Homeostasis and Cellular Physiology

These flashcards cover the fundamental concepts of homeostasis, feedback mechanisms, cell membrane structure, membrane transport, and osmolarity based on the biology lecture notes.

Homeostasis

The maintenance of physical and chemical variables within a normal range to ensure proper body function.

Set Point

The optimal value for a homeostatically regulated variable.

Dynamic Equilibrium

A state in which variables fluctuate within a narrow, acceptable range rather than being perfectly constant.

Receptor

A component that detects changes in a variable and sends input signals to the control center.

Control Center

A component, often the brain or glands like the pancreas, that interprets input and determines an appropriate response.

Effector

A component such as a muscle, gland, or tissue that carries out commands to correct deviations and restore homeostasis.

Negative Feedback

The most common homeostatic mechanism where the response of the effectors counteracts the initial change to stabilize a variable.

Positive Feedback

A mechanism that reinforces the initial change, leading to a greater deviation from the set point; examples include childbirth, blood clotting, and the $LH$ surge.

Type 2 Diabetes

A state of homeostatic imbalance where cells become insulin resistant, resulting in high blood glucose levels.

Cytoplasm

The contents within the cell membrane, excluding the nucleus, which contains the cytosol, organelles, and cytoskeleton.

Cytoskeleton

Structures such as microtubules and microfilaments that maintain cell shape.

Amphipathic

A molecule having both a polar, hydrophilic (water-loving) head and a nonpolar, hydrophobic (water-fearing) tail, characteristic of phospholipids.

Cholesterol

A lipid interspersed between phospholipids that maintains membrane fluidity and stability by preventing excessive packing or dispersal.

Integral (Transmembrane) Proteins

Proteins that span the phospholipid bilayer and are essential for transport, signaling, and structural support.

Peripheral Proteins

Proteins loosely bound to the cytosolic side or to other proteins that function as enzymes or signaling molecules.

Glycocalyx

A layer formed by glycoproteins and glycolipids on the extracellular surface of the membrane used for cell recognition and immune system roles.

Simple Diffusion

Passive transport where small or nonpolar molecules move down their concentration gradient directly through the phospholipid bilayer.

Facilitated Diffusion

Passive transport that uses carrier-mediated or channel-mediated proteins to move specific substances across the membrane.

Osmosis

The movement of water across a semipermeable membrane from an area of high water concentration to an area of low water concentration.

Osmolarity

The total number of solute particles per liter of solution; for human body fluids, this is approximately $290\,milliOsmoles/L$.

Isosmotic

A term describing two solutions that have the same total osmolarity.

Hyperosmotic

A solution that has a higher osmolarity (more solutes) compared to a reference solution.

Hypoosmotic

A solution that has a lower osmolarity (fewer solutes) compared to a reference solution.

Osmotic Pressure ($\pi$)

The pressure required to prevent water movement across a semipermeable membrane, representing the "pull" drawing water into a compartment.

Tonicity

The ability of an extracellular solution to cause water movement into or out of a cell, thereby affecting cell volume.

Isotonic Solution

A solution with the same osmolarity as the cell, resulting in no net water movement and unchanged cell volume.

Hypertonic Solution

A solution with a higher solute concentration than the cell, causing water to leave the cell and the cell to shrink.

Hypotonic Solution

A solution with a lower solute concentration than the cell, causing water to enter the cell and making it swell.

Intracellular Fluid (ICF)

Fluid inside the cell characterized by high concentrations of $K^+$ and proteins.

Interstitial Fluid

Extracellular fluid similar to plasma but containing very low protein levels because proteins are too large to cross capillary walls easily.