- Positive Feedback
>Example 1:
Onset of labor in childbirth
- once labor begins, local regulators and hormones (estradiol and oxytocin) induce and regulate contractions of the uterus: this action forms a positive-feedback loop with contractions stimulating the secretion of oxytocin, which in turn stimulates further contractions, then causing the actual childbirth
>Example 2:
Lactation in mammals
- unique to mammals
- production of mother's milk
- in response to suckling by the newborn, the hypothalamus in the brain signals the pituitary gland to secrete prolactin, which then stimulates the mammary glands to produce milk
- suckling also stimulates secretion of oxytocin, which triggers release of milk from the mammary glands
- Negative Feedback
>Example 1:
Temperature regulation in animals
- managing state of internal environment is a major challenge for the animal body (maintaining homeostasis)
- an animal is said to be a regulator if it uses internal feedback mechanisms to control internal change in the face of external fluctuation (river otter keeps its body temperature independent from the temperature of the river in which it inhabits)
- an animal is said to be a conformer if it allows internal conditions to change in correlation with the external changes (large-mouth bass conforms to temperature of lake it lives in)
>Example 2:
Plant responses to water limitations
- plants adapted to arid environments complete short life cycles during brief rainy seasons
- another adaptation is CAM plants, which take in carbon dioxide at night instead of during the day (stomata can remain closed then, when water is more likely to evaporate)
- plants also respond to loss of water by closing their stomata as quickly as possible
- Alteration in feedback results in deleterious consequences
Dehydration in response to decreased antidiuretic hormone
- this hormone is made in the hypothalamus: it controls blood pressure through its primary task: conservation of fluids by increasing the permeability of a specific region in the kidney so urine concentration rises and water loss is reduced
- decreased levels of antidiuretic hormone will cause the kidneys to excrete too much water and this high volume of urine will lead to dehydration as well as fall in blood pressure