Control Systems and Cell Membrane Composition

Vocabulary practice flashcards covering physiological control systems, body fluid compartments, cell membrane lipid composition, and membrane proteins.

Local Control System

A homeostatic control mechanism whose response is restricted to a small, localized region of the body.

Reflex Control System

A systemic, widespread control system that uses nervous or endocrine pathways to regulate distant targets throughout the body.

Positive Feedback Loop

A non-homeostatic pathway that reinforces an initial stimulus, driving the system farther away from its normal setpoint until an outside factor shuts it off.

Feedforward Control

A control mechanism that allows the body to anticipate a coming change and initiate an early response before the stimulus fully occurs.

Biorhythms

Predictable, repeating cycles of changes in regulated biological setpoints over time, such as the $24\,\text{hr}$ circadian rhythm.

Extracellular Fluid (ECF)

The body fluid compartment located outside of cells, composed mainly of blood plasma and interstitial fluid.

Intracellular Fluid (ICF)

The fluid compartment contained entirely within individual body cells.

Interstitial Fluid

The extracellular fluid that directly surrounds and bathes most cells in tissues.

Blood Plasma

The liquid extracellular fluid compartment contained inside blood vessels.

Fluid Mosaic Model

The structural model of biological membranes depicting a phospholipid bilayer with floating proteins and extracellular glycoproteins and glycolipids.

Phospholipid

An amphipathic lipid consisting of a hydrophilic phosphate head and hydrophobic fatty acid tails, making up more than $50\%$ of cell membrane lipids.

Sphingolipid

A class of membrane lipids constituting approximately $30\%$ of membrane lipids that aggregate with cholesterol to form specialized lipid rafts.

Cholesterol (Cell Membrane)

A membrane lipid comprising approximately $20\%$ of membrane lipids that inserts between phospholipid heads to increase viscosity, stiffen the bilayer, and lower permeability to small water-soluble molecules.

Amphipathic

Describing a chemical molecule that possesses both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions.

Micelle

A spherical droplet of phospholipids formed in an aqueous environment with hydrophobic tails pointing inward, important in lipid digestion.

Liposome

A spherical structure formed by a phospholipid bilayer surrounding an aqueous center.

Integral Membrane Protein

A protein tightly bound to the lipid bilayer, including transmembrane and lipid-anchored proteins, serving roles as receptors, adhesion molecules, transporters, enzymes, or signal mediators.

Transmembrane Protein

An integral membrane protein that spans completely across the lipid bilayer, typically via one or more \alpha-helical domains of about $20$ amino acids.

Lipid-Anchored Protein

An integral protein covalently linked directly to fatty acid chains, prenyl groups, or GPI (glycosylphosphatidylinositol) sugar-phosphate complexes embedded in the membrane.

Peripheral Membrane Protein

A protein loosely attached to integral proteins or phospholipid heads, participating in intracellular signaling and forming the submembraneous cytoskeleton.

Lipid Raft

A specialized, highly viscous membrane microdomain formed by sphingolipids and concentrated cholesterol ($3\text{ to }5\times$ higher content) that concentrates proteins involved in signal transduction.

Glycocalyx

A protective sugar coating on the extracellular surface of the cell membrane formed by the carbohydrate portions of glycoproteins and glycolipids.

Glycoprotein

A membrane protein attached to carbohydrates on the extracellular surface, involved in forming the glycocalxy and in cell-cell recognition and interaction.

Glycolipid

A membrane lipid attached to carbohydrates on the extracellular surface, involved in cell-to-cell recognition and forming the glycocalyx.

Anatomical Body Cavities

Internal spaces divided into posterior (cranial cavity) and anterior compartments (thoracic cavity containing pleural and pericardial sacs, and abdominopelvic cavity containing abdominal and pelvic cavities).

Phospholipid Structural Arrangements

The three structural forms adopted by phospholipids in aqueous solutions: planar phospholipid bilayers, micelles with nonpolar centers, and liposomes with hollow aqueous centers.

Cell Membrane Protein Types

The classification of membrane proteins into peripheral proteins (noncovalently attached) and integral proteins (membrane-spanning or linked via GPI anchors or fatty acid chains).

Planar Lipid Raft and Caveolae

Membrane domains rich in sphingolipids and cholesterol that occur as flat planar lipid rafts or invaginated caveolae, both organizing proteins for signal transduction.