1. Homeostasis and Feedback Loops
Keeping it stable

2. Your group will be assigned a feedback loop present in the human body.
On your white board complete the following:
What is the homeostasis point for your feedback loop?
Identify whether it is negative feedback or positive feedback. Justify your response
Fill in the parts of the feedback loop using the organizer. (Stimulus, Receptor, Control Center, Effector, Response)
Identify what body systems are involved/interact in this feedback loop.
What are the consequences if this feedback loop does not work as it should?
Directions

3. Temperature: Cold Stimulus: Response: Receptor: Control Center:
Effector:
Response:
Temperature: Cold
The body temperature drops when going outside during a snowstorm. Cold Thermoreceptors are triggered and send a message to the hypothalamus in the brain. The brain will stimulate the muscles in our body to contract and cause shivering. The brain will also stimulate dermal (skin) blood vessels to constrict which decreases blood flow to the skin which in turn reduces the amount of heat loss through the skin. As a result of the these changes body temperature increases.

4. Temperature: Hot Stimulus: Response: Receptor: Control Center:
Effector:
Response:
Temperature: Hot
The body temperature increases when stepping outside of your air conditioned house on a hot summer day. Heat Thermoreceptors are triggered and send a message to the hypothalamus in the brain. The brain will stimulate the sweat glands to release sweat which will evaporate and pull heat away from the body. The brain will also stimulate dermal (skin) blood vessels to dilate to which increases blood flow which in turn increases the amount of heat loss through the skin as sweat evaporates. As a result of the these changes body temperature decreases.

5. Blood pressure Stimulus: Response: Receptor: Control Center: Effector:
In the example of blood pressure increasing due to stress, Baroreceptors in blood vessels detect the change in blood pressure and send a message to the brain. The brain will cause the heart to beat slower and thus decrease the blood pressure. Decreasing the heart rate results in decrease blood pressure.

6. Carbon Dioxide Stimulus: Response: Receptor: Control Center: Effector:
When we exercise our muscles give off carbon dioxide as waste. This increases the level of carbon dioxide in the blood. Chemoreceptors in arteries sense the change in carbon dioxide blood levels and send a message to the brain. The brain stimulates the lungs to increase respiration. This results in less carbon dioxide in the blood.

7. Childbirth Stimulus: Response: Receptor: Control Center: Effector:
During childbirth the contractions are initiated as the baby moves into position, stretching the cervix beyond its normal position. The feedback increases the strength and frequency of the contractions until the baby is born. After birth, the stretching stops and the loop is interrupted.

8. Lactation Stimulus: Response: Receptor: Control Center: Effector:
During lactation a mother produces milk for her infant. During pregnancy, levels of the hormone prolactin increase. Prolactin normally stimulates milk production, but during pregnancy, progesterone inhibits milk production. At birth, when the placenta is released from the uterus, progesterone levels drop. As a result, milk production surges. As the baby feeds, its suckling stimulates the breast, promoting further release of prolactin, resulting in yet more milk production. This positive feedback ensures the baby has sufficient milk during feeding. When the baby is weaned and no longer nurses from the mother, stimulation ceases and prolactin in the mother’s blood reverts to pre-breastfeeding levels. 

9. Blood Clotting Stimulus: Response: Receptor: Control Center: Effector:
When tissue is torn or injured, a chemical is released. This chemical causes platelets in the blood to activate. Once these platelets have activated, they release a chemical which signals more platelets to activate, until the wound is clotted.

10. Osmoregulation (non human ex.)
Stimulus:
Receptor:
Control Center:
Effector:
Response:
Osmoregulation (non human ex.)
The concentration of salt in the water surrounding the fish is much higher than that of the liquid in the fish. This water enters the fish diffusion through the gills, through food consumption, and through drinking. Also, because the concentration of salt is higher outside than inside the fish, there is passive diffusion of salt into the fish and water out of the fish. The salt concentration is then too high in the fish, and salt ions must be released through excretion. This occurs via the skin, and in very concentrated urine. In addition, high salt levels in the blood are removed via active transport by the chloride secretory cells in the gills. The correct salt concentration is thus maintained.

11. Blood Glucose Levels Stimulus: Response: Receptor: Control Center:
Effector:
Response:
Blood Glucose Levels
After you have eaten a meal, the blood glucose levels will begin to rise because the carbohydrates in the food are digested and absorbed. This rise is detected by beta cells, which then will produce more insulin. This insulin then binds to receptor proteins in cell membranes (particularly in the liver). This causes more protein channels to open so that more glucose can enter the cell. As well as this, insulin encourages enzymes to convert glucose to glycogen (glycogenesis) for storage.

12. Fever Stimulus: Response: Receptor: Control Center: Effector:
Fever occurs when the hypothalamus raises the body's temperature to a new set point. White blood cells called monocyte-macrophages release proteins called pyrogens when the cells encounter pathogenic microorganisms. The pyrogens act on the hypothalamus, causing it to reset the body's "thermostat" upward. The vessels that supply the skin with blood often narrow as the body's temperature is rising. This process, which is called vasoconstriction, reduces sweating and causes the body to retain more heat than it loses. Vasoconstriction in the skin and extremities allows the body to move blood toward its core, which increases the rate of metabolism and induces shivering. The chills that often accompany a fever are caused by this movement of blood to the body's core, which leaves the skin surface and extremities relatively cool. When the infection or disease process resolves, the hypothalamus attempts to reset the body'sthermoregulation at its normal set point. The body's cooling mechanisms switch on as the blood returns to the extremities and skin surface, and sweating occurs.