Enrico Tiepolo
Hypothalamus - integrated vegetative controls
The hypothalamus in the central hub for all general homoeostatic controls.
It governs visceral and vegetative functions through
the regulation (via neural paths) of the activity of the
autonomic nervous system and the control (via
liberins) of endocrine system. (It can be defined as a
crossroad between nervous system and endocrine system)
This may not be enough to grant appropriate
homoeostatic and/or anticipatory adaptation, so it
also generates motivational drives for voluntary
behaviours. When it is really cold we usually wear a
sweater or look for a place in the sun, when it is really
warm we usually take off the sweater or go into the
shade. So, it is not sufficient to simply regulate the
visceral and vegetative aspects. Think of glucose, we
regulate glucose, but if we do not have glucose in the
body, we have to gather it. So, we have to stand up,
go collect and then eat some food.
The interesting aspect is that even the simplest homeostatic regulations require enacting appropriate
behaviors in addition to a series of internal controls. This suggests that the hypothalamus, in addition to
regulating whatever it can regulate on its own, will be able to generate behavioral drives that
make us perform the actions that allow us to maintain homeostasis.
The hypothalamus is comprised of many nuclei with complex topology and nomenclature. However, its
main functions can be summarized in a relatively simple way:
- Temperature:
o anterior portion of the hypothalamus (preoptic area) → response to heat → activation
of parasympathetic
o posterior regions → shivering and response to cold → activation of sympathetic
- Wakefulness:
o posterior regions → promotes wakefulness (contain histaminergic neurons that project
to the thalamus)
o anterior portion → promotes sleep (GABAergic neurons that depress the histaminergic
ones)
- GI and feeding:
o lateral hypothalamus: hunger centre and related behavioral responses
o ventromedial nucleus: satiety centre
176 Body At Work II
, Enrico Tiepolo
o anterior arcuate nucleus: increase/decrease appetite. It’s very important as it is a
regulation center that receives different signals and tries to coordinate them. For
example:
§ Hunger stimuli: hypoglycemia, raphe nuclei, lack of glucose
§ Satiety stimuli: distension of the stomach (sensed by vagus), release of
cholecystokinin (released by duodenum).
§ Also purely neural stimuli can reach the arcuate nucleus, such as smelling food,
or seeing someone eating.
o mammillary bodies: feeding reflexes
- Body water:
o lateral hypothalamus: thirst centre
o ADH release from supraoptic nuclei (magnocellular) in response to thirst
- Cardio-vascular:
o posterior / lateral hypothalamus: increase in arterial pressure + heart rate
o preoptic area: decrease heart rate and arterial pressure
- Endocrine functions:
o parvocellular neurons in anterior (supraoptic) region
§ paraventricular nucleus (PVN): TRH, CRH, SST
§ medial preoptic nucleus: GnRH
o parvocellular neurons in middle, tuberal region:
§ Arcuate nucleus: GHRH, PIF (prolactin inhibiting factor: DA)
o magnocellular neurons in anterior (supraoptic) region
§ paraventricular nucleus (PVN), supraoptic nucleus : oxytocin, AVP
- Behavioural responses:
o lateral hypothalamus → thirst + eating + activity (rage and fighting)
o ventromedial nucleus and surrounding areas: opposite to the above
o most anterior and most posterior portions: sexual drive and behaviours
Body Temperature
Body temperature should not exceed the limits 36 to 38 °C (97 to 101 °F). In order to maintain core
body (brain and internal thoracic & abdominal) temperature within this range, it must be possible to
disperse heat to the environment; thus, the maximum tolerable external temperature is in the order 54
°C in dry air, but only 35 °C in water, as heat exchange in
water is very effective. When heavily exercising or working,
the maximum tolerable temperature falls down to some 32
°C. Similarly, the capability of producing and dispersing heat
is limited, so a very low temperature cannot be tolerated very
long without protection, and 20-30 min in iced water are
sufficient to be lethal.
The temperature can be quite significantly lower in limbs and
extremities than in the core (typically down to 25 °C, which
is the minimum core temperature compatible with life).
The hypothalamus is in charge of temperature
regulation, and the input for such regulation is sensory
information from peripheral thermoceptors combined with
thermoceptors present in the hypothalamus itself.
Body temperature can be raised by either decreasing heat dispersion or increasing heat
production:
• Heat dispersion can typically be decreased by reducing the temperature of the
skin, which is obtained by producing peripheral (cutaneous) vasoconstriction.
Obviously, it can also be decreased by moving to a warmer place or putting on some warm
clothes
• Heat production can be increased by increasing any energy transformation
process:
® Shivering, i.e., useless muscular activity that produces heat
177 Body At Work II
Hypothalamus - integrated vegetative controls
The hypothalamus in the central hub for all general homoeostatic controls.
It governs visceral and vegetative functions through
the regulation (via neural paths) of the activity of the
autonomic nervous system and the control (via
liberins) of endocrine system. (It can be defined as a
crossroad between nervous system and endocrine system)
This may not be enough to grant appropriate
homoeostatic and/or anticipatory adaptation, so it
also generates motivational drives for voluntary
behaviours. When it is really cold we usually wear a
sweater or look for a place in the sun, when it is really
warm we usually take off the sweater or go into the
shade. So, it is not sufficient to simply regulate the
visceral and vegetative aspects. Think of glucose, we
regulate glucose, but if we do not have glucose in the
body, we have to gather it. So, we have to stand up,
go collect and then eat some food.
The interesting aspect is that even the simplest homeostatic regulations require enacting appropriate
behaviors in addition to a series of internal controls. This suggests that the hypothalamus, in addition to
regulating whatever it can regulate on its own, will be able to generate behavioral drives that
make us perform the actions that allow us to maintain homeostasis.
The hypothalamus is comprised of many nuclei with complex topology and nomenclature. However, its
main functions can be summarized in a relatively simple way:
- Temperature:
o anterior portion of the hypothalamus (preoptic area) → response to heat → activation
of parasympathetic
o posterior regions → shivering and response to cold → activation of sympathetic
- Wakefulness:
o posterior regions → promotes wakefulness (contain histaminergic neurons that project
to the thalamus)
o anterior portion → promotes sleep (GABAergic neurons that depress the histaminergic
ones)
- GI and feeding:
o lateral hypothalamus: hunger centre and related behavioral responses
o ventromedial nucleus: satiety centre
176 Body At Work II
, Enrico Tiepolo
o anterior arcuate nucleus: increase/decrease appetite. It’s very important as it is a
regulation center that receives different signals and tries to coordinate them. For
example:
§ Hunger stimuli: hypoglycemia, raphe nuclei, lack of glucose
§ Satiety stimuli: distension of the stomach (sensed by vagus), release of
cholecystokinin (released by duodenum).
§ Also purely neural stimuli can reach the arcuate nucleus, such as smelling food,
or seeing someone eating.
o mammillary bodies: feeding reflexes
- Body water:
o lateral hypothalamus: thirst centre
o ADH release from supraoptic nuclei (magnocellular) in response to thirst
- Cardio-vascular:
o posterior / lateral hypothalamus: increase in arterial pressure + heart rate
o preoptic area: decrease heart rate and arterial pressure
- Endocrine functions:
o parvocellular neurons in anterior (supraoptic) region
§ paraventricular nucleus (PVN): TRH, CRH, SST
§ medial preoptic nucleus: GnRH
o parvocellular neurons in middle, tuberal region:
§ Arcuate nucleus: GHRH, PIF (prolactin inhibiting factor: DA)
o magnocellular neurons in anterior (supraoptic) region
§ paraventricular nucleus (PVN), supraoptic nucleus : oxytocin, AVP
- Behavioural responses:
o lateral hypothalamus → thirst + eating + activity (rage and fighting)
o ventromedial nucleus and surrounding areas: opposite to the above
o most anterior and most posterior portions: sexual drive and behaviours
Body Temperature
Body temperature should not exceed the limits 36 to 38 °C (97 to 101 °F). In order to maintain core
body (brain and internal thoracic & abdominal) temperature within this range, it must be possible to
disperse heat to the environment; thus, the maximum tolerable external temperature is in the order 54
°C in dry air, but only 35 °C in water, as heat exchange in
water is very effective. When heavily exercising or working,
the maximum tolerable temperature falls down to some 32
°C. Similarly, the capability of producing and dispersing heat
is limited, so a very low temperature cannot be tolerated very
long without protection, and 20-30 min in iced water are
sufficient to be lethal.
The temperature can be quite significantly lower in limbs and
extremities than in the core (typically down to 25 °C, which
is the minimum core temperature compatible with life).
The hypothalamus is in charge of temperature
regulation, and the input for such regulation is sensory
information from peripheral thermoceptors combined with
thermoceptors present in the hypothalamus itself.
Body temperature can be raised by either decreasing heat dispersion or increasing heat
production:
• Heat dispersion can typically be decreased by reducing the temperature of the
skin, which is obtained by producing peripheral (cutaneous) vasoconstriction.
Obviously, it can also be decreased by moving to a warmer place or putting on some warm
clothes
• Heat production can be increased by increasing any energy transformation
process:
® Shivering, i.e., useless muscular activity that produces heat
177 Body At Work II
