Feedback Loops and Homeostatic Regulation (3A) - MCAT Biological and Biochemical Foundations of Living Systems

A response that amplifies the initial change. Positive feedback intensifies a process to completion, like oxytocin enhancing uterine contractions during childbirth.

Maintenance of internal conditions near a set point. Homeostasis ensures physiological stability by regulating variables like temperature and pH around optimal levels despite external changes.

Stability through change by adjusting the set point. Allostasis achieves stability by adapting set points to chronic stressors, differing from fixed homeostasis.

Effector action that changes the regulated variable. The response corrects the deviation detected by the sensor, bringing the system back toward the set point.

Deviation of a regulated variable from its set point. The stimulus triggers the feedback loop by signaling a need for adjustment to maintain homeostasis.

Carries out the response to adjust the variable. Effectors execute commands from the control center to restore the regulated variable to its set point.

Compares to set point and generates an output signal. The integrator evaluates sensor input against the set point to initiate appropriate corrective actions via effectors.

Detects a change in a regulated variable (stimulus). Sensors monitor environmental or internal changes and relay information to maintain homeostasis.

Sensor, integrator (control center), effector. These components form the basic structure of feedback systems, detecting changes, processing information, and enacting responses.

A measurable condition maintained within a narrow range. Regulated variables are essential parameters like blood pressure that homeostasis keeps stable for optimal function.

A response that counteracts the initial change. Negative feedback restores equilibrium by opposing deviations, such as insulin lowering high blood glucose.

Target value or range for a regulated variable. The set point represents the ideal physiological value that feedback mechanisms aim to restore when deviations occur.

Anticipatory response that occurs before a variable changes. Feedforward mechanisms preemptively adjust physiology, like salivation before eating to aid digestion.

Platelet aggregation during blood clotting. Initial platelet activation releases factors that recruit more platelets, accelerating clot formation.

Oxytocin-driven labor (parturition). Oxytocin release amplifies contractions, creating a positive loop that progresses labor to delivery.

Increases blood glucose. Glucagon stimulates glycogenolysis and gluconeogenesis to elevate blood sugar during fasting states.

Decreases blood glucose. Insulin facilitates glucose uptake by cells and inhibits gluconeogenesis, normalizing high blood sugar.

Decreased blood glucose. Low glucose triggers glucagon to mobilize stores and raise levels, preventing hypoglycemia.

Increased blood glucose. Elevated glucose levels prompt insulin release to promote uptake and storage, restoring normoglycemia.

Shivering and cutaneous vasoconstriction. These responses reduce heat loss and increase heat production to restore normal body temperature.

Hypothalamus. The hypothalamus integrates thermal signals and coordinates responses to maintain core body temperature.

Two effectors that produce opposing effects on a variable. Antagonist pairs allow precise control by balancing increases and decreases in the regulated variable.

Dynamic equilibrium. Dynamic equilibrium describes the steady state where variables fluctuate minimally around the set point.