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12h functions of hypothalamus - Coggle Diagram
12h
functions of hypothalamus
1.Autonomic functions
The hypothalamus is described as the head ganglion of the autonomic
nervous system.
Anterior hypothalamus
is the parasympathetic area
It has an excitatory effect on this system.
Posterior hypothalamus
is the sympathetic area
has an excitatory effect on it.
Cardiovascular regulation.
regulates the cardiovascular system through
cardiovascular control centres in the reticular regions of medulla and pons.
Stimulation of posterior and
lateral nuclei of hypothalamus
increases the heart rate and arterial blood pressure and
produces cutaneousvasoconstriction.
Stimulation of preoptic area
decreases the heart rate and arterial blood pressure and
produces cutaneous vasodilatation.
Regulation of pupil size
Stimulation of posterior and
lateral hypothalamus
causes dilatation of pupil
Stimulation of anterior and medial parts of preoptic and supraoptic areas
produce constriction of pupil
Regulation of peristaltic and secretomotor functions of alimentary tract
Stimulation of posterior and
lateral hypothalamus
diminishes the secretion and motility of gastrointestinal tract (ergotropic function).
Stimulation of anterior and
medial hypothalamus
increases peristalsis and secretomotor functions of alimentary tract (trophotropic function).
Endocrinal functions
Control of anterior pituitary.
The hypothalamus controls the functions of anterior pituitary by secreting certain ‘releasing’ and ‘inhibiting’ hormones which reach the
anterior pituitary by a neurovascular link through the tuberoinfundibular tract and hypophyseal portal vessels.
Hypothalamus does the following functions through the releasing hormones:
Controls the metabolism by
controlling thyroid gland.
controls the metabolism of different foodstuffs
and maintains electrolyte balance.
Through its influence over the adrenal cortex,
Keeps the gonads inhibited till the physical growth is complete.
-After physical growth is complete, this inhibition is removed so that gonads
start functioning and gametes are produced (propagation of species).
Gonadal hormones acting on the brain bring about physiological
changes for mating of male and female.
Controls the formation of milk by the breasts
by controlling prolactin secretion.
Regulation of posterior pituitary functions.
The hypothalamus regulates the posterior pituitary functions through the hypothalamic–hypophyseal tract.
Neural control of posterior pituitary with the secretion of antidiuretic hormone (ADH) by the supraoptic and paraventricular nuclei helps in regulation of water balance by controlling water excretion by kidneys.
Regulation of uterine contractility and regulation of milk ejection from the breast.
Stimulation of paraventricular nucleus of hypothalamus causes its cells
to secrete the hormone oxytocin.
-Oxytocin increases the contractility ofuterus.
-It also contracts the myoepithelial cells that surround the alveoli
of breast and cause milk ejection.
-At the end of pregnancy, especially large quantities of oxytocin are secreted.
-Oxytocin helps to promote labour contractions.
When the baby suckles the breast, signals from nipple to hypothalamus
cause reflex oxytocin release which causes expulsion of milk through
nipples.
Regulation of sleep–wake cycle
The hypothalamus plays an important role in sleep–wake cycle:
Anterior hypothalamus is considered a sleep facilitatory centre, as its stimulation leads to sleep.
Posterior hypothalamus acts as waking centre, as its stimulation causes wakefulness.
Sleep is also considered to occur as a
negative phenomenon
, i.e. inhibition of wakefulness centre in the posterior hypothalamus by the anterior hypothalamus also contributes to occurrence of sleep.
Lesions in the posterior hypothalamus produce severe coma.
stimulation of Anterior hypothalamus
& inhibition posterior hypothalamus
(of wakefulness centre)
causes sleep
stimulation of Posterior hypothalamus
causes wakefulness
lesions of posterior hypothalamus
produce severe coma
Control of circadian rhythm
Circadian rhythm refers to **rhythmic fluctuations in certain physiological
parameters of the body**.
-These are called circadian rhythms because they often show 24-h cycles (circadian around a day).
-Many of the rhythms are coordinated with each other.
The circadian rhythms are internally driven.
-The suprachiasmatic nuclei of hypothalamus is the main site of most circadian rhythms in the body.
-These are believed to contain the ‘biological clock’, which regulates the
circadian rhythm according to the 24-h light–dark cycles.
The suprachiasmatic nuclei receive important inputs from the eyes via
retinohypothalamic fibres and the lateral geniculate nuclei.
suprachiasmatic nuclei
main site of most circadian rhythms in the body.
contain the ‘biological clock’, which regulates the
circadian rhythm according to the 24-h light–dark cycles.
receive important inputs from the
eyes
via
-retinohypothalamic fibres and
-the lateral geniculate nuclei.
5.Regulation of food intake
The regulation of food intake is an essential vegetative function of the hypothalamus which maintains the body weight of an individual
relatively constant over a long period.
To regulate the food intake, hypothalamus has 2 centres,
-the feeding centre and
-satiety centre located
in the tuberal region.
Feeding centre
The
lateral hypothalamic nucleus
serves as the
-feeding centre or hunger centre.
When this is stimulated, in animals it creates a sensation of hunger and leads to increased food intake
(hyperphagic).
This causes obesity.
The destruction of feeding centre leads to loss of appetite
(anorexia)
.
Normally, the feeding centre is always active and its activity is inhibited by satiety centre after food intake.
Satiety centre
Satiety is opposite to hunger, i.e. it is a feeling of fulfilment after food intake.
The
ventromedial nucleus
of hypothalamus acts as satiety centre.
Stimulation of this in animals causes sensation of food intake (fulfilment).
Destruction of satiety centre leads to
hyperphagia.
hyperphagia
caused by:
stimulation of feeding center- lateral hypothalamic nucleus
destruction of satiety center- ventromedial nucleus
hypothesis of regulation of food intake:
Glucostatic theory,
Lipostatic theory,
Gut peptide theory and
Thermostatic theory.
The balanced activity of
satiety and feeding centres
is responsible for
the normal food intake.
Role of neurotransmitters in food intake.
food intake increased
by the stimulation of α2-adrenergic receptors in
medial hypothalamus and
centrally acting opioids.
Food intake is decreased
by the stimulation of β-adrenergic and
dopaminergic in lateral hypothalamus and
by stimulation of serotonergic pathways.
Role of hypothalamic peptides.
increase the food intake
Principal hypothalamic polypeptides
(-neuropeptide Y,
-orexin-A and
-orexin-B,
-melanin-concentrating hormone (MCH) and
-ghrelin)
decrease food intake
α MSH,
CART (cocaine- and amphetamine-regulated transcript)
6.Regulation of sexual behaviour and reproduction
In animals, the hypothalamus plays an important role in maintaining the sexual function, especially in females. A decorticate female animal will have regular oestrous cycle provided the hypothalamus is intact.
A pathway of sex regulation has been identified as amygdala—stria
terminalis–preoptic area–tuberal region of hypothalamus.
The
tuberal region
of hypothalamus
maintains the basal secretion of gonadotropin- releasing hormone (GnRH)
, and its connection with the preoptic area is essential for the cyclical surge of gonadotropin before ovulation.
7.Role in emotional and instinctual behaviour
is mainly regulated by
limbic cortex.
The hypothalamus along with the limbic structures is concerned
with affective nature of sensory impulses,
i.e. whether the sensations are pleasant or unpleasant.
These affective qualities are also called a reward and punishment.
The two centres in hypothalamus involved in such a behaviour and
emotional changes are called reward centre and punishment centre.
Reward and punishment centres
reward centre
is located along the course of medial forebrain bundle,
especially in lateral and ventromedial nucleus of hypothalamus.
Electrical stimulation of this area encourages the animal to seek more of such stimulation.
punishment centre
is located in medial hypothalamus (periventricular zone).
The electrical stimulation of this area leads to pain, fear,
defence, escape reactions and the other elements of punishment.
-The experimental animal avoids further stimulation of this area.
Rage
Strong stimulation of punishment centres produces a violent and aggressive emotional state called rage.
Normally, it is kept in check by counterbalancing activity
-of ventromedial nuclei of hypothalamus,
-hippocampus, amygdala and
-anterior portion of limbic cortex.
Rage reaction is characterized by:
Development of a defence posture,
Extension of limbs,
Lifting of tail,
Hissing and splitting,
Piloerection,
Wide opening of eyes,
Dilation of pupil and
Severe savage attack, even on mild provocation.
Role of reward and punishment centres.
Almost anything that we do is related in some way to reward and punishment.
If we do something that is rewarding, we continue to do it. If we do something that is punishing, we cease to do it.
Therefore, reward and punishment centres constitute one of the most
important of all the controllers of our bodily activities,
our drives, our aversions and our motivation.
Sensory experience that is causing
neither reward nor punishment
-this type of sensory experience
is remembered hardly at all;
-the animal becomes habituated to such
sensory experience and then ignores it.
-But when the sensory experience causes either reward or punishment, the cortical response becomes
progressively more and more intense.
Thus, reward and punishment centres help in selecting the
information that we learn.
Role in regulation of body temperature
The hypothalamus acts as a principal integrating centre for heat regulation.
By adjusting a balance between heat production and heat loss, it helps to maintain body temperature at 37°C.
Hypothalamus accomplishes this function by two centres:
Heat loss centre
Anterior hypothalamus
, especially
preoptic area
, acts as heat loss centre.
Increase in the temperature of blood flowing through this area increases the activity of temperature-sensitive neurons which results
in cutaneous vasodilatation and increased sweating causing more heat loss.
Lesions of anterior hypothalamus abolish the physiological response to heat exposure.
Heat gain centre
The posterior hypothalamus
acts as
a heat gain centre.
Electrical stimulation of posterior hypothalamus results in cutaneous vasoconstriction and shivering.
A lesion of the posterior hypothalamus abolishes not only body response to cold but to heat as well,
because this area is the final integration
centre for all thermoregulatory signals.
Final efferent signals for heat production or heat loss emerge from the posterior hypothalamus.
9.Role in regulation of water balance
Hypothalamus regulates the water balance of the body by 2 mechanisms:
-Through
thirst centre by controlling water intake and
osmoreceptors in supraoptic nucleus by controlling water loss.
Through thirst centre
Thirst centre located in the lateral nucleus of hypothalamus
is stimulated by plasma hypertonicity
(which occurs when the water
content of the body is reduced).
This causes intense desire for water and
the animal drinks large quantities of water.
It has been observed that:
Discrete lesions of thirst centre abolishes fluid intake and the animal dies of dehydration.
Electrical stimulation of this area in conscious animals (through chronically implanted electrodes) causes the animal to drink water as long as the stimulation continues.
Injection of hypertonic saline in this area induces the animal to drink large amount of water.
However, injection of isotonic saline, distilled
water and even hypertonic urea do not induce drinking.
These experiments suggest that the thirst centre
-
monitors plasma osmolality
-
and is separate from the osmoreceptors involved in ADH release.
Further, it has been observed that the sensation of thirst is satisfied simply by the act of drinking,
even before sufficient water is absorbed
from the gastrointestinal tract to correct the plasma osmolality. Oropharyngeal and upper gastrointestinal receptors appear to be involved in this response.
However, relief of the thirst sensation via
these receptors is short lived.
Thirst is completely satisfied only when
the plasma osmolality, blood volume and arterial pressure are corrected.
Through osmoreceptors in supraoptic nucleus.
The increased plasma osmolality also stimulates osmoreceptors in supraoptic nucleus.
The stimulated neurons of supraoptic nucleus in turn send impulses to posterior pituitary gland to secrete hormone ADH.
This hormone reaches the kidney tubules through blood and causes increased absorption of water from the collecting ducts of the kidneys.
Thus, water loss is decreased.
When body has excess water, exactly opposite events occur.
Other factors regulating water intake include:
Parandial drinking
: Increased intake of liquids during eating is considered to be learned or a habit, but it may be associated with:
Increased plasma osmolality occurring due to absorption of food and
Action of certain GIT hormone
If protein intake is high
, the metabolic products of protein cause osmotic diuresis;
therefore, to maintain water balance, intake of water increases.
Psychological factors
also play an important role in water intake.
It has been observed that in patients of psychosis or some hypothalamic disease,
dehydration causes hypernatremia, but they cannot increase their water intake on stimulation of thirst centre.
Local factors
.- Dryness of the pharyngeal mucus membrane causes sensation of thirst.
Dehydrated animals, such as dogs and cats, can drink lots of water to make up the water deficit but stop drinking even before the water is absorbed and plasma osmolality is still higher.
This observation suggests that some gastrointestinal metering mechanism is also involved.