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 ever- changing 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

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.