Lecture Homeostasis Homeostasis Homeostasis can be defined as staying the same or maintaining a dynamic equilibrium involving environmental forces that might change the internal environment of an organism except for the organism's internal control mechanisms that act against the change. Homeostasis involves negative feedback mechanisms. When blood sugar levels drop in between eating the pancreas secretes a second hormone, glucagon which causes adipose tissue to break down fat and the liver to convert glycogen to glucose. Thus blood sugar is in homeostasis due to the negative feedback provided by the two hormones. Body temperature can be ectothermic where temperature originates with the external environment or endothermic where temperature originates within the body of the organism.
Humans are endothermic.
A fever breaks when the set point is changed back to the original temperature and the pyrogens are broken down. Acclimatization allows people to adjust to living or working under high temperatures, e.g. in deep mines. Osmoregulation in freshwater fish is accomplished by secreting a dilute urine in large amounts and actively transporting salt from the environment by salt glands located on the gills. Saltwater fish secrete a concentrated urine that is high in salt and secrete slat from the body to the surrounding water. Terrestrial animals have to replenish water and get rid of waste materials in the blood that include ammonia, urea and uric acid.