lecture 5 endocrine 1
TRANSCRIPT
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ENDORINE SYSTEM
The endocrine system is one of the two coordinatingand integrating systems of the body, the other being the
nervous system. It acts through chemical messengers
(hormones) carried in the circulation.
1. Endocrine Control Mechanisms
A.Nervous and Endocrine Systems Function Together
to Promote Homeostasis
nervous system endocrine system
neuroendocrine system
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B. Hormones
Definition
A hormone can be defined as a chemical substance
which is synthesized and secreted by a specific cell
type, is transported in the circulation and at very low
concentrations elicits a specific response in distant
target tissues
Differences of endocrine, paracrine and autocrinemechanisms
Classification
peptide hormones, e.g. growth hormone, insulin
steroid hormones, e.g. aldosterone, testosterone
amino acid derivatives, e.g. thyroxine and
adrenaline
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Hormone synthesis and secretion
synthesis of peptide hormones follow the sameway as protein synthesis
Precursors proteolytic cleavage peptidehormones or proteins stored in vesicles release upon appropriate stimulus into the
blood synthesis of steroid hormones
- Types of steroid hormones:1) Glucocorticoids
2) Mineralocorticoids
3) Androgens
4) estrogens
5) progestins
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A
B
C
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They all come from a common precursor
cholesterol
Once they are synthesized, they diffuse across
the cell membrane into the interstitial fluid then
into the blood so that their rate of release is
determined by their rate of synthesis.
synthesis and secretion of hormones from
tyrosine derivatives
Hormone transport and inactivation
Once released into the blood stream, lipid-solublehormones, e.g. thyroid and steroid hormones, are
carried bound to various plasma proteins.
Free form bound form = a dynamic equilibrium
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half-life of hormones: minutes to days
Inactivation may occur in the blood, in the liver,
or kidney, or in the target tissues.
Hormone actions
membrane permeability
activity of rate-limiting enzymes in reactionpathways
protein synthesis
gene activation leading to the transcription of
new mRNA species
Control of hormone secretion
negative feedback mechanism
positive feedback mechanism
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Mechanisms ofHormone Action
second messenger model
1) cyclic AMP
2) inositol triphosphate (IP3 ) and diacyglycerol
(DG)3) ions
gene expression model
The time of action for hormone using the twomodels
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The two second messengers: diacylglycerol (DAG) and
inositol triphosphate (IP3)
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2. The Important Endocrine Glands and Their Hormones
A. The pituitary hormones
anatomy of the pituitary gland and its relation to thehypothalamus
anterior lobe
intermediate lobe
posterior lobe
pituitary stalk
supraoptic neucleus
paraventricular nucleus
hypothalamus-pituitary portal system
short portal system
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Regulation of pituitary hormone secretion by thehypothalamus
secretion of posterior pituitary hormones: a typicalneuroendocrine regulatory mechanism
secretion of anterior pituitary hormones: a typical
endocrine regulatory mechanism
important releasing/inhibiting hormones producedin hypothalamus:
- Corticotropin-releasing hormone (CRH)
- Thyrotropin-releasing hormone (TRH)
- Gonadotropin-releasing hormone (GnRH)
- Growth-hormone-releasing hormone (GHRH)
- Prolactin-releasing hormone (PRH)
- Prolactin-inhibitory hormone (PIH)
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Posterior pituitary hormones
Antidiuretic hormone (ADH, vasppressin)
- chemistry: 9 amino acid peptide, produced
primarily by supraoptic nucleus and small
amount by paraventricular nucleus
- actions:
1) water retention by the kidney
qurine volume and o ECF
2) vasoconstriction (in large amounts)
- regulation/stimuli:
1) blood (or ECF) osmolality/osmoreceptors
2) blood volume
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3) others: alcohol, nicotine, barbiturates, etc.
- abnormality: diabetes insipidus Oxytocin
- chemistry: 9 amino acid peptide, produced
primarily by paraventricular nucleus and small
amount by supraoptic nucleus
- actions: 1) regulating breast milk release
2) contraction of pregnant uterus
- regulation/stimuli:
suckling by a nursing infant
crying sounds from a baby
fear and stress inhibit release
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anterior pituitary hormones
Growth hormone
Prolactin
Thyroid-stimulating hormone
Adrenocorticotrophic hormone
Folicle-stimulating hormone
Luteinizing hormone
Growth hormone (GH)
- chemistry:191 peptide
- actions: see Fig.13-7
- regulation/stimuli:
Growth hormone releasing hormone (GHRH)
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Growth hormone inhibitory hormone
(somatostadin)
other stimuli:
deep sleep
low blood glucose
stress
amino acids (arginine)
- abnormality:dwarfism
gigantism (acromegaly)
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