Hormones and Feedback Mechanisms
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Transcript of Hormones and Feedback Mechanisms
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Hormonesand
Feedback Mechanisms04/26/13
How the endocrine system controls everything
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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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Where are Hormones Made ?
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Endocrine System
• Hypothalamus• Pituitary gland• Thyroid gland• Parathyroid glands• Adrenal gland• Pineal body• Reproductive glands• Pancreas
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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
• 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
• Inflammation• Immune system
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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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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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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)
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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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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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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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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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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 = 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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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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Too many steroids
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Adrenal gland