Question

Negative and positive feedback mechanisms used to maintain homeostasis. Describe one negative and one positive feedback regulation (8pts).

For each negative and positive feedback:

What is the variable? (0.5pt)

What is the normal range? (0.5 pt)

Which conditions may change the variable? (0.5 pt)

How the changes to be detected? (1 pt)

What is/are the responses(s)? (1pt)

What is the final effect? (0.5 pt)

Answer 1

Homeostasis is the stable internal environment that is maintained within the body.Organisms maintain homeostasis by balancing each of the following factors;nutrients,wastes,temperature,the immune system,reproductive cycles.Endotherms are organisms that regulate their temperature internally,while ectotherms regulate their temperature through environment.The term homeostasis was coined by American physiologist Walter Cannon to explain this tendency of the body to maintain stable internal environment.The cells in a body must communicate with each other in order to maintain homeostasis.A set point is the optimal value of a physiological variable.Violations of a body's set point trigger homeostatic responses in the body.In the positive feedback loop,an effector elicits a response to a stimulus,which exaggerates the stimulus.An example of positive feedback is the mechanism for uterine contractions during labor.A negative feed back loop occurs when an effector elicits a response to a stimulus,which removes the stimulus.An example of negative feed back is temperature regulation during labor.Uterine contractions during labor are controlled by a positive feedback mechanism .Distoration of the uterus signals stretch receptors in the uterine wall.In response,the hormone oxytocin,which triggers contractions,is released.As the uterus contracts,more oxytocin is released,causing even more contractions.Until baby is born,contractions are continuously being stimulated by this positive feedback loop.The maintenance of body temperature during exercise,is an example of negative feedback.As the body temperature rises during exercise,the increase in body temperature will be detected by the brain and activate mechanisms to lose heat hence hypothalamus will send signals and central nervous system is signaled to cause vasodilation and warm blood flows closure to the body surface and looses heat to surrounding air.If it is not enough to return to normal body temperature sweating occurs through activation of sweat glands.Sweat causes evaporative cooling and heat from the body is released at the skin's surface.As a result,the body's temperature decreases.When the body's internal temperature returns to normal brain's hypothalamus heat lost centre shut's off through negative feedback.

A baby suckling on the mother's nipple will activate mechanoreceptors in the nipple the receptors will send signals to the brain via neurons and pituitary gland releases two important hormones prolactin and oxytocin.Prolactin is hormone which stimulates milk production in the breast tissue. Oxytocin stimulates smooth muscle contraction of the breast allowing the milk produced to be ejected out of the nipple and is taken by the baby and the whole process continues this is a positive feed back loop because nothing is suppressed and it is amplifying a response in the same direction.