Physiological Regulatory Mechanisms: Ingestion, Water Balance, and Feeding

A set of vocabulary-style flashcards covering key terms related to ingestion, thirst regulation, fluid balance, and feeding behavior from the lecture notes.

Homeostasis

Process by which the body’s substances and characteristics are maintained at their optimal level.

System Variable

A parameter controlled by a regulatory mechanism.

Set Point

Optimal value of the system variable in a regulatory mechanism.

Detector

Sensor that signals when the system variable deviates from the set point.

Correctional Mechanism

Mechanism capable of changing the value of the system variable.

Negative Feedback

Process whereby the effect produced by an action serves to diminish or terminate that action.

Satiety Mechanism

Process that signals fullness and inhibits further drinking or eating.

Drinking

Ingesting fluids to restore fluid balance.

Inhibition

Suppression of a behavior (e.g., drinking) once the needed amount is reached.

Intracellular Fluid

Fluid contained within cells.

Extracellular Fluid

All body fluids outside cells.

Intravascular Fluid

Fluid found within blood vessels.

Interstitial Fluid

Fluid that bathes cells, filling the space between them.

Isotonic

Having equal osmotic pressure to the contents of a cell.

Hypertonic

Solution with higher solute concentration than another; draws water out of cells.

Hypotonic

Solution with lower solute concentration; water moves into cells.

Osmometric (Osmotic) Thirst

Thirst produced by increased osmotic pressure of interstitial fluid relative to intracellular fluid.

Osmoreceptor

Neuron that detects changes in solute concentration of the interstitial fluid.

Circumventricular Organs

Specialized brain regions with rich blood supply along the ventricular system, often lacking a blood-brain barrier.

OVLT (Organum Vasculosum of the Lamina Terminalis)

Circumventricular organ with many osmoreceptors; lacks a blood-brain barrier.

SFO (Subfornical Organ)

Circumventricular organ involved in thirst regulation and contains osmoreceptors.

Median Preoptic Nucleus (MPON)

Hypothalamic region where signals for osmoregulation are integrated and drinking is driven.

Vasopressin (Antidiuretic Hormone, ADH)

Hormone from the posterior pituitary that promotes water reabsorption and constricts blood vessels; helps raise blood pressure.

Antidiuretic Hormone (ADH)

Another name for vasopressin; hormone that conserves water by reducing urine output.

Prader-Willi Syndrome

Genetic condition associated with insatiable appetite and obesity; linked to ghrelin signaling.

Ghrelin

Stomach- and digestive tract-derived hormone that stimulates hunger.

Glucose

Primary blood sugar; main fuel for body and especially important for brain energy.

Insulin

Pancreatic hormone that promotes glucose uptake; high levels after a meal generally decrease appetite.

Glucagon

Pancreatic hormone that raises blood glucose by converting glycogen to glucose.

Lipoprivation

Dramatic fall in fatty acids available to cells; can trigger eating.

Glucoprivation

Dramatic fall in glucose availability; triggers eating.

Leptin

Hormone from adipose tissue signaling long-term energy stores and satiety.

Arcuate Nucleus

Hypothalamic nucleus containing hunger- and satiety-related neurons that regulate feeding.

Lateral Hypothalamus (LH)

Hunger center; promotes feeding.

Ventromedial Hypothalamus (VMH)

Satiety center; promotes cessation of eating.

MCH (Melanin-Concentrating Hormone)

Hypothalamic peptide that stimulates feeding.

Orexin

Hypothalamic peptide that promotes feeding and arousal.

NPY Neurons

Neuropeptide Y neurons in the arcuate nucleus; promote hunger.

CART Neurons

Neurons that promote satiety; inhibited NPY activity supports fullness.

Ghrelin Secretion (Pre-Meal)

Ghrelin levels rise before a meal to stimulate hunger.

Distension (Stomach)

Stretch of stomach walls sensed by stretch receptors; signals fullness via the vagus nerve.

Vagus Nerve

Cranial nerve X; transmits signals from stomach to brain related to fullness.

Cholecystokinin (CCK)

Digestive hormone that closes the pyloric sphincter and slows gastric emptying, contributing to fullness.

Angiotensin II

Peptide hormone that constricts blood vessels, promotes sodium/water retention, and stimulates thirst.

Renin

Kidney enzyme that converts angiotensinogen to angiotensin II.

Hypovolemia

Reduction in intravascular fluid volume; triggers volumetric thirst.

Renin–Angiotensin System

Hormonal system where renin and angiotensin II regulate blood pressure, fluid balance, and thirst.

SFO (Angiotensin Detection)

Subfornical organ contains neurons that detect angiotensin in the blood and initiate drinking.

Osmotic Thirst vs Hypovolemic Thirst

Osmotic: thirst from high extracellular solute concentration; Hypovolemic: thirst from reduced blood/intravascular volume.

Adipsia

Lack of drinking due to damage to brain regions regulating thirst.

Feeding Circuitry in Brain

Networks involving LH, VMH, arcuate nucleus, MCH, orexin, NPY, and CART that regulate hunger and satiety.

Balance Between Inhibition and Excitation

Core principle: drinking/feeding is controlled by opposing neural forces and signals.