1. The Endocrine System: Part 1

2. Endocrine System: Overview
Acts with nervous system to coordinate and integrate activity of body cells
Influences metabolic activities via hormones transported in blood
Response slower but longer lasting than nervous system
Endocrinology
Study of hormones and endocrine organs
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3. Endocrine System: Overview
Exocrine glands
Nonhormonal substances (sweat, saliva)
Have ducts to carry secretion to membrane surface
Endocrine glands
Produce hormones
Lack ducts
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4. Pineal gland Hypothalamus Pituitary gland Thyroid gland
Figure Location of selected endocrine organs of the body.
Pineal gland
Hypothalamus
Pituitary gland
Thyroid gland
Parathyroid glands
(on dorsal aspect
of thyroid gland)
Thymus
Adrenal glands
Pancreas
Gonads
• Ovary (female)
• Testis (male)
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5. Hormones: long-distance chemical signals; travel in blood or lymph
Chemical Messengers
Hormones: long-distance chemical signals; travel in blood or lymph
Autocrines: chemicals that exert effects on same cells that secrete them
Paracrines: locally acting chemicals that affect cells other than those that secrete them
Autocrines and paracrines are local chemical messengers; not considered part of endocrine system
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6. 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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7. Mechanisms of Hormone Action
Though hormones circulate systemically only cells with receptors for that hormone affected
Target cells
Tissues with receptors for specific hormone
Hormones alter target cell activity
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8. Mechanisms of Hormone Action
Hormones act at receptors in one of two ways
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
2. Lipid-soluble hormones (steroid and thyroid hormones)
Act on intracellular receptors that directly activate genes
Can enter cell
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9. Figure 16.2 Cyclic AMP second-messenger mechanism of water-soluble hormones.
Slide 1
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
GDP
Inactive
protein
kinase
Active
protein
kinase
GTP
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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10. Cytoplasm Nucleus mRNA New protein
Figure Direct gene activation mechanism of lipid-soluble hormones.
Slide 1
Steroid
hormone
Extracellular
fluid
Plasma
membrane
The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor. 1
Cytoplasm
Receptor
protein
Receptor-
hormone
complex
The receptor-
hormone complex enters the nucleus. 2
Receptor
Binding region
Nucleus
The receptor- hormone complex binds a specific DNA region. 3
DNA
Binding initiates transcription of the gene to mRNA. 4
mRNA
The mRNA directs protein synthesis. 5
New protein
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11. 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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12. 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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13. 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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14. 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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15. Hormone release caused by altered levels of certain critical ions or
Figure 16.4a Three types of endocrine gland stimuli.
Slide 1
Humoral Stimulus
Hormone release caused by altered
levels of certain critical ions or
nutrients.
Capillary (low Ca2+
in blood)
Thyroid gland
(posterior view)
Parathyroid
glands
Parathyroid
glands
PTH
Stimulus: Low concentration of Ca2+ in
capillary blood.
Response: Parathyroid glands secrete
parathyroid hormone (PTH), which
increases blood Ca2+.
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16. Hormone release caused by neural input.
Figure 16.4b Three types of endocrine gland stimuli.
Slide 1
Neural Stimulus
Hormone release caused by neural input.
CNS (spinal cord)
Preganglionic
sympathetic
fibers
Medulla of
adrenal gland
Capillary
Stimulus: Action potentials in preganglionic
sympathetic fibers to adrenal medulla.
Response: Adrenal medulla cells secrete
epinephrine and norepinephrine.
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17. Hormone release caused by another hormone (a tropic hormone).
Figure 16.4c Three types of endocrine gland stimuli.
Slide 1
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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18. 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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19. Hormones circulate in blood either free or bound
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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20. 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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21. Amino Acid based hormones
Water soluble
May be stored and release later
Most are free – metabolized quickly
Shorter half-live
Example – Amino acid based hormones except Thyroxin
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22. Transported by plasma proteins Half life is longer
Steroid Homones
Lipid-soluble
Cannot be stored
Transported by plasma proteins
Half life is longer
Less fluctuation in blood
Example: Estrogen, progesterone, testosterone, aldosterone, corticol
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23. The Pituitary Gland and Hypothalamus
Pituitary gland (hypophysis) has two major lobes
Posterior pituitary (lobe)
Neural tissue
Anterior pituitary (lobe) (adenohypophysis)
Glandular tissue
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24. Paraventricular nucleus
Figure 16.5a The hypothalamus controls release of hormones from the pituitary gland in two different ways (1 of 2).
Slide 1
Paraventricular nucleus
Hypothalamus 1
Hypothalamic neurons synthesize oxytocin or antidiuretic hormone (ADH).
Posterior lobe
of pituitary
Optic
chiasma
Supraoptic
nucleus
Infundibulum
(connecting stalk) 2
Oxytocin and ADH are transported down the axons of the hypothalamic- hypophyseal tract to the posterior pituitary.
Inferior
hypophyseal
artery
Hypothalamic-
hypophyseal
tract
Axon terminals 3
Oxytocin and ADH are stored in axon terminals in the posterior pituitary.
Posterior lobe
of pituitary 4
Oxytocin
ADH
When hypothalamic neurons fire, action potentials arriving at the axon terminals cause oxytocin or ADH to be released into the blood.
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25. they stimulate or inhibit
Figure 16.5b The hypothalamus controls release of hormones from the pituitary gland in two different ways (2 of 2).
Slide 1
Hypothalamus
Hypothalamic
neurons synthesize
GHRH, GHIH, TRH,
CRH, GnRH, PIH.
Anterior lobe
of pituitary
Superior
hypophyseal
artery
When appropriately stimulated, hypothalamic neurons secrete releasing or inhibiting hormones into the primary capillary plexus. 1 2
Hypothalamic hormones travel through portal veins to the anterior pituitary where
they stimulate or inhibit
release of hormones made in the anterior pituitary.
Hypophyseal
portal system
• Primary capillary
plexus 3
A portal system is two capillary plexuses (beds) connected by veins.
In response to releasing hormones, the anterior pituitary secretes hormones into the secondary capillary plexus. This in turn empties into the general circulation.
• Hypophyseal
portal veins
• Secondary
capillary plexus
GH, TSH, ACTH,
FSH, LH, PRL
Anterior lobe
of pituitary
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26. Posterior Pituitary and Hypothalamic Hormones
Oxytocin and ADH
Each composed of nine amino acids
Almost identical – differ in two amino acids
What are the actions of Oxytocin?
How about ADH?
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27. Inhibits or prevents urine formation
ADH (Vasopressin)
Inhibits or prevents urine formation
Primary purpose water balance – osmolarity of body fluids – normal 285 – 300 milliosmols
Targets kidney tubules  reabsorb more water
Release also triggered by pain, low blood pressure, and drugs
Inhibited by alcohol, diuretics
High concentrations  vasoconstriction
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28. Determining Osmolality
Osmolality = concentration based on # solutes/liter
Lab reports do not show osmolality – show electrolyte concentration – need to double Na+ concentration
Hypertonicity = >300 mOsm
Edema = <285 mOsm
Osmoreceptors respond to change in osmolality of plasma
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29. Syndrome of inappropriate ADH secretion (SIADH)
Diabetes insipidus
ADH deficiency due to hypothalamus or posterior pituitary damage
Must keep well-hydrated
Syndrome of inappropriate ADH secretion (SIADH)
Retention of fluid, headache, disorientation
Fluid restriction; blood sodium level monitoring
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