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Human A&P BIO 304 · American River College ← Course home (Week 1)

BIO 304 . WEEK 1 . TUESDAY . LAB WORKBOOK

Homeostasis and Feedback Loops

How the body maintains a stable internal environment despite outside change.

Print this page. You will draw your own diagrams from the directions below, then hand-label the structures listed. Drawing by hand is the integrity mechanism for this course.

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Part 1 of 2

Anatomy Lab

1A. What you will draw

Homeostasis is the maintenance of a stable internal environment. Negative feedback corrects deviations and is the body's default. Positive feedback amplifies a signal and only runs in a few specific cases (birth, blood clotting). Draw the loop architecture first, then a specific example.

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).

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.

1C. Structures to label (12)

After you finish each drawing, label every structure below directly on your sketch.

  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 2 of 2

Physiology Lab

2A. Trace: blood glucose rises after a meal

Trace the negative feedback loop that lowers blood glucose after a meal. Fill in each step. Be specific about cells, hormones, and target tissues.

2B. Synthesis questions

Answer each in 2 to 4 sentences. Use the language from this week's lecture and your drawings as evidence.

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.

3. What to submit

Complete both the Anatomy Lab (your own drawings, hand-labeled, plus the structures list) and the Physiology Lab (activity and synthesis questions). Photograph or scan every page and upload to Canvas before the deadline listed on the schedule. Hand-drawn, hand-labeled work is the integrity mechanism for this course. Typed or AI-generated diagrams are not accepted.