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BI 4: Feedback Mechanisms

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Kimberly Christian

on 13 March 2017

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Transcript of BI 4: Feedback Mechanisms


Identify one specific example of a disruption in your body's homeostasis. How is your body programmed to respond?
Homeostasis & Feedback
maintenance of a stable internal environment despite environmental changes
any deviation from a homeostatic state (caused internally or externally)
coordination of body systems meant to return to homeostasis
body's reaction to disruption; moderated by feedback mechanism
Types of
Feedback Mechanisms

mechanism whereby response is meant to DECREASE the initial disruption

mechanism whereby response is meant to INCREASE the initial disruption
Feedback in Biological Systems
feedback mechanisms can be used to moderate any level of the structural hierarchy of life
chemical: regulation of blood pH
cellular: moderation of ATP production during exercise
organismal: endothermic body temperature regulation
ecological: balance of predator/prey
In humans, feedback generally relies on two body systems:
endocrine system: composed of glands that produce chemical hormones which travel in bloodstream to communicate between organs
nervous system: network of specialized neurons (nerve cells) that receive, process, and transmit messages via electrical impulses
Feedback in Organisms
to maintain homeostasis, organisms must be able to receive information from the environment and coordinate and carry out an appropriate reaction
1. stimulus: environmental change or signal
2. receptor: organ that receives information from environment
3. integrating center: organ that coordinates stimulus with relevant response
4. effector: organ that carries out reaction
5. response: body's reaction to stimulus meant to maintain homeostasis
Illustrate how your home heating and cooling system works using the five feedback terms:
integrating system
Does this example illustrate positive or negative feedback?
Negative Feedback
mechanisms maintain dynamic homeostasis by returning the changing condition back to its target set point
Temperature Regulation in Humans
disruption: body temperature INCREASES
feedback: hypothalamus (in brain) activates cooling response
skin capillaries dilate (increase blood flow to skin)
sweat glands activate driving evaporative cooling
response: body temperature drops
disruption: body temperature DECREASES
feedback: hypothalamus activates warming response
skin blood vessels constrict (reduce blood flow to skin)
shivering of skeletal muscle generates heat
response: body temperature increases
Lactose Digestion in E. coli
disruption: lactose levels increase
feedback: repressor is inactivated; lac operon is read; proteins for lactose digestion are produced
response: lactose levels decrease
Positive Feedback
mechanisms amplify responses moving system further from initial target set point (away from homeostasis)
Malfunctions in Feedback
alteration in the mechanisms of feedback often results in negative consequences
Onset of Labor in Humans
disruption: oxytocin release (from pituitary) triggered by thinning of cervix (opening to uterus)
feedback: uterine contractions are triggered; baby moves further into birth canal; oxytocin production increases
response: baby is delivered
Ripening of Fruit
disruption: fruit starts producing ethylene gas (hormone)
feedback: cellulose begins to breakdown; ethylene production increases in fruit and nearby fruit
response: fruit ripens faster
Diabetes: Imbalance in Blood Glucose
ADH Deficiency: Failure in Osmoregulation
disruption: blood glucose increases after eating a meal
feedback: pancreas produces insulin; liver converts and stores glucose as glycogen
response: blood glucose decreases
pancreas fails to produce insulin; blood glucose cannot be regulated
disruption: blood becomes more concentrated due to decrease in water
feedback: pituitary releases antidiuretic hormone (ADH); kidneys increase reabsorption of water from urine
response: water is conserved; urine becomes more concentrated
lack of ADH decreases water reabsorption, accelerates dehydration
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