Download The Human Digestive System

The Human Digestive System
DR. JIM WHITFIELD, PH.D.
Digestion in Humans
 As we all know we take in food through our mouths
(ingestion), we then break down that food
(digestion), the nutrients that are of value to us then
pass through our digestive system (absorption) for
use in the body. The remaining material is then
excreted from our bodies in the process of
defecation.
Digestion in Humans
 The digestive system can be divided into various
sections
Digestion in Humans
 The digestive system can be divided into various
sections
 First we have the organs of digestion – these are the
organs that come into physical contact with the food,
they include
Digestion in Humans
 The digestive system can be divided into various
sections
 First we have the organs of digestion – these are the
organs that come into physical contact with the food,
they include
 The buccal cavity (mouth), the esophagus, the
stomach, the small intestine, the large intestine and
the rectum
Digestion in Humans
 Second we have the accessory organs of digestion
Digestion in Humans
 Second we have the accessory organs of digestion
 These organs are important for digestion but do not
actually come into contact with the food, they
include
Digestion in Humans
 Second we have the accessory organs of digestion
 These organs are important for digestion but do not
actually come into contact with the food, they
include
 The salivary glands, the pancreas, the gall bladder,
and the liver
Monogastric digestive
systems
The Mouth and Buccal Cavity
 The purpose of the mouth is to take in the food
(ingestion) and to begin the process of digestion.
The Mouth and Buccal Cavity
 The purpose of the mouth is to take in the food
(ingestion) and to begin the process of digestion.
 Both mechanical and chemical digestion begins in
the mouth
The Mouth and Buccal Cavity
 The purpose of the mouth is to take in the food
(ingestion) and to begin the process of digestion.
 Both mechanical and chemical digestion begins in
the mouth
 Mechanical digestion occurs through the use of the
teeth and the tongue. Mechanical digestion causes
the food to be broken down into smaller parts
The Mouth and Buccal Cavity
 The purpose of the mouth is to take in the food
(ingestion) and to begin the process of digestion.
 Both mechanical and chemical digestion begins in
the mouth
 Mechanical digestion occurs through the use of the
teeth and the tongue. Mechanical digestion causes
the food to be broken down into smaller parts
 Chemical digestion involves the use of amylase
(found in saliva) to begin to break down complex
carbohydrates into simple sugars
The Mouth and Buccal Cavity
 The tongue also contains “taste buds” that allow us
to distinguish between sweet, salty, sour and bitter
substances
The Mouth and Buccal Cavity
 The tongue also contains “taste buds” that allow us
to distinguish between sweet, salty, sour and bitter
substances
 We all have two sets of teeth. The first set, called the
baby or deciduous teeth, and the second adult set.
The Mouth and Buccal Cavity
 The tongue also contains “taste buds” that allow us
to distinguish between sweet, salty, sour and bitter
substances
 We all have two sets of teeth. The first set, called the
baby or deciduous teeth, and the second adult set.
 Humans have 20 baby teeth and 32 adult teeth
The esophagus
 The esophagus is the muscular tube that connects
the mouth to the stomach
The esophagus
 The esophagus is the muscular tube that connects
the mouth to the stomach
 There is no digestion in the stomach
The esophagus
 The esophagus is the muscular tube that connects
the mouth to the stomach
 There is no digestion in the stomach
 The movement of food from mouth to stomach is
caused by the constricting and relaxing of muscles
and is called peristalsis
The Stomach
 The stomach receives the food bolus from the
esophagus. It continues with both mechanical and
chemical digestion and passes the chyme into the
small intestine
The Stomach
 The stomach receives the food bolus from the
esophagus. It continues with both mechanical and
chemical digestion and passes the chyme into the
small intestine
 The chyme is the food that has been liquefied
through the digestive process
The Stomach
 The stomach receives the food bolus from the
esophagus. It continues with both mechanical and
chemical digestion and passes the chyme into the
small intestine
 The chyme is the food that has been liquefied
through the digestive process
 The inner lining of the stomach produces mucus,
which protects it from the hydrochloric acid (pH 2.1)
being produced by other stomach lining cells
The Stomach
 The stomach receives the food bolus from the
esophagus. It continues with both mechanical and
chemical digestion and passes the chyme into the
small intestine
 The chyme is the food that has been liquefied
through the digestive process
 The inner lining of the stomach produces mucus,
which protects it from the hydrochloric acid (pH 2.1)
being produced by other stomach lining cells
 This acid is primarily responsible for the killing of
bacteria we consume with our food
The Stomach
 Digestion of starch is continued in the stomach. The
stomach also produces proteases (which break down
proteins) and lipases (which break down fats)
The Stomach
 Digestion of starch is continued in the stomach. The
stomach also produces proteases (which break down
proteins) and lipases (which break down fats)
 Mechanical digestion also occurs with the help of the
strong muscular lining of the stomach called the
rugae.
Rugae
The Small Intestine
 Chyme exits the stomach and enters into the
stomach through the pyloric sphincter
The Small Intestine
 Chyme exits the stomach and enters into the
stomach through the pyloric sphincter
 In the cadaver the stomach is about 7.5 meters long.
It is considerably shorter in living individuals
The Small Intestine
 Chyme exits the stomach and enters into the
stomach through the pyloric sphincter
 In the cadaver the stomach is about 7.5 meters long.
It is considerably shorter in living individuals
 Digestion is complete in the stomach and virtually all
absorption occurs here
The Small Intestine
 Chyme exits the stomach and enters into the
stomach through the pyloric sphincter
 In the cadaver the stomach is about 7.5 meters long.
It is considerably shorter in living individuals
 Digestion is complete in the stomach and virtually all
absorption occurs here
 The small intestine receives secretions from the liver,
gall bladder and pancreas
The Small Intestine
 Chyme exits the stomach and enters into the




stomach through the pyloric sphincter
In the cadaver the stomach is about 7.5 meters long.
It is considerably shorter in living individuals
Digestion is complete in the stomach and virtually all
absorption occurs here
The small intestine receives secretions from the liver,
gall bladder and pancreas
The liver produces bile (a fat) that is stored in the
gall bladder and is used for the breakdown of fat
The Small Intestine
 The pancreas, which has both digestive and
endocrine functions, produces pancreatic juice which
helps to complete the process of digestion of
carbohydrates, fats and proteins
The Small Intestine
 The pancreas, which has both digestive and
endocrine functions, produces pancreatic juice which
helps to complete the process of digestion of
carbohydrates, fats and proteins
The Small Intestine
 The pancreas, which has both digestive and
endocrine functions, produces pancreatic juice which
helps to complete the process of digestion of
carbohydrates, fats and proteins
 REMEMBER – carbohydrates and broken down into
simple sugars, proteins are broken down into amino
acids and fats are reduced to fatty acids and glcerol
Absorption in the Small Intestine
 The food, which has now been reduced to its nutrient
components can pass through the intestinal wall in
the process of absorption
Absorption in the Small Intestine
 The food, which has now been reduced to its nutrient
components can pass through the intestinal wall in
the process of absorption
 Absorption occurs through the finger-like
projections called villi
Absorption in the Small Intestine
 The food, which has now been reduced to its nutrient
components can pass through the intestinal wall in
the process of absorption
 Absorption occurs through the finger-like
projections called villi
 The villi dramatically increase the surface area
available for absorption
Absorption in the Small Intestine
 The food, which has now been reduced to its nutrient
components can pass through the intestinal wall in
the process of absorption
 Absorption occurs through the finger-like
projections called villi
 The villi dramatically increase the surface area
available for absorption
 The nutrients pass from high concentration in the
small intestine to low concentration in the capillaries
found in the villi and then into the blood stream
Villi in the
small
intestine
The Large Intestine
 The large intestine is smaller and wider than the
small intestine
The Large Intestine
 The large intestine is smaller and wider than the
small intestine
 The function of the large intestine is to absorb water
and some salts and some B vitamins
The Large Intestine
 The large intestine is smaller and wider than the
small intestine
 The function of the large intestine is to absorb water
and some salts and some B vitamins
 Anything that is not digested by this time continues
through the large intestine and passes out of the
body into the rectum and out through the anus. This
process is called egestion
Digestion in Ruminants
 Ruminants are animals the have a single stomach
divided into four separate chambers (rumen,
reticulum, abomasum and omasum)
Digestion in Ruminants
 Ruminants are animals the have a single stomach
divided into four separate chambers (rumen,
reticulum, abomasum and omasum)
 Ruminants are grass eating animals that chew their
cud
Digestion in Ruminants
 Ruminants are animals the have a single stomach
divided into four separate chambers (rumen,
reticulum, abomasum and omasum)
 Ruminants are grass eating animals that chew their
cud
 During this process, ruminants chew grass and
swallow it. It goes into the rumen and is partially
digested by specialized microbes. It is then brought
back up the esophagus and is chewed a second time.
When it is swallowed it by-passes the rumen and
enters the rest of the stomach
Digestion in Ruminants
 This process is called rumination
Digestion in Ruminants
 This process is called rumination
 Ruminants also have a cecum found between the
small and large intestine. This cecum also contains
specialized bacteria capable of breaking down
cellulose (a carbohydrate found in the cell wall of
plants)
Digestion in Ruminants
 This process is called rumination
 Ruminants also have a cecum found between the
small and large intestine. This cecum also contains
specialized bacteria capable of breaking down
cellulose (a carbohydrate found in the cell wall of
plants)
 Rumination plus the cecum allows ruminants to
maximize the amount of energy they receive from
relatively low energy grass
Other Systems
 It should be noted that there are two other types of
digestive systems. Those found in birds (avian
systems) and pseudo-ruminants (horses, hamsters,
guinea pigs, rabbits,..) these animals have a cecum
but have a single stomach like a monogastric