The active principles of the endocrine glands are called hormones.
Hormones are specific chemical substances discharged directly into the blood.
The blood distributes the hormones through out the body.
Coordinating systems of human body.
Science of Endocrinology
What is a hormone? Salient features.
Chemical classes of hormones
Mechanism of hormone action
Endocrine disrupting chemicals.
Regulating the rate
Maintaining the constancy of
Of physiological processes
Dual role of nerve cells
Conduction of nerve impulses – as neurons
Secretion of neuro-humors - as endocrine cells
The science dealing with the chemical
integration of the physiological functions
of an organism.
The science of Endocrinology was born
through the experiments of Bayliss and
Starling(1902 to 1905).
Pende introduced the term
‘Endocrinology’ (Greek, endon=within;
krinein= to separate).
Exocrine glands or glands
with duct or Glands of
external secretion e.g.
Endocrine glands or ductless
glands or Glands of internal
secretion e.g. pituitary gland
The active principles of the endocrine
glands are called hormones.
Hormones are specific chemical
substances discharged directly into the
The blood distributes the hormones
through out the body.
But hormones produce specific
physiological effect on certain target
A hormone is a regulatory
chemical that is secreted into
the blood by an endocrine
•The word hormone is
derived from the Greek
word ‘hormon’ which
means ‘to excite’.Bayliss
and Starling in 1905 coined
the term’ hormone’.
of endocrine glands
products of nerve
cells and released
Neurohumorsproducts of nerve
cells and released
Parahormonesproducts of dead or
injured tissue e.g.
Hormones are low molecular weight
They are secreted in trace amounts in
response to specific secretary stimuli .
They are soluble in water and act as
A single hormone have multiple effects
on a single target tissue or on several
Hormones have high degree of action
They are not species specific and nonantigenic.
They are inactivated as soon as their
functions are over.
Endocrine glands are under the control
• Secreted by gland cells of
• Adrenaline, ADH
• Secreted by glands
derived from coelomic
• Corticosteroids, estrogens,
• Hormones made up of
amino acids and
• Thyroxine, calcitonin, STH
Steroid hormones are formed from
They are lipid-soluble hydrophobic
They are secreted by the
gonads, adrenal cortex and placenta.
aldosterone, cotisol, estrogen, testostero
ne and progesterone.
Peptide hormones are short chains of
They are water-soluble.
They are secreted by pituitary and
E.g. oxytocin, vasopressin, calcitonin,
They are derived from the amino acid
They are secreted from the thyroid and
the adrenal medulla.
• Hormones activate or inhibit
enzyme systems e.g phosporylase
• Insulin promote transfer of
• Ecdysone causes puffing of
Humoral signal-secretion depend upon the
level of blood ions and nutrients. E.g. insulin
production controlled by blood glucose.
Neuronal signal- secretion depend on
nerve impulses-stimulation of symphathetic
nervous system release catecholamines
Hormonal signal- some hormones control
the release of hormones from another
endocrine tissue-hypothalamus hormones.
Plasma concentrations of
Neurons & mental activity
e.g. light, temperature
The production of a hormone by an
endocrine gland is controlled by its
A reciprocal relationship exists between
the blood level of a hormone and rate of
its synthesis and secretion.
Feedback mechanisms help in
maintaining homeostasis within the
This concept is proposed by Moore and
Price in 1932.
It is a two-way communication between
the endocrine gland and the target
It is a self-balancing mechanism.
In a negative feedback system, a gland
is sensitive to the concentration of the
substance it regulates.
When the concentration of the
regulated substance reaches a certain
threshold level, it inhibits the gland from
secreting more hormone until the
concentration returns to normal.
Neurons in the hypothalamus
secrete thyroid releasing
hormone (TRH), which
stimulates the anterior
pituitary to secrete thyroidstimulating hormone (TSH).
TSH stimulates the synthesis
and secretion of thyroid
When blood levels of thyroid
hormones increase above a
certain threshold, TRHsecreting neurons in the
hypothalamus are inhibited
and stop secreting TRH. This is
an example of "negative
The increased activity of an endocrine
gland is followed by stimulation.
Positive feedback is not common.
E.g. action of oxytocin on uterine muscle
during child birth. Loop stops when baby
leaves birth canal.
Positive feedback is easily observed
under experimental conditions e.g.
muscular injection of estrogen in female
Hormones are normally present in blood
Steroid and thyroid hormones bind to
transport proteins in the plasma.
Amines and peptide hormones are
hydrophilic and mix easily with blood
Unbound hormones have shorter half life
and bound hormones exhibit longer half
life. Transport proteins protect circulating
Hormones activate only those cells that
have receptors for them.
Hormone receptors are located on plasma
membrane, in the cytoplasm or in the
Hormone – receptor interactions exhibit
specificity and saturation.
Protein hormones react with receptors on
the surface of the cell. Steroid hormones
react with receptor sites inside a cell.
control of metabolic
function can lead to
cascade or step-bystep amplification.
• Regulate body fluid composition
• Rate of gaseous exchange
• Activity of cardiovascular system
• Supports the role of nervous system
• Influences embryonic development
• Certain hormones require the presence of another hormone for the
expression of their activity.
EDCs are both natural or man-made
chemicals that may mimic or interfere
with the function of hormones in the
Environmental endocrine disrupting
chemicals include persistent organic
pollutants (POPs) such as pesticides
(DDT), dioxins, polychlorinated
biphenyls(PCBs) and plasticizers
Endocrine disruption is an important
public health concern.
EDCs produce adverse developmental,
reproductive, neurological and immune
effects in both humans and wildlife.
In humans, EDCs may cause:
Reduce male fertility
Induce abnormalities in male reproductive organs
Cause reproductive diseases in females
Neuro-developmental disorders in children
Dr.B.Victor is a highly experienced postgraduate
professor, recently retired from the reputed
educational institution - St. Xavier’ s College,
He was the dean of sciences and assistant controller
He has more than 32 years of teaching and research
He has taught a diversity of courses ranging from
pre- university to post graduate classes.
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