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Glossary of Physiology Terms
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Definition:
Moving along an axon away from the neuronal cell body toward the axon terminal.

Related glossary terms/phrases:
Retrograde



Definition:
Refers to the concentration gradient of an ion or molecule. The concentration gradient may exist across a biological membrane, where the concentration is higher on one side of the membrane compared to the other side. Concentration gradient may also exist in a solution without an apparent barrier separating the area of higher concentration from the area of lower concentration. In both cases, the free energy that results from the concentration difference drives the movement of the ion/molcule from the area of higher concentration to the area of lower concentration. In free solution, the ion/molecule simply diffuses down its gradient. Movement across a biological membrane is more complicated and is a function of lipid solubility of the ion/molecule as well as the presence of channels or transport proteins that can allow the ion/molecule to cross the membrane (see Lipid Bilayer Permeability and Summary of Membrane Transport Processes).

Related glossary terms/phrases:
Electrical gradient
Electrochemical gradient



Definition:
In biological solutions, electrical gradient refers to the electrical potential that acts on an ion to drive the movement of the ion in one or another direction (see Resting Membrane Potential - Establishment of the Membrane Potential).

Related glossary terms/phrases:
Chemical gradient
Electrochemical gradient



Abbreviation:
ECG or EKG

Definition:
A recording of the electrical activity of the heart measured by placing multiple (3 to 10) electrodes on the surface of the skin.



Definition:
Refers to the balance of chemical and electrical gradients that act on an ion, particularly as it relates to the movement of an ion across a biological membrane (see Resting Membrane Potential - Establishment of the Membrane Potential and Resting Membrane Potential - Nernst Equilibrium Potential).

Related glossary terms/phrases:
Chemical gradient
Electrical gradient



Definition:
Electrochemical gradient

See:
Electrochemical gradient



Definition:
Refers to synaptic or receptor potentials that can vary in amplitude and direction. Graded potentials can be depolarizing or hyperpolarizing and do not have a threshold.

Related glossary terms/phrases:
Action potential

See also:
Neuronal Action Potential - Introduction
Neuronal Action Potential - Graded Potentials versus Action Potentials



Abbreviation:
PCG

Definition:
A recording of the sounds produced by the heart during the cardiac cycle. The main sounds recorded are those associated with turbulent blood flow caused by the closure of heart valves.



Definition:
Moving from the axon terminal back toward the neuronal cell body.

Related glossary terms/phrases:
Anterograde



Definition:
An enzyme found in the synaptic cleft at cholinergic synapses. It degrades acetylcholine to choline and acetate and, thus, terminates the action of acetylcholine at the synapse. Neither choline nor acetate can bind to acetylcholine receptors (nicotinic or muscarinic).



Abbreviation:
BMI

Definition:
The body mass index is measured by dividing body weight (in kilograms) by body height (in meters) squared (kg / m2). It is highly correlated with body composition, and higher BMI values are correlated with higher body fat content. The BMI value is used to classify one's weight in several categories including underweight, normal, overweight, and obese. The range of BMI values considered to be normal is 18.5 to 24.9. Higher BMI values are associated with an increased risk for diseases such as diabetes mellitus type II, hypertension, and cardiovascular disease.

See also:
Body Mass Index Calculator

Other resources:
Body mass index (Wikipedia)



Definition:
An integral membrane protein which contains a pore through which ions, water, or polar molecules permeate. For any given channel, the pore is usually very selective for the particular ion or molecule. For example, sodium (Na+) channels are very selective for Na+ over other cations.

The channel pore may be constitutively open, or it may be gated to the open state by various stimuli such as chemical ligands, voltage, temperature, or mechanical stimulation of the membrane.



Definition:
A type of secondary active transport across a biological membrane in which a transport protein couples the movement of an ion (usually Na+ or H+) down its electrochemical gradient to the movement of another ion or molecule against a concentration or electrochemical gradient. The ion moving down its electrochemical gradient is referred to as the driving ion. The ion/molecule being transported against a chemical or electrochemical gradient is referred to as the driven ion/molecule.

In cotransport, the direction of transport is the same for both the driving ion and driven ion/molecule (into the cell or out of the cell).

An example is the Na+/glucose cotransporter (SGLT), which couples the movement of Na+ into the cell down its electrochemical gradient to the movement of glucose into the cell against its concentration gradient.

Cotransport is also commonly referred to as symport.

Transport proteins that are involved in this type of transport are referred to as cotransporters or symporters.

See:
Symport

Related glossary terms/phrases:
Secondary active transport
Exchange

See also:
Lecture notes on Secondary Active Transport



Abbreviation:
VDF

Definition:
When an ion is not at its electrochemical equilibrium, an electrochemical driving force (VDF) acts on the ion, causing the net movement of the ion across the membrane down its own electrochemical gradient.

The electrochemical driving force is generally expressed in millivolts and is calculated according the following equation:

VDF = VmVeq

where VDF is the electrochemical driving force, Vm is the membrane potential, and Veq is the equilibrium potential.

Related glossary terms/phrases:
Membrane potential
Equilibrium potential
Electrochemical gradient

See also:
Resting Membrane Potential - Electrochemical Driving Force Acting on Ions
Electrochemical Driving Force Calculator






Definition:
Electrophysiology is the study of the electrical properties of biological macromolecules, cells, tissues, and organs. Electrical signals such as voltage and/or current are generally measured. Examples include measuring changes in the membrane voltage of excitable cells (e.g., neurons, muscle cells, and some endocrine cells) during an action potential. The current carrried by ions as they permeate the pore of ion channels can also be measured - both at the single-channel level (single-channel current), as well as the macroscopic current resulting from the activity of a population of channels. As another example, electrical measurements may involve recording voltage changes at the surface of the skin that result from the activity of skeletal muscles (electromyogram, EMG), cardiac myocytes (electrocardiogram, ECG), or neurons in the brain (electroencephalogram, EEG).



Definition:
Endocrine cells are responsible for producing and releasing hormone molecules into the bloodstream. Endocrine cells are typically grouped together in organs referred to as endocrine glands.

Related glossary terms/phrases:
Endocrine gland
Hormone



Definition:
A type of secondary active transport across a biological membrane in which a transport protein couples the movement of an ion (usually Na+ or H+) down its electrochemical gradient to the movement of another ion or molecule against a concentration or electrochemical gradient. The ion moving down its electrochemical gradient is referred to as the driving ion. The ion/molecule being transported against a chemical or electrochemical gradient is referred to as the driven ion/molecule.

In exchange, the driving ion and the driven ion/molecule are transported across the biological membrane in opposite directions.

An example is the Na+/Ca2+ exchanger (NCX), which couples the movement of 3 Na+ ions into the cell down its electrochemical gradient to the movement of 1 Ca2+ ion out of the cell against its electrochemical gradient.

Exchange is also commonly referred to as antiport.

Transport proteins that are involved in this type of transport are referred to as exchangers or antiporters.

See:
Antiport

Related glossary terms/phrases:
Secondary active transport
Cotransport

See also:
Lecture notes on Secondary Active Transport



Definition:
Facilitated diffusion (or facilitated transport) is a form of passive transport across biological membranes and refers to carrier-mediated transport of molecules/ions down a concentration gradient. Facilitated transport is mediated by facilitative transporters (also referred to as uniporters).

See also:
Facilitated Diffusion



Definition:
Abnormal, unwanted, and excessive hair growth on the face and body. Particularly used to refer to women with such a condition.

Related glossary terms/phrases:
Hirsute



Definition:
A total plasma calcium level that is greater than the normal range of 2.2 - 2.6 mM (9 - 10.5 mg/dL). The free calcium concentration in the plasma is approximately 1.5 mM (6 mg/dL), and the remaining amount is bound to plasma proteins.

Related glossary terms/phrases:
Hypocalcemia



Definition:
Hyperthyroidism refers to a pathophysiological condition in which the thyroid gland produces and releases abnormally high levels of the thyroid hormones (T3 and T4).

The symptoms of hyperthyroidism may include high metabolic rate, weight loss, nervousness, excess heat production, tachycardia, and tremor.

Two main forms of hyperthyroidism exist: (1) Primary hyperthyroidism, and (2) Secondary hyperthyroidism.

In primary hyperthyroidism, the thyroid gland produces high levels of the thyroid hormones, either as a result of a secretory tumor of the thyroid gland, or under the control of thyroid stimulating immunoglobulins (such as in Graves' disease).

Secondary hypothyroidism is caused by high levels of thyroid stimulating hormone (TSH) produced by the anterior pituitary gland. TSH then stimulates the thyroid gland to produce excessive amounts of the thyroid hormones.

Related glossary terms/phrases:
Hypothyroidism
Euthyroidism



Definition:
Refers to the ability of the thyroid gland to accumulate iodide (I) against a steep electrochemical gradient. While the iodide concentration in plasma and interstitial fluid is approximately 300 nL, iodide concentration in the cytoplasm of thyroid follicular cells, as well as the lumen of thyroid follicles can be many folds higher. The protein that enables iodide transport into the thyroid gland against an electrochemical gradient is the Na+/iodide symporter (NIS), which is located in the basolateral membrane of thyroid follicular cells. Within the lumen of thyroid follicles, iodide is incorporated into the tyrosine residues of thyroglobulin during thyroid hormone biosynthesis, hence, allowing very high iodide concentrations in the colloid.



Definition:
The tapping sounds heard through a stethoscope placed over a partially compressed peripheral artery.

For the purpose of non-invasive blood pressure measurements, the stethoscope is usually placed on the skin overlying the brachial artery just distal to an inflated pressure cuff wrapped around the upper arm. As the pressure cuff is gradually deflated, the Korotkoff sounds result from the pulsations of the blood through the partially constricted brachial artery. With each ventricular systole, blood is forced to flow through the partially constricted brachial artery, and the turbulence in blood flow leads to the generation of the Korotkoff sounds. When the pressure cuff is fully deflated, flow through the artery resumes its normal laminar flow and, at that time, the Korotkoff sounds disappear.



Definition:
A motor unit is composed of a motor neuron and all of the muscle fibers (i.e., muscle cells) it innervates.

Alternatively, a motor unit is a group of muscle fibers innervated by a single motor neuron.



Definition:
An equation used to calculate the equilibrium potential (Veq.) of an ion. The equilibrium potential for an ion is also referred to as the Nernst potential for that ion. It is the membrane potential at which no net movement of the ion in question occurs across the membrane.

General form of the Nernst equation

where Veq. is the equilibrium potential, R is the universal gas constant, T is the temperature in Kelvin, z is the valence of the ionic species, F is the Faraday's constant, and [X]o and [X]i are the extracellular and intracellular, respectively, concentrations of the ion in question.

See also:
Resting Membrane Potential - Nernst Equilibrium Potential
Derivation of the Nernst Equation



Definition:
The component of the electrocardiogram (ECG) that corresponds to the depolarization of atrial myocytes. Atrial depolarization precedes atrial contraction.

Related glossary terms/phrases:
QRS complex
T wave



Definition:
Gradual hearing loss associated with aging.



Definition:
Peptide hormone produced by the anterior pituitary gland. Prolactin is best known for its action in stimulating the mammary glands to produce milk (lactation).

Prolactin is known to be involved in many other physiological processes including enlargement of the mammary glands in preparation for milk production, sexual gratification, metabolism, regulation of the immune system, and others.

Other resources:
Prolactin (Wikipedia)



Definition:
A period of rapid physical growth and change, brought about by hormonal changes, that culminates in sexual maturity. In most human girls and boys, it starts between the ages of 10 and 14 and it is complete by the age of 16 in most girls, and by the age of 17 in most boys.

Related glossary terms/phrases:
Adrenarche
Menarche
Pubarche
Thelarche



Definition:
The component of the electrocardiogram (ECG) that corresponds to the depolarization of ventricular myocytes. Ventricular depolarization precedes ventricular contraction.

Related glossary terms/phrases:
P wave
T wave



Definition:
Secondary active transport is a type of active transport across a biological membrane in which a transport protein couples the movement of an ion (typically Na+ or H+) down its electrochemical gradient to the movement of another ion or molecule against a concentration or electrochemical gradient. The ion moving down its electrochemical gradient is referred to as the driving ion. The ion/molecule being transported against a chemical or electrochemical gradient is referred to as the driven ion/molecule.

This transport process is referred to as active transport because the driven ion/molecule is transported against a concentration or electrochemical gradient. It is referred to as secondary active transport because no ATP hydrolysis is involved in this process (as opposed to primary active transport). The energy required to drive transport resides in the transmembrane electrochemical gradient of the driving ion.

Secondary active transport is also referred to as ion-coupled transport. Those utilizing Na+ as the driving ion are called Na+-coupled transporters. Those utilizing H+ as the driving ion are called H+-coupled transporters.

Two types of secondary active transport exist: cotransport (also known as symport) and exchange (also known as antiport). Na+/glucose cotransporter and H+/dipeptide cotransporter are examples of cotransporters. Na+/Ca2+ exchanger and Na+/H+ exchanger are examples of exchangers.

Related glossary terms/phrases:
Cotransport
Symport
Exchange
Antiport

See also:
Lecture notes on Secondary Active Transport



Definition:
Endocrine cell of the anterior pituitary gland responsible for synthesizing and releasing growth hormone (GH).



Definition:
The component of the electrocardiogram (ECG) that corresponds to the repolarization of the ventricles. Therefore, the T wave also corresponds to relaxation of the ventricles.

Related glossary terms/phrases:
P wave
QRS complex









Posted: Sunday, March 31, 2013
Last updated: Friday, August 28, 2015