Human A&PBIO 304 · American River College ← Week 1 pre-work

BIO 304 · Week 1 · Interactive Workbook

Homeostasis & Feedback Loops

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Part 1 of 4 · Recall

Fill in the blanks

Type the term that completes each statement, using the word bank. Pull it from memory first.

Word bank

1 · Stimulus2 · Sensor (receptor)3 · Control centerResponseSet pointNormal rangeBody temperatureBlood glucoseBlood pressureChildbirth (oxytocin)Blood clottingAction potentialDirection of correctionFrequency in the body

  1. a variable moves outside the normal range · body temp rises to 37.8°C
  2. detects the change and reports it · nerve cells in skin and brain
  3. compares incoming value to the set point · hypothalamic temperature center
  4. the variable returns toward set point · body temp drops back to 37°C
  5. the target value the body defends · ~37°C, ~90 mg/dL glucose, pH 7.4
  6. the narrow window around set point where function is preserved
  7. sweating, shivering, vasodilation, vasoconstriction
  8. insulin (after a meal), glucagon (between meals)
  9. baroreceptors → ANS adjusts heart rate & vessel tone
  10. cervical stretch → oxytocin → stronger contractions → more stretch · endpoint: delivery
  11. vessel injury → platelet plug → more platelet recruitment · endpoint: sealed clot
  12. Na+ opens more Na+ channels until peak · endpoint: depolarization
  13. Negative reverses the stimulus. Positive amplifies it.
  14. Negative: nearly every system, all day. Positive: a handful of moments.

Define it: high-yield vocabulary

Write a clear definition in your own words for each term.

  1. Homeostasis
  2. Set point
  3. Stimulus
  4. Receptor
  5. Control center
  6. Effector
  7. Negative feedback
  8. Positive feedback

Part 2 of 4 · Anatomy lab

Draw and label

Box A. Negative feedback loop (generic)

Directions

  1. Draw 5 boxes arranged in a circle, connected by arrows clockwise.
  2. Box 1: Stimulus (a change away from setpoint). Box 2: Sensor (detects the change). Box 3: Control center (compares to setpoint, decides action). Box 4: Effector (produces the response). Box 5: Response (returns variable toward setpoint).
  3. Draw an arrow from Box 5 back to Box 1 with a minus sign. Label it Negative feedback: response opposes the original change.
  4. At the center of the loop, write Setpoint and one example variable (e.g., body temperature, blood glucose, blood pressure).
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Your uploaded drawing for Box A. Negative feedback loop (generic)

Box B. Worked example: body temperature drops

Directions

  1. Use the same 5-box loop. Fill in each box with the body's response to cold.
  2. Stimulus: cold environment, body temperature drops below 37 C.
  3. Sensor: thermoreceptors in skin and hypothalamus.
  4. Control center: hypothalamus.
  5. Effector: name at least two (e.g., skeletal muscles, smooth muscle in blood vessels, arrector pili muscles).
  6. Response: shivering, vasoconstriction, piloerection, behavioral changes. Body temperature rises back toward 37 C.
  7. On the side, draw a small box labeled Positive feedback. Inside, name one example (childbirth, blood clotting, action potential firing). Note the arrow has a PLUS sign.
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Your uploaded drawing for Box B. Worked example: body temperature drops

Structures to label

Label each on your drawing.

  1. Stimulus
  2. Sensor (receptor)
  3. Control center
  4. Effector
  5. Response
  6. Setpoint
  7. Negative feedback
  8. Positive feedback
  9. Hypothalamus
  10. Thermoreceptor
  11. Shivering
  12. Vasoconstriction

Part 3 of 4 · Physiology lab

Reason it through

A. Trace: blood glucose rises after a meal

Explain the main idea of this topic.

B. Synthesis

1. Distinguish negative feedback from positive feedback in one sentence each. Why is negative feedback used for most homeostatic variables but positive feedback used for childbirth?
2. Type 1 diabetes destroys the beta cells of the pancreas. Walk through the blood-glucose loop and explain what happens after a meal in a patient with untreated Type 1 diabetes.
3. A fever is a temporary upward reset of the hypothalamic setpoint. Predict what a febrile patient will FEEL at the moment the setpoint resets to 39 C, and explain why they shiver even though their body temperature is technically high.

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