Homeostasis and Feedback Mechanisms

A state where a vital parameter (e.g., blood glucose level) is well-regulated but isn't in equilibrium. The body actively maintains this parameter at a constant value by balancing actions that lower and raise it.

The most common feedback mechanism in the body. Works to reverse any deviation from a stable point by initiating changes to return the factor to a certain mean value.

A feedback mechanism that maintains and accelerates the direction of a stimulus. This can lead to instability and even death.

The pressure exerted by a solution that determines the movement of water across a semipermeable membrane. It's related to the concentration of solutes.

A measure of how easily a solute can cross a semipermeable membrane. A reflection coefficient of 0 means the substance cannot cross the membrane.

A solution with the same osmotic pressure as another solution. This means water doesn't move between them.

A solution with the same concentration of solutes as another solution. This means the total solute concentration is the same.

A solution that has the same osmotic pressure as the body fluids, but may not have the same concentration of solutes due to the reflection coefficient.

The membrane potential at which the chemical and electrical forces on an ion are equal, resulting in no net movement of that ion across the membrane.

The difference in electrical charge across the cell membrane.

The movement of ions across the cell membrane is driven by the difference between the membrane potential and the equilibrium potential for that ion.

The tendency of an ion to move across the membrane due to its concentration gradient.

The tendency of an ion to move across the membrane due to the electrical potential difference.

Urea is a molecule that can freely pass through cell membranes, leading to rapid equilibration between different fluid compartments. It doesn't contribute significantly to osmotic pressure because it moves freely.

The concentration of impermeant solutes, those that cannot cross the membrane, determines osmotic pressure and subsequently the movement of water.

Isotonic solutions have the same osmotic pressure as the cell's interior, causing no net movement of water and maintaining the cell's volume.

Hypotonic solutions have lower osmotic pressure than the cell's interior, causing water to move into the cell and potentially making it swell.

Hypertonic solutions have higher osmotic pressure than the cell's interior, causing water to move out of the cell and potentially making it shrink.

Simple diffusion is the movement of molecules across a membrane along their concentration gradient, without the need for energy or protein assistance.

Facilitated diffusion is the movement of molecules across a membrane along their concentration gradient, with the assistance of a protein carrier. It still doesn't require energy.

Primary active transport moves molecules against their concentration gradient, requiring energy directly from ATP. This often uses protein pumps.

The amount of a substance that moves through a unit area per unit time. It's like measuring how much water flows through a pipe per second.

A measure of how easily a substance can pass through a membrane. It's like how easily water flows through a filter.

The ratio of a substance's concentration in a lipid (like oil) to its concentration in water. It reflects how well a substance dissolves in fat.

Measures how fast a substance moves through a solution, based on its size and the solution's viscosity. Think of it as how easily a substance can 'swim' through a solution.

The distance a substance needs to travel to cross a membrane.

The difference in concentration of a substance between two areas. Think of it as a pressure difference driving the flow.

The process where carrier proteins bind to a solute and facilitate its transport across the membrane.

The point where all binding sites on carrier proteins are occupied, limiting the maximum transport rate. It's like a taxi reaching its maximum capacity.

The ability of an action potential to maintain its size and shape as it travels down the axon without weakening.

A stimulus that is strong enough to trigger an action potential.

A stimulus that is too weak to trigger an action potential. It doesn't reach the threshold needed for the neuron to fire.

The period during which no action potential can be generated, regardless of the strength of the stimulus.

The period during which an action potential can be generated, but only with a stronger-than-usual stimulus.

The process by which action potentials are transmitted along the axon.

The resistance to electrical current flowing across the membrane of the neuron.

The resistance to electrical current flowing through the cytoplasm inside the neuron.

The difference in electrical potential between the inside and outside of a cell membrane. Measured in millivolts (mV).

The specific membrane potential at which the electrical force and chemical force for a particular ion are equal and opposite, resulting in no net movement of that ion across the membrane.

The difference between the membrane potential and the equilibrium potential for a specific ion. The driving force for the movement of that ion across the membrane.

The inward or outward movement of ions across the cell membrane due to the combination of electrical and chemical forces.

The potential difference across the cell membrane when the cell is at rest. Usually around -70 mV in most excitable cells.

A rapid, transient change in membrane potential that propagates along the membrane of a neuron or muscle cell.

The property of action potentials to maintain a constant amplitude and shape regardless of the strength of the initiating stimulus.