Homeostasis, Membranes, Osmosis, & Ion Transport

Vocabulary-style flashcards covering the fundamentals of homeostasis, cellular membrane dynamics, osmosis types, and mechanisms of ion transport based on the Week 1 lecture notes.

Homeostasis

The process of maintaining internal conditions regardless of changes in the environment.

Negative Feedback Loop

A system where a change triggers a sensor to compare the new state to an internal set point, resulting in a response that moves the property back towards that set point.

Positive Feedback Loop

A system where a change is detected by a sensor and the response is amplified until a specific goal is completed, such as in childbirth.

Osmoregulation

The process by which kidneys regulate solute concentration and fluid balance; in humans, kidneys remove about $45$ gallons of water daily, most of which is reabsorbed.

Hyperthermia

A condition resulting from a body temperature above $40^{\circ}\text{C}$, also known as heat stroke.

Amphoteric

The chemical property of being able to react as both an acid or a base, a characteristic of water.

Diffusion

The net movement of solute from an area of higher to lower concentration by passive movement, which does not require energy.

Entropy

The driving force behind the process of diffusion.

Fick’s Law

A law stating the rate of diffusion is determined by membrane surface area ($A$), concentration gradient ($C_2-C_1$), membrane thickness ($L$), and a specific diffusion constant ($D$).

Membrane flux ($J$)

The amount of solute crossing a membrane per unit time, calculated by the selective permeability equation $J = P(C_1-C_2)$.

Permeability constant ($P$)

A value specific to each solute that determines its ability to cross a membrane; the best predictor of this value is the molecule's polarity.

Aquaporins

Specialized channels that allow water to move rapidly across the cell membrane.

Hydrostatic pressure

Pressure that is due to the weight of a fluid.

Osmotic pressure

Pressure due to osmosis caused by differences in osmolarity; it follows the ideal gas law.

Isotonic

A solution equal in concentration to the inside of the cell, resulting in no change in cell shape.

Hypotonic

A solution that is less concentrated than the cell, causing water to enter and the cell to swell or burst.

Hypertonic

A solution more concentrated than the inside of the cell, causing water to leave and the cell to shrink.

Donnan Equilibrium

An unequal distribution of ions on either side of a membrane that occurs when the membrane is permeable to all but one solute.

Active Transport

The movement of a solute against its concentration gradient, requiring a transporter and a source of energy like $ATP$.

$Na^+/K^+$ ATPase

An enzyme found on the surface of all cells that uses active transport to move $3\,Na^+$ ions out of the cell and $2\,K^+$ ions into the cell.

Resting potential

The electrical gradient of a cell, which is typically $-70\,\text{mV}$ where the inside of the cell is negative.

Facilitated diffusion

A type of passive transport that uses a transporter (like uniports or symporters) but does not require energy ($ATP$).

Secondary active transport

A type of transport that uses cotransporters and energy but does not use $ATP$ directly.

Gap junctions

Clusters of membrane channels made of $6$ connexin monomers that form a hydrophilic channel for direct intercellular communication.

Tight junctions

Complexes of multiple proteins found between cells that act as a "traffic cop" to prevent unregulated movement of solutes.