endocrine system, hormones & feedback mechanisms
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Endocrine System, Hormones & Feedback Mechanisms. How the endocrine system controls everything. The Endocrine System. General Overview Basic Anatomy Control of the endocrine system Specific endocrine events. I. A General Overview. ES (endocrine system) and homeostasis Anatomy - PowerPoint PPT PresentationTRANSCRIPT
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Endocrine System, Hormones & Feedback MechanismsHow the endocrine system controls
everything
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The Endocrine System
I. General OverviewII. Basic AnatomyIII. Control of the endocrine systemIV. 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 –NOT ES! =(– Ducts– Lumen and surfaces
B. Endocrine gland - HormonesA. Hypothalamus, Pituitary, Pineal Gland,
Thyroid, parathyroid, thymus, adrenal, pancreas, testes, ovaries
– Chemical messengers– Blood stream
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Hormones
• Chemical messenger– Secreted by endocrine
gland– Specific to target– Activate cellular
change– Of 4 different chemical
types
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4 Classes of Hormones
1. Peptide/ Protein2. Steroid3. Amine4. Eicosanoid
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Protein/Peptide Hormones
• Hydrophilic• Large• Can't fit through membrane• Most hormones
– Example: Insulin
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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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Steroid Hormones
• Small• Hydrophobic/Lipophilic• Travel in blood with carrier• Cytoplasmic receptors• change protein synthesis
– Example: estradiol
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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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Amine• Synthesized from a single
amino acid• Melatonin from tryptophan
• Thyroid hormone from tyrosine
• Catecholamines• Released from adrenal
medulla / adrenal gland• Epinephrine,
Norepinephrine, Dopamine
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Eicosanoid• Produced from 20-carbon fatty
acid• Produced in all cells except
RBCs• Inflammation
• (Omega 3, Omega 6)• Essential Fatty Acids
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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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D. Neurosecretory Cells
1. Specialized neurosecretory cells– 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
• Antidiuretic Hormone (ADH)– Responsible for increasing
water absorption in the collecting ducts of the kidney nephron
• Oxytocin– Social Behavior
• Sexual behavior – Pair bonding?
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Why is the Hypothalamus so Important?
• Secretes regulatory homones
• RH = Pituitary releasing hormones
• RIH = Pituitary release inhibiting hormones
• "Directs" pituitary– Ex. A releasing
hormone controls the release of other hormones.
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STIMULUS
HypothalamusReleasing Hormone
(Release-Inhibiting Hormone)
PituitaryStimulating HormoneGland
Hormone Target
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Hypothalamic Hormomes
• Release Inhibiting Hormones– Somatostatin
• growth hormone-inhibiting hormone– Prolactin release inhibiting hormone-PIH
• Peptide hormone involved in lactation
• Releasing Hormones– Thyrotropin releasing hormone-TRH– Growth hormone releasing hormone-GHRH
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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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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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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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IV. Specific Endocrine Events
A. Thyroid HormoneB. Growth HormoneC. Adrenal Cortex HormonesD. Sex Steroids
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A. Thyroid Hormone• “Thyronines” act on nearly every
cell in the body. Made from “I”– Metabolic rate– Protein synthesis– Bone growth– Sensitivity to Cetacholamines
(Adrenaline)– Vitamin absorption
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Growth
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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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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 (used in males, precursor of estrogen), Aldosterone (electrolyte absorption)
• Inner part = medulla– SNS control– Secretes EPI & NEPI (fight or flight)
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Adrenal Insufficiency
• Addison’s disease--hyposecretion of cortisol
• Weight loss, hypoglycemia• Inability to handle stress
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4. Sex Steroids
• Stimulus = low circulating T or E• Hypothalamus = GnRH (Gonadotropin)• Anterior Pituitary = FSH(Folicle stimulating)• Gonads produce T and E• High T and E shut off GnRH and FSH
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Importance
• Reproduction/Mating Behavior• Formation of reproductive organs
– gonads– brain
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4 Classes of Hormones
A. Peptide/ Protein 2MB. Steroid 1MC. Amine 2MD. Eicosanoid 2M