P Flashcards
P_50
The partial pressure at which a respiratory pigment is 50 percent saturated with oxygen.
Pacemaker
A cell or group of cells whose output of action potentials occurs in a rhythmic pattern.
Pacemaker Cell
An excitable cell that spontaneously fires action potentials in a rhythmic pattern.
Pacemaker Potentials
Spontaneous depolarizations of the resting membrane potential that ultimately trigger action potentials within pacemaker cells.
Pacinian Corpuscle
A type of vertebrate skin mechanoreceptor.
Pancreas
A vertebrate organ that produces endocrine hormones including insulin and glucagon and also produces exocrine secretions that are involved in digestion.
Pancreatic Beta Cells
Cells within the vertebrate pancreas that secrete the hormone insulin.
Panting
A mode of thermoregulation whereby an increase in the frequency of respiration enhances heat loss from the body core.
Papillary Muscles
Muscles connected to the chordae tendineae of the mammalian heart that help to anchor the atrioventricular valves.
Parabronchi
Smallest airways of a bird lung.
Paracellular Pathway
The pathway via which paracellular transport occurs.
Paracellular Transport
Passage of solutes or water between cells; in most epithelial tissues, tight junctions and other cell-cell junctions prevent paracellular movement of fluids.
Paracellular Transport
Passage of solutes or water between cells; in most epithelial tissues, tight junctions and other cell-cell junctions prevent paracellular movement of fluids.
Paracrine
A type of chemical messenger that is involved in local signaling between nearby cells; paracrine messengers move through the interstitial fluid by diffusion.
Parafacial Respiratory Group
A group of neurons in the vertebrate brain that is involved in the generation of respiratory rhythms.
Parallel Evolution
The evolution of a shared underlying trait in similar ways in two distinct but related lineages.
Paralogs
see also homologs, orthologs
Genes that are the result of a gene duplication event within a lineage.
Parasympathetic Nervous System
Part of the vertebrate autonomic nervous system; generally active during periods of rest; releases acetylcholine onto target organs.
Parathyroid Glands
Glands located on the posterior surface of the thyroid gland that release parathyroid hormones in response to changes in extracellular calcium.
Parathyroid Hormone
Peptide hormone that regulates blood calcium levels.
Parietal Cells
The acid-secreting cells within the gastric mucous membrane.
Parthenogenesis
A mode of asexual reproduction whereby offspring are produced by a female as a result of a variation on the meiotic pathway. Because meiosis is involved, chromosomal recombination is possible and the parthenogenic offspring are not clones of the parent.
Partial Pressure
The pressure exerted by one of the gases in a gas mixture. The sum of the partial pressures of all the gases in a mixture gives the total pressure.
Partition Coefficient
A measure of the relative ability of a solute to dissolve in two different solutes, such as oil and water.
Parturition
The birthing process by which offspring of viviparous and ovoviviparous females are expelled from the reproductive tract.
Parvalbumin
A Ca2+-binding protein in the cytoplasm of some muscles, which buffers Ca2+ levels to accelerate relaxation.
Passive Diffusion
A type of passive transport that does not require a protein carrier.
Passive Transport
Movement across a cell membrane without an energy investment other than the chemical gradient of the transported molecule; includes both passive diffusion and facilitated diffusion.
Patch Clamping
A method used by neurobiologists to study the function of ion channels, in which the voltage or current across a small patch of membrane is manipulated using a small glass microelectrode applied to the surface of the cell.
Pathogen-Associated Molecular Patterns (PAMPs)
Molecules arising from pathogens that can be recognized as foreign by immune cells.
Pattern Generator
A group of neurons whose rhythmic firing coordinates a rhythmic physiological process or behavior, such as breathing or locomotion.
Pattern-Recognition Receptors (PRRs)
Proteins produced by the immune system that bind PAMPs.
Pavement Cells
Cells within the gills of fish that are responsible for gas exchange.
Pejus Temperature
The temperatures at which physiological processes start to decline in function when temperature is above or below the optimum for function.
Pentose
A five-carbon monosaccharide, such as ribose and deoxyribose.
Peptide Bond
A carbon-nitrogen bond (–C–N–); most common in polymers of amino acids
Perfusion
Movement of fluid through a tissue (e.g., flow of blood through a capillary bed).
Pericardium
The sac surrounding a heart.
Pericyte Cell
Contractile cells that wrap around capillaries.
Perilymph
The fluid found in the cochlea of the inner ear.
Peripheral Chemoreceptors
Chemoreceptors located in the aortic and carotid bodies of vertebrates that detect changes in blood chemistry.
Peripheral Membrane Protein
A protein that is weakly bound to the membrane through an interaction with a lipid or integral membrane protein.
Peripheral Nervous System (PNS)
All of the neurons outside of the central nervous system.
Peristalsis
The rhythmic contractions of intestinal smooth muscle; involved in propelling a bolus of food along the gastrointestinal tract and in moving blood through the circulatory systems of some animals.
Permeability
The ability of a molecule to cross a barrier, such as a membrane.
Permeability
The ability of a molecule to cross a barrier, such as a membrane.
Permease
A transporter that mediates facilitated diffusion, but is neither a channel nor a porin.
pH Scale
A measure of acidity, expressed as the negative log_10 of the proton concentration.
pH-Bicarbonate Plot (Davenport diagram)
A graphical depiction of the relationship between the pH and bicarbonate concentration of a solution. Usually used to describe these relationships in arterial blood.
Phagocyte
A cell that carries out phagocytosis.
Phagocytosis
The endocytosis of large particles from the extracellular space.
Phagocytosis
The endocytosis of large particles from the extracellular space.
Phasic Muscle
A type of muscle that undergoes rapid contractions and relaxations; a twitch muscle.
Phasic Receptor
A sensory receptor that produces action potentials only during part of the stimulus (usually at stimulus onset and removal).
Phenotype
The physical characteristics of an organism; the result of an interaction between the genotype and the environment.
Phenotypic Plasticity
see also acclimation
Production of different phenotypes by a single genotype as a result of environmental cues; may be reversible or irreversible.
Pheromones
Chemical messengers released by an animal into the environment that have an effect on another animal of the same species.
Phosphagens
Energy-rich compounds that transfer energy in reactions in which a large change in free energy results when a phosphate bond is broken.
Phosphatase
An enzyme that removes a phosphate group from a molecule; important in signal transduction pathways because it reverses the phosphorylations catalyzed by kinases.
Phosphodiester Bond
–P–O–P–.
Phosphodiesterase
An enzyme that breaks down the phosphodiester bonds of cyclic nucleotides such as cAMP and cGMP.
Phosphoglycerides
The major class of phospholipids of biological membranes, consisting of a glycerol backbone, two fatty acids, and a polar head group linked to the glycerol via phosphate.
Phospholipase
An enzyme that breaks down phospholipids, releasing either diacylglycerol, polar head groups, or fatty acids, depending on the type of phospholipase.
Phospholipids
Phosphoglycerides and sphingolipids.
Phosphorylation
The addition of a phosphate group via a kinase, expending ATP (e.g., a protein kinase catalyzes the phosphorylation of a protein).
Phosphorylation Cascade
A type of signal transduction pathway that involves multiple phosphorylation steps.
Phosphorylation Potential
An expression of energy status; the mass action ratio for an ATPase reaction ([ATP]/[ADP][Pi]).
Photon
The fundamental particle of electromagnetic radiation. Streams of photons can have differing wavelengths, in which case the resulting radiation is given different names (e.g., X-rays, gamma rays, visible light).
Photoperiod
The length of the light and dark phases of a day.
Photopigments
Molecules specialized for detecting photons; consist of a chromophore and an associated protein.
Photoreceptors
Sensory receptors that detect photons with wavelengths in the visible spectrum (i.e., light). Can be used to describe either the receptor proteins or the cells that contain them.
Phototaxis
Movement in response to light, either toward (positive phototaxis) or away (negative phototaxis).