Download File - E - Physiology

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DR. JITENDRA PATEL (MBBS, MD)
Medical Educator & Researcher
Assistant Professor, Department of Physiology
Email: [email protected] Web: www.esphys.weebly.com
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OUTLINE
 A Role of hypothalamus
 Post. Pituitary Hormones
 Physiological Action
 Regulation of main Hormones
 Applied Aspect
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Posterior Pituitary Hormones
 Antidiuretic hormone (ADH) / Vasopressin
 Oxytocin (OTC)
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The ADH
 Antidiuretic hormone, as the name indicates,
prevents diuresis and is chiefly concerned
with the conservation of body water.
 Since it also causes vasoconstriction, it is
also called vasopressin or more precisely
arginine vasopressin.
Synthesis
 ADH as well as OTC are synthesized in the cell bodies
of magnocellular neurons of both paraventricular
and supraoptic nuclei of the hypothalamus.
 However,
contains
supraoptic
ADH
nucleus
forming
predominately
neurons
while
paraventricular nucleus contains mainly the OTC
synthesizing neurons.
Storage
 The axons of ADH and OTC synthesizing
neurons end in the posterior pituitary gland as
terminal swelling.
 The secretory granules containing hormone
precursors, known as Herring bodies, are
transported down the axons by axoplasmic flow
to the nerve endings in the posterior pituitary.
Receptors
 V1–A receptors:
These are involved in the vasoconstrictor effect of
ADH.
 V1–B receptors:
These are involved in the action of ADH on the
anterior pituitary.
 V2 receptors:
These are involved in the action of ADH on kidney.
Actions of ADH
 Action on kidney:
The main role of ADH is regulation of water
balance in the body by acting on the kidney (DCT,
CD), where it decreases the excretion of free
water i.e. antidiuretic and concentrating effect on
kidney (Through Aquaporins channel).
Actions of ADH…
 Vasoconstrictor effect:
Antidiuretic hormone in large doses
cause vasoconstriction and leads to
rise in blood pressure. Haemorrhage is
a potent stimulus to ADH secretion.
Actions of ADH…
 Action on anterior pituitary:
Antidiuretic hormone travels to the
anterior pituitary via the portal veins and
combines with the V1–B receptors (also
called V3 receptors) and causes increased
ACTH secretion from the corticotrophs.
Actions of ADH…
 Action on the liver:
ADH causes glycogenolysis by combining with the V1–A
receptor.
 Action on the brain:
V1–A receptors are also found in brain, where ADH acts
as a neurotransmitter and is involved in memory,
regulation of temperature, regulation of blood
pressure, circadian rhythms and brain development.
Regulation of Secretion
A. Effective osmotic pressure of
plasma or plasma osmolality
B. Changes in blood volume
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Regulation of Secretion…

Other factors affecting ADH secretion:
Stress of pain, chronic emotional stress and surgical
procedures cause increase in ADH secretion, Cortisol and
thyroid hormones release ADH. Some other factors that
increase ADH secretion include nausea, vomiting, standing
posture and cytokines. Elderly individuals secrete more ADH
than do younger individuals.
Adrenaline decreases the ADH, Alcohol reduces ADH
secretion.
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Synthesis
 ADH as well as OTC are synthesized in the cell bodies
of magnocellular neurons of both paraventricular
and supraoptic nuclei of the hypothalamus.
 However,
contains
supraoptic
ADH
nucleus
forming
predominately
neurons
while
paraventricular nucleus contains mainly the OTC
synthesizing neurons.
Storage
 The axons of ADH and OTC synthesizing
neurons end in the posterior pituitary gland as
terminal swelling.
 The secretory granules containing hormone
precursors, known as Herring bodies, are
transported down the axons by axoplasmic flow
to the nerve endings in the posterior pituitary.
Actions of Oxytocin
 Action on breast:
Oxytocin causes contraction of myoepithelial
cells, thus plays an important role in milk
ejection.
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Actions of Oxytocin…
 Action on uterus:
Oxytocin
causes
contraction
of
uterine
smooth muscles, thus plays an important role
during parturition (labour).
Oxytocin also acts on non-pregnant uterus and
facilitates the transport of sperm in the
female genital tract.
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Actions of Oxytocin…
 In males:
The circulating levels of oxytocin increases
during ejaculation, which causes increased
contraction of smooth muscles of vas
deferens and helps in propelling the
sperms towards urethra.
Regulation of Secretion
 Stimuli which increase oxytocin release are:
Oxytocin secretion increases on cholinergic
stimulation
Suckling
stimulates
oxytocin
release (suckling reflex).
Genital tract simulation during coitus and
labour increases oxytocin release.
Regulation of Secretion…
 Factors which decrease oxytocin release
are:
Emotional stress, Sympathetic stimulation,
and Drugs such as ethanol and enkephaline
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“Either be selected or be elected”
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