Digestive System

Section 9

The Digestive System

Disease and Injury

Foodstuffs and Vitamins

Disease and Injury


The Digestive System

The digestive
system
[Figure 9 – 1] is based around the alimentary canal,
a long muscular tube which extends through the body between the mouth and the
anus. Glands lying outside the alimentary canal produce enzymes which are
used in the digestive process.

These glands produce many
litres of secretions in a day, but most of this volume is re-absorbed.

Figure 9 – 1 the digestive system

Frontal section
showing the main organs of the digestive system

The heart is not shown

digestive system

Apart
from the acts of eating and defaecation, the digestive process is not under
the control of the conscious will; the movement of foods through the
digestive system is effected by smooth muscle.

The digestive system is
divided into four main areas following the passage of food: the mouth and
oesophagus, the stomach, the small intestine, and the large intestine.

Alimentary Canal

With the
exception of the mouth and pharynx, the alimentary canal [Figure 9 – 2]
is formed from four layers of tissue:

Adventitia. (outer covering) This consists
of loose fibrous tissue in the thoracic region, and peritoneum in the
abdominal regions. (peritoneum is described separately).

Muscle layer. In most areas, this is smooth
muscle, arranged in two layers enclosing blood vessels and nerve fibres.

Submucous layer. This is composed of loose
connective tissue, together with blood vessels and nerve fibres.

Mucous membrane. (inner layer) This layer varies
in nature along the alimentary canal. In areas where food has already been
softened, the membrane is composed of columnar epithelium with glands which
secrete digestive juices.

Although it mainly
follows this same basic structure, the exact formation of the alimentary
canal varies along its length.

Figure 9 – 2 the alimentary canal

The basic
formation of the alimentary canal

alimentary canal

Peritoneum

The peritoneum
[Figure 9 – 3] forms a lining for the abdominal cavity. It consists of
two layers of serous membrane:

Parietal layer. This lines the abdominal wall.

Visceral layer. This covers the abdominal
organs.

The potential space between
the two layers is occupied by serous fluid to allow ease of movement.

Figure 9 – 3 the peritoneum

A sagittal
section through the female abdomen, indicating the abdominal organs and the
peritoneum

Potential spaces have been much exaggerated for clarity

peritoneum

The
peritoneum forms a closed sac, the abdominal organs being invaginated from
‘outside’. Some organs such as the stomach, spleen, liver, and
intestines, are completely covered by double folds of peritoneum;.
other organs such as the pancreas and kidneys are only partially covered.

A fold of peritoneum
attaching an organ to the abdominal wall is termed a mesentery.
Mesenteries not only support abdominal organs, they provide a route for blood
vessels, lymph vessels, and nerves.

Omenta

An omentum is a
loose fold of peritoneum. The lesser omentum extends from the liver to
the stomach. The greater omentum is a large folded, fatty membrane
which starts at the stomach and hangs like an apron over the anterior of the
abdominal organs, ending at the level of the transverse colon.

Mouth

The mouth
is the orifice by which food enters the alimentary canal.

The mouth is bounded by
muscles and bones, and is lined with mucous membrane. It contains the tongue
and the teeth, which assist in the initial processing of food.

The digestive process
begins as soon as food is placed in the mouth, although no nutrients are
actually absorbed.

Tongue

The tongue
is a muscular structure attached to the floor of the mouth.

The tongue is involved in
the actions of chewing and swallowing, and holds the majority of nerve
endings associated with the sense of taste.

Teeth

The teeth
serve the functions of cutting, tearing, and grinding food during the eating
process.

A tooth [Figure
9 – 4
] is formed mainly from an ivory-like substance named dentine,
in the centre of which is the pulp cavity. The pulp cavity contains
nerves and blood vessels. Enamel, which is extremely hard, protects
the outer surface.

The teeth are set into
the frontal opposing margins of the maxilla and mandible, and are arranged in
a symmetrical layout.

[Figure 9 – 5]

There are 32 teeth in a
full set for an adult:

Incisors. (8) These are the frontal
cutting teeth.

Canines. (4) These slightly pointed teeth
are used for tearing food.

Premolars (8) and molars. (12) These
irregular shaped teeth are used for grinding food during chewing.

 

 

Figure
9 – 4
a tooth

A section
through a tooth showing the structure

tooth

Figure
9 – 5
the teeth

The arrangement
of the teeth

teeth

Chewing and Swallowing

The act
of chewing breaks up the food, and mixes it with saliva. The tongue
then pushes small pieces of food (boluses) into the pharynx for
swallowing.

The start of a swallowing
action is controlled by the conscious will, but the continuation of the
action is involuntary.

During the swallowing
action, the soft palate prevents the food entering the nasal pharynx, and the
epiglottis moves to prevent the entry of the food into the trachea.

Saliva

The
presence (or anticipation) of food stimulates a reflex action secretion of
saliva from three pairs of glands: the parotid in the cheeks, the submandibular
below the angle of the jaw, and the sublingual beneath the tongue.

Saliva is a mixture of secretions,
containing mucin to ease the act of swallowing, ptyalin which
breaks down starch into maltose (a sugar), amylase – a digestive
enzyme which initiates the breakdown of carbohydrates, and minerals. Calcium
phosphate in saliva is deposited onto the teeth as tartar.

Oesophagus

The oesophagus
is a muscular tube linking the lower part of the laryngopharynx to the
stomach, via an opening in the diaphragm. The formation of the oesophagus
follows the general structure of the alimentary canal.

Food is propelled down
the oesophagus by peristalsis, waves of muscular contraction,
controlled by the autonomic nervous system.

Sphincter muscles at the
top and bottom of the oesophagus prevent unwanted flows: the cricopharyngeal
sphincter
protects against air passing into the oesophagus during
respiration, and the cardiac sphincter guards the entry into the
stomach against regurgitation.

Stomach

The stomach
[Figure 9 – 6] is a hollow organ, with muscular walls, situated in the
epigastric, umbilical, and left hypochondriac regions of the abdominal
cavity.

Figure 9 – 6 the stomach

The main areas of
the stomach

stomach

The
composition of the stomach follows the general structure of the alimentary
canal, but with some modifications:

The folds of the
peritoneum enclosing the stomach continue to form the greater omentum.

The muscle layer is
formed from three complementary layers of muscle fibre which allow for a
churning movement of stomach contents, as well as peristalsis.

The mucous membrane
contains numerous gastric glands which secrete gastric juice.

Very little actual
digestion takes place in the stomach; it acts more as a reservoir for
ingested food, releasing it gradually into the small intestine.

Within the stomach, food
and gastric juice mix to form chyme. This then passes from the stomach
into the duodenum via the pyloric sphincter.

Gastric Juice

Gastric
juice
is secreted
by the mucous lining of the stomach in response to the release of the hormone
gastrin, secretion of which is stimulated by the presence of food in the
stomach.

Gastric juice contains
around 0.5% Hydrochloric acid, and is thus strongly acidic. The enzymes
pepsin and rennin are also present.

Gastric juice serves the
purposes of initiating the breakdown of proteins, and of destroying bacteria
in food.

Small Intestine

The small intestine
[Figure 9 – 7] is a thin tube, approximately 5m in length, irregularly
coiled in the abdomen.

Figure 9 – 7 the small intestine

The layout of the
small intestine

The length and complexity of the small intestine have been much reduced for
clarity

small intestine

The small
intestine is described in three parts – each continuous with the next:

Duodenum. This is the first 250mm,
connecting to the stomach.

Jejunum. This is the central part, and is
approximately 2m long.

Ileum. This is the final, largest part,
and is about 3m long. It connects into the large intestine.

The walls of the small
intestine follow the general structure of the alimentary canal, but with some
modifications:

A mesentery attaches the
majority of the small intestine to the posterior abdominal wall.

The mucous membrane of
the small intestine contains small projections, approximately 0.5mm – 1mm
long, called villi.

The villi serve the
double purpose of increasing the absorbent surface area of the intestines,
and of accommodating intestinal glands and lymph vessels. The surfaces of the
villi are covered with additional microscopic hair like projections known as microvilli.

The main digestive
processes take place within the small intestine, aided by intestinal juice,
secreted from the villi. Intestinal juice is a mixture of the enzyme
enteropeptidase, water and mucus. Enteropeptidase assists in the final
digestion of most foodstuffs.

Additional substances
from external glands assist the digestive processes:

Bile. This is secreted by the liver.
It emulsifies fats.

Pancreatic juice. This is secreted by the
pancreas. It assists in the breakdown of fats, carbohydrates, and proteins.

Digestive Glands

Pancreas

The pancreas
is a pale grey coloured gland, situated in the epigastric and left
hypochondriac regions of the abdominal cavity. It secretes pancreatic juice
into the duodenum. Secretion is controlled partly by reflex nervous action,
but more by a stimulating agent, secretin, which is released into the
circulation whenever acidic stomach contents enter the duodenum.

Pancreatic juice is alkaline, to the extent that
it neutralises the acidity from the stomach. It also contains three enzymes:

Trypsin. This assists in the digestion of
proteins into amino acids.

Amylase. This breaks down carbohydrates
into sugars.

Lipase. This breaks down fats into fatty
acids and other simpler compounds.

The pancreas has a second
function, as an endocrine gland; this is considered as part of the endocrine
system.

Liver

The liver
[ Figure 9 – 8] is the largest gland in the body, occupying the
majority of the right hypochondriac region of the abdominal cavity, and
spreading across the epigastric region into the left hypochondriac region. It
is composed of many small lobules, each receiving blood from both the
systemic and portal circulations. The liver is thus an initial recipient of
substances absorbed from food.

The liver is covered by a
thin capsule, and partially by a layer of peritoneum, which acts as a main
support.

The liver is formed in
four lobes:

The large right lobe
and smaller left lobe form the majority, with the caudate and quadrate
lobes as small areas on the posterior surface of the right lobe.

Blood vessels, lymph
vessels, and nerve fibres, together with the hepatic ducts, join the liver at
the portal fissure (or porta hepatis) on the posterior surface.

Figure 9 – 8 the liver

A frontal view of
the liver

liver

The liver
has a variety of functions:

Chemical breakdown. Amino acids, old tissue cells,
alcohol, and hormones are broken down, mainly for later excretion.

Storage. Excess fats, glucose (as
glycogen), vitamins, iron compounds, and copper compounds are stored, for
release when intake does not meet the requirements of the body.

Synthesis. Vitamin A is synthesised from
carotene. Some amino acids, plasma protein, and blood clotting factors are
synthesised from amino acids available in the bloodstream.

Conversion. Glucose is converted into
glycogen in the presence of insulin. Glycogen is conversely converted to
glucose by glucagon.

Stored fats are converted
into glucose.

Heat production. The liver is the main heat
producing organ in the body because of its considerable chemical activity.

Secretion. The liver secretes bile, which
is used in the digestive process.

Bile is a slightly alkaline, greenish,
viscous fluid. Bile contains complex salts, the pigment bilirubin as a
by-product of old cell breakdown, as well as water, mucus, and cholesterol.

Bile Ducts and Gall Bladder

The liver
produces bile continuously. As bile is only required during digestion, that
produced at other times is stored in the gall bladder.

Bile from the liver
passes via the hepatic ducts which link with the cystic duct from
the gall bladder to form the common bile duct. When bile is not
required for digestive purposes, it flows through the cystic duct into the
gall bladder.

The gall bladder [Figure
9 – 9
] is a hollow organ, formed from the same four layers of tissue as the
alimentary canal, situated beneath the right lobe of the liver. Its muscular
layer allows it to contract and empty its contents into the duodenum, via the
cystic duct and common bile duct.

Figure 9 – 9 the gall bladder

The arrangement
of the bile ducts and gall bladder

gall bladder

The
common bile duct links with the pancreatic duct just outside the duodenum,
the connection to which is controlled by the sphincter of Oddi.

Large Intestine

The large
intestine
forms the final sections of the alimentary canal. It is much
larger in section than the small intestine.

[Figure 9 – 10]

The large intestine is
formed from the same four layers of tissue as the main alimentary canal. The
muscle layer is formed in bands, to give the large intestine a slightly
bulging appearance.

Figure 9 – 10 the large intestine

The layout of the
large intestine

large intestine

The large
intestine is described in seven parts, each continuous with the next:

Caecum. This is the first part,
connecting to the end of the ileum at the ileocaecal valve.

The vermiform appendix
is small closed tube leading from the inferior closed end of the caecum.

Ascending colon. This leads from the caecum,
vertically up the right side of the abdomen to the right colic flexure
or hepatic flexure, situated under the right lobe of the liver.

Transverse colon. This starts at the hepatic
flexure, and leads across the abdominal cavity, in front of the stomach, to
the left colic flexure or splenic flexure, anterior to the
spleen.

Descending colon. This starts at the splenic
flexure, and leads down the left side of the abdominal cavity.

Sigmoid colon. This is the continuation of the
descending colon into the pelvic area.

Rectum. This is a slightly dilated
section of the large intestine, and forms the end of the digestive areas.

Anal canal. This is the final part of the
alimentary canal, leading to outside the body at the anus.

The main functions of the
large intestine are those of absorbing water, minerals, and vitamins, and
temporarily storing waste matter prior to excretion.

The chyme which passes
into the caecum is liquid, although some water has been absorbed in the small
intestine. The majority of water will have been absorbed by the time this
chyme reaches the descending colon.

The absorption of water
(particularly the reabsorption of most digestive enzymes) is an important
factor in preventing the body becoming dehydrated. The residue remaining
after final absorption has occurred is excreted as faeces.

The movement of matter
along the large intestine takes place at infrequent intervals (not regular
peristalsis). This is known as mass movement, and is often caused by
ingesting food.

Defaecation

When mass
movement forces faeces into the rectum, the desire to defaecate is triggered.

The opening of the anus
is controlled by two sphincter muscles. The internal anal sphincter is
composed of smooth muscle and is under autonomic control. The external
anal sphincter
is composed of striated muscle and is under conscious
control.

When a decision is made
to defaecate, the external anal sphincter is relaxed. Abdominal
pressure is raised by a lowering of the diaphragm, a contraction of abdominal
muscles, and by trying to force air out of the lungs against a closed
epiglottis.

This forces faeces from
the rectum out of the anus; a continuation of pressure then forces expulsion
of faeces from the descending and sigmoid colons.

Digestive Process

The digestive
process
is a series of complex biochemical reactions which differ
slightly between carbohydrates, proteins, and fats.

Table 9 – 1 digestion of carbohydrates

The main
biochemical activities involved in the digestion of carbohydrates

Organ

Digestive
enzymes and activity

Mouth

Salivary
amylase begins the conversion of carbohydrates to sugars

Stomach

No action
– as Hydrochloric acid in gastric juice stops the action of salivary amylase

Small
intestine

Amylase from
pancreatic juice converts all starches to sugars

Sucrase, maltase and
lactase from the intestinal glands convert all sugars to glucose

Absorption

Glucose
is absorbed into capillaries in the villi, and is carried to the liver via
the portal circulation

Utilisation

Glucose
provides energy for all cells when broken down in the presence of Oxygen

Excess glucose is stored,
partly as glycogen in the liver and muscles, and partly as fat in adipose
tissue

Table 9 – 2 digestion of proteins

The main
biochemical activities involved in the digestion of proteins

Organ

Digestive
enzymes and activity

Mouth

No action

Stomach

Hydrochloric
acid in gastric juice converts pepsinogen to pepsin, which then converts
proteins to less complex polypeptides

Small
intestine

Enteropeptidase
from intestinal juice converts inactive enzymes in pancreatic juice to those
which then convert polypeptides to di- and tripeptides

Peptidase from intestinal
glands breaks peptides into amino acids

Absorption

Amino
acids are absorbed into capillaries in the villi, and are carried to the
liver via the portal circulation

Utilisation

Amino
acids are widely used throughout the body for cell repair and replacement,
the production of secretions, and in producing substances such as blood
clotting agents

Excess amino acids are
either broken down in the liver and excreted as urea, used to provide heat
and energy, or are stored as fat in adipose tissue

Table 9 – 3 digestion of fats

The main
biochemical activities involved in the digestion of fats

Organ

Digestive
enzymes and activity

Mouth

No action

Stomach

No action

Small
intestine

Bile
emulsifies fats

Lipase from pancreatic
juice converts fats to fatty acids and glycerol

Absorption

Fatty
acids and glycerol are absorbed via the villi into lymph vessels, from where
they pass into the thoracic duct, left subclavian artery, and into the
circulating blood. From this they reach the liver for reorganisation and
recombination

Utilisation

Fats are
used to provide heat and energy in the presence of Oxygen

Excess fats are stored in
adipose tissue

Top


Disease and Injury

Appendicitis

Appendicitis is an inflammation of the
vermiform appendix.

The initial cause may not
be identifiable – bacterial infection, together with a blockage of the
appendix, perhaps by solid food matter, are likely contributors.

Initial inflammation
causes swelling and ulceration of the inner mucous membranes. This leads to
pain – first in the centre of the abdomen, and then in the area around the
appendix.

If the inflammation does
not subside (with or without treatment), it will soon block the small lumen
of the appendix and lead to an abscess. As this continues, the blood vessels
associated with the appendix become occluded, the appendix begins to atrophy,
and may well rupture – with serious consequences.

Cholera

Cholera is a totally debilitating
infection by the vibrio cholerae bacterium. It spreads through faeces into
water and food.

The disease has a sudden
onset and causes serious diarrhoea, stomach and leg cramps, violent vomiting,
and exhaustion. Hypovolaemic shock can result if lost fluids are not
replaced.

Cholera can be fatal,
especially if not treated.

Cirrhosis

Cirrhosis is a condition which affects the
liver. Cirrhosis occurs when liver cells have become damaged by some other
condition – chronic alcohol abuse, hepatitis, or other liver disease – and
fibrous tissue begins to grow in a mesh between areas of regenerating liver
cells.

The condition leads to a
failure of normal liver function, which in turn causes a general degeneration
in health, weight loss, vomiting, jaundice, a build-up of fluid in the
abdomen, and oedema of the legs.

Cirrhosis is incurable
and may eventually prove fatal.

Coeliac Disease

Coeliac
disease
is an
inherited condition in which the small intestine develops an abnormal
sensitivity to gluten and other proteins found in grain foodstuffs. The
problem may develop at any time of life.

The villi in the small
intestine become damaged and are then unable to absorb nutrients properly.

As a result, there is a risk
of malnutrition.

Indications of coeliac
disease vary widely from person to person, but will probably include
abdominal distension and pain, nausea and vomiting, diarrhoea, an unexplained
weight loss, and a general falling in the level of overall health.

Crohn’s Disease

Crohn’s
disease
most
commonly affects the ileum, although it may affect any part of the alimentary
canal.

It is a chronic
condition, causing thickening and inflammation to the walls of the digestive
tract, which may then become deeply ulcerated. This then leads to abdominal
pain and diarrhoea, with a reduced ability to digest food.

The condition may be
complicated by intestinal obstruction, and the creation of holes – fistulae
– between the intestine and other organs or tissues.

The cause is unknown,
although infection may contribute, as may genetic factors.

Dental Problems

Apical abscess

An apical abscess
occurs following decay of a tooth, with that decay extending through the pulp
and into the root area. Infection, usually bacterial, reaches the tooth
socket and sets up inflammation and an accumulation of pus.

An apical abscess is
usually extremely painful, but if a chronic abscess forms, this may be
painless.

Dental caries

Dental caries is the decay and degeneration of
teeth. Plaque – a mixture of food debris, bacteria, and saliva – forms
a sticky coating over teeth. The bacteria then act on sugars in food and form
acids which attack the tooth enamel. Small cavities form, allowing the acids
then to destroy the structure of the dentine.

Initially, this decay is
painless, but if it reaches the nerve in a tooth, toothache will be
triggered.

Decayed tooth structure
is not regenerated, so must be removed and replaced with artificial filling
material if eventual complete destruction of a decayed tooth is to be
prevented.

Gingivitis

Gingivitis is an inflammation of gum tissue,
causing swollen gums which are prone to bleeding.

The cause of gingivitis
is almost always a build-up of plaque, particularly in the areas of the teeth
nearest the gums.

Knocked out tooth

A tooth which has been
knocked out of its socket may be replaced, and may well re-connect to the gum
tissue as long as certain conditions are met:

Replacement is within 24
hours, and preferably within one hour.

The tooth has not been
contaminated, or more important, cleaned and disinfected.

The severed root
structures have not dried out or been further damaged, and have not been
contaminated by touching or cleaning them.

Diverticular Disease

Diverticula are small protrusions from the
colon, sometimes caused by the pressure of chronic constipation resulting
from a low fibre diet. In the majority of cases, diverticula do not cause
problems or symptoms.

Diverticulosis or uncomplicated diverticular
disease
is the term applied to relatively mild and intermittent symptoms
of the presence of diverticula.

Diverticulitis is a potentially serious
condition which results from faeces being trapped in a diverticulum. Bacteria
multiply around the blockage causing inflammation and infection.

Symptoms of severe
abdominal pain, fever, diarrhoea (or occasionally constipation), nausea and
vomiting often start suddenly, without warning. There may also be a palpable
lump in the abdomen, or rectal bleeding – originating from weakened blood
vessels passing through the diverticulum.

There is a risk that
diverticula may perforate or rupture and lead on to further infection and
peritonitis.

Gallstones

Gallstones are hard lumps of material which
build up in the gall bladder or bile duct.

Most gallstones are
around 6mm in diameter, although the size may vary from small sand-like
grains to up to 25mm in diameter – or more.

Gallstones tend to occur
if the composition of the bile is abnormal, if the flow of bile is blocked,
or if a local infection occurs. A susceptibility to developing gallstones may
be inherited.

Gallstones form when
substances – often involving calcium compounds – precipitate out of the bile.

In the majority of cases,
gallstones are asymptomatic. However, their existence may cause cholecystitis
– inflammation of the gall bladder, with pain in the right hypochondriac
region, and possibly fever, nausea, and vomiting.

If gallstones block the
bile duct, obstructive jaundice may result, with yellowing of the skin
and whites of the eyes, darkening of the urine, and pale coloured faeces. A
gallstone passing through the bile duct into the duodenum causes intense pain
(known as biliary colic) in the upper abdominal areas.

Gastritis

Gastritis is an inflammation of the mucous
membrane in the stomach. This results in a sensation of indigestion and
nausea. Bleeding into the stomach may also cause vomiting of blood or blood
stained faeces.

Gastritis has a variety
of causes, including repeated use of medications such as Ibuprofen,
swallowing of corrosive poisons, over-use of alcohol, infections, and extreme
stress. Other contributory factors include trauma, and failure of kidneys, or
the liver.

Gastroenteritis

Gastroenteritis is an inflammation of the stomach
and the intestines.

A common cause is
infection by either the rotavirus or the Norwalk virus. Alternative causes
are infection by bacteria or other organisms.

Gastroenteritis causes
abdominal pain, fever, diarrhoea and vomiting.

The condition usually
passes quickly, but a prolonged or severe attack may lead to dehydration and
hypovolaemic shock.

Food poisoning

Food poisoning is a specific cause of
gastroenteritis, associated with the ingestion of contaminated or inherently
poisonous food or water.

Examples of causative
agents include:

poisonous materials such as Lead or Mercury,

residues from insecticides and other chemicals,

poisons in certain fungi or plants,

bacteria such as salmonella, and campylobacter,

toxins produced by bacteria such as Escherichia coli (E-coli), variants of
staphylococcus, clostridium per fringens, and clostridium botulinum – which
causes the very dangerous condition of botulism.

Heartburn

Heartburn is a symptom of oesophageal
reflux
– a gentle regurgitation of stomach contents into the oesophagus.

This occurs because of
relaxation of the cardiac sphincter. There are many reasons for this,
including poor posture and dietary habits. Fatty foods, caffeine, chocolate,
and alcohol may also encourage reflux.

The acid in the
regurgitated material irritates the inner lining of the oesophagus, producing
discomfort and a burning sensation in the central thoracic area.

Severe heartburn may
mimic the pain of cardiac problems.

Hepatitis

Hepatitis is an inflammation of the liver,
through bacteria, toxic substances, or viruses.

Overdoes of some
medications, such as Paracetamol, may also cause hepatitis-like conditions.

The viral types exist in
several forms: A, B, C, D, E, F, and G have been identified to date.

The most common forms are
hepatitis A – spread from faeces into food and water, hepatitis B and
hepatitis C – both spread in the blood and by sexual contact.

Exact signs and symptoms
vary with the type, but hepatitis usually causes abdominal pain, with nausea,
diarrhoea and vomiting. The skin will probably be jaundiced.

If not treated, there is
a risk that hepatitis will become chronic and lead to cirrhosis, eventually
proving fatal.

Hernia

A hernia
occurs when part of an organ – usually abdominal – protrudes through a tear
or hole in the muscular tissue which normally holds it in place.

Hernias often occur
spontaneously, and may be present at birth, but may occur through muscular
strain associated with heavy lifting, a chronic cough, or persistent
straining against chronic constipation.

Hiatus hernia. This is a breakthrough of part
of the stomach into the thoracic cavity – through an enlargement of the
opening in the diaphragm through which the oesophagus passes.

The hernia itself rarely
leads to symptoms, but it will tend to lead to oesophageal reflux and
heartburn. Chest pain and difficulty in swallowing may also occur.

Inguinal hernia. This is more common in males. It
appears as a swelling in the groin area or scrotum, and occurs when a portion
of the peritoneum or the large intestine breaks through the lower wall of the
abdomen.

Femoral hernia. This is similar to an inguinal
hernia, but is more common in females. It occurs when part of the intestine
breaks through the abdominal wall via the opening taken by the femoral
artery, appearing as a swelling in the upper thigh.

Umbilical hernia. This is caused by a weakness in
the muscles around the navel, allowing protrusion of the intestine.

Incisional hernia. This occurs when a wound or
operation incision has not healed fully and a weakness in the containing
tissues has resulted.

Hernias are generally
relatively minor problems, leading often to no more than a slight
compressible bulge under the skin. They are, however, susceptible to the
complication of strangulation. This occurs when the herniated tissue
becomes constricted and cannot be pushed back into the abdominal cavity. The
blood supply to the strangulated portion is cut off by the pressure of the
surrounding tissue, leading to gangrene.

Irritable Bowel Syndrome

Irritable
bowel syndrome
is
a term used for a series of symptoms which occur in the digestive system, but
without identifiable cause.

Symptoms are mainly
caused by abnormal muscular contractions in the intestinal walls, sometimes
brought on by external factors.

Previous intestinal
infection, stress, low-fibre diets, and use of laxatives may contribute to
the problem.

Symptoms include
alternating diarrhoea and constipation, vomiting, abdominal pain and
tenderness, with abdominal bloating and a sense of internal gas.

Mumps

Mumps (epidemic parotitis) is a
droplet spread viral infection which affects the parotid gland.

Mumps may affect people
of all ages, although children are most vulnerable.

Mumps brings fever,
swelling of the parotid glands, a dry mouth with a ‘furred
tongue’, and swollen lymph nodes in the neck. There may also be
difficulty in swallowing and earache.

The condition may lead to
encephalitis and orchitis (swollen testicles) – more commonly in
adults.

Pancreatitis

Pancreatitis is a potentially fatal
inflammation of the pancreas.

Acute pancreatitis is usually caused by gall bladder
problems, such as gallstones blocking the pancreatic duct, or by chronic
alcohol abuse. The exact mechanism of pancreatitis is not known, but it is
believed that trapped digestive enzymes become active inside the pancreas and
begin to digest the gland itself. Haemorrhage, oedema, and tissue damage
result. The enzyme damage may spread to surrounding tissues, and may be
distributed via the circulation to cause more widespread damage.

The condition is marked
by severe pain in the upper abdomen, often occurring within twelve hours of a
heavy meal with alcohol. This pain may extend to all abdominal areas, the
back, and the shoulders, with nausea and vomiting – maybe leading to
hypovolaemic shock. Complications may include bowel obstruction, bleeding
into the bowel, and jaundice resulting from bile duct obstruction.

Chronic pancreatitis is often associated with alcohol
abuse or chronic pancreatic duct obstruction, although a cause may not be
identifiable.

The condition may follow
attacks of acute pancreatitis and usually begins with severe high abdominal
pain – extending through to the back.

Attacks often last for 24
hours or more and tend to recur. Inflammation and fibrosis slowly destroy the
glandular tissue with knock-on effects on the effectiveness of the overall
digestive process.

Peptic Ulcer

A peptic
ulcer
is a breakdown in the mucous membrane lining the alimentary canal.
The basic cause is that this mucous membrane is damaged by the action of
gastric acid or pepsin, either because these are present in abnormally high
concentration, or because the normal protective mechanisms have broken down.

Common ulcer sites are
the stomach and duodenum.

Gastric ulcer. This occurs in the stomach. The
main causes are the over-use of medications such as Aspirin or Ibuprofen, and
infection by helicobacter pylori bacteria.

The ulcer may well
produce no symptoms, but abdominal pain – increased after eating – and
vomiting are likely.

Duodenal ulcer. This occurs in the duodenum. It
is usually caused by over-production of gastric acid, and infection by
helicobacter pylori bacteria is very common.

Abdominal pain –
increased when the stomach is empty – and vomiting are the most likely
indications.

All gastric ulcers are at
risk of haemorrhage, which will lead to vomiting of blood (haematemesis),
or perforation, which will allow gastric contents into the abdominal cavity
and potentially lead to peritonitis.

Peritonitis

Peritonitis is an inflammation of the
peritoneum. This generally occurs as a result of some other condition,
although a blood borne bacterial infection may be the cause.

Liver or kidney failure
may cause peritonitis through a build-up of fluid in the abdominal cavity.

Bacteria may infect the
peritoneum from the digestive system via a perforated ulcer, a ruptured
appendix, from an inflamed pancreas, or because of a penetrating abdominal
wound.

Peritonitis is indicated
by abdominal pain (often sever and acute) and distension, a fever, and
reduced urine production. There may also be signs of shock or an inability to
pass faeces.

Typhoid

Typhoid is a bacterial infection of the
intestines by the salmonella typhi bacillus. It is spread in excrement, by
insects, and via food and water.

The bacteria enter the
lymphoid tissue of the intestines. They then spread to the liver, spleen, and
gall bladder via the circulation. Inflammation results, together with damage
to the intestinal lymphoid tissue which leads to ulcers forming in the mucous
membrane.

Initially, typhoid
manifests itself with a high fever and headache.

As the condition worsens,
it brings nosebleeds, spots on the thorax and abdomen, a distended abdomen,
and constipation which then possibly changes to diarrhoea, and finally
delirium.

Intestinal haemorrhage
and peritonitis may lead on to intestinal perforation which may be fatal.

Vomiting

Vomiting is the body’s way of
removing a possibly dangerous substance from the stomach, or simply removing
stomach contents in reaction to some other problem.

There are many potential
causes of vomiting, including: viral infection, reactions to medications,
poisons, motion sickness, migraine, hormonal changes (such as during
pregnancy), food allergies, and visual stimulus such as witnessing an
unpleasant or horrific situation.

The action is controlled
from the vomiting reflex centre in the medulla oblongata. The mechanism
involves a sharp downward contraction of the diaphragm, a pulling in of the
abdominal muscles, a relaxation of the stomach itself and an opening of the
cardiac sphincter.

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Foodstuffs and Vitamins

In order
to survive, the human body must receive a balanced diet of foods. This
balanced diet must include appropriate proportions of: carbohydrates,
proteins, fats, mineral salts, fibre, and water, together with vitamins.

Failure to receive any of
the constituents of a balanced diet can result in malnutrition.

Foodstuffs

Carbohydrates

Carbohydrates are formed from the elements
Carbon, Hydrogen, and Oxygen. They vary in chemical complexity from simple
sugars to complex cellulose:

Monosaccharides. These are simple sugars, which
are readily absorbed by the body. eg. glucose, fructose.

Disaccharides. These, in molecular terms, are
combinations of two monosaccharides. eg. sucrose, lactose.

Polysaccharides. These are complex molecular
combinations of many monosaccharides. eg. starches, cellulose.

Not all polysaccharides
can be digested by the human body; cellulose and other similar vegetable
fibres pass through the alimentary canal virtually unchanged.

Carbohydrates provide
energy for heat and movement. Excess carbohydrate is converted to fat and
stored.

Proteins

Proteins are combinations of amino
acids
, which are formed from the elements Carbon, Hydrogen, Oxygen,
Nitrogen, Sulphur, and Phosphorus.

Proteins are split into
their constituent amino acids during the digestive process, and absorbed
through the intestinal wall.

Amino acids are classed
as either ‘essential’ or ‘non-essential’.

Essential amino acids cannot be synthesised in the
body, and must be available from the diet.

Non-essential amino
acids
can be
synthesised in the body from other amino acids, in a process called transamination.

Depending on their amino
acid content, proteins are graded as either ‘first class’ – those
which contain all the essential amino acids – and ‘second class’
– those which do not.

First class proteins are derived from animal products
and soya beans. Second class proteins are mainly of vegetable origin.

Amino acids from proteins
are used for:

Growth and repair of body
cell tissues,

Production of hormones, enzymes, and antibodies,

Production of energy (only when insufficient is available from
carbohydrates).

Amino acids provide the
only usable source of Nitrogen to the body.

Excess protein is broken
down; the nitrogenous part is excreted via the kidneys as urea, and the
remainder is stored as fat.

Fats

Fats are complex compounds formed from
the elements Carbon, Hydrogen, and Oxygen. (although these are the same
elements which form carbohydrates, the chemical composition is different).

Fats are considered in
two groups according to their source:

Animal fats. These are derived from meat,
oily fish, and dairy products. All animal protein sources also contain some
fat. Animal fats are mainly ‘saturated’. ie. their molecular
bonding structure is fully utilised.

Vegetable fats. These are found in vegetable
oils. Vegetable fats are mainly ‘polyunsaturated’.

ie. their molecular bonding structure is not fully utilised.

Vegetable fats are
essential in the diet, and assist in the formation of prostaglandins and
blood clotting factors.

Fats, in general, provide
energy to the body. They also serve the purposes of:

Transporting the fat
soluble vitamins,

Contributing to the secretions from sebaceous glands,

Assisting in the formation of cholesterol, and steroid hormones.

Excess fats are stored in
the body’s fat depots – under the skin, and in the mesentery.

Mineral Salts

Mineral
salts
are inorganic
compounds which are essential for all body processes. Many mineral salts are
required, although usually only in small quantities. [Table 9 – 4]

Table 9 – 4 essential minerals

The more common
mineral elements, together with their sources and uses

Mineral

Source

Main
Functions

Calcium

Dairy
products, green vegetables, some fish

Hardening
of teeth and bones, mechanism of muscle contractions, mechanism of blood
clotting

Iodine

Some fish,
some vegetables, a common artificial additive to table salt

Formation
of thyroid hormones

Iron

Liver,
kidney, beef, eggs, grain, green vegetables

Formation
of haemoglobin

Magnesium

Green
vegetables, milk, meat, nuts

Formation
of bone structure, regulation of muscular and nervous activity

Phosphorus

Cheese,
liver, kidney

Hardening
of teeth and bones, regulation of body fluids

Potassium

Almost
all foods

Many
cellular activities, mechanism of muscle contractions, transmission of nerve
impulses, maintenance of body electrolyte levels

Sodium

Most
foods, table salt

Mechanism
of muscle contractions, transmission of nerve impulses, maintenance of body
electrolyte levels

Fibre

Fibre, or roughage, consists of
indigestible vegetable substances, in the form of complex polysaccharides and
cellulose.

It is found in
‘whole meal’ grain products, bran, and many vegetables.

Some fibre is partially
digested by microbes in the large intestine to form gaseous products, or flatus.

Fibre is necessary in the
diet as it stimulates peristalsis and bowel movement. It may also contribute
in the prevention of some gastro-intestinal disorders.

Water

Water is essential to continuing life.
Approximately 60% of the total body weight is water. Unlike other foods,
considerable quantities of water are lost through evaporation from the skin
and the lungs.

Water is taken into the
body either as a liquid, or as a constituent of other foods. A small amount
is produced within the body as the result of Hydrogen from foods reacting
with Oxygen.

Water provides a moist
environment for living cells. It participates in, and facilitates, all
biochemical reactions in the body.

Water is a major
constituent of blood, and acts as a transport medium for both benevolent and
malevolent substances.

Some water is excreted
with faeces, but the majority of excess water is excreted as urine.

Vitamins

A vitamin
is an organic substance, found in minute quantities in specific foods, and
which is essential for healthy survival, but which provides no actual energy
or physical contribution to the body. Vitamin deprivation causes specific
disease depending on the vitamin involved.

Vitamins A, D, E, and K
are fat soluble and excess amounts are stored in adipose tissue, mainly the
liver. [Table 9 – 6]

The remaining vitamins
are water soluble and are not stored; the effects of a reduced intake are
therefore much more rapid.

[Table 9 – 5]

Table 9 – 5 water soluble vitamins

The main water
soluble vitamins

Figures given as daily need are approximate upper limits

Vitamin

Main
sources

Main
functions

Consequence
of deficiency

Daily
need

B1

(thiamine)

Cereal
roughage, yeast, milk, meat, yeast

Catalyses
oxidation of carbohydrates in cells

General
fatigue, loss of muscle tone, nerve changes, beriberi

1.5mg

B2

(riboflavin)

Milk,
eggs, beef, cereals, nuts, yeast

Assists
cellular respiration

Eye
problems, skin disorders, digestive problems

2mg

B3

(niacin, nicotinic acid)

Whole
grain, liver, sea food, beans

Assists
carbohydrate metabolism, assists production of sex hormones, reduces
cholesterol

Pellagra

20mg

B5

(pantothenic acid)

Most
foods

Promotes growth,
assists utilisation of other vitamins and energy

Fatigue,
sleep disorders, cardiovascular and neurone problems, eczema

not known

B6

(pyridoxine)

Cereals,
liver, milk, green vegetables

Assists
in metabolism of amino acids

Skin and
nervous disorders, learning disabilities, anaemia

2.5mg

B12

(cyano-cobalamin)

Meat,
dairy products, synthesised in the body

Assists
red blood cell production

Anaemia,
nervous disorders, general weakness

2m g

B

(biotin)

Liver, vegetables,
eggs, synthesised in the body

Assists
cell growth, and synthesis of non-essential amino acids

Dermatitis,
muscle pains, weakness, insomnia

100m g

B

(folic acid, folacin)

Meat,
eggs, milk, green vegetables, synthesised in the body

Assists
red blood cell production and DNA formation

Anaemia,
gastro-intestinal problems

200m g

C

(ascorbic acid)

Fruit and
vegetables (destroyed by cooking)

Assists
oxidation reactions, assists formation of collagen, teeth, and bones, assists
healing

Scurvy,
low infection resistance, anaemia, poor connective tissue formation

60mg

Table 9 – 6 fat soluble vitamins

The main fat
soluble vitamins

Figures given as daily need are approximate upper limits

Vitamin

Main
sources

Main functions

Consequence
of deficiency

Daily
need

A

(retinol)

Dairy
produce, liver, fish liver oils

Maintains
epithelial tissues, corneas of eyes, assists formation of rhodopsin

Stunting,
low disease resistance, poor healing, night blindness

2mg

D

(calciferol)

Dairy
produce, eggs, liver, formed in skin by sunlight

Promotes
Calcium and Phosphorus absorption from food, and bone and tooth formation

Rickets,
dental caries, osteomalacia, diarrhoea, insomnia

10m g

E

(tocopherols)

Eggs,
dairy produce, green vegetables, nuts

Strengthens
red blood cells, assists muscle and nerve maintenance

Anaemia

15mg

K

(phylloquinone)

Synthesised
in the body, fruit, vegetables

Enables
clotting function of blood

Poor blood
clotting actions

10m g

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Disease and Injury

Malnutrition

Malnutrition is the result of a failure to
maintain a balance between the intake of foods required for health and foods
actually taken.

The condition is usually
associated with a much reduced and poor diet as a result of poverty or
deprivation. However, it may also result from a straightforward imbalance in
the intake of basic foods – perhaps through personal desire – or from a
metabolic disorder which prevents the proper uptake of nutritional
essentials.

The signs and symptoms
vary widely, although weakness, a susceptibility to other diseases, and
eventual death are common factors.

Anorexia nervosa

Anorexia nervosa is a psychological condition,
which causes either a direct refusal to take food, or the use of laxatives or
emetics to prevent the uptake of food.

The causes of the
condition are complex, with factors such as emotional rejection being
contributory, and are usually based around a desire to lose and control body
weight with an assumption that low body weight is desirable. Delusions of
being overweight are often prevalent.

Vitamin Deficiencies

Deficiencies
of individual vitamins in the diet will lead to various different general
problems, as indicated in Table 9 – 5 and

Table 9 – 6.

Some vitamin deficiencies
lead to specific conditions.

Beriberi

Beriberi is the result of a deficiency of
vitamin B1. It is most common amongst those whose principal diet is based on rice.

Wet beriberi leads to excessive tissue fluid.

Dry beriberi lead to extreme wasting.

Degeneration of nervous
tissue is a feature of both forms of the condition, with a common outcome of
heart failure and death.

Pellagra

Pellagra is a result of a deficiency of
vitamin B3. It is most common amongst those whose principal diet is maize.

Pellagra leads to skin
disease, diarrhoea, and depression.

Rickets

Rickets is a result of a deficiency of
vitamin D. It is primarily a childhood condition. The lack of vitamin D
causes there to be insufficient Calcium salts in the bones, which are then
soft and slightly pliable. They thus tend to deform. This shows mainly in the
long bones, particularly in the legs, which curve unnaturally.

Osteomalacia is a softening of the bones
occurring in adulthood through a lack of vitamin D.

Bone pain is the main
symptom.

Scurvy

Scurvy is a result of a deficiency of
vitamin C. It may occur in alcoholics, or in those who eat very few fresh
vegetables or fruit.

Initial indications are
swollen and bleeding gums, followed by a rash of fine bleeding spots.
Subcutaneous bleeding is a late sign.

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