Transcript The Digestive System 1

The Digestive System
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Monash Science Centre © 2006
Eat your Jelly Bean
•Put your jelly bean on your tongue
•Suck it for a while
•Chew
•Swallow
Think about what is ACTUALLY
happening!
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What happened?
•What did you need to taste the jelly
bean?
•What happened when it left your mouth?
•What happens once its in your stomach?
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Our own food breakdown factory!
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Interesting Facts about the Digestive
System…
•We eat about 500kg of food per year.
•We produce 1.7 litres of saliva each day.
•In the mouth, food is either cooled or warmed to a more suitable temperature.
•The oesophagus is approximately 25cm long.
•Muscles contract in waves to move the food down the esophageus. This means that food would get to a
person's stomach, even if they were standing on their head.
•An adults stomach can hold approximately 1.5 litres of material and produces about 2.5 litres of gastric
juice everyday.
•In an average person, it takes 8 seconds for food to travel down the food pipe, 3-5 hours in small intestine and
3-4 days in the large intestine.
•The human body takes 6 hours to digest a high fat meal and takes 2 hours for a carbohydrate meal.
•Every day 11.5 litres of digested food, liquids and digestive juices flow through the digestive system, but only
100mls is lost in faeces.
•Most of us pass somewhere between 200 and 2,000 ml of gas per day. These emissions are composed of five
gasses: nitrogen (N2), oxygen (O2), carbon dioxide (CO2), hydrogen (H2), and methane (CH4).
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Overview of the Digestive System
Mouth - the first part of the digestive system, where food enters the body. Chewing and salivary
enzymes in the mouth are the beginning of the digestive process (breaking down the food).
Salivary glands - glands located in the mouth that produce saliva. Saliva contains enzymes that
break down carbohydrates (starch) into smaller molecules.
Esophageus - the long tube between the mouth and the stomach. It uses rhythmic muscle
movements (called peristalsis) to force food from the throat into the stomach.
Peristalsis - rhythmic muscle movements that force food in the esophagus from the throat into the
stomach. Peristalsis is involuntary - you cannot control it. It is also what allows you to eat and drink
while upside-down.
Liver - a large organ located above and in front of the stomach. It filters toxins from the blood, and
makes bile (which breaks down fats) and some blood proteins.
Stomach - a sack-like, muscular organ that is attached to the esophagus. Both chemical and
mechanical digestion takes place in the stomach. When food enters the stomach, it is churned in a
bath of acids and enzymes.
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Overview of the Digestive System
Chyme - food in the stomach that is partly digested and mixed with stomach acids. Chyme goes on
to the small intestine for further digestion.
Gall bladder - a small, sac-like organ located by the duodenum. It stores and releases bile (a
digestive chemical which is produced in the liver) into the small intestine.
Bile - a digestive chemical that is produced in the liver, stored in the gall bladder, and secreted into
the small intestine.
Pancreas - an enzyme-producing gland located below the stomach and above the intestines.
Enzymes from the pancreas help in the digestion of carbohydrates, fats and proteins in the small
intestine.
Duodenum - the first part of the small intestine; it is C-shaped and runs from the stomach to the
jejunum.
Jejunum - the long, coiled mid-section of the small intestine; it is between the duodenum and the
ileum.
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Overview of the Digestive System
Ileum - the last part of the small intestine before the large intestine begins.
Cecum - the first part of the large intestine; the appendix is connected to the cecum.
Appendix - a small sac located on the cecum.
Ascending colon - the part of the large intestine that run upwards; it is located after the cecum.
Transverse colon - the part of the large intestine that runs horizontally across the abdomen.
Descending colon - the part of the large intestine that run downwards after the transverse colon and
before the sigmoid colon.
Sigmoid colon - the part of the large intestine between the descending colon and the rectum.
Rectum - the lower part of the large intestine, where faeces are stored before they are excreted.
Anus - the opening at the end of the digestive system from which faeces (waste) exits the body
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The Digestive System
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Answers
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Starting at the Beginning
• What is needed before our digestive system can be
put into action?
Food
•Where is the first place that digestion starts?
Mouth
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What is needed for the initial stages of
digestion to occur?
•Mandible (jaw)
•Teeth
Facilitates mechanical digestion.
The food is physically broken into smaller pieces by
our teeth which are attached and moved by to our
jaw.
This process is called mastication
•Saliva
•Tongue
•Taste buds
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Lets Test our Taste Buds
•In groups, decide who will taste each liquid
(A,B,C,D,E).
•One person should come up and get the
containers.
•Use a new straw to taste each substance.
(Why?)
•Write down on a list what you think each one is.
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What did you taste?
A – Pineapple juice
B – Coffee
C – Salty water
D – chicken stock
E – lemon juice
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How do we know what things taste
like?
•Tongue
•Taste buds
Each taste bud can detect all tastes, but
prefers some more than others.
Saliva
Cells on the tongue secrete either:
Watery or mucous fluid
-water
-electrolytes
-enzymes
Turns food into “bolus”
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Esophageus
•Once the food is chewed and moisturized by the saliva, it is pushed back by
the tongue into the throat.
•When we swallow the food it goes into a tube called the esophageus.
•This food pipe is a muscular tube that is connected to the stomach. The
muscles that surround the esophagus help to squeeze and push the food into
the stomach, through a process called peristalsis.
•These contractions, which push the food down into the stomach, are powerful
enough to allow us to swallow even if lying down — or upside down.
•Between the esophagus and the stomach a sphincter ensures that the passage
normally opens only one way
— from the esophagus into the stomach.
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Peristalsis
The esophagus pushes the food downward by an action that we call
peristalsis, which is basically an orderly sequence of contractions like the
wave motion moving across stadium bleachers.
Volunteers to mimic the muscular
action called peristalsis.
•It enables food to move down the
esophageus as well as the small and large
intestine.
•It causes mixing of the gastric juices and
food stuff in the stomach.
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Stomach
Four main roles of the Stomach:
1. Short term storage
2. Enzymes start to digest proteins
3. Churning of the stomach turning
food into “chyme”.
4. Liquefying the food to pass slowly
into intestine.
The lower part works
harder than the upper part
Food must be ground to 1-2mm to pass
through the gate-keeper called
“pylorus”.
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A Real Stomach
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Small Intestine
•Absorbs ALL nutrients into the bloodstream.
•With the help of the liver and pancreas it breaks down large
particles so they can be absorbed.
•Liver secretes bile to break down fat.
•Pancreas secretes enzymes to breakdown everything and
neutralize acid to protect small intestine lining.
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How Long are the Intestines?
•How long is the small
intestine?
- 6.0 meters
•How long is the large
intestine?
-1.5 meters
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Large Intestine
•Absorbs water
•Has good bacteria that help
to digest food that can’t be
digested by our own body.
•Stores faeces
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What goes in must come out!
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