Digestive System
Digestive System
Slide 1 – Purpose of the Digestive System
Now that we know the types of compounds we need to obtain from our food, let’s look at how
we get those compounds out of the food and into our bodies. We will now take a look at the
digestive system. The purpose of the digestive system is to breakdown organic compounds like
fats, proteins, and carbohydrates into their smallest parts, so that they can be absorbed. We also
need to absorb vitamins and minerals.
Slide 2 – Digestion begins in the Mouth
Digestion begins in the mouth. Recall that we said if you chew on a piece of bread or a cracker
and letting the bolus of food sit on your tongue for a few minutes you will start to notice a sweet
sensation on your tongue. An enzyme in your salvia called salivary amylase begins to
breakdown the starch in the bread or cracker. Enzymes are involved in chemical digestion.
Salvia also contains substances that kill bacteria and is important in dissolving your food.
Mechanical digestion also begins in the mouth. In mechanical digestion large pieces are broken
into small pieces. The teeth and tongue are responsible for mechanical digestion. When food
items are made smaller there is a greater surface area for the enzymes of the digestive tract to
work.
Slide 3 – Peristalsis
Food is swallowed in small clumps called a bolus. The bolus will pass from the mouth to the
stomach through a long tube called the esophagus. Food moves through the esophagus by wave
like contractions called peristalsis. Peristalsis is similar to the movement of an earthworm.
Muscles will pinch the food from behind and push it forward.
Slide 4 – Cardiac Sphincter
Contrary to what you may have been told, very little digestion occurs in the stomach. The
stomach acts as a storage organ and allows food to pass slowly into the small intestine. Food
enters the stomach from the esophagus through the cardiac or gastroesophogeal sphincter. A
sphincter is a circular closure similar to a drawstring on a garbage bag. In some people this
sphincter does not close properly. This can lead to heartburn or the more severe acid reflux
disease. Acid from the stomach enters the sphincter and burns the esophagus.
Slide 5 – Protective mechanisms of the stomach
The stomach is very acidic. The stomach secretes gastric juice, which contains hydrochloric acid
and an inactive form of the enzyme pepsin. The pepsin begins to breakdown proteins into
smaller peptides. Little other digestion occurs in the stomach. Since the stomach is very acidic,
the cells of the stomach must have mechanisms to protect themselves from damage. Cells in the
stomach are constantly being replaced and some cells lining the stomach secrete mucous which
acts as a protective barrier against acid. In addition the cells of the stomach contain protein; this
is why pepsin is secreted in an inactive form, so that the cells are not damaged. Pepsin does not
become acid until it is exposed to the acid of the stomach.
Slide 1 – Purpose of the Digestive System
Now that we know the types of compounds we need to obtain from our food, let’s look at how
we get those compounds out of the food and into our bodies. We will now take a look at the
digestive system. The purpose of the digestive system is to breakdown organic compounds like
fats, proteins, and carbohydrates into their smallest parts, so that they can be absorbed. We also
need to absorb vitamins and minerals.
Slide 2 – Digestion begins in the Mouth
Digestion begins in the mouth. Recall that we said if you chew on a piece of bread or a cracker
and letting the bolus of food sit on your tongue for a few minutes you will start to notice a sweet
sensation on your tongue. An enzyme in your salvia called salivary amylase begins to
breakdown the starch in the bread or cracker. Enzymes are involved in chemical digestion.
Salvia also contains substances that kill bacteria and is important in dissolving your food.
Mechanical digestion also begins in the mouth. In mechanical digestion large pieces are broken
into small pieces. The teeth and tongue are responsible for mechanical digestion. When food
items are made smaller there is a greater surface area for the enzymes of the digestive tract to
work.
Slide 3 – Peristalsis
Food is swallowed in small clumps called a bolus. The bolus will pass from the mouth to the
stomach through a long tube called the esophagus. Food moves through the esophagus by wave
like contractions called peristalsis. Peristalsis is similar to the movement of an earthworm.
Muscles will pinch the food from behind and push it forward.
Slide 4 – Cardiac Sphincter
Contrary to what you may have been told, very little digestion occurs in the stomach. The
stomach acts as a storage organ and allows food to pass slowly into the small intestine. Food
enters the stomach from the esophagus through the cardiac or gastroesophogeal sphincter. A
sphincter is a circular closure similar to a drawstring on a garbage bag. In some people this
sphincter does not close properly. This can lead to heartburn or the more severe acid reflux
disease. Acid from the stomach enters the sphincter and burns the esophagus.
Slide 5 – Protective mechanisms of the stomach
The stomach is very acidic. The stomach secretes gastric juice, which contains hydrochloric acid
and an inactive form of the enzyme pepsin. The pepsin begins to breakdown proteins into
smaller peptides. Little other digestion occurs in the stomach. Since the stomach is very acidic,
the cells of the stomach must have mechanisms to protect themselves from damage. Cells in the
stomach are constantly being replaced and some cells lining the stomach secrete mucous which
acts as a protective barrier against acid. In addition the cells of the stomach contain protein; this
is why pepsin is secreted in an inactive form, so that the cells are not damaged. Pepsin does not
become acid until it is exposed to the acid of the stomach.
Digestive System
Slide 6 – What is an Ulcer?
Many of you may have heard that ulcers are caused by stomach acid; this is not technically true.
We now know that ulcers are caused by bacteria called H.Pylori. These bacteria damages the
cells of the stomach that secrete mucous, which leaves areas of the stomach susceptible to the
stomach acid. Today ulcers are treated with a regime of antibiotics, which helps the body rid
itself of the H. pylori infection.
Slide 7 – Alcohol absorption
The stomach also contracts and aids in mechanical digestion. In addition, a few substances such
as alcohol are absorbed directly from the stomach. This is why you become intoxicated more
rapidly on an empty stomach compared to a stomach full of food. The presence of food in the
stomach slows the absorption of alcohol.
Slide 8 – Pyloric sphincter
At the bottom of the stomach is another sphincter, the pyloric sphincter. This sphincter is much
stronger than the cardiac sphincter. The pyloric sphincter regulates the passage of food into the
small intestine. Only a small amount of food enters the small intestine at a time. It takes several
hours after a meal for the stomach to empty its contents into the small intestine. Food entering
the small intestine must be in small amounts, so that the enzymes can effective breakdown the
organic compounds into their smaller units, so that they can eventually be absorbed.
Slide 9 – Accessory organs
It is in the small intestine that most of the digestion occurs. The small intestine can be broken
into three parts: the duodenum, the ileum, and the jejunum. It is the duodenum that several other
accessory organs secrete their enzymes and other substances for the chemical digestion of food.
The liver produces a substance called bile, which is stored in the gallbladder. Bile is necessary
for the digestion of fat. Recall that fats do not dissolve in water and food is mostly water. Bile is
needed to keep fats from sticking together in large clumps that would not be able to be digested.
The pancreas secretes several enzymes into the small intestine; these enzymes breakdown
proteins, fats, and carbohydrates. The pancreas also secretes bicarbonate, which neutralizes the
acid in the food that just came from the stomach. The small intestine itself also produces several
enzymes to breakdown food.
Slide 6 – What is an Ulcer?
Many of you may have heard that ulcers are caused by stomach acid; this is not technically true.
We now know that ulcers are caused by bacteria called H.Pylori. These bacteria damages the
cells of the stomach that secrete mucous, which leaves areas of the stomach susceptible to the
stomach acid. Today ulcers are treated with a regime of antibiotics, which helps the body rid
itself of the H. pylori infection.
Slide 7 – Alcohol absorption
The stomach also contracts and aids in mechanical digestion. In addition, a few substances such
as alcohol are absorbed directly from the stomach. This is why you become intoxicated more
rapidly on an empty stomach compared to a stomach full of food. The presence of food in the
stomach slows the absorption of alcohol.
Slide 8 – Pyloric sphincter
At the bottom of the stomach is another sphincter, the pyloric sphincter. This sphincter is much
stronger than the cardiac sphincter. The pyloric sphincter regulates the passage of food into the
small intestine. Only a small amount of food enters the small intestine at a time. It takes several
hours after a meal for the stomach to empty its contents into the small intestine. Food entering
the small intestine must be in small amounts, so that the enzymes can effective breakdown the
organic compounds into their smaller units, so that they can eventually be absorbed.
Slide 9 – Accessory organs
It is in the small intestine that most of the digestion occurs. The small intestine can be broken
into three parts: the duodenum, the ileum, and the jejunum. It is the duodenum that several other
accessory organs secrete their enzymes and other substances for the chemical digestion of food.
The liver produces a substance called bile, which is stored in the gallbladder. Bile is necessary
for the digestion of fat. Recall that fats do not dissolve in water and food is mostly water. Bile is
needed to keep fats from sticking together in large clumps that would not be able to be digested.
The pancreas secretes several enzymes into the small intestine; these enzymes breakdown
proteins, fats, and carbohydrates. The pancreas also secretes bicarbonate, which neutralizes the
acid in the food that just came from the stomach. The small intestine itself also produces several
enzymes to breakdown food.
Digestive System
Slide 10 – Villi and microvilli
After your food has been broken down into its smallest parts or monomers, these small particles
are absorbed in the small intestine. The small intestine is very long and is covered on the inside
by small finger like projections called villi. These villi are covered by smaller finger like
projection called microvilli. The villi and microvilli increase the surface area of the small
intestine. The greater surface area increases the amount of nutrients that are absorbed by the
body.
Inside of the villi are small lymph vessels called lacteals and small blood vessels called
capillaries. Food components, such as amino acids, that are able to dissolve in water are
absorbed directly into the blood. Fat soluble substances, such as fatty acids, are absorbed into
the lacteals. The villi are specially designed and are only one cell in thickness. They also
contain absorptive cells that aid in the absorption of nutrients. It is through the blood or lymph
systems that foods you eat enter your body. Eventually the lymph system connects to the blood,
and it is through the blood that the nutrients in your food reach your cells.
Slide 11 – End products of digestion
At the time your food is absorbed, you have broken down carbohydrates into monosaccharides,
proteins into amino acids, fats into glycerol and fatty acids, and nucleic acids into nucleotides.
Recall that the breakdown of the polymers into monomers occurs through the process of
hydrolysis.
Slide 12 – Large intestine
What about substance like cellulose that are not broken down and absorbed by the body? These
substances continue through the digestive system to the large intestine. The large intestine
absorbs water and salt. At the end of the large intestine, substances that can not be digested are
excreted out of the body through the anus.
The image on this slide presents a review of the digestive system.
Slide 13 – Digestive System Review
YouTube Video – Digestive System
https://www.youtube.com/watch?v=Og5xAdC8EUI
Slide 14 – Check Your Understanding
Now that we have learned about the digestive system, let’s check your knowledge of the subject.
The following slides will have a series of questions on the topic. Be sure to click “Submit” after
answering each question.
Slides 15 through 30– Interactive Digestive System Quiz
A non–graded assessment of your knowledge of the digestive system.
Slide 31 – Summary
This slide is a summary of all of the “Check Your Understanding” questions from this lecture.
Be sure to review the questions you answered incorrectly.
Slide 10 – Villi and microvilli
After your food has been broken down into its smallest parts or monomers, these small particles
are absorbed in the small intestine. The small intestine is very long and is covered on the inside
by small finger like projections called villi. These villi are covered by smaller finger like
projection called microvilli. The villi and microvilli increase the surface area of the small
intestine. The greater surface area increases the amount of nutrients that are absorbed by the
body.
Inside of the villi are small lymph vessels called lacteals and small blood vessels called
capillaries. Food components, such as amino acids, that are able to dissolve in water are
absorbed directly into the blood. Fat soluble substances, such as fatty acids, are absorbed into
the lacteals. The villi are specially designed and are only one cell in thickness. They also
contain absorptive cells that aid in the absorption of nutrients. It is through the blood or lymph
systems that foods you eat enter your body. Eventually the lymph system connects to the blood,
and it is through the blood that the nutrients in your food reach your cells.
Slide 11 – End products of digestion
At the time your food is absorbed, you have broken down carbohydrates into monosaccharides,
proteins into amino acids, fats into glycerol and fatty acids, and nucleic acids into nucleotides.
Recall that the breakdown of the polymers into monomers occurs through the process of
hydrolysis.
Slide 12 – Large intestine
What about substance like cellulose that are not broken down and absorbed by the body? These
substances continue through the digestive system to the large intestine. The large intestine
absorbs water and salt. At the end of the large intestine, substances that can not be digested are
excreted out of the body through the anus.
The image on this slide presents a review of the digestive system.
Slide 13 – Digestive System Review
YouTube Video – Digestive System
https://www.youtube.com/watch?v=Og5xAdC8EUI
Slide 14 – Check Your Understanding
Now that we have learned about the digestive system, let’s check your knowledge of the subject.
The following slides will have a series of questions on the topic. Be sure to click “Submit” after
answering each question.
Slides 15 through 30– Interactive Digestive System Quiz
A non–graded assessment of your knowledge of the digestive system.
Slide 31 – Summary
This slide is a summary of all of the “Check Your Understanding” questions from this lecture.
Be sure to review the questions you answered incorrectly.
Digestive System
Slide 32 – Review of unit 2
We have now reached the end of unit 2. In this unit we have covered the basics of chemistry,
studied organic molecules, as well as explored the digestive system.
Slide 32 – Review of unit 2
We have now reached the end of unit 2. In this unit we have covered the basics of chemistry,
studied organic molecules, as well as explored the digestive system.
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