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Medicine LibreTexts

Glossary

  • Page ID
    84753
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    Glossary Entries
    Word(s) Definition Image Caption Link Source
    FR free radical        
    LP lipid peroxide        
    NO nitric oxide        
    O2 super oxide free radical        
    OH hydroxyl free radical        
    VO2 max the amount of oxygen used per kilogram of body weight per minute while engaging in exercise at the fastest rate attainable by the person performing the exercise; aerobic capacity        
    β-A, beta-amyloid a protein of unknown function that is abundant in senile plaques        
    Absorption the passage of materials contained within the GI tract into the circulatory system        
    Accommodation the process of adjusting the curvature of the lens to focus light from – objects located at different distances from the eye        
    Acetylcholine a neurotransmitter used in numerous activities (e.g., memory; controlling skeletal muscle, cardiac muscle, smooth muscle, and certain glands)        
    Acquired active immunity the ability to produce a secondary immune response that is strong enough to prevent significant adverse effects from any subsequent encounter with the antigen        
    Action potential the process by which an impulse travels along a neuron or a muscle cell        
    Acute gastritis an abnormal condition consisting of short term inflammation of the stomach        
    AD Alzheimer’s disease        
    Ad libitum, AL with reference to diet, being able to eat as much as desired at any time        
    ADH antidiuretic hormone        
    Advanced glycation end-product, AGE a protein chain containing glucose cross-links        
    Afterimage a lingering perception that an image is present after the actual image in the eye has changed or disappeared        
    AGE advanced glycation end product        
    Age changes developmental changes that occur in the later years of life        
    Age-related macular degeneration, AMD a disease of the eye that reduces vision by causing degeneration of the cones in the macular region of the retina        
    AL (ad libitum) with reference to diet, being able to eat as much as desired at any time        
    Allergic response an excessive undesirable immune response against a foreign antigen        
    Alveolus (pl., alveoli) a small cup-shaped outpocketing in the lung where gas exchange occurs        
    Alzheimer's disease , AD a form of dementia characterized by memory loss and by the presence of excessive senile plaques and neurofibrillar tangles in the brain        
    Amino acid a molecular unit that makes up protein molecules        
    Amyloid a specific type of protein found within or between cells        
    Amyloid precursor protein, APP a protein in cell membranes whose breakdown yields beta-amyloid and other products        
    Anemia an abnormal condition consisting of a low concentration of red blood cells in the blood        
    Aneurysm an abnormal outpocketing of either a blood vessel or the wall of the heart        
    Antagonistic pleiotropy having several effects that oppose one another        
    Antibody a protein molecule that is produced by immune system plasma cells and that adheres to antigens and assists in combating antigens        
    Antigen a substance that causes an immune response        
    Antigen-specific receptor a type of surface receptor on a T-cell that allows that T-cell to bind to one and only one substance capable of initiating an immune response        
    Antioxidant, AOX a substance that converts free radicals into substances that are not free radicals by donating one or more electrons to other molecules        
    AOX (Antioxidant) a substance that converts free radicals into substances that are not free radicals by donating one or more electrons to other molecules        
    APO apolipoprotein        
    APOE apolipoprotein E        
    Apolipoprotein E , APOE a lipoprotein that helps move cholesterol and other lipoproteins from cell to cell and through cell membranes, and also seems to help in neuron development and repair        
    Apoptosis programmed cell death        
    APP amyloid precursor protein        
    Appendicitis an abnormal condition involving inflammation of the appendix        
    Aqueous humor the liquid that fills the region in the eye behind the cornea and in front of the lens        
    Arthritis an abnormal condition that involves inflammation of joints between bones        
    Ascites the presence of extra fluid in the abdominal cavity        
    Atherosclerosis a disease involving the formation and enlargement of a weak scar-like material in the walls of arteries        
    ATP, adenosine triphosphate a nucleotide used for transferring energy within a cell        
    Atrophic gastritis an abnormal condition resulting in excessive thinning of the lining of the stomach        
    Auerbach's plexus a network of nerve cells in the wall of the GI tract that helps to control functions of the GI tract        
    Auto-antibody an antibody that can act against a native body material        
    Autoimmune reaction an immune response against a normal body part        
    Autonomic motor neuron a motor neuron involved in controlling either cardiac muscle, smooth muscle, or a gland        
    Axon a neuron projection that conducts impulses away from the nerve cell body of that neuron        
    Basement membrane a non-cellular layer between a layer of cells and the material under the layer of cells        
    Basilar membrane a flexible membrane within the cochlea of the ear that supports the organ of corti        
    B-cell a type of specialized lymphocyte that can produce antibody-secreting cells as part of an immune response; B-lymphocyte        
    Bed sore a patch of skin that has died because it received insufficient blood flow; a decubitus ulcer        
    Benign neoplasm a neoplasm that does not spread to other areas        
    Benign prostatic hypertrophy, BPH an abnormal non-cancerous condition in which the prostate gland grows and becomes excessively enlarged        
    Bile a liquid secreted by the liver and stored in the gall bladder and that contains bilirubin, cholesterol and other waste materials        
    Bilirubin a substance consisting of remnants of hemoglobin molecules from red blood cells        
    Biological aging aging in the physical structures and functioning of the body that affects either the body’s ability to survive or its appearance        
    Biorhythm a cyclic fluctuation or oscillation of a biological process        
    BMR, basal metabolic rate the rate of energy use needed to sustain body functions when a person is awake and in a state of complete rest        
    Bone marrow the specialized tissue that is housed within bones and that produces blood platelets and some types of blood cells        
    Bone marrow the specialized tissue that is housed within bones and that produces blood platelets and some types of blood cells        
    Bone matrix the material between bone cells in bone tissue        
    BPH, benign prostatic hypertrophy an abnormal non-cancerous condition in which the prostate gland grows and becomes excessively enlarged        
    Bruch's membrane a non-cellular membrane that lies between the pigmented epithelium of the retina and the choroid layer        
    Caloric restriction, CR receiving a diet that is limited in the number of calories it contains        
    Cancer a disease consisting of the uncontrolled reproduction and spreading of cells; a neoplasm that spreads to other areas; a malignant neoplasm        
    Carbohydrate a molecule consisting of one or more simple sugar molecules        
    Cardiac muscle the type of muscle that is found only in the heart        
    Cardiac output, CO the amount of blood pumped by each ventricle of the heart in one minute        
    Cataracts the condition of having so many opacities close to the center of the lens of the eye that vision is greatly impaired        
    Cavity a spot of decay on a tooth        
    CCK, cholecystokinin a hormone from the small intestine that stimulates emptying of the gall bladder        
    Cells the living structural and functional units of the body        
    Central nervous system , CNS the combination of the brain and the spinal cord        
    Cerumen a semi-solid waxy material that is secreted into the ear canal by ceruminous glands; ear wax        
    Cervix the narrow lower portion of the uterus        
    Chain reaction with free radicals, a sequence of chemical reactions where free radicals react with substances that are not free radicals and form new free radicals        
    Chronological aging the passage of time since birth        
    Cilia microscopic hair-like structures that project from cells and that swing back and forth        
    Circadian rhythm a cyclic fluctuation or oscillation that repeats itself approximately every 24 hours        
    Cirrhosis an abnormal condition characterized by the presence of much scar tissue within the liver because of chronic liver damage        
    Clonal selection the process of destroying lymphocytes capable of binding to native body materials and initiating an immune response against native body materials        
    CNS central nervous system        
    Collagen a tough non-elastic fibrous structural protein that is found outside of cells        
    Colorectal cancer cancer of the large intestine        
    Compact bone the type of bone tissue that is dense and that forms the outer layer of bone; cortical bone        
    Compliance the ability to increase or decrease in volume as a result of a change in pressure        
    Conduction the process by which an impulse travels along a neuron        
    Cones photoreceptors in the eye that have different responses to different colors of light        
    Coronary artery a blood vessel that transports blood to capillaries within heart muscle        
    Cortical bone the type of bone tissue that is dense and that forms the outer layer of bone; compact bone        
    Cosmetic aging changes in outward appearance with advancing age        
    Cough reflex a reflex that causes bursts of air to be expired rapidly to force materials out of airways located below the pharynx        
    CR caloric restriction        
    Creatinine a waste material from muscle cells        
    Cross-link a chemical connection between molecules        
    Cross-sectional study a study that places individuals with similar ages into groups and evaluates them one time        
    Cross-sequential study a study method that combines the cross-sectional method and the longitudinal method. Cross-sectional studies on age categories are repeated on the same population as time passes.        
    Crush fracture a type of fracture caused by compression forces acting on a bone that result in collapse of the bone        
    Crystallized intelligence using cognitive skills with familiar learned activities        
    cT-cells cytotoxic T-cell        
    Cytoskeleton a network of microfilaments and microtubules that provides support within a cell        
    Dead space the volume of air in the lower airways that does not reach the alveoli during ventilation but that remains in the lower airways during ventilation        
    Declarative memory remembering specific facts that a person tried to learn so they could be        
    Defecation the elimination of feces through the anus; a bowel movement        
    Dementia an abnormal condition that involves a serious decline in memory functioning accompanied by a major decline in at least one other mental function        
    Dementia with Lewy bodies a type of age-related dementia characterized by the presence of excess round masses of clumped microfilaments in neurons        
    Dendrite a neuron projection that conducts impulses toward the nerve cell body of that neuron        
    Dentin a firm layer located internal to the enamel of a tooth        
    Depth perception the perception of the distance from the eyes to an object being viewed; binocular vision        
    Dermis the layer of the skin underlying the epidermis        
    Development developmental changes that occur before birth or during childhood        
    Developmental changes irreversible normal changes in a living organism that occur as time passes        
    DHEA dehydroepiandrosterone; a steroid hormone of unknown function        
    DHT a principal sex hormone in men, much of which is produced by the testes and the prostate gland; 5-alpha-dihydrotestosterone        
    Diabetes mellitus a disease that involves inadequate insulin production or inadequate sensitivity of cells to insulin and that results in inhibition of the regulation of blood glucose levels        
    Diabetic retinopathy (DR) a disease of the eye that is associated with diabetes mellitus and that reduces vision because of sorbitol accumulation in the retina        
    Diarrhea the condition of having more than three relatively liquid and voluminous bowel movements in one day        
    Diastolic pressure the lowest blood pressure attained between contractions of the ventricles of the heart        
    Dietary Reference Intakes, DRIs a comprehensive method for establishing and evaluating recommended dietary intake recommendation        
    Dietary restriction, DR receiving a diet that is limited in the amount of food        
    Diffusion the movement of materials from an area where they are in high concentration to an area where they are in lower concentration        
    Diglyceride a lipid molecule composed of one glycerol and two fatty acid molecules        
    Disaccharide a molecule consisting of two simple sugar molecules        
    Diurnal rhythm a repetitive cycle of events that occurs once in each 2-hour period; circadian rhythm        
    Diverticula deep outpocketings in the wall of the large intestine        
    Diverticulitis the abnormal condition of having inflamed diverticula        
    Diverticulosis a disease condition consisting of the presence of deep outpocketings in the wall of the large intestine        
    Dizziness the sensation that the body is unstable        
    DM diabetes mellitus        
    DNA, deoxyribonucleic acid the nucleic acid that makes up genes        
    DR dietary restriction        
    dT-cells delayed hypersensitivity T-cell        
    Duodenal peptic ulcer a peptic ulcer in the duodenum        
    Early onset AD a form of Alzheimer's disease with onset before age 65, usually during the sixth decade of life        
    Economic aging age changes in financial status        
    Edema the presence of extra fluid between cells        
    Ejaculation the expulsion of semen from the penis caused by reflexive rhythmic peristaltic contractions of the urethra, other male reproductive ducts, and muscles at the base of the penis        
    Elastase an enzyme that breaks down elastic fibers into elastin peptides        
    Elastin a resilient structural protein that is found outside of cells        
    Elastin peptides short pieces of the protein chain that composed elastin        
    Electron small negatively charged particle that moves about at a distance from the nucleus of an atom        
    Electron transport a series of steps where electrons lose energy        
    Embolus, emboli a mass (usually a blood clot) that is transported within a blood vessel        
    Enamel a hard substance that covers the exposed surface a tooth        
    Endocrine gland a structure that has hormone secretion as its primary function        
    Endolymph the fluid that fills the membranous chambers of the inner ear        
    Endometrium the innermost layer of the uterus        
    Endothelium the innermost layer of a blood vessel        
    Endurance the length of time that vigorous activities can be performed without stopping        
    Energy the power that makes things happen; the ability to do work        
    Energy balance the condition of having the amount of energy taken in over a period of time equal the amount of energy used during the same period        
    Enzyme a protein substance that increases the rate of chemical reactions in a regulated manner        
    Epidermis the outer layer of the skin        
    Episodic memory remembering the times and places at which events happened        
    Erectile tissue the spongy tissue in the penis and the clitoris that fills with blood and becomes firm during sexual arousal        
    Erection the swelling, elongating, and stiffening of the penis due to engorgement of the erectile tissue with blood        
    ERT, estrogen replacement therapy the administration of estrogen-like substances to bolster the effects of estrogen in the body when levels of endogenous estrogen become low        
    Estrogen a principal sex hormone, most of which is produced by the ovaries        
    Evolutionary theory a theory that attempts to explain how aging developed in concert with natural selection        
    Expiration the movement of air out of the respiratory system; exhalation        
    Expiratory reserve volume, ERV the amount of air that can be forcefully expired after expiring the tidal volume        
    Explicit memory remembering specific facts that a person tried to learn so they could be remembered        
    External ear the region of the ear external to the eardrum        
    Familial AD, FAD a form of Alzheimer's disease with onset before age 65, usually during the sixth decade of life        
    Fat lipid molecules composed of one glycerol and three fatty acid molecules; triglycerides        
    Fecal incontinence the abnormal condition of eliminating feces at inappropriate times at least once per month        
    Feces a mixture consisting largely of undigested materials, waste products, and bacteria that is located in the large intestine        
    Fiber dietary polysaccharides that cannot be broken down by digestive enzymes        
    Fibroblast a cell that can produce and secrete proteins that form collagen and elastin fibers        
    Fibrocartilage the type of cartilage that consists of a smooth, slippery, and resilient substance that contains many thick collagen fibers and that has the consistency of hard rubber        
    Filtration the separation of small substances from large ones when fluid pressure forces the small substances through the pores in a membrane        
    Fluid intelligence using cognitive skills in new situations to learning novel problem-solving, motor activities, or reasoning        
    Foam cell a fat-filled macrophage in a vessel wall        
    Follicle in the ovary, a cluster of cells that surrounds a developing egg cell        
    Fovea centralis the central region of the macula lutea that contains the highest concentration of cones        
    Free radical, FR an atom or molecule with an unpaired electron (* = unpaired electron)        
    FSH follicle stimulating hormone        
    Gag reflex a reflex that causes closure of the openings into the larynx and the esophagus when irritating materials enter the pharynx        
    Gall stone a solid mass formed from materials in bile        
    Gas exchange the movement of gases between the atmosphere and the blood        
    Gastric peptic ulcer a peptic ulcer in the stomach        
    Gastric refluxing the movement of stomach contents upward and into the esophagus        
    Gene a length of DNA used to direct the formation of an amino acid chain        
    Genitalia external reproductive structures        
    Gerontology the study of aging        
    GFR, glomerular filtration rate the rate of filtration through the glomeruli        
    GH growth hormone        
    GI tract, gastrointestinal tract the portion of the digestive system that consists of a tube extending from the mouth to the anus        
    Glare seeing bright areas in the wrong places in the field of view because of scattered light striking the retina in the wrong places and in a disorganized way        
    Glaucoma a disease of the eye that reduces vision by causing an increase in pressure within the eye due to an accumulation of aqueous humor        
    Glomerulus a tuft of capillaries in each nephron in the kidney        
    Glucagon a hormone from the pancreas that tends to increase blood sugar levels        
    Glucose a simple sugar that is found in abundance in the body and that provides major source of energy for cells        
    Glycation using glucose to form cross-links between protein chains        
    Glycoprotein a molecule consisting of a combination of carbohydrate and protein        
    Glycosylation using glucose to form cross-links between protein chains        
    Glycoxydation using glucose to form cross-links between protein chains        
    Gonads the primary reproductive organs (i.e., testes in males, ovaries in females), which produce hormones and sperm cells or egg cells        
    H2O2 hydrogen peroxide        
    Hair cells neurons in the inner ear that respond to bending caused by different stimuli (e.g., vibrations, gravity, rotation of the head)        
    Hayflick limit the maximum number of divisions a cell can undergo        
    HCl an acid secreted by the stomach; hydrochloric acid        
    HDL high density lipoprotein        
    Hearing the conscious perception of sound vibrations        
    Heart rate (HR) the number of times the heart beats in one minute        
    Heat shock proteins proteins produced by cells when they are stressed. Heat shock proteins have a protective effect.        
    Hemorrhoid a varicose vein in the rectum or the anal canal        
    Heterochromatin masses of tightly wound DNA and protein        
    Histamine a substance from cells that initiates inflammation        
    HLA protein a type of protein molecule on a cell surface that serves to identify that cell as belonging to a specific person        
    HLA receptor a surface receptor molecule on a T-cell that is able to bind to specific identification molecules (i.e., HLA protein) found on other body cells        
    Homeostasis the state of having proper and fairly steady conditions        
    Hormone a substance that result from manufacturing processes in cells, that is secreted into the blood, and that alters the activities of cells in other parts of the body        
    hT-cell helper T-cell        
    Hyaline cartilage the type of cartilage that consists of a smooth, slippery, white substance having the consistency of hard rubber        
    Hydrogen peroxide (H2O2) a reactive oxygen species containing two hydrogen atoms and two oxygen atoms        
    Hydroxyl radical, OH a free radical containing hydrogen atom and one oxygen atom and having 17 electrons        
    IDDM, insulin-dependent diabetes mellitus the type of diabetes mellitus wherein death ensues unless insulin therapy is provided        
    IL-2, interleukin-2 a substance secreted by hT-cells that enhances an immune response by stimulating macrophages to phagocytize more antigen, stimulating the production of more of the hT-cells and cT-cells, and stimulating the proliferation and activity of B cells        
    IL-1, interleukin-1 a secretion that stimulates T-cells to produce more identical T-cells during an immune response        
    IL-6, interleukin-6 an interleukin that stimulates inflammation, macrophages, osteoclasts, and other activities        
    Immune response the activities of the immune system whereby the system combats an antigen        
    Implicit memory remembering specific facts that a person did not try intentionally to learn so they could be remembered        
    Impotence the inability of a man to engage in sexual intercourse because the penis is not sufficiently erect to be inserted into the vagina        
    Incidental memory remembering information or skills that were self-taught        
    Inhibin a sex hormone from gonads that helps regulate sex hormone production by the        
    Initiation with free radicals, a chemical that converts a molecule to a free-radical        
    Inner ear the region of the ear internal to the oval window        
    Inspiration the movement of air into the respiratory system; inhalation        
    Inspiratory reserve volume, IRV the amount of air that can be forcefully inspired after inspiring the tidal volume        
    Insulin a hormone from the pancreas that tends to decrease blood sugar levels        
    Insulin-like growth factor, IGF signaling substances from cells that stimulate growth and regulate other cell activities        
    Intercellular material substances located between cells        
    Interleukin, IL a signaling substance that helps regulate immune responses and other body functions        
    Interneuron a neuron that carries impulses from one neuron to another neuron        
    Interstitial cells of Leydig the cells among the seminiferous tubules in the testes that produce sex hormones        
    Intervertebral disc a pad of fibrocartilage located between the vertebrae in the spinal column        
    Intrinsic factor a substance secreted by the stomach that promotes the absorption of vitamin B12 by the small intestine        
    Ion an atom that has lost or gained one or more electrons        
    Ischemia the condition of having inadequate blood flow        
    Jaundice the condition wherein parts of the body have a yellow or brown color because of the accumulation of bilirubin        
    Joint capsule the thick layer of fibrous material that encases a synovial membrane and that helps to bind bones together        
    Kcal, kilocalorie the unit of energy most often used in measuring the energy content in food        
    Keratin a structural protein found in the outermost layer of the epidermis, in air, and in the nails of the fingers and toes        
    Keratinocyte a cell that can make keratin        
    Ketoacid a small molecule resulting from the breakdown of a fatty acid or an amino acid; ketone        
    Ketoacidosis the abnormal condition of having excess ketoacids in the body        
    Ketone a small molecule resulting from the breakdown of a fatty acid or an amino acid; ketoacid        
    Lacrimal fluid a liquid secreted by the lacrimal glands that bathes the front surface of the eye        
    Lactase an enzyme that assists in the breakdown of lactose        
    Lactic acid a substance produced by the partial breakdown of glucose in cells that have a low amount of oxygen        
    Lactose a type of sugar that consists of one glucose molecule joined to one galactose molecule; milk sugar        
    Lactose intolerance the condition of producing an insufficient quantity of lactase to properly digest dietary lactose        
    Langerhans cell a cell in the epidermis of the skin that carries out phagocytosis and assists in initiating an immune response        
    Late onset AD a form of Alzheimer's disease with onset usually after age 60        
    LDL low density lipoprotein        
    Lewy body a round mass of clumped microfilaments in neurons found in excess numbers in types of dementia including Parkinson's disease        
    LH luteinizing hormone        
    Life expectancy of a population the average age at which death occurs for the members of a population        
    Ligament a cable-like structure composed largely of collagen fibers that binds one bone to another bone        
    Lipid peroxide, LP a lipid molecule that is a free radical        
    Lipofuscin a mixture of certain chemical waste products from normal cell activities        
    Lipoprotein a molecule consisting of a combination of lipid and protein        
    Localization of sound the perception of the direction from which a sound originates        
    Longitudinal study a study that evaluates individuals over a period of time        
    Lower airways air passages within the lungs that conduct air to and from alveoli        
    Lymphocyte a type of white blood cell that functions as part of the immune system        
    Lymphokines a group of substances from lymphocytes that augments the defensive effects of an immune response in several ways including by activating macrophages and certain lymphocytes, by causing inflammation, and by protecting normal body cells from viruses        
    Macrophage a cell outside of the blood that performs phagocytosis and that assists in immune responses        
    Macula lutea the region of the retina that is in line with the center of the cornea and the lens and that has a high concentration of cones        
    Maillard reaction a reaction that forms glucose cross-links between protein chains        
    Malignant neoplasm a neoplasm that spreads to other areas, cancer        
    Malnutrition the condition of lacking nutritional homeostasis        
    Maltose a molecule that consists of two glucose molecules linked together        
    Maturation developmental changes that result in the transformation of a child into an adult        
    Maximum longevity (XL) the greatest age ever achieved by any member of a species        
    mB-cell memory B-cell        
    Mean longevity (ML) the average age at which death occurs for the members of a population        
    Melanin a brown pigment found in the epidermis, in hair, and in other places        
    Melanocyte a cell that can make melanin        
    Memory with regard to the immune system, the ability of the system to respond to an antigen more quickly and more intensely when the antigen is encountered a second or subsequent time        
    Menopause the time when age changes in the ovaries cause menstrual cycles to cease for at least one year        
    Menstrual cycle a sequence of events in the uterus that repeats itself and that involves thickening, deterioration, and shedding of the endometrium; uterine cycle        
    Menstruation the shedding and passage of the endometrium and blood through the vagina        
    Metastasis the spreading of cancer from one location to another        
    Metastatic cancer cancer that is transported to other parts of the body through blood, lymph, or other body fluids        
    Middle ear the region of the ear between the eardrum and the oval window        
    Minute volume the volume of air that is inspired or expired per minute        
    Mitochondria organelles that release useful energy for cells        
    Mitochondrial DNA, mtDNA DNA in mitochondria        
    ML mean longevity        
    Molecule a group of atoms or ions bound together in a specific ratio        
    Monoglyceride a lipid molecule composed of one glycerol and one fatty acid molecule        
    Monosaccharide a single simple sugar molecule        
    Motor end plate the modified area of a muscle cell membrane that contains receptor molecules to receive and respond to neurotransmitter molecules from a motor neuron        
    Motor neuron a nerve cell that conducts impulses that control the actions of a muscle or a gland        
    Motor unit the combination of one motor neuron and all the muscle cell it controls        
    mRNA (messenger RNA) a nucleic acid that carries information to determine the sequence of amino acids in a protein molecule        
    mT-cell memory T-cell        
    mtDNA mitochondrial DNA        
    Myelin a substance that coats axons and dendrites and that allows impulses to travel faster along these structures        
    Myocardium the layer of muscle in the heart, which is the middle layer of the heart        
    Myofilament a protein filament in a muscle cell that is involved in producing contraction of the cell        
    Myoglobin a type of protein in muscle cells that attracts oxygen from the blood into muscle cells and stores oxygen        
    Myometrium the muscular middle layer of the uterus        
    Near point (of accommodation) the smallest distance from the eye that an object can be located and still be seen clearly        
    Negative energy imbalance the condition wherein the amount of energy taken in over a period of time is less than the amount of energy used during the same period        
    Negative feedback a process that prevents or reverses changes        
    Neoplasm a group of cells that continue cell reproduction in an uncontrolled fashion        
    Nephron a unit of structure and function in the kidney consisting of a glomerulus, Bowman's capsule, and a renal tubule        
    Neurofibrillar tangle (NTs) a network of fibers composed of one or two protein fibers in a neuron twisted into a helix        
    Neuromuscular junction the site of transmission of an impulse from a neuron to a muscle cell        
    Neuron a nerve cell        
    Neurotransmitter a substance that transmits an impulse from a neuron to another structure        
    NIDDM (non-insulin dependent diabetes mellitus) the type of diabetes mellitus wherein survival is not dependent upon the administration of insulin therapy        
    Nitric oxide (*NO) a free radical that serves as a signaling substance in the body        
    NK cell (natural killer cell) a non-specific lymphocyte that destroys cancer cells        
    Non-enzymatic glycation reactions forming glucose cross-links between protein chains without the use of enzymes        
    Norepinephrine a substance that is used as a neurotransmitter and as a hormone and the causes effects of the sympathetic nervous system other than those in the skin        
    NT neurofibrillar tangle        
    Obesity having a body weight that is greater than 20 percent more than the desirable body weight and a percent body fat that exceeds 25 percent (men)or 30 percent (women), or having a body mass index of more than 30        
    Opacities opaque spots in the lens of the eye        
    Optic disc the region of the retina to which the optic nerve is attached        
    Oral mucosa the lining of the oral cavity        
    Organ an organized group of different tissues that performs certain functions        
    Organ of Corti the rows of neurons on the basilar membrane of the inner ear that respond to vibrations        
    Organelle a structural component of a cell that is composed of several or many molecules        
    Osmotic pressure a measure of the total concentration of dissolved materials in a liquid        
    Osteoarthritis a type of arthritis that is characterized by the deterioration of cartilage and the formation of extra bone        
    Osteoblast the type of cell in bone tissue that produces bone matrix        
    Osteoclast the type of bone cell that removes bone matrix from a bone        
    Osteocyte the type of bone cell that remains quiescent unless some severe condition develops in the bone        
    Osteon a long thick tube of bone matrix which, when fused with other osteons, composes compact bone tissue        
    Osteoporosis a disease of the skeletal system that causes substantial reductions in the quantity and strength of bone matrix        
    Otolith a heavy crystal that is embedded in the gel attached to the ends of the protruding hair cells in the utricle and the saccule of the inner ear        
    Ovarian cycle a sequence of events in the ovaries that repeats itself and that results in the production of hormones and ova        
    Overweight having a body weight that is 10=20 percent greater than the desirable body weight        
    Ovulation the release of an ovum from an ovary        
    Oxidation removing one or more electrons from an atom or molecule        
    Oxidative phosphorylation chemical reactions where phosphate groups and the energy from electrons are transferred to molecules (e.g., ATP)        
    Pancreatitis inflammation of the pancreas        
    Pentosidine glucose cross-links between certain specific amino acids in protein chains        
    Peptic ulcer an abnormal condition consisting of a pit created by the death and pealing away of cells because of the presence of secretions from the stomach        
    Perfusion the passage of blood through the vessels in a body part        
    Perilymph the fluid that fills the bony chambers of the inner ear        
    Periodontal disease a disease at the base of teeth        
    Peripheral nervous system (PNS) all parts of the nervous system outside of the brain and the spinal cord, all nerves        
    Peristalsis a wave of contraction that travels along a tube-shaped structure and that causes material contained within the tube to move along progressively        
    Peroxyl radical (*ROO) a free radical containing an organic molecule joined to two oxygen atoms        
    Peroxynitrite anion (ONOO-) a reactive oxygen species that is toxic to cells        
    Phagocytosis the process by which a cell engulfs a particle and takes it into the cell        
    Photoreceptor a neuron in the sensory retina that responds to light by starting impulses in the form of action potentials        
    Physiological theory a theory that attempts to explain how aging occurs in a living animal        
    Pigmented epithelium the outer layer of the retina        
    Plasma the liquid portion of blood        
    Plasma cells a B-cell that produces antibodies        
    PMN polymorphonuclear leukocyte (a type of white blood cell)        
    PNS peripheral nervous system        
    Polysaccharide a molecule consisting of many simple sugar molecules        
    Polyunsaturated fatty acid, PUFA a fatty acid molecule with more than one double bond in the carbon chain        
    Positive energy imbalance the condition wherein the amount of energy taken in over a period of time is greater than the amount of energy used during the same period        
    Post-menopausal osteoporosis the type of osteoporosis that occurs most commonly in women during the years following menopause; Type I osteoporosis        
    Presbycusis the ear disorder consisting of a significant decrease in the ability to hear due to aging        
    Presbyopia farsightedness caused by age-related stiffening of the lens        
    Presenilin a protein which when mutated is correlated with increased risk of Alzheimer’s disease        
    Primary immune response the immune response initiated by the first encounter with an antigen        
    Procedural memory remembering how to perform a process or series of steps        
    Progeroid syndrome a series of manifestations of aging that occur prematurely        
    Progesterone a principal sex hormone, most of which is produced by the ovaries        
    Programmed theory a theory based on the premise that aging occurs in a directed manner        
    Propagation with free radicals, a sequence of chemical reactions where free radical convert other molecules to a free radicals, leaving the original free radicals in an abnormal shape        
    Prostate gland a donut-shaped gland in men that surrounds the urethra below its point of connection to the bottom of the urinary bladder        
    Protein a molecule composed of one or more chains of amino acids        
    Psychological aging age changes that affect the way a person thinks and behaves        
    PUFA polyunsaturated fatty acid        
    Pulmonary congestion an accumulation of blood in pulmonary vessels        
    Pulmonary edema an accumulation of fluid in the lungs from blood vessels in the lungs        
    Pulmonary embolism the disease condition of having one or more emboli move into the lungs        
    Pulmonary vessel a blood vessel involved in perfusion of the lungs (e.g., pulmonary artery, pulmonary capillary, pulmonary vein)        
    Pulp the nerves, blood vessels, and other soft materials in the innermost region of a tooth        
    RBC red blood cell        
    RBF, renal blood flow the amount of blood flow through the kidneys per unit time        
    RDA, Recommended Dietary Allowance the recommended dietary intake of a nutrient as established by the Food and Nutrition Board of the National Academy of Science        
    Reaction time the time needed to begin a voluntary motion in response to a stimulus        
    Reactive oxygen species, ROS highly reactive substances that contain oxygen        
    Reception the process in a neuron of having an impulse generated in response to environmental conditions or to messages from other neurons        
    Receptor for advanced glycation end product, RAGE a receptor molecule on a cell that bonds to an advanced glycation end product (AGE)        
    Receptor molecule a molecule in a cell or on a cell membrane that binds to a substance that is carrying a message to the cell        
    Reflex an involuntary response to a stimulus        
    Reinitiation chemical reactions where molecules that were formerly free radical interact and form one or more new free radicals        
    Renin a substance produced by the kidneys that helps to regulate blood pressure, osmotic pressure, and sodium concentration in the body        
    Replicative senescence, RS the cessation of cell division by a cell as it ages        
    Residual volume, RV the amount of air left in the lungs after expiring as much as possible        
    Respiratory rate the number of breaths per minute        
    Rheumatoid arthritis a type of arthritis characterized by the destruction of cartilage and bone in a joint        
    RNA, ribonucleic acid the nucleic acid used to guide the synthesis of protein        
    Rods photoreceptors in the eye that can respond to dim light but that cannot respond differently to different colors of light        
    ROS reactive oxygen species        
    Sarcolemma the cell membrane of a muscle cell        
    Sarcomere a cluster of myofilaments in a muscle cell        
    Sarcopenia gradual loss of muscle mass by shrinkage of muscle        
    Sarcoplasmic reticulum the membranes within a muscle cell that constitutes its endoplasmic reticulum        
    Saturated fat a molecule of fat having fatty acids containing the maximum number of hydrogen atoms        
    Schwann cells cells in the peripheral nervous system that form myelin        
    SDAT Senile dementia of the Alzheimer's type        
    Sebaceous gland a skin gland that secretes sebum        
    Sebum an oily substance secreted by sebaceous glands        
    Secondary immune response an immune response produced by the second or subsequent encounter with an antigen        
    Self-antigen a native body material that can bind to an antigen-specific receptor and therefore can initiate an immune response against a body component        
    Semen the mixture of sperm cells and secretions that is released from a man's body during sexual activity        
    Seminiferous tubule a long and highly coiled tube that produces sperm cells in the testes        
    Senescence age changes that have detrimental effects        
    Senile dementia of the Alzheimer's type, SDAT a form of Alzheimer's disease with onset usually after age 60        
    Senile osteoporosis the type of osteoporosis that occurs most commonly in people of more advanced age, especially those over age 60; Type II osteoporosis        
    Senile plaque, SPs a round microscopic masses found near brain synapses and having various mixtures and densities of materials        
    Sensory neuron a nerve cell that monitors conditions and conducts impulses toward the brain or spinal cord        
    Sensory retina the layer of the retina that is closest to the vitreous humor and that contains several layers of neurons including rods and cones        
    Skeletal muscle the type of muscle that is almost always attached to bones of the skeletal system        
    Sleep apnea, SA a condition consisting of having least five temporary cessation of ventilation per hour or exhibiting at least 10 occasions of depressed ventilation and cessation of ventilation per hour when asleep        
    Sliding hiatal hernia a structural abnormality wherein a portion of the stomach is situated above the diaphragm and is between the diaphragm and the lower end of the esophagus        
    Smooth muscle a type of muscle that lacks striations and that is under involuntary control by the nervous system and the endocrine system; visceral muscle        
    Social aging age changes in the interactions people have with others        
    Somatic motor neuron a motor neuron that controls skeletal muscle        
    Sorbitol a type of sugar that is derived from glucose and that tends to accumulate in certain        
    SP senile plaque        
    Speed of movement the time from the beginning of a motion to the end of that motion        
    Spongy bone the type of bone tissue that consists of an open network of trabeculae that are fused together; trabecular bone        
    Sporadic Alzheimer's disease a form of Alzheimer's disease with onset usually after age        
    Stamina the ability to perform vigorous activity continuously for more than a few seconds        
    sT-cells suppressor T-cell        
    Stochastic theory a theory based on the premise that aging occurs by random chance events that occur with no direction or control        
    Stricture a ring of scar tissue that inhibits the movement of materials through a tube-shaped structure by causing a narrowing of the structure        
    Stroke a disease condition involving an injury to or death of brain cells caused by low blood flow or bleeding in an area of the brain        
    Stroke volume, SV the amount of blood pumped by one contraction of a ventricle of the heart-        
    Subcutaneous layer the layer of the integumentary system that underlies the skin        
    Superoxide radical an oxygen molecule containing two oxygen atoms and having 17 electrons        
    Suprachiasmatic nucleus, SCN a region in the hypothalamus of the brain that regulates circadian rhythms        
    Surface tension the force of attraction between substances on a surface        
    Surfactant a substance that reduces surface tension        
    Survival curve a graph depicting the percentage of a population that is still alive as time passes from a reference point        
    Suspensory ligaments fibers within the eye that radiate outward from the lens and attach to the ciliary body        
    Sustentacular cells cells in the wall of seminiferous tubules that promote sperm production; Sertoli cells        
    SV the amount of blood pumped by one contraction of a ventricle of the heart        
    Swallowing reflex a reflex that clears the pharynx by pushing materials down into the esophagus        
    Synapse the site of transmission of an impulse from one neuron to another neuron        
    Synovial cavity the space between bones joined by a freely movable joint        
    Synovial fluid the fluid that lubricates and cushions the ends of the bones joined by freely movable joint        
    Synovial membrane the membrane that surrounds a synovial cavity and that produces and removes synovial fluid        
    Systemic vessel a blood vessel other than one involved in perfusion of the lungs (i.e., other than a pulmonary vessel)        
    Systolic pressure the peak blood pressure attained by contraction of the ventricles of the heart        
    Target with regard to a hormone, a structure that responds to the hormone        
    Tau protein, τ-protein a protein that seems to promote microtubule formation and that is abundant in neurofibrillar tangles        
    T-cell a type of immune system cell formed from an unspecialized lymphocyte because of the influence of the thymus on the lymphocyte; T-lymphocyte        
    Telomerase an enzyme that repairs and replaces telomeres on chromosomes during DNA replication)        
    Telomere a strand of DNA on the end of a chromosome        
    Termination a chemical reaction where a free radical is converted to a substance that is not a free radical without forming another free radical        
    Testosterone a principal sex hormone, most of which is produced by the testes        
    Thrombus, thrombi a stationary blood clot inside a vessel        
    Tidal volume, TV the volume of air that is inspired or expired per breath when a person is at rest and breathing quietly        
    Time-lag study a study method that uses a cross-sectional study procedure more than one time. The cross-sectional procedure is repeated on different groups that have the same age at different times in the study.        
    Tinnitus the perception of sound by a person when there is no sound external to the person        
    Tissue an organized group of similar cells and associated intercellular material that performs certain functions        
    TMJ, temporomandibular joint the joint that attaches the bone of the lower jaw to the skull        
    Total lung capacity, TLC the total amount of air that the lungs can hold        
    Trabeculae small pieces of bone tissue which, when fused together, compose trabecular bone        
    Trabecular bone the type of bone tissue that consists of an open network of trabeculae that are fused together; spongy bone        
    Transmission the process by which an impulse is passed from a neuron to another structure        
    Triglyceride a lipid molecule composed of one glycerol and three fatty acid molecules; a molecule of fat        
    Type I fiber a muscle cell that contracts slowly and can work longer than other types of muscle cells before becoming fatigued        
    Type IIA fiber a type of muscle cell that contracts quickly and resists becoming fatigued        
    Type IIB fiber a type of muscle cell that contracts quickly and becomes fatigued quickly        
    Type IIC fiber a type of muscle cell that contracts at a moderate speed and that becomes fatigued at a moderate period of contraction        
    Underweight having a body weight that is below the range for desirable body weight        
    Unsaturated fat a molecule of fat having one or more fatty acids that can contain additional hydrogen atoms linked to their carbon atoms        
    Upper airways air passages that conduct air into and out of the lungs        
    Urea a waste product resulting from the detoxification of ammonia by the liver or from the breakdown of proteins        
    Urinary incontinence the elimination of urine at inappropriate times        
    Uterine fibroid an abnormal growth consisting of a spherical mass of smooth muscle within        
    Vaccine a substance that contains an antigen and that is administered to produce an acquired active immunity to that antigen or to antigens that are very similar to it        
    Varicose vein a vein that has developed and retains an abnormally large diameter        
    Ventilation the movement of air into and out of the respiratory system; breathing        
    Vertigo the sensation that either the body or the surrounding environment is pinning when no spinning is actually occurring        
    Vision the conscious perception of images formed on the retina of the eye        
    Visual acuity the amount of detail that can be seen        
    Vital capacity, VC the maximum volume of air that a person can expire after taking the        
    Vitamin D a vitamin that assists in the absorption of calcium by the small intestine        
    Vitreous humor the transparent soft gel that fills the region of the eye behind the lens and in        
    Voiding releasing urine from the body        
    Work of breathing the amount of energy used or the amount of oxygen consumed to perform ventilation        
    Working memory remembering information at or close to the level of consciousness so it can be used in cognitive processing        
    XL maximum longevity