A Flashcards
A-band
or anisotropic band
The region of a muscle sarcomere where the thick filaments occur
Absolute Refractory Period
The period during and immediately following an action potential in which an excitable cell cannot generate another action potential, no matter how strong the stimulus
Absolute Temperature
A measure of temperature in kelvins, where 0 k (absolute zero) is the temperature at where there is no atomic or molecular movement. 1 unit on the Kelvin scale equals 1 degree on the Celsius scale. 0 K = -273 degrees Celsius.
Acclimation
see also acclimatization
A persistent but reversible change
in a physiological function that occurs as a
result of an alteration in an environmental
parameter, such as temperature or photoperiod.
Acclimation usually occurs as a result
of an experimental manipulation
Acclimatization
see also acclimation
A reorganization of physiological
functions that occurs as a result of complex
environmental changes, such as season
or altitude
Accommodation
The process by which an eye
changes its focal length. Accommodation allows the eye to produce a focused image of
objects at different distances.
Acetyl CoA
An activated form of acetate that
serves as the entry point for carbon into the
TCA cycle.
Acetylcholine A
Neurotransmitter found in
most animal species in many types of neurons, including motor neurons and the autonomic ganglia of vertebrates.
Acetylcholinesterase
An enzyme that catalyzes the breakdown of acetylcholine into choline and acetate.
Acid
see also base
A chemical that donates a proton
Acidosis
A decrease in pH arising through respiration
(respiratory acidosis) or metabolism
(metabolic acidosis)
Acrosome
A vesicle in sperm that contains digestive
enzymes that enable the sperm to
penetrate the outer layers of an ovum
Acrosome Reaction
The exocytosis of the enzymeladen
acrosomal vesicle of sperm in response
to contact with the ovum
Actin
see also myosin
G-actin is a monomeric protein that can
be polymerized to construct filamentous actin
(F-actin). Actin is the basis of both cytoskeletal microfilaments (composed of the
α-actin isoform of G-actin) and skeletal thin
filaments (composed of the β-actin isoform
of G-actin)
Actinomyosin
The combination of actin and
myosin, joined by a cross-bridge
Action Potential
A relatively large-amplitude, rapid change in the membrane potential of an excitable cell as a result of the opening and closing of voltage-gated ion channels; involved in transmitting signals across long
distances in the nervous system
Activation Energy (E_A)
The energetic barrier that must be reached before a reactant can be transformed into a product
Activation Gate
see also inactivation gate
One of the two gates that open
and close voltage-gated sodium channels
Active Site
A region of an enzyme that binds the substrate and undergoes conformational
changes to catalyze the reaction.
Active State
The phase of a cross-bridge cycle in
which myosin is attached to actin and generating force.
Active Transport
(see also facilitated diffusion, passive
transport)
Protein-mediated movement of a substance across a membrane with the utilization of some form of energy. Primary active transport uses ATP. Secondary active transport uses an electrochemical gradient.
Acuity
The ability to resolve fine detail of a
stimulus.
Acute Response
The rapid phase of response to
an external or internal change in conditions,
usually within seconds to minutes.
Adaptation
Used in two contexts in physiology:
(1) a change in the genetic structure of a population as a result of natural selection;
(2) a reversible change in a physiological parameter that provides a beneficial response to an environmental change. Evolutionary and comparative physiologists prefer to use only the first definition.
Adaptive Immune System
The components of the immune system that deal with specific pathogens, in contrast to the innate immune system, which deals with pathogens more generally. Central to the adaptive (or acquired) immune system is receptors that bind to specific molecular motifs, initiating an immune response.
Adenine
A purine nitrogenous base component
of nucleotides, including nucleic acids.
Adenosine
A nucleoside composed of adenine and the sugar deoxyribose, important as a signaling molecule.
Adenosine Diphosphate (ADP)
A nucleotide composed of the nucleoside adenine with two phosphate groups, with a single high-energy phosphodiester bond.
Adenosine Triphosphate (ATP)
A nucleotide composed of the nucleoside adenine with three phosphate groups, with two high-energy phosphodiester bonds.
Adenylate Cyclase (adenylyl cyclase)
The enzyme that converts ATP to cyclic AMP.
Adequate Stimulus
The stimulus modality to which a sensory receptor is the most sensitive.
Adhesion Plaque
A membrane protein complex that anchors thin filaments to the membrane.
Adipose Tissue
A tissue composed of fat cells (adipocytes) that produce and store lipid.
Adrenal Gland
A gland near the kidney, which in mammals is composed of an outermost layer (the adrenal cortex) and an inner layer (adrenal medulla).
Adrenergic Receptor
A G protein–linked cell membrane receptor that binds norepinephrine preferentially, with a lower affinity for epinephrine.
Adrenergic Receptors
Receptors for the catecholamines
norepinephrine and epinephrine.
Aerobic
Occurring in, or depending on, the
presence of oxygen.
Aerobic Dive Limit
The maximum length of a dive prior to any increase in blood lactate levels.
Aerobic Scope
The ratio of the maximal aerobic metabolic rate to the basal metabolic rate, typically in the range of 3–10.
Aerofoil
A surface, teardrop shaped in profile,
that moves through air to generate lift. An
aerial version of a hydrofoil.
Afferent
see also efferent
Leading toward a region of interest.
Afferent Arteriole
An arteriole that enters the
glomerulus of a kidney tubule.
Afferent Division
The part of the peripheral nervous system that conducts sensory information from sensory receptors and organs toward the central nervous system.
Afferent Neuron
see also sensory neuron
A neuron that conducts a signal from the periphery to an integrating center.
Affinity
see also K_m
A measure of the degree of attraction
between a ligand and a molecule that binds
the ligand.
Affinity Constant (or Ka)
Reciprocal of the dissociation
constant.
After-Hyperpolarization Phase
A prolonged hyperpolarization
following an action potential.
Aglomerular Kidney
A derived form of kidney, with tubules that lack a glomerulus, found in many lineages of marine fish.
Agonist
A substance that binds to a receptor
and initiates a signaling event. May include
both the natural endogenous ligand as well
as pharmaceutical agents that mimic the natural substance.
Albumen
A protein found in eggs that cushions
the embryo.
Albumin
A binding globulin (carrier protein) that is one of the primary proteins of vertebrate plasma; makes a major contribution to blood osmotic pressure.
Aldosterone
Mineralocorticoid hormone secreted
by the adrenal cortex. Its main function
is to alter the levels of Na+ and K+ in the
urine, secondarily affecting water transport.
Alkaloids
A large group of compounds derived from plants that have pharmacological effects
in animals.
Alkalosis
see also metabolic alkalosis, respiratory alkalosis
The condition of being alkaline.
Allantoic Membrane
One of four membranes in
an amniote egg.
Allantoin
An intermediate in nucleotide breakdown
and uric acid synthesis; an important form of nitrogenous waste for some animals.
Allatostatin
A neuropeptide hormone in arthropods
that inhibits the corpus allatum from secreting juvenile hormone.
Allatotropin
A neuropeptide hormone in arthropods
that stimulates the corpus allatum to secrete juvenile hormone.
Alleles
Different forms of the same protein that
are encoded by the same gene but differ
slightly in primary sequence.
Allelochemical
A chemical produced by one species that affects the growth, survival, or reproduction of other species.
Allometry (or allometric scaling)
The pattern seen when comparing structural or functional parameters in relation to body size.
Allostasis
The process by which stability is achieved through changes in physiological systems. In contrast to homeostasis, this emphasizes that aspects of physiology actively change to maintain constancy in other parameters.
Allosteric Regulator
A molecule that binds an enzyme at a site distinct from the substrate binding site to regulate activity.
Allosteric Site
A region of an enzyme, distinct
from the active site, that binds a molecule other than the substrate or product, triggering
a structural change that alters the catalytic properties of the enzyme.
Allozyme
An allelic variant of an enzyme.
Alpha-Helix (α-helix)
A secondary structure of protein or DNA in which the molecule twists
in a characteristic pattern, with structure stabilized by hydrogen bonds between adjacent regions.
Alternative Splicing
One of the processes that can result in different mRNAs being coded
by a single gene. Different exons of the gene are spliced out in each mRNA, resulting in a number of possible combinations.
Alveoli (singular: alveolus)
The site of gas exchange in mammalian lungs.
Ambient
External or environmental conditions,
such as ambient temperature.
Amine
A class of molecules based on ammonia, with a side group substituting for at least one N atom.
Amino Acid
Organic molecules with at least one amino group and at least one carboxyl group.
The amino acids that are used to build proteins are α-amino acids.
Ammonia
A general term that includes both NH3 and NH4 + (ammonium), potent
neurotoxins.
Ammoniotele
see also ureotele, uricotele
An animal with an excretory
strategy in which more than half of the nitrogen
is excreted as ammonia.
Amniote
Vertebrates with an amnion, namely reptiles, birds, and mammals.
Amphibolic Pathway
A metabolic pathway that both synthesizes (catabolic) and degrades
(anabolic) metabolites.
Amphipathic
A molecule with both hydrophobic and hydrophilic parts.
Amplification
An exponential increase in activity from one step of a pathway to the next; typically
used in the context of signal transduction pathways.
Ampulla
see also ampullae of Lorenzini
Any saclike enlargement of a tube or duct, such as the terminal ends of the semicircular canals of the inner ear of vertebrates or the modified neuromasts of the lateral line system in sharks and rays
Ampullae of Lorenzini
A series of pits found on the noses of sharks and rays acting as polymodal
receptors that detect both electrical and mechanical stimuli.
Amygdala
A part of the limbic system of the vertebrate brain that is involved in emotional
responses such as fear and anger
Amylase
An enzyme that breaks down starch
amylose, amylopectin
Anabolic Pathways (or anabolism)
Metabolic reactions or pathways that build complex molecules from simpler molecules.
Anadromous
see also catadromous
The life history strategy of an animal living most of its life in the sea, then returning to freshwater to reproduce.
Anaerobic
see also aerobic
Without oxygen. Pertains to an environment without oxygen, or a pathway that
occurs in the absence of oxygen
Anaplerotic Pathway (or anaplerosis)
A metabolic reaction that replenishes intermediates of pathways.
Anastomosis
A convergence of two or more branches of a tubular structure; e.g., a direct
connection between two arteries in the circulatory system.
Anatomical Dead Space
The portion of a respiratory structure that cannot participate in gas exchange (e.g., the trachea and bronchi).
Androgens
Steroid hormones structurally related to testosterone that control masculine
features.
Anemia
A condition in which the number of erythrocytes or hemoglobin in the blood is
lower than normal.
Angiogenesis
Synthesis of new blood vessels, often in response to local hypoxia.
Angiotensin II
A peptide hormone that controls blood pressure. Its precursor is angiotensinogen,
which is cleaved by renin to form angiotensin I. This decapeptide is cleaved to
the final form, angiotensin II, an octapeptide.
Angiotensin-Converting Enzyme (ACE)
An enzyme that converts angiotensin I to angiotensin II.
Angle of Attack
The angle at which a surface meets the fluid it encounters, as with aerofoils
and hydrofoils.
Anhydrobiosis
Literally “life without water,”
this refers to the physiological responses that permit animals to survive in the absence of water.
Anion
An ion with a negative charge.
Antagonist
A substance that binds to a receptor but does not stimulate a signaling event.
Antagonists interfere with the binding of the natural ligand.
Antagonistic Controls
For a given step or pathway, sets of controls that exert opposing effects.
Antagonistic Muscle
A muscle that opposes the movement of another muscle.
Anterior Pituitary Gland
The anterior lobe of the pituitary gland of vertebrates, also called the adenohypophysis; secretes tropic hormones.
Antidiuretic
A substance that induces a reduction in urine volume.
Antidiuretic Hormone (ADH)
Also known asvasopressin, by increasing the permeability of the collecting duct of the nephron, this peptide hormone regulates physiological processes that help conserve water, and reduce the loss of water in the urine.
Antifreeze Protein
A protein that disrupts the growth of ice crystals, allowing an organism to survive subzero temperatures.
Antigen
A substance, usually a protein, that induces the formation of an antibody that can
bind the antigen.
Antigen-Presenting Cells (APCs)
These immune cells ingest pathogens or foreign material, digest it into smaller fragments, and exocytose the material to display it on the cell surface as an antigen. Recognition of the material by other cells triggers an immune response.
Antiport (or exchanger)
A transport protein that exchanges one ion (or molecule) for another ion (or molecule) on the opposite side of a membrane.
Anus
The sphincter through which feces exit the gastrointestinal tract.
Aorta
The major artery exiting the heart.
Aortic body
A sensory structure located in the vertebrate aorta that contains baroreceptors
and chemoreceptors.
Aortic Semilunar Valve
The valve between the left ventricle and the aorta of the mammalian
cardiovascular system.
Apex
The bottom of the heart in mammals.
Apical
The end of a structure opposite the base.
Apical Membrane
The end of the cell furthest from the basolateral membrane; the membrane
oriented away from the circulatory system.
Apnea
A period without breathing.
Apocrine
A type of secretion whereby the cell sheds the apical region of plasma membrane
as part of a signaling pathway.
Apoenzyme
The proteinaceous part of an enzyme.
Aquaporin
A large tetrameric channel that allows the passage of water through the plasma
membrane.
Aqueous Humor
A thin, watery fluid found in the vertebrate eye between the cornea and the lens.
Arginine Phosphate
A major phosphagen in invertebrates, which performs the same role as creatine phosphate in vertebrates.
Arrhenius Plot
A curve relating temperature to activity, enabling the calculation of activation energy.
Arteriole
see also venule
A small branch of the arterial network immediately preceding a capillary bed.
Artery
A large blood vessel carrying blood away from the heart.
Asexual Reproduction (see also automictic parthenogenesis)
Production of offspring without the fertilization of an ovum by a sperm.
Assimilation
Conversion of dietary nutrients into metabolizable fuels.
Assimilation Efficiency
Proportion of dietary nutrients successfully assimilated.
Astrocytes
Vertebrate glial cells that help to support and regulate the action of neurons in
the central nervous system.
Asynchronous Flight Muscle
A muscle in which a single neuronal stimulation causes multiple cycles of contraction and relaxation.
ATP-Binding Cassette
A common structural motif found in diverse proteins that binds ATP.
ATPase
A class of proteins, including enzymes and transporters, that couples ATP hydrolysis to a mechanical or chemical process.
ATPS
Standardized reference condition for measuring gas volumes: ambient temperature, pressure, and saturated with water.
Atresia
The programmed cell death (apoptosis) of follicles other than the dominant follicle
that matures during the ovulatory cycle.
Atrial Natriuretic Peptide (ANP)
A peptide hormone produced in the heart that exerts effects on ion and water balance that tend to reduce blood pressure. It increases urine volume and Na+ excretion.
Atrioventricular Node (AV node)
Part of the conducting pathways of the mammalian heart; delays conduction of the electrical signal between the atrium and ventricles.
Atrioventricular (AV) Valves
Valves located between the atrium and the ventricle of vertebrate hearts.
Atrium (plural: atria)
One of the chambers of a heart. Blood moves from the atrium to the ventricle.
Atrophy
Loss of tissue mass as a result of dying cells; often seen with locomotor muscle
in response to prolonged periods of inactivity.
August Krogh Principle
Principle that for every biological problem, there is an organism on which it can most conveniently be studied.
Autocrine
A type of cell signaling in which a single cell signals another cell of the same type, including itself.
Automictic Parthenogenesis
Production of offspring by a female in which the second polar body fuses with the ovum to produce a diploid offspring.
Autonomic Ganglia
Ganglia of the vertebrate peripheral nervous system.
Autonomic Nervous System
Part of the vertebrate peripheral nervous system that controls largely involuntary functions such as heart rate. It is divided into three main branches: the sympathetic, parasympathetic, and enteric nervous systems.
Autoregulation
see also Frank-Starling effect
Regulation of an organ by intrinsic mechanisms (within the same organ). For
example, regulation of the force of cardiac contraction by the pressure exerted by the blood within the heart.
Autotrophy
An organism that synthesizes its own nutrients from inorganic material, using
the energy of the sun (photoautotroph) or inorganic reactions (chemoautotrophs).
Avogadro’s Number
The number of molecules in a mole (6.02252 × 10^23).
Axoaxonic Synapse
A synapse formed between the axon terminal of one neuron and the axon of another neuron (at any point along its length).
Axodendritic Synapse
A synapse formed between the axon terminal of one neuron and the dendrite of another neuron.
Axon
A projection of the cell body of a neuron that is involved in carrying information, usually in the form of action potentials, from the cell body to the axon terminal.
Axon Hillock
The junction between the cell body and axon of a neuron. In many neurons,
the axon hillock is the site of action potential initiation, acting as the trigger zone
for the neuron.
Axon Terminal
The distal end of an axon that forms a synapse with an effector cell or neuron.
Axon Varicosity
A type of synapse in which the presynaptic cell releases neurotransmitter at a series of swellings along the axon.
Axonal Transport
Cytoskeletal-mediated movement of organelles and vesicles along the length of an axon.
Axonemal Dyneins
Motor proteins that enable the sliding of microtubules in cilia and flagella.
Axoneme
The microtubule-based structure that underlies flagella and cilia.
Axosomatic Synapse
A synapse formed between the axon terminal of one neuron and the soma (cell body) of another neuron.
