Homeostasis scenarios.docx



1. Imagine you are stranded in a small boat on the Pacific Ocean. You’re thirsty, but your options are quite limited. You vaguely remember someone telling you not to drink seawater but can’t remember why. You also have one small can of Red Bull, a diuretic energy drink. a. Which option(s) could make you dehydrated? Why? The diuretic Red Bull would dehydrate you because a diuretic is a substance that signals to your urinary system to release urine. If you lose that urine, there is less available water for reabsorption, which would quickly reduce the amount of water to hydrate cells throughout your body. The sea water would cause the concentration of salt in your bloodstream to increase. This, in turn, would cause cells in contact with blood to release water into the bloodstream. Eventually, you will urinate more, causing dehydration. b. How is this scenario similar to the Eggs-periment? (Use “hypertonic” and/or “hypotonic” in your answer.)In the Eggs-periment, you placed an egg with the shell removed in a solution of corn syrup. Both the corn syrup solution and the seawater are hypertonic solutions, relative to the cells that they surround. In the eggs-periment, the cell is the single chicken egg. In the seawater scenario, the cells are all the cells of your body. Since these solutions are hypertonic there is a higher concentration of solute outside of the cells than inside the cells so water will move down its concentration gradient, causing it to leave the cell. This makes the cells lose mass and shrink in both cases. c. You quickly become dehydrated. How do your nervous, endocrine, and urinary systems cooperate to detect and decrease your dehydration? (See “Careful Coordination” essay on p 261-264 if you get stuck.)Your nervous system first needs to detect dehydration. The sensory neurons of your hypothalamus detect an increased sodium (salt) concentration in your blood. Once your nervous system knows there is more sodium in your blood, the hypothalamus causes your pituitary gland (part of the endocrine system) to release a hormone called vasopressin. Vasopressin is carried in the blood stream to other parts of your body, including your kidneys (urinary system). Your kidney cells have receptors for vasopressin, and when the hormones reach those receptors, your kidneys respond. The response is that the membranes of the kidney tubules become more permeable to water, allowing for more reabsorption of water to be used by the body. This is the same effect as an anti-diuretic, making the dehydration less severe. 2. A friend of yours, Jenny, has been experiencing flu-like symptoms (headaches, runny nose, fever, vomiting, and cough). She remembers that her mom put penicillin tablets in the medicine cabinet from a time when she was sick before. Jenny has heard about penicillin being used for different kinds of problems and figures if she takes the antibiotic, it will have to make her better. a. What advice would you give Jenny about her choice to take penicillin? Why?Jenny should not take the penicillin. Penicillin is an antibiotic, and antibiotics are only effective against bacteria. Jenny has the flu, which is caused by a virus. Viruses are not alive, and thus cannot be killed by antibiotics. b. Jenny’s fever is an attempt by her body to defend itself against some pathogen. Would this be an example of positive or negative feedback. Why?This would be positive feedback. Your body has a normal temperature range (close to 37 degrees Celsius), but in this case, your body responds to a stimulus (infection by pathogen) by pushing the temperature beyond its normal range. The high temperature could cause some of the pathogens to die (pathogens also need certain conditions to function properly). It is not normal to have a fever. c. Jenny starts to think that maybe whatever she has is NOT the flu because she remembers getting a flu shot last year. Can Jenny be sure that this is not the flu? Why or why not?Jenny cannot be sure that her illness is not the flu. The influenza virus evolves at a rapid rate, and every year, pharmaceutical (drug) companies create a new vaccine which targets the flu virus that they think will be prevalent and that many people may be exposed to. However, there is a chance that Jenny has been infected with a strain that has evolved from the prevalent strain from last year and that is not recognizable to Jenny’s immune system. 3. Joseph goes swimming with a group of friends but forgets to bring a change of dry clothes. The sun is starting to set, the temperature is falling, and his clothes are still very wet. Joseph becomes hypothermic.a. What is an example of a behavioral response that Joseph may attempt to raise his temperature?Behavioral responses are outwardly observable – some behaviors are done consciously and some are not. Joseph may rub his shoulders to increase his temperature. Joseph may try drying his clothes (using a towel). Joseph may walk into a room with a heating system or go into a bed with blankets. There are many possible behavioral responses Joseph could have to raise his temperature. Joseph may also shiver (contract the muscles) to warm the body, which is an involuntary behavioral response.b. What is an example of a physiological response that will occur as a result of these stimuli?Physiological responses are automatic and internal. Joseph’s blood vessels to his extremities will constrict (get smaller) so more blood can remain in his core to keep his vital organs functioning. c. Describe how your answer from part b demonstrates negative feedback.Your cells ideally need to be in contact with blood in the circulatory system so that they can receive fresh oxygen and release waste. They also need to be within a specific temperature range in order to function properly. The reason why some parts of the body (fingers, toes, arms, legs, etc.) do not get normal blood supply is to conserve heat for your body as a whole. The sensory neurons of your hypothalamus detect the decrease in temperature (hypothermia). Once your nervous system knows the body is too cold, the hypothalamus sends signals to constrict the blood vessels in the extremities to make sure that the most essential parts of the body (such as vital organs in the body’s core) can continue to function. Once Joseph goes back to a warm environment, those constricted vessels can dilate again, restoring blood flow to the cells of your extremities. d. What body systems are affected by Joseph’s hypothermia?Circulatory, nervous, and respiratory systems are affected. (Also muscular)4. Kristen has a pretty severe allergy to peanuts and noticed that her allergy can affect her even when she’s being careful about what she eats. Kristen goes to Five Guys for lunch with her friends, and she notices her eyes begin to produce excessive tears almost immediately. a. Is Kristen’s crying an example of the specific or nonspecific immune system at work? This is tricky. There are elements of specific and nonspecific responses at work. Crying is a nonspecific immune response. Nonspecific immune responses do not recognize one specific type of pathogen; rather they are general defenses that offer protection against a number of pathogens. Tears contain enzymes which are useful to fight against a number of different pathogens. Other nonspecific defenses include skin/hair/nails, mucus, “good” bacteria on the skin, saliva, and sweat. Kristen is having an allergic reaction, which is a specific response, when she cries. A person with allergies has antibodies against something that is not necessarily harmful (like food, insect venom, animal dander and pollen). Once the antibodies in Kristen’s body recognize peanut antigens, it causes a reaction that leads to histamines being released. These histamines lead to swelling, sneezing, crying, and itching. b. What simple remedy would you recommend for Kristen’s problem? (leaving the restaurant is not an option)Kristen could take an anti-histamine (like Benadryl, Zyrtec, Claritin, etc.) to counteract the histamines that are causing her symptoms. Kristen’s friend Kenny offers her some french fries while she waits for her burger. After eating a couple of fries, she notices a sign “Fries are cooked in 100% peanut oil.” She spits out what is in her mouth, but already, she notices that it becoming more difficult to breathe. c. Describe how the circulatory, respiratory, and nervous systems cooperate to restore homeostasis while she waits to receive medical attention. This scenario is similar to the exercise lab you did in class. Kristen’s airway is more constricted than normal, which reduces the amount of oxygen she can inhale when she breathes. This leads to an increase in carbon dioxide concentration in her blood, lowering the blood pH. The nervous system detects this decreased pH, signaling to the lungs and diaphragm to contract (your breathing rate increases). This, in turn, causes your heart to pump blood to other parts of the body at a higher rate, in an attempt to bring the blood pH back to its normal range. Once your nervous systems detects the normal pH, your breathing rate goes back to normal, as well. ................
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