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1-10 A B C D E F G H I J K L M N O P Q R S T U V W XYZHabitability
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Habitability is a term used to describe the capacity of a specific environment to maintain a certain quality of life. This term is often applied to the living resources and conditions of space vehicles.
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Hair cells are sensory cells that react to mechanical stimuli and transmit information to the brain; they are the basic sensory unit of the inner ear.
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The hamstring is any of the tendons at the back of the thigh; they attach the five hamstring muscles to their insertions on the bones of the lower leg.
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The Hand Grip Dynamometer (HGD) is a device that measures the performance of the wrist flexor muscles. The subject has to actively push against a plate, thereby bending the wrist. At the same time, sensors inside the HGD measure the force applied.
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Haptic means referring to the sense of touch.
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Haptoglobin is a protein present in blood serum that combines with hemoglobin to form a complex that is rapidly removed from the circulation by the liver.
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The Harvard step test is a type of cardiovascular endurance test. The test measures the ability to exercise continuously for extended periods without tiring. The subject steps up and down on a platform at a rate of 30 steps per minute for 5 minutes or until exhaustion. Exhaustion is the point at which the subject cannot maintain the stepping rate for 15 seconds. The subject immediately sits down on completion of the test, and the heart beats are counted for 1 to 1.5, 2 to 2.5, and 3 to 3.5 minutes.
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Harvest means to gather (at maturity).
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Harvestmen are arachnids that resemble spiders but have a small rounded body and very long slender legs; also called "daddy longlegs."
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Head down tilt bed rest is prolonged bed rest with a slight head down tilt (usually with a 5-6 degree tilt from the horizontal) can reproduce some of the effects caused by exposure to microgravity. Head down tilt is a laboratory procedure wherein a subject lies flat on his back on a tilted table so that the head is below the feet; it is used to cause a headward fluid shift.
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The heart period is the duration of one heart beat, also measured as the time between two heart contractions.
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Heart rate is the number of heart beats per unit time, usually expressed as beats per minute.
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A heat sink is a device which absorbs or removes heat from a thermal system.
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A heavy ion is an ion with mass greater than the normal mass for that element; an ion of a heavy isotope.
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Outside Earth's atmosphere, radiation from heavy ions, such as iron, exists. This kind of radiation is potentially more harmful than any other kind of radiation.
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Helper T cells are a type of white blood cell that contribute to ("help" with) the activation of the B lymphocytes in the immunological process, thus helping to rid the body of foreign antigens.
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Hematocrit is the percentage of the volume of a blood sample occupied by cells, as determined by a centrifuge or device which separates the cells and other particulate elements of the blood from the plasma. The remaining fraction of the blood sample is called plasmocrit (blood plasma volume).
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Hematological means of or relating to blood or hematology.
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Hematology is the study of blood and the blood forming tissues.
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Hematopoiesis is the formation of blood cells.
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Heme is a subunit of the hemoglobin molecule that consists of an organic part and iron atom. The organic part is made up of four rings. The four rings are linked together to form a tetra structure. The iron atom is in the center of the four rings and binds to oxygen.
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Hemin is the chloride of heme in which the ferrous form of iron has become ferric (hematin is the hydroxide). Also termed hematin chloride; chlorohemin; ferriheme chloride; ferriprotoporphyrin; ferriporphyrin chloride; Teichman's crystals; factor X for Haemophilus.
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Hemoconcentration is an increase in the proportion of red blood cells relative to the plasma, brought about by a decrease in the volume of plasma. Hemoconcentration may occur in any condition in which there is a severe loss of water from the body.
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A hemocytometer is an apparatus used to estimate the number of blood cells in a quantitatively measured volume of blood.
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Hemodilution is an increase in plasma volume in relation to red blood cells; reduced concentration of red blood cells in the circulation.
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Hemodynamic means of or relating to the physical dynamics of blood circulation.
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Hemodynamics is a study of the forces involved in circulating blood through the body.
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Hemoglobin is a substance contained within the red blood cells and is responsible for their color. It has the unique property of combining reversibly with oxygen and is the medium by which oxygen is transported within the body. It takes up oxygen as blood passes through the lungs and releases it as blood passes through the tissues.
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Hemoglobin-oxygen affinity reflects the binding strength or attraction of oxygen to hemoglobin.
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Hemolysis is the destruction of red blood cells with the release of hemoglobin into the surrounding fluid.
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Hemolytic refers to the destruction of red blood cells with the release of hemoglobin into the surrounding fluid.
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Henry-Gauer response is the inhibition of antidiuretic hormone secretion due to a rise in atrial pressure which stimulates atrial stretch receptors.
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Heparin is a natural substance which inhibits blood clotting.
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Heparinize is a colloquial term pertaining to the administration of heparin, a blood anticoagulant.
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Hepatic means relating to the liver.
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Two types of herpes simples viruses exist: type 1 and type 2. Type 1 infections are marked by the eruption of one or more groups of vesicles on the vermilion border of the lips or at the external nares (fever blister or cold sore). Type 2 infections are characterized by such lesions on the genitalia. Both types commonly are recrudescent and reappear during other febrile illnesses or even physiologic states such as menstruation.
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Herpesvirus is one of a group of DNA containing viruses causing latent infections in man and animals.
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Herpetic means pertaining to, or of the nature of, herpes.
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Hexokinase (HK) is an enzyme present in muscle and other tissues. It catalyzes the phosphorylation (adding a phosphor group) of glucose and other hexoses to form a hexose 6-phosphate.
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The Hand Grip Dynamometer (HGD) is a device that measures the performance of the wrist flexor muscles. The subject has to actively push against a plate, thereby bending the wrist. At the same time, sensors inside the HGD measure the force applied.
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Linear energy transfer refers to the measurement of the number of ionizations which radiation causes per unit distance as it traverses the living cell or tissue. The concept involves lateral damage along the path, in contrast to path length or penetration capability. Medical X-rays and most natural background radiation are low LET radiation, while alpha particles have high LET.
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High Performance Liquid Chromatography (HPLC) is the separation and detection of non-volatile chemicals (i.e., chemicals with boiling points greater than 200-250 degrees Celsius) in a mixture. A sample amount, typically 10-20 microliters of liquid samples, is injected onto the chromatographic column. The column is packed with a material called a stationary phase with very specific properties which determine the column type. The mobile phase is constantly flowing through the column. When the sample is injected in to the injector it is swept onto the column by the mobile phase. Since all chemicals are different, they will have different affinities (attractions) to both the stationary phase and the mobile phase, called partitioning (i.e., some will have a strong attraction to the mobile phase and pass through the column very slowly, while others will have less of an attraction and therefore pass more quickly through the column). By optimizing parameters, the compounds in the sample to elute (exit the column) individually. When the compounds elute, they must be detected (measured). This is done using a detector that is appropriate to the chemicals being measured.
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Histochemical refers to the study of intracellular distribution of chemicals, reaction sites, and enzymes.
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Histochemistry is the study of the identification and distribution of chemical compounds within and between cells, by means of stains, indicators, and light and electron microscopy.
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A histogram is a form of statistical graph in which values are plotted in the form of rectangles on a chart; also known as a bar chart.
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Histological refers to the science concerned the identification and distribution of chemical compounds within and between cells, by means of stains, indicators, and light and electron microscopy.
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A histological examination is a method of studying the structure of tissues by means of special staining techniques combined with light and electron microscopy.
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The Hoffman Reflex (H-Reflex) is a spinal reflex that can be modulated by a nerve pathway from the otolith receptors.
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Homeostasis is the physiological process by which the internal systems of the body (e.g. blood pressure, body temperature, acid-base balance) are maintained at equilibrium despite variations in the external conditions.
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Homeostatic means relating to homeostasis, which is the physiological process by which the internal systems of the body (e.g. blood pressure, body temperature, acid-base balance) are maintained at equilibrium despite variations in the external conditions.
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Horizontality is the state of being horizontal.
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Hormonal relates to hormones. A hormone is a substance that is produced in one part of the body, passes into the bloodstream and is carried to other distant organs or tissues where it acts to modify their structure or function.
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A hormone is a substance that is produced in one part of the body, passes into the bloodstream and is carried to other distant organs or tissues where it acts to modify their structure or function.
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Housing is the type of cage used to contain animals during space flight.
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Human factors research is concerned with the interaction of humans with equipment, their environment, and each other to optimize the design of interactive workplaces for peak performance. In space flight, studying human factors has a special importance because of the time-critical interactions required between humans, machines and the environment.
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The humerus is the bone of the upper arm.
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Humidityis the amount of water vapor or moisture in the air.
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Humoral means circulating in the bloodstream.
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Humoral immunity is the immediate response to an antigen which triggers antibody production. This is opposed to cell-mediated immunity, which involves white blood cells and is a delayed response to an antigen.
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Hydration is the chemical process in which water is taken into the body.
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A hydrocarbon is a compound containing only hydrogen and carbon.
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Hydrogen is a colorless, highly flammable gaseous element, the lightest of all gases and the most abundant element in the universe. As a component of water, hydrogen is crucial in the metabolic interaction of acids, bases, and salts within the body and in the fluid balance necessary for the body to survive.
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Hydrology refers to the study of the distribution and circulation of water on land, in soil and rock and in the atmosphere.
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Hydrostatic relates to the pressure of fluids or to their properties.
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A hydrostatic gradient is a change in the force, or pressure, of a fluid. The hydrostatic gradient in an adult standing upright and absolutely still is +90 mm Hg between the veins of the feet and heart. This pressure difference is caused simply because of the weight of the blood in the veins between the heart and the feet.
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Hydroxyapatite is the primary mineral component of bone. It has the chemical formula of 3Ca3(PO4)2+Ca(OH)2 and in crystal form is a needle-shaped crystal that is arranged with other needles in a rosette. It melts above 1100ŚC and cannot be dissolved in water.
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Hydroxylysine is one of the alpha amino acids.
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Hydroxyproline is a compound similar in structure to the amino acids and is found only in collagen.
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Hygiene is the science or principles of health and the prevention of disease.
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Hyper- and hypobaric physiology is a discipline concerned with the study of ambient gases. Hyperbaric pertains to the pressure of ambient gases above 1 atmosphere, and hypobaric refers to the pressure of ambient gases below 1 atmosphere.
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Hyperaldosteronism is caused by the overproduction of the adrenal hormone aldosterone, causing abnormalities in the sodium, water, and potassium levels in the body.
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Hyperbolic describes a specific correlation/relationship of two variables to each other. When the first variable is zero, the second variable reaches its maximum; inversely, when the second variable is zero, the first variable is at its peak.
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Hypercalcemia is the presence of an abnormally high concentration of calcium in the blood.
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Hypercalcinuria is the presence of an abnormally high concentration of calcium in the urine.
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Hypercapnic refers to the term hypercapnia, which describes an abnormally increased level of arterial carbon dioxide.
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Hyperemic refers to hyperemia, or the presence of an increased amount of blood in a body part or organ.
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Hypergravity means gravity forces higher than the "normal" Earth gravity.
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Hyperosmolality is the increased concentration of a solution expressed as osmoles of solute per kilogram of serum water.
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Hyperoxaluria is an increased excretion of oxalate in the urine.
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Hyperoxia is an increased concentration of oxygen in the tissues and organs.
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Hyperoxic refers to an increased concentration of oxygen in the air or environment.
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Hyperreflexia is defined as lowering the response threshold consequent to electrical or mechanical stimuli applied at the muscle or the tendon, respectively. When the response threshold is lowered, the muscle will respond not only faster, but also to lower levels of stimuli.
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Hypersecretory Gastric Syndrome is the condition of abnormally increased secretion of gastric juices.
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Hypertext is text (appearing in electronic media) which is not constrained to be sequential; by using highlighted words and images, the user can access other web pages by clicking on the word or image, thus progressing through the information in a non-sequential manner.
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Hypertrophy is an increase in the size of a muscle or organ.
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Hyperuricosuria is the increased excretion of uric acid in the urine.
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Hyperventilation, or overventilation, is described by an increase in alveolar ventilation relative to metabolic carbon dioxide production and causes a decrease of alveolar carbon dioxide pressures to below normal.
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Hyphomycete is a class of fungi that produces asexual spores. They are widely distributed in soil and air.
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Hypnotics are a class of drugs often used as sedatives.
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Hypocalcemia is the presence of an abnormally low concentration of calcium in the blood.
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Hypocalciuria is the presence of an abnormally low concentration of calcium in the urine.
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Hypocitraturia is the decreased excretion of citrate in the urine.
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A hypodermic syringe is a small syringe used with a hollow needle for injection or removal of fluids beneath the skin.
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Hypokinesis is a condition of abnormally diminished motor activity.
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Hyposecretory Gastric Syndrome is the condition of diminished secretion of gastric juices.
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Hypotension is a condition in which the arterial blood pressure is abnormally low. It occurs after excessive fluid loss or following severe blood loss from any cause.
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The hypothalamus is the region of the brain which contains several important centers which control body temperature, thirst, hunger, water balance, and sexual function. It is also closely connected with emotional activity and sleep, and functions as a center for the integration of hormonal and autonomic nervous activity through its control of pituitary secretions.
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A hypothesis is an assumption not proved by experiment or observation that is made for the sake of testing its soundness.
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Hypovolemia (oligemia) is a decrease in the volume of circulating blood.
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Hypoxemia is an abnormal deficiency of oxygen in the arterial blood.
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Hypoxia describes a state of below-normal levels of oxygen in the arterial blood or tissue. Six different kinds of hypoxia are defined by the various causes.
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Hypoxic refers to a decreased concentration of oxygen in the air or environment.
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HZE particles are highly charged and energetic components of cosmic rays. These particles can deposit energy in tissue which is capable of killing a cell if the particle passes near the cell's nucleus.