Addiction and neural ageing
Addiction and neural ageing

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Glossary


Glossary for SD805_2
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H

habitat

The environment in which an organism lives.


helicase

An enzyme that, during the process of replication, breaks the hydrogen bonds linking the two strands of double-stranded DNA.


heritability

(1) broad (H2): the proportion of total phenotypic variation in a particular trait at the population level that is attributable to variation in the 10 genotype;

(2) narrow (h2): the proportion of phenotypic variation that can be attributed to additive genetic variation, and which can be used to predict the response of the population to natural selection or selective breeding.


hexose

A single-ring sugar with six carbon atoms; all hexoses have the molecular formula C6H12O6.


high density lipoproteins (HDL)

Molecular aggregates in the bloodstream consisting of about equal proportions of protein and lipid (i.e. 50 per cent protein and 50 per cent lipid, of which about two-fifths is cholesterol). HDL returns cholesterol to the liver where it is broken down to waste products that are excreted in bile. The proportion of HDL in the circulation is increased by the consumption of unsaturated fatty acids.


hippocampus

The evolutionarily oldest part of the cerebral cortex, which has become folded under the temporal lobe. It is involved in memory processes.


holistic

(noun: holism) A type of approach to describing or analysing a complex phenomenon, which takes account of all possible levels of explanation and their interactions; the phenomenon itself is considered as a ‘whole’ which is more than the sum of its component parts or influences.


homeostasis

The process of maintaining the stability of important internal variables and the instigation of corrective action when these deviate from optimum.


homozygous

The condition in which the two alleles at a particular locus on a pair of homologous (matching) chromosomes are the same.


hormone

A chemical that is secreted into a blood vessel at one location and carried in the blood to effect action at some other site, which may be a large distance away.


humanistic psychology

A branch of psychology which emphasises that humans are free agents in possession of consciousness and able to influence events in the world.


hydrogen bonding

An important type of intra- and intermolecular attraction which is particularly important in and between biological molecules. Hydrogen bonds occur between H atoms that are attached to O or N atoms, and O or N atoms elsewhere in the same molecule or in an adjacent molecule.


hydrophilic

Literally, ‘water-loving’, i.e. having a tendency to associate with (polar) water molecules.


hydrophobic

Literally, ‘water-hating’, i.e. having a tendency to associate with non-polar molecules (such as each other) and away from water.


hyperalgesia

Excessive pain sensitivity to a given noxious stimulus. (Adjective: hyperalgesic.)


hyperglycaemia

Elevated concentration of glucose in the circulation (above about 140 mg ml-1).


hyperthermia

The state of the body resulting from elevated temperature. Fever is the usual index of hyperthermia but there can also be heat exhaustion and heat stroke.


hypoglycaemia

Lowered concentration of glucose in the circulation (below about 70 mg ml-1).


hypothalamo-pituitary-adrenal (HPA) axis

The hypothalamus is the brain region that lies at the base of the thalamus and is involved in the control of the body’s endocrine secretion. It is linked to the pituitary and adrenal glands through neuroendocrine links and the portal blood system.


hypothalamus

The collection of nuclei below the thalamus which, amongst other things, helps to regulate the activities of the hormonal system and the autonomic nervous system.


hypothermia

Reduction of body temperature below the normal range of values (i.e. 36–38 °C).



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