Hepatitis B (HBV)
Medical Author: Mohamad El Mortada, MD and Mary Nettleman, MD, MS
Medical Editor: Jay W. Marks, MD
Liver...The Largest Gland in the Body!
Medical Author: Leslie J. Schoenfield, M.D., Ph.D.
Medical Editor: Jay W. Marks, M.D.
The liver is the largest solid organ in the body. I think a lot of people
probably know that. But they may not know that it is also the largest gland in
the body. You see, the liver is also considered a gland because, among its
various functions, it makes and secretes bile. (Just for your reference, the
stomach and intestine are large hollow organs. Glands are organs or parts of
organs that make and secrete substances. And bile is a fluid that both aids in
digestion and transports fats as well as waste products into the intestine.)
Actually, there are all sorts of glands in the body that make and secrete
substances, including the pancreas (digestive enzymes), thyroid and other
endocrine glands (hormones), gastric glands in the stomach (acid), and lymph
glands or nodes (lymph). The liver is even larger, I think, than most mammary
glands (milk).
The liver weighs about three and a half pounds (1.6 kilograms). It measures
about 8 inches (20 cm) horizontally (across) and 6.5 inches (17 cm) vertically
(down) and is 4.5 inches (12 cm) thick.
You know, sometimes I'm surprised by how little information some people
have about the liver. Therefore, in this article, I want to relate a few other
special facts about the liver, which, I must admit, is my favorite organ.
What is hepatitis?
The term 'hepatitis' simply means
inflammation of the liver. Hepatitis may be
caused by a virus or a toxin such as alcohol. Other viruses that can cause
injury to liver cells include the hepatitis A and
hepatitis C viruses. These
viruses are not related to each other or to hepatitis B virus and differ in
their structure, the ways they are spread among individuals, the severity of
symptoms they can cause, the way they are treated, and the outcome of the
infection.
What is the scope of the problem?
Hepatitis B is an infection of the liver caused by the
hepatitis B virus (HBV). It is estimated that 350 million individuals worldwide
are infected with the virus, which causes 620,000 deaths worldwide each year.
According to the Centers for Disease Control (CDC), approximately 46,000 new cases of hepatitis B
occurred in the United States in 2006.
In the United States, rates of new infection were highest
among people aged 25 to 44 years (3.1 cases per 100,000 population) and lowest
among those younger than 15 years of age (0.02 per 100,000). This reflects the
major modes of transmission of hepatitis B (sexual transmission, illicit drug
use, exposure to infected blood) and the effect of universal vaccination of infants. In the
United States, there has been a 75% decrease in newly diagnosed cases of
hepatitis B during the past decade. This decrease is attributed to increased
vaccination and to heightened public awareness of HIV/AIDS and the resulting
safer sexual practices.
When a person first gets hepatitis B, they are said to have an 'acute'
infection. Most people are able to eliminate the virus and are cured of the
infection. Some are not able to clear the virus and have 'chronic' infection
with hepatitis B that is usually life-long (see below). In the United States an
estimated 800,000 to 1.4 million people are chronically infected with hepatitis
B.
Hepatitis B is found throughout the world. Some countries have much higher
rates of infection than the United States; for example, in Southeast Asia and
Sub-Saharan Africa, as many as 15% to 20% of adults are chronically infected with
hepatitis B.
What kind of a virus is hepatitis B?
The hepatitis B virus is a DNA virus, meaning that its genetic material is
made up of deoxyribonucleic acids. It belongs to a family of viruses known as
Hepadnaviridae. The virus is primarily found in the liver but is also present in
the blood and certain body fluids.
Hepatitis B virus consists of a core particle (central portion) and a
surrounding envelope (outer coat). The core is made up of DNA and the core
antigen (HBcAg). The
envelope contains the surface antigen (HBsAg). These antigens are present in the
blood and are markers that are used in the diagnosis and evaluation of patients
with suspected viral hepatitis.
How does hepatitis B virus cause liver injury?
The hepatitis B virus reproduces in liver cells, but the virus itself is not
the direct cause of damage to the liver. Rather, the presence of the virus
triggers an immune response from the body as the body tries to eliminate the virus and recover
from the infection. This immune response causes inflammation and may seriously
injure liver calls. Therefore, there is a balance between the
protective and destructive effects of the immune response to the hepatitis B
virus.
Next: How is the hepatitis B virus spread (transmitted)? »
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