Positive Feedback Loop
EXAMPLE 1: Childbirth
Labor: rhythmic contractions in the uterus that start childbirth
(Stage 1) Dilation: opening of the cervix (lower end of uterus)
(Stage 2) Expulsion: baby is delivered
(Stage 3) Delivery of the Placenta: placenta detaches from uterus
Watch the video to see how Positive Feedback takes place in labor.
EXAMPLE 1: Childbirth
Labor: rhythmic contractions in the uterus that start childbirth
(Stage 1) Dilation: opening of the cervix (lower end of uterus)
(Stage 2) Expulsion: baby is delivered
(Stage 3) Delivery of the Placenta: placenta detaches from uterus
Watch the video to see how Positive Feedback takes place in labor.
EXAMPLE 2: Lactation: production of mother's milk
for example: mammals
1. Newborn suckles on mother's breast
Post pregnancy changes the mother's Estrodiol levels
2. All this sends messages to the hypothalamus (homeostasis maintaining portion of the brain) to release Prolactin (a growth hormone produced by the Anterior Pituitary Gland).
3. This stimulates mammary glands to produce milk.
4. The cycle continues whenever the newborn suckles for milk.
(photos/videos for this example are not available on this website)
Negative Feedback Loop
EXAMPLE 1: Temperature Regulation: ability to control heat loss and gain
heat transfers from high temperature-----> low temperature
for example: "warm blooded" animals such as land animals and birds
All three forms are very similar and follow a basic cycle:
Behavior
1. Environment becomes colder
2. Nervous System detects a drop in the animal's body temperature and stimulates the muscles to shiver, producing metabolic heat.
3. Animal's body temperature increases
4. Nervous System detects a healthy body temperature and sends signals to the muscle to return to its normal state.
for example: mammals
1. Newborn suckles on mother's breast
Post pregnancy changes the mother's Estrodiol levels
2. All this sends messages to the hypothalamus (homeostasis maintaining portion of the brain) to release Prolactin (a growth hormone produced by the Anterior Pituitary Gland).
3. This stimulates mammary glands to produce milk.
4. The cycle continues whenever the newborn suckles for milk.
(photos/videos for this example are not available on this website)
Negative Feedback Loop
EXAMPLE 1: Temperature Regulation: ability to control heat loss and gain
heat transfers from high temperature-----> low temperature
for example: "warm blooded" animals such as land animals and birds
All three forms are very similar and follow a basic cycle:
Behavior
1. Environment becomes colder
2. Nervous System detects a drop in the animal's body temperature and stimulates the muscles to shiver, producing metabolic heat.
3. Animal's body temperature increases
4. Nervous System detects a healthy body temperature and sends signals to the muscle to return to its normal state.
Insulation
1. Environment becomes colder
2. Nervous System detects a drop in the animal's body temperature and stimulates the skin to raise fur, trapping an air layer and strengthening the fur's insulation
3. Animal's body temperature increases
4. Nervous System detects a healthy body temperature and sends signals to the skin to return to its normal state.
Evaporation
1. Environment becomes warmer
2. Nervous System detects an increase in the animal's body temperature and stimulates the skin to release sweat, moistening the skin and enhancing evaporation.
3. The sweat absorbs heat and carries it away with evaporation, causing a decrease in body temperature.
4. Nervous System detects a healthy body temperature and sends signals to the skin to return to its normal state.
EXAMPLE 2: Operons: form of gene regulation; set of genes and switches
RNA Polymerase: transcribes new RNA
Promoter: binding site of RNA
Operator: binding sit of repressor
Regulator Gene: codes for repressor
Repressible (Tryptophan) Operon: stays on until activated by the repressor
1. Environment becomes colder
2. Nervous System detects a drop in the animal's body temperature and stimulates the skin to raise fur, trapping an air layer and strengthening the fur's insulation
3. Animal's body temperature increases
4. Nervous System detects a healthy body temperature and sends signals to the skin to return to its normal state.
Evaporation
1. Environment becomes warmer
2. Nervous System detects an increase in the animal's body temperature and stimulates the skin to release sweat, moistening the skin and enhancing evaporation.
3. The sweat absorbs heat and carries it away with evaporation, causing a decrease in body temperature.
4. Nervous System detects a healthy body temperature and sends signals to the skin to return to its normal state.
EXAMPLE 2: Operons: form of gene regulation; set of genes and switches
RNA Polymerase: transcribes new RNA
Promoter: binding site of RNA
Operator: binding sit of repressor
Regulator Gene: codes for repressor
Repressible (Tryptophan) Operon: stays on until activated by the repressor
Inducible (Lac) Operon: repressor inactivated by the inducer in order to continue transcription
Alteration in Feedback Loop has Harmful Consequences
Type 1 Diabetes: does not produce insulin needed to break down glucose
Type 2 Diabetes: target cells do not respond to insulin
EXAMPLE: Diabetes Mellitus: caused by lack of insulin
1. Glucose levels rise
2. Enzymes lack the metabolism needed to handle the increase
3. The enzymes break down fat as a substrate in order to undergo cellular respiration
4. Acidic metabolites form and accumulate in the patient's bloodstream
Consequences
1. Blood pH lowers to a life threatening level
2. Kidneys can not reabsorb all of the glucose, so remaining glucose is excreted through an excessive amount of pee.
Type 1 Diabetes: does not produce insulin needed to break down glucose
Type 2 Diabetes: target cells do not respond to insulin
EXAMPLE: Diabetes Mellitus: caused by lack of insulin
1. Glucose levels rise
2. Enzymes lack the metabolism needed to handle the increase
3. The enzymes break down fat as a substrate in order to undergo cellular respiration
4. Acidic metabolites form and accumulate in the patient's bloodstream
Consequences
1. Blood pH lowers to a life threatening level
2. Kidneys can not reabsorb all of the glucose, so remaining glucose is excreted through an excessive amount of pee.