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Anatomy and Physiology
Unit 5
Sophie Bevan
•
‘The same state’
• Equilibrium
• Negative feedback
Homeostasis
• The way your body attempts to maintain
constant internal conditions in an everchanging external environment.
Objectives
• Make your own notes on the regulation
of the following for your assignment
- Blood Glucose Regulation
- Heart Rate Regulation
- Respiratory rate Regulation
• Body Temperature Regulation
Body Temperature Regulation
• Hypothermia
• Hyperthermia
• Negative feedback
• ……Thermoregulation!
Body Temperature Regulation
• Body temperature is regulated by
negative feedback in order to keep the
body in homeostasis
_______________ normal level
(body in equilibrium)
What happens if you are too
cold?
Cold
Thermoreceptors
Skin and blood vessels
Hypothalamus
Shivering
Vasoconstriction
What happens if you are too hot?
Hot
Thermoreceptors
Skin and blood vessels
Hypothalamus
Hairs flatten
Sweat
Spread out Vasoconstriction
RESPONSES TO COLD
• Standing outside in underwear in a January snow storm
drops your skin temperature quickly. This stimulates skin
cold receptors (increase in their activity) and cools the
blood flowing into the skin.
• These signals are received by both the hypothalamic
thermostat and higher cortical centers. The thermostat is
also activated by the change in blood temperature. It
initiates responses that promote heat gain and inhibits
centers that promote heat loss.
• The activation of Sympathetic Centers results in several
responses including 1) Norepinephrine release from
sympathetic fibers constricts skin vessels. 2) Brown fat
(found in infants and some animals) oxidation increases
causing thermogenesis. 3) Piloerection, occurs which traps
air close to skin. 4) Epinephrine secretion from adrenal
medulla increases thermogenesis.
• A Shivering Center in the hypothalamus is
also activated which activates the
Brainstem Motor Centers to initiate
involuntary contraction of skeletal muscles
causing shivering, which generates heat.
• Cold also activates some compensatory
behavioral responses including huddling,
voluntary physical activity (hand rubbing,
pacing), sheltering next to a heat source
and wearing warm clothing. Voluntary or
semivoluntary behaviors in response to
cold are activated by the higher brain
centers, mainly the cortex and limbic
system.
When the environmental temperature decreases
gradually (ex. summer to fall), the hypothalamus
releases Thyrotropin Releasing Hormone which
activates the anterior pituitary gland to release
Thyroid Stimulating Hormone (TSH). TSH induces
the thyroid gland to liberate large amounts of
thyroid hormone (T3 and T4) into the blood.
Thyroid hormone increases metabolic rate, which
increases the amount of body heat production. As
the body gets warmer, the hypothalamic sensors
detect the warmth and diminish the heat producing
and heat loss prevention responses.
RESPONSES TO HEAT
When the body is exposed to heat
(sun,fire, too much clothing), body
temperature rises. Skin warmth
receptors and blood convey these
changes to the hypothalamic
thermostat.
• The thermostat inhibits the adrenergic
activity of the sympathetic nervous
system, which control vasoconstriction and
metabolic rate, thus causing cutaneous
vasodilation and reducing BMR
• This causes an increase in heat loss via the
skin and a decrease in heat production in
the core. If the heat is sufficiently
intense, the cholinergic sympathetic
fibers, which innervate sweat glands
release ACh, stimulating sweat
Sweating is the most effective involuntary
heat fighting response in man.
Behavioral responses to heat, such as
lethargy, resting or lying down with limbs
spread out, decreases heat production and
increases heat loss.
Wearing loose and light clothing, fanning and
drinking cold drinks also helps with heat
loss.