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Estrella Mountain - Anatomy terms Category: Education > Body parts Date & country: 25/03/2011, USA Words: 586

abiogenesis
Early theory that held that some organisms originated from nonliving material.

abscisic acid
A plant hormone that promotes dormancy in perennial plants and causes rapid closure of leaf stomata when a leaf begins to wilt.

absorption
The process by which the products of digestion are transferred into the body's internal environment, enabling them to reach the cells.

absorptive feeders
Animals such as tapeworms that ingest food through the body wall.

acetyl CoA
An intermediate compound formed during the breakdown of glucose by adding a two-carbon fragment to a carrier molecule (Coenzyme A or CoA).

acetylcholine
A chemical released at neuromuscular junctions that binds to receptors on the surface of the plasma membrane of muscle cells, causing an electrical impulse to be transmitted. The impulse ultimately leads to muscle contraction.

acid
A substance that increases the number of hydrogen ions in a solution.

acid rain
The precipitation of sulfuric acid and other acids as rain. The acids form when sulfur dioxide and nitrogen oxides released during the combustion of fossil fuels combine with water and oxygen in the atmosphere.

acoelomates
Animals that do not have a coelom or body cavity; e.g., sponges and flatworms.

actin
The protein from which microfilaments are composed; forms the contractile filaments of sarcomeres in muscle cells.

action potential
A reversal of the electrical potential in the plasma membrane of a neuron that occurs when a nerve cell is stimulated; caused by rapid changes in membrane permeability to sodium and potassium.

adaptive radiation
The development of a variety of species from a single ancestral form; occurs when a new habitat becomes available to a population. Evolutionary pattern of divergence of a great many taxa from a common ancestral species as a result of novel adaptations or a recent mass extinction. Examples: mammals during the Cenozoic Era after the extinction of din...

adrenocorticotropic hormone (ACTH)
A hormone produced by the anterior pituitary that stimulates the adrenal cortex to release several hormones including cortisol.

adventitious roots
Roots that develop from the stem following the death of the primary root. Branches from the adventitious roots form a fibrous root system in which all roots are about the same size; occur in monocots.

age structure
The relative proportion of individuals in each age group in a population.

aldosterone
A hormone secreted by the adrenal glands that controls the reabsorption of sodium in the renal tubule of the nephron.

alleles
Alternate forms of a gene.

allergens
Antigens that provoke an allergic reaction.

altitudinal gradient
As altitude increases, a gradient of cooler, drier conditions occurs.

alveoli
Tiny, thin-walled, inflatable sacs in the lungs where oxygen and carbon dioxide are exchanged.

amensalism
A symbiotic relationship in which members of one population inhibit the growth of another population without being affected.

amniote egg
An egg with compartmentalized sacs (a liquid-filled sac in which the embryo develops, a food sac, and a waste sac) that allowed vertebrates to reproduce on land.

amoebocytes
Amoeboid cells in sponges that occur in the matrix between the epidermal and collar cells. They transport nutrients.

anabolic reactions
Reactions in cells in which new chemical bonds are formed and new molecules are made; generally require energy, involve reduction, and lead to an increase in atomic order.

anaerobic
Refers to organisms that are not dependent on oxygen for respiration.

analogous structures
Body parts that serve the same function in different organisms, but differ in structure and embryological development; e. g., the wings of insects and birds.

anaphylactic shock
See anaphylaxis.

anaphylaxis
A severe allergic reaction in which histamine is released into the circulatory system; occurs upon subsequent exposure to a particular antigen; also called anaphylactic shock.

aneuploidy
Variation in chromosome number involving one or a small number of chromosomes; commonly involves the gain or loss of a single chromosome.

angina
Chest pain, especially during physical exertion or emotional stress, that is caused by gradual blockage of the coronary arteries.

angiosperms
Flowering plants. First appearing at least 110 million years ago from an unknown gymnosperm ancestor, flowering planbts have risen to dominance in most of the world's floras. The male gametophyte is 2-3 cells contained within a pollen grain; the female gametophyte is usually eight cells contained within an ovule which is retaind on the sporophyte p...

antagonistic muscles
A pair of muscles that work to produce opposite effects&emdash;one contracts as the other relaxes: for example, the bicep and tricep muscles on opposite sides of your upper arm.

antibiotics
Substances produced by some microorganisms, plants, and vertebrates that kill or inhibit the growth of bacteria.

antibody-mediated immunity
Immune reaction that protects primarily against invading viruses and bacteria through antibodies produced by plasma cells; also known as humoral immunity.

antidiuretic hormone (ADH)
A hormone produced by the hypothalamus and released by the pituitary gland that increases the permeability of the renal tubule of the nephron and thereby increases water reabsorption; also known as vasopressin.

antigens
Molecules carried or produced by microorganisms that initiate antibody production; mostly proteins or proteins combined with polysaccharides.

anus
The posterior opening of the digestive tract.

aorta
The artery that carries blood from the left ventricle for distribution throughout the tissues of the body. The largest diameter and thickest walled artery in the body.

apical meristem
A meristem (embryonic tissue) at the tip of a shoot or root that is responsible for increasing the plant's length.

apnea
A disorder in which breathing stops for periods longer than 10 seconds during sleep; can be caused by failure of the automatic respiratory center to respond to elevated blood levels of carbon dioxide.

apocrine glands
Sweat glands that are located primarily in the armpits and groin area; larger than the more widely distributed eccrine glands.

appendicular skeleton
The bones of the appendages (wings, legs, and arms or fins) and of the pelvic and pectoral girdles that join the appendages to the rest of the skeleton; one of the two components of the skeleton of vertebrates.

aridity
The condition of receiving sparse rainfall; associated with cooler climates because cool air can hold less water vapor than warm air. Many deserts occur in relatively warm climates, however, because of local or global influences that block rainfall.

arrector pili
A muscle running from a hair follicle to the dermis. Contraction of the muscle causes the hair to rise perpendicular to the skin surface, forming "goose pimples."

arteries
Thick-walled vessels that carry blood away from the heart. Singular=artery.

arterioles
The smallest arteries; usually branch into a capillary bed.

artificial selection
The process in which breeders choose the variants to be used to produce succeeding generations.

asexual reproduction
A method of reproduction in which genetically identical offspring are produced from a single parent; occurs by many mechanisms, including fission, budding, and fragmentation.

assortment
A way in which meiosis produces new combinations of genetic information. Paternal and maternal chromosomes line up randomly during synapsis, so each daughter cell is likely to receive an assortment of maternal and paternal chromosomes rather than a complete set from either.

asthma
A respiratory disorder caused by allergies that constrict the bronchioles by inducing spasms in the muscles surrounding the lungs, by causing the bronchioles to swell, or by clogging the bronchioles with mucus.

atmosphere
The envelope of gases that surrounds the Earth; consists largely of nitrogen (78%) and oxygen (21%).

atom
The smallest indivisible particle of matter that can have an independent existence.

atomic number
The number of protons in the nucleus of an atom.

atomic weight
The sum of the weights of an atom's protons and neutrons, the atomic weight differs between isotopes of the same element.

atrioventricular (AV) node
Tissue in the right ventricle of the heart that receives the impulse from the atria and transmits it through the ventricles by way of the bundles of His and the Purkinje fibers.

atrioventricular (AV) valve
The valve between each auricle and ventricle of the heart.

auricle
The chamber of the heart that receives blood from the body returned to the heart by the veins. Also referred to as atrium.

autonomic system
The portion of the peripheral nervous system that stimulates smooth muscle, cardiac muscle, and glands; consists of the parasympathetic and sympathetic systems.

autosomes
The chromosomes other than the sex chromosomes. Each member of an autosome pair (in diploid organisms) is of similar length and in the genes it carries.

autotrophic
Refers to organisms that synthesize their nutrients and obtain their energy from inorganic raw materials.

autotrophs
Organisms that synthesize their own nutrients; include some bacteria that are able to synthesize organic molecules from simpler inorganic compounds.

auxins
A group of hormones involved in controlling plant growth and other functions; once thought responsible for phototropism by causing the cells on the shaded side of a plant to elongate, thereby causing the plant to bend toward the light.

axial skeleton
The skull, vertebral column, and rib cage; one of the two components of the skeleton in vertebrates.

axons
Long fibers that carry signals away from the cell body of a neuron.

basal body
A structure at the base of a cilium or flagellum; consists of nine triplet microtubules arranged in a circle with no central microtubule.

base
A substance that lowers the hydrogen ion concentration in a solution.

basidia
Specialized club-shaped structures on the underside of club fungi (Basidiomycetes) within which spores form (sing.: basidium).

basidiospores
The spores formed on the basidia of club fungi (Basidiomycetes).

benthic zone
One of the two basic subdivisions of the marine biome; includes the sea floor and bottom-dwelling organisms.

bicarbonate ions
A weak base present in saliva that helps to neutralize acids in food.

big bang theory
A model for the evolution of the universe that holds that all matter and energy in the universe were concentrated in one point, which suddenly exploded. Subsequently, matter condensed to form atoms, elements, and eventually galaxies and stars.

bilateral symmetry
In animals, refers to those that have a single axis of symmetry.

biliary system
The bile-producing system consisting of the liver, gallbladder, and associated ducts.

binary fission
The method by which bacteria reproduce. The circular DNA molecule is replicated; then the cell splits into two identical cells, each containing an exact copy of the original cell's DNA.

binomial system of nomenclature
A system of taxonomy developed by Linnaeus in the early eighteenth century. Each species of plant and animal receives a two-term name; the first term is the genus, and the second is the species.

biogeography
The study of the distribution of plants and animals across the Earth.

bioluminescent
Refers to organisms that emit light under certain conditions.

biomass
The total weight of living tissue in a community.

biome
A large-scale grouping that includes many communities of a similar nature.

biosphere
All ecosystems on Earth as well as the Earth's crust, waters, and atmosphere on and in which organisms exist; also, the sum of all living matter on Earth.

birth rate
The ratio between births and individuals in a specified population at a particular time.

bladder
A hollow, distensible organ with muscular walls that stores urine and expels it through the urethra.

blastocoel
The fluid-filled cavity at the center of a blastula.

blood group or type
One of the classes into which blood can be separated on the basis of the presence or absence of certain antigens; notably, the ABO types and the Rh blood group.

body fossil
The actual remains (however permineralized, compressed or otherwise post-mortem altered) of an organism; includes bones, shells, and teeth.

bottlenecks
Drastic short-term reductions in population size caused by natural disasters, disease, or predators; can lead to random changes in the population's gene pool.

bronchi
Tubes that carry air from the trachea to the lungs (sing.: bronchus).

bronchioles
Small tubes in the lungs that are formed by the branching of the bronchi; terminate in the alveoli.

bronchitis
A respiratory disorder characterized by excess mucus production and swelling of the bronchioles; caused by long-term exposure to irritants such as cigarette smoke and air pollutants.

brush border
The collection of microvilli forming a border on the intestinal side of the epithelial cells of the small intestine.

bud sports
Buds that produce fruit that is different from the rest of the fruit on the tree; vegetatively propagated by grafting cuttings onto another plant.

buffers
Chemicals that maintain pH values within narrow limits by absorbing or releasing hydrogen ions.

bulbourethral glands
Glands that secrete a mucus-like substance that is added to sperm and provides lubrication during intercourse.

calcitonin
A hormone produced by the thyroid that plays a role in regulating calcium levels.

campodactyly
A dominant trait in which a muscle is improperly attached to bones in the little finger, causing the finger to be permanently bent.

capillary bed
A branching network of capillaries supplied by arterioles and drained by venules.

carbohydrates
Organic molecules composed of carbon, hydrogen, and oxygen that serve as energy sources and structural materials for cells of all organisms.

cardiac cycle
One heartbeat; consists of atrial contraction and relaxation, ventricular contraction and relaxation, and a short pause.

carpals
The bones that make up the wrist joint.

catabolic reactions
Reactions in cells in which existing chemical bonds are broken and molecules are broken down; generally produce energy, involve oxidation, and lead to a decrease in atomic order.