Circulating levels of glucose are
controlled by two enzymes, insulin and glucagon. As shown in the diagram, when the blood
glucose level is high (mainly occurs after eating), the pancreas releases
insulin, causing the liver to take up glucose and store it as glycogen and the
body cells to take up more glucose, which in the end should lower the blood
glucose level. When the blood glucose level is low, the pancreas releases
glucagon and the liver breaks down glycogen into glucose, which in the end
should raise the blood glucose level.
Thermoregulation
(body temperature homeostasis) refers to the process of keeping the internal
body environment in a steady state, when the external environment is changed.
As shown in the diagram, when the internal body temperature rises above normal,
thermoregulation in the brain is activated, causing sweat glands to secrete
sweat that evaporates, eventually cooling the body, or blood vessels in the
skin to dilate, allowing heat to escape, which should allow the internal body
temperature to decrease. When the internal body temperature falls below normal,
thermoregulation in the brain is activated, causing skeletal muscles to rapidly
contract, causing shivering, which eventually generates heat and blood vessels
in the skin to constrict, minimizing heat loss, which should allow the internal
body temperature to increase.
