hormones from final target organs inhibit release of anterior pituitary hormones
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43. Hormone release caused by another hormone (a tropic hormone).
Figure 16.4c Three types of endocrine gland stimuli.
Slide 2
Hormonal Stimulus
Hormone release caused by another
hormone (a tropic hormone).
Hypothalamus
Anterior
pituitary
gland
Thyroid
gland
Adrenal
cortex
Gonad
(Testis)
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44. Hormone release caused by another hormone (a tropic hormone).
Figure 16.4c Three types of endocrine gland stimuli.
Slide 3
Hormonal Stimulus
Hormone release caused by another
hormone (a tropic hormone).
Hypothalamus
Anterior
pituitary
gland
Thyroid
gland
Adrenal
cortex
Gonad
(Testis)
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45. Hormone release caused by another hormone (a tropic hormone).
Figure 16.4c Three types of endocrine gland stimuli.
Slide 4
Hormonal Stimulus
Hormone release caused by another
hormone (a tropic hormone).
Hypothalamus
Anterior
pituitary
gland
Thyroid
gland
Adrenal
cortex
Gonad
(Testis)
Stimulus: Hormones from hypothalamus.
Response: Anterior pituitary gland secretes
hormones that stimulate other endocrine glands to secrete hormones.
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46. Nervous System Modulation
Nervous system modifies stimulation of endocrine glands and their negative feedback mechanisms
Example: under severe stress, hypothalamus and sympathetic nervous system activated
 body glucose levels rise
Nervous system can override normal endocrine controls
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47. Hormones in the Blood Hormones circulate in blood either free or bound
Steroids and thyroid hormone are attached to plasma proteins
All others circulate without carriers
Concentration of circulating hormone reflects
Rate of release
Speed of inactivation and removal from body
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48. Hormones in the Blood Hormones removed from blood by Degrading enzymes
Kidneys
Liver
Half-life—time required for hormone's blood level to decrease by half
Varies from fraction of minute to a week
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49. Onset of Hormone Activity
Some responses ~ immediate
Some, especially steroid, hours to days
Some must be activated in target cells
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50. Duration of Hormone Activity
Limited
Ranges from 10 seconds to several hours
Effects may disappear as blood levels drop
Some persist at low blood levels
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51. Interaction of Hormones at Target Cells
Multiple hormones may act on same target at same time
Permissiveness: one hormone cannot exert its effects without another hormone being present
Synergism: more than one hormone produces same effects on target cell  amplification
Antagonism: one or more hormones oppose(s) action of another hormone
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52. Autocrine and Paracrine diagram
Thryoid cells photo
Autocrine and Paracrine diagram
Leonardo and Goiter
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