Question

HOMEOSTATIC REGULATION: Choose 3 different parameters and describe the negative feedback loop for each one, including the type of message and the final effect that occurs at the target cell. (*You must do at least one from each type of message)

Answer 1

There are two feedback mechanisms in our body to maintain and control all physiological processes.They are called positive and negative feedback mechanisms.Homeostatic processes are regulated by negative feedback and so these systems occur commonly within the body.In negetive feedback mechanism a response that is the reverse of the change is detected and it functions to reduce the change.A change in condition is recognized by a receptor and an effector activates to induce an opposite effect thus maintains equilibrium.
First example in negetive feedback loop is thermoregulation.Thermoregulation is a process to maintain its internal temperature.This mechanism returns your body to homeostasis.A person has a body temperature between 37°C to 37.8°C.But if the temperature falls below 35°C ,then it is a condition called hypothermia and its a serious condition that may cause brain damage or cardiac arrest or if its higher as 42°C,then causes brain damage.Factors that may cause these changes are fever,drug use,metabolic conditions etc.So any change in internal temperature the thermoreceptors senses and send signal to hypothalamus and it sends signals to muscles ,organs,glands and nervous system to bring down the temperature if its high.The mechanisms to reduce temperature includes sweating and vasodilation.The sweat glands releases sweat and as it evapourates body starts cooling down.Vasodilation is when the blood vessels under the skin increases blood flow to the skin to cool down the inner body.This helps to release heat out of the body.If the body heat is low then the mechanisms to warm up the body occurs through vasoconstriction,thermogenesis,hormonal thermogenesis.Vasoconstriction is narrowing of bllod vessels under the skin to reduce blood flow to skin,so that heat rstains inside the body.Thermogenesis is creating heat by the organs or muscles by methods like shivering.Hormonal thermogenesis is by releasing hormones from thyroid glands and increases available enrgy by changes in appetite,pulse,fat build up etc.

Second example of negetive feedback mechanism is Blood sugar regulation.When we have a meal, a negative feedback mechanism controls the sugar levels in our blood. The sugar is found in the body as glucose.The body absorbs the glucose from the bloodstream and increases the concentration of glucose.The G-protein-coupled receptors signals the hypothalamus and it stimulates pancreas to release a chemical called insulin.This helps the muscle cells and liver cells to uptake the glucose.Liver stores the extra glucose as glycogen and muscle cells uses glucose for muscle contraction or stores as ATP.Thus the concentration of glucose is maintained in normal levels.When glucose level is low then the insulin production cuts off and the stored glucose is released in to the blood .A blood sugar less than 140 mg/dL is normal and is maintained by negetive feedback mechanism.

Third example is blood calcium level regulation.Normal blood calcium level is 8.5 to 10.3mg/dL.The parathyroid glands regulates the levels of calcium in the blood. If calcium decreases,a class C G-protein coupled receptor called calcium sensing receptor sends signal to parathyroid glands and sense the decrease.It secretes a hormone called parathyroid hormone. The parathyroid hormone stimulates release of calcium from bones and increases uptake of the calcium into the bloodstream from the collecting tubules in the kidneys.Osteoclasts releasescalcium from bones. If blood calcium increases, there is reduction in parathyroid hormonal prodution.Thyroid gland produces calcitonin hormone so that calcium reabsorption from kidneys is decreased.Osteoclasts activity reduced or inhibited.Thus maintaining homeostasis. These responses are negative feedback loop because the effects are -ve to the stimuli.