Biology: Homeostasis Case Studies: Temperature, Glucose, and Water
Analyzing feedback loops that keep internal conditions stable
Biology: Homeostasis Case Studies: Temperature, Glucose, and Water
Analyzing feedback loops that keep internal conditions stable
Biology - Grade 9-12
- 1
A student runs outside on a hot day. Their body temperature rises from 37.0°C to 38.2°C. They begin sweating and blood vessels near the skin widen. Identify the regulated variable, the response, and whether this is negative or positive feedback.
Negative feedback reverses a change away from the set point.
The regulated variable is body temperature. The response is sweating and widening of blood vessels near the skin, which helps release heat. This is negative feedback because the response works to bring body temperature back toward normal. - 2
After sitting in a cold classroom, a student begins to shiver and their skin feels cool. Explain how shivering helps maintain homeostasis.
Shivering helps maintain homeostasis because rapid muscle contractions produce heat. This raises body temperature back toward the normal set point of about 37°C. - 3
A graph shows body temperature increasing from 37°C to 39°C during a fever, then returning to 37°C after several hours. Describe what is happening to the set point during a fever and how that affects body responses.
A fever is different from ordinary overheating because the brain changes the target temperature.
During a fever, the body's temperature set point is temporarily raised. The body may respond as if it is too cold, causing chills or shivering until the higher set point is reached. When the set point returns to normal, sweating may occur to lower temperature back to about 37°C. - 4
A person eats a meal high in carbohydrates. Their blood glucose level rises. Explain the role of insulin in restoring homeostasis.
Focus on what insulin tells cells to do with glucose.
Insulin is released by the pancreas when blood glucose rises. Insulin signals body cells to take in glucose and signals the liver and muscles to store glucose as glycogen. These actions lower blood glucose back toward the normal range. - 5
A person has not eaten for many hours, and their blood glucose level drops. Explain the role of glucagon in restoring homeostasis.
Glucagon is released by the pancreas when blood glucose is low. It signals the liver to break down glycogen into glucose and release glucose into the blood. This raises blood glucose back toward the normal range. - 6
A patient has type 1 diabetes, in which the pancreas produces little or no insulin. After eating a high-carbohydrate meal without taking insulin, predict what will happen to the patient's blood glucose and explain why.
Consider what happens when the signal for glucose uptake is missing.
The patient's blood glucose will remain too high or rise higher than normal. Without enough insulin, many body cells cannot take in glucose effectively, and the liver and muscles do not store glucose as glycogen as efficiently. - 7
Complete the feedback pathway: Blood glucose rises after a meal. The pancreas detects the change. The pancreas releases insulin. Body cells take in glucose and the liver stores glucose. What happens next, and why is this negative feedback?
Next, blood glucose decreases toward the normal range. This is negative feedback because the response reduces the original change, which was the rise in blood glucose. - 8
A student drinks a large bottle of water quickly. Their blood becomes slightly more dilute. Predict how the kidneys help restore water balance.
Extra water in the blood usually means more water can be removed in urine.
The kidneys restore water balance by producing more dilute urine and removing extra water from the body. This helps return the concentration of water and solutes in the blood toward normal. - 9
A person exercises for an hour and sweats heavily but does not drink water. Their blood becomes more concentrated. Explain how the hormone ADH helps maintain homeostasis.
ADH stands for antidiuretic hormone, which reduces water loss in urine.
When the blood becomes more concentrated, more ADH is released. ADH causes the kidneys to reabsorb more water back into the blood, so less water is lost in urine. This helps restore water balance. - 10
A urine sample is very dark yellow and low in volume. Based on homeostasis, what might this indicate about the person's hydration status and ADH level?
This might indicate that the person is dehydrated or has low water intake. Their ADH level is likely high, causing the kidneys to conserve water and produce a small amount of concentrated urine. - 11
Compare temperature regulation and blood glucose regulation. Name one similarity and one difference between the two homeostatic systems.
Think about the variable being controlled and the effectors used.
One similarity is that both systems use negative feedback to return a variable toward a normal range. One difference is that temperature regulation often uses effectors such as sweat glands, blood vessels, and muscles, while blood glucose regulation uses hormones such as insulin and glucagon that act on cells and the liver. - 12
A runner finishes a race. Their body temperature is high, blood glucose is lower than before the race, and they have lost water through sweat. Identify one homeostatic response for each variable.
For high body temperature, the runner may sweat and widen blood vessels near the skin to lose heat. For low blood glucose, the pancreas may release glucagon to raise blood glucose. For water loss, ADH may increase so the kidneys conserve water. - 13
The diagram shows a feedback loop with these steps: stimulus, receptor, control center, effector, response. Use the example of low body temperature to fill in each step.
The hypothalamus is a major control center for body temperature.
The stimulus is a drop in body temperature. Receptors in the skin and brain detect the temperature change. The control center is the hypothalamus in the brain. Effectors include skeletal muscles and blood vessels. The response is shivering and narrowing of skin blood vessels, which helps raise body temperature. - 14
A person with untreated diabetes may have glucose in their urine. Explain why glucose might appear in urine when blood glucose is extremely high.
Kidneys filter blood and normally reabsorb useful molecules, but this process has limits.
Glucose may appear in urine when blood glucose is so high that the kidneys cannot reabsorb all of it. The extra glucose remains in the filtrate and is excreted in urine. - 15
Analyze this case: A hiker is lost in a dry desert for several hours. They are hot, thirsty, sweating less than before, and producing very little urine. Explain how at least two homeostatic systems are responding and why these responses matter.
The hiker's temperature regulation system may reduce sweating to conserve water, although this makes cooling harder. Blood vessels near the skin may still help release heat if possible. The water balance system increases ADH, causing the kidneys to reabsorb more water and produce very little urine. These responses matter because the body must balance cooling with preventing dangerous dehydration.