The Digestive SystemThe Digestive System

Dr. TimmelDr. Timmel

What is the digestive What is the digestive system?system? The digestive system is a one-way tube the The digestive system is a one-way tube the

begins at the mouth and ends at the anus. It begins at the mouth and ends at the anus. It is also known as the alimentary canal.is also known as the alimentary canal.

The purpose of the digestive system is to The purpose of the digestive system is to break down large organic molecules break down large organic molecules (Carbohydrates, Proteins, and Lipids) into (Carbohydrates, Proteins, and Lipids) into smaller ones that can diffuse into the smaller ones that can diffuse into the circulatory system.circulatory system.

The digestive system also absorbs vitamins, The digestive system also absorbs vitamins, minerals and water (inorganic molecules). minerals and water (inorganic molecules). These do not need to be broken down into These do not need to be broken down into smaller molecules.smaller molecules.

Lets eat!Lets eat!

To understand what happens in the digestive system To understand what happens in the digestive system we will investigate the path a roast beef sandwich we will investigate the path a roast beef sandwich with mayo and lettuce takes when we eat it.with mayo and lettuce takes when we eat it.

Roast beef= Protein; Bread= Carbs;Roast beef= Protein; Bread= Carbs; Mayo = Lipid; Lettuce = roughage. (Vitamins, Mayo = Lipid; Lettuce = roughage. (Vitamins,

minerals and water are also present in the sandwich)minerals and water are also present in the sandwich)

Enter the mouthEnter the mouth As you bite into the sandwich, your teeth As you bite into the sandwich, your teeth

help to shred and mash up the food. This is help to shred and mash up the food. This is a type of physical or mechanical digestion.a type of physical or mechanical digestion.

As you chew, your 3 salivary glands secrete As you chew, your 3 salivary glands secrete saliva which helps moisten your food. Saliva saliva which helps moisten your food. Saliva also contains Salivary Amylase, an enzyme also contains Salivary Amylase, an enzyme which begins to break down the bread of which begins to break down the bread of your sandwich. This is a type of chemical your sandwich. This is a type of chemical digestion.digestion.

Your tongue helps to position the food Your tongue helps to position the food between your teeth for chewing, and then between your teeth for chewing, and then helps move the food to the back of your helps move the food to the back of your mouth for swallowing.mouth for swallowing.

Once your food leaves your mouth and Once your food leaves your mouth and enters your throat it is known as bolus.enters your throat it is known as bolus.

Down the gulletDown the gullet

Once the bolus leaves the mouth it goes through Once the bolus leaves the mouth it goes through your throat and into your esophagus.your throat and into your esophagus.

No digestion occurs here, the esophagus is just a No digestion occurs here, the esophagus is just a tube which connects your mouth to your tube which connects your mouth to your stomach.stomach.

Prior to entering the stomach it passes through Prior to entering the stomach it passes through the gastro-esophogeal spincter. This muscular the gastro-esophogeal spincter. This muscular ring helps prevent the contents of your stomach ring helps prevent the contents of your stomach from moving back into the esophagus.from moving back into the esophagus.

Sometimes the acidic contents of your stomach Sometimes the acidic contents of your stomach does get into the esophagus. This is what causes does get into the esophagus. This is what causes the painful condition known as “heart burn”.the painful condition known as “heart burn”.

Going down the Going down the “wrong pipe.”“wrong pipe.” As you swallow, a flap of tissue called the As you swallow, a flap of tissue called the

epiglottis covers the top of the trachea to epiglottis covers the top of the trachea to prevent food from entering the lungs.prevent food from entering the lungs.

Sometimes food or drinks can get past Sometimes food or drinks can get past the trachea which causes a fit of the trachea which causes a fit of coughing to help get it out of there and coughing to help get it out of there and back into the esophagus.back into the esophagus.

It is impossible to breathe and swallow at It is impossible to breathe and swallow at the same time.the same time.

Get in my belly!Get in my belly!

The environment of the stomach is very The environment of the stomach is very acidic. This is because the enzymes acidic. This is because the enzymes present which begin the digestion of present which begin the digestion of proteins are only active at a pH of about proteins are only active at a pH of about 2. Enzymes which break down proteins 2. Enzymes which break down proteins are called proteases. The roast beef are called proteases. The roast beef begins to broken down into amino acids.begins to broken down into amino acids.

The acidic environment also helps to kill The acidic environment also helps to kill the bacteria which are present in/on all the bacteria which are present in/on all food. food.

Stomach continued.Stomach continued. The churning of your stomach The churning of your stomach

is a type of physical digestion. is a type of physical digestion. All the food you eat All the food you eat becomes completely liquefied becomes completely liquefied in the stomach.in the stomach.

This semi-digested, acidic This semi-digested, acidic liquid is now referred to as liquid is now referred to as chyme.chyme.

Chyme is then squirted Chyme is then squirted through the pyloric spincther through the pyloric spincther into the small intestine.into the small intestine.

The small intestine.The small intestine.

It is here in the small intestine It is here in the small intestine where most of the business of where most of the business of digestion takes place. The digestion takes place. The remaining carbs and proteins, remaining carbs and proteins, as well as the fats in the mayo as well as the fats in the mayo are digested here.are digested here.

The first 10 centimeters of the The first 10 centimeters of the small intestine is called the small intestine is called the duodenum.duodenum.

The chyme is very acidic when The chyme is very acidic when it first enters the S.I., so it it first enters the S.I., so it needs to be neutralized.needs to be neutralized.

The Pancreas and the The Pancreas and the LiverLiver These are two very important These are two very important

organs in the digestive system.organs in the digestive system. Though food never enters into Though food never enters into

either the pancreas or the liver, either the pancreas or the liver, their secretions are vital to their secretions are vital to digestion.digestion.

First we will look at the pancreasFirst we will look at the pancreas

The pancreasThe pancreas

The pancreas neutralizes The pancreas neutralizes stomach acid by secreting stomach acid by secreting bicarbonate into the duodenum.bicarbonate into the duodenum.

The pancreas also secretes The pancreas also secretes three types of digestive three types of digestive enzymes: Proteases, Amylases enzymes: Proteases, Amylases and Lipases.and Lipases.

These secretions travel from the These secretions travel from the pancreas to the duodenum pancreas to the duodenum through the common bile duct.through the common bile duct.

The liverThe liver

The liver secretes a The liver secretes a substance called bile.substance called bile.

Bile helps in the digestion of Bile helps in the digestion of lipids by emulsifying them. lipids by emulsifying them. This means it breaks a large This means it breaks a large glob of fat into smaller ones glob of fat into smaller ones for easier digestion.for easier digestion.

Bile is stored in the gall Bile is stored in the gall bladder and secreted into the bladder and secreted into the duodenum through the duodenum through the common bile duct.common bile duct.

Duodenum summary.Duodenum summary.

In this first section of the small In this first section of the small intestine:intestine:– The chyme is neutralized.The chyme is neutralized.– Carbohydrates complete their Carbohydrates complete their

chemical digestion.chemical digestion.– Proteins complete their chemical Proteins complete their chemical

digestiondigestion– Lipids begin and complete their Lipids begin and complete their

chemical digestion.chemical digestion.

Absorption in the S.I.Absorption in the S.I.

As your nutrients pass out of the duodenum As your nutrients pass out of the duodenum into the rest of the S.I., they begin to be into the rest of the S.I., they begin to be absorbed into the blood stream.absorbed into the blood stream.

Absorption is carried out by special finger-Absorption is carried out by special finger-like extensions in the walls of the S.I. called like extensions in the walls of the S.I. called villi.villi.

The villi’s shape greatly increases the surface The villi’s shape greatly increases the surface area of the S.I., allowing it to absorb area of the S.I., allowing it to absorb nutrients at a much faster rate.nutrients at a much faster rate.

By the time your food reaches the end of the By the time your food reaches the end of the S.I., all that remains are roughage, water and S.I., all that remains are roughage, water and bacteria.bacteria.

Drawing of villiDrawing of villi

The AppendixThe Appendix

Near the point where the small Near the point where the small intestine and large intestine intestine and large intestine meet, there is a small meet, there is a small fingerlike projection called the fingerlike projection called the appendix.appendix.

In modern humans, the In modern humans, the appendix serves no purpose. appendix serves no purpose.

Or so we all were taught. Now Or so we all were taught. Now it is believed that the appendix it is believed that the appendix helps to repopulate the S.I. helps to repopulate the S.I. with helpful bacteria after a with helpful bacteria after a disease wipes them out.disease wipes them out.

The Large intestineThe Large intestine

Here in the large intestine Here in the large intestine most everything useful most everything useful except water and some except water and some vitamins has been vitamins has been absorbed.absorbed.

The main job of the large The main job of the large intestine is to reabsorb intestine is to reabsorb water.water.

When the Large intestine When the Large intestine removes too much water, removes too much water, constipation is the result. If constipation is the result. If not enough water is not enough water is reabsorbed, diarrhea is the reabsorbed, diarrhea is the result. Both conditions can result. Both conditions can actually kill!actually kill!

Bacteria and the large Bacteria and the large intestine.intestine. The large The large

intestine is also intestine is also home to E.coli home to E.coli bacteria.bacteria.

These bacteria These bacteria produce vitamin produce vitamin K, which is K, which is something that something that we need for we need for proper health.proper health.

Rectum and AnusRectum and Anus

Our food now consists Our food now consists of roughage, bacteria of roughage, bacteria and water.and water.

It is now called feces.It is now called feces. Feces is temporarily Feces is temporarily

stored in the rectum, stored in the rectum, and then leaves the and then leaves the body through the anus.body through the anus.

Recap.Recap.

Here is the pathway your food Here is the pathway your food takes through your body.takes through your body.

MouthMouthEsophagusEsophagusStomachStomach Small IntestineSmall IntestineLarge Intestine Large Intestine

Rectum Rectum Anus.Anus.

Chemical digestionChemical digestion

Chemical digestion for Chemical digestion for carbohydrates begins in the mouth carbohydrates begins in the mouth and ends in the Small Intestine.and ends in the Small Intestine.

Chemical digestion of proteins Chemical digestion of proteins begins in the stomach and ends in begins in the stomach and ends in the small intestine.the small intestine.

Chemical digestion of lipids begins Chemical digestion of lipids begins and ends in the Small intestine.and ends in the Small intestine.

Physical (mechanical) Physical (mechanical) digestion.digestion. In the mouth, all food in In the mouth, all food in

physically digested by the action physically digested by the action of your teeth, tongue and jaws.of your teeth, tongue and jaws.

In the stomach, all food is In the stomach, all food is physically digested by churning.physically digested by churning.

In the duodenum lipids are In the duodenum lipids are physically digested by bile. physically digested by bile. (Emulsification).(Emulsification).

Interactive digestive Interactive digestive systemsystem Anatomically Correct - Digestive S

ystem Interactive Diagram