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Clinical Anatomy of the Abdomen
and Gastrointestinal Tract
This chapter will descr ibe the following:
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Location of the abdominal organs
Structure of the gastrointestinal tract
Function of the organs of the gastrointestinal tract
Structure of the other intra-abdominal organs
Structure and function of the peritoneum
The Anatomy of the Abdomen
Before assessing patients with abdominal symptoms, it is important to
understand the anatomy of the abdomen and the organs that are in it.
c The abdominal cavity is a space.
c Directly above the abdominal cavity is the chest cavity, which contains the
heart and lungs. This is separated from the abdomen by the diaphragm.
c Below the abdominal cavity and continuous with it, is the pelvis. This is part
of the same space, so that disease of the pelvic organs may also affect the
abdominal cavity.
c The abdominal cavity is surrounded by the abdominal wall, which is formed
by the muscle and skin around it.
c The abdominal cavity contains many different organs with a variety of
functions. Although these functions may be quite separate, all the organs
in the abdominal cavity and behind it are very close together.
c The whole space is lined with a thin membrane called the peritoneum,
this covers all the organs as well as the walls of the cavity.
So the abdominal cavity is often known as the peritoneal cavity .
Chest
cavity
Diaphragm
Abdominal
wall
Peritneum
Peritoneal
cavity
Pelvis
The assessment of abdominal symptoms is often difficult because there are many
different organs very close together. Disease affecting any of these organs could
be the cause of the symptoms and it may sometimes be difficult to tell the
difference between the symptoms caused by a kidney infection, appendicitis
or an ectopic pregnancy !!
The different organs within the abdominal cavity include organs of the
gastrointestinal tract, urinary tract and genital tract
The Gastrointestinal tract
All of the following abdominal organs are part of the gastrointestinal tract.
oesophagus)
stomach)
duodenum)
small intestine (ileum)
large intestine (colon)
appendix
These organs comprise what is often
known as the ‘gut’- they form a continuous
tube from the mouth to the anus through
which the food passes. During this process the
food is digested, nutrients are absorbed and
the waste products rectumare excreted
liver)
gallbladder)
pancreas)
These organs are also part of the
gastro-intestinal tract, they lie alongside the
gut and take part in the process of digestion
Oesophagus
Liver
Gall
bladder
Duodenum
Large
intestine
(colon)
Appendix
Stomach
Pancreas
Small
intestine
(ileum)
Rectum
The urinary and genital tract
These organs have a separate function to those of the gastrointestinal tract
but they are also either in the abdominal cavity or immediately behind it.
This means that diseases in any of these organs can cause very similar
symptoms to diseases of the gastrointestinal tract.
uterus)
These organs are part of the female genital tract.
fallopian tubes) They are found in the lower abdomen (pelvis) and
ovaries)
disease here may also cause abdominal pain.
kidneys)
ureter)
bladder)
These organs form part of the urinary tract, although
the kidneys and ureter are actually behind the
abdominal cavity they may still give rise to symptoms
in the abdomen.
Kidneys
Ureter
Bladder
Fallopian
tubes
Ovaries
Uterus
This manual is mainly concerned with the organs of the gastrointestinal tract.
However it is important to always consider conditions of the renal
or genital tract in a patient with abdominal symptoms. The diseases
of the urinary and genital tract are discussed further in the manual
GENITOURINARY DISEASE.
The following diagrams show the position of these organs within the
abdominal cavity. Note the following important points:
c all of the organs described above lie very close together within the same space
c the lower end of the oesophagus and stomach are at an angle, this prevents
the stomach contents from going back up into the oesophagus.
c the gallbladder and pancreas have ducts which lead to the duodenum, this a
lows secretions of enzymes from these organs to enter the duodenum.
c the position of the liver which is tucked under the ribs on the right side,
and the position of the spleen which is tucked under the ribs on the left side.
c the position of the kidneys, these lie behind all the other abdominal organs
and behind the peritoneum.
c the position of the internal female genitalia which are in the pelvis but
are very closely related to the other pelvic and abdominal organs
Kidneys
Ureter
Fallopian
tubes
Ovaries
Uterus
Bladder
The function of the gastrointestinal tract
The body requires nutrients for growth and repair of tissues as well as
for energy. The function of the gastrointestinal tract is to change the food that
you eat into its simplest parts. These simple nutrients are then absorbed into
the blood and can then be used by the tissues of the body. There are three
steps to this process. These steps are digestion, absorption and excretion.
Digestion is the process by which the food that you eat is broken down to
simple nutrients within the gastrointestinal tract. The food is broken down
into smaller pieces by the movements of the gut and by enzymes that are
secreted in the mouth, stomach and duodenum. Enzymes help to breakdown
the foodstuffs chemically to their smallest constituents.
Absorption is the process by which the simple nutrients produced by digestion
leave the gut and enter the blood stream so that they can be used by the body
for growth and to provide energy.
After the body has digested and absorbed all the useful nutrients there is still
undigested food which cannot been used by the body. Excretion is the process
by which these and other waste products are removed from the body.
Other waste products include those which are produced by the cells and
tissues of the body, these may either be excreted in the urine or in the stool.
An enzyme is a chemical substance which speeds up chemical reactions in the
body. Digestive enzymes are produced by the gut and act on the food,
converting nutrients into simpler forms that can be absorbed. Different enzymes
from different parts of the gut act on each different type of food.
The structure and functions of the gastrointestinal tract
The GI tract starts at the mouth and forms a continuous tube to the anus.
The mouth - the process of digestion begins here. The teeth and tongue
break up the food into smaller pieces during chewing. The salivary glands
produce enzymes and fluid which also helps with this. When the food has
been made softer it is then swallowed.
During swallowing the food passes through the oesophagus. This is a muscular
tube leading to the stomach. Digestion continues as the movements of the
stomach mix the food. The glands in the stomach lining produce enzymes and
acid, these break down the food into simpler nutrients.
The food then passes out of the stomach to the next part of the gut, this
is the duodenum.
The pancreas produces enzymes and bile is produced by the gallbladder.
These substances pass through ducts into the duodenum and are mixed with
the food as it comes from the stomach. Before leaving the duodenum the foods
have now been broken down to their simplest parts - fats, proteins and simple
carbohydrates.
Liver
Stomach
Gall
bladder
Enzymes
Gall
bladder
Pancreas
Duodenum
Bile
duct Pancreantic
duct
Pancreas
Food
Absorption into
the blood stream
Organs responsible for digestion prepare food to be absorbed into the body
The food then passes into the small intestine and this is where most of the
absorption of nutrients occurs. The small bowel has a very good blood supply
and a large area so that the nutrients can pass from the gut into the blood stream.
The remaining food, which has not been digested, stays in the gut and passes
into the large intestine (colon). In the large bowel more water and salts are
absorbed into the bloodstream. The body also excretes from the blood stream
into the large bowel some waste products, these leave the body with the
undigested food as faeces.
The peritoneum
A thin lining called the peritoneum covers the organs in the abdomen as well
as the cavity itself. The peritoneum is a continuous membrane, which lines the
abdominal cavity and forms folds as it covers each of the abdominal organs.
It allows the organs to move freely over each other within the abdominal cavity
but also keeps them in position. Another name for the abdominal cavity is the
peritoneal cavity.
Since all abdominal organs are covered by peritoneum, anything that causes
inflammation of an abdominal organ will also cause inflammation of the
peritoneum around it. This is known as peritonitis. Peritonitis may be localised
to a small area of peritoneum surrounding the inflamed organ or it may be
generalised involving the whole peritoneal cavity. Localised peritonitis may
become generalised if left untreated.
Intestine
Normal appendix
Peritoneum
Intestine
Inflammed appendix
- Irritates surronding
peritoneum
Inflammation of the appendix causes ‘peritonitis’ by
irritating the overlying peritoneum
The liver
The liver is the largest organ in the body, it lies under the ribs on the right side
of the abdomen just below the diaphragm.
The liver produces bile and the bile passes into the gall bladder where it is
stored. During digestion the bile is released into the duodenum where it helps in
the digestion of fatty foods. This is only one of the many functions of the liver.
After the digested nutrients have been absorbed into the bloodstream, the blood
from the small intestine passes directly to the liver. The nutrients may then be
kept in the liver for future use or passed on to the rest of the body. In this way
the liver acts like the body’s ‘bank’ by keeping excess nutrients and distributing
them as required. The liver stores fats, carbohydrates, vitamins and iron.
The liver has many other functions and is also very important in the breakdown
of the body’s waste products. This means that if the liver is affected by a
disease like hepatitis, these waste products will build up in the blood. This can be
most easily seen as a yellowish discolouration of the whites of the eyes, which is
known as jaundice. This is caused by the build up of a waste product called bilirubin.
Jaundice occurs in liver disease and is caused by the build up of waste products,
including bilirubin, in the blood.
The gallbladder
The gallbladder is a small sac which lies directly under the liver. Bile is formed
in the liver and is then stored in the gallbladder until it is needed for digestion.
The function of the bile is to allow digestion of fats and it is secreted
into the duodenum.
The bile also contains some waste products which are then excreted in the
faeces, these include bilirubin which gives the bile its characteristic colour.
Since a build up of bilirubin in the body causes jaundice, another cause of
jaundice in a blockage to the outflow of the gallbladder. The most common
reason for this is gallstones.
Liver
A stone obstructing the
gall bladder can lead to
attacks of biliary colic or
cholecystitis(inflammation
of the gall bladder)
Gall stone blocks the
flow of bile leading to
build up in the body and
jaundice
A stone in the optic duet causes ‘biliar y colic’.
A stone in the common bile duct leads to jaundice .
The Pancreas
The pancreas lies behind the stomach and has a duct or opening into the
duodenum. The pancreas produces enzymes which are also released as food
passes into the duodenum from the stomach. These enzymes together with
bile act to break down the foodstuffs in the final phase of digestion.
Another important function of the pancreas is to secrete the hormones insulin and
glucagon into the bloodstream. These regulate the level of glucose in the blood.