Hormones and Feedback Mechanisms
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Transcript of Hormones and Feedback Mechanisms
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Hormonesand
Feedback Mechanisms03.01.05
How the endocrine system controls everything
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The Endocrine System
I. General Overview
II. Basic Anatomy
III. Control of the endocrine system
IV. Specific endocrine events
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I. A General Overview
• ES (endocrine system) and homeostasis
• Anatomy– Endocrine glands, cells, neurosecretory cells– Hormones– Target cells
• ES as a Control System– Hormone + target = change in cell function
(return to homeostasis)
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ES and Homeostasis• Homeostasis
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Feedback Mechanisms
• Stimulus– change in homeostatic environment– signal sent to CNS
• Response– signal sent from CNS– produce effect – body returns to homeostasis
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Basic ES cont.• ES and NS = 2 main
control systems of body
• Endocrine organs located throughout body
• Actions mediate all tissues
• Control of ES through feedback mechanisms
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II. ES anatomy basics
A. Exocrine gland
– Ducts
– Lumen and surfaces
B. Endocrine gland
– Chemical messengers
– Blood stream
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C. Hormones
• Chemical messenger– Secreted by endocrine
gland
– Specific to target
– Activate cellular change
– Of 4 different chemical types
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C. 4 Classes of Hormones
1. Peptide/ Protein
2. Steroid
3. Amine
4. Eicosanoid
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Hormone + Receptor
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Protein/Peptide Hormones
• Hydrophilic
• Large
• Can't fit through membrane
• Second messenger mechanism of action
• Most hormones
• Example: Insulin
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Steroid Hormones
• Small
• Hydrophobic/Lipophilic
• Travel in blood w/carrier
• Cytoplasmic or nuclear receptors
• change protein synthesis
• Example: estradiol
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Amine
• Synthesized from a single amino acid
• Melatonin from tryptophan
• Thyroid hormone from tyrosine
• Catecholamines (EPI, DA) from tyrosine
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Eicosanoid• Produced from 20-
carbon fatty acid, arachadonic acid
• Produced in all cells except RBCs
• 2nd messenger• Prostaglandins and
leukotrienes• inflammation
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Hormone + Receptor
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Where are Hormones Made ?
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The H-P-AHypothalamic-Pituitary Axis
• Most feedback loops run through this axis
• HPA mediates growth, metabolism, stress response, reproduction.
• is secondarily in charge of almost everything else.
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p. 503
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D. Neurosecretory Cells
1. Specialized neurons– Synthesize and
secrete hormones
2. Extend from HYPOTHALAMUS to POSTERIOR PITUITARY
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2. Neurosecretory cells in Hypothalamus
• Nuclei synthesize and secrete hormones
• Neuronal connection to POSTERIOR pituitary
• Antidiuretic Hormone (ADH), Oxytocin
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E. Hypothalamus (general)• Connection to
pituitary– Neuronal to
POSTERIOR PITUITARY
– Endocrine to ANTERIOR PITUITARY
• RH = Pituitary releasing hormones
• RIH = Pituitary release inhibiting hormones
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Why is the Hypothalamus so Important?
• Secretes regulatory homones– RH– RIH
• "Directs" pituitary
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STIMULUS
HypothalamusReleasing Hormone
(Release-Inhibiting Hormone)
PituitaryStimulating Hormone
GlandHormone
Target
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Hypothalamic Hormomes
• Release Inhibiting Hormones– Somatostatin– Prolactin release inhibiting hormone-PIH
• Releasing Hormones– Thyrotropin releasing hormone-TRH– Growth hormone releasing hormone-GHRH
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1. Posterior Pituitary Hormones
• Manufactured in Hypothalamus, released from Post. Pit.
• Oxytocin– Target = smooth ms. Uterus and Breast (&brain)– Function = labor and delivery, milk ejection,(pair
bonding)
• ADH (Vasopressin AVP)– Target = kidneys– Function = water reabsorption
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How about in frogs ?
• Hormone structure/function tightly conserved
• Mesotocin– yolking of eggs– egg-laying
• Vasotocin (AVT)– water balance– REPRODUCTIVE BEHAVIORS
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E. Pituitary gland
MASTER GLAND• Anterior and
posterior portions1. Posterior connected
to hypothalamus by infundibulum
2. Anterior connected via blood stream
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2. Anterior Pituitary HormonesHORMONE TARGET FUNCTION
Thyroid (TSH) Stimulating
Thyroid gland TH synthesis &
release
Growth (GH) Many tissues growth
Adrenocortico-
Tropin (ACTH)
Adrenal cortex Cortisol release
(androgens)
Prolactin (Prl) Breast Milk production
Follicle (FSH) Gonads Egg/sperm prod.
Luteinizing (LH)
Gonads Sex hormones
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Hormones To Study
• Hypothalamic Hormones
• Posterior Pituitary (Neurohypophysis)
• Anterior Pituitary (Adenohypophysis)– Thyroid– Growth– Sex Steroid
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III.Control of Endocrine Function
A. Positive
B. or Negative Feedback mechanisms
• Self-regulating system
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STIMULUS
HypothalamusReleasing Hormone(Release-Inhibiting
Hormone)
PituitaryStimulating Hormone
GlandHormone
Target
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A. Positive Feedback
• Not common• Classic example:
Action of OXYTOCIN on uterine muscle during birth.
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Positive Feedback
• Baby pushes on cervix
• Nervous signal to Hypothalamus
• Hypothal. manufactures OXY
• OXY transported to POSTERIOR PITUITARY & released
• OXY stimulates uterine contraction
• Loop stops when baby leaves birth canal
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Same with frogs?
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B. Negative Feedback
• Most common control mechanism
• Level of hormone in blood or body’s return to homeostasis shuts off loop at hypothalamus and pituitary
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Negative Feedback: Thyroid
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Basic Structure of Feedback Loop
• Environmental Stimulus • Stimulates Control Center (Brain-hypothal.)• Hypothalamic hormones stim. Pituitary• Pituitary hormone stim. Target area• Target area produces change• Change acts negatively or positively on the cycle.
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IV. Specific Endocrine Events
A. Thyroid Hormone
B. Growth Hormone
C. Adrenal Cortex Hormones
D. Sex Steroids
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A. Thyroid Hormone
T3 & T4 stim. Or environmental stim. Hypothalamus
• TRH stim. Anterior Pituitary
• TSH stim. Thyroid T3 & T4 shuts off
TRH and TSH production
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Growth
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metabolism andgrowth
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Thyroid Problems
• What would happen if the thyroid could no longer produce T3 and T4?
• No negative feedback to hypothalamus and anterior pituitary
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Goiter
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Hypersecretion of TSH or TH
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Hyposecretion of TH
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B. Growth Hormone
• Stimulus = Tissue growth/ repair
• Hypothalamus releases GHRH
• Anterior Pituitary releases GH Protein synthesis, growth, etc.GH and release of somatostatin shuts off
GHRH and GH release
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What happens with excess GH?
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GH as Juvenile
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GH as an Adult
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How Does Hypersecretion of GH Happen?
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GH = pituitary dwarfism
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Adrenal Gland
• Adrenal gland located atop kidney
• Outer part = cortex– Secretes Cortisol (stress), Androgens,
Aldosterone (electrolytes)
• Inner part = medulla– SNS control– Secretes EPI & NEPI (fight or flight)
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Adrenal Insufficiency
• Addison’s disease--hyposecretion of cortisol
• JFK
• Darkened skin (ACTH mimics MSH)
• Weight loss, hypoglycemia
• Find the anomaly in the feedback loop.
• Inability to handle stress
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4. Sex Steroids
• Stimulus = low circulating T or E
• Hypothalamus = GnRH
• Anterior Pituitary = FSH & LH
• Gonads produce T and E
• High T and E shut off GnRH and FSH/LH
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Importance
• Reproduction/Mating Behavior (duh)
• Formation of reproductive organs– gonads– brain
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Too many steroids
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Invertebrates
• Hormones involved in:– Molting– Pupation– Metamorphosis
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Insect Hormones
• Juvenile Hormone– maintains juvenile cuticle for pre-adulthood molts
– secreted by corpus allatum near brain
• Ecdysone– Molting Hormone
– Prothoracic Glands (in thorax of insect)
– PTTH = Brain hormone that stimulates Prothoracic Glands
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Ecdysone Ecdysone
Juvenile Hormone
p.523
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Points
• History
• Anatomy
• Terms
• Hormones
• Feedback control
• Specific Points discussed
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I. Endocrine History
• Claude Bernard (mid 1800s)– pancreas, liver
– brain, smooth ms.
– internal environ.
• A.A. Berthold (1849)– repro hormones and
behavior
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Endocrine History
• Charles Brown-Sequard (1889)– Harvard 1864-1868– M.D. in NY 1873-1878– bull testis extracts
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Important Physiologists
• Walter Cannon– homeostasis
– sympathetic nervous system
• Bodily Changes in Hunger, Fear, and Rage
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1. Peptide/Protein Hormones
• Most common hormone
• translated, packaged, & sent
• Hydrophilic/Lipophobic
• Bind surface receptors at target
• Binding mediates signal transduction/2nd messenger system
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Peptide Hormones cont.
• Short 1/2-life• Pancreas
– Insulin/glucagon
• Hypothalamus– RH (releasing
hormones)
– RIH (release inhibiting hormones)
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2. Steroid Hormones
• Derived from cholesterol
• Hydrophobic/Lipophilic
• Travel with a protein carrier
• Long 1/2-life
• Binds to cytoplasmic or nuclear receptor– 1st Messenger
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Steroid hormones cont.
• Genomic effect– Activates genes– Directs synthesis of
new proteins
• Lag time between hormone binding and effect = long time.
• Gonads & placenta• Adrenal cortex
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3. Amine Hormones
• Synthesized from a single amino acid
• Melatonin from tryptophan
• Thyroid hormone from tyrosine
• Catecholamines (EPI, DA) from tyrosine
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4. Eicosanoid hormones
• Produced from 20-carbon fatty acid, arachadonic acid
• Produced in all cells except RBCs
• 2nd messenger• Prostaglandins and
leukotrienes• inflammation
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4 Classes of Hormones
A. Peptide/ Protein 2M
B. Steroid
C. Amine
D. Eicosanoid
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4 Classes of Hormones
A. Peptide/ Protein 2M
B. Steroid 1M
C. Amine
D. Eicosanoid
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4 Classes of Hormones
A. Peptide/ Protein 2M
B. Steroid1M
C. Amine2M
D. Eicosanoid
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4 Classes of Hormones
A. Peptide/ Protein 2M
B. Steroid 1M
C. Amine 2M
D. Eicosanoid 2M
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Negative Feedback
• Low levels of T3 or T4 in blood or low BMR = stimulus
• Hypothalamus releases TRH• TRH stimulates the ANTERIOR
PITUITARY to release TSH• TSH stim. Thyroid to release T3 & T4• Levels of T3 & T4 shut off Hypothal. &
Anterior Pituitary
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Adrenal cortex feedback
• Low glucocorticoid (cortisol) levels or low blood sugar
• Stim. Hypothal. = CRH
• CRH stim. Anterior Pit. = ACTH
• ACTH stim. Adrenal Cortex.
• Increase glucocort. Level then blood sugar level
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Adrenal gland
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Adrenal Problems
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Hypersecretion of Adrenal Cortex
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What Would the Feedback Loop Look Like for Cushing’s
Syndrome?