Physiology Terms
Physiology explains how the body works: how organs and systems function and keep conditions inside the body steady. These terms cover the heart and circulation, the kidneys, hormones, muscles, nerves, digestion and homeostasis.
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- AcetylcholineNeuroscienceAcetylcholine is the neurotransmitter motor neurons use to make skeletal muscles contract, and a key messenger in the autonomic nervous system and brain.
- Action potentialNeuroscienceAn action potential is a brief, all-or-none reversal of the voltage across a nerve or muscle cell membrane that travels along the cell as a signal.
- Active transportCell BiologyActive transport is the movement of a substance across a cell membrane against its concentration gradient, powered by energy, usually from ATP.
- Adaptive immunityImmunologyAdaptive immunity is the branch of the immune system that learns to recognize specific antigens and remembers them, so it responds faster next time.
- Adrenal glandHuman AnatomyAn adrenal gland is one of two small endocrine glands atop the kidneys, with a cortex that makes steroid hormones and a medulla that makes epinephrine.
- AgonistPharmacologyAn agonist is a drug or natural substance that binds to a receptor and activates it, producing a biological response.
- AldosteronePhysiologyAldosterone is a steroid hormone from the adrenal cortex that makes the kidneys keep sodium and water and excrete potassium, raising blood volume.
- AlveolusPhysiologyAn alveolus is one of the tiny air sacs at the end of the lung's airways, where oxygen passes into the blood and carbon dioxide passes out.
- AngiogenesisOncologyAngiogenesis is the growth of new blood vessels from existing ones, needed for growth and healing and exploited by tumors to feed themselves.
- Antidiuretic hormonePhysiologyAntidiuretic hormone is a peptide hormone made in the hypothalamus and released by the posterior pituitary that makes the kidneys keep water.
- AortaHuman AnatomyThe aorta is the body's largest artery, carrying oxygenated blood out of the heart's left ventricle to the arteries that supply every organ.
- AtrophyPathologyAtrophy is the shrinking of a cell, tissue or organ that had reached normal size, usually as cells lose substance in response to reduced demand or support.
- Autonomic nervous systemNeuroscienceThe autonomic nervous system is the division of the nervous system that runs involuntary functions such as heart rate, digestion and gland secretion.
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- Basal metabolic rateFood NutritionBasal metabolic rate is the energy the body uses per unit of time just to stay alive when awake, lying at rest, fasting and in a comfortable temperature.
- Blood pressurePhysiologyBlood pressure is the force that circulating blood exerts on the walls of the arteries, recorded as systolic over diastolic pressure in mm Hg.
- BoneHuman AnatomyBone is the hard, mineralized connective tissue that makes up most of the adult skeleton, and the name for each skeletal organ built from it.
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- CalorieFood NutritionA calorie is a unit of energy, the heat needed to warm one gram of water by one degree Celsius; food energy is given in kilocalories, often written Calories.
- Cardiac cyclePhysiologyThe cardiac cycle is the sequence of contraction and relaxation of the heart's chambers that makes up one complete heartbeat.
- Cardiac outputPhysiologyCardiac output is the volume of blood each ventricle of the heart pumps in one minute, equal to heart rate multiplied by stroke volume.
- CartilageHuman AnatomyCartilage is a tough, flexible connective tissue without blood vessels that cushions joints and shapes the nose, ears and airways.
- CholesterolBiochemistryCholesterol is a waxy steroid lipid found in animal cell membranes and used to make steroid hormones, vitamin D and the bile salts that digest fat.
- Chronic kidney diseaseMedicineChronic kidney disease is a gradual, lasting loss of kidney function in which the kidneys filter blood less well, so wastes and fluid build up in the body.
- Circadian rhythmNeuroscienceA circadian rhythm is a roughly 24-hour cycle in an organism's body and behavior, driven by an internal clock and reset each day mainly by light.
- CortisolPhysiologyCortisol is a steroid hormone made by the adrenal cortex that helps the body cope with stress, raises blood glucose and dampens inflammation.
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- Diabetes mellitusMedicineDiabetes mellitus is a chronic disease in which blood glucose stays too high because the body makes too little insulin or cannot use it well.
- DiaphragmHuman AnatomyIn anatomy, the diaphragm is the dome-shaped sheet of muscle and tendon dividing the chest from the abdomen, and the main muscle of breathing.
- DiffusionCell BiologyDiffusion is the net movement of molecules from a region of higher concentration to one of lower concentration, driven by their random motion.
- DigestionPhysiologyDigestion is the process by which the body breaks food down, by chewing, churning and enzymes, into molecules small enough to absorb into the blood.
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- EctothermZoologyAn ectotherm is an animal whose body temperature depends mainly on heat from its surroundings rather than on heat made by its own metabolism.
- EdemaPathologyEdema is swelling caused by excess fluid collecting in the spaces between the cells of a tissue, most often seen in the feet, ankles and legs.
- ElectrolyteFood NutritionAn electrolyte is a substance that forms ions in water so the solution conducts electricity; in the body, it means charged minerals such as sodium.
- Endocrine systemPhysiologyThe endocrine system is the set of glands and cells that release hormones into the blood to regulate growth, metabolism, reproduction and more.
- EndothermZoologyAn endotherm is an animal that keeps its body warm mainly with heat produced by its own metabolism, as mammals and birds do.
- EsophagusHuman AnatomyThe esophagus is the muscular tube, about 25 centimeters long, that carries swallowed food and liquid from the pharynx down to the stomach.
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- Gas exchangePhysiologyGas exchange is the movement of oxygen into the blood and carbon dioxide out of it by diffusion across thin membranes, mainly in the lungs and tissues.
- Glomerular filtration ratePhysiologyGlomerular filtration rate is the volume of fluid both kidneys filter out of the blood each minute, the standard measure of kidney function.
- GlucagonPhysiologyGlucagon is a peptide hormone made by alpha cells of the pancreas that raises blood glucose, mainly by making the liver release glucose.
- GluconeogenesisBiochemistryGluconeogenesis is the metabolic pathway that makes new glucose from non-carbohydrate sources such as lactate, glycerol and certain amino acids.
- Glycemic indexFood NutritionThe glycemic index is a scale up to 100 ranking carbohydrate foods by how much they raise blood glucose after eating, compared with the same amount of glucose.
- GlycogenBiochemistryGlycogen is a large, highly branched polymer of glucose that animals and fungi use to store carbohydrate, mainly in the liver and skeletal muscle.
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- HeartHuman AnatomyThe heart is the hollow, muscular organ in the chest whose four chambers pump blood through the lungs and then around the rest of the body.
- Heart failureMedicineHeart failure is a long-term condition in which the heart fails to pump as much blood as the body needs, even though it has not stopped beating.
- HemoglobinPhysiologyHemoglobin is the iron-containing protein in red blood cells that picks up oxygen in the lungs and releases it to the body's tissues.
- HemostasisPhysiologyHemostasis is the body's process for stopping bleeding from a damaged blood vessel, through vessel constriction, a platelet plug and a fibrin clot.
- HomeostasisPhysiologyHomeostasis is the body's ability to keep internal conditions, such as temperature, blood glucose and pH, steady while conditions around it change.
- HormonePhysiologyA hormone is a chemical messenger released into the blood by a gland or cell that changes the activity of distant target cells with matching receptors.
- HyperplasiaPathologyHyperplasia is the enlargement of a tissue or organ through a rise in its number of cells, which still look normal under the microscope.
- HypertensionMedicineHypertension is a long-term condition in which the pressure of blood against artery walls stays higher than normal, straining the heart and vessels.
- HyperthyroidismMedicineHyperthyroidism is a condition in which the thyroid gland releases more hormone than the body needs, speeding up metabolism and many body functions.
- HypertrophyPathologyHypertrophy is the enlargement of a tissue or organ because its individual cells grow larger, rather than because the number of cells increases.
- HypothyroidismMedicineHypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone, so metabolism and many body functions slow down.
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- InflammationImmunologyInflammation is the body's protective response to infection or injury, in which leaky, widened blood vessels bring immune cells and fluid to the site.
- Innate immunityImmunologyInnate immunity is the inborn, fast-acting set of body defenses that reacts to any invader in the same general way, with no prior exposure needed.
- InsulinPhysiologyInsulin is a peptide hormone made by beta cells in the pancreas that lowers blood glucose by helping body cells take up and store sugar.
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- JaundiceMedicineJaundice is yellowing of the skin and the whites of the eyes that occurs when the pigment bilirubin builds up in the blood.
- JejunumHuman AnatomyThe jejunum is the middle stretch of the small intestine, lying between the duodenum and ileum, and a main site where digested nutrients are absorbed.
- Jugular veinHuman AnatomyA jugular vein is one of the large paired veins in the neck that return blood from the brain, face and scalp toward the heart.
- Juxtaglomerular apparatusPhysiologyThe juxtaglomerular apparatus is a cluster of specialized kidney cells beside each glomerulus that senses salt and blood pressure and releases renin.
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- Ketone bodyBiochemistryA ketone body is a water-soluble fuel made by the liver from fatty acids when glucose is scarce and used for energy by the brain, heart and muscle.
- KidneyHuman AnatomyThe kidneys are two bean-shaped organs that filter the blood to make urine, balancing the body's water, salts and acid and helping set blood pressure.
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- LigamentHuman AnatomyA ligament is a band of tough, fibrous connective tissue that joins one bone to another and keeps a joint stable while letting it move.
- LiverHuman AnatomyThe liver is the largest gland and internal organ, lying in the upper right abdomen, where it makes bile, processes nutrients and clears toxins.
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- MacronutrientFood NutritionA macronutrient is a nutrient needed in large amounts, namely carbohydrate, protein or fat, which together supply energy and the raw materials for growth.
- Menstrual cyclePhysiologyThe menstrual cycle is the roughly monthly series of hormone-driven changes in the ovaries and uterus that prepares the body for a possible pregnancy.
- MetabolismBiochemistryMetabolism is the full set of chemical reactions in a cell or organism, both those that break molecules down for energy and those that build them up.
- MicrobiomeMicrobiologyA microbiome is the community of bacteria, fungi, viruses and other microbes, with their genes, that lives in a particular place, such as the human gut.
- MicronutrientFood NutritionA micronutrient is a vitamin or mineral that the body needs only in tiny amounts but cannot do without, such as iron, iodine, vitamin A or folate.
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- Negative feedbackPhysiologyNegative feedback is a control process in which a change in a body variable sets off responses that reverse the change, keeping it near a set point.
- NephronPhysiologyA nephron is the microscopic functional unit of the kidney, which filters blood and then adjusts the filtered fluid to form urine.
- NeutrophilImmunologyA neutrophil is the most common white blood cell in human blood, a short-lived phagocyte that rushes to infections and destroys bacteria and fungi.
O
- OogenesisDevelopmental BiologyOogenesis is the process by which egg cells form in the ovary, beginning before birth and yielding one mature egg and small polar bodies from each oocyte.
- OsmosisCell BiologyOsmosis is the diffusion of water across a selectively permeable membrane, from the side with fewer dissolved solutes to the side with more.
P
- PancreasHuman AnatomyThe pancreas is a gland behind the stomach that sends digestive enzymes to the small intestine and releases insulin and glucagon into the blood.
- Parasympathetic nervous systemNeuroscienceThe parasympathetic nervous system is the autonomic division that conserves energy and controls rest-and-digest activities such as digestion.
- pHBiochemistrypH is a number, usually on a scale of 0 to 14, that shows how acidic or basic a water-based solution is from its concentration of hydrogen ions.
- Pituitary glandHuman AnatomyThe pituitary gland is a pea-sized endocrine gland below the brain that, under hypothalamic control, releases hormones governing growth and other glands.
- PlateletPhysiologyA platelet is a small cell fragment in the blood that helps stop bleeding by plugging damaged vessels and helping a blood clot form.
- Positive feedbackPhysiologyPositive feedback is a control process in which a change triggers responses that amplify that same change, driving a process quickly to an end point.
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- ReceptorPharmacologyA receptor is a protein, on a cell's surface or inside it, that binds a specific signaling molecule and triggers a response in the cell.
- Red blood cellPhysiologyA red blood cell, or erythrocyte, is a disc-shaped blood cell without a nucleus that is packed with hemoglobin and carries oxygen around the body.
- Renin–angiotensin–aldosterone systemPhysiologyThe renin–angiotensin–aldosterone system is a hormone cascade, begun by renin from the kidneys, that raises blood pressure and blood volume when they fall.
- Resting membrane potentialPhysiologyThe resting membrane potential is the steady voltage across a cell's membrane when it is not signaling, about -70 mV in a typical neuron, inside negative.
- Rigor mortisForensic MedicineRigor mortis is the temporary stiffening of muscles after death, caused by loss of ATP, which leaves myosin locked onto actin until muscle proteins break down.
S
- SarcomerePhysiologyA sarcomere is the repeating contractile unit of striated muscle, the section of a myofibril between two Z-discs where actin and myosin interact.
- ShockPathologyShock is a life-threatening state in which the circulation fails to bring tissues the oxygen and nutrients their cells need.
- Skeletal muscleHuman AnatomySkeletal muscle is the striated, voluntary muscle tissue attached to bones by tendons that moves the body, holds posture and produces heat.
- Sliding filament theoryPhysiologyThe sliding filament theory is the model of muscle contraction in which thin actin filaments slide past thick myosin filaments, shortening each sarcomere.
- Small intestineHuman AnatomyThe small intestine is the long, coiled tube between the stomach and the large intestine where most digestion and nearly all nutrient absorption happen.
- Sodium–potassium pumpPhysiologyThe sodium–potassium pump is a membrane enzyme that uses ATP to move three sodium ions out of a cell and two potassium ions in on each cycle.
- SpermatogenesisDevelopmental BiologySpermatogenesis is the process by which diploid stem cells in the testes divide and develop into haploid sperm, continuing from puberty through adult life.
- StomachHuman AnatomyThe stomach is a J-shaped, muscular sac of the digestive tract that stores food, churns it with acid and enzymes, and starts the digestion of protein.
- Stroke volumePhysiologyStroke volume is the volume of blood that one ventricle of the heart pumps out with each beat, about 70 mL in a resting adult.
- Sympathetic nervous systemNeuroscienceThe sympathetic nervous system is the division of the autonomic nervous system that readies the body for action, producing the fight-or-flight response.
- SynapseNeuroscienceA synapse is the junction where a neuron passes a signal to another cell, usually by releasing a neurotransmitter across a narrow gap.
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- TendonHuman AnatomyA tendon is a tough cord of dense connective tissue linking a muscle to a bone, which passes on the muscle's pull to move it.
- ThermoregulationPhysiologyThermoregulation is the set of processes an organism uses to keep its body temperature within a set range by balancing heat gain and heat loss.
- Thyroid glandHuman AnatomyThe thyroid gland is a butterfly-shaped endocrine gland in the front of the neck whose iodine-containing hormones set the body's metabolic rate.
- Tidal volumePhysiologyTidal volume is the amount of air that moves into or out of the lungs in one normal, relaxed breath, about 500 mL in a healthy adult.
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