Glossary – A

absolute V02

the amount of oxygen consumed over a given time period; expressed as liters • min- I.

acidosis

an abnormal increase in blood hydrogen ion concentration (i.e., arterial pH below 7 35).

acids

compounds capable of giving up hydrogen ions into solution.

acromegaly

a condition caused by hypersecretion of growth hormone from the pituitary gland; character-ized by enlargement of the extremi-ties, such as the jaw, nose, and hngers.

actin

a structural protein of muscle that works with myosin in permitting muscular contraction.

action potential

the all-or-none elec-trical event in the neuron or muscle cell in which the polarity of the cell membrane is rapidly reversed and then reestablished.

 adenosine diphosphate (ADP)

a molecule that combines with inor-ganic phosphate to form ATP.

adenosine triphosphate (ATP)

the high-energy phosphate compound synthesized and used by cells to release energy for cellular work.

adenylate cyclase

enzyme found in cell membranes that catalyzes the conversion of ATP to cyclic AMP.

adequate intake (AI)

recommenda-tions for nutrient intake when insuf-ficient information is available to set an RDA standard.

adrenal cortex

the outer portion of the adrenal gland. Synthesizes and secretes corticosteroid hormones, such as cortisol, aldosterone, and androgens.

adrenaline

see epinephrine.

adrenocorticotrophic hormone (ACTH) a

hormone secreted by the anterior pituitary gland that stimu-lates the adrenal cortex.

 aerobic

in the presence of oxygen. afferent fibers nerve fibers (sensory  fibers) that carry neural informa-tion back to the central nervous system.

afferent neuron

sensory neuron carrying information toward the central nervous system.

aldosterone

a corticosteroid hormone involved in the regulation of electrote balance.

alkalosis

an abnormal increase in blood concentration of 01 1- ions. resulting in a rise in arterial pH above 7.45.

alpha receptors

a subtype cf adrenergic receptors located on cell membranes of selected tissues

alveolar ventilation (VA)

the volume of gas that reaches the al seolar region of the lung.

alveoli

microscopic air sacs located in the lung where gas exchange occurs between respiratory gases and the blood.

amenorrhea

the absence of menses.

anabolic steroid

a prescription drug that has anabolic, or growth-stimulating, characteristics similar to that of the male androgen, testosterone.

anaerobic

without oxygen.

anaerobic threshold

a commonly used term meant to describe the level of oxygen consumption at which there is a rapid and systematic increase in blood lactate concen-tration. Also termed the lactate threshold.

anatomical dead space

the total volume of the lung (i.e., conducting airways) that does not participate in gas exchange.

androgenic steroid

a compound that has the qualities of an androgen; associated with masculine characteristics.

Androgens

 male sex hormones. Syn-thesized in the testes and in limited amounts in the adrenal cortex. Steroids that have masculinizing effects.

angina pectoris

chest pain due to a lack of blood flow (ischemia) to the myocardium.

angiotensin I and II

these com-pounds are polypeptides formed from the cleavage of a protein (angiotensinogen) oy tne action of the enzyme renin produced by the kidneys, and converting enzyme in the lung, respectively.

 

Anorexia nervosa

 an eating disorder characterized by rapid weight loss due to failure to consume adequate amounts of nutrients.

anterior hypothalamus

 the anterior portion of the hypothalamus. The hypothalamus is an area of the brain below the thalamus that regulates the autonomic nervous system and the pituitary gland.

anterior pituitary

the anterior portion of the pituitary gland that secretes follicle-stimulating hormone, luteinizing hormone, adrenocorticotrophic hormone, thyroid-stimulating hormone, growth hormone, and prolactin.

antidiuretic hormone (ADH)

hormone secreted by the posterior pituitary gland that promotes water retention by the kidney.

 

aortic bodies

receptors located in the arch of the aorta that are capable of detecting changes in arterial P02.

apophyses

sites of muscle-tendon insertion in bones.

 Arrhythmia

 abnormal electrical activity in the heart (e.g., a prema-ture ventricular contraction).

arteries

large vessels that carry arterialized blood away from the heart.

arterioles

a small branch of an artery that communicates with a capillary network.

articular cartilage

cartilage that covers the ends of bones in a synovial joint.

atherosclerosis

a pathological condi-tion in which fatty substances collect inside the lumen of arteries.

ATPase

 enzyme capable of breaking down ATP to ADP + P1 + energy.

ATP-PC system

term used to describe the metabolic pathway involving muscle stores of ATP and the use of phosphocreatine to rephosphorylate ADP. This pathway is used at the onset of exercise and during short-term, high-intensity work.

atrioventricular node (AV node)

a specialize° mass of muscle tissue located in the interventricular sep-tum of the heart; functions in the

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