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Pharmacology · chapter 4 · Introduction to Homeostasis

Negative Feedback Loop

The 14 things this section of the textbook says that you are most likely to be asked about — quoted word for word, not retold. Then 6 practice questions with the reasoning.

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Key points

  1. Three kinds of feedback

    Feedback loops provide a mechanism for the body to maintain homeostasis. Feedback loops include negative feedback, the homeostatic response system, and positive feedback.

  2. Negative feedback counteracts deviation

    These inhibitory loops allow the body to self-regulate by counteracting any deviation from normal conditions.

  3. How a negative loop starts

    The process begins with an increase in output from a body system, leading to higher levels of specific proteins or hormones.

  4. Rising levels switch production off

    This increase subsequently triggers the homeostatic response system to inhibit or reverse the production of those proteins or hormones, preventing their levels from rising further.

  5. Result: balance within normal limits

    The body thus reduces the number of these proteins or hormones, maintaining a balance within the normal physiologic limits (Chakravarty et al., 2023; Molnar Gair, n.d.)

  6. The response system keeps things stable

    The homeostatic response system is vital for maintaining a stable internal environment.

  7. Fever: sensor and control center

    When the body experiences a stimulus, such as an elevated body temperature, a neuron (nerve cell) within the brain acts as a receptor or sensor, relaying the message to the control center, which may be the hypothalamus, pituitary gland, or nervous system.

  8. Effectors counteract the stimulus

    The control center then activates effectors, whose role is to counteract the stimulus, thereby restoring homeostasis (Libretti Puckett, 2023).

  9. Positive feedback amplifies the stimulus

    Positive Feedback In positive feedback, the body responds to a stimulus by amplifying or enhancing it rather than inhibiting it.

  10. The runaway effect

    This mechanism leads to a continuous increase in the stimulus, also known as a runaway effect, creating a self-reinforcing cycle.

  11. Blood clotting as positive feedback

    This recruitment of platelets leads to the formation of a blood clot, which further activates more platelets and reinforces the clotting process.

  12. Lactation as positive feedback

    As breast milk is released, the sucking action of the infant continues, and this further stimulates the nerve endings in the breast, creating a positive feedback loop.

  13. Oxytocin and contractions in childbirth

    As contractions intensify, more oxytocin is released, resulting in positive feedback until the infant is delivered (Libretti Puckett, 2023).

  14. Unregulated positive feedback is dangerous

    Nonetheless, when not properly regulated, positive feedback loops may give rise to instability and potentially adverse consequences.

Terms to know

Negative feedback
Negative Feedback and Homeostasis Negative feedback is critical in regulating the body’s homeostasis to promote optimal health and well-being.
positive feedback
Positive Feedback In positive feedback, the body responds to a stimulus by amplifying or enhancing it rather than inhibiting it.

Practice questions

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Every question here, with the answer

  1. A client's body temperature rises. Which sequence describes the negative feedback response?

    1. The control center amplifies the rise until it stops on its own.
    2. A neuron in the brain senses the change, signals the control center, and effectors counteract the rise.
    3. Effector detects the change, receptor responds, control center stores the message.
    4. Platelets are recruited to lower the temperature.

    Answer: A neuron in the brain senses the change, signals the control center, and effectors counteract the rise.

    With an elevated temperature, a neuron in the brain acts as the sensor and relays the message to the control center, which activates effectors that counteract the stimulus. Amplifying the change is positive feedback, and platelets belong to clotting.

  2. Which body processes are examples of positive feedback? Select all that apply.

    1. Lowering an elevated body temperature
    2. Reducing hormone production when levels rise
    3. Uterine contractions during childbirth
    4. Milk release during lactation
    5. Blood clotting after an injury

    Answer: Uterine contractions during childbirth, Milk release during lactation, Blood clotting after an injury

    Blood clotting, lactation and uterine contraction during childbirth amplify their own stimulus, which is positive feedback. Lowering a raised temperature and reducing hormone production when levels rise counteract the change, which is negative feedback.

  3. A laboring client's contractions are getting stronger. The nurse explains what is driving this. Which statement is accurate?

    1. Oxytocin is released only after delivery.
    2. Stronger contractions lower oxytocin release.
    3. As contractions intensify, more oxytocin is released until the infant is delivered.
    4. Contractions are controlled by negative feedback.

    Answer: As contractions intensify, more oxytocin is released until the infant is delivered.

    Pressure against the cervix causes uterine contraction and oxytocin release, which stimulates stronger contractions; more oxytocin follows until delivery. This is positive feedback, not negative feedback.

  4. Which statement best describes how negative feedback regulates a hormone?

    1. Rising hormone levels trigger even more production.
    2. Hormone levels are never allowed to change.
    3. Negative feedback works only during childbirth.
    4. Rising hormone levels trigger a response that inhibits further production.

    Answer: Rising hormone levels trigger a response that inhibits further production.

    When output rises, the homeostatic response system inhibits or reverses production, keeping levels within normal limits. Triggering more production describes positive feedback.

  5. Which structures may act as the control center in the homeostatic response system? Select all that apply.

    1. Pituitary gland
    2. Nervous system
    3. Myoepithelial cells
    4. Hypothalamus
    5. Platelets

    Answer: Pituitary gland, Nervous system, Hypothalamus

    The control center may be the hypothalamus, pituitary gland or nervous system. Platelets take part in clotting, and myoepithelial cells contract during lactation; neither is a control center.

  6. A student says positive feedback is always safe because it helps the body respond quickly. How should the nurse respond?

    1. Positive feedback is the same as negative feedback.
    2. When not properly regulated, positive feedback can cause instability and adverse consequences.
    3. That is correct; positive feedback cannot cause harm.
    4. Positive feedback only occurs in disease.

    Answer: When not properly regulated, positive feedback can cause instability and adverse consequences.

    Positive feedback supports rapid responses, but when not properly regulated it can lead to instability and adverse consequences. It occurs in normal processes such as clotting and childbirth and is the opposite of negative feedback.

Where every quote comes from

Section 4.4 Negative Feedback Loop of Pharmacology for Nurses by Tina Barbour-Taylor, Leah Mueller (Sabato), Donna Paris, Dorie Weaver, OpenStax, 2024. Read the whole section free at openstax.org.

The textbook is licensed under CC BY-NC-SA 4.0. This page quotes it word for word and adds the headings, the order and the practice questions; references to the book's figures and stray spaces left by its formatting are removed. The page is shared under the same licence. Nothing here is sold.