Transcript DIGESTIVE SYSTEM

THE DIGESTIVE SYSTEM
Structure: organs
• Food is carried from the mouth to the stomach by the
oesophagus (also esophagus). This tube descends from the
mouth, and through an opening in the diaphragm (a dome
shaped muscle that separates the lungs and heart from the
abdomen and assists in breathing), connecting with the
stomach.
• Immediately after passing through the diaphragm's opening,
the esophagus empties into the stomach where the acids that
break down the food are produced. From the stomach, the
food flows directly into the first part of the small intestine,
called the duodenum. It is here in the duodenum that bile and
pancreatic fluids enter the digestive system.
Mastication
• Mastication or chewing is the process by which
food is crushed and ground by teeth. It is the first
step of digestion and it increases the surface area
of foods to allow more efficient break down by
enzymes. During the mastication process, the food
is positioned between the teeth for grinding by the
cheek and tongue. As chewing continues, the food
is made softer and warmer, and the enzymes in
saliva begin to break down carbohydrates in the
food. After chewing, the food (now called a bolus)
is swallowed. It enters the esophagus and via
peristalsis continues on to the stomach, where the
next step of digestion takes place.
Insalivation
• Insalivation is the mixture of the nourishments (aliments)
crushed by the teeth with the saliva that moistens, lubricates,
and begins their chemical treatment.
•
After mastication and insalivation, aliments crushed by the
teeth form a mass called food bolus.
• The saliva also has functions:
-It eases the passage of the food bolus to the pharynx and the
esophagus.
-It begins the digestion of the starch molecules in many
aliments (bread, potatoes, rice…),transforming them into
simpler sugars. This is due to amylase (a digestive enzyme
present in saliva).
-It Destroys some of the bacteria existing in the food.
Swallowing
• Is the process that makes something
(e.g. the food bolus) pass from the
mouth, to the pharynx, and into the
esophagus,
while
shutting
the
epiglottis. If the latter fails, and the
object goes through the trachea, then
choking or pulmonary aspiration can
occur.
In the stomach
• Food enters the stomach through the cardiac sphincter. In the
stomach, the food is further broken down and mixed
thoroughly with gastric juice (gastric acid, pepsin and other
digestive enzymes to break down proteins).
• The enzymes in the stomach have an acid optimum pH. This
means that they work better at a specific acid pH.
• The gastric acid itself does not break down food molecules. It
rather provides an optimum pH for the reaction of the pepsin
enzyme, and kills many microorganisms that are ingested with
food.
• The gastric acid can also denature proteins.
• Other small molecules such as alcohol are absorbed in the stomach,
passing through the membrane of the stomach directly entering the
circulatory system.
• Food in the stomach is in semi-liquid form, which upon completion is
known as chyme. After food consumption, the digestive "tonic" and
peristaltic contractions begin. This helps to break down the food and
move it through.
• When the chyme reaches pylorus (the sphincter connecting the
stomach to the duodenum) contractions "squirt" the food back into
the stomach through a process called retropulsion, which exerts
additional force and further grinds down food into smaller particles.
• Gastric emptying is the release of food from the stomach into the
duodenum. This process is tightly controlled where liquids are
emptied much quicker than solids.
• Gastric emptying has attracted medical interest as rapid gastric
emptying is related to obesity, and delayed gastric emptying
syndrome is associated with diabetes mellitus, aging, and
gastroesophageal reflux.
The Liver and the Pancreas
•
The liver (located under the ribcage in the right upper part of the abdomen),
the gallbladder (hidden just below the liver), and the pancreas (located
beneath the stomach) are gland organs. These organs are not part of the
alimentary canal, but they are essential to digestion.
•
The liver also plays a major role in the handling and processing of nutrients,
which are carried to the liver in the blood from the small intestine.
•
The liver produces bile, which helps the body absorb fats. Bile is stored in the
gallbladder until it is needed.
•
The pancreas produces enzymes that help digest proteins, fats, and
carbohydrates. It also synthesises sodium bicarbonate that neutralizes stomach
acid. These enzymes, along with the bile, travel through channels (called ducts)
directly into the small intestine, where they help break down food. It is in the
duodenum that the bile and the pancreatic fluids enter the digestive system.
•
The pancreas is an integral part of the digestive system. The flow of the
digestive system is often altered during the surgical treatment of pancreatic
cancer. Therefore, it is helpful to review the normal flow of food before reading
about surgical treatment.
The liver
The pancreas
Nutrient absorption
The nutrients in digestion must come to the
cells, thus passing through the intestine into
the blood. This process is called absorption.
Microvilli are a large number of folds that
line the inner surface of the small intestine.
This increases the surface and efficiency of
absorption.
The products of fats digestion are collected
by lymphatic capillaries.
Small intestine
• In vertebrates, the small intestine is the part
of the gastrointestinal tract (gut) following
the stomach and followed by the large
intestine, and is where the vast majority of
digestion and absorption of food takes
place. In invertebrates such as worms, the
terms "gastrointestinal tract" and "large
intestine" are often used to describe the
entire intestine.
• The primary function of the small intestine is
the absorption of nutrients found in food.
Small intestine
The microvilli
Large Intestine
• -Caecum (also cecum): It contains the appendix.
-Colon: It has 3 segments (ascending, transverse
and descending) in which symbiotic bacteria grow
and generate vitamins.
-Rectum: Flows into the anus.
• When the absorption of nutrients is finished, the
remains go to the large intestine that doesn’t have
villi.
In the large intestine water is absorbed and faeces
are constructed.
The food waste is expelled through the anus, where
in addition to food waste, it contains cells of the
intestinal mucosa and bacteria.
The large intestine
Digestive System: Diseases
• Some diseases can be of infectious or
noninfectious origin:
• -Oral cavity:
• Cavities: caused by bacteria that
live in the mouth and break down
food scraps that fall between the
teeth (mainly sugars).
Cavities
• Gingivitis: painful inflammation of the
gums that are red and bleed.
• -Stomach:
• Gastritis: due to irritation of the gastric
mucosa which often causes inflammation.
• Ulcer: injury caused by the destruction
of the gastric mucose. Caused by the
bacteria Helicobacter pilori whose
optimum pH is quite acid.
• -Liver:
•Hepatitis: inflammation of the liver
caused by a virus, abuse of alcohol or
medications.
• Cirrhosis: A chronic disease of the liver
characterized by the replacement of
normal tissue with fibrous tissue and the
loss of functional liver cells.
•
Gallstones: solid particles formed in the gallbladder
by cholesterol and mineral salts found in bile.
• - Intestine:
• Intestinal infections: infections caused by bacteria
from water or food.
• Salmonellosis: infectious disease
caused by the bacteria Salmonella
tiphy present in spoiled food.
• Appendicitis: inflammation of the appendix
which causes intense pain, caused by the
retention of waste in it’s interior. This
enhances the action of bacteria.
• Constipation: difficulty passing stools due
to low mobility of the large intestine. The
remains of digestion stay in the colon for a
long time where a high absorption of water
hardens the stool.
• Diarrhoea (also diarrhea): an intestinal
disorder characterized by abnormal
frequency and fluidity of fecal evacuations.
Digestive System: Healthy Habits
• These are some healthy diet and hygiene habits :
 Chew food slowly and grind it up. This will facilitate the
digestive process and stimulate salivation.
 Brush your teeth after every meal and floss thoroughly to
clean the space between the teeth.
 Respect meal times and try not to eat out which can
overwork your digestive system.
 Do not consume food or hot drinks that may cause irritation
of the mucous membranes of the mouth, pharynx and even
the esophagus, or eat spicy foods, as they can cause irritation
of stomach lining.
•  Wash your hands before eating and preparing meals.
 Ensure that food and drinks are in good condition to
prevent infections and food poisoning.
 Eat foods with fiber which help prevent constipation.
 Do regular physical activity as it helps prevent the onset of
intestinal gas and constipation.
 Avoid alcoholic beverages because they cause irreversible
damage to the liver and the pancreas, and also faciliate
stomach and esophageal cancer.
 Do not smoke because it causes cancer.
CREDITS
• Alberto Gullón
• José Carlos González
• Rosario Guerrero
• Adela Granero
• Marta García