Feedback systems – components and types MCQs With Answer

Introduction: Feedback systems are essential control mechanisms in physiology and process control, linking components, signals, and responses to maintain stability. This guide for B.Pharm students explains feedback systems – components and types, including sensors (receptors), comparators (integrators), effectors (actuators), negative feedback, positive feedback, and feedforward control. You’ll learn how feedback regulates homeostasis, hormonal axes (HPA, HPT, HPG), drug-induced receptor regulation, and clinical implications for dosing and therapeutic monitoring. Clear examples like insulin-glucose regulation and oxytocin-driven labor show practical relevance for pharmacy practice and pharmacotherapy. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the best simple definition of a feedback system?

• A system where the output is ignored and functions independently
• A system that adjusts its input based on the difference between desired and actual output
• A system that only amplifies input signals without control
• A system that operates only once without sensing

Correct Answer: A system that adjusts its input based on the difference between desired and actual output

Q2. Which are the three primary components of most biological feedback loops?

• Sensor, comparator, effector
• Receptor, enzyme, transporter
• Input, resistor, capacitor
• Drug, carrier, metabolite

Correct Answer: Sensor, comparator, effector

Q3. In physiological feedback, what role does the sensor perform?

• Generates the final response to restore balance
• Compares actual value to set point
• Detects changes in a variable and sends a signal
• Eliminates the need for a comparator

Correct Answer: Detects changes in a variable and sends a signal

Q4. What is the primary function of the comparator in a feedback system?

• To generate the controlled variable
• To compare the measured value with the set point and produce an error signal
• To physically move effectors
• To store hormones for later use

Correct Answer: To compare the measured value with the set point and produce an error signal

Q5. Which statement best characterizes negative feedback?

• It amplifies the change to produce a larger deviation
• It reduces the difference between the current state and the set point
• It always leads to oscillatory instability
• It only exists in engineered systems, not biology

Correct Answer: It reduces the difference between the current state and the set point

Q6. Which is a hallmark of positive feedback?

• It opposes change to maintain homeostasis
• It enhances or amplifies an initial change, often leading to a rapid outcome
• It eliminates transient errors
• It is synonymous with negative feedback

Correct Answer: It enhances or amplifies an initial change, often leading to a rapid outcome

Q7. Which physiological system is a classic example of negative feedback?

• Oxytocin release during labor
• Insulin secretion regulating blood glucose
• Parturition leading to stronger contractions
• Blood clotting cascade amplification

Correct Answer: Insulin secretion regulating blood glucose

Q8. Which physiological process is commonly cited as positive feedback?

• Thermoregulation in cold environment
• Oxytocin release during childbirth
• Glucose homeostasis by insulin
• Renal sodium reabsorption

Correct Answer: Oxytocin release during childbirth

Q9. How does an open-loop system differ from a closed-loop (feedback) system?

• Open-loop measures output and adjusts input automatically
• Closed-loop does not use sensors or comparators
• Open-loop does not use feedback from the output to adjust the input
• Closed-loop cannot correct disturbances

Correct Answer: Open-loop does not use feedback from the output to adjust the input

Q10. What is the ‘set point’ in a biological feedback system?

• The variable being measured (like glucose)
• The desired reference value the system maintains
• The sensor that detects changes
• The effector organ producing response

Correct Answer: The desired reference value the system maintains

Q11. What is an ‘error signal’ in a feedback loop?

• The final corrective action sent to the effector
• The difference between measured value and set point
• A noise signal unrelated to control
• The sensor’s baseline output when inactive

Correct Answer: The difference between measured value and set point

Q12. In control terminology, what does ‘gain’ refer to?

• The delay between sensor and effector
• The sensitivity or amplification of the controller response to an error
• The maximum possible sensor output
• The baseline set point value

Correct Answer: The sensitivity or amplification of the controller response to an error

Q13. Which factor commonly causes oscillations in feedback-controlled systems?

• Excessive damping with no delay
• High gain and time delay between measurement and action
• Perfectly tuned proportional control
• Complete absence of feedback

Correct Answer: High gain and time delay between measurement and action

Q14. What is the effect of time delay in a biological feedback loop?

• It speeds up response and prevents oscillation
• It can cause overshoot and instability if large relative to response time
• It eliminates the need for sensors
• It converts negative feedback to positive feedback

Correct Answer: It can cause overshoot and instability if large relative to response time

Q15. What is feedforward control?

• A reactive control that waits for error before acting
• An anticipatory control that adjusts input based on expected disturbances
• A synonym for negative feedback
• A method that removes sensors completely

Correct Answer: An anticipatory control that adjusts input based on expected disturbances

Q16. How does feedback help maintain homeostasis?

• By amplifying disturbances to create rapid change
• By detecting deviations and activating responses to restore set points
• By preventing any change from ever occurring
• By randomly altering physiological variables

Correct Answer: By detecting deviations and activating responses to restore set points

Q17. In PID controllers, what does ‘I’ (integral) action do?

• It predicts future trend of the error
• It multiplies the error by a constant gain only
• It accumulates past errors to eliminate steady-state error
• It senses the environment without correction

Correct Answer: It accumulates past errors to eliminate steady-state error

Q18. What is the primary role of derivative (D) action in control systems?

• To reduce steady-state error by integration
• To amplify noise without benefit
• To predict error trend and dampen oscillations
• To replace the sensor

Correct Answer: To predict error trend and dampen oscillations

Q19. Proportional control primarily provides which effect?

• Completely removes all error regardless of gain
• Produces a response proportional to the magnitude of the error
• Prevents any transient response
• Acts only on accumulated past errors

Correct Answer: Produces a response proportional to the magnitude of the error

Q20. Which hormonal axis shows classic negative feedback from circulating hormone to hypothalamus and pituitary?

• Hypothalamic-pituitary-thyroid (HPT) axis
• Adrenal medulla catecholamine surge
• Positive feedback loop of oxytocin
• Insulin-independent glucose uptake

Correct Answer: Hypothalamic-pituitary-thyroid (HPT) axis

Q21. In the HPA axis, cortisol typically inhibits which components by negative feedback?

• Adrenal cortex only
• Hypothalamus and anterior pituitary
• Muscle and fat tissues directly
• The pancreas and thyroid

Correct Answer: Hypothalamus and anterior pituitary

Q22. Which feedback is involved in the regulation of sex hormones through the HPG axis?

• Only positive feedback at all times
• Both negative feedback and occasional positive feedback (e.g., LH surge)
• No feedback; hormones are constant
• Feedforward without any feedback

Correct Answer: Both negative feedback and occasional positive feedback (e.g., LH surge)

Q23. Chronic antagonist drug treatment can lead to receptor upregulation. This is best described as:

• A direct effect of the antagonist increasing receptor synthesis unrelated to feedback
• A compensatory homeostatic response often mediated by negative feedback mechanisms
• Positive feedback that reduces receptor numbers further
• Immediate receptor internalization caused by agonists

Correct Answer: A compensatory homeostatic response often mediated by negative feedback mechanisms

Q24. Receptor downregulation after long-term agonist exposure is primarily due to which process?

• Homeostatic adaptation reducing receptor number or sensitivity
• Increased gene transcription of receptor proteins
• Immediate increase in effector activity indefinitely
• Elimination of the comparator

Correct Answer: Homeostatic adaptation reducing receptor number or sensitivity

Q25. End-product inhibition in a biosynthetic pathway is an example of which type of feedback?

• Positive feedback
• Negative feedback
• Open-loop control
• Feedforward excitation

Correct Answer: Negative feedback

Q26. Which is an example of the hypothalamic-pituitary-thyroid axis negative feedback?

• Thyroxine stimulates TRH release
• Thyroxine inhibits TSH and TRH secretion
• TSH directly inhibits thyroxine production
• TRH is inhibited by peripheral insulin

Correct Answer: Thyroxine inhibits TSH and TRH secretion

Q27. Blood clotting cascade demonstrates positive feedback primarily because:

• Each step inhibits the next, slowing clot formation
• Activation of clotting factors accelerates further activation and amplification
• It maintains a stable baseline with no amplification
• It only involves feedforward control

Correct Answer: Activation of clotting factors accelerates further activation and amplification

Q28. Physiological sensors in feedback loops are most often:

• Effectors that produce hormones
• Receptors specialized to detect a physical or chemical variable
• Comparators that make decisions
• Drugs that modulate neurotransmission

Correct Answer: Receptors specialized to detect a physical or chemical variable

Q29. Which of the following is a common effector in biological feedback?

• Neuron only with no action on tissue
• Muscle or gland that changes activity to restore balance
• Comparator inside the receptor
• Set point value stored in DNA

Correct Answer: Muscle or gland that changes activity to restore balance

Q30. Where is the comparator function often localized in endocrine negative feedback loops?

• In peripheral target tissues exclusively
• In central integrative centers such as the hypothalamus or pituitary
• Only in the effector organ
• Within extracellular matrix proteins

Correct Answer: In central integrative centers such as the hypothalamus or pituitary

Q31. What does the time constant of a biological response determine?

• The color of the tissue involved
• The speed at which the system responds to a change
• The set point numerical value only
• The number of receptors present

Correct Answer: The speed at which the system responds to a change

Q32. Hysteresis in feedback systems refers to:

• Identical response in both increasing and decreasing stimulus
• A dependency of the output on the history of input, causing different responses for rising vs falling stimulus
• Immediate elimination of error
• Permanent loss of feedback control

Correct Answer: A dependency of the output on the history of input, causing different responses for rising vs falling stimulus

Q33. Increasing gain in a negative feedback loop typically does what?

• Reduces sensitivity to disturbances
• Always stabilizes the system further without risk
• Increases corrective action but may risk instability if too high
• Has no effect on system behavior

Correct Answer: Increases corrective action but may risk instability if too high

Q34. Therapeutic drug monitoring with dose adjustment based on measured drug levels is an example of:

• Open-loop pharmacotherapy
• Closed-loop or feedback-controlled dosing
• Feedforward-only control without measurement
• Randomized dosing

Correct Answer: Closed-loop or feedback-controlled dosing

Q35. Which is a major advantage of negative feedback in physiology?

• It magnifies disturbances for quick elimination
• It maintains stability around a physiological set point
• It prevents any corrective action ever
• It always causes irreversible changes

Correct Answer: It maintains stability around a physiological set point

Q36. Autoinduction of drug metabolism (drug increases its own metabolism) is an example of:

• Feedforward control unrelated to feedback
• Pharmacokinetic adaptation often involving regulatory feedback mechanisms
• Positive hormonal feedback only
• Immediate elimination of the drug without enzymes

Correct Answer: Pharmacokinetic adaptation often involving regulatory feedback mechanisms

Q37. Which describes insulin secretion in response to a rise in blood glucose?

• Glucose rise inhibits insulin directly
• Glucose rise stimulates insulin release, lowering glucose and closing the negative feedback loop
• Insulin release increases glucose further in a positive feedback loop
• No feedback; glucose levels remain unchanged

Correct Answer: Glucose rise stimulates insulin release, lowering glucose and closing the negative feedback loop

Q38. Prolactin secretion is primarily inhibited by which hypothalamic factor?

• Growth hormone-releasing hormone (GHRH)
• Dopamine
• Thyrotropin-releasing hormone (TRH)
• Corticotropin-releasing hormone (CRH)

Correct Answer: Dopamine

Q39. True or false: Chronic administration of a competitive antagonist may lead to increased receptor density (upregulation).

• True
• False
• Only in in vitro systems
• Only with irreversible antagonists

Correct Answer: True

Q40. Positive feedback loops usually require what to prevent uncontrolled escalation?

• No termination is needed; they are always self-limiting
• An external terminating event or limiting factor to stop the amplification
• Only increased gain to stop them
• Permanent activation of the comparator

Correct Answer: An external terminating event or limiting factor to stop the amplification

Q41. How does feedforward differ from feedback in physiological control?

• Feedforward reacts after the change; feedback anticipates the change
• Feedforward anticipates disturbances and acts before the controlled variable changes
• They are identical in timing and mechanism
• Feedforward always uses sensors downstream of the effector

Correct Answer: Feedforward anticipates disturbances and acts before the controlled variable changes

Q42. Which is an example of feedforward control in the body?

• Insulin release only after blood glucose rises
• Salivation at the sight or smell of food preparing the digestive tract
• Thyroid hormone inhibition of TSH
• Cortisol negative feedback on pituitary

Correct Answer: Salivation at the sight or smell of food preparing the digestive tract

Q43. Signal transduction pathways are important in feedback loops because they:

• Convert extracellular signals into intracellular responses that modulate effectors
• Always eliminate the need for sensors
• Stop any hormonal action permanently
• Only occur in engineered systems

Correct Answer: Convert extracellular signals into intracellular responses that modulate effectors

Q44. Negative feedback generally has what effect on biological fluctuations?

• It increases the amplitude of fluctuations
• It dampens fluctuations and maintains variables near set point
• It permanently eliminates variability
• It converts fluctuations into oscillations always

Correct Answer: It dampens fluctuations and maintains variables near set point

Q45. Chronic hypertension can result from a reset of which feedback element?

• Peripheral effector muscles only
• Baroreceptor set point becoming less sensitive or reset to higher pressure
• Immediate increase in insulin secretion
• Complete removal of kidneys

Correct Answer: Baroreceptor set point becoming less sensitive or reset to higher pressure

Q46. Positive feedback often leads to which of the following effects on error magnitude?

• Error is reduced to zero automatically
• Error is amplified, potentially causing runaway processes
• Error becomes irrelevant due to feedforward
• Error always stabilizes faster than negative feedback

Correct Answer: Error is amplified, potentially causing runaway processes

Q47. In control system analysis, the steady-state response differs from the transient response in that:

• Transient is long-term, steady-state is immediate
• Steady-state is the long-term output after transients decay; transient is the short-term behavior after disturbance
• They are identical for all systems
• Steady-state is only relevant for open-loop systems

Correct Answer: Steady-state is the long-term output after transients decay; transient is the short-term behavior after disturbance

Q48. A standard block diagram of a feedback control system commonly includes which elements?

• Controller, plant (process), sensor, and feedback path
• Only a transmitter and a battery
• Set point and nothing else
• Drug, receptor, and placebo only

Correct Answer: Controller, plant (process), sensor, and feedback path

Q49. Which general statement about negative feedback and stability is true?

• Negative feedback always destabilizes a system
• Negative feedback tends to increase stability but can destabilize if poorly tuned
• Negative feedback has no impact on system behavior
• Negative feedback always eliminates delays

Correct Answer: Negative feedback tends to increase stability but can destabilize if poorly tuned

Q50. Which physiological process best illustrates a rapid amplification cascade often described as positive feedback?

• Insulin-mediated glucose uptake
• Blood clotting leading to rapid fibrin formation
• Thyroid hormone negative feedback
• Renal autoregulation maintaining GFR

Correct Answer: Blood clotting leading to rapid fibrin formation

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