Encyclopedia of Health and Medicine

islet cell transplantation 149
throughout the body do not respond to the normal
amounts of INSULIN the ISLETS OF LANGERHANS produce.
The short-term result is an excessive level of
GLUCOSE in the BLOOD circulation and the need for
the islet cells to produce increasing amounts of
insulin. Over the long term a constellation of health
conditions appears that may include OBESITY, HYPER-
LIPIDEMIA, type 2 DIABETES, CORONARY ARTERY DISEASE
(CAD), HYPERTENSION (high BLOOD PRESSURE), and
POLYCYSTIC OVARY SYNDROME (PCOS). Doctors diagnose
insulin resistance when a person has two or more
of these health conditions.
Treatment must first target the health condition,
and may include medications to reduce blood
pressure and blood cholesterol levels. CAD may
have significant implications for cardiovascular
function, and is a major risk for HEART ATTACK as
well as HEART FAILURE, CARDIOMYOPATHY, and
ISCHEMIC HEART DISEASE (IHD). Weight loss is crucial
as OBESITY is a key factor in these conditions as
well as in insulin resistance. Lifestyle measures
such as nutritious EATING HABITS and daily physical
exercise help improve metabolic efficiency and
sensitivity to insulin and also aid weight-management
efforts. These lifestyle measures practiced
consistently over time are often able to reverse
some of the health consequences as insulin resistance
diminishes, in particular facilitating improvements
in obesity, hypertension, and type 2
diabetes.
See also BODY MASS INDEX (BMI); DIABETES AND
CARDIOVASCULAR DISEASE; DIET AND HEALTH; EXERCISE
AND HEALTH; HEALTH RISK FACTORS; INFERTILITY;
LIFESTYLE AND HEALTH; WEIGHT LOSS AND WEIGHT MAN-
AGEMENT.
islets of Langerhans Clusters of endocrine cells
distributed throughout the PANCREAS that produce
INSULIN, GLUCAGON, and SOMATOSTATIN. There are
about a million islet clusters, each containing several
hundred islet cells. Each islet contains all
three types of islet cells: alpha islet cells, beta islet
cells, and delta islet cells.
In the center of each islet are the beta cells,
which secrete insulin. Insulin’s primary role in the
body is the regulation of carbohydrate METABOLISM.
Arranged in somewhat of a circle around the core
of the islet beta cells are the alpha cells, which
secrete glucagon, and the delta cells, which secrete
somatostatin. Glucagon stimulates the LIVER to
convert glycogen to GLUCOSE, making more energy
available to cells. Somatostatin suppresses the
release of GROWTH HORMONE (GH). It also slows the
release of insulin and glucagon, as well as the gastrointestinal
system’s secretion of DIGESTIVE HOR-
MONES.
The most significant disorder affecting the islets
of Langerhans is DIABETES. Type 1 diabetes, an
autoimmune disorder, destroys the islet cells.
Though other cells in the body synthesize the hormones
of alpha and delta islet cells—glucagon and
somatostatin, respectively—no other cells in the
body synthesize insulin. People who have type 1
diabetes must take insulin therapy (injections of
pharmaceutical insulin) to meet the needs of their
bodies for this crucial hormone. PANCREATITIS, an
INFLAMMATION of the pancreas, also can interfere
with islet cell functions. Though HORMONE production
usually returns when the inflammation subsides,
sometimes extensive scarring destroys islet
cells, resulting in type 2 (insulin-deficient) diabetes.
For further discussion of the islets of Langerhans
within the context of the endocrine system’s
structure and function please see the overview
section “The Endocrine System.”
See also AUTOIMMUNE DISORDERS; DIGESTIVE
ENZYMES; POLYGLANDULAR DEFICIENCY SYNDROME.
islet cell transplantation An experimental treatment
for DIABETES in which the surgeon injects
clusters of healthy ISLET OF LANGERHANS cells from a
donor (most often a cadaver donor) into the PAN-
CREAS of a person who has type 1 diabetes. Islet
cells produce the HORMONE INSULIN as well as two
other hormones, GLUCAGON and SOMATOSTATIN. A
healthy pancreas contains about a million clusters
of islet cells distributed widely throughout the
pancreatic tissue. Type 1 diabetes occurs when an
autoimmune response destroys the islet cells,
eliminating the body’s ability to produce insulin.
Islet cell transplantation replaces the destroyed
cells with healthy islet cells. It may take weeks to
months for the transplanted islet cells to establish
networks of BLOOD vessels that connect them to
the recipient and provide the outlet for the