KP222/HN220 Human Physiology I: Introduction & Cell Transport

This set of vocabulary flashcards covers introductory human physiology concepts, homeostasis, cellular communication, and the various mechanisms of membrane transport from the first unit of KP222/HN220.

Physiology

The study of the functions of living organisms and their parts, serving as a dynamic and integrated science that requires active experimentation to understand.

Homeostasis

The ability to maintain a relatively constant internal environment (temperature, volume, and composition) through organ system integration.

Teleological approach

An approach to physiology that explains the "why" or the function of a process, such as "cells need oxygen and red blood cells bring it to them."

Mechanistic approach

An approach to physiology that describes the "how" or the process/mechanism, such as "oxygen binds to hemoglobin molecules contained in the red blood cells."

Cell

The basic unit of life and the first level of organization in the human body.

Epithelial cells

One of the four major cell groups in the body; these cells line the surface of organs.

Negative feedback control

A homeostatic control mechanism where the effector response works to get a regulated variable back to its set point.

Receptors

Structures that enable homeostasis by sensing changes, including thermoreceptors (temperature), chemoreceptors (chemical changes), and baroreceptors (blood pressure).

Integrating centers

Components, often found in the brain, that orchestrate an appropriate response to signals from receptors.

Effectors

Components responsible for the body's response in homeostasis, such as muscles and glands.

Electrical signals

One of two basic types of cell communication, involving changes in the membrane potential ($V_m$).

Chemical signals

The primary type of communication in the body, involving molecules secreted by cells into the extracellular fluid (ECF).

Target cells

Cells that respond to electrical or chemical signals.

Signal Transduction

The process of cell communication consisting of three fundamental stages: reception, transduction, and response.

Gap Junctions

Intercellular junctions composed of connexins that link the cytosol of two adjacent cells, allowing ions and molecules to move directly between them.

Tight Junctions

Impermeable barriers found in the epithelium formed by occludins that force molecules to cross through the epithelial cell layer itself.

Desmosomes

Filamentous junctions found in tissues subject to mechanical stress (like heart muscle) that bind cells together for strength.

Autocrine signals

Local chemical signals that act on the same cell that secreted them.

Paracrine signals

Local chemical signals that are secreted by one cell and diffuse to adjacent cells.

Hormones

Chemicals secreted by endocrine glands or cells into the blood, reaching only target cells with specific receptors.

Neurotransmitters

Chemicals secreted by neurons that diffuse across a small gap (synapse) to a target cell.

Neurohormones

Chemicals released by neurons into the blood for action at distant targets.

Selective permeability

The property of membranes that allows some substances to pass through (nonpolar molecules like $O_2$, $CO_2$, fatty acids) while restricting others (ions and polar molecules like glucose and proteins).

Passive transport

The spontaneous movement of molecules "downhill" from areas of high to low concentration or down an electrochemical gradient without requiring cell energy.

Active transport

The non-spontaneous movement of molecules "uphill" against a concentration or electrochemical gradient, requiring cell energy.

Chemical driving force

A force created by a concentration gradient ($\Delta C$) that pushes particles from higher to lower concentration areas.

Membrane potential ($V_m$)

A force caused by the unequal distribution of anions and cations across the cell membrane, usually measured in millivolts ($mV$).

Electrochemical driving force

The sum of the chemical and electrical forces acting on an ion.

Equilibrium Potential ($E_x$)

The membrane potential ($V_m$) at which the electrical force is equal to and opposite in direction to the chemical force for a specific ion, resulting in no net transport.

Nernst Equation

The formula used to compute the equilibrium potential for a specific ion: $E_l = \frac{61\,mV}{Z} \times \log\frac{[I]_o}{[I]_i}$.

Simple diffusion

Passive transport that does not require membrane proteins, affected by the magnitude of the driving force, membrane surface area, and permeability.

Facilitated diffusion

Passive transport through a carrier protein that has specific binding sites and undergoes random conformational changes.

Aquaporins

Specific membrane channels that allow the diffusion of water.

Ion channels

Transmembrane proteins that function as passageways for specific ions; they can be leak channels, gated channels, or bidirectional.

Ligand gating

The regulation of a channel's "open time" through the binding of specific molecules to the channel.

Primary active transport

Transport that directly uses energy from a high-energy compound, usually through $ATP$ hydrolysis by a "pump."

$Na^+/K^+$ Pump

A primary active transporter that uses $ATP$ to move $Na^+$ and $K^+$ against their concentration gradients to maintain membrane potential.

Secondary active transport

Transport driven indirectly by energy from an ion concentration gradient (usually sodium) created by previous active transport.

Cotransport

A form of secondary active transport where the driving ion and the transported solute move in the same direction (e.g., sodium-linked glucose transport).

Countertransport

A form of secondary active transport where the driving ion and the transported solute move in opposite directions (e.g., sodium-proton exchange).

Osmosis

The passive diffusion of water through a membrane in response to a solute concentration gradient, moving to dilute the more concentrated side.

Osmolarity

The total solute concentration of a solution, measured in osmoles or milliosmoles ($mOsm$); the normal osmolarity of $ICF/ECF$ is approximately $300\,mOsm$.

Osmotic Pressure

The pressure that would be applied to stop any water movement, reflecting the total solute concentration and its ability to "pull" water.

Tonicity

A measure of the concentration of non-penetrating solutes in the extracellular fluid relative to the inside of the cell, determining the direction of water gradient.

Isotonic

A solution that does not alter cell volume because its concentration of non-penetrating solutes is equal to that of the cell ($300\,mOsm$).

Hypertonic

A solution with a higher concentration of non-penetrating solutes ($>300\,mOsm$) than the cell, causing the cell to shrink.

Hypotonic

A solution with a lower concentration of non-penetrating solutes ($<300\,mOsm$) than the cell, causing the cell to swell.

Phagocytosis

A type of endocytosis often called "cell-eating" where the cell membrane engulfs a large particle.

Exocytosis

The process where a secretory vesicle fuses with the plasma membrane to release its contents into the extracellular fluid.

Transcytosis

The transport of macromolecules across an epithelial cell involveing both endocytosis at one membrane and exocytosis at the other.

Apical membrane

The membrane of an epithelial cell that faces the lumen of a body cavity.

Basolateral membrane

The membrane of an epithelial cell that faces the internal environment and interstitial fluid ($ISF$).