口腔生理学术语(H)

    Habitat - a location which has a suitable environment for an organism to live in. Caves are natural habitats for bats, trees for birds; oral surfaces and crevices, for some bacteria.

    Haemostasis - the prevention of blood loss through a damaged vessel wall. There are three main mechanisms, vasoconstriction, formation of a platelet plug and blood clotting.

    Heparin sulphate - a glycosaminoglycan which is unusual in that it is stored inside the cell (mast cells) surrounding the liver. Heparin prevents blood clotting.

    Herbivorous- an animal whose diet consists of grass, leaves, roots or other plant matter.

    Heterodont- a dentition in which some of the teeth have different shapes and special functions. Form "hetero" = different) see also homodont.

    Hierarchy - an order of power between individuals. A ranking of most dominant to least dominant.

    Hippocampus - part of the limbic system, it seems to provide a spatial map, useful in the event of a sudden need to escape from an unpleasant sensory experience.

    Hypothalamus - this small body of nerve cells controls the activity of the pituitary gland, the source of several hormones which control the activity of other hormones, including ACTH which in turn controls the level of glucocorticoid secretion. The hypothalamus also has powerful connections with the other members of the limbic system, from which nerve pathways descend to control nerves in the spinal cord. The influence of the limbic system on the hypothalamus explains the raised levels of glucocorticoids in response to emotional stress. This bridge with the peripheral nervous system, provides a link between the emotional state of a person, as influenced by the activity of the limbic system, and the excitability of neurones in the spinal cord, to in-coming pain impulses.

    Histamine - is a product of the amino acid, histidene and is released by damaged cells. Histamine causes an increase in capillary permeability and vasodilation, two vascular events which are the first stages of inflammation. Histamine is also a neurotransmitters substance, released at nerve synapses mostly in the hypothalamus.

    Homeostasis - control of an organism