H
H. flu: See
Haemophilus influenzae type b.
H. flu immunization: See HIB immunization.
Haemophilus influenzae (also H. flu): (Not the cause of
influenza as it was once thought to be), H. flu is a bacteria
capable of causing ear infections, meningitis, cellulitis (soft
tissue infection), upper respiratory infections, pneumonia and
other infections, especially in young children.
Haemophilus influenzae type B immunization: See HIB
immunization,
Hair follicle: A sac from which a hair grows.
Hairy cell leukemia: A rare type of chronic leukemia in which
the abnormal white blood cells appear to be covered with tiny
hairs. Hammer toe: A flexed (curly) toe but with no abnormal
rotation of the toe. May require surgical correction.
Hansen disease: Leprosy.
Haploid: A set of chromosomes with only one member of each
chromosome pair. The sperm and egg are haploid and, in humans,
have 23 chromosomes.
Hard palate: The bony part of the roof of the mouth. The hard
palate is the front of the palate and is in front of the soft
palate.
HAVRIX: A vaccine against hepatitis A made of killed hepatitis A
virus to stimulate the body’s immune system to produce
antibodies against the hepatitis A virus.
Hay fever: Allergic rhinitis.
HBIG: Hepatitis B immune globulin, which contains antibodies to
hepatits B virus and offers prompt but short lived protection.
hCG: Human chorionic gonadotropin, a human hormone produced by
the fetal part of the placenta that stimulates the gonads. The
abbreviation can also be written entirely in capital (upper
case) letters as "HCG". For more on this hormone in key lab
tests, please see: Human chorionic gonadotropin.
Hct: Hematocrit.
HDL: High-density lipoprotein.
HDL cholesterol: High-density lipoprotein cholesterol (the
"good" cholesterol).
Health care proxy: A health care proxy is one form of advance
medical directive. Advance medical directives preserve the
person’s right to accept or reject a course of medical treatment
even after that person becomes mentally or physically
incapacitated to the point of being unable to communicate those
wishes. There are two basic forms of advance directives: (1) a
living will, in which the person outlines specific treatment
guidelines that are to be followed by health care providers; (2)
a health care proxy (also called a power of attorney for
healthcare decision-making) in which the person designates a
trusted individual to make medical decisions in the event that
he or she becomes too incapacitated to make such decisions.
Advance directive requirements vary greatly from one
jurisdiction to another and should therefore be drawn up in
consultation with an attorney who is familiar with the laws of
the particular jurisdiction. (This entry is based upon material
from the National MS Society).
Heart: The heart is a muscle which pumps blood it receives from
veins into arteries throughout the body. The heart is composed
of specialized muscle called "cardiac muscle." (see muscle). The
heart, veins and arteries make up the circulatory system.
Heart attack: A coronary artery occlusion or myocardial
infarction (MI).
Heart block: A block in the conduction of the normal electrical
impulses in the heart.
Heartburn: Heartburn has nothing to do with the heart. It is an
uncomfortable feeling of burning and warmth occurring in waves
rising up behind the breastbone (sternum) toward the neck. It is
usually due to gastroesophageal reflux, the return of stomach
acid back up into the esophagus, the soft tube-like portion of
the digestive tract connecting the pharynx with the stomach.
Heart failure: Inability of the heart to keep up with the
demands on it and pump the blood with normal efficiency.
Heart murmur: An unusual heart sound which may be innocent or
reflect disease.
Heart rate: The number of heart beats per unit time, usually per
minute. The heart rate is based on the number of contractions of
the ventricles (the lower chambers of the heart). The heart rate
may be too fast (tachycardia) or too slow (bradycardia). The
pulse is bulge of an artery from the wave of blood coursing
through the blood vessel as a result of the heart beat. The
pulse is often taken at the wrist to estimate the heart rate.
Hecht syndrome: Inherited disorder transmitted as an autosomal
dominant trait in which short tight muscles make it impossible
to open the mouth fully or keep the fingers straight when the
hand is flexed back. The small mouth creates feeding problems.
The hands may be so tightly fisted the infant crawls on the
knuckles. Also called the trismus pseudocamptodactyly syndrome.
Helicobactor pylori: Bacteria that cause inflammation and ulcers
in the stomach.
Hemangioma: A birth irregularity where a localized tissue mass
grows rich in small blood vessels. Capillary hemangiomas are
composed nearly entirely of tiny capillary vessels. Cavernous
hemangiomas are composed of blood-filled "lakes" and channels.
Hemarthrosis: Blood in a joint.
Hematemesis: Bloody vomit.
Hematocrit: The percentage, by volume, of red cells in blood.
Normal range for males is about 40-54 and for females 37-47
(values may vary slightly between laboratories).
Hematologist: A doctor who specializes in treating diseases of
the blood.
Hematoma: A hematoma is a localized swelling filled with blood.
The blood is usually clotted or partially clotted and exists
within an organ or a soft tissue space, such as muscle.
Hematopoiesis: The formation and development of blood cells.
Hematuria: Blood in the urine.
Hemiparesis: Weakness on one side of the body.
Hemiplegia: One side of the body is paralyzed.
Hemizygous: Having only a single set of genes as, for example,
on the single X chromosome in the male.
Hemodialysis: Filtration and cleansing of the blood. Commonly
called dialysis.
Hemoglobin: The oxygen-carrying pigment of red blood cells.
Hemoglobin A: The main type of hemoglobin after early infancy.
The A stands for Adult.
Hemoglobin F: The main type of hemoglobin in the fetus and still
at birth. The F stands for Fetal.
Hemoglobin S: The most common type of abnormal hemoglobin,
hemoglobin S is found in sickle cell trait and sickle cell
anemia. It differs from hemoglobin A only by a single amino acid
substitution. Recognition of this tiny change marked the opening
of molecular medicine.
Hemoglobinuria: Hemoglobin in the urine.
Hemolysis: Breakdown of red blood cells.
Hemolytic anemia: Anemia due to the destruction (rather than
underproduction) of red blood cells.
Hemolytic disease of the newborn: Abnormal breakup of red blood
cells in the fetus or newborn.
Hemophilia: A set of bleeding disorders.
Hemophilia A: Classic hemophilia (the disease of the Russian
royal house and other descendants of Queen Victoria). Due to
profound deficiency of factor VIII which is necessary for normal
blood clotting. The hemophilia A gene is on the X chromosome so
females carry the gene and each of their sons stands a 50%
chance of receiving the gene and having hemophilia. Treatment of
hemophiliacs with contaminated blood products exposed many to
HIV.
Hemophilia B: Also called Christmas disease (so-named for the
first patient studied in detail with the disease). Due to
deficiency of coagulation factor IX. The hemophilia B gene is
also on the X chromosome.
Hemoptysis: Spitting up blood or blood-tinged sputum.
Hemorrhage: Hemorrhage refers to bleeding or a flow of blood. It
can be internal, and not be visible, or external, and therefore,
visible on the body.
Hemorrhoids: Dilated veins around the rectum.
Heparin: An anticoagulant (anti-clotting) medication. Heparin is
useful in preventing thromboembolic complications (clots that
travel from their site of origin through the blood stream to
clog up another vessel). Heparin is also used in the early
treatment of blood clots in the lungs (pulmonary embolisms).
Hepatic: Having to do with the liver.
Hepatitis: Inflammation of the liver.
Hepatitis A: Hepatitis due to the hepatitis A virus which is
usually transmitted by poor hygiene. (One reason why food
service employees are required to wash their hands after using
the toilet.)
Hepatitis A immunization: When immediate protection against
hepatitis A (infectious hepatitis) is needed, immunoglobulins
are used. Protection is effective only if given within 2 weeks
of exposure and lasts but 2-4 months. Immunoglobulins can be
used to protect household contacts of someone with acute viral
hepatitis and travelers to regions with poor sanitation and high
hepatitis A rates, when the traveler has to depart sooner than
the vaccines can take effect (about 2 weeks). Travelers can
receive the immunoglobulin and vaccine simultaneously and be
protected immediately and for longer term. When immediate
protection is not needed, hepatitis A vaccines are considered
for individuals in high-risk settings, including frequent world
travelers, sexually active individuals with multiple partners,
homosexual men, individuals using illicit drugs, employees of
daycare centers, and certain healthcare workers, and sewage
workers. Two hepatitis A vaccines called HAVRIX and VAQTA are
commercially available in the U.S. Both are highly effective and
provide protection even after only one dose. Two doses are
recommended for adults and 3 doses for children (under 18 years
of age) to provide prolonged protection.
Hepatitis B: Hepatitis due to the hepatitis B virus once thought
to be passed only through blood products and so called serum
hepatitis. Now known to be passed also by needle sticks, body
piercing and tattooing (if proper sterilization or disposable
one-use instruments are not used), dialysis, sexual and even
less intimate close contact, and childbirth.
Hepatitis B immunization: Hepatits B (hep B) vaccine gives
prolonged protection, but 3 shots over a half year are usually
required. In the U.S., all infants receive hep B vaccine. Two
vaccines (ENGERIX-B, and RECOMBIVAX-HB) are available in the US.
The first dose of hep B vaccine is frequently given while the
newborn is in the hospital or at the first doctor visit
following birth. The second dose is given about 30 days after
the initial dose. A booster dose is performed approximately six
months later. Babies born to mothers testing positive for hep B
receive, in addition, HBIG (hep B immune globulin) for prompt
protection. Older children (11-12 years) are advised to receive
a hep B booster as are adults in high-risk situations including
healthcare workers, dentists, intimate and household contacts of
patients with chronic hep B infection, male homosexuals,
individuals with multiple sexual partners, dialysis patients, IV
drug users, and recipients of repeated transfusions. Healthcare
workers accidentally exposed to materials infected with hep B
(such as needle sticks), and individuals with known sexual
contact with hep B patients are usually given both HBIG and
vaccine to provide immediate and long term protection.
Hepatitis C: Hepatitis due to the hepatitis C virus (HCV) which
is usually spread by blood transfusion, hemodialysis, and needle
sticks. Causes most transfusion-associated hepatitis.
Transmission of the virus by sexual contact is rare. At least
half of patients develop chronic hepatitis C infection.
Hepatitis C was previously called "non-A, non-B hepatitis.
Hepatitis D, E, F, and G: Lesser known (than hepatitis A, B, and
C), the most significant of these seems to be type D, or the
delta agent, which only causes disease in the presence of the
hepatitis B virus.
Hepatitis, infectious: See Hepatitis A.
Hepatitis, non-A, non-B: The old name for hepatitis C when the
causative virus had not been identified but it was known not to
be hepatitis A or B.
Hepatitis, viral: Liver inflammation caused by viruses. Specific
hepatitis viruses have been labeled A, B, C, D, E, F, and G.
While other viruses, such as the mononucleosis (Epstein-Barr)
virus and cytomegalovirus, can also cause hepatitis, the liver
is not their primary target.
Hepatomegaly: An enlarged liver.
Hepatosplenomegaly: Enlargement of the liver and spleen.
Hepatotoxic: Injurious to the liver. For example, acetaminophen
(TYLENOL) can be hepatotoxic.
Herbalist: One versed in herbal lore and, in regard to therapy,
an herb doctor.
Heritable: Capable of being transmitted from parent to child.
Heritability: The degree to which something is inherited.
Hereditary angioedema: A genetic form of angioedema. (Angioedema
is also referred to as Quinke’s disease.) Persons with it are
born lacking an inhibitor protein (called C1 esterase inhibitor)
that normally prevents activation of a cascade of proteins
leading to the swelling of angioedema. Patients can develop
recurrent attacks of swollen tissues, pain in the abdomen, and
swelling of the voice box (larynx) which can compromise
breathing. The diagnosis is suspected with a history of
recurrent angioedema. It is confirmed by finding abnormally low
levels of C1 esterase inhibitor in the blood. Treatment options
include antihistamines and male steroids (androgens) that can
also prevent the recurrent attacks. Also called hereditary
angioneurotic edema.
Hereditary angioneurotic edema: A genetic form of angioedema. (Angioedema
is also referred to as Quinke’s disease.) Persons with it are
born lacking an inhibitor protein (called C1 esterase inhibitor)
that normally prevents activation of a cascade of proteins
leading to the swelling of angioedema. Patients can develop
recurrent attacks of swollen tissues, pain in the abdomen, and
swelling of the voice box (larynx) which can compromise
breathing. The diagnosis is suspected with a history of
recurrent angioedema. It is confirmed by finding abnormally low
levels of C1 esterase inhibitor in the blood. Treatment options
include antihistamines and male steroids (androgens) that can
also prevent the recurrent attacks. Also called hereditary
angioedema.
Hereditary mutation: A gene change that occurs in a germ cell
(an egg or sperm) to become incorporated in every cell in the
body. Hereditary mutations (also called germline mutations) play
a role in cancer as, for example, the eye tumor retinoblastoma
and Wilms' tumor of the kidney.
Hereditary spherocytosis (HS): Genetic disorder of red blood
cells. In HS, the red cells are abnormal in shape. They are
spherical rather than the normal svelt biconcave-disk shape.
They are also unusually fragile. The rotund HS red cells tend to
get trapped in narrow blood passages (such as in the spleen) and
break up (hemolyze) easily, leading to anemia.
Heredity: Genetic transmission from parent to child.
Hernia: Also called rupture, "hernia" is a general term
referring to a protrusion of a tissue through the wall of the
cavity in which it is normally contained.
Hernia, hiatus: Protrusion of the stomach up into the opening
normally occupied by the esophagus in the diaphragm, the muscle
that separates the chest (thoracic) cavity from the abdomen.
Hiatus in Latin means an opening.
Herniation: Abnormal protrusion of tissue through an opening.
For example, a intervertebral disk (one situated between the
vertebral bodies) can protrude and impinge on a nerve root.
Heroin: Semisynthetic drug derived from morphine. Discovered in
1874, it was introduced commercially in 1898 by the Bayer
company in Germany. The name heroin was coined from the German
heroisch meaning heroic, strong. Heroin is stronger (more
potent) than morphine.
Herpes, genital: A viral infection transmitted through intimate
contact with the moist mucous linings of the genitals. This
contact can involve the mouth, the vagina or the genital skin.
The herpes simplex type 2 virus enters the mucous membranes
through microscopic tears. Once inside, the virus travels to
nerve the roots near the spinal cord and settles there
permanently. When an infected person has a herpes outbreak, the
virus travels down the nerve fibers to the site of the original
infection and when it reaches the skin, the classic redness and
blisters occur. The outbreak of herpes is closely related to the
functioning of the immune system. Women who have suppressed
immune systems, either through stress, disease, or medications,
have more frequent and longer-lasting outbreaks. Commonly just
called "herpes."
Herpes simplex type 1: A virus that causes cold sores and fever
blisters.
Herpes simplex type 2: Different from herpes simplex type 1,
herpes simplex 2 causes genital herpes.
Herpesvirus: A member of the herpes family of viruses. One type
of herpesvirus is sexually transmitted and causes sores on the
genitals.
Herpes zoster: Also called shingles, zona, and zoster. The
culprit is the varicella-zoster virus. Primary infection with
this virus causes chickenpox (varicella). At this time the virus
infects nerves (namely, the dorsal root ganglia) where it
remains latent (lies low) for years. It can then be reactivated
to cause shingles with blisters over the distribution of the
affected nerve accompanied by often intense pain and itching.
Hetero-: Combining form from the Greek heteros meaning
different. The opposite is homo- from the Greek homos meaning
same. For example, heterogeneous and homogeneous, heterosexual
and homosexual, etc.
Heterochromatin: A genetically inactive part of the genome,
heterochromatin was so named because it was chromosomal material
(chromatin) that stained differently, more darkly, all through
the cell cycle, than most chromosomal material (which was named
euchromatin). There are two types, namely constituitive
heterochromatin and facultative heterochromatin.
Heterochromatin, constituitive: Heterochromatin that is fixed
and irreversible. Regions of constituitive heterochromatin are
located at very specific spots in the genome (on chromosomes 1,
9, 16 and the Y chromosome, the tiny short arms of chromosomes
13-15 and 21 and 22, and near the centromeres of chromosomes)
and consists of DNA that contains many tandem (not inverted)
repeats of a short basic repeating unit (known as satellite
DNA).
Heterochromatin, facultative: Heterochromatin that need not
always be heterochromatic but has the faculty to return to the
normal euchromatic state. The inactive X chromosome is made up
of facultatative heterochromatin. When a woman transmits that X
to a son, it reverts to euchromatin and genetic activity.
Heterochromia: Different colors.
Heterochromia iridis: A difference of color between the iris of
one eye and the other. (A person with one brown and one blue eye
has heterochromia iridis.) Also, a difference in color within an
iris (sectoral heterochromia iridis).
Heteroerotic: Having to do with sexual excitement toward the
opposite sex. By contrast with alloerotic.
Heterokaryon: A cell with two separate nuclei formed by the
experimental fusion of two genetically different cells. (Heterokaryons,
for example, composed of nuclei from Hurler syndrome and Hunter
syndrome, both diseases of mucopolysaccharide metabolism, have
normal mucopolysaccharide metabolism proving that the two
syndromes affect different proteins and so can correct each
other in the heterokaryon).
Heteromorphism: Something different in form. Chromosome
heteromorphisms are normal variations in the appearance of
chromosomes.
Heteroploid: A different chromosome number than the normal
number of chromosomes.
Heterosexual: A person sexually attracted to persons of the
opposite sex. The word "straight" has become synonymous with
heterosexual. Heterosexual can also be an adjective.
Heterosexuality: Sexuality directed toward someone of the
opposite sex.
Heterozygote: An individual with different genes at a particular
spot (locus) on a pair of chromosomes. (A heterozygote for
cystic fibrosis (CF) has the CF gene on one chromosome 7 and the
normal paired gene on the other chromosome 7. That makes them a
carrier for CF.)
Heterozygous: The state of being heterozygous.
Hexoseaminidase A: Deficiency of this enzyme causes Tay-Sachs
disease, a progressive, fatal neurologic disorder concentrated
in people of European Jewish (Ashkenazi) descent.
Hiatus hernia: Protrusion of the stomach up into the opening
normally occupied by the esophagus in the diaphragm, the muscle
that separates the chest (thoracic) cavity from the abdomen.
Hiatus in Latin means an opening.
HIB: Haemophilus influenzae type b.
HIB immunization: This vaccine is to prevent disease caused by
the Haemophilus influenzae type B (HIB) bacteria. The H.
influenzae (H. flu) bacteria can cause a range of serious
diseases including meningitis with potential brain damage and
epiglottitis with airway obstruction poisoning. The HIB vaccine
is usually given at 2, 4 and 6 months of age. A final booster is
given at 12-15 months of age. HIB vaccine rarely causes severe
reactions.
Hiccups: Spasmodic contractions of the diaphragm that are
involuntary and often rhythmic. Usually just a minor nuisance,
prolonged hiccups can become a major problem.
Hidradenitis suppurativa: This is an illness characterized by
multiple abscesses that form under the arm pits and in the groin
area.
High blood pressure: A repeatedly elevated blood pressure
exceeding 140 over 90 mmHg. High blood pressure (hypertension)
is "the silent killer." Chronic high blood pressure can
stealthily cause blood vessel changes in the back of the eye
(retina), abnormal thickening of the heart muscle, kidney
failure, and brain damage. No specific cause for high blood
pressure is found in 95% of patients. High blood pressure is
treated with salt restriction, regular aerobic exercise, and
medications.
Hippocampus: An area buried deep in the forebrain that helps
regulate emotion and memory.
Hip bursitis: A bursa is a fluid-filled sac that functions as a
gliding surface to reduce friction between moving tissues of the
body. There are two major bursae of the hip. Bursitis is usually
not infectious, but the bursa can become infected. Treatment of
non-infectious bursitis includes rest, ice, and medications for
inflammation and pain. Infectious bursitis is treated with
antibiotics, aspiration, and surgery.
Hip pointer: Sportstalk for an iliac crest contusion (a bruise
of the upper edge of the ilium, one of the hip bones).
Hirschsprung's disease: Absence of nerves (ganglia) in the bowel
wall starting in the anus and extending up a variable distance
with enlargement of the bowel above that point. Hirschsprung's
disease is the commonest cause of lower intestinal obstruction
in the newborn and, later, one of the causes of chronic
constipation. Also called congenital aganglionic megacolon.
Hirsute: Overly hairy.
Hirudin: An anticoagulant (anti-clotting) agent that prevents
thromboembolic complications (clots that travel through the
blood stream to clog up a vessel). Hirudin is the active
principle in the secretion of leeches. Desirudin and lepirudin (REFLUDAN)
are genetically engineered recombinant forms of hirudin.
Histoplasma: A fungus found worldwide. In the USA, it is so
common in the Midwest that in parts of Kentucky and Tennessee
nearly 90% of adults show evidence of exposure (with a positive
histoplasma skin test).
Histoplasmosis: Infection with histoplasma. Most patients have
no symptoms However, histoplasma can cause acute or chronic lung
disease or progessive disseminated histoplasmosis (a particular
hazard for persons with HIV).
Histamine: Substance that plays a major role in many allergic
reactions. Histamine dilates blood vessels and makes the vessel
walls abnormally permeable.
Histocompatible: The prefix histo- means tissue. The term
histocompatible is literally tissue compatible. If a donor and
recipient are histocompatible (like identical twins), a
transplant will be easily accepted.
Histones: Proteins associated with DNA in chromosomes.
History: In medicine, the patient's past and present which may
hopefully contain clues helpful to their future health.
HIV: Acronym for the Human Immunodeficiency Virus, the cause of
AIDS.
Hives: Urticaria. Raised, itching areas of skin, often a sign of
an allergic reaction. Also called "welts" or "nettle rash."
HLA: The HLA complex is the major human histocompatibility
system. HLA-typing is done before transplantation to determine
the degree of histocompatability. HLA is an acronym for Human
Leukocyte Antigens).
Hodgkin's disease (Hodgkin's lymphoma): A disease of the lymph
nodes named after the English physician Thomas Hodgkin
(1798-1866) who discovered it. ("Perfecting the World" is an
excellent biography of Dr. Hodgkin by A. M. and E. H. Kass).
Homeobox: A short stretch of nucleotides (DNA or RNA) with an
almost identical base sequence in all genes that contain that
stretch. Homeoboxes occur in many organisms from fruit flies to
human beings and appear to determine when particular groups of
genes are expressed during development.
Homeopath: A person who practices homeopathy.
Homeopathy: A system of therapy founded in the 19th century
based on the concept that disease can be treated with drugs (in
minute doses) thought capable of producing the same symptoms in
healthy people as the disease itself.
Homocystinuria: A genetic disease due to an enzyme deficiency.
Among other events, there is a buildup of the amino acid
homocystine. Progressive mental retardation is common in
untreated cases. The finding of vascular disease and premature
arteriosclerosis in persons with homocystinuria led to the
theory that homocystine may be a factor in heart disease.
Homolog (homologue): One chromosome of a pair.
Homologies: Similarities in DNA or protein sequences between
individuals or between species.
Homologous: The relationship between two chromosomes that are
paired and so are homologs of each other.
Homologous chromosomes: A pair of chromosomes containing the
same gene sequences, each derived from one parent.
Homosexual: A person sexually attracted to persons of the same
sex. Homosexuals include males (gays) and females (lesbians).
Homosexual can also be an adjective.
Homosexuality: Sexuality directed toward someone of the same
sex.
Hormone: Chemical substance produced in the body that controls
and regulates the activity of certain cells or organs. A hormone
originally denoted a chemical made by a special gland for export
to another part of the body. Now a hormone is more broadly any
chemical, irrespective of whether it is produced by a special
gland or not, for export or domestic use, that "controls and
regulates the activity of certain cells or organs.". The word "hormao"
which means "I set in motion" or "I stir up" was used in ancient
Greece to covey the "vital principle" of "getting the juices
flowing." The word "hormone" was resurrected in 1902 (not 1906,
as the Oxford English Dictionary states) by the English
physiologists Wm. M. Bayliss and Ernest H. Starling who that
year reported their discovery of a substance made by glands in
the small intestine that stimulated pancreatic secretion. They
called the substance "secretin" and dubbed it a "hormone", the
first known hormone.
Hormone, aldosterone: Hormone produced by the outer portion
(cortex) of the adrenal gland that regulates the balance of
water and electrolytes (ions such as potassium and sodium) in
the body. Aldosterone encourages the kidney to excrete potassium
into the urine and to retain sodium, thereby retaining water.
Aldosterone is classified as a mineralocorticoid hormone.
Hormone, androgenic: Any hormone that promotes the development
and maintenance of male sex characteristics. Testosterone is an
androgen.
Hormone, cortisol: The primary stress hormone. Cortisol is the
major natural glucocorticoid in humans.
Hormone, estrogenic: A female hormone produced by the ovaries
(or an equivalent hormone synthesized in the laboratory).
Estrogen deficiency can lead to osteoporosis.
Hormone, glucocorticoid: A hormone that predominantly affects
the metabolism of carbohydrates and,to a lesser extent, fats and
proteins (and has other effects). Glucocorticoids are made in
the outside portion (the cortex) of the adrenal gland and
chemically classed as steroids. Cortisol is the major natural
glucocorticoid. The term glucocorticoid also applies to
equivalent hormones synthesized in the laboratory.
Hormone, human chorionic gonadotropin (hCG): A human hormone
made by chorionic cells (in the fetal part of the placenta), hCG
is directed at the gonads and stimulates them. hCG becomes
detectable (by immunologic means) within days of the time of
fertilization. It therefore forms the foundation of most common
pregnancy tests. The level of hCG in maternal serum enters as
one component in the "double" and the "triple" screens used
during pregnancy to assign risks of Down syndrome and other
fetal disorders.
Hormone, mineralocorticoid: A group of hormones, the most
important being aldosterone, that regulate the balance of water
and electrolytes (ions such as sodium and potassium) in the
body. The mineralocorticoid hormones act specifically on the
tubules of the kidney.
Hormone, parathormone: Hormone made by the parathyroid gland
(behind the thyroid gland in the neck). Parathormone (pronounced
para-thor-mone) is critical to calcium and phosphorus balance.
Deficiency of parathormone results in abnormally low calcium in
the blood (hypocalcemia). Also call parathyrin.
Hormone, parathyrin: See Hormone, parathormone.
Hormone, parathyroid: See Hormone, parathormone.
Hormone, progesterone: A female hormone, progesterone is the
principal progestational hormone. Progestational hormones
prepare the uterus (the womb) to receive and sustain the
fertilized egg.
Hormone, secretin: Hormone made by glands in the small intestine
that stimulates pancreatic secretion. The word "hormone" was
coined by the English physiologists Wm. M. Bayliss and Ernest H.
Starling in connection with their discovery of secretin, the
first hormone, in 1902.
Hormone, T3: Triiodothyronine, a thyroid hormone. The number 3
is usually in subscript.
Hormone,T4: Thyroxine, a thyroid hormone. The number 4 is
usually in subscript.
Hormone therapy: A form of treatment that takes advantage of the
fact that certain cancers depend on hormones to grow. The
treatment may include giving hormones to the patient or
decreasing the level of hormones in the body.
Hormone, thyroid: Chemical substance made by the thyroid gland
which is located in the front of the neck. The thyroid gland
uses iodine to make thyroid hormones. The two most important
thyroid hormones are thyroxine (T4) and triiodothyronine (T3).
Hormone, thyroid stimulating (TSH): A hormone produced by the
pituitary gland (at the base of the brain) that promotes the
growth of the thyroid gland (in the neck) and stimulates it to
produce its thyroid hormones. Normally, the rate of thyroid
hormone production is controlled by the pituitary. When there
are insufficient thyroid hormones in the body for normal
functioning of the cells, the pituitary releases TSH. TSH in
turn "stimulates" the thyroid gland to produce more thyroid
hormones. In contrast, when there is excessive amount of thyroid
hormones, the pituitary gland stops producing TSH. The TSH level
then falls and thyroid hormone production is reduced. This
mechanism maintains a relatively constant level of thyroid
hormones circulating in the blood. This phenomenon is analogous
to a thermostat used for temperature regulation in a room: when
the temperature rises, the thermostat shuts the heater off and
the room temperature falls back to normal. High levels of
thyroid hormones cause the TSH level to fall, resulting in no
further stimulation of the thyroid gland. In hyperthyroidism,
there are continuously elevated levels of the thyroid hormones.
TSH is also known as thyrotropin.
Hormone, thyrotropin: A hormone produced by the pituitary gland
(at the base of the brain) that promotes the growth of the
thyroid gland (in the neck) and stimulates it. The suffix -tropin
indicates "an affinity for". Thyrotropin has an affinity for the
thyroid. Thyrotropin is known also as thyroid stimulating
hormone (TSH).
Hormone, thyroxine: A chemical substance made by the thyroid
gland The thyroid gland uses iodine to make thyroid hormones.
Thyroxine (T4), one of the most important thypoid hormones, has
four iodine molecules attached to its molecular structure.
Hormone, triiodothyronine: A hormone made by the thyroid gland.
The thyroid gland uses iodine to make thyroid hormones.
Triiodothyronine (T3) has three iodine molecules attached to its
molecular structure. Iodine is found in seafood, bread, seaweed,
and ordinary table salt.
Hormone, TSH: Stands for Thyroid Stimulating Hormone. Also known
as thyrotropin.
Horner syndrome: A complex of abnormal findings, namely sinking
in of one eyeball, ipsilateral ptosis (drooping of the upper
eyelid on the same side) and miosis (constriction of the pupil
of that eye) together with anhidosis (lack of sweating) and
flushing of the affected side of the face. Due to paralysis of
certain nerves (specifically, the cervical sympathetic nerves).
Also called Horner-Bernard syndrome, Bernard syndrome,
Bernard-Horner syndrome and Horner’s ptosis (but best known as
Horner syndrome).
Hornet stings: Stings from hornets and other large stinging
insects such as bees, yellow jackets and wasps can trigger
allergic reactions varying greatly in severity. Avoidance and
prompt treatment are essential. In selected cases, allergy
injection therapy is highly effective. (The three "A’s" of
insect allergy are Adrenaline, Avoidance and Allergist.)
HPV: Human papilloma virus.
Ht: Abbreviation for height (and also heart).
HUGO: Human Genome Organization (the international organization
concerned with human genome research).
Human chorionic gonadotropin (hCG): A human hormone made by
chorionic cells (in the fetal part of the placenta), hCG is
directed at the gonads and stimulates them. hCG becomes
detectable (by immunologic means) within days of fertilization
and forms the foundation of the common pregnancy tests. The
level of hCG in maternal serum also enters as one component in
the "double" and the "triple" screens used during pregnancy to
assign risks of Down syndrome and other fetal disorders.
Human gene therapy: Insertion of normal DNA directly into cells
to correct a genetic defect. The treatment of disease by
replacing, altering, or supplementing a gene that is absent or
abnormal that is responsible for the disease. In gene therapy
for cancer, for example, researchers are trying to bolster the
body’s natural capacity to combat cancer and make the tumor more
sensitive to other kinds of therapy. Gene therapy, still in its
early stages, holds great promise for the treatment of many
diseases.
Human immunodeficiency virus: See HIV.
Human papilloma virus (HPV): A family of over 60 viruses
responsible for causing warts. The majority of the viruses
produce warts on the hands, fingers, and even the face. Most of
these viruses are innocuous, causing nothing more than cosmetic
concerns. Several types of HPV are confined primarily to the
moist skin of the genitals, producing genital warts and
elevating the risk for cancer of the cervix. The papilloma
viruses that cause wartlike growths on the genitals are sexually
transmitted.
Humerus: The long bone in the upper arm which extends from the
shoulder to the elbow.
Humidifier: A machine that puts moisture in the air.
Humor: In medicine, humor refers to a fluid (or semifluid)
substance. Thus, the aqueous humor is the fluid normally present
in the front and rear chambers of the eye.
Humoral: Pertaining to elements in the blood or other body
fluids.
Human genome: The full collection of genes in a human being.
Human Genome Project: International effort aimed at identifying
and sequencing (ordering) all of the bases in the human genome.
American participation in this monumental undertaking has been
supported by funds from the National Institutes of Health (NIH)
and the Department of Energy (DOE).
Huntington's disease: An hereditary disorder with mental and
physical deterioration leading to death. Although characterized
as an "adult-onset" disease (as is usually the case), we have
seen children with full-blown Huntington's disease.
Hurler syndrome: A genetic error of metabolism. There is
incomplete breakdown and accumulation of a substance (a
mucopolysaccharide) which is abnormally stored in the brain and
other places. This usually leads to death of the individual with
Hurler syndrome by their early teen years. See gargoylism.
Hybrid: The result of a cross between genetically unlike
parents.
Hybridoma: A cell hybrid resulting from the fusion of a cancer
cell and a normal lymphocyte (a type of white blood cell). The
hybridoma is immortal in the laboratory and makes the same
products as its parent cells forever.
Hydatid (hydatidiform) mole: An abnormal pregnancy without a
placenta or embyro that eventuates in a mass of cysts resembling
a bunch of grapes.
Hydrocele: Accumulation of fluid in the coat around the testis.
Small hydroceles tend to disappear by a year of age while larger
hydroceles may persist and warrant surgery.
Hydrocephalus: Abnormal buildup of cerebrospinal fluid in the
ventricles of the brain. The fluid is often under increased
pressure and can compress and damage the brain. Treatment is by
insertion of a shunt to let the excess fluid exit and relieve
the pressure.
Hydrocephaly: See hydrocephalus.
Hydronephrosis: Distention of the kidney with urine. Due to
obstruction of urine outflow (for example, by a stone blocking
the ureter, the tube going from the kidney to the bladder).
Hymen: A thin membrane which completely or partially occludes
the vaginal opening.
Hyper-: Prefix meaning high, beyond, excessive, above normal.
For example, hypercalcemia is high calcium in the blood.
Hyperadrenocorticism: Excess hormone called "cortisol". Often
called Cushing’s syndrome, it is an extremely complex condition
that involves many areas of the body. It results from an excess
of cortisol and its effects on the human body. Common symptoms
are thinning of the skin, weakness, weight gain, bruising,
hypertension, diabetes, weak bones (osteoporosis), facial
puffiness, and in women cessation of periods. One of the
commonest causes of Cushing’s syndrome is the administration of
"cortisol-like medications" for the treatment of diverse
diseases. All other cases of Cushing’s syndrome are due to
excess production of cortisol by the adrenal gland including 1)
an abnormal growth of the pituitary gland, which stimulates the
adrenal gland, 2) a benign or malignant growth within the
adrenal gland itself, which produces cortisol and 3) production
within another part of the body (ectopic production) of a
hormone that directly or indirectly stimulates the adrenal gland
to make cortisol. Harvey Cushing (1869-1939), a neurosurgeon,
described hyperadrenocorticism due specifically to an
ACTH-secreting basophilic pituitary adenoma, a benign pituitary
tumor that puts out ACTH (AdrenoCorticoTropic Hormone) that, in
turn, drives (or overdrives) the adrenal gland.
Hyperaldosteronism: Overproduction of the hormone aldosterone
from the outer portion (cortex) of the adrenal gland or a tumor
containing that type of tissue. Excess aldosterone (pronounced
al-do-ster-one) results in low potassium levels (hypokalemia),
underacidity of the body (alkalosis), muscle weakness, excess
thirst (polydipsia), excess urination (polyuria), and high blood
pressure (hypertension). Also called aldosteronism and Conn’s
syndrome.
Hyperbilirubinemia: An elevated level of the pigment bilirubin
in the blood. A sufficient elevation will produce jaundice. Some
degree of hyperbilirubinemia is very common in babies right
after birth, especially premies.
Hypercalcemia: A higher-than-normal level of calcium in the
blood. This can cause a number of nonspecific symptoms,
including loss of appetite, nausea, thirst, fatigue, muscle
weakness, restlessness, and confusion. Excessive intake of
calcium may cause muscle weakness and constipation, affect the
conduction of electrical impulses in the heart (heart block)
lead to calcium stones (nephrocalcinosis), in the urinary tract,
impair kidney function, and interfere with the absorption of
iron predisposing to iron deficiency. According to the National
Academy of Sciences, adequate intake of calcium is 1 gram daily
for both men and women. The upper limit for calcium intake is
2.5 grams daily.
Hypercholesterolemia: High blood cholesterol. See familial
hypercholesterolemia.
Hyperglycemia: Elevated level of the sugar glucose in the blood.
Hyperkalemia: Elevated blood potassium.
Hyperlipidemia: High lipid (fat) levels in the blood.
Hypermagnesemia: Excess magnesium. Persons with impaired kidney
function should be especially careful about their magnesium
intake because they can accumulate magnesium, a dangerous (and
sometimes fatal) situation. According to the National Academy of
Sciences, the Recommended Dietary Allowances of magnesium are
420 milligrams per day for men and 320 milligrams per day for
women. The upper limit of magnesium as supplements is 350
milligrams daily, in addition to the magnesium from food and
water. Too much magnesium is hypermagnesemia.
Hypermobility syndrome: A common benign childhood condition
involving hypermobile joints (that can move beyond the normal
range of motion). Symptoms include pains in knees, fingers,
hips, and elbows. The affected joints may sprain or dislocate.
Scoliosis (curvature of the spine) is more frequent. Usually
improves with adulthood. Also called the joint hypermobility
syndrome.
Hypernatremia: Elevated blood sodium.
Hyperphosphatemia: A higher than normal blood level of
phosphate. Phosphate molecules are particularly important as
part of larger molecules in cell energy cycles. Higher than
normal levels can be caused by ingestion of phosphate rich foods
(diary products) or kidney failure.
Hyperpigmented: Overly pigmented.
Hyperplasia: A precancerous condition in which there is an
increase in the number of normal cells lining the uterus.
Hypertension: High blood pressure, defined as a repeatedly
elevated blood pressure exceeding 140 over 90 mmHg. High blood
pressure (hypertension) is "the silent killer." Chronic high
blood pressure can stealthily cause blood vessel changes in the
back of the eye (retina), abnormal thickening of the heart
muscle, kidney failure, and brain damage. No specific cause for
high blood pressure is found in 95% of patients. High blood
pressure is treated with salt restriction, regular aerobic
exercise, and medications.
Hyperthermia: Treatment that involves heating a tumor.
Hyperthyroid: Excess of thyroid hormone resulting from an
overactive thyroid gland (or taking too much thyroid hormone).
Hypertonia: Increased tone of skeletal muscles. Basically, too
tight muscles.
Hypertonic solution: One with more salt than in normal cells and
blood.
Hyperuricemia: Abnormally elevated blood level of uric acid.
Uric acid is a breakdown product of purines that are part of
many foods we eat. While hyperuricemia may indicate an increased
risk of gout, the relationship between hyperuricemia and gout is
unclear. Many patients with hyperuricemia do not develop gout,
while some patients with repeated gout attacks have normal or
low blood uric acid levels. Among the male population in the
United States, approximately ten percent have hyperuricemia.
However, only a small portion of those with hyperuricemia will
actually develop gout.
Hyperventilation: Overbreathing. Due to anxiety. Overbreathing
causes dizziness, lightheadedness, a sense of unsteadiness and
tingling around the mouth and fingertips. Relief can be gotten
by breathing in and out of a paper bag (to increase the level of
carbon dioxide). Opposite, hypoventilation or underbreathing.
Hypo-: Prefix meaning low, under, beneath, down, below normal.
For example, hypocalcemia is olow calcium in the blood.
Hypocalcemia: Lower-than-normal blood calcium. Low blood calcium
makes the nervous system highly irritable with tetany (spasms of
the hands and feet, muscle cramps, abdominal cramps, overly
active reflexes, etc.) Chronic calcium deficiency contributes to
poor mineralization of bones, soft bones (osteomalacia) and
osteoporosis; and, in children, rickets and impaired growth.
Food sources of calcium include dairy foods, some leafy green
vegetables such as broccoli and collards, canned salmon, clams,
oysters, calcium-fortified foods, and tofu. According to the
National Academy of Sciences, adequate intake of calcium is 1
gram daily for both men and women. The upper limit for calcium
intake is 2.5 grams daily.
Hypoglycemia: Low level of the sugar glucose in the blood.
Hypokalemia: Low blood potassium.
Hypomagnesemia: Too little magnesium. Magnesium deficiency can
occur due to inadequate intake or impaired intestinal absorption
of magnesium. Low magnesium (hypomagnesemia) is often associated
with low calcium (hypocalcemia) and low potassium (hypokalemia).
Deficiency of magnesium causes increased irritability of the
nervous system with tetany (spasms of the hands and feet,
muscular twitching and cramps, spasm of the larynx, etc.).
According to the National Academy of Sciences, the Recommended
Dietary Allowances of magnesium are 420 milligrams per day for
men and 320 milligrams per day for women. The upper limit of
magnesium as supplements is 350 milligrams daily, in addition to
the magnesium from food and water.
Hyponatremia: Low blood sodium.
Hypoplasia of the thymus and parathyroids: Also known as the
DiGeorge syndrome (DGS), this disorder is characterized by (1)
low blood calcium levels (hypocalcemia) due to underdevelopment
(hypoplasia) of the parathyroid glands needed to control
calcium; (2) underdevelopment (hypoplasia) of the thymus, an
organ behind the breastbone in which lymphocytes mature and
multiply; and (3) defects of the outflow tracts from the heart.
Most cases of DGS are due to a microdeletion in chromosome band
22q11.2. A small number of cases have defects in other
chromosomes, notably 10p13. Named after the American pediatric
endocrinologist Angelo DiGeorge. Another name for DGS is the
third and fourth pharyngeal pouch syndrome (since the faulty
structures in DGS are embryologically derived from the third and
fourth pharyngeal pouches).
Hypophosphatemia: A less than normal blood level of phosphate.
The opposite of hyperphosphatemia.
Hypopigmented: Underpigmented.
Hypoplasia: Underdevelopment or incomplete development of a
tissue or organ.For example, there can be hypoplasia
(underdevelopment) of the enamel of the teeth. Hypoplasia is
less drastic than aplasia where there is no development at all.
Hypotension: Low (abnormally low) blood pressure. Hypotension is
a consistent finding in shock but is also found in other
conditions and so is not necessarily diagnostic of shock. The
word hypotension is a hybrid of the Greek "hypo" meaning "under"
and the Latin "tensio" meaning "to stretch." In French, "la
tension" is "the blood pressure."
Hypotension, orthostatic: Some symptoms of dizziness such as
wooziness, feeling about to black out, and tunnel vision can be
due to insufficient blood flow to the brain. The cause is
transient low blood pressure (hypotension) due usually to
suddenly standing up (orthostatic). The symptoms are typically
worse when standing, improve with lying down and may be
experienced by healthy individuals who rise quickly from a
chair, often after a meal, and have a few seconds of
disorientation.
Hypothalamus: The area of the brain that controls body
temperature, hunger, and thirst.
Hypothermia: Abnormally low body temperature. Someone who falls
asleep in a snowbank may become hypothermic. Hypothermia is
intentionally produced to slow the metabolism during some types
of surgery.
Hypothyroid: Deficiency of thyroid hormone.
Hypotonia: Decreased tone of skeletal muscles. In a word,
floppiness.
Hypotonic solution: One with less salt than in normal cells and
blood.
Hypovolemia: Abnormal decrease in blood volume (strictly
speaking, in the blood plasma).
Hypovolemic shock: See shock.
Hypoxia: Concentration of oxygen in arterial blood that is less
than normal. Anoxia refers to complete lack of oxygen.
Hypoxia-ischemia: See hypoxia. Ischemia refers to blood flow to
cells and organs that is not sufficient to maintain their normal
function.
Hypoxic-ischemic encephalopathy: Damage to cells in the central
nervous system (the brain and spinal cord) from inadequate
oxygen. Hypoxic-ischemic encephalopathy allegedly may cause in
death in the newborn period or result in what is later
recognized as developmental delay, mental retardation, or
cerebral palsy. This is an area of considerable medical and
medicolegal debate.
Hysterectomy: An operation to remove the uterus and sometimes
also the cervix.
Hysterectomy, abdominal: Surgical removal of the uterus through
an incision made in the abdominal wall. As opposed to a vaginal
hysterectomy.
Hysterectomy, complete: Complete surgical removal of the uterus
and cervix. Also called a total hysterectomy.
Hysterectomy, partial: The uterus is sugically removed but the
cervix is left is left in place. Also called a subtotal
hysterectomy.
Hysterectomy, subtotal: The uterus is surgically removed but the
cervix is left is left in place. Also called a partial
hysterectomy.
Hysterectomy, total: Complete surgical removal of the uterus and
cervix. Also called a complete hysterectomy.
Hysterectomy, vaginal: Removal of the uterus through a surgical
incision, not of the abdomen but, within the vagina. With a
vaginal hysterectomy, the scar is not outwardly visible. A
vaginal hysterectomy is in contrast to an abdominal
hysterectomy. |