Download Endocrine System

Endocrine System
Lecture # 1
Prof Kumlesh K. Dev
Department of Physiology
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Endocrine Lectures
Thu 16th Apr
10-11 hr
Hormones
– basics on hormone signaling
Fri 17th Apr
14-15 hr
Hormones II
– hypothalamus, pituitary, adrenal glands
Mon 20th Apr
09-10 hr
Cancelled
– no lecture
Thu 23rd Apr
10-11 hr
Hormones III
– thyroid, parathyroid, pineal glands
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
1
Types of cellular communication
Classification
Communication is critical for cell survival
2 major regulatory systems:
– Nervous System
– Endocrine System
Chapter 4 Principles of Neural and Hormonal Communication
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Four types of chemical messengers
Classification
1) Autocrine/Paracrine
• Local chemical messengers
• Exert effect on neighbouring cells (paracrine)
or on same cell (autocrine)
2) Neurotransmitter
• Short-range chemical messengers
• Diffuse across narrow space (synapse) to act
on adjoining target cell (another neuron, a
muscle, or a gland)
2
Four types of chemical messengers
Classification
3) Neurohormones
• Hormones released into blood by
neurosecretory neurons
• Distributed through blood to distant target cells
4) Hormones
• Long-range messengers
• Secreted into blood by endocrine glands in
response to appropriate signal and act on
distant target cells
1. Autocrine/Paracrine
Classification
Secretory Cell
– chemical messenger
released from a cell :
– can act on itself
(autocrine)
– can act on another cell
close-by (paracrine)
Cell #2
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2. Neurotransmitters
Classification
– Neurotransmitters
released from
synaptic vesicles
– Diffuse across
synapse between two
cells
synapse
with
muscles
synapse
with
glands
– Transmitter binds a
receptor
– Receptor activation
stimulates the cell
synapse
with
another
neuron
3. Neurohormones
Classification
– Released from
synaptic vesicles
by neuron
– Released into
blood
– Acts in manner
similar to hormones
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4. Hormones
Classification
– Messengers of
endocrine system
– Released from
endocrine gland into
blood
– Transported in blood
– Target cell:expresses
specific receptors
Nervous and Endocrine Systems
Classification
Property
Nervous System
Endocrine System
Structure
Wired system of neurons Wireless system of glands
Chemical Messenger Neurotransmitter
Hormones
Target site
Very close
Far away
Distance of Action
Across synaptic cleft
Carried by blood
Speed of Response
milliseconds
mins to hours
Duration of Action
milliseconds
mins to days
Major Function
fast precise responses
long duration responses
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Neuroendocrine cells
Classification
Neuroendocrine cells release neurohormones
and are found in, for example:
•
•
•
•
•
•
•
•
adrenal medulla
thyroid
islet of Langerhangs
pituitary cells
renin-secreting cells
mucosa of the gastro-intestinal tract
pancreas
lower respiratory tract
Types of hormone
Classification
• Two hormone categories based on solubility
– Hydrophilic (lipophobic, water soluble)
• Peptide hormones
• Catecholamines
– Lipophilic (hydrophobic, water insoluble)
• Thyroid hormone
• Steroid hormones
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Types of hormone
Classification
Property
Peptide
Catecholamines
Thyroid
Steriods
Structure
amino acids
tyrosine
derivative
iodinated
tyrosine
cholesterol
derivative
Solubility
hydrophilic
lipophobic
hydrophilic
lipophobic
lipophilic
hydrophobic
lipophilic
hydrophobic
Synthesis
in ER
in cytosol
organelles
intracell
Storage
granules
granules
colloid
lipd droplets
Secretion
exocytosis
of granules
exocytosis
of granules
endocytosis
of colloid
diffusion
Blood
Transport
free hormone
plasma bound
plasma bound
plasma bound
Receptors
on cell surface
on cell surface
inside cell
inside cell
Hormone
hypothalamic,
pituitary, pineal,
pancreas,
parathyroid, GIT,
kidney, liver, heart
adrenal medulla
thyroid
follicular
adrenal cortex
gonads, Vit D
Steroid hormone
Synthesis
female sex
hormone
male sex
hormone
adrenal cortex
hormone
-
adrenal cortex
hormone
female sex
hormone
steroid hormones derived from cholesterol
are small lipid-soluble molecules
diffuse throw cell membrane
receptor is intracellular
7
Steroid hormone
Synthesis
All steroid hormones are produced via cholesterol modification
Extracellular Receptors
Receptors
• all cells maybe exposed to
hormones via circulation
ion channel
• only cells with receptors
for hormone can respond
enzyme
• extracellular chemical
(hormone) binds to
receptor
• receptor activation alters
– channel function
– second-messenger
systems
change in
ion flow
(e.g. Na,
Ca, K, Cl)
Increased
product signal
(eg cAMP)
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Intracellular/Nuclear Receptors
Receptors
• steroid receptors bind
steroid hormone
• hormone-receptor complex
becomes a transcription
factor (alters gene
transcription)
• each steroid receptor binds
a unique DNA sequence
(response element within
an enhancer region)
plasma
protein
carrier
oestrogen
oestrogen receptor
protein
synthesis
mRNA
transcription
trans
loca
tion
• this alters the rate of
transcription
Receptor Regulation
Receptors
• target cell may be unresponsive due to lack of
receptors (physiological, genetic, disease)
• one hormone can influence activity of another hormone
by regulation of its receptor:
Permissiveness
– one hormone is required for another hormone to work
Synergism
– actions of several hormones are complimentary
– combined effect is greater than sum of separate effects
Antagonism
– one hormone inhibits another hormone’s receptors
– reduces effectiveness of second hormone
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Steroid hormone receptors
Receptors
• Type I receptors
– Sex hormone receptors
• Androgen receptor
• Estrogen receptor
• Progesterone receptor
– Glucocorticoid receptor
– Mineralocorticoid receptor
• Type II receptors (No HSP association)
– Vitamin A receptor (vitamin A)
– Vitamin D receptor (vitamin D)
– Retinoid receptor
– Thyroid hormone receptor
Types of Endocrine Glands
Endocrine System
– Derived from
epithelial tissue
– Primary endocrine
organs
– Secondary
endocrine organs
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Primary & Secondary Endocrine Glands
Endocrine System
endocrine glands are composed
of clumps of secretory cells of
epithelial origin
surrounded by capillaries
(fenestrated)
unlike exocrine glands, endocrine
glands have no duct system
endocrine glands may exist in
discrete organs - pituitary, thyroid,
parathyroid, adrenal and pineal
glands
ENDOCRINE SECRETION
AS PRIMARY FUNCTION
- Pituitary gland
- Adrenal glands
- Thyroid gland
- Parathyroid glands
- Pineal gland
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Hypothalamus
Thymus
Pancreas
Gonads
Kidney
Heart
Adipose tissue
Endocrine System
Endocrine System
Overall functions
– regulate organic metabolism
– controls water and electrolyte balance
– induces adaptive changes to help cope with
stress
– promotes smooth, growth and development
– controls reproduction
– regulates red blood cell production
– controls circulation, digestion, absorption of food
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Hormone Signalling
Endocrine System
Hormones secreted by endocrine gland cells
• enter blood and distributed throughout body
• can act at distant target sites
Hormone secretion by endocrine glands triggered by
many signals:
• Insulin secretion regulated by blood glucose conc
• Secretion of sex hormones from ovaries and testes
controlled by anterior pituitary hormones
• Oxytocin secretion from posterior pituitary
regulated by neurotransmitter release
Hormone Concentrations
Endocrine System
• plasma conc. of hormones is controlled by rate of
secretion
• secretory output of endocrine cells controlled by
– neural input
– another hormone
• plasma conc. also influenced by
– rate of removal from blood by metabolism and
excretion
– rate of activation or its extent of binding to
plasma proteins
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Endocrine Dysfunction: Hyposecretion
Endocrine System
Primary hyposecretion
• due to abnormality within gland
• causes
–
–
–
–
–
–
–
genetic
dietary (eg lack of iodine)
chemical or toxic
immunologic (autoimmune diseases)
cancer
Iatrogenic (eg surgical removal)
idiopathic (unknown)
Secondary hyposecretion
• deficiency of tropic hormone
Endocrine Dysfunction: Hypersecretion
Endocrine System
• Causes
– Tumours continuously secrete hormone
– Immunologic factors
• Primary hypersecretion
– too much hormone secreted due to
abnormality within gland
• Secondary hypersecretion
– excessive stimulation of gland causes
oversecretion
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Tropic Hormones
Endocrine System
• regulates secretion of other hormones
• stimulates/maintains endocrine target tissues
• example
– Thyroid-stimulating hormone (TSH)
– secreted from anterior pituitary
– stimulates thyroid hormone secretion from
thyroid gland
– maintains structural integrity of thyroid gland
Control by Feedback Mechanisms
Endocrine System
Gland 1
-
Positive Feedback
e.g. Hormone 3 activates
Gland 2
Hormone 1
Gland 2
Negative Feedback
Hormone 2
e.g. Hormone 3 inhibits
Gland 1
Gland 3
+
Hormone 3
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