M Flashcards
Macula Densa
A group of cells in the juxtaglomerular apparatus that senses the sodium chloride concentration of the tubular fluid.
Macrophage
A type of white blood cell that ingests foreign invaders and dead or dying cells.
Magnetite
A crystalline aggregation of a magnetic metal (usually iron); found in some magnetoreceptors.
Magnetoreceptor
A sensory receptor that responds to magnetic fields.
Malleus (hammer)
One of the three small bones of the mammalian middle ear involved in transmitting sound vibrations to the inner ear.
Malpighian Tubule
The functional equivalent of a kidney tubule in insects, releasing the urine into the gut.
Mannose-Binding Lectin
A protein secreted from the liver into the blood, which binds to mannose moieties of pathogens, enabling the pathogen to be recognized, an example of opsonization.
Mantle Cavity
A cavity formed by the body wall (mantle) of mollusks; generally contains the respiratory structures.
Mass Action Ratio
Ratio of products to substrates; when more than one product (or substrate) is involved, their concentrations are multiplied together. When a reaction is at equilibrium, the mass action ratio equals the equilibrium constant (K_eq).
Mass-Specific Metabolic Rate
The metabolic rate of an animal (usually described as oxygen consumption) expressed relative to body mass.
Mast Cells
Immune cells that release histamine when stimulated.
Mastication
Mechanical disruption of food in an oral cavity (chewing).
Maximum Velocity (Vmax)
The maximal enzymatic rate calculated from a substrate-velocity curve; can be estimated by the enzymatic rate observed when product is absent and substrate concentrations are optimal.
Maximum Velocity (Vmax)
The maximal enzymatic rate calculated from a substrate-velocity curve; can be estimated by the enzymatic rate observed when product is absent and substrate concentrations are optimal.
Mean Arterial Pressure (MAP)
The weighted average of the systolic and diastolic pressures, taking into account the relative length of each of these phases of the cardiac cycle.
Mechanical Energy
A form of energy arising from the movement or position of an object; can be either kinetic energy (as in a moving leg) or potential energy (as in a loaded spring).
Mechanogated Channel (or mechanically gated channel)
An ion channel that opens or closes in response to the stress (or stretch) on a membrane.
Mechanoreceptor
A sensory receptor that detects forces applied to cell membranes (such as touch or pressure). Can be used to describe either the receptor protein or cells containing these receptors.
Medulla Oblongata (Also called the medulla)
A region of the vertebrate brainstem containing centers that regulate heart rate, breathing depth and frequency, and blood pressure.
Medullary Cardiovascular Control Center
The region within the medulla that regulates cardiac-function.
Medullary Respiratory Center
The region within the medulla that regulates breathing depth and frequency.
Melanopsin
A photopigment found in the retinal ganglion cells of the vertebrate eye.
Melatonin
A hormone found in all animal groups that regulates sleep-wake cycles.
Melting Point
The temperature at which a solid can become a liquid; when the melting point and the freezing point are not the same temperature, this hysteresis suggests the presence of a solute that acts in a noncolloidal manner, such as an antifreeze protein.
Membrane Fluidity
A state that allows the two-dimensional movement of lipids and proteins within a lipid bilayer membrane.
Membrane Potential
The electrical gradient across a cellular membrane.
Membrane Recycling
The exchange of membrane lipids and protein between the plasma membrane and the internal membrane network.
Memory B Cells
A subclass of B cell lymphocytes that become quiescent but retain the ability to produce specific antibodies, conferring immunological memory.
Menarche
The age at which a female mammal with a menstrual cycle experiences her first menstruation.
Meninges
Membranes covering the vertebrate central nervous system. Mammals have three meninges; birds, reptiles, and amphibians have two; and fish have one.
Menses
In female mammals, the periodic shedding of the endometrial layer of uterine tissue that occurs if there is no implantation of a fertilized ovum; also known as menstruation.
Menstrual Cycle
The estrous cycle of humans and some other primates.
Mesangial Cells
Contractile cells between the capillaries of the glomerulus, which control blood flow, and thereby control blood pressure within the glomerulus.
Mesoderm
The middle of the three primary germ layers in a developing embryo; eventually gives rise to tissues such as bone, muscle, and connective tissue.
Metabolic Acidosis or Alkalosis
A decrease or increase, respectively, in blood pH as a result of metabolic activity.
Metabolic Depression
A reduction in metabolic rate below resting levels; associated with a period of dormancy.
Metabolic Flux
The flow rate through a metabolic pathway.
Metabolic Rate
The rate of heat production by a tissue or organism, usually approximated by oxygen consumption or carbon dioxide production.
Metabolic Theory of Ecology
An extension of the theory of allometric scaling of metabolic rate with body size that attempts to make predictions about processes at higher levels of biological organization (e.g., populations and communities).
Metabolic Water
The water produced by the metabolic breakdown of macromolecules.
Metabolism
The sum of all chemical reactions in a biologic entity.
Metabolizable Energy
The proportion of digestible energy retained by the body; the remainder is unmetabolizable energy lost in excretory products.
Metabolon
A group of enzymes that are spatially localized within the cell and perform a function together.
Metabotropic Receptor
see also ionotropic receptor
A receptor that signals via a signal transduction pathway.
Metalloprotein
A protein with a metal ion integrated into its structure; enzymatic metalloproteins typically involve their metal in oxidation-reduction reactions.
Metamer
In developmental biology, this refers to a body segment.
Metamorphosis
The transition between distinct developmental stages, typically from a larva to an adult.
Metazoan
A multicellular animal.
Methemoglobin
An oxidized form of hemoglobin that can no longer carry oxygen.
Micelle
A lipid monolayer that rolls onto itself to form a sphere with a hydrophobic inner core and hydrophilic exterior.
Michaelis Monstant (K_m)
The concentration of substrate that yields half maximal velocity in an enzymatic reaction.
Michaelis-Menten Equation
V = Vmax × [S] / ([S] + Km).
Microclimate
see also microenvironment
The external environment within a confined space, typically distinct from the broader conditions, such as a subterranean burrow; typically used to describe the conditions experienced by an organism.
Microelectrode
A very small electrode used to record electrical signals from cells.
Microenvironment
Like a microclimate, but can apply to the environment surrounding anything from individual molecules to whole animals.
Microfilaments
A polymer of β-actin used to construct the cytoskeleton.
Microglia
One of the glial cells of the vertebrate central nervous system.
Microtubule
A large, hollow tube consisting of a polymerized tubulin; used to build the cytoskeleton.
Microtubule-Associated Protein (MAP)
A protein that binds to microtubules to alter structural or functional properties.
Microtubule-Organizing Center (MTOC)
A multiprotein complex near the center of the cell from which microtubules grow.
Microvilli
Fingerlike extensions from individual cells, supported by microfilaments, which serve to increase surface area.
Micturition
Urination.
Midbrain
Also called the mesencephalon
The middle portion of the vertebrate brain consisting of the tectum and tegmentum.
Middle Ear
A part of the vertebrate ear that consists of the tympanic membrane and one or more small bones (in mammals, the incus, malleus, and stapes) that help to amplify sounds.
Milieu Intérieur
The internal environment of a cell or organism.
Mineralocorticoids
Steroid hormones involved in water and ion balance.
Mirror Neurons
A neuron that is active when an organism performs a particular action and also when it observes another organism performing that action.
Mitochondria
Organelles within most eukaryotic cells that produce energy by oxidative phosphorylation; organized in many tissues as a network or reticulum.
Mitochondria-Rich Muscle Cell
see also chloride cell
Usually refers to the epithelial cells specialized for ion pumping, which have abundant mitochondria to meet the energy demands of active transport.
M-Line
The midpoint of a sarcomere where the thick filament lacks myosin heads.
Mobile Element
A region of DNA that can be excised and inserted elsewhere within the genome.
Model Organism
Model Organism (see also August Krogh principle).
A species that is widely used in biological research because it has properties that make it particularly suitable for research purposes.
Molal (molality)
Moles of an ion or molecule expressed relative to kilograms of solvent (usually water).
Molar (molarity)
Moles of an ion or molecule expressed relative to liters of solvent (usually water).
Mole
6.02252 × 1023 molecules of a substance; the molecular weight of a substance is the mass of one mole of that substance.
Molecular Chaperone
A protein that uses the energy of ATP hydrolysis to help fold or stabilize denatured proteins; includes heat shock proteins.
Molecular Phylogeny
The evolutionary relationships among organisms as reconstructed based on molecular sequence data.
Monoacylglyceride (or monoglyceride)
A single fatty acid esterified to a glycerol molecule.
Monocyte
A large white blood cell that, in the tetrapod immune system, ingests foreign particles such as microbes; when it leaves the blood stream it differentiates into a macrophage.
Monogastric Stomach
An animal that has a stomach with one (usually acidic) compartment.
Monomer
A single subunit of a multimer, such as a dimer or trimer.
Monosaccharide
A sugar, usually composed of a 6-carbon (sometimes 5-carbon) ring, such as glucose.
Monounsaturated Fatty Acid
A fatty acid with a single double bond.
Monozygotic
Arising from a single zygote.
Morphology
The shape or form of an organism.
Motor End Plate
The location on a muscle that forms synapses with a motor neuron; the muscle side of a neuromuscular junction.
Motor Neuron
A neuron that transmits signals from the central nervous system to skeletal muscles.
Motor Proteins
Mechanoenzymes, such as myosin, that use the energy of ATP hydrolysis to move along cytoskeletal tracks.
Motor Unit
A group of muscle fibers under the control of a single neuron.
mRNA
Messenger RNA; the form of RNA that is used as a template during translation to form protein.
Mucin
The lipopolysaccharide that is the main component of mucus.
Mucosa
see also serosa
Refers to the inside layer of a tissue or organ, often that surface exposed to the lumen of an organ, such as the gastrointestinal tract.
Multipolar Neuron
A nerve cell with a single axon and many dendrites.
Mucous Cells
Cells that secrete a complex mucopolysaccharide onto the surface of a tissue; goblet cells are a type of mucous cell found in the intestinal and respiratory surfaces.
Mucus
A mucopolysaccharide mixture secreted from specialized epithelial cells onto the external surface of a tissue.
Multipolar Neurons
Neurons with many processes leading from the cell body; most of these processes are dendrites, but one may be an axon.
Multipolar Neurons
Neurons with many processes leading from the cell body; most of these processes are dendrites, but one may be an axon.
Muscarinic Acetylcholine Receptors
G protein–coupled receptors that bind acetylcholine.
Muscle
A multicellular tissue composed of myocytes, fibroblasts, and vascular cells; the contraction of the myocytes leads to force generation or shortening.
Muscle Fiber
A single muscle cell; can be mononucleated (as in cardiomyocytes) or multinucleated (as in skeletal muscle fibers).
Muscle Myosin
Myosin II, which is the myosin isoform found in muscle.
Muscle Spindle
A muscle stretch receptor.
Mutation
A heritable alteration in the nucleotide sequence of genomic DNA.
Myelin Sheath
The insulating wrappings of vertebrate axons that are composed of multiple
layers of glial cell plasma membrane. Invertebrate axons have analogous wrappings, but they are not generally termed a myelin sheath.
Myelination
The process of forming the myelin sheath around a vertebrate axon.
Myenteric Plexus
A network of neurons found within the smooth muscle of the gastrointestinal tract that controls its muscular and secretory actions.
Myoblast
A mononucleated, proliferating cell that can differentiate to form a muscle cell.
Myocardium
The muscle of the heart.
Myocyte
A general term for a muscle cell, including smooth muscle cells, cardiomyocytes, and myofibers.
Myofiber
A multinucleated skeletal muscle fiber.
Myofibril
A long bundle of actin, myosin, and associated proteins in muscle cells.
Myogenic
Refers to something originating in the muscle, as in myogenic autoregulation of blood flow or myogenic muscle, which triggers its own activation.
Myogenic Autoregulation
Regulation of blood flow via contraction of vascular smooth muscle that is regulated by processes intrinsic to the muscle.
Myogenic Muscle
Muscles whose contraction is initiated by processes intrinsic to the muscle or organ. For example, a myogenic heart contracts spontaneously without input from the nervous system.
Myoglobin
A type of hemoglobin found in muscle.
Myometrium
The smooth muscle layers of the uterus.
Myosin
A large multigene family of ATP-dependent motor proteins that work in conjunction with actin. The thick filament of muscle is composed of myosin, which is organized into hexamers consisting of two myosin heavy chains (MHC) and four myosin light chains (two regulatory MLC and two essential MLC).
Myosin Heavy Chain
The motor protein that interacts with actin.
Myosin Light Chain
A protein that binds the motor protein myosin II, regulating its structure or function.
Myosin Light Chain Kinase (MLCK)
An enzyme associated with hexameric myosin that phosphorylates myosin light chain.
Myosin Light Chain Phosphatase (MLCP)
An enzyme associated with hexameric myosin that dephosphorylates myosin light chain.
Myotome
A repeating segment in the body musculature of adult fish; also, the embryonic form of muscle derived from a body segment, or somite.
Myotube
An early stage of muscle differentiation n which multiple myoblasts fuse together to form a multinucleated contractile tubular cell.
