Chapter 1: Cell Physiology I - Flashcards

Vocabulary flashcards covering homeostatic mechanisms, cell membrane structure and transport, body fluid compartments, and fluid balance principles from Chapter 1: Cell Physiology I.

Homeostasis

The coordinated physiological processes that maintain a relatively stable internal environment held around a set point and within a normal range.

Milieu intérieur

The internal environment concept described by Claude Bernard, referring to the extracellular fluid bathing cells whose stability is necessary for an independent life.

Dynamic steady state

A condition in which continuous background fluctuations and exchanges (inputs and outputs) yield a stable, balanced internal environment.

Controlled variable

The specific physical or chemical factor in a physiological system that is being monitored and regulated, such as blood pressure.

Sensor (receptor)

A component of a reflex control system that detects a controlled variable or changes in its level (for example, carotid sinus baroreceptors).

Afferent pathway

The route, typically consisting of sensory nerves or the bloodstream, that carries information from a sensor to the integrator.

Integrator (control centre)

The component of a control system that evaluates incoming sensory signals against a predetermined set point to select an appropriate response (such as the medulla oblongata).

Efferent pathway

The neurological or hormonal pathway that transmits motor or regulatory commands away from the integrator to an effector.

Effector

A muscle, organ, or secretory cell that executes a targeted physiological response to alter the controlled variable (for example, blood vessels or the heart).

Negative feedback

The dominant homeostatic control mechanism wherein the resulting response opposes the initiating disturbance, driving the controlled variable back toward its set point.

Gain (of a feedback system)

A quantitative index of feedback system efficacy defined by the relationship: $\text{Gain} = \frac{\text{correction}}{\text{remaining error}}$.

Positive feedback

A self-amplifying, destabilizing control mechanism that enhances the original stimulus to drive an explosive, self-completing physiological event (e.g., childbirth, blood clotting).

Feedforward control

An anticipatory adaptive response that acts before an actual change occurs in the controlled variable, reducing delay and minimizing overshoot.

Fluid mosaic model

The structural model of the plasma membrane describing it as a fluid phospholipid bilayer roughly $7\text{--}10\,\text{nm}$ thick with embedded and floating proteins.

Phospholipids

Amphipathic membrane lipids possessing a polar hydrophilic head and two nonpolar hydrophobic fatty acid tails that spontaneously align into a bilayer in aqueous environments.

Cholesterol

A membrane steroid lipid intercalated between phospholipids that limits bilayer permeability to small water-soluble solutes and stabilizes membrane fluidity across temperatures.

Glycocalyx

A carbohydrate-rich outer surface layer composed of glycolipids and glycoproteins, functioning in cell-cell recognition, intercellular adhesion, and mechanical protection.

Integral (transmembrane) proteins

Membrane proteins that span across the hydrophobic lipid bilayer, serving as channels, carrier proteins, active pumps, or cell-surface receptors.

Peripheral proteins

Proteins attached to one face of the plasma membrane (predominantly the cytoplasmic side) that act as intracellular enzymes or anchor the cytoskeleton.

Fick's law

The physical relation describing net diffusion rate across a membrane: $J = P \times A \times (C_1 - C_2)$, where $J$ is net flux, $P$ is membrane permeability, $A$ is surface area, and $(C_1 - C_2)$ is concentration gradient.

Facilitated diffusion

Passive, carrier- or channel-mediated transport down an electrochemical gradient requiring no cellular metabolic energy, characterized by specificity, competition, and saturation.

Transport maximum ($T_{\text{max}}$)

The plateaued upper limit of transport velocity observed when all carrier binding sites in facilitated diffusion or carrier systems are fully occupied.

Primary active transport

Transport that moves a solute against its electrochemical gradient directly coupled to the hydrolysis of $\text{ATP}$.

$$\text{Na}^+/\text{K}^+\text{-ATPase}$$

An electrogenic primary active transport pump that hydrolyzes one $\text{ATP}$ molecule to transport $3\,\text{Na}^+$ out of the cell and $2\,\text{K}^+$ into the cell.

Secondary active transport

Transport of a solute against its gradient coupled to the downhill movement of another solute (usually $\text{Na}^+$) whose gradient was generated by primary active transport.

Co-transport (symport)

A form of secondary active transport in which the driving ion and the driven solute move simultaneously in the same direction across the membrane (e.g., $\text{SGLT1}$).

Counter-transport (antiport)

A form of secondary active transport in which the driving ion and the coupled solute move in opposite directions across the membrane (e.g., $\text{Na}^+/\text{Ca}^{2+}$ exchanger).

Oral rehydration therapy (ORT)

A treatment for dehydrating diarrhoeal illness utilizing an oral glucose-and-electrolyte solution to leverage functional $\text{SGLT1}$ transporters, driving water absorption by osmosis.

Osmosis

The passive net movement of water molecules across a selectively permeable membrane toward a region with a higher solute concentration.

Aquaporins

Selective channel proteins that facilitate rapid transmembrane water movement, highly concentrated in renal collecting ducts under the control of $\text{ADH}$.

Osmolarity

The measurement of total solute concentration expressed as the number of osmotically active particles per litre of solution ($\text{mOsm/L}$).

Osmotic pressure

The hydrostatic pressure needed to completely stop the osmotic influx of pure water across a membrane, calculated by van 't Hoff's relation: $\pi = nCRT$.

Tonicity

The relative ability of an extracellular solution to alter cell volume, governed specifically by the concentration of non-penetrating solutes (effective osmoles).

Ineffective osmole

A solute (such as urea) that readily diffuses through plasma membranes and therefore contributes to osmolarity without producing sustained transcellular osmotic pressure shifts.

Endocytosis

An active, $\text{ATP}$-dependent process wherein the plasma membrane invaginates and pinches off inward to ingest extracellular particles or fluids into vesicles.

Phagocytosis

A specific form of endocytosis ('cell eating') through which cells such as macrophages ingest large insoluble particles, debris, or microorganisms.

Pinocytosis

A non-specific form of endocytosis ('cell drinking') by which small invaginations engulf extracellular fluid and dissolved solutes into tiny internal vesicles.

Receptor-mediated endocytosis

A selective mode of vesicular import where specific target ligands bind dedicated transmembrane receptors concentrated in clathrin-coated membrane pits.

Exocytosis

An $\text{ATP}$-dependent transport process where intracellular secretory vesicles fuse with the cell membrane to expel luminal contents into the extracellular space.

Transcytosis

A transport mechanism wherein macromolecules are internalized by endocytosis on one cell boundary, traversed across the cytoplasm, and secreted on the opposite boundary by exocytosis.

Total body water (TBW)

The complete fluid content of the human body, constituting approximately $60\%$ of total body weight (around $42\,\text{L}$) in a standard $70\,\text{kg}$ adult male.

60–40–20 rule

A physiological rule of thumb defining the fluid distribution of a lean adult: total body water is $60\%$ of body weight, intracellular fluid is $40\%$, and extracellular fluid is $20\%$.

Intracellular fluid (ICF)

The fluid located within cell membranes, comprising about two thirds of total body water ($40\%$ of body mass; approximately $28\,\text{L}$ in a $70\,\text{kg}$ man), characterized by high $\text{K}^+$ and phosphate ions.

Extracellular fluid (ECF)

All bodily fluids external to cells, representing one third of total body water ($20\%$ of body mass; approximately $14\,\text{L}$ in a $70\,\text{kg}$ man), characterized by high $\text{Na}^+$ and $\text{Cl}^-$ concentrations.

Interstitial fluid

The extracellular fluid compartment that directly bathes tissue cells outside vascular walls, representing roughly three fourths of the $\text{ECF}$ (about $10.5\,\text{L}$ in a $70\,\text{kg}$ man).

Plasma

The liquid, non-cellular constituent of blood contained within capillaries and larger vessels, comprising one fourth of the $\text{ECF}$ (about $3.5\,\text{L}$ in a $70\,\text{kg}$ man) and enriched with proteins ($\approx 7\,\text{g/dL}$).

Dilution principle

A laboratory method to determine fluid compartment volume by introducing a known mass of tracer and measuring equilibrium concentration: $\text{Volume} = \frac{\text{Amount injected} - \text{Amount excreted}}{\text{Concentration}}$.

Starling forces

The hydrostatic and oncotic pressure differentials across the capillary endothelial barrier that govern the transcapillary movement of fluid between plasma and interstitium.

Oedema

The accumulation of excess interstitial fluid that arises whenever capillary filtration outpaces the draining capacity of both lymphatic return and venular absorption.