H

hay fever See ALLERGIC RHINITIS.

healing The processes and mechanisms by
which the body repairs itself. Healing represents
complex and cascading interactions among vari-
ous of the body’s systems and mechanisms.
Among the first to respond are the COAGULATION
cascade, to stop bleeding, and the IMMUNE
RESPONSE, which mobilizes T-cell lymphocytes,
macrophages, antibodies, the COMPLEMENT CASCADE,
and the release of CYTOKINESand PROSTAGLANDINS.
Fibroblasts (cells that build collagen) converge at
the site about 48 hours after the injury occurs to
begin construction of SCARtissue. After about six
weeks the healing process turns its focus to
remodeling the collagen tissue, restoring the tis-
sues at the site of the injury to relatively normal
structure and appearance. This final phase of heal-
ing lasts six months to two years, depending on
the extent of the injury.
Disease processes influence healing as well.
Chronic conditions such as DIABETESand PERIPHERAL
VASCULAR DISEASE(PVD), themselves likely the result
of inflammatory dysfunction of some sort, damage
the fine networks of nerves and BLOODvessels that
intertwine through the tissues, limiting the ability
of these structures to carry signals (nerves) and
transport molecules and cells vital to immune func-
tion (blood vessels). Serious injury—whether from
disease process, trauma, or major surgery—affects
endocrine and hormonal activity throughout the
body, which influence the rate and processes of
healing. Serious injury temporarily stuns the THY-
ROID GLAND, for example, resulting in reduced pro-
duction of thyroid hormones and consequential
slowing of METABOLISM(EUTHYROID SICK SYNDROME).
Although researchers can map the physiologic
steps of healing, much of healing remains a mys-

tery. Researchers do not fully understand what

starts, regulates, and ends the healing process.

Many integrations across neurologic, endocrine,

and immune functions are factors in healing.

Some researchers are exploring connections

between emotions and the numerous biochemical

substances that are key to the healing process.

Researchers know, for example, that emotional

stress influences the release of numerous hor-

mones in the body and the release of these hor-

mones—such as the hormone CORTISOL, a powerful

immunosuppressant—directly affects the func-

tions of theIMMUNE SYSTEM. Research has shown

that pain is a stressor and affects the rate of heal-

ing. Studies continue to explore the relationship

between the mind and healing.

See also AYURVEDA; HORMONE; INTEGRATIVE MEDI-

CINE; MIND–BODY INTERACTIONS; PATHOGEN; REIKI;

STRESS RESPONSE HORMONAL CASCADE; TRADITIONAL

CHINESE MEDICINE(TCM); WOUND CARE.

histamine A chemical that acts as an IMMUNE

RESPONSEmediator. Large, granulated leukocytes

called mast cells, which reside in the mucous

membrane lining of the respiratory and gastroin-

testinal tracts, store histamine in their granules

and release it during the immune response. Mast

cells are most abundant in the nasal passages

(including the SINUSES), the TRACHEA, and the

bronchi. Histamine receptors on the surfaces of

cell membranes determine how histamine affects

the cell. ANTIHISTAMINE MEDICATIONS, the corner-

stone of treatment for type I HYPERSENSITIVITY REAC-

TION (allergic reaction), work by blocking

histamine receptors.

Though there is only one form of histamine, its

release can activate any of three types of hista-

mine receptors: H1, H2, and H3. CYTOKINES,

266