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ENDOCRINOLOGYThe Scientific Study of the Endocrine
Glands and their Hormones
Picture : Insulin-containing cells on direct immunofluorescence of islets of Langerhans
MIFTAHRACHMAN, DR, SPPD-MKES
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Outline Lecture 1
General Features of the Endocrine System
and Important definitions
Evolution of the Endocrine System
Classes of Hormones
Actions of Hormones
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General Features of theEndocrine System
Endocrine glands are :
- ductless
- have a rich supply of blood.Hormones, produced by the endocrine glands are
secreted into the bloodstream.
Hormones travel in the blood to target cells closeby or far away from point of secretion.
Hormones receptors are specific binding sites onthe target cell.
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Important Definitions
What are hormones?- Hormones are organic chemical messengers produced
and secreted by endocrine cells into the bloodstream.
- Hormones regulate, integrate and control a wide rangeof physiologic functions.
Silverthorn, Human Physiology, 3rd
edition Figure 6-1&2
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Important Definitions Cont.
What are endocrine glands?
Endocrine glands are ductless glands comprised of endocrine cells.
This means that these glands do not have ducts that lead to the outsideof the body.
For example, sweat glands are NOT endocrine glands(they are insteadexocrine glands) because sweat glands have ducts that lead to theoutside surface of your skin (thats how the sweat gets out).
The fact that endocrine glands are ductless means that these glandssecrete hormones directly into the blood stream (instead of to theoutside of your body).
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Important Definitions Cont.
What are target cells?Target cells refer to cells that contain specific receptors
(binding sites) for a particular hormone.
Once a hormone binds to receptors on a target cell, a
series of cellular events unfold that eventually impactgene expression and protein synthesis.
Silverthorn, Human Physiology, 3rd
edition Figure 6-1&2
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Important Definitions Cont.
What are hormone receptors?
Hormone receptors are binding sites on the target cell
(either on the surface or in the cytoplasm or nucleus ofthe target cell) that are activated only when specific
hormones bind to them.
If a hormone does not/cannot bind to its receptor, then nophysiologic effect results.
See next slide for a picture of a hormone bound to its receptor
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Growth hormone regulates cell growth by bindingto growth hormone receptors on target cells.
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Hormones Cytokines GrowthfactorsProduction Only specialized
cells
Many cell types
Few places Many places
Action Long-range Mostly short-
range
Short-
range
Pleiotropy Low High Medium
Redundance Low High Medium
Regulation Tight Loose
Function Homeostasis
Ontogenesis
Defence Remo-
deling
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Outline Lecture 1
General Features of the Endocrine System
and Important definitions
Evolution of the Endocrine System
Classes of Hormones
Actions of Hormones
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Types of humoral signalization
Endocrine from gland via blood to a distance
Neurocrine via axonal transport and then via blood
Paracrine neighboring cells of different types
Autocrine neighboring cells of the same type or thesecreting cell itself
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Silverthorn, Human Physiology, 3rd
edition Figure 6-1&2
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Outline Lecture 1
General Features of the Endocrine System
and Important definitions
Evolution of the Endocrine System
Classes of Hormones
Actions of Hormones
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Chemical characteristicsof hormones
Amines (from tyrosine) hydroxylation - catecholamines
iodination - thyroid hormones Peptides/proteins
Steroids (from cholesterol)
adrenocortikoids sex hormones
active metabolites of vitamin D
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Classes of Hormones
Steroids vs. Peptide Hormones
Hormones fall into 2 general classes based
on their molecular structure and synthesis.
All steroid hormones are made initially
from the precursor (precursor = first step inbiosynthetic pathway) cholesterol.
See next slide for a diagram of the biosynthetic pathway of steroid hormones
from cholesterol.
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Steroid Hormones
Steroid hormones are produced by thegonads and adrenal cortex.
Thyroid hormones are not steroids, but willbe categorized with steroids for simplicity.
Steroid hormones are made from cholesterol in
the smooth endoplasmic reticulum and
mitochondria of endocrine cells.
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Steroid Hormones
Steroid hormones cannot be stored in vesicles inthe endocrine cells that produce them.
As soon as steroid hormones are produced, theydiffuse out of the endocrine cell and enter thebloodstream.
Steroid hormones are lipid soluble and theirreceptors are located inside their target cell.
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Peptide Hormones
Peptide hormones are comprised of chains on
amino acids.
Like most proteins, peptide hormones aresynthesized on ribosomes of the (rough)
endoplasmic reticulum of endocrine cells.
Peptide hormones can be stored in vesicles in
endocrine cells until they are needed at some
later point.
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Peptide Hormones
Peptide hormones do not readily pass
through cell membranes (lipid bilayers)
and they are referred to as water soluble.
Receptors for peptide hormones are found
on the cell surface of their target cells.
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Outline Lecture 1
General Features of the Endocrine System
and Important definitions
Evolution of the Endocrine System
Classes of Hormones
Actions of Hormones
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Regulation of hormone release
Feedback Negative
Gland Target tissue
hormone
product
inhibition
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Regulation of hormone release
Feedback Negative
Positive (only narrow dose range)
Gland Target tissue
hormone
product
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Regulation of hormone release
Feedback Negative
Positive (only narrow dose range) Nerve regulation
pain, emotions, sex, injury, stress,...
e.g. oxytocin with nipple stimulation
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Combined feedbackStress etc.
CRH secretion in hypothalamus
ACTH secretion in pituitary
plasma ACTH
cortisol secretion in adrenals
plasma cortisol
stimulation
inhibition
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Regulation of hormone release
Rhythms circadian
light/dark fine/tune endogenous rhythm of cells &suprachiasmatic nucleus of hypothalamus
melatonin, cortisol monthly
seasonal (day length; atavistic)
developmental (puberty, menopause)
Pulsations/oscillations gonadotropins
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Regulation of hormone release
Rhythms circadian
0
100
200
300
400
500
600
Cortisol(nM)
Time of day
09 0921
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Pulsatility inGnRH & LH release
0
2
4
6
8
10
12
14 GnRH (pg/10 min)
LH (ng/ml)
12:00 16:0014:00
Time of day
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Actions of Hormones
Fetal development and differentiation
Cell growth and cancer
Metabolism
Cardiovascular function Renal function
Skeletal function
Reproductive function
Immune function
Central nervous system function
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Hormone production:
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Hormone production:Less traditional sources
Placenta:All hormones
Adipocytes:Leptin
Cardiocytes:ANP
Kidney:ErythropoietinRAS
GIT:GastrinCholecystokininSecretin,...
Endothelium:
EndothelinsNOProstanoids,...
Immune system:Cytokines
Platelets, mesenchyme:
Growth factors
Gonads:Inhibins
Activins
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THANK YOU