Search for notes by fellow students, in your own course and all over the country.
Browse our notes for titles which look like what you need, you can preview any of the notes via a sample of the contents. After you're happy these are the notes you're after simply pop them into your shopping cart.
Document Preview
Extracts from the notes are below, to see the PDF you'll receive please use the links above
The hypothalamus
• The hypothalamus is the part of the
diencephalon which forms the floor and part of
the lateral wall of the third ventricle
...
• It is connected to the pituitary gland by the
pituitary stalk (hypophyseal stalk)
...
Anatomical
and
Functional
Connection
Between the
Hypothalamu
s and
Pituitary
(hypothalamohypophyseal
portal system
and tract)
• The hypothalamus controls the secretion of
hormones from the anterior and posterior
pituitary glands
...
• That is why the hypothalamus is considered by
many authors as “the control center” of the
endocrine system
...
• It also receives signals from the sensory
reticular formation of the brainstem, the retina,
through the retinohypothalamic tract and the
thalamus
...
• Accordingly, the hypothalamus can sense a
wide variety of signals, i
...
nervous chemical,
or physical
...
neocortex
Reituclar
activating
substance
Sleep/
wake
Thalamus
Limbic
system
pain
Emotion, fright,
rage, smell
Heat regulation
(temperature)
Water balance (blood
volume, intake--thirst,
output—urine volume)
Energy
regulation
(hunger,
BMI)
Optical
system
vision
Autonomic
regulation
(blood pressure
etc)
Regulation
of
Hypothalamus
Metabolic rate, stress
response, growth,
reproduction, lactation)
posterior
pituitary
hormones
Anterior
pituitary
hormones
• As the hypothalamus is connected to the
limbic-system and cerebral cortex, its secretion
of hormones is influenced by psychological
conditions and emotions
...
g
...
Hypothalamic control of anterior pituitary
secretions
• Some nuclei of the hypothalamus contain
neurosccretory cells which produce releasing or
inhibiting hormones
...
• The secretory hypothalamic cells are grouped
together in an area called “the hypophysiotropic
area”
...
e
...
• The releasing and inhibiting’ hormones are
packaged in secretory vesicles which move
inside the hypothalamic neurons by
axoplasmic flow to their terminals in the
median eminence where they are released
...
Hypothalamus and anterior pituitary
Midsagital view
illustrates
parvicellular
neurosecretory
cells secrete
releasing factors
into capillaries of
the pituitary
portal system at
the median
eminence which
are then
transported to the
anterior pituitary
gland to regulate
the secretion of
pituitary
• The release of the anterior pituitary hormones
is controlled mainly by their hypothalamic
releasing hormones, except prolactin hormone
whose release is controlled mainly by its
hypothalamic inhibiting hormone PIH
(dopamine)
...
• If the anterior pituitary is damaged or
separated from the hypothalamus by cutting
the pituitaiy stalk, the secretion of all the
anterior pituitary hormones is markedly
decreased except prolactin secretion which
increases
...
e
...
• Both hormones are made in the hypothalamus
...
• The axons of these neurons make the
hypothalamo-hypophysial tract, and their
terminals make the posterior pituitary gland
...
e
...
• Both hormones are made in both the
supraoptic and paraventricular nuclei, but most
of the ADH (85%) is made in the supraoptic
nucleus, whilst most of the oxytocin (85%) is
made in the paraventricular nucleus
...
• Each precursor molecule consists of a
nonapeptide’ which is the hormone itself
(ADH or oxytocin) joined to another
polypeptide
called
“neurophysin”
(neurophysin-l in case of oxytocin, and
neurophysin-II in case of ADH)
...
The
vesicles are transported along the axons of the
magnocellular cells by axonal flow down to
the nerve terminals in the posterior pituitary
where they are stored
...
• The hormone and the neurophysin are secreted
from the nerve terminal by exocytosis on the
arrival of a nerve impulse
...
• The function of the neurophysins is so far
unknown
...
• It is connected with the hypothalamus by the
pituitary stalk (hypophyseal stalk)
...
Location of the Pituitary
• Developmentally, the posterior pituitary arises
from an evagination from the floor of the third
ventricle of the brain
...
• Because of its neural origin, the posterior
pituitary
is
also
“called the neurohypophysis”
...
• This evagination makes a structure called
Rathke ‘s pouch, the pouch is then separated
and comes close to the posterior pituitary to
make the anterior and intermediate lobes
...
• The intermediate lobe regresses and becomes
rudimentary in humans
...
The posterior pituitary gland
(Neurohypophysis)
The posterior pituitary gland secretes two
hormones, i
...
the antidiuretic hormone (ADH)
and oxytocin
...
It is formed in the hypothalamus but secreted
from the posterior pituitary
...
Actions of the antidiuretic hormone
• Water retention (antidiuresis):
• By acting on the V2 receptors in the distal
convoluted tubules and collecting ducts of the
kidney
...
• The urine volume decreases and its osmolality
increases because reabsorption of water occurs in
excess to reabsorption of salt
...
• In the absence of ADH, the volume of urine
markedly increases, and its tonicity markedly
decreases
...
• ADH acts on the vIA receptors on the smooth
muscles of the vascular wall —> vasoconstriction
— elevation of arterial blood pressure
...
• The vasoconstriction it produces is severe,
involving all the vessels, even the coronaries
...
This action is carried out through the VIB
receptors
...
The vasopressin V2
agonist desmopressin is used to treat certain types
of hemophilia (type I Von Willebrand disease)
...
Control of ADH secretion
• There is a basal ADH secretion which is sufficient
to act on the kidney to conserve water without any
vasopressor effect
...
It is inactivated by the
liver and Kidney
...
Plasma hypertonicity: This is the principal
physiological stimulus for ADH secretion
...
Hypertonicity stimulates osmoreceptors
of the OVLT (organum vasculosum of lamina
terminalis in the anterior hypothalamus
...
• 2
...
• Marked hypovolemia leads to hypotension
...
• (b) Release of renin from the kidney —
formation of angiotensin II- which stimulates
the OVLT in the anterior hypothalamus—
stimulation of the magnocellular neurons —
release of the ADH
...
• This decrease does not usually occur under
physiological conditions
...
Severe
hypovolemia is a powerful stimulus which
releases
large
amounts
of
ADH:
Other less important factors that stimulate the
release of ADH include: Pain, emotions, stress,
exercise, nausea, vomiting, nicotine, and
morphine
...
Plasma hypotonicity
2
...
Alcohol
Disorders of ADH secretion
• Excess ADH secretion
• The syndrome of inappropriate secretion of
ADH (SIADH)
• SIADH has a wide variety of causes and is
very common
...
Chest
diseases:
Bronchocarcinoma,
tuberculosis, emphysema, bronchial asthma,
artificial ventilation
...
Intracranial diseases: Brain tumors,
meningitis, hemorrhage, acute psychosis
• 3
...
• 4
...
• A mild form of SIADH occurs after general
anesthesia, that is why fluid administration is
restricted in the first 24 hours after surgery
...
• Mild cases could be asymptomatic, but in
severe cases symptoms of water intoxication
and hyponatremia appear
...
Treatment of SIADH
• 1
...
Only 500 -800 mL of
water
are
allowed
per
day
...
Concentrated
saline
furosemide as diuretic
...
• There are two types of DI, depending on the
underlying cause:
• 1
...
This is due to damage of the
supraoptic and paraventricular nuclei of the
hypothalamus by tumors or trauma
...
• 2
...
This
is due to either a congenital defect in V2
receptors or following hypercalcemia,
hypokalemia, or treatment with lithium in
cases of manic depression
...
Manifestations
• 1
...
e
...
Urine volume could go up to 23
L/day (normal 1
...
• 2
...
e
...
• In the presence of polyuria, polydipsia is life
saving
...
If thirst sensation is suppressed for any
reason and water is taken blindly to substitute the
lost water, dehydration or overhydration can
rapidly develop which could be fatal
...
So, it
produces antidiuresis without vasoconstriction
...
Oxytocin
• Oxytocin is one of the two hormones formed
in the hypothalamus but secreted from the
posterior pituitary, the other being the ADH
...
Contraction of the myoepithelial cells
around the mammary ducts —> squeezing of
the preformed milk — ejection of milk out
through the nipple
...
Contraction of the myometrium of the
pregnant uterus
...
• Oxytocin facilitates and accelerates delivery of
the baby during labor, but delivery can occur
in its absence
...
Contraction of the myometrium of the non
pregnant uterus during sexual intercourse —
special coordinated uterine contractions which
help the transport of sperms up in the uterus
and the uterine tubes for fertilizing the ovum
...
Induction of luteolysis (degeneration of the
corpus luteum)
...
•
• 5
...
• This stimulates contractions of the smooth
muscles of the vas deferens which helps
emission of semen
...
Tactile stimulation of the nipple and
areola of the breast, e
...
during suckling by the
baby
...
Sexual excitement, e
...
tactile stimulation
of the genitalia
...
Emotions, e
...
milk ejection might occur
when a lactating mother hears the crying of her
baby, calling for his meal
...
Stretch of the uterine cervix, as occurs
during labor
...
Fear
...
Pain
...
Alcohol
There are no known syndromes which result
from hypo- or hypersecretion of oxytocin in
humans