Biology Flashcards
(484 cards)
1
Q
Abductor
A
A muscle that moves a limb away from the center of the body
2
Q
Absorption
A
The process by which substances are taken up into or across tissues
3
Q
Acetylcholine
A
A neurotransmitter found throughout the nervous system (somatic motor neurons, preganglionic parasympathetic and sympathetic nerves, and postganglionic parasympathetic neurons); metabolized by acetylcholinesterase
4
Q
Acrosome
A
The large visible at the head of a sperm cell containing enzymes that degrade the ovum cell membrane to allow fertilization
5
Q
Actin
A
A protein found in the cytoskeleton and muscle cells; it is the principle constituent of the thin filaments and microfilaments
6
Q
Action potential
A
An abrupt change in the membrane potential of a nerve or muscle caused by changes in membrane ionic permeability; results in conduction of an impulse in nerves or contraction in muscles
7
Q
Active immunity
A
An immune response (antibody production or cellular immunity) acquired in response to exposure to an antigen
8
Q
Active site
A
Substrate-binding region of an enzyme
9
Q
Adaptation
A
The development of characteristics that enable an organism to survive and reproduce in its habitat
10
Q
Adaptive immunity
A
Highly specific form of immunity that retains chemical memory of each invader encountered and os able to tailor the immune response to the specific pathogen
11
Q
Adaptive radiation
A
The evolutionary process by which one species gives rise to several species, each specialized for different niches
12
Q
Adductor
A
A muscle that moves a limb toward the center of the body
13
Q
Adenine
A
A purine base present in DNA and RNA; it forms hydrogen bonds with thymine and uracil
14
Q
Adenine triphosphate (ATP)
A
A nucleotide molecule consisting of adenine, ribose, and three phosphate moieties; the outer two phosphates are bound by high-energy bonds
15
Q
Adipose
A
Refers to fatty tissue, fat-storing tissue, or fat within cells
16
Q
Aerobic
A
Refers to a biological process that occurs in the presence of molecular oxygen (O2) or to organisms that cannot live without molecular oxygen
17
Q
Afferent (sensory) neuron
A
A neuron that picks up impulses form sensory receptors and transmits them toward the central nervous system
18
Q
Agranulocyte
A
Type of leukocyte that does not contain cytoplasmic granules, including lymphocytes and monocytes
19
Q
Albumin
A
Protein synthesized in the liver that maintains the oncotic pressure of the blood and serves as a carrier for many drugs and hormones
20
Q
Allantois
A
One of four embryonic membranes; it contains the growing embryo’s waste products
21
Q
Allele
A
Alternative forms of the same gene coding for a particular trait; alleles segregate during meiosis
22
Q
Allergy
A
A type of autoimmunity in which a person’s immune system becomes over activated by common substances in the environment
23
Q
Alveolus
A
Basic functional unit of the lung; a tiny sac specialized for passive gas exchange between the funds and the blood
24
Q
Amino acids
A
The building blocks of proteins, each containing an amino group, a carboxylic acid group, and a side chain (or R group) attached to the α-carbon
25
Amnion
The innermost fluid-filled embryonic membrane; it forms a protective sac surrounding the embryos of birds, reptiles, and mammals
26
Amplification
Characteristic of a signaling cascade, in which the binding of a single peptide hormone to a membrane-bound receptor results in a signal that increases in strength through the signaling cascade
27
Anaerobic
Refers to a biological process that can occur without oxygen or to organisms that can live without molecular oxygen
28
Anaphase
The stage of mitosis or meiosis characterized by the migration of chromatids or homologous chromosomes to opposite poles of the dividing cell
29
Androgen
Any male sex hormone, such as testosterone
30
Antibiotic
Substance that kills or inhibits the growth of bacteria or fungi (usually by disrupting cell wall assembly or by binding to ribosomes, this inhibiting protein synthesis)
31
Antibody
Immune or protective protein evoked by the present of foreign substances (antigens) in the body; each antibody binds to a specific antigen in an immune response; also called immunoglobulin
32
Antigen
A substance that binds to an antibody; may be a foreign or a self-antigen
33
Antigen-binding region
Portion of an antibody that is specific for a particular antigen; the area of the antibody to which the antigen binds
34
Aortic valve
One of the semilunar valves, separating the left ventricle from the aorta
35
Apoptosis
Process by which a cell undergoes programmed cell death in a highly organized manner in response to either external or internal signals
36
Appendicular skeleton
Peripheral portion of the skeleton consisting of arms, legs, and pelvic and pectoral girdles
37
Archenteron
The central cavity in the gastrula stage of embryological development; it is lined by endoderm and ultimately gives rise to the adult digestive tract
38
Arterioles
Small arterial structures that link that arteries to the capillaries
39
Artery
Thick-walled, muscular blood vessel that generally carries blood away from the heart
40
Articular cartilage
Cartilaginous coating at the ends of bones that provides a smooth surface for articulation of bones within a joint
41
Asexual reproduction
Any reproductive process that does not involve the fusion of gametes (such as budding)
42
Asters
Star-shaped structures that form around the centrosome during mitosis
43
Atrium
One of two paired structures on either side of the heart, into which blood returning from either the body (right atrium) or the lungs (left atrium) flows
44
Autocrine
Form of cell-cell communication in which a cell releases a substance that then binds to the membrane of the releasing cell to either inhibit or activate a cellular activity
45
Autoimmunity
Inappropriate immune response that targets self-antigens
46
Autonomic nervous system
Subdivision of the peripheral nervous system responsible for involuntary activities, which is further subdivided into the parasympathetic and sympathetic nervous system
47
Autosome
Any chromosome other than a sex chromosome
48
Axial skeleton
Midline structures of the skeleton including the skill, vertebral column, and ribcage; provides the central framework of the body
49
Axon
The long fiber of a neuron; it conducts impulses away from the cell body toward the synapse
50
Axon hillock
Transition point between the cell body (soma) and the axon of a neuron; the site of action potential initiation
51
Bacillus
Rod-shaped bacterium
52
Bacteriophage
A virus that invades bacteria and sometimes uses bacterial RNA and ribosomes to self-replicate
53
Basophil
Type of granulocytic leukocyte that largely participates in allergic reactions and local inflammation
54
Bile
A solution of salts, pigments, and cholesterol produced by the liver and stored in the gallbladder; it emulsifies large fat droplets when secreted into the small intestine via the bile duct
55
Bilirubin
Product of the breakdown of hemoglobin that is modified to a more soluble form in the liver
56
Binary fission
A type of asexual reproduction characteristic of prokaryotes in which there is equal nuclear and cytoplasmic division
57
Blastocoel
The fluid-filled central cavity of the blastula
58
Blastocyst
A mammalian blastula, consisting of the trophoblastic cells and in inner cell mass
59
Blastopore
Opening of the archenteron to the external environment in the gastrula stage of embryonic development
60
Blastula
The early embryonic stage during which the embryo is a hollow, fluid-filled sphere of undifferentiated cells
61
Blastulation
Process by which a solid mass of early embryonic cells, known as the morula, becomes the blastula, a hollow fluid-filled sphere of undifferentiated cells
62
Bohr effect
Changes in the affinity of hemoglobin for oxygen caused by changes in the environment; when pH is low (increased concentration of hydrogen ions), the oxyhemoglobin dissociation curve shifts right, indicating a decreased affinity of hemoglobin for oxygen and more efficient off-loading of oxygen from hemoglobin
63
Bolus
An initial dose of medication; in the digestive system, chewed food leaving the mouth, traveling through the esophagus, and entering the stomach
64
Bone marrow
Central portion of bones, especially long bones, that contains fat and developing blood cells, including erythrocytes, leukocytes, and megakaryocytic
65
Bone matrix
Organic and inorganic minerals that provide strength to compact bone; organic components include collaged, glycoproteins, and other peptides; inorganic components include calcium, phosphate, and hydroxide ions (in hydroxyapatite)
66
Bowman's capsule
The cuplike structure of the nephron; it collects the globular filtrate and channels it into the proximal convoluted tubule
67
Bronchi
Tubelike passages for air that connect the trachea to the bronchioles
68
Bronchioles
Passageways for air that start at the bronchi, dividing into continuously smaller passageways that eventually lead to the alveoli, where gas exchange occurs
69
Brush-border enzymes
Group of enzymes present on the luminal surface of cells lining the duodenum that break down larger biomolecules into monomers that are able to be absorbed
70
Bundle of His
Part of the conduction system of the heart; it carries impulses from the AV node to the ventricles
71
Callus
Area of excessive deposition of keratin in response to repeated strain due to friction
72
Canaliculi
Small canals connecting lacunae with the bone matrix with Haversian canals, allowing for the flow of nutrients and wastes
73
Capillary
Small, thin-walled blood vessel where gas, nutrient, and waste exchange occurs between blood and tissues
74
Capsid
Protein coat surrounding a virus
75
Cardiac output
Total blood volume pumped by the left ventricle in one minute, found by multiplying the heart rate times the stroke volume
76
Cartilage
A firm, elastic, translucent connective tissue produced by cells called chondrocytes
77
Catabolism
The chemical breakdown of complex substances (macromolecules) to yield simpler substances and energy
78
Cecum
The first part of the large intestine; accepts material flowing through the ileocecal valve and is the site of the appendix
79
Cell-mediated immunity
Type of immunity that uses cytotoxic chemicals released from cells to cause death of cells that have been infected by viruses
80
Cell body
Portion of neuron where the nucleus, endoplasmic reticulum, and ribosomes are located; also known as the soma
81
Cell theory
A fundamental belief in modern biology that all living things are composed of cells, that the cell is the basic functional unit of life, that all cells arise from preexisting cells, and that DNA is genetic material
82
Central nervous system (CNS)
The brain and spinal cord
83
Centriole
A small organelle in the cytoplasm oaf animal cells; it organizes the spindle apparatus during mitosis or meiosis
84
Centromere
The area of a chromosome where sister chromatids are joined; it is also the point of attachment to the spindle fiber during mitosis and meiosis
85
Centrosomes
Paired cylindrical organelles, located in the cytoplasm, that contain the centrioles
86
Cerebellum
The section of the mammalian hindbrain that controls muscle coordination and equilibrium
87
Cerebral cortex
The outer layer of the forebrain, consisting of grey matter; it is the site of higher cognitive functions in humans
88
Cervix
Lower end of the uterus that marks the transition between the vagina and the uterus
89
Chemical digestion
Enzymatic cleavage of chemical bonds within foodstuffs, resulting in smaller molecules
90
Chemotaxis
Movement of cells toward or away from a chemical within the environment
91
Chiasmata
Sites where crossing over occurs between homologous chromosomes during meiosis
92
Chief cells
Cells within the stomach that secrete pepsinogen, a zymogen that is converted to its active form, pepsin, by the acidic environment of the stomach
93
Chondrin
Elastic cartilage matrix substance secreted by chondrocytes
94
Chondrocyte
A differentiated cartilage cell that synthesizes the cartilaginous matrix
95
Chromatid
Each of the two chromosomal strands formed by DNA replication in the S phase of the cell cycle; held together by the centromere
96
Chromosome
A filamentous body found within the nucleus of a eukaryotic cell of nucleoid region a prokaryotic cell, composed of DNA
97
Chylomicron
Soluble lipid molecule that consists of triglycerides and esterified cholesterol molecules; absorbed into lacteals from the digestive tract
98
Chyme
Aqueous mixture of food and secretions that leaves the stomach to enter the duodenum
99
Cilia
Projection from a cell involved in movement of material on the outside of the cell
100
Circadian rhythm
A behavioral pattern based on a 24-hour cycle, rated to a consistent cycling of hormones such as cortisol and melatonin
101
Cleavage
A series of mitotic divisions of the zygote immediately following fertilization, resulting in progressively smaller cells with increased nucleus-to-cytoplasm ratios
102
Clonal selection
Phenomenon in which only B- or T-cells specific to a particular pathogen are activated
103
Coccus
Spherically-shaped bacterium
104
Codominance
A genetic effect in which the phenotype of a heterozygote is a reflection of both alleles at a particular locus
105
Competent
Describes a cell capable of responding to induction signals
106
Conjugation
The temporary joining of two organisms via a tube called a pilus, through which genetic material is exchanged; a form of sexual reproduction used by bacteria
107
Connective tissue
Animal tissue composed of cells lying in an extracellular proteinaceous network that supports, connects, and surrounds the organs and structures of the body
108
Constant region
Portion of an antibody molecule that is not variable and participates in the binding of other immune modulators
109
Convergent evolution
The process by which unrelated organisms living in a similar environment develop analogous structures
110
Corona radiata
Layer of cells surrounding an oocyte that aid in the development of the ovum
111
Corpus luteum
The remnant of the ovarian follicle, which after ovulation continues to secrete progesterone. Its degeneration leads to menstruation; maintains uterine lining during pregnancy
112
Cortex
The external layer found in many organs of the body, including the brain, adrenal glands, and kidney
113
Cortical reaction
Release of calcium ions by an ovum after fertilization, resulting in the creation of a fertilization membrane, a structure that prevents fertilization of an ovum by multiple sperm cell
114
Corticosteroids
Steroid hormones produced in the adrenal cortex, including glucocorticoids (cortisol), mineralocorticoids (aldosterone), and cortical sex hormones
115
Crossing over
The exchange of genetic material between homologous chromosomes during meiosis
116
Cyclins adenosine monophosphate (cAMP)
An intracellular second messenger in the signaling cascade initiated by a peptide hormone; synthesized from ATP by adenylate cyclase
117
Cytokine
Chemical substance that stimulates inflammation and recruits additional immune cells to a specific area
118
Cytokinesis
The division and distribution of parent cell cytoplasm to the two daughter cells during mitotic and meiotic cell division
119
Cytoplasm
The fluid and solutes within a cell membrane, external to the nucleus and cellular organelles
120
Cytotoxic T-cell
T-cell that seeks out infected cells and induces apoptosis in these cells to prevent spread of the pathogen
121
Deletion
A type of genetic mutation in which some variable amount of DNA is removed
122
Dendrite
The portion of a neuron that receives stimuli and converts them toward the cell body
123
Dermis
The layer of skin cells under the epidermis. Contains sweat glands, hair follicles, fat, and blood vessels
124
Determinate cleavage
Rapid mitotic divisions occurring in an embryo that result in cells with predetermined fates; these cells are only capable of differentiating into certain groups of tissues within an organism
125
Determination
Designation of a cell within an embryo as having a particular future function
126
Diaphragm
Thin, muscular structure that divides the thorax from the abdomen and provides the driving force for inhalation
127
Diaphysis
Cylindrical shaft of a long bone
128
Diastole
The period of relaxation of cardiac muscle during which the atrioventricular valves open and the ventricles fill with blood
129
Differentiation
The process by which unspecialized cells become specialized. Involves selective transcription of the genome
130
Digestion
The breakdown of macromolecular nutrient material via mechanical and chemical means to simple molecular building blocks; this facilitates absorption
131
Diploid
Having two chromosomes of each type per cell; symbolized by 2n
132
Direct hormone
Substance secreted into the bloodstream that causes a change in the physiological activity of cells without requiring an intermediary
133
Directional selection
Selective pressure favor the development of an extreme phenotype that provides a selective advantage; this phenotype emerges as the primary phenotype over time
134
Disruptive selection
Selection pressure favoring extreme phenotypes over the norm
135
Divergent evolution
A process of change whereby organisms with a common ancestor evolve dissimilar structures (such as dolphin flippers and human arms)
136
Dominant
Refers to an allele that requires only one copy for expression
137
Ductus arteriosus
Fetal structure that shunts blood from the pulmonary artery to the aorta to bypass the developing lungs
138
Ductos venosus
Shunt from the umbilical vein to the inferior vena data, allowing oxygenated blood returning from the placenta to bypass the liver and enter the systemic circulation
139
Duodenum
First segment of the small intestine; the contents of the stomach and the pancreatic and bile ducts empty into it; site of digestion and some absorption
140
Ectoderm
Outermost embryonic germ layer; it gives rise to the skin, nervous system, inner ears, lens of the eye, and other structures
141
Effector
An organ, muscle, or gland used by an organism to respond to a stimulus
142
Efferent (motor) neuron
A neuron that transmits nervous impulses from the central nervous system to an effector
143
Embryo
The early developmental stage of an organism; in humans, the term refers to the first eight weeks after fertilization
144
Endocrine
A form of cell-cell communication that involves the secretion of hormones into the bloodstream by ductless glands; these hormones then travel to distant locations within the organism to cause a change in cellular expression
145
Endoderm
Innermost embryonic germ layer; it later gives rise to the linings of the alimentary canal and of the digestive and respiratory organs
146
Endometrium
Uterine lining that is regenerated each month in preparation for implantation of an embryo; absence of an embryo results in sloughing off of the endometrium in a process known as menstruation
147
Endoplasmic reticulum
Membrane-bound channels in the cytoplasm that transport proteins and lipids to various parts of the cell
148
Endothelium
Lining of blood vessels consisting of endothelial cells
149
Enteric nervous system
Collection of neurons within the gastrointestinal tract that govern peristalsis
150
Eosinophil
Type of granulocytic leukocyte that largely participates in the immune response against parasites; also involves in the pathogenesis of allergies
151
Epidermis
The outermost layer of the skin
152
Epididymis
The coiled tube in which sperm gains motility and is stored after its production in the testes
153
Epiglottis
The small flap of cartilage that covers the glottis during swallowing, preventing food from entering the larynx
154
Epinephrine
A hormone synthesized by the adrenal medulla; it stimulates the fight-or-flight response; also a neurotransmitter in the sympathetic nervous system
155
Epiphyseal plate
Cartilaginous structure in the epiphysis where growth occurs
156
Epiphysis
Dilated end of a long bone
157
Episomes
A specialized subset of plasmids capable of integrating into the genome of bacteria under specific circumstances
158
Epithelium
The cellular layer that covers internal and external surfaces of body structures and cavities
159
Erythrocyte
Red blood cell; a bi-concave, disk-shaped cell that contains hemoglobin and has no nucleus
160
Esophagus
Portion of the alimentary canal connecting the pharynx and the stomach
161
Eukaryote
A unicellular or multicellular organism composed of cells that contain a membrane-bound nucleus and other membrane-bound organelles
162
Evolution
The changes in the gene pool from one generation to the next cause by mutation, nonrandom mating, natural selection, and genetic drift
163
Exocrine glands
Glands that release their secretions into ducts (such as the liver and sweat glands)
164
Expressivity
Varying expression of disease symptoms despite identical genotypes
165
Extensor
A muscle used in the straightening of a limb
166
Facultative anaerobes
Prokaryotes that can exist with or without oxygen
167
Fertilization
Fusion of two gametes
168
Fertilization membrane
Structure created by the cortical reaction after fertilization of an ovum by a sperm cell; prevents fertilization of an ovum by multiple sperm cells
169
Fetus
A developing organism that has passed the early developmental stages. In humans, the term refers to an embryo from the ninth week after fertilization until birth
170
Fibrin
The insoluble protein that forms the bulk of a blood clot
171
Filial generation
Offspring in a genetic cross; may be supplemented with a subscript to show how many generations out from the parents
172
Filtration
In the nephron, the process by which blood plasma is forced (under high pressure) out of the glomerulus into Bowman’s capsule
173
Fitness
Reproductive success of an individual, measured in increased number and survival of offspring
174
Flagellum
A microscopic, whip-like filament that functions in the locomotion of sperm cells and some unicellular organisms; composed of microtubules
175
Flexor
A muscle used in the bending of a limb
176
Follicle
The set of cells surrounding a developing or mature ovum. Secretes nutrients and estrogen and atrophies into the corpus luteum after ovulation
177
Foramen ovale
Shunt within the fetal heart between the right and left atria that allows circulation to largely bypass the developing lungs
178
Gallbladder
Organ below the liver that stores bile; contracts in response to stimulation by cholecystokinin, resulting in release of blue into the biliary system and eventually into he duodenum
179
Gamete
Sperm or ovum; a cell that has half the number of chromosomes of a somatic cell (haploid) and can fuse with another gamete to form a zygote
180
Ganglion
A mass of neuron cell bodies outside the central nervous system
181
Gastrula
The embryonic stage characterized by the presence of ectoderm, mesoderm, and endoderm
182
Gene
The basic unit of heredity; a region on a chromosome that codes for a specific product
183
Gene pool
All of the alleles for every gene in every individual in a given population
184
Genetic drift
Variations in the gene pool caused by chance
185
Genetic map
A diagrammatic representation of a chromosome indicating distance between two genes on a chromosome as determined by recombination frequencies
186
Genome
An organism's complete set of chromosomes
187
Genotype
The genetic composition of an entire organism or in reference to a particular trait
188
Glomerulus
The network of capillaries encapsulated by Bowman’s capsule. Acts as a filter for blood entering the nephron
189
Glottis
The opening to the trachea
190
Golgi apparatus
Organelle that plays a role in the packaging and secretion of proteins and other molecules produced intracellularly
191
Gonad
Ovary or testis; the reproductive organic which gametes are produced
192
Gram staining
A process of staining bacterial cells such that cells containing large amounts of peptidoglycan within the cell wall are stained purple, while cells with less peptidoglycan within their cell walls appear pink-red after counter-staining
193
Granulocyte
Type of leukocyte with cytoplasmic granules that are visible under a microscope, such as neutrophils, basophils, or eosinophils
194
Grey matter
Any region in the central nervous system that consists largely of neuron cell bodies, dendrites, and synapses
195
Growth factors
Substances that cause induction during embryonic development and ensure the development of the correct structure in the right location
196
Haploid
Having only one of each type of chromosome per cell; symbolized by n
197
Hardy-Weinberg Principle
States that gene ratios and allelic frequencies remain constant through the generations in a nonevolving population
198
Haversian canal
Central channel within the osteon (Haversian system) containing blood vessels, nerve fibers, and lymph vessels
199
Heavy chain
One of two types of chains, made of peptides, that create an antibody; each antibody consists of two heavy chains and two light chains
200
Helper T-cells
Type of T-cell that secretes lymphokines; the specific combination of lymphokines secreted will determine the nature of the immune response; activation of Th1 cells will result in a cytotoxic response, while a Th2 response will rely on B-cells
201
Hematocrit
Measurement of how much a blood sample consists of red blood cells, expressed as a percentage
202
Hemoglobin
Iron-containing protein found in red blood cells that binds O2 and transports it throughout the body
203
Heterozygous
Having two different alleles for a particular trait
204
Hilum
area of an organ where large vessels or other structures enter or exit; the renal hilum is where the renal artery enters the kidney, the renal vein leaves the kidney, and the ureter exits the kidney to transport urine to the bladder
205
Histamine
An inflammatory mediator that causes vasodilation and results in increased movement of fluid and cells out of the blood vessels and into the tissues
206
Homeostasis
Maintenance of a stable internal physiological environment in an organism
207
Homologous chromosomes
Chromosomes in a diploid cell that cay corresponding genes of the same traits as corresponding loci
208
Homozygous
Having two identical alleles for a given trait
209
Hormones
Chemical messengers secreted by cells of one part of the body and carried by the bloodstream to cells elsewhere in the body, where they regulate biochemical activity
210
Humoral immunity
Form of adaptive immunity driven by B-cells and antibodies
211
Hybrid
The resultant offspring of a cross (mating) either between two different gene types of between two different species
212
Hypodermis
Subcutaneous layer beneath the dermis in the skin
213
Hypothalamus
The region of the vertebrate forebrain that controls the autonomic nervous system and is the control center for hunger, thirst, body temperature, and other visceral functions; also secretes factors that stimulate or inhibit pituitary secretions
214
Ileum
The terminal portion of the small intestine
215
Impulse propagation
Movement of an action potential down an axon, resulting in neurotransmitter release at the synaptic bouton and transmission of the impulse to the target neuron or organ
216
Inborn error of metabolism
Genetic mutation that causes a change in an enzyme required for metabolism; early intervention is necessary to prevent the development of life-threatening conditions; some inborn errors of metabolism are ultimately incompatible with life
217
Incomplete dominance
A genetic effect in which the phenotype of a heterozygote is a mixture of the two parental phenotypes
218
Indeterminate cleavage
Rapid mitotic divisions resulting in cells that are individually capable of becoming complete organisms
219
Independent assortment
Unlinked genes within a primary germ cell separate randomly during gametogenesis
220
Inducer
A chemical substance passed from and organizing cell to a responsive cell, resulting in differentiation of the responsive cell
221
Induction
The initiation of cell differentiation in a developing embryo due to the influence of other cells
222
Innate immunity
Form of immunity that is nonspecific and does not require activation
223
Integument
The outer layer of the body (skin); provides function for thermoregulation and innate immunity
224
Intermediate filament
Collection of fibers that help to maintain the overall integrity of the cytoskeleton
225
Interneuron
A neuron that has its cell body and nerve terminals confined to one specific area; often involved in spinal reflexes
226
Interphase
The stage between successive nuclear divisions; it is divided into the G1, S, and G2 stages; cell growth and DNA replication occur during interphase
227
Intracellular digestion
Oxidation of fatty acids and glucose for energy within cells
228
Intrapleural space
Fluid-filled potential space between the parietal and visceral pleura that lubricates the two pleural surfaces and allows for a pressure differential between the intrapleural space and the lungs
229
Inversion
A chromosomal mutation in which a section of a chromosome breaks off, flips over, and then reattaches in its original spot
230
Isolation
Mechanism that prevents genetic exchange between individuals of different species or populations
231
Jejunum
The middle portion of the small intestine
232
Joint cavity
Space between two bones in a joint; enclosed and maintained by fibrous tissues
233
Juxacrine
A form of cell-cell communication in which a cell releases a substance that binds to receptors on cells directly adjacent to the releasing cell
234
Keratin
Protein present in the outermost layer of the skin that is largely responsible for preventing the loss of fluids and salts as well as the entry of foreign substances into the body; also present as an intermediate filament within cells
235
Keratinocytes
Cells within the epidermis that produce keratin
236
Kidney
Vertebrate organ that regulates water and salt concentration in the blood and is responsible for urine formation
237
Kinetochore
A protein structure, located at the centromere, that provides a place for spindle fibers to attach tot he chromosome
238
Lacteal
Small lymphatic vessel that runs int he center of the villi in the small intestine; site of lipid absorption into the lymphatic system
239
Lacunae
Small spaces within the bone matrix where osteocytes reside
240
Lamellae
Concentric circles of bony matrix within the Haversian systems of bone
241
Langerhans cells
Specialized macrophages that reside within the skin
242
Large intestine
Tubelike structure, shorter but wider than the small intestine, largely responsible for resorption of water and the formation of semisolid feces; consists of the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum
243
Larynx
Pathway for air between the pharynx and the trachea. The epiglottis closes to prevent food from entering the larynx
244
Latent period
The short interval between the application of a stimulus to a muscle and the contraction of the muscle
245
Leakage
Flow of genes between closely related species
246
Leukocytes
White blood cells; can be subdivided into granulocytes and agranulocytes
247
Ligament
Connective tissue that joins two bones
248
Light chain
One of two types of chains, made of peptides, that create antibodies; each antibody consists of two heavy chains and two light chains
249
Linkage
Tendency for certain alleles to be inherited together due to primality on the same chromosome
250
Lipase
Enzyme that specifically cleaves the bonds of lipids
251
Locus
In genetics, an area or region of a chromosome
252
Loop of Henle
The U-shaped section of a mammalian nephron
253
Lower esophageal sphincter
Ring-shaped muscular structure that separates the esophagus from the stomach; also known as the cardiac sphincter
254
Lumen
The space within a tube or sac
255
Lymph
Clear fluid derived from blood plasma and transported through lymph vessels to the lymphatic ducts, which empty into the circulatory system
256
Lymph node
Small, bean-shaped structure that provides a location for antigen presentation and mounting of an attack of the adaptive immune system
257
Lymphocyte
A type of white blood cell involved in an organism’s specific immune response
258
Lysogenic cycle
Bacteriophage infection involving the integration of viral DNA into the bacterial genome without disrupting or destroying the host. The virus may subsequently reemerge and enter a lytic cycle
259
Lysosome
A membrane-bound organelle that stores hydrolytic enzymes
260
Lytic cycle
Bacteriophage infection involving the destruction (lysis) of the host bacterium
261
Macrophage
A phagocytic white blood cell
262
Map unit
A unit used to denote a 1 percent recombination frequency between two genes when creating a genetic map; also measured as one centimorgan
263
Mast cell
A granulocyte that relates histamine and causes inflammation
264
Mastication
Breaking up of large food particle using the teeth, tongue, and lips; chewing
265
Mechanical digestion
Physical breakdown of large food particles into smaller food particles
266
Medulla
The internal section of an organ (such as the adrenal glands and the kidney); may generally refer to the medulla oblongata of the mammalian hindbrain
267
Medulla oblongata
The part of the brainstem closest to the spinal cord. It controls vital functions, such as breathing and heartbeat
268
Megakaryocyte
Precursor cell that gives off platelets
269
Meiosis
A process of cell division in which two successive nuclear divisions produce up to four gametes from one diploid germ cell
270
Melanocytes
Melanin-producing cells of the skin
271
Melanin
Skin pigment produced by melanocytes that protects the skin from UV radiation and provides color to skin
272
Memory cell
Lymphocyte of B- or T-cell lineage that remains after an infection is gone in order to recognize the previous invader and rapidly induce a humoral immune response
273
Menstruation
The shedding of the uterine lining that occurs every four weeks in a nonpregnant, sexually mature female
274
Mesoderm
The middle embryonic germ layer; it gives rise to the muscular, skeletal, urogenital, and circulatory systems
275
Metabolism
The sum of all biochemical reactions that occur in an organism
276
Metaphase
The stage of mitosis or meiosis during which single chromosomes or tetrads line up on the central axis of the dividing cell and become attracted to spindle fibers
277
Microfilaments
Small polymerized rods of actin that participate in muscle contraction, movement of material within the cellular membrane, and amoeboid movement
278
Microglia
Phagocytic white blood cells that reside in the central nervous system
279
Microtubule
A small, hollow tube composed of two types of protein subunits; serves numerous functions in the cell, such as comprising the internal structures of cilia and flagella and allowing vesicle movement in the cell
280
Missense mutation
Type of mutation that result in the substitution of one amino acid for another
281
Mitochondria
Membrane-bound cellular organelles in which the reactions of aerobic respiration and ATP synthesis occur
282
Mitosis
Cellular division that results in the formation of two daughter cells that are genetically identical to each other and to the parent cell
283
Mitral valve
One of the atrioveenticalular valves separating the left atrium from the left ventricle
284
Mixed nerve
Nerve carrying both afferent (sensory) and efferent (motor) fibers
285
Monocyte
A white blood cell that transforms into a macrophage once it enters tissues
286
Monohybrid cross
A cross between two members of a species that seeks to study only one trait
287
Monosaccharide
A sugar consisting of one monomer (glucose, fructose, or galactose)
288
Morula
The solid ball of cells that result from the early stages of cleavage in an embryo
289
Morphogen
Molecule that causes nearby cells to proceed in a specific developmental pathway during embryonic development
290
Mucosa
The type of epithelial tissue that lines moist body cavities; a mucus membrane
291
Mucus cells
Type of cell within the gastric glands of the stomach; secretes a mucus that protects the mucusoa of the stomach from the harshly acidic conditions
292
Multipotent
Stem cell that is able to differentiate into various cells within a particular lineage
293
Mutagen
An agent, either chemical or physical, that can cause mutations
294
Mutation
A change in DNA sequence
295
Myelin
The white, lipid-containing material surrounding the axons of many neurons in the central and peripheral nervous systems
296
Myogenic activity
Ability of a muscle cell to contract without input from the nervous system; found in smooth and cardiac muscle types
297
Myoglobin
Heme-containing protein that binds molecular oxygen in muscle cells
298
Myosin
A protein found in muscle cells that functions in muscle contraction; myosin fibers are also called thick filaments
299
Natural selection
An ongoing evolutionary process resulting in changes in gene frequencies, leading to the differentiate development of phenotypes in a population
300
Negative sense
Describes the genome of an RNA virus that contains an RNA genome that is complementary to the actual transcript for viral protein synthesis
301
Nephron
The functional unit of the vertebrate kidney
302
Nerve
A bundle of neurons
303
Nerve impulse
The self- propagating change in electrical potential across the axon membrane
304
Nerve terminal
End of the axon from which neurotransmitter molecules are released; also called a synaptic bouton
305
Neural crest cells
Cells that originate at the tip of the neural fold and then migrate outward to form the peripheral nervous system, melanocytes, C-cells of the thyroid, and others
306
Neural fold
Group of ectodermal cells that slide together to create fold, which later becomes the neural tube
307
Neural tube
Embryonic hollow tube that subsequently gives rise to the central nervous system
308
Neuroglia
Support cells for neurons; responsible for functions such as holding neurons in place, supplying neurons with oxygen and nutrients, insulating neurons from other neurons, destroying pathogens, and removing dead neurons
309
Neuron
A cell that conducts electrical impulses: the functional unit of the nervous system
310
Neurotransmitter
A chemical agent released into the synaptic cleft by the synaptic bouton of a neuron; binds to receptor sites on postsynaptic neurons or effector membranes to alter activity
311
Neutrophil
Type of granulocytic leukocyte that largely participates in the nonspecific immune response against bacteria
312
Niche
The specific way of life occupied by a given organism within the environment, including its interactions with other organisms and with the physical environment
313
Nodes of Ranvier
Points on a militated axon that are not covered by myelin
314
Nondisjunction
Failure of homologous chromosomes to separate during meiosis
315
Nonsense mutation
A change in nucleotide sequence of DNA that results in a premature stop codon in the mRNA sequence
316
Norepinephrine
A hormone synthesized by the adrenal medulla; it stimulates the fight-or-flight response; also, a neurotransmitter in the sympathetic nervous system
317
Notochord
A supportive rod running just ventral to the neural tube in lower chordates and in vertebrate embryos that induces neurulation
318
Nuclear membrane
Double membrane enveloping the nucleus, interrupted periodically by pores; found in eukaryotic cells only; also known as the nuclear envelope
319
Nuclear pore
Small hole in the nuclear membrane that allows for two-way exchange of material between the cytoplasm and nucleus
320
Nucleoid region
Location in prokaryotic cells where the chromosome is found
321
Nucleolus
Dense body visible in a nondividing nucleus; site of ribosomal RNA synthesis
322
Nucleus
The eukaryotic membrane-bound organelle that contains the cell’s chromosomes; in neuroscience, a collection of cell bodies in the central nervous system
323
Oligodendrocyte
Myelin-producing cells int he central nervous system
324
Oocyte
An undifferentiated cell that undergoes meiosis to produce an egg cell (ovum)
325
Oogenesis
Gametogenesis in the ovary leading to the formation of mature ova
326
Osmotic pressure
A “sucking” pressure generated by the presence of solutes drawing in water
327
Osteoblast
Bone cell responsible for the generation of new bone due to bone remodeling or storage of minerals within the bone matrix
328
Osteoclast
Bone cell responsible for the resorption of bone due to bone remodeling or mobilization of minerals from the bone matrix
329
Osteocytes
Mature bone cells housed within the bone matrix
330
Ovary
The female egg-producing gonad
331
Oviduct
The tube leading from the ovary to the uterus; generally, the site of fertilization; also called the fallopian tube
332
Ovulation
The release of the mature ovum from the ovarian follicle
333
Ovum
The female gamete; egg cell
334
Oxygen debt
The amount of oxygen needed to reconvert lactic acid to pyruvate following strenuous exercise of muscle tissue; the difference between the amount of oxygen needed by the tissue and the amount of oxygen available
335
Pancreas
A gland that secretes digestive enzymes into the duodenum via a duct and synthesizes and secretes the hormones insulin, glucagon, and somatostatin; located between the stomach and the duodenum
336
Papillary layer
Upper layer of the dermis, right below the epidermis, that consists of loose connective tissue
337
Paracrine
A form of cell-cell communication in which a cell releases a substance into the extracellular fluid and the substance binds to receptors on nearby cells to cause a change in cellular activities
338
Parasympathetic nervous system
The subdivision of the autonomic nervous system involved in rest and homeostasis; it is generally antagonistic tot he sympathetic nervous system
339
Parathyroid glands
Two pairs of glands located on the thyroid that secrete hormones that regulate calcium and phosphorous metabolism
340
Parietal cells
Cells within the stomach that are responsible for the secretion of the acid into the lumen of the stomach
341
Passive immunity
Immunity conferred by the transfer or injection of previously formed antibodies
342
Pathogen
An infectious disease-causing ages; includes bacteria, viruses, fungi, parasites, and prions
343
Pattern recognition receptor
Type of receptor on macrophages and dendritic cells that is able to recognize the nature of the invader (bacteria, virus, or fungi) and release the appropriate cytokines to attract the right immune cells to the area
344
Penetrance
Percent of individuals with a particular genotype that actually express the associated phenotype
345
Peptidase
Enzyme that cleaves peptide bonds
346
Periosteum
Fibrous sheath surrounding long bones
347
Peripheral nervous system
Includes all neurons outside the central nervous system, including sensory and motor neurons; it is subdivided into the somatic and autonomic nervous systems
348
Peristalsis
Rhythmic waves of muscular contraction that move a substance through a tube (most commonly, food through the digestive tract)
349
Peroxisome
Organelle that contains hydrogen peroxide and participates in the breakdown of very long chain fatty acids
350
Pharynx
Pathway for food from the mouth to the esophagus, and for air from the nose and mouth to the larynx
351
Phenotype
The physical manifestation of an organism’s genotype
352
Pineal gland
Structure within the brain that secretes melatonin, a hormone that aids in the regulation of sleep-wake cycles
353
Pituitary
The bilobed endocrine gland that lies just below the hypothalamus; because many of its hormones regulate other endocrine glands, it is known as the “master gland”
354
Placenta
The structure formed by the wall of the uterus and the chorion of the embryo; contains a network of capillaries through which exchange between maternal and fetal circulation occurs
355
Plasma
The fluid component of blood containing dissolved solutes, minus the cells
356
Plasma cells
Derived from B-lymphocytes; have the ability to produce and secrete antibodies
357
Plasmid
Small circular ring of extrachromosomal DNA found in bacteria
358
Platelets
Small, enucleated, disk-shaped shards of blood cells that play an important role in clotting
359
Pleura
Connective tissue that surrounds each lung and aids in providing attachment of the lungs to the chest wall; the parietal pleura lies along the chest wall, while the visceral pleura's adherent to the lungs
360
Pluripotent
Stem cell that has undergone gastrulation and is able to differentiate into any cell type within the same primary germ layer
361
Polar body
A small, nonfunctional haploid cell created during oogenesis
362
Population
A group of organisms of the same species living together in a given location
363
Portal system
A circuit of blood in which there are two capillary beds in tandem connected by an artery or vein; examples include the hypophyseal, hepatic, and renal portal systems
364
Positive sense
Describes the genome of an RNA virus containing RNA that serves directly as the transcript for viral protein production
365
Potency
Term used to describe the ability or inability of a stem cell to differentiate into different cell types
366
Primary response
Humoral immune response against an invader during the first encounter; takes seven to ten days to become effective
367
Prion
Infectious protein that causes disease by causing changes in the three-dimensional structure of other proteins from alpha-helices to beta-pleated sheets
368
Prokaryote
Cell lacking a nuclear membrane and membrane-bound organelles, such as bacterium
369
Prophase
The stage of mitosis or meiosis during which the DNA strands condense to form visible chromosomes; during prophase I or meiosis, homologous chromosomes align
370
Prostate
A gland in the mammalian male that secrets alkaline seminal fluid
371
Pulmonary valve
One of the semilunar valves, separating the right ventricle from the pulmonary arteries
372
Pukinje fibers
The terminal fibers of the heart’s conduction system; located in the walls of the ventricles
373
Pyloric sphincter
The valve that regulates the flow of chyme from the stomach into the small intestine
374
Recessive
An allele that requires two copies to be expressed
375
Recombination
New gene combinations achieved by sexual reproduction or crossing over in eukaryotes and by transformation, transduction, or conjugation in prokaryotes
376
Recombination frequency
Measurement of how often genes recombine in different combinations; genes that are closer together have lower recombination frequencies
377
Rectum
Terminal portion of the large intestine, where feces is stored until defecation
378
Reflex
An involuntary nervous pathway consisting of sensory neurons, interneurons, motor neurons, and effectors; it occurs in response to a specific stimulus
379
Refractory period
The period of time following an action potential during which the neuron in incapable of depolarization
380
Releasing hormones
Proteins synthesized and secreted by the hypothalamus that stimulate the pituitary to synthesize and release its hormones. Also known as tropic hormones
381
Renal pelvis
The widest part of the ureter, located within the kidney; location into which all collecting ducts eventually empty
382
Renin-angiotensin-aldosterone system
Hormonal pathway that, among other functions, rises blood pressure
383
Repolarization
Restoration of the resting membrane potential in neurons from being depolarized by both active and passive processes
384
Respiration
In biochemistry, the series of oxygen-requiring biochemical reactions that lead to ATP synthesis; in physiology, the inhalation and exhalation of gases and their exchange in the lungs
385
Responder
Embryonic cell that is undergoing induction
386
Resting potential
The electrical potential of a cell at rest, approximately -70 mV in most excitable cells
387
Restriction point
A point in the cell cycle that prevents the cell from entering the next portion of the cell cycle unless certain criteria are met
388
Reticular layer
Lower layer of the dermis, consisting of dense connective tissue
389
Retrovirus
An RNA virus that contains the enzyme reverse transcriptase, which transcribes RNA into DNA
390
Rh factor
An antigen on a red blood cell, the presence or absence of which is indicated by + or -, respectively, in blood type notation; may also be called the D allele
391
Ribosome
Organelle composed of RNA and protein; it translates mRNA during protein synthesis
392
Rough endoplasmic reticulum
Portion of the endoplasmic reticulum that appears rough microscopically due to the presence of ribosomes attached to the outer surface; site of protein synthesis for proteins destined to be membrane-bound or secreted
393
Saltatory conduction
Process by which an electrical signal jumps across the nodes of Ranvier to travel down the axon
394
Sarcolemma
Muscle cell membrane capable of propagating action potentials
395
Sarcomere
The functional contractile unit of striated muscle
396
Sarcoplasmic reticulum
The endoplasmic reticulum of a muscle cell; it envelops myofibrils
397
Schwann cell
Myelin-producing cell in the peripheral nervous system
398
Second messenger
Substance that is mobilized within a cell after the binding of a hormone to its receptor
399
Secondary response
Humoral immune response against a previously encountered invader; results in activation of memory cells and an immediate response
400
Semen
Fluid released during ejaculation consisting of sperm cells suspended in seminal fluid
401
Seminal vesicle
A gland found in mammalian males that produces seminal fluid
402
Sex factor
Plasmid containing genetic material for the formation of a sex pili, required for conjugation
403
Sex-linked gene
A gene located only on a sex chromosome (almost always the X chromosome); such genes exhibit different inheritance patterns in males and females
404
Sex pilus
Appendage made from the donor male (+) bacterial cell to the recipient female (-), allowing for the formation of the cytoplasmic bridge and transfer of genetic material
405
Sexual reproduction
Any reproductive process that involves the fusion of gametes, resulting in the passage of combined genetic information to offspring
406
Silent mutation
Change of one nucleotide for another that does not result in a change in the protein due to degenerative nature of the genetic code (multiple codons code for the same amino acid)
407
Small intestine
Long tubelike structure, longer, but narrower than the large intestine, largely responsible for chemical digestion of foodstuffs and absorption of nutrients; consists of the duodenum, jejunum, and ilium
408
Smooth endoplasmic reticulum
Portion of the endoplasmic reticulum that lacks ribosomes on its surface; location of lipid synthesis and detoxification of drugs and poisons
409
Somatic cells
All cells in the body except germ cells and gametes
410
Somatic nervous
Subdivision of the peripheral nervous system that governs all voluntary actions
411
Species
The largest group of organisms capable of mating to produce viable, fertile offspring
412
Specific immune response
An organism’s target fight against a specific pathogen using both antibodies and cytotoxic immunity
413
Sperm
The mature male gamete or sex cell
414
Spermatids
Immature haploid sperm cells
415
Spermatogenesis
Gametogenesis in the testes leading to sperm formation
416
Spermatogonia
Diploid stem cells in males that eventually give rise to sperm cells
417
Spermatozoa
Mature haploid sperm cells
418
Sphincter
A ring-shaped muscle that closes and opens a tube (such as the pyloric sphincter)
419
Sphygmomanometer
Device used to measure blood pressure, consisting of an inflatable cuff and a gauge that measures pressure
420
Spindle
A structure within dividing cells composed of microtubules; it is involved in the separation of chromosomes during mitosis and meiosis
421
Spirilli
Spiral-shaped bacteria
422
Spleen
Highly vascular organ in the left upper quadrant of the abdomen; serves as a location for disposal of aged red blood cells and the presentation of antigens to B-cells
423
Stabilizing selection
Selective pressure resulting in the elimination of extremes
424
Starling forces
A sum of the forces generated by hydrostatic and osmotic pressures; results in a greater attraction of fluid to one side of a membrane
425
Stroke volume
Amount of blood ejected from a ventricle with each heartbeat
426
Summation
Process that occurs when the postsynaptic neuron or target organ requires stimulation from multiple presynaptic neurons in order to respond to the stimulus; may be spatial or temporal
427
Suppressor T-cells
Also known as regulatory T-cells (Treg), these T-cells limit the immune response to prevent detrimental immune reactions, such as autoimmunity
428
Surfactant
A detergent that lowers surface tension and prevents collapse of the alveoli
429
Symbiote
Organism living closely with a host and engaging in a mutually beneficial relationship
430
Sympathetic nervous system
The subdivision of the autonomic nervous system that produces the “flight-or-fight” response
431
Synapse
The junction between two neurons into which neurotransmitters are released
432
Synapsis
The pairing of homologous chromosomes during prophase I of meiosis
433
Synovial capsule
Fluid-filled space between bones in a joint; enclosed by fibrous tissue; synovial fluid lubricates the joint
434
Systole
The period of the cardiac cycle during which the ventricles contract and pump blood into the aorta and pulmonary arteries
435
T-cells
Type of leukocyte that matures in the thymus and participates in adaptive immunity
436
Telophase
The final stage of mitosis or meiosis during which the chromosomes uncoil, nuclear membranes reform, and cytokinesis occurs
437
Tendon
A fibrous connective tissue that connects a bone to a muscle
438
Test cross
A cross between an organism showing a dominant trait and an organism showing a recessive trait to determine whether the former organism is homozygous or heterozygous for that trait
439
Testis
The male sperm-producing organ; also secretes testosterone
440
Tetanus
Sustained muscle contraction that results from continuous stimulation
441
Tetrad
A pair of homologous chromosomes synapsing during prophase I of meiosis. Each chromosome consists of two sister chromatids; thus, each tetrad consists of four chromatids
442
Thermoregulation
Process by which an organism regulates its internal temperature by using the respiratory, integumentary, and circulatory systems
443
Thoracic duct
The main lymphatic vessel that empties lymph into the bloodstream
444
Threshold
The lowest magnitude of stimulus strength that will induce a response
445
Thrombin
An enzyme that participates in blood clotting; it converted fibrinogen to fibrin
446
Thymus
A ductless gland in the upper chest region of vertebrates; it functions in the development of the immune system
447
Thyroid
A vertebrae endocrine gland located in the neck that synthesizes triiodothyronine, thyroxine, and calcitonin
448
Tissue
A mass of similar cells and support structures organized into a functional unit
449
Tonus
A continuous state of low-level muscle contraction
450
Tripotent
Type of stem-cell potency describing cells that are able to differentiate into all cell types within an organism
451
Trachea
The tube that connects the pharynx to the bronchi
452
Transduction
The transposition of genetic material from one organism to another by a virus
453
Transformation
Uptake and incorporation of DNA from the environment by a recipient bacterial cell
454
Transposon
Genetic element capable of inserting and removing itself from the genome
455
Tricuspid valve
One of the atrioventricular valves, separating the right atrium from the right ventricle
456
Trophoblast
Embryonic cells that line the blastocoel and give rise to the chorion and the placenta
457
Tropic hormone
Hormone that is secreted and travels to a target cell or organ, where it triggers release of another hormone, which causes changes in the physiological activity of target cells
458
Tubulin
Protein constituent of microtubules
459
Universal donor
A person (O- blood) whose blood is able to be given to all types without inducing an immune response
460
Universal recipient
A person (AB+ blood) receiving a blood transfusion who is able to receive all blood types without causing an immune response
461
Urea
A nitrogenous waste product produced in the liver from ammonia
462
Ureter
The tube that carries urine from the kidneys to the bladder
463
Urethra
The tube that carries urine from the bladder to the exterior
464
Urine
Liquid waste resulting from the filtration, reabsorption, and secretion of filtrate in the nephron
465
Uterus
Organ in the mammalian female reproductive system that is the site of embryonic development
466
Vaccine
A solution of fractionated, dead, or attenuated live pathogenic material that is introduced into an individual for the purpose of stimulating a primary immune response of “boosting” a previously produced anamnestic state
467
Vagina
Passageway through which childbirth occurs; location into which sperm is deposited during sexual intercourse
468
Vagus nerve
The tenth cranial nerve; it innervates the palate, pharynx, larynx, heart, lungs, and abdominal viscera; responsible for maintaining homeostatic activity through the parasympathetic response
469
Vas deferens
The tube carrying sperm from the testis to the urethra in mammalian males
470
Vasa recta
Secondary capillary bed within the kidney that removes substances from the interstitium of the kidney to be returned to the systemic circulation
471
Vein
Thin-walled blood vessel that carries blood toward the heart
472
Venae kava
Two large veins (superior and inferior) that return deoxygenated blood from the periphery to the right atrium of the heart
473
Ventricles
The chambers of the heart that pump blood into pulmonary and systemic circulation
474
Vestigial
Referring to an organ or limb that has no apparent function now, but was functional at some time in the organism’s evolutionary past
475
Ventilation center
Groups of neurons in the medulla oblongata that regulate respiration
476
Venue
Small venous structure that links that capillaries to the veins
477
Villus
A small projection from the wall of the small intestine that increases the surface area for digestion and absorption
478
Viroid
A small plant pathogen consisting of a very short, circular, single strand of RNA
479
Virus
A tiny, organism-like particle composed of protein-encased nucleic acid; viruses are obligate parasites
480
Vitamin
An organic nutrient that an organism cannot produce itself and that is required by the organism in small amounts to aid in proper metabolic functioning; vitamins often function as cofactors for enzymes
481
White matter
The portion of the central nervous system consisting primarily of myelinated axons
482
Zona pellucida
One of two layers of cells surrounding an oocyte
483
Zygote
The diploid (2n) cell that results from he fusion of two haploid (n) gametes
484
Zymogen
An inactive enzyme precursor that is converted into an active enzyme
